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MUO Lab VivaChemical Engineering

ContentsArticles

Unit operation 1Compression (physical) 2Impact (mechanics) 3Grinding (abrasive cutting) 5Mill (grinding) 10Sieve analysis 17Ball mill 23Filtration 26Crusher 29Pulverizer 34Froth flotation 37Mechanical screening 43

ReferencesArticle Sources and Contributors 47Image Sources, Licenses and Contributors 48

Article LicensesLicense 49

Unit operation 1

Unit operation

An ore extraction process broken into its constituent unit operations(Quincy Mine, Hancock, MI ca. 1900)

In chemical engineering and related fields, a unitoperation is a basic step in a process. Unit operationsinvolve bringing a physical change such as separation,crystallization, evaporation, filtration etc. For example,in milk processing, homogenization, pasteurization,chilling, and packaging are each unit operations whichare connected to create the overall process. A processmay have many unit operations to obtain the desiredproduct.

Historically, the different chemical industries wereregarded as different industrial processes and withdifferent principles. Arthur Dehon Little propounded theconcept of "unit operations" to explain industrialchemistry processes in 1916.[1] In 1923, WilliamH.Walker, Warren K. Lewis and William H. McAdamswrote the book The Principles of ChemicalEngineering[2] and explained the variety of chemicalindustries have processes which follow the samephysical laws. They summed-up these similar processesinto unit operations. Each unit operation follows thesame physical laws and may be used in all chemicalindustries. The unit operations form the fundamentalprinciples of chemical engineering.

Chemical engineering unit operations consist of fiveclasses:1. Fluid flow processes, including fluids transportation, filtration, solids fluidization2. Heat transfer processes, including evaporation, condensation3. Mass transfer processes, including gas absorption, distillation, extraction, adsorption, drying4. Thermodynamic processes, including gas liquefaction, refrigeration5. Mechanical processes, including solids transportation, crushing and pulverization, screening and sievingChemical engineering unit operations also fall in the following categories:• Combination (mixing)• Separation (distillation)• Reaction (chemical reaction)Chemical engineering unit operations and chemical engineering unit processing form the main principles of all kindsof chemical industries and are the foundation of designs of chemical plants, factories, and equipment used.

Unit operation 2

References[1] "The MIT Connection"http:/ / libraries. mit. edu/ archives/ exhibits/ adlittle/ mit-connection. html Retrieved March 6, 2010.[2] The Encyclopedia of Earth. "Walker, William H. http:/ / www. eoearth. org/ article/ Walker,_William_H. Accessed April 4, 2010.

Compression (physical)

Compression test on a universal testing machine

Physical compression is the result of the subjection ofa material or structure to compressive stress, whichresults in reduction of volume as compared to anuncompressed but otherwise identical state. Theopposite of compression in a solid is tension. In anymedium transmitting waves, the opposite ofcompression is rarefaction. In simple terms,compression is a pushing force.

Explanation

Compression has many implications in materialsscience, physics and structural engineering, forcompression yields noticeable amounts of stress andtension.

By inducing compression, mechanical properties such as compressive strength or modulus of elasticity, can bemeasured. Scientists and engineers may utilize compression machines to measure the resistance of materials andstructures to compression.

Compression machines range from very small table top systems to ones with over 53 MN capacity.[1]

In engines

Internal combustion enginesIn internal combustion engines it is a necessary condition of economy to compress the explosive mixture before it isignited: in the Otto cycle, for instance, the second stroke of the piston effects the compression of the charge whichhas been drawn into the cylinder by the first forward stroke.

Steam enginesThe term is applied to the arrangement by which the exhaust valve of a steam engine is made to close, shutting aportion of the exhaust steam in the cylinder, before the stroke of the piston is quite complete. This steam beingcompressed as the stroke is completed, a cushion is formed against which the piston does work while its velocity isbeing rapidly reduced, and thus the stresses in the mechanism due to the inertia of the reciprocating parts arelessened. This compression, moreover, obviates the shock which would otherwise be caused by the admission of thefresh steam for the return stroke.

Compression (physical) 3

References[1] NIST, Large Scale Structure Testing Facility (http:/ / www. nist. gov/ bfrl/ facilities_instruments/ large_scale_struct_testing_fac. cfm), ,

retrieved 04-05-2010.

• Beer, Ferdinand Pierre; Elwood Russell Johnston, John T. DeWolf (1992). Mechanics of Materials. McGraw-HillProfessional. ISBN 0-07-112939-1.

Impact (mechanics)In mechanics, an impact is a high force or shock applied over a short time period when two or more bodies collide.Such a force or acceleration usually has a greater effect than a lower force applied over a proportionally longer timeperiod of time. The effect depends critically on the relative velocity of the bodies to one another.At normal speeds, during a perfectly inelastic collision, an object struck by a projectile will deform, and thisdeformation will absorb most, or even all, of the force of the collision. Viewed from the conservation of energyperspective, the kinetic energy of the projectile is changed into heat and sound energy, as a result of the deformationsand vibrations induced in the struck object. However, these deformations and vibrations cannot occurinstantaneously. A high-velocity collision (an impact) does not provide sufficient time for these deformations andvibrations to occur. Thus, the struck material behaves as if it were more brittle than it is, and the majority of theapplied force goes into fracturing the material. Or, another way to look at it is that materials actually are more brittleon short time scales than on long time scales: this is related to time-temperature superposition. Impact resistance willbe decreased with an increase in the modulus of elasticity, which means that stiffer materials will have less impactresistance. Resilient materials will have better impact resistance.Different materials can behave in quite different ways in impact when compared with static loading conditions.Ductile materials like steel tend to become more brittle at high loading rates, and spalling may occur on the reverseside to the impact if penetration doesn't occur. The way in which the kinetic energy is distributed through the sectionis also important in determining its response. Projectiles apply a Hertzian contact stress at the point of impact to asolid body, with compression stresses under the point, but with bending loads a short distance away. Since mostmaterials are weaker in tension than compression, this is the zone where cracks tend to form and grow.

Applications

A crane with a pile driver.

A nail is pounded with a series of impacts, each by a single hammer blow. These highvelocity impacts overcome the static friction between the nail and the substrate. A piledriver achieves the same end, although on a much larger scale, the method beingcommonly used during civil construction projects to make building and bridgefoundations. An impact wrench is a device designed to impart torque impacts to bolts totighten or loosen them. At normal speeds, the forces applied to the bolt would bedispersed, via friction, to the mating threads. However, at impact speeds, the forces acton the bolt to move it before they can be dispersed. In ballistics, bullets utilize impactforces to puncture surfaces that could otherwise resist substantial forces. A rubber sheet,for example, behaves more like glass at typical bullet speeds. That is, it fractures, anddoes not stretch or vibrate.

Impact (mechanics) 4

A 1/2" drive pistol-grip air impact wrench

Accidents involving impact

A Chevrolet Malibu involved in a rollover crash

Road traffic accidents usually involve impact loading, such as when acar hits a traffic bollard, water hydrant or tree, the damage beinglocalized to the impact zone. When vehicles collide, the damage isproportionate to the relative velocity of the vehicles, the damageincreasing as the square of the velocity since it is the impact kineticenergy (1/2 mv2) which is the variable of importance. Much designeffort is made to improve the impact resistance of cars so as tominimize user injury. It can be achieved in several ways: by enclosingthe driver and passengers in a safety cell for example. The cell isreinforced so will survive in high speed crashes, and so protect theusers. Parts of the body shell outside the cell are designed to crumple

progressively, absorbing most of the kinetic energy which must be dissipated by the impact.

Various impact test are used to assess the effects of high loading, both on products and standard slabs of material.The Charpy test and Izod test are two examples of standardized methods which are used widely for testing materials.Ball or projectile drop tests are used for assessing product impacts.

The Columbia disaster was caused by impact damage when a chunk of polyurethane foam impacted the carbon fibrecomposite wing of the space shuttle. Although tests had been conducted before the disaster, the size of the chunkswas much smaller than that which fell away from the booster rocket and hit the exposed wing.

Impact (mechanics) 5

A mock-up of a space shuttle leading edge made with an RCC-paneltaken from Discovery showing impact damage during a test

References

•• Goldsmith, W, Impact; The Theory and PhysicalBehaviour of Colliding Solids, 2001, DoverPublications, ISBN 0-486-42004-3

• Poursartip, A, “Instrumented Impact Testing at HighVelocities”, Journal of Composites Technology andResearch, 1993, vol 15 issue 1,

• Toropov, AI, “Dynamic Calibration of Impact TestInstruments”, Journal of Testing and Evaluation,1998, vol 24, no 4

Grinding (abrasive cutting)

Sketch of how abrasive particles in a grindingwheel remove material from a workpiece.

Grinding is an abrasive machining process that uses a grinding wheelas the cutting tool.

A wide variety of machines are used for grinding:• Hand-cranked knife-sharpening stones (grindstones)• Handheld power tools such as angle grinders and die grinders• Various kinds of expensive industrial machine tools called grinding

machines• Bench grinders often found in residential garages and basementsGrinding practice is a large and diverse area of manufacturing andtoolmaking. It can produce very fine finishes and very accuratedimensions; yet in mass production contexts it can also rough out large volumes of metal quite rapidly. It is usuallybetter suited to the machining of very hard materials than is "regular" machining (that is, cutting larger chips withcutting tools such as tool bits or milling cutters), and until recent decades it was the only practical way to machinesuch materials as hardened steels. Compared to "regular" machining, it is usually better suited to taking very shallowcuts, such as reducing a shaft's diameter by half a thousandth of an inch (thou) or 12.7 um.

Grinding is a subset of cutting, as grinding is a true metal-cutting process. Each grain of abrasive functions as amicroscopic single-point cutting edge (although of high negative rake angle), and shears a tiny chip that is analogousto what would conventionally be called a "cut" chip (turning, milling, drilling, tapping, etc.). However, amongpeople who work in the machining fields, the term cutting is often understood to refer to the macroscopic cuttingoperations, and grinding is often mentally categorized as a "separate" process. This is why the terms are usually usedin contradistinction in shop-floor practice, even though, strictly speaking, grinding is a subset of cutting.Similar abrasive cutting processes are lapping and sanding.

Grinding (abrasive cutting) 6

ProcessesSelecting which of the following grinding operations to be used is determined by the size, shape, features and thedesired production rate.

Surface grinding

Surface grinder

Surface grinding uses a rotating abrasive wheel to smooth the flatsurface of metallic or nonmetallic materials to give them a morerefined look or to attain a desired surface for a functional purpose. Thetolerances that are normally achieved with grinding are ± 2 × 10−4

inches for a grinding a flat material, and ± 3 × 10−4 inches for aparallel surface (in metric units: 5 μm for flat material and 8 μm forparallel surface).

The surface grinder is composed of an abrasive wheel, a workholdingdevice known as a chuck, either electromagnetic or vacuum, and areciprocating table.

Typical workpiece materials include cast iron and minor steel. Thesetwo materials do not tend to clog the grinding wheel while beingprocessed. Other materials are aluminum, stainless steel, brass and some plastics.

Cylindrical grindingCylindrical grinding (also called center-type grinding) is used in the removing the cylindrical surfaces and shouldersof the workpiece. The workpiece is mounted and rotated by a workpiece holder, also known as a grinding dog orcenter driver. Both the tool and the workpiece are rotated by separate motors and at different speeds. The axes ofrotation tool can be adjusted to produce a variety of shapes.The five types of cylindrical grinding are: outside diameter (OD) grinding, inside diameter (ID) grinding, plungegrinding, creep feed grinding, and centerless grinding.[1]

A cylindrical grinder has a grinding (abrasive) wheel, two centers that hold the workpiece, and a chuck, grindingdog, or other mechanism to drive the machine. Most cylindrical grinding machines include a swivel to allow for theforming of tapered pieces. The wheel and workpiece move parallel to one another in both the radial and longitudinaldirections. The abrasive wheel can have many shapes. Standard disk shaped wheels can be used to create a tapered orstraight workpiece geometry while formed wheels are used to create a shaped workpiece. The process using a formedwheel creates less vibration than using a regular disk shaped wheel.Tolerances for cylindrical grinding are held within five ten-thousandths of an inch (+/- 0.0005) (metric: +/- 13 um)for diameter and one ten-thousandth of an inch(+/- 0.0001) (metric: 2.5 um) for roundness. Precision work can reachtolerances as high as fifty millionths of an inch (+/- 0.00005) (metric: 1.3 um) for diameter and ten millionths (+/-0.00001) (metric: 0.25 um) for roundness. Surface finishes can range from 2 to 125 microinches (metric: 50 nm to3 um), with typical finishes ranging from 8-32 microinches. (metric: 0.2 um to 0.8 um)

Creep-feed grindingCreep-feed grinding (CFG) was invented in Germany in the late 1950s by Edmund and Gerhard Lang. Unlikenormal grinding, which is used primarily to finish surfaces, CFG is used for high rates of material removal,competing with milling and turning as a manufacturing process choice. Depths of cut of up to 6 mm (0.25 inches) areused along with low workpiece speed. Surfaces with a softer-grade resin bond are used to keep workpiecetemperature low and an improved surface finish up to 1.6 micrometres Rmax

Grinding (abrasive cutting) 7

With CFG it takes 117 sec to remove 1 in.3 of material, whereas precision grinding would take more than 200 sec todo the same. CFG has the disadvantage of a wheel that is constantly degrading, and requires high spindle power,51 hp (38 kW), and is limited in the length of part it can machine.[2]

To address the problem of wheel sharpness, continuous-dress creep-feed grinding (CDCF) was developed in the1970s. It dresses the wheel constantly during machining, keeping it in a state of specified sharpness. It takes only 17sec. to remove 1 in3 of material, a huge gain in productivity. 38 hp (28 kW) spindle power is required, and runs atlow to conventional spindle speeds. The limit on part length was erased.High-efficiency deep grinding (HEDG) uses plated superabrasive wheels, which never need dressing and lastlonger than other wheels. This reduces capital equipment investment costs. HEDG can be used on long part lengths,and removes material at a rate of 1 in3 in 83 sec. It requires high spindle power and high spindle speeds.[2]

Peel grinding, patented under the name of Quickpoint in 1985 by Erwin Junker Maschinenfabrik, GmbH inNordrach, Germany, uses a tool with a with superabrasive nose and can machine cylindrical parts.[2]

VIPER (Very Impressive Performance Extreme Removal), 1999, is a process patented by Rolls-Royce and is used inaerospace manufacturing to produce turbine blades. It uses a continuously dressed aluminum oxide grinding wheelrunning at high speed. CNC-controlled nozzles apply refrigerated grinding fluid during the cut. VIPER is performedon equipment similar to a CNC machining center, and uses special wheels.[2]

Ultra-high speed grinding (UHSG) can run at speeds higher than 40,000 fpm (200 m/s), taking 41 sec to remove 1in.3 of material, but is still in the R&D stage. It also requires high spindle power and high spindle speeds.[2]

Others

Centerless grinding

Form grinding is a specialized type of cylindrical grinding where thegrinding wheel has the exact shape of the final product. The grindingwheel does not traverse the workpiece.[3]

Internal grinding is used to grind the internal diameter of theworkpiece. Tapered holes can be ground with the use of internalgrinders that can swivel on the horizontal.

Centerless grinding is when the workpiece is supported by a bladeinstead of by centers or chucks. Two wheels are used. The larger one isused to grind the surface of the workpiece and the smaller wheel isused to regulate the axial movement of the workpiece. Types of centerless grinding include through-feed grinding,in-feed/plunge grinding, and internal centerless grinding.

Pre-grinding When a new tool has been built and has been heat-treated, it is pre-ground before welding orhardfacing commences. This usually involves grinding the OD slightly higher than the finish grind OD to ensure thecorrect finish size.Electrochemical grinding is a type of grinding in which a positively charged workpiece in a conductive fluid iseroded by a negatively charged grinding wheel. The pieces from the workpiece are dissolved into the conductivefluid.

A schematic of ELID grinding

Electrolytic in-process dressing (ELID) grinding is one of the mostaccurate grinding methods. In this ultra precision grinding technologythe grinding wheel is dressed electrochemically and in-process tomaintain the accuracy of the grinding. An ELID cell consists of a metalbonded grinding wheel, a cathode electrode, a pulsed DC power supplyand electrolyte. The wheel is connected to the positive terminal of the

Grinding (abrasive cutting) 8

DC power supply through a carbon brush whereas the electrode is connected to the negative pole of the powersupply. Usually alkaline liquids are used as both electrolytes and coolant for grinding. A nozzle is used to inject theelectrolyte into the gap between wheel and electrode. The gap is usually maintained to be approximately 0.1mm to0.3 mm. During the grinding operation one side of the wheel takes part in the grinding operation whereas the otherside of the wheel is being dressed by electrochemical reaction. The dissolution of the metallic bond material iscaused by the dressing which in turns results continuous protrusion of new sharp grits.[4]

Grinding wheelA grinding wheel is an expendable wheel used for various grinding and abrasive machining operations. It isgenerally made from a matrix of coarse abrasive particles pressed and bonded together to form a solid, circularshape, various profiles and cross sections are available depending on the intended usage for the wheel. Grindingwheels may also be made from a solid steel or aluminium disc with particles bonded to the surface.

LubricationThe use of fluids in a grinding process is necessary to cool and lubricate the wheel and workpiece as well as removethe chips produced in the grinding process. The most common grinding fluids are water-soluble chemical fluids,water-soluble oils, synthetic oils, and petroleum-based oils. It is imperative that the fluid be applied directly to thecutting area to prevent the fluid being blown away from the piece due to rapid rotation of the wheel.

Work Material Cutting Fluid Application

Aluminum Light duty oil Flood

Brass Light duty oil Flood

Cast Iron Heavy duty emulsifiable oil, light duty chemical oil, synthetic oil Flood

Mild Steel Heavy duty water soluble oil Flood

Stainless Steel Heavy duty emulsifiable oil, heavy duty chemical oil, synthetic oil Flood

Plastics Water soluble oil, dry, heavy duty emulsifiable oil, dry, light duty chemical oil, synthetic oil Flood

The workpiece

Workholding methodsThe workpiece is manually clamped to a lathe dog, powered by the faceplate, that holds the piece in between twocenters and rotates the piece. The piece and the grinding wheel rotate in opposite directions and small bits of thepiece are removed as it passes along the grinding wheel. In some instances special drive centers may be used toallow the edges to be ground. The workholding method affects the production time as it changes set up times.

Workpiece materialsTypical workpiece materials include aluminum, brass, plastics, cast iron, mild steel, and stainless steel. Aluminum,brass and plastics can have poor to fair machinability characteristics for cylindrical grinding. Cast Iron and mild steelhave very good characteristics for cylindrical grinding. Stainless steel is very difficult to grind due to its toughnessand ability to work harden, but can be worked with the right grade of grinding wheels.

Grinding (abrasive cutting) 9

Workpiece geometryThe final shape of a workpiece is the mirror image of the grinding wheel, with cylindrical wheels creating cylindricalpieces and formed wheels creating formed pieces. Typical sizes on workpieces range from .75 in. to 20 in. (metric:18mm to 1 m) and .80 in. to 75 in. in length (metric: 2 cm to 4 m), although pieces between .25 in. and 60 in. indiameter (metric: 6 mm to 1.5 m) and .30 in. and 100 in. in length (metric: 8 mm to 2.5 m) can be ground. Resultingshapes can range from straight cylinders, straight edged conical shapes, or even crankshafts for engines thatexperience relatively low torque.

Effects on Workpiece MaterialsMechanical properties will change due to stresses put on the part during finishing. High grinding temperatures maycause a thin martensitic layer to form on the part, which will lead to reduced material strength from microcracks.Physical property changes include the possible loss of magnetic properties on ferromagnetic materials.Chemical property changes include an increased susceptibility to corrosion because of high surface stress.

References[1] Stephenson, David. Metal Cutting Theory and Practice. 2nd. Boca Raton: CRC Press, 1997. 52-60.[2] Salmon, Stuart, "What is Abrasive Machining?," Manufacturing Engineering Feb. 2010, Society of Manufacturing Engineers.[3] Adithan & Gupta 2002, p. 129.[4] (http:/ / www. sciencedirect. com/ science/ article/ B6TGJ-4NJ0TF6-C/ 2/ 677965db64474d9ca41a35f207939171)), T. Saleh, M. Sazedur

Rahman, H.S. Lim, M. Rahman, Development and performance evaluation of an ultra precision ELID grinding machine, Journal of MaterialsProcessing Technology, Volumes 192-193, Pages 287-291.

Bibliography• Adithan, M.; Gupta, A. B. (2002), Manufacturing Technology (http:/ / books. google. com/

?id=zeGOjAOZ-sMC), New Age International Publishers, ISBN 978-81-224-0817-1.

Mill (grinding) 10

Mill (grinding)

Attrition Mill

A tabletop hammer mill

Other names Grinding mill

Uses Grinding

Related items Mortar and pestleExpellerExtruder

A grinding mill is a unit operation designed to break a solid material into smaller pieces. There are many differenttypes of grinding mills and many types of materials processed in them. Historically mills were powered by hand(mortar and pestle), working animal (horse mill), wind (windmill) or water (watermill). Today they are also poweredby electricity.The grinding of solid matters occurs under exposure of mechanical forces that trench the structure by overcoming ofthe interior bonding forces. After the grinding the state of the solid is changed: the grain size, the grain sizedisposition and the grain shape.Grinding may serve the following purposes in engineering:•• increase of the surface area of a solid•• manufacturing of a solid with a desired grain size•• pulping of resources

Grinding lawsIn spite of a great number of studies in the field of fracture schemes there is no formula known which connects thetechnical grinding work with grinding results. To calculate the needed grinding work against the grain size changingthree half-empirical models are used. These can be related to the Hukki relationship between particle size and theenergy required to break the particles. In stirred mills, the Hukki relationship does not apply and instead,experimentation has to be performed to determine any relationship.[1]

• Kick for d > 50 mm

• Bond[2] for 50 mm > d > 0.05 mm

Mill (grinding) 11

• Von Rittinger for d < 0.05 mm

with W as grinding work in kJ/kg, c as grinding coefficient, dA as grain size of the source material and dE as grainsize of the ground material.A reliable value for the grain sizes dA and dE is d80. This value signifies that 80% (mass) of the solid matter has asmaller grain size. The Bond's grinding coefficient for different materials can be found in various literature. Tocalculate the KICK's and Rittinger's coefficients following formulas can be used

with the limits of Bond's range: upper dBU = 50 mm and lower dBL = 0.05 mm.To evaluate the grinding results the grain size disposition of the source material (1) and of the ground material (2) isneeded. Grinding degree is the ratio of the sizes from the grain disposition. There are several definitions for thischaracteristic value:• Grinding degree referring to grain size d80

Instead of the value of d80 also d50 or other grain diameter can be used.•• Grinding degree referring to specific surface

The specific surface area referring to volume Sv and the specific surface area referring to mass Sm can be foundout through experiments.

•• Pretended grinding degree

The discharge die gap a of the grinding machine is used for the ground solid matter in this formula.

Mill (grinding) 12

Grinding machinesIn materials processing a grinder is a machine for producing fine particle size reduction through attrition andcompressive forces at the grain size level. See also crusher for mechanisms producing larger particles. In general,grinding processes require a relatively large amount of energy; for this reason, an experimental method to measurethe energy used locally during milling with different machines was recently proposed.[3]

Operation of a ball mill

Ball mill

A typical type of fine grinder is the ball mill. A slightly inclined orhorizontal rotating cylinder is partially filled with balls, usually stoneor metal, which grinds material to the necessary fineness by frictionand impact with the tumbling balls. Ball mills normally operate with anapproximate ball charge of 30%. Ball mills are characterized by theirsmaller (comparatively) diameter and longer length, and often have alength 1.5 to 2.5 times the diameter. The feed is at one end of thecylinder and the discharge is at the other. Ball mills are commonlyused in the manufacture of Portland cement and finer grinding stagesof mineral processing. Industrial ball mills can be as large as 8.5 m(28 ft) in diameter with a 22 MW motor,[4] drawing approximately0.0011% of the total world's power (see List of countries by electricityconsumption). However, small versions of ball mills can be found in laboratories where they are used for grindingsample material for quality assurance.

The power predictions for ball mills typically use the following form of the Bond equation:[2]

where

Mill (grinding) 13

• E is the energy (kilowatt-hours per metric or short ton)• Wi is the work index measured in a laboratory ball mill (kilowatt-hours per metric or short ton)• P80 is the mill circuit product size in micrometers• F80 is the mill circuit feed size in micrometers.

Rod millA rotating drum causes friction and attrition between steel rods and ore particles. But note that the term 'rod mill' isalso used as a synonym for a slitting mill, which makes rods of iron or other metal. Rod mills are less common thanball mills for grinding minerals.The rods used in the mill, usually a high-carbon steel, can vary in both the length and the diameter. However, thesmaller the rods, the larger is the total surface area and hence, the greater the grinding efficiency[5]

Autogenous millAutogenous mills are so-called due to the self-grinding of the ore: a rotating drum throws larger rocks of ore in acascading motion which causes impact breakage of larger rocks and compressive grinding of finer particles. It issimilar in operation to a SAG mill as described below but does not use steel balls in the mill. Also known as ROM or"Run Of Mine" grinding.

SAG mill

Principle of SAG Mill operation

SAG is an acronym forSemi-Autogenous Grinding. SAGmills are essentially autogenous mills,but utilize grinding balls to aid ingrinding like in a ball mill. A SAG millis generally used as a primary or firststage grinding solution. SAG mills usea ball charge of 8 to 21%.[6][7] Thelargest SAG mill is 42' in diameter,powered by a 28 MW (38,000 HP)motor.[8] A SAG mill with a diameter44' in diamter has been designed with apower of 35 MW (47,000 HP).[9]

Attrition between grinding balls andore particles causes grinding of finerparticles. SAG mills are characterizedby their large diameter and short lengthas compared to ball mills. The insideof the mill is lined with lifting plates to lift the material inside the mill, where it then falls off the plates onto the restof the ore charge. SAG mills are primarily used at gold, copper and platinum mines with applications also in thelead, zinc, silver, alumina and nickel industries.

Mill (grinding) 14

Pebble millA rotating drum causes friction and attrition between rock pebbles and ore particles. May be used where productcontamination by iron from steel balls must be avoided. Quartz or silica is commonly used because it is inexpensiveto obtain.

High pressure grinding rollsThe high pressure grinding rolls, often referred to as HPGRs or roller press, consists out of two rollers with the samedimensions, which are rotating against each other with the same circumferential speed. The special feeding of bulkmaterial through a hopper leads to a material bed between the two rollers. The bearing units of one roller can movelinearly and are pressed against the material bed by springs or hydraulic cylinders. The pressures in the material bedare greater than 50 MPa. In general they achieve 100 to 300 MPa. By this the material bed is compacted to a solidvolume portion of more than 80%.The roller press has a certain similarity to roller crushers and roller presses for the compacting of powders, butpurpose, construction and operation mode are different.Extreme pressure causes the particles inside of the compacted material bed to fracture into finer particles and alsocauses microfracturing at the grain size level. Compared to ball mills HPGRs are achieving a 30 to 50% lowerspecific energy consumption, although they are not as common as ball mills since they are a newer technology.A similar type of intermediate crusher is the edge runner, which consists of a circular pan with two or more heavywheels known as mullers rotating within it; material to be crushed is shoved underneath the wheels using attachedplow blades.

Buhrstone millAnother type of fine grinder commonly used is the buhrstone mill, which is similar to old-fashioned flour mills.

Vertical shaft impactor mill (VSI mill)Type of fine grinder which uses a free impact of rock or ore particles with a wear plate. High speed of the motion ofparticles is achieved with a rotating accelerator. This type of mill uses the same principle as VSI Crusher

Tower millTower mills, often called vertical mills, stirred mills or regrind mills, are a more efficient means of grinding materialat smaller particle sizes, and can be used after ball mills in a grinding process. Like ball mills, grinding (steel) ballsor pebbles are often added to stirred mills to help grind ore, however these mills contain a large screw mountedvertically to lift and grind material. In tower mills, there is no cascading action as in standard grinding mills. Stirredmills are also common for mixing quicklime (CaO) into a lime slurry. There are several advantages to the tower mill:low noise, efficient energy usage, and low operating costs.

Mill (grinding) 15

Types of grinding mills• windmill, wind powered• watermill, water powered• horse mill, animal powered• treadwheel, human powered (archaic: "treadmill")• ship mill, floats near a river bank or bridge• arrastra, simple mill for grinding and pulverizing (typically) gold or silver ore.• roller mill, an equipment for the grinding or pulverizing of grain and other raw materials using cylinders• Stamp mill, a specialized machine for reducing ore to powder for further processing or for fracturing other

materials•• a place of business for making articles of manufacture. The term mill was once in common use for a factory

because many factories in the early stages of the Industrial Revolution were powered by a watermill, butnowadays it is only used in a few specific contexts; e.g.,• bark mill produces tanbark for tanneries• cider mill crushes apples to give cider• gristmill grinds grain into flour• oil mill, see expeller pressing, extrusion• paper mill produces paper• sawmill cuts timber•• starch mill• steel mill manufactures steel• sugar mill (also called a sugar refinery) processes sugar beets or sugar cane into various finished products•• textile mill (disambiguation)

• silk mill, for silk• flax mill, for flax• cotton mill, for cotton

• huller (also called a rice mill, or rice husker) is used to hull rice• powder mill produces gunpowder

•• Ball mill•• Colloid mill•• Conical mill•• Disintegrator•• Disk mill•• Edge mill• Gristmill, also called flour mill or corn mill•• Hammer mill•• Jet mill•• Mortar and pestle•• Pellet mill•• Planetary mill•• Stirred mill•• Vibratory mill•• VSI mill•• Wiley mill•• Windmill

Mill (grinding) 16

References[1] Thomas, A; Filippov, L.O. (1999). "Fractures, fractals and breakage energy of mineral particles". International Journal of Mineral Processing

57 (4): 285. doi:10.1016/S0301-7516(99)00029-0.[2] Mineral Beneficiation – The Third Theory of Comminution – Document Summary (http:/ / www. onemine. org/ search/ summary. cfm/

Mineral-Beneficiation--The-Third-Theory-of-Comminution?d=33A4C4B0EF40AA84EB2CE2F8607CDBC29A9E29D95F765C17CE2C0815BCC2006D18644&fullText=The Third Theory of Comminution& author=Fred Bond). Onemine.org. Retrieved on 2010-10-09.

[3] Baron, M.; Chamayou, A.; Marchioro, L.; Raffi, J. (2005). "Radicalar probes to measure the action of energy on granular materials".Advanced Powder Technology 16 (3): 199. doi:10.1163/1568552053750242.

[4] "ABB" (http:/ / www. abb. com/ cawp/ seitp202/ 8231666baa1c0a45c1257842002fe89b. aspx). ABB Communications. ABBCommunications. .

[5] Wills, B.A.. Mineral Processing Technology: An Introduction to the Practical Aspects of Ore Treatment and Mineral Recovery. 7th ed.Amsterdam ; Boston, MA. p. 157.

[6] S. Strohmayr and W. Valery, Jr. SAG MILL CIRCUIT OPTIMISATION AT ERNEST HENRY MINING (http:/ / www. metso. com/miningandconstruction/ mct_service. nsf/ WebWID/ WTB-120106-22576-29D77/ $File/ 057. pdf). metso.com

[7] Andrew L. Mular; Doug N. Halbe; Derek J. Barratt (2002). Mineral Processing Plant Design, Practice, and Control: Proceedings (http:/ /books. google. com/ books?id=GibosO9NKWwC& pg=PA2369). SME. pp. 2369–. ISBN 978-0-87335-223-9. . Retrieved 26 October 2012.

[8] Maarten van de Vijfeijken (October 2010). "Mills and GMDs" (http:/ / www04. abb. com/ global/ seitp/ seitp202. nsf/ 0/bbe9642b2886578cc1257842003f2c64/ $file/ Mills+ and+ GMDs. pdf). International Mining: 30. .

[9] Gearless mill drives (http:/ / www05. abb. com/ global/ scot/ scot244. nsf/ veritydisplay/ b5413bc88649e680c1257a5300514f7e/ $file/Gearless mill drives_3BHS 490275 RevD_low. pdf). abb.com

External links• Animation of Horizontal Grinder (http:/ / www. vecoplanllc. com/ technology/ concepts/ horizontal-grinder. asp)• Video of fine grinder in mining application (http:/ / www. deswik. com/ mills_deswik_video. asp)• Image of SAG mill during installation (http:/ / www. fmt. biz/ var/ em_plain_site/ storage/ images/ medien/

bilder/ fmt/ referenzen/ stein-erde_und_zement/ chelopech-mining-ead/ 20018-1-ger-DE/Chelopech-Mining-EAD_overlay. jpg)

Sieve analysis 17

Sieve analysisA sieve analysis (or gradation test) is a practice or procedure used (commonly used in civil engineering) to assessthe particle size distribution (also called gradation) of a granular material.The size distribution is often of critical importance to the way the material performs in use. A sieve analysis can beperformed on any type of non-organic or organic granular materials including sands, crushed rock, clays, granite,feldspars, coal, soil, a wide range of manufactured powders, grain and seeds, down to a minimum size depending onthe exact method. Being such a simple technique of particle sizing, it is probably the most common.[1]

Procedure

Sieves used for gradation test.

A mechanical shaker used for sieve analysis.

A gradation test is performed on a sample of aggregate in a laboratory.A typical sieve analysis involves a nested column of sieves with wiremesh cloth (screen). See the separate Mesh (scale) page for details ofsieve sizing.

A representative weighed sample is poured into the top sieve which hasthe largest screen openings. Each lower sieve in the column hassmaller openings than the one above. At the base is a round pan, calledthe receiver.The column is typically placed in a mechanical shaker. The shakershakes the column, usually for some fixed amount of time. After theshaking is complete the material on each sieve is weighed. The weightof the sample of each sieve is then divided by the total weight to give apercentage retained on each sieve.The size of the average particle on each sieve is then analysed to get acut-off point or specific size range, which is then captured on a screen.The results of this test are used to describe the properties of theaggregate and to see if it is appropriate for various civil engineeringpurposes such as selecting the appropriate aggregate for concrete mixesand asphalt mixes as well as sizing of water production well screens.The results of this test are provided in graphical form to identify thetype of gradation of the aggregate. The complete procedure for this testis outlined in the American Society for Testing and Materials (ASTM)C 136[2] and the American Association and State Highway andTransportation Officials (AASHTO) T 27[3]

A suitable sieve size for the aggregate should be selected and placed inorder of decreasing size, from top to bottom, in a mechanical sieveshaker. A pan should be placed underneath the nest of sieves to collectthe aggregate that passes through the smallest. The entire nest is thenagitated, and the material whose diameter is smaller than the meshopening pass through the sieves. After the aggregate reaches the pan,the amount of material retained in each sieve is then weighed.[4]

Sieve analysis 18

PreparationIn order to perform the test, a sample of the aggregate must be obtained from the source. To prepare the sample, theaggregate should be mixed thoroughly and be reduced to a suitable size for testing. The total weight of the sample isalso required.[4]

ResultsThe results are presented in a graph of percent passing versus the sieve size. On the graph the sieve size scale islogarithmic. To find the percent of aggregate passing through each sieve, first find the percent retained in each sieve.To do so, the following equation is used,

%Retained = ×100%

where WSieve is the weight of aggregate in the sieve and WTotal is the total weight of the aggregate. The next step isto find the cumulative percent of aggregate retained in each sieve. To do so, add up the total amount of aggregatethat is retained in each sieve and the amount in the previous sieves. The cumulative percent passing of the aggregateis found by subtracting the percent retained from 100%.%Cumulative Passing = 100% - %Cumulative Retained.The values are then plotted on a graph with cumulative percent passing on the y axis and logarithmic sieve size onthe x axis.[4]

There are two versions of the %Passing equations. the .45 power formula is presented on .45 power gradation chart,whereas the more simple %Passing is presented on a semi-log gradation chart. version of the percent passing graph isshown on .45 power chart and by using the .45 passing formula..45 power percent passing formula

% Passing = Pi = x100%

Where:SieveLargest - Largest diameter sieve used in (mm).Aggregatemax_size - Largest piece of aggregate in the sample in (mm).Percent passing formula

%Passing = x100%

Where:WBelow - The total mass of the aggregate within the sieves below the current sieve, not including the current sieve'saggregate.WTotal - The total mass of all of the aggregate in the sample.

Sieve analysis 19

MethodsThere are different methods for carrying out sieve analyses, depending on the material to be measured.

Throw-action sieving

Throw-action sieving

Here a throwing motion acts on the sample. The vertical throwingmotion is overlaid with a slight circular motion which results indistribution of the sample amount over the whole sieving surface. Theparticles are accelerated in the vertical direction (are thrown upwards).In the air they carry out free rotations and interact with the openings inthe mesh of the sieve when they fall back. If the particles are smallerthan the openings, they pass through the sieve. If they are larger, theyare thrown upwards again. The rotating motion while suspendedincreases the probability that the particles present a differentorientation to the mesh when they fall back again, and thus mighteventually pass through the mesh.Modern sieve shakers work with an electro-magnetic drive whichmoves a spring-mass system and transfers the resulting oscillation tothe sieve stack. Amplitude and sieving time are set digitally and arecontinuously observed by an integrated control-unit. Therefore sievingresults are reproducible and precise (an important precondition for asignificant analysis). Adjustment of parameters like amplitude andsieving time serves to optimize the sieving for different types ofmaterial. This method is the most common in the laboratory sector.

Horizontal sieving

Horizontal sieving

In a horizontal sieve shaker the sieve stack moves in horizontal circlesin a plane. Horizontal sieve shakers are preferably used forneedle-shaped, flat, long or fibrous samples, as their horizontalorientation means that only a few disoriented particles enter the meshand the sieve is not blocked so quickly. The large sieving area enablesthe sieving of large amounts of sample, for example as encountered inthe particle-size analysis of construction materials and aggregates.

Sieve analysis 20

Tapping sieving

Tapping sieving

A horizontal circular motion overlies a vertical motion which is createdby a tapping impulse. These motional processes are characteristic ofhand sieving and produce a higher degree of sieving for denserparticles (e.g. abrasives) than throw-action sieve shakers.

Sonic sieving

The particles are lifted and forcibly dropped in a column of oscillatingair at a frequency of thousands of cycles per minute. Sonic sievers areable to handle much finer dry powders than woven mesh screens.

Wet sievingMost sieve analyses are carried out dry. But there are some applications which can only be carried out by wetsieving. This is the case when the sample which has to be analysed is e.g. a suspension which must not be dried; orwhen the sample is a very fine powder which tends to agglomerate (mostly < 45 µm) – in a dry sieving process thistendency would lead to a clogging of the sieve meshes and this would make a further sieving process impossible. Awet sieving process is set up like a dry process: the sieve stack is clamped onto the sieve shaker and the sample isplaced on the top sieve. Above the top sieve a water-spray nozzle is placed which supports the sieving processadditionally to the sieving motion. The rinsing is carried out until the liquid which is discharged through the receiveris clear. Sample residues on the sieves have to be dried and weighed. When it comes to wet sieving it is veryimportant not to change to sample in its volume (no swelling, dissolving or reaction with the liquid).

Air Jet SievingAir jet sieving machines are ideally suited for very fine powders which tend to agglomerate and cannot be separatedby vibrational sieving. The reason for the effectiveness of this sieving method is based on two components: Arotating slotted nozzle inside the sieving chamber and a powerful industrial vacuum cleaner which is connected tothe chamber. The vacuum cleaner generates a vacuum inside the sieving chamber and sucks in fresh air through theslotted nozzle. When passing the narrow slit of the nozzle the air stream is accelerated and blown against the sievemesh, dispersing the particles. Above the mesh, the air jet is distributed over the complete sieve surface and issucked in with low speed through the sieve mesh. Thus the finer particles are transported through the mesh openingsinto the vacuum cleaner.

Sieve analysis 21

Air jet sieving machine

Types of gradation

Dense gradationA dense gradation refers to a sample that is approximately ofequal amounts of various sizes of aggregate. By having a densegradation, most of the air voids between the material are filledwith particles. A dense gradation will result in an even curve onthe gradation graph.[5]

Narrow gradationAlso known as uniform gradation, a narrow gradation is asample that has aggregate of approximately the same size. Thecurve on the gradation graph is very steep, and occupies a smallrange of the aggregate.[4]

Gap gradationA gap gradation refers to a sample with very little aggregate inthe medium size range. This results in only coarse and fineaggregate. The curve is horizontal in the medium size range onthe gradation graph.[4]

Open gradationAn open gradation refers an aggregate sample with very little fine aggregate particles. This results in many airvoids, because there are no fine particles to fill them. On the gradation graph, it appears as a curve that ishorizontal in the small size range.[4]

Rich gradationA rich gradation refers to a sample of aggregate with a high proportion of particles of small sizes.[5]

Limitations of sieve analysisSieve analysis has, in general, been used for decades to monitor material quality based on particle size. For coarsematerial, sizes that range down to #100 mesh (150μm), a sieve analysis and particle size distribution is accurate andconsistent.However, for material that is finer than 100 mesh, dry sieving can be significantly less accurate. This is because themechanical energy required to make particles pass through an opening and the surface attraction effects between theparticles themselves and between particles and the screen increase as the particle size decreases. Wet sieve analysiscan be utilized where the material analyzed is not affected by the liquid - except to disperse it. Suspending theparticles in a suitable liquid transports fine material through the sieve much more efficiently than shaking the drymaterial.Sieve analysis assumes that all particle will be round (spherical) or nearly so and will pass through the squareopenings when the particle diameter is less than the size of the square opening in the screen. For elongated and flatparticles a sieve analysis will not yield reliable mass-based results, as the particle size reported will assume that theparticles are spherical, where in fact an elongated particle might pass through the screen end-on, but would beprevented from doing so if it presented itself side-on.

Sieve analysis 22

PropertiesGradation affects many properties of an aggregate. It affects bulk density, physical stability and permeability. Withcareful selection of the gradation, it is possible to achieve high bulk density, high physical stability, and lowpermeability. This is important because in pavement design, a workable, stable mix with resistance to water isimportant. With an open gradation, the bulk density is relatively low, due to the lack of fine particles, the physicalstability is moderate, and the permeability is quite high. With a rich gradation, the bulk density will also be low, thephysical stability is low, and the permeability is also low. The gradation can be affected to achieve the desiredproperties for the particular engineering application.[5]

Engineering applicationsGradation is usually specified for each engineering application it is used for. For example, foundations might onlycall for coarse aggregates, and therefore an open gradation is needed.

ForecastWithin the last years some methods for particle size distribution measurement were developed which work by meansof laser diffraction or digital image processing.

"Sieving" with digital image processing

The scope of information conveyed by sieve analysis is relativelysmall. It does not allow for a clear statement concerning the exact sizeof a single particle; it is just classified within a size range which isdetermined by two sieve sizes ("a particle is smaller than sieve size xand greater than sieve size y"). And there is no additional informationconcerning other relevant properties like opacity or shape available.Devices which work with digital image processing enable to recalleven this information and a lot more (surface analysis, etc.). Theresults can be fitted to sieve analysis so that a comparison betweenmeasurement results obtained with different methods is possible.

References[1][1] p231 in "Characterisation of bulk solids" by Donald Mcglinchey, CRC Press, 2005.[2] ASTM International - Standards Worldwide. (2006). ASTM C136-06. http:/ / www. astm. org/ cgi-bin/ SoftCart. exe/ DATABASE. CART/

REDLINE_PAGES/ C136. htm?E+ mystore[3] AASHTO The Voice of Transportation. T0 27. (2006). http:/ / bookstore. transportation. org/ item_details. aspx?ID=659[4] Pavement Interactive. Gradation Test. (2007). http:/ / pavementinteractive. org/ index. php?title=Gradation_Test[5] M.S. Mamlouk and J.P. Zaniewski, Materials for Civil and Construction Engineers, Addison-Wesley, Menlo Park CA, 1999

External links• The Basic Principles of Sieve Analysis (http:/ / www. retsch. com/ products/ sieving/ dlDetails/ 1/ file/ 5930/ ?L=)

Ball mill 23

Ball millFor the type of end mill, see Ball nose cutter.

Ball mill

A ball mill is a type of grinder used to grind materials into extremelyfine powder for use in mineral dressing processes, paints, pyrotechnics,and ceramics.

Description

Bench top ball mill

Laboratory scale ball mill

A ball mill, a type of grinder, is a cylindrical device used in grinding(or mixing) materials like ores, chemicals, ceramic raw materials andpaints. Ball mills rotate around a horizontal axis, partially filled withthe material to be ground plus the grinding medium. Differentmaterials are used as media, including ceramic balls, flint pebbles andstainless steel balls. An internal cascading effect reduces the materialto a fine powder. Industrial ball mills can operate continuously, fed atone end and discharged at the other end. Large to medium-sized ballmills are mechanically rotated on their axis, but small ones normallyconsist of a cylindrical capped container that sits on two drive shafts(pulleys and belts are used to transmit rotary motion). A rock tumblerfunctions on the same principle. Ball mills are also used inpyrotechnics and the manufacture of black powder, but cannot be usedin the preparation of some pyrotechnic mixtures such as flash powderbecause of their sensitivity to impact. High-quality ball mills arepotentially expensive and can grind mixture particles to as small as 5nm, enormously increasing surface area and reaction rates. Thegrinding works on the principle of critical speed. The critical speed canbe understood as that speed after which the steel balls (which areresponsible for the grinding of particles) start rotating along thedirection of the cylindrical device; thus causing no further grinding.

Ball mills are used extensively in the Mechanical alloying process[1] in which they are not only used for grinding butfor cold welding as well, with the purpose of producing alloys from powders.[2]

Ball mill 24

High-energy ball milling

Lead antimony grinding media with aluminiumpowder.

A ball mill inside the Mayflower Mill near Silverton, Colorado.

The ball mill is a key piece of equipment forgrinding crushed materials, and it is widelyused in production lines for powders such ascement, silicates, refractory material,fertilizer, glass ceramics, etc. as well as forore dressing of both ferrous non-ferrousmetals. The ball mill can grind various oresand other materials either wet or dry. Thereare two kinds of ball mill, grate type andoverfall type due to different ways ofdischarging material. There are many typesof grinding media suitable for use in a ballmill, each material having its own specificproperties and advantages. Key properties ofgrinding media are size, density, hardness,and composition.•• Size: The smaller the media particles, the

smaller the particle size of the finalproduct. At the same time, the grindingmedia particles should be substantiallylarger than the largest pieces of materialto be ground.

•• Density: The media should be denserthan the material being ground. Itbecomes a problem if the grinding mediafloats on top of the material to be ground.

•• Hardness: The grinding media needs tobe durable enough to grind the material,

but where possible should not be so tough that it also wears down the tumbler at a fast pace.•• Composition: Various grinding applications have special requirements. Some of these requirements are based on

the fact that some of the grinding media will be in the finished product. Others are based in how the media willreact with the material being ground.

Ball mill 25

•• Where the color of the finished product is important, the color and material of the grinding media must beconsidered.

•• Where low contamination is important, the grinding media may be selected for ease of separation from thefinished product (i.e.: steel dust produced from stainless steel media can be magnetically separated fromnon-ferrous products). An alternative to separation is to use media of the same material as the product beingground.

• Flammable products have a tendency to become explosive in powder form. Steel media may spark, becomingan ignition source for these products. Either wet-grinding, or non-sparking media such as ceramic or lead mustbe selected.

• Some media, such as iron, may react with corrosive materials. For this reason, stainless steel, ceramic, and flintgrinding media may each be used when corrosive substances are present during grinding.

The grinding chamber can also be filled with an inert shield gas that does not react with the material being ground, toprevent oxidation or explosive reactions that could occur with ambient air inside the mill.

VarietiesAside from common ball mills there is a second type of ball mill called planetary ball mill. Planetary ball mills aresmaller than common ball mills and mainly used in laboratories for grinding sample material down to very smallsizes. A planetary ball mill consists of at least one grinding jar which is arranged eccentrically on a so-called sunwheel. The direction of movement of the sun wheel is opposite to that of the grinding jars (ratio: 1:-2 or 1:-1 or else).The grinding balls in the grinding jars are subjected to superimposed rotational movements, the so-called Coriolisforces. The difference in speeds between the balls and grinding jars produces an interaction between frictional andimpact forces, which releases high dynamic energies. The interplay between these forces produces the high and veryeffective degree of size reduction of the planetary ball mill.

HistoryDevices for shaking materials along with hard balls might be old, but it was not until the industrial revolution and theinvention of steam power that a machine could be built. It is reported to have been used for grinding flint for potteryin 1870.[3]

References[1] M. I. Florez-Zamora et al. Comparative study of Al-Ni-Mo alloys obtained by mechanical alloying in different ball mills (http:/ / www. ipme.

ru/ e-journals/ RAMS/ no_31808/ martinez3. pdf) Rev. Adv. Mater. Sci. 18 (2008) 301[2] Mechanical Alloying Technology (http:/ / www. imp. mtu. edu/ webform/ index. htm), Institute of Materials Processing[3] Lynch, A., Rowland C (2005). The history of grinding (http:/ / books. google. com/ books?id=Kj7PSOqTZ3IC& printsec=frontcover). SME.

ISBN 0-87335-238-6. .

Filtration 26

Filtration

Diagram of simple filtration: oversize particles in the feed cannot pass through thelattice structure of the filter, while fluid and small particles pass through, becoming

filtrate.

Filtration is commonly the mechanical orphysical operation which is used for theseparation of solids from fluids (liquids orgases) by interposing a medium throughwhich only the fluid can pass. Oversizesolids in the fluid are retained, but theseparation is not complete; solids will becontaminated with some fluid and filtratewill contain fine particles (depending on thepore size and filter thickness). Filtration isalso used to describe some biologicalprocesses, especially in water treatment andsewage treatment in which undesirableconstituents are removed by absorption intoa biological film grown on or in the filtermedium.

Applications• Filtration is used to separate particles and fluid in a suspension, where the fluid can be a liquid, a gas or a

supercritical fluid. Depending on the application, either one or both of the components may be isolated.• Filtration, as a physical operation is very important in chemistry for the separation of materials of different

chemical composition. A solvent is chosen which dissolves one component, while not dissolving the other. Bydissolving the mixture in the chosen solvent, one component will go into the solution and pass through the filter,while the other will be retained. This is one of the most important techniques used by chemists to purifycompounds.

• Filtration is also important and widely used as one of the unit operations of chemical engineering. It may besimultaneously combined with other unit operations to process the feed stream, as in the biofilter, which is acombined filter and biological digestion device.

• Filtration differs from sieving, where separation occurs at a single perforated layer (a sieve). In sieving, particlesthat are too big to pass through the holes of the sieve are retained (see particle size distribution). In filtration, amultilayer lattice retains those particles that are unable to follow the tortuous channels of the filter.[1] Oversizeparticles may form a cake layer on top of the filter and may also block the filter lattice, preventing the fluid phasefrom crossing the filter (blinding). Commercially, the term filter is applied to membranes where the separationlattice is so thin that the surface becomes the main zone of particle separation, even though these products mightbe described as sieves.[2]

• Filtration differs from adsorption, where it is not the physical size of particles that causes separation but theeffects of surface charge. Some adsorption devices containing activated charcoal and ion exchange resin arecommercially called filters, although filtration is not their principal function.[3]

• Filtration differs from removal of magnetic contaminants from fluids with magnets (typically lubrication oil,coolants and fuel oils), because there is no filter medium. Commercial devices called "magnetic filters" are sold,but the name reflects their use, not their mode of operation.[4]

The remainder of this article focuses primarily on liquid filtration.

Filtration 27

MethodsThere are many different methods of filtration; all aim to attain the separation of substances. Separation is achievedby some form of interaction between the substance or objects to be removed and the filter. The substance that is topass through the filter must be a fluid, i.e. a liquid or gas. Methods of filtration vary depending on the location of thetargeted material, i.e. whether it is dissolved in the fluid phase or suspended as a solid.

Filter mediaTwo main types of filter media are employed in the chemical laboratory— surface filter, a solid sieve which trapsthe solid particles, with or without the aid of filter paper (e.g. Büchner funnel, Belt filter, Rotary vacuum-drum filter,Cross-flow filters, Screen filter), and a depth filter, a bed of granular material which retains the solid particles as itpasses (e.g. sand filter). The first type allows the solid particles, i.e. the residue, to be collected intact; the secondtype does not permit this. However, the second type is less prone to clogging due to the greater surface area wherethe particles can be trapped. Also, when the solid particles are very fine, it is often cheaper and easier to discard thecontaminated granules than to clean the solid sieve.Filter media can be cleaned by rinsing with solvents or detergents. Alternatively, in engineering applications, such asswimming pool water treatment plants, they may be cleaned by backwashing. Self-cleaning screen filters utilizepoint-of-suction backwashing to clean the screen without interrupting system flow.

Achieving flow through the filterFluids flow through a filter due to a difference in pressure — fluid flows from the high pressure side to the lowpressure side of the filter, leaving some material behind. The simplest method to achieve this is by gravity and can beseen in the coffeemaker example. In the laboratory, pressure in the form of compressed air on the feed side (orvacuum on the filtrate side) may be applied to make the filtration process faster, though this may lead to clogging orthe passage of fine particles. Alternatively, the liquid may flow through the filter by the force exerted by a pump, amethod commonly used in industry when a reduced filtration time is important. In this case, the filter need not bemounted vertically.

Filter aidCertain filter aids may be used to aid filtration. These are often incompressible diatomaceous earth, or kieselguhr,which is composed primarily of silica. Also used are wood cellulose and other inert porous solids such as the cheaperand safer perlite.These filter aids can be used in two different ways. They can be used as a precoat before the slurry is filtered. Thiswill prevent gelatinous-type solids from plugging the filter medium and also give a clearer filtrate. They can also beadded to the slurry before filtration. This increases the porosity of the cake and reduces resistance of the cake duringfiltration. In a rotary filter, the filter aid may be applied as a precoat; subsequently, thin slices of this layer are slicedoff with the cake.The use of filter aids is usually limited to cases where the cake is discarded or where the precipitate can bechemically separated from the filter.

Filtration 28

AlternativesFiltration is a more efficient method for the separation of mixtures than decantation, but is much more timeconsuming. If very small amounts of solution are involved, most of the solution may be soaked up by the filtermedium.An alternative to filtration is centrifugation — instead of filtering the mixture of solid and liquid particles, themixture is centrifuged to force the (usually) denser solid to the bottom, where it often forms a firm cake. The liquidabove can then be decanted. This method is especially useful for separating solids which do not filter well, such asgelatinous or fine particles. These solids can clog or pass through the filter, respectively.

Examples

Filter flask (suction flask, with sintered glass filter containingsample). Note the almost colourless filtrate in the receiver

flask.

Examples of filtration include• The coffee filter to keep the coffee separate from the

grounds.• HEPA filters in air conditioning to remove particles from

air.• Belt filters to extract precious metals in mining.• Horizontal plate filter, also known as Sparkler filter.•• Furnaces use filtration to prevent the furnace elements

from fouling with particulates.• Pneumatic conveying systems often employ filtration to

stop or slow the flow of material that is transported,through the use of a baghouse.

• In the laboratory, a Büchner funnel is often used, with afilter paper serving as the porous barrier.

An experiment to prove the existence of microscopicorganisms involves the comparison of water passed throughunglazed porcelain and unfiltered water. When left in sealedcontainers the filtered water takes longer to go foul,demonstrating that very small items (such as bacteria) can beremoved from fluids by filtration.

In the kidney, renal filtration is the filtration of blood in theglomerulus, followed by selective reabsorbtion of manysubstances essential for the body to maintain homeostasis.

References[1][1] Lecture notes, Postgraduate course on Filtration and Size separation at the Department of Chemical Engineering, University of Lougborough,

England[2] Sterlitech (http:/ / www. sterlitech. com/ 37617/ Membrane-Disc-Filters. html)[3] How does a Brita water filter work FAQ (http:/ / www. brita. net/ uk/ faqs_household. html?L=1#10)[4] Eclipse Magnetics – Magnetic filter supplier (http:/ / www. eclipse-magnetics. co. uk/ product-categories/ magneticfiltration)

Filtration 29

External links• The Encyclopedia of Filters - Liquid Filtration (http:/ / www. qfilter. com/ Resource. aspx/ DocumentDetail/ 16)

An overview of the many types of liquid filtration.

CrusherA crusher is a machine designed to reduce large rocks into smaller rocks, gravel, or rock dust.Crushers may be used to reduce the size, or change the form, of waste materials so they can be more easily disposedof or recycled, or to reduce the size of a solid mix of raw materials (as in rock ore), so that pieces of differentcomposition can be differentiated. Crushing is the process of transferring a force amplified by mechanical advantagethrough a material made of molecules that bond together more strongly, and resist deformation more, than those inthe material being crushed do. Crushing devices hold material between two parallel or tangent solid surfaces, andapply sufficient force to bring the surfaces together to generate enough energy within the material being crushed sothat its molecules separate from (fracturing), or change alignment in relation to (deformation), each other. Theearliest crushers were hand-held stones, where the weight of the stone provided a boost to muscle power, usedagainst a stone anvil. Querns and mortars are types of these crushing devices.

Industrial useIn industry, crushers are machines which use a metal surface to break or compress materials. Mining operations usecrushers, commonly classified by the degree to which they fragment the starting material, with primary andsecondary crushers handling coarse materials, and tertiary and quaternary crushers reducing ore particles to finergradations. Each crusher is designed to work with a certain maximum size of raw material, and often delivers itsoutput to a screening machine which sorts and directs the product for further processing. Typically, crushing stagesare followed by milling stages if the materials need to be further reduced. Additionally rockbreakers are typicallylocated next to a crusher to reduce oversize material too large for a crusher. Crushers are used to reduce particle sizeenough so that the material can be processed into finer particles in a grinder. A typical processing line at a minemight consist of a crusher followed by a SAG mill followed by a ball mill. In this context, the SAG mill and ball millare considered grinders rather than crushers.In operation, the raw material (of various sizes) is usually delivered to the primary crusher's hopper by dump trucks,excavators or wheeled front-end loaders. A feeder device such as an apron feeder, conveyor or vibrating gridcontrols the rate at which this material enters the crusher, and often contains a preliminary screening device whichallows smaller material to bypass the crusher itself, thus improving efficiency. Primary crushing reduces the largepieces to a size which can be handled by the downstream machinery.Some crushers are mobile and can crush rocks as large as 60 inches. Primarily used in-pit at the mine face these unitsare able to move with the large infeed machines (mainly shovels) to increase the tonnage produced. In a mobile roadoperation, these crushed rocks are directly combined with concrete and asphalt which are then deposited on to a roadsurface. This removes the need for hauling over-sized material to a stationary crusher and then back to the roadsurface.

Crusher 30

Types of crushers

Portable Close Circuit Cone Crushing Plant

Cornish stamps used in the 19thcentury for breaking tin ore

A portable rock crusher fromthe early 20th century

The entrance bin of a mine rockcrusher

Mobile crusher

The following table describes typical uses of commonly used crushers:

Type Hardness Abrasionlimit

Moisture content Reductionratio

Main use

Jaw crushers Soft to very hard No limit Dry to slightly wet,not sticky

3/1 to 5/1 Heavy mining, Quarried materials,sand & gravel, recycling

Gyratory crushers Soft to very hard Abrasive Dry to slightly wet,not sticky

4/1 to 7/1 Heavy mining, Quarried materials

Cone crushers Medium hard tovery hard

Abrasive Dry or wet, notsticky

3/1 to 5/1 Quarried materials, Sand & gravel

Compound crusher Medium hard tovery hard

Abrasive Dry or wet, notsticky

3/1 to 5/1 Mine, Building Materials

Horizontal shaft impactors Soft to mediumhard

Slightlyabrasive

Dry or wet, notsticky

10/1 to 25/1 Quarried materials, sand & gravel,recycling

Vertical shaft impactors(shoe and anvil)

Medium hard tovery hard

Slightlyabrasive

Dry or wet, notsticky

6/1 to 8/1 Sand & gravel, recycling

Vertical shaft impactors(autogenous)

Soft to very hard No limit Dry or wet, notsticky

2/1 to 5/1 Quarried materials, sand & gravel

Mineral sizers Hard to soft Abrasive Dry or wet and sticky 2/1 to 5/1 Heavy mining

Crusher 31

Jaw crusher

Operation of a jaw crusher

A jaw or toggle crusher consists of a set of vertical jaws, one jaw beingfixed and the other being moved back and forth relative to it by a camor pitman mechanism, acting as a class II lever, like a nutcracker. Thejaws are farther apart at the top than at the bottom, forming a taperedchute so that the material is crushed progressively smaller and smalleras it travels downward until it is small enough to escape from thebottom opening. The movement of the jaw can be quite small, sincecomplete crushing is not performed in one stroke. The inertia requiredto crush the material is provided by a weighted flywheel that moves ashaft creating an eccentric motion that causes the closing of the gap.

Single and double toggle jaw crushers are constructed of heavy duty fabricated plate frames with reinforcing ribsthroughout. The crusher's components are of high strength design to accept high power draw. Manganese steel isused for both fixed and movable jaw faces. Heavy flywheels allow crushing peaks on tough materials. DoubleToggle jaw crushers may feature hydraulic toggle adjusting mechanisms.There are 3 types of jaw crushers according to the place the movable plate has been fixed around which position therotates the movable jaw.1.1. Blake crusher-fixed in the lower point2.2. Dodge crusher-fixed in the upper point3.3. Universal crusher-fixed in the midpoint

Gyratory crusher

Ruffner Red Ore Mine gyratory crusher

A gyratory crusher is similar in basic concept to a jaw crusher,consisting of a concave surface and a conical head; both surfaces aretypically lined with manganese steel surfaces. The inner cone has aslight circular movement, but does not rotate; the movement isgenerated by an eccentric arrangement. As with the jaw crusher,material travels downward between the two surfaces beingprogressively crushed until it is small enough to fall out through thegap between the two surfaces.

A gyratory crusher is one of the main types of primary crushers in amine or ore processing plant. Gyratory crushers are designated in sizeeither by the gape and mantle diameter or by the size of the receivingopening. Gyratory crushers can be used for primary or secondarycrushing. The crushing action is caused by the closing of the gapbetween the mantle line (movable) mounted on the central verticalspindle and the concave liners (fixed) mounted on the main frame ofthe crusher. The gap is opened and closed by an eccentric on thebottom of the spindle that causes the central vertical spindle to gyrate.The vertical spindle is free to rotate around its own axis. The crusher illustrated is a short-shaft suspended spindletype, meaning that the main shaft is suspended at the top and that the eccentric is mounted above the gear. Theshort-shaft design has superseded the long-shaft design in which the eccentric is mounted below the gear.

Crusher 32

Cone Crusher

Cone crusher

A cone crusher is similar in operation to a gyratory crusher, with lesssteepness in the crushing chamber and more of a parallel zone betweencrushing zones. A cone crusher breaks rock by squeezing the rockbetween an eccentrically gyrating spindle, which is covered by a wearresistant mantle, and the enclosing concave hopper, covered by amanganese concave or a bowl liner. As rock enters the top of the conecrusher, it becomes wedged and squeezed between the mantle and thebowl liner or concave. Large pieces of ore are broken once, and thenfall to a lower position (because they are now smaller) where they arebroken again. This process continues until the pieces are small enoughto fall through the narrow opening at the bottom of the crusher.

A cone crusher is suitable for crushing a variety of mid-hard and above mid-hard ores and rocks. It has the advantageof reliable construction, high productivity, easy adjustment and lower operational costs. The spring release system ofa cone crusher acts an overload protection that allows tramp to pass through the crushing chamber without damage tothe crusher.

Impact crusherImpact crushers involve the use of impact rather than pressure to crush material. The material is contained within acage, with openings on the bottom, end, or side of the desired size to allow pulverized material to escape. There aretwo types of impact crushers: horizontal shaft impactor and vertical shaft impactor.

Horizontal shaft impactor (HSI) / Hammer mill

The HSI crushers break rock by impacting the rock with hammers that are fixed upon the outer edge of a spinningrotor. HSI machines are sold in Stationary, trailer mounted and crawler mounted configurations. HSI's are used inrecycling, hard rock and soft materials. In earlier years the practical use of HSI crushers is limited to soft materialsand non abrasive materials, such as limestone, phosphate, gypsum, weathered shales, however improvements inmetalurgy has changed the application of these machines.HS

Vertical shaft impactor (VSI)

Scheme of a VSI crusher with air-cushion support

VSI crushers use a different approach involving a high speed rotor withwear resistant tips and a crushing chamber designed to 'throw' the rockagainst. The VSI crushers utilize velocity rather than surface force asthe predominant force to break rock. In its natural state, rock has ajagged and uneven surface. Applying surface force (pressure) results inunpredictable and typically non-cubical resulting particles. Utilizingvelocity rather than surface force allows the breaking force to beapplied evenly both across the surface of the rock as well as throughthe mass of the rock. Rock, regardless of size, has natural fissures(faults) throughout its structure. As rock is 'thrown' by a VSI Rotoragainst a solid anvil, it fractures and breaks along these fissures. Finalparticle size can be controlled by 1) the velocity at which the rock isthrown against the anvil and 2) the distance between the end of the

Crusher 33

VSI crusher

rotor and the impact point on the anvil. The product resulting from VSICrushing is generally of a consistent cubical shape such as thatrequired by modern SUPERPAVE highway asphalt applications. Usingthis method also allows materials with much higher abrasiveness to becrushed than is capable with an HSI and most other crushing methods.

VSI crushers generally utilize a high speed spinning rotor at the centerof the crushing chamber and an outer impact surface of either abrasiveresistant metal anvils or crushed rock. Utilizing cast metal surfaces'anvils' is traditionally referred to as a "Shoe and Anvil VSI". Utilizingcrushed rock on the outer walls of the crusher for new rock to becrushed against is traditionally referred to as "rock on rock VSI". VSIcrushers can be used in static plant set-up or in mobile tracked equipment.

Mineral sizersThe basic concept of the mineral sizer is the use of two rotors with large teeth, on small diameter shafts, driven at alow speed by a direct high torque drive system. This design produces three major principles which all interact whenbreaking materials using sizer technology. The unique principles are the three-stage breaking action, the rotatingscreen effect, and the deep scroll tooth pattern.The three-stage breaking action: initially, the material is gripped by the leading faces of opposed rotor teeth. Thesesubject the rock to multiple point loading, inducing stress into the material to exploit any natural weaknesses. At thesecond stage, material is broken in tension by being subjected to a three point loading, applied between the fronttooth faces on one rotor, and rear tooth faces on the other rotor. Any lumps of material that still remain oversize, arebroken as the rotors chop through the fixed teeth of the breaker bar, thereby achieving a three dimensional controlledproduct size.The rotating screen effect: The interlaced toothed rotor design allows free flowing undersize material to pass throughthe continuously changing gaps generated by the relatively slow moving shafts.The deep scroll tooth pattern: The deep scroll conveys the larger material to one end of the machine and helps tospread the feed across the full length of the rotors. This feature can also be used to reject oversize material from themachine.[1]

TechnologyFor the most part advances in crusher design have moved slowly. Jaw crushers have remained virtually unchangedfor sixty years. More reliability and higher production have been added to basic cone crusher designs that have alsoremained largely unchanged. Increases in rotating speed have provided the largest variation. For instance, a 48 inch(120 cm) cone crusher manufactured in 1960 may be able to produce 170 tons/h of crushed rock, whereas the samesize crusher manufactured today may produce 300 tons/h. These production improvements come from speedincreases and better crushing chamber designs.The largest advance in cone crusher reliability has been seen in the use of hydraulics to protect crushers from beingdamaged when uncrushable objects enter the crushing chamber. Foreign objects, such as steel, can cause extensivedamage to a cone crusher, and additional costs in lost production. The advance of hydraulic relief systems hasgreatly reduced downtime and improved the life of these machines.

Crusher 34

References[1][1] The MMD Group of Companies."MMD Sizers". The MMD Group of Companies, 2005, p 3.

PulverizerA pulverizer or grinder is a mechanical device for the grinding of many different types of materials. For example,they are used to pulverize coal for combustion in the steam-generating furnaces of fossil fuel power plants.

Types of pulverizersCoal pulverizers may be classified by speed, as follows:[1]

•• Low Speed•• Medium Speed•• High Speed

Low Speed

Ball and tube mills

A ball mill is a pulverizer that consists of a horizontal rotating cylinder, up to three diameters in length, containing acharge of tumbling or cascading steel balls, pebbles, or rods.A tube mill is a revolving cylinder of up to five diameters in length used for fine pulverization of ore, rock, and othersuch materials; the material, mixed with water, is fed into the chamber from one end, and passes out the other end asslime (slurry).Both types of mill include liners that protect the cylindrical structure of the mill from wear. Thus the main wear partsin these mills are the balls themselves, and the liners. The balls are simply "consumed" by the wear process and mustbe re-stocked, whereas the liners must be periodically replaced. The ball and tube mills are low-speed machines thatgrind the coal with steel balls in a rotating horizontal cylinder. Due to its shape only, people call it as Tube Mill anddue to use of Grinding Balls for crushing, it is called Ball Mill. Hence, is the name Ball Tube Mill. These Mills arealso designated as BBD-4772, Where- B – Broyer (Name of inventor). B – Boulet (French word for Balls). D –Direct firing. 47 – Diameter of shell (in Decimeters) i.e. 4.7m dia. 72 – Length of shell (in Decimeters) i.e. 7.2 mlengthBy the name the grinding in the ball and tube mill is produced by rotating quantity of steel balls by their fall and liftdue to rotation of tube. The ball charge may occupy one third to half of the total internal volume of the shell. Thesignificant feature incorporated in the BBD mills is its double end operation, each end catering to one elevation of aboiler. The system facilitated entry of raw coal and outlet of pulverized fuel from same end simultaneously. Thishelps in reducing the number of installations per unit.

Mill Constructions And DetailsA ball Tube mill may be described as a cylinder made of steel plate having separate heads or trunion attached to theends with the trunion resting on suitable bearings for supporting the machine. The trunion are hollow to allow for theintroduction of discharge of the materials undergoing reduction in size. The mill shell is lined with chilled iron,carbon steel, manganese steel, High Chrome liners attached to shell body with counter sunk bolts.These liners aremade in different shapes so that the counter inside surface of the mill is suited for requirement of application.The Shells are of three pieces. The Intermediate shell connects to the end shells by flange joints and the total lengthof shell is 7.2 m. The liners are fastened to the inner side of mill shell (cylindrical part) to protect the shell from the

Pulverizer 35

impact of steel balls. There are 600 nos. of liners of ten variants in each shell weighing 60.26 MT. The original liftvalue of the liners is 55 mm. and the minimum lift allowed is 20 mm.

WorkingPrimary air in the case of Tube Mill have dual function to perform. It is used as drying as well as transporting mediaand by regulating the same the Mill output is regulated. Governed by the pulverize fuel outlet temperaturerequirement the combination of cold air and hot air dampers are regulated to have proper primary air temperature. Inaddition to raising the coal temperature Inside the Mill for drying and better grinding the same air works carryingmedia for pulverized coal through annular space between fixed trunnion tube and rotating hot air tube on way toclassifier. Coal-laden air passing through Double cone static classifiers with adjustable classifier vanes forsegregation Into pulverized fuel of desired fineness and coarse particles continues its journey towards coal burnersfor combustion. Coarse particles rejected in classifier find their way back to mill for another cycle of grinding. Inorder to avoid excess sweeping of coal from Mill Only Part Of the primary air, directly proportional to the boilerload demand is passed through Mill. Further to ensure and maintain sufficient velocity of pulverized fuel and toavoid settling in P.F. pipes an additional quantity of primary air is fed in to mixing box on raw coat circuit. Thisby-pass air tapped from the primary air duct going in Mill makes appreciable contribution for drying of raw coal byflash drying effect in addition to picking pp the pulverized fuel from Mill outlet for its transportation towardsclassifiers. Tube mill output while responding to boiler load demand is controlled by regulating primary air-flow.Such regulation by sweeping away of pulverized fuel from Mill being very fast rather well comparable with oil firingresponse, needs coal level to be maintained in the Mill. Mill level control circuit sensing the decreased coat level inMill increases the speed of raw coal feeder and vice avers. Maintaining the coal level in Mill offers built-in-capacitycushion of pulverized fuel to take care of short interruption in raw coal circuit. The mill is pressurized and thetightness is ensured by plenum chambers around the rotating trunnion filled with pressurized seal air. Bleeding sealair from plenum chamber to Mill provides air cushion between pulverized fuel in the Mill and the outsideatmosphere. Inadequacy or absence of seal air will allow escape of pulverized fuel into atmosphere. On the otherhand excess of seal air leaking into Mill will affect the Mill outlet temperature. As such the seal air is controlled by alocal control damper by maintaining just sufficient differential pressure for sealing.

Medium Speed

Ring and ball mill

This type of mill consists of two rings separated by a series of large balls, like a thrust bearing. The lower ringrotates, while the upper ring presses down on the balls via a set of spring and adjuster assemblies, or pressurisedrams. The material to be pulverized is introduced into the center or side of the pulverizer (depending on the design).As the lower ring rotates, the balls to orbit between the upper and lower rings, and balls roll over the bed of coal onthe lower ring. The pulverized material is carried out of the mill by the flow of air moving through it. The size of thepulverized particles released from the grinding section of the mill is determined by a classifier separator - if the coalis fine enough to be picked up by the air, it is carried through the classifier. Coarser particles return to be furtherpulverized.

Vertical spindle roller millSimilar to the ring and ball mill, this mill uses large "tires" to crush the coal. These are usually found in utility plants.Raw coal is gravity-fed through a central feed pipe to the grinding table where it flows outwardly by centrifugalaction and is ground between the rollers and table. Hot primary air for drying and coal transport enters the windboxplenum underneath the grinding table and flows upward through a swirl ring having multiple sloped nozzlessurrounding the grinding table. The air mixes with and dries coal in the grinding zone and carries pulverized coalparticles upward into a classifier.

Pulverizer 36

Fine pulverized coal exits the outlet section through multiple discharge coal pipes leading to the burners, whileoversized coal particles are rejected and returned to the grinding zone for further grinding. Pyrites and extraneousdense impurity material fall through the nozzle ring and are plowed, by scraper blades attached to the grinding table,into the pyrites chamber to be removed. Mechanically, the vertical roller mill is categorized as an applied force mill.There are three grinding roller wheel assemblies in the mill grinding section, which are mounted on a loading framevia pivot point. The fixed-axis roller in each roller wheel assembly rotates on a segmentally-lined grinding table thatis supported and driven by a planetary gear reducer direct-coupled to a motor. The grinding force for coalpulverization is applied by a loading frame. This frame is connected by vertical tension rods to three hydrauliccylinders secured to the mill foundation. All forces used in the pulverizing process are transmitted to the foundationvia the gear reducer and loading elements. The pendulum movement of the roller wheels provides a freedom forwheels to move in a radial direction, which results in no radial loading against the mill housing during thepulverizing process.Depending on the required coal fineness, there are two types of classifier that may be selected for a vertical rollermill. The dynamic classifier, which consists of a stationary angled inlet vane assembly surrounding a rotating vaneassembly or cage, is capable of producing micron fine pulverized coal with a narrow particle size distribution. Inaddition, adjusting the speed of the rotating cage can easily change the intensity of the centrifugal force field in theclassification zone to achieve coal fineness control real-time to make immediate accommodation for a change in fuelor boiler load conditions. For the applications where a micron fine pulverized coal is not necessary, the staticclassifier, which consists of a cone equipped with adjustable vanes, is an option at a lower cost since it contains nomoving parts. With adequate mill grinding capacity, a vertical mill equipped with a static classifier is capable ofproducing a coal fineness up to 99.5% or higher <50 mesh and 80% or higher <200 mesh, while one equipped with adynamic classifier produces coal fineness levels of 100% <100 mesh and 95% <200 mesh, or better.In 1954 a Jet Pulverizer was developed in which operates like a Vertical Pulverizer only the item is pulverized bythe high speed air action. For example forcing coal against coal. [2]

Bowl mill

Similar to the vertical roller mill, it also uses tires to crush coal. There are two types, a deep bowl mill, and a shallowbowl mill.

High Speed

Attrition Mill

Rotor, Stationary Pegs

Hammer Mill

Used on farms for grinding grain and chaff for feed

Demolition pulverizerAn attachment fitted to an excavator. Commonly used in demolition work to break up large pieces of concrete.

Pulverizer 37

References[1][1] Coal Pulverising Mill Types, by Glenn Schumacher, 2010[2] "Jet Pulverizer." (http:/ / books. google. com/ books?id=Nd8DAAAAMBAJ& pg=PA156& dq=1954+ Popular+ Mechanics+ January&

hl=en& sa=X& ei=Q3YzT6TaKu2o0AHgjvW_Ag& ved=0CDMQ6AEwATgK#v=onepage& q& f=true) Popular Mechanics, April 1954, p.156.

Bibliography• Schumacher, Glenn (201). Coal Pulverising Mill Types. ISBN 978-0-646-53759-7.

Froth flotation

Diagram of a cylindrical froth flotation cell with camera and light used in imageanalysis of the froth surface.

Froth flotation is a process for selectivelyseparating hydrophobic materials fromhydrophilic. This is used in severalprocessing industries. Historically this wasfirst used in the mining industry.

History

Initially, naturally occurring chemicals suchas fatty acids and oils were used as flotationreagents in a large quantity to increase thehydrophobicity of the valuable minerals.Since then, the process has been adapted andapplied to a wide variety of materials to beseparated, and additional collector agents,including surfactants and syntheticcompounds have been adopted for variousapplications.

William Haynes in 1869 patented a processfor separating sulfide and gangue mineralsusing oil and called it bulk-oil flotation. In1885 Carrie Everson expanded upon this and patented a process calling for oil[s] but also an acid or a salt.

The first successful commercial flotation process for mineral sulphides was invented by Frank Elmore[1] whoworked on the development with his brother, Stanley. The Glasdir copper mine at Llanelltyd, near Dolgellau inNorth Wales was bought in 1896 by the Elmore brothers in conjunction with their father, William. In 1897, theElmore brothers installed the world's first industrial size commercial flotation process for mineral beneficiation at theGlasdir mine. The process was not froth flotation but used oil to agglomerate (make balls of) pulverised sulphidesand buoy them to the surface, and was patented in 1898 with a description of the process published in 1903 in theEngineering and Mining Journal. By this time they had recognized the importance of air bubbles in assisting the oilto carry away the mineral particles. The Elmores had formed a company known as the Ore Concentration SyndicateLtd to promote the commercial use of the process worldwide. However developments elsewhere, particularly inAustralia by Minerals Separation Ltd., led to decades of hard fought legal battles and litigations which, ultimately,

were lost as the process was superseded by more advanced techniques. Charles Butters, beginning about 1899, and working with both the Elmores and Minerals Separation's representative E.H. Nutter developed what was known to

Froth flotation 38

contemporaries as the "Butters Process". [2] The flotation process was independently invented in the early 1900s inAustralia by Charles Vincent Potter and around the same time by Guillaume Daniel Delprat..[3] [4] This process(developed circa 1902) did not use oil, but relied upon flotation by the generation of gas formed by the introductionof acid into the pulp. In 1902, Froment combined oil and gaseous flotation using a modification of the Potter-Delpratprocess.Another process was developed in 1902 by Cattermole, who emulsified the pulp with a small quantity of oil,subjected it to violent agitation, then slow stirring which coagulated the target minerals into nodules which wereseparated from the pulp by gravity. This was the basis of the Minerals Separation Ltd. process. By 1904, theMacQuisten process (a surface tension based method) was developed but this would not work when slimes werepresent. in 1912 Hyde modified the Minerals Separation Process and installed it in the Butte and Superior Mill inBasin, Montana. [5]

John M. Callow, of General Engineering of Salt Lake City, had followed flotation from technical papers and theintroduction in both the Butte and Superior Mill, and at Inspiration Copper in Arizona and determined thatmechanical agitation was a drawback to the existing technology. Introducing a porous brick with compressed air, anda mechanical stirring mechanism, Callow applied for a patent in 1914.[6] This method, known as PneumaticFlotation, was recognized to revolutionize the process of flotation concentration. A detailed description of the historyof flotation and this process can be found in Callows "Notes on Flotation" found in the Transactions of the AmericanInstitute of Mining Engineers; Vol 53-54, originally presented in New York in February 1916. The AIME presentedCallow the James Douglas Gold Medal in 1926 for his contributions to the field of flotation.In the 1960s the froth flotation technique was adapted for deinking recycled paper.

Industries

Mining

Froth flotation to separate plastics, ArgonneNational Laboratory

Froth flotation cells to concentrate copper andnickel sulfide minerals, Falconbridge, Ontario.

Froth flotation is a process for separating minerals from gangue bytaking advantage of differences in their hydrophobicity.Hydrophobicity differences between valuable minerals and wastegangue are increased through the use of surfactants and wetting agents.The selective separation of the minerals makes processing complex(that is, mixed) ores economically feasible. The flotation process isused for the separation of a large range of sulfides, carbonates andoxides prior to further refinement. Phosphates and coal are alsoupgraded (purified) by flotation technology.

Waste water treatment

The flotation process is also widely used in industrial waste watertreatment plants, where it removes fats, oil, grease and suspendedsolids from waste water. These units are called Dissolved air flotation(DAF) units.[7] In particular, dissolved air flotation units are used inremoving oil from the wastewater effluents of oil refineries,petrochemical and chemical plants, natural gas processing plants andsimilar industrial facilities.

Froth flotation 39

Paper recyclingFroth flotation is one of the processes used to recover recycled paper. In the paper industry this step is calleddeinking or just flotation. The target is to release and remove the hydrophobic contaminants from the recycled paper.The contaminants are mostly printing ink and stickies. Normally the setup is a two stage system with 3,4 or 5flotation cells in series.[8]

Principle of operationFroth flotation commences by comminution (that is, crushing and grinding), which is used to increase the surfacearea of the ore for subsequent processing and break the rocks into the desired mineral and gangue in a process knownas liberation, which then has to be separated from the desired mineral. The ore is ground into a fine powder andmixed with water to form a slurry. The desired mineral is rendered hydrophobic by the addition of a surfactant orcollector chemical. The particular chemical depends on which mineral is being refined. As an example, SEX isadded as a collector in the selective flotation of galena and sphalerite, after the addition of other flotation reagents.This slurry (more properly called the pulp) of hydrophobic particles and hydrophilic particles is then introduced to awater bath which is aerated, creating bubbles. The hydrophobic particles attach to the air bubbles, which rise to thesurface, forming a froth. The froth is removed and the concentrate (con) is further refined.

Science of flotationTo be effective on a given ore slurry, the collectors are chosen based upon their selective wetting of the types ofparticles to be separated. A good collector will adsorb, physically or chemically, with one of the types of particles.This provides the thermodynamic requirement for the particles to bind to the surface of a bubble. The wettingactivity of a surfactant on a particle can be quantified by measuring the contact angles that the liquid/bubble interfacemakes with it. Another important measure for attachment of bubbles to particles is induction time. The inductiontime is the time required for the particle and bubble to rupture the thin film separating the particle and bubble. Thisrupturing is achieved by the surface forces between the particle and bubble.The mechanisms for the bubble-particle attachment is very complex and consists of three steps, collision, attachmentand detachment. The collision is achieved by particles being within the collision tube of a bubble and this is affectedby the velocity of the bubble and radius of the bubble. The collision tube corresponds to the region in which aparticle will collide with the bubble, with the perimeter of the collision tube corresponding to the grazing trajectory.The attachment of the particle to the bubble is controlled by the induction time of the particle and bubble. Theparticle and bubble need to bind and this occurs if the time in which the particle and bubble are in contact with eachother is larger than the required induction time. This induction time is effected by the fluid viscosity, particle andbubble size and the forces between the particle and bubbles.The detachment of a particle and bubble occurs when the force exerted by the surface tension is exceeded by shearforces and gravitational forces. These forces are complex and vary within the cell. High shear will be experiencedclose to the impeller of a mechanical flotation cell and mostly gravitational force in the collection and cleaning zoneof a flotation column.Significant issues of entrainment of fine particles occurs as these particles experience low collision efficiencies aswell as sliming and degradation of the particle surfaces. Coarse particles show a low recovery of the valuablemineral due to the low liberation and high detachment efficiencies.

Froth flotation 40

Flotation equipment

Diagram of froth flotation cell. Numbered triangles show directionof stream flow. A mixture of ore and water called pulp [1] enters

the cell from a conditioner, and flows to the bottom of the cell. Air[2] or nitrogen is passed down a vertical impeller where shearing

forces break the air stream into small bubbles. The mineralconcentrate froth is collected from the top of the cell [3], while the

pulp [4] flows to another cell.

Flotation can be performed in rectangular or cylindricalmechanically agitated cells or tanks, flotation columns,Jameson cells or deinking flotation machines.Mechanical cells use a large mixer and diffusermechanism at the bottom of the mixing tank to introduceair and provide mixing action. Flotation columns use airspargers to introduce air at the bottom of a tall columnwhile introducing slurry above. The countercurrentmotion of the slurry flowing down and the air flowing upprovides mixing action. Mechanical cells generally have ahigher throughput rate, but produce material that is oflower quality, while flotation columns generally have alow throughput rate but produce higher quality material.

The Jameson cell uses neither impellers nor spargers,instead combining the slurry with air in a downcomerwhere high shear creates the turbulent conditions requiredfor bubble particle contacting.

Mechanics of flotation

The following steps are followed, followinggrinding to liberate the mineral particles:1.1. Reagent conditioning to achieve

hydrophobic surface charges on thedesired particles

2.2. Collection and upward transport bybubbles in an intimate contact with air ornitrogen

3.3. Formation of a stable froth on the surfaceof the flotation cell

4.4. Separation of the mineral laden frothfrom the bath (flotation cell)

Simple flotation circuit for mineralconcentration. Numbered triangles showdirection of stream flow, Various flotationreagents are added to a mixture of ore andwater (called pulp) in a conditioning tank. The flow rate and tank size are designed to give the minerals enough timeto be activated. The conditioner pulp [1] is fed to a bank of rougher cells which remove most of the desired mineralsas a concentrate. The rougher pulp [2] passes to a bank of scavenger cells where additional reagents may be added.The scavenger cell froth [3] is usually returned to the rougher cells for additional treatment, but in some cases maybe sent to special cleaner cells. The scavenger pulp is usually barren enough to be discarded as tails. More complexflotation circuits have several sets of cleaner and re-cleaner cells, and intermediate re-grinding of pulp orconcentrate.

Froth flotation 41

Chemicals of flotation

CollectorsCollectors either chemically bond (chemisorption) on a hydrophobic mineral surface, or adsorb onto the surface inthe case of, for example, coal flotation through physisorption. Collectors increase the natural hydrophobicity of thesurface, increasing the separability of the hydrophobic and hydrophilic particles.Xanthates

• Potassium amyl xanthate (PAX)• Potassium isobutyl xanthate (PIBX)• Potassium ethyl xanthate (KEX)• Sodium isobutyl xanthate (SIBX)• Sodium isopropyl xanthate (SIPX)• Sodium ethyl xanthate (SEX)Dithiophosphates

• Thiocarbamates• Xanthogen Formates• Thionocarbamates•• ThiocarbanilidePalmatic acidAmines

Frothers•• Pine oil• Alcohols (methyl isobutyl carbinol (MIBC))• Polyglycols• Polyoxyparafins|• Cresylic Acid (Xylenol)

ModifierspH modifiers such as:• Lime CaO• Soda ash Na2CO3• Caustic soda NaOH• Acid H2SO4, HClCationic modifiers:• Ba2+, Ca2+, Cu+, Pb2+, Zn2+, Ag+

Anionic modifiers:• SiO3

2-, PO43-, CN-, CO3

2-, S2-

Organic modifiers:• Dextrin, starch, glue, CMC

Froth flotation 42

Chemicals for deinking of recycled paper• pH control: sodium silicate and sodium hydroxide• Calcium ion source: hard water, lime or calcium chloride• Collector: fatty acid, fatty acid emulsion, fatty acid soap and/or organo-modified siloxane[9]

Specific ore applications

Sulfide ores

• Copper (see copper extraction) •• Copper-Molybdenum •• Lead-Zinc

•• Lead-Zinc-Iron •• Copper-Lead-Zinc-Iron •• Gold-Silver

•• Oxide Copper and Lead •• Nickel •• Nickel-Copper

Nonsulfide ores

•• Fluorite •• Tungsten •• Lithium

•• Tantalum •• Tin •• Coal

References[1] "Wales - The birthplace of Flotation" (http:/ / www. maelgwyn. com/ birthplaceflotation. html#top). . Retrieved 2010-01-13.[2] Rickard, Thomas A. (1922). Interviews with Mining Engineers. San Francisco: Mining and Scientific Press. pp. 119–131.[3] Osborne, Graeme (1981). "Guillaume Daniel Delprat" (http:/ / adb. anu. edu. au/ biography/ delprat-guillaume-daniel-5947). Australian

Dictionary of Biography. Canberra: Australian National University. . Retrieved 7 June 2012.[4] "Historical Note" (http:/ / www. austehc. unimelb. edu. au/ guides/ mine/ historicalnote. htm). Minerals Separation Ltd. . Retrieved

2007-12-30.[5][5] Callow; 1916[6] Rickard, Thomas A. (1922). Interviews with Mining Engineers. San Francisco: Mining and Scientific Press. pp. 142.[7] Beychok, Milton R. (1967). Aqueous Wastes from Petroleum and Petrochemical Plants (1st ed.). John Wiley & Sons Ltd.. LCCN 67019834.[8] Voith EcoCell flotation plant http:/ / www. voithpaper. com/ applications/ productsearch/ files/ 594_VPR-PB-07-0001-GB-07. pdf[9] METHOD OF DEINKING. 2004 (published 05.02.2004).

Mechanical screening 43

Mechanical screeningMechanical screening, often just called screening, is the practice of taking granulated ore material and separating itinto multiple grades by particle size.This practice occurs in a variety of industries such as mining and mineral processing, agriculture, pharmaceutical,food, plastics, and recycling.[1]

General categoriesScreening falls under two general categories: dry screening and wet screening. From these categories, screeningseparates a flow of material into grades, these grades are then either further processed to an intermediary product or afinished product. Additionally the machines can be categorised into moving screen and static screen machines, aswell as by whether the screens are horizontal or inclined.

ApplicationsThe mining and mineral processing industry uses screening for a variety of processing applications. For example,after mining the minerals, the material is transported to a primary crusher. Before crushing large boulder are scalpedon a shaker with 0.25 in (6.4 mm) thick shielding screening. Further down stream after crushing the material canpass through screens with openings or slots that continue to become smaller. Finally, screening is used to make afinal separation to produce saleable products based on a grade or a size range.

ProcessA screening machine consist of a drive that induces vibration, a screen cloth that causes particle separation, and adeck which holds the screen cloth and the drive and is the mode of transport for the vibration.There are physical factors that makes screening practical. For example, vibration, g force, bed density, and materialshape all facilitate the rate or cut. Electrostatic forces can also hinder screening efficiency in way of water attractioncausing sticking or plugging, or very dry material generate a charge that causes it to attract to the screen itself.As with any industrial process there is a group of terms that identify and define what screening is. Terms likeblinding, contamination, frequency, amplitude, and others describe the basic characteristics of screening, and thosecharacteristics in turn shape the overall method of dry or wet screening.In addition, the way a deck is vibrated differentiates screens. Different types of motion have their advantages anddisadvantages. In addition cloth types also have their different properties that lead to advantages and disadvantages.Finally, there are issues and problems associated with screening. Screen tearing, contamination, blinding, anddampening all affect screening efficiency.

Mechanical screening 44

Physical principles• Vibration - either sinusoidal vibration or gyratory vibration.

•• Sinusoidal Vibration occurs at an angled plane relative to the horizontal. The vibration is in a wave patterndetermined by frequency and amplitude.

•• Gyratory Vibration occurs at near level plane at low angles in a reciprocating side to side motion.•• Gravity - This physical interaction is after material is thrown from the screen causing it to fall to a lower level.

Gravity also pulls the particles through the screen cloth.•• Density - The density of the material relates to material stratification.•• Electrostatic Force - This force applies to screening when particles are extremely dry or is wet.

Screening terminologyLike any mechanical and physical entity there are scientific, industrial, and layman terminology. The following is apartial list of terms that are associated with mechanical screening.• Amplitude - This is a measurement of the screen cloth as it vertically peaks to its tallest height and troughs to its

lowest point. Measured in multiples of the acceleration constant g (g-force).•• Acceleration - Applied Acceleration to the screen mesh in order to overcome the van der waal forces• Blinding - When material plugs into the open slots of the screen cloth and inhibits overflowing material from

falling through.[2]

•• Brushing - This procedure is performed by an operator who uses a brush to brush over the screen cloth todislodged blinded opening.

• Cloth, screening cloth - it is the material defined by mesh size, which can be made of any type of material suchsteel, stainless steel, rubber compounds, brass, etc.[3]

•• Contamination - This is unwanted material in a given grade. This occurs when there is oversize or fine sizematerial relative to the cut or grade. Another type of contamination is foreign body contamination.•• Oversize contamination occurs when there is a hole in the screen such that the hole is larger than the mesh size

of the screen. Other instances where oversize occurs is material overflow falling into the grade from overhead,or there is the wrong mesh size screen in place.

•• Fines contamination is when large sections of the screen cloth is blinded over, and material flowing over thescreen does not fall through. The fines are then retained in the grade.

•• Foreign body contamination is unwanted material that differs from the virgin material going over and throughthe screen. It can be anything ranging from tree twigs, grass, metal slag to other mineral types andcomposition. This contamination occurs when there is a hole in the scalping screen or a foreign material'smineralogy or chemical composition differs from the virgin material.

•• Deck - a deck is frame or apparatus that holds the screen cloth in place. It also contains the screening drive. It cancontain multiple sections as the material travels from the feed end to the discharge end. Multiple decks are screendecks placed in a configuration where there are a series of decks attached vertically and lean at the same angle asit preceding and exceeding decks. Multiple decks are often referred to as single deck, double deck, triple deck,etc.

• Frequency - Measured in hertz (Hz) or revolutions per minute (RPM). Frequency is the number of times thescreen cloth sinusoidally peaks and troughs within a second. As for a gyratory screening motion it is the numberof revolutions the screens or screen deck takes in a time interval, such as revolution per minute (RPM).

• Gradation, grading - Also called "cut" or "cutting." Given a feed material in an initial state, the material can bedefined to a have a particle size distribution. Grading is removing the maximum size material and minimum sizematerial by way of mesh selection.[4]

•• Shaker - A generic term that refers to the whole assembly of any type mechanical screening machine.

Mechanical screening 45

• Stratification - This phenomenon occurs as vibration is passed through a bed of material. This causes coarse(larger) material to rise and finer (smaller) material to descend within the bed. The material in contact with screencloth either falls through a slot or blinds the slot or contacts the cloth material and is thrown from the cloth to fallto the next lower level.[5]

• Mesh - Mesh refers to the number of open slots per linear inch. Mesh is arranged in multiple configuration. Meshcan be a square pattern, long-slotted rectangular pattern, circular pattern, or diamond pattern.[6]

•• Scalp, scalping - this is the very first cut of the incoming material with the sum of all its grades. Scalping refers toremoving the largest size particles. This includes enormously large particles relative to the other particle's sizes.Scalping also cleans the incoming material from foreign body contamination such as twigs, trash, glass, or otherunwanted oversize material.

Types of mechanical screeningThere are a number of types of mechanical screening equipment that cause segregation. These types are based on themotion of the machine through its motor drive.• Circle-throw vibrating equipment - This type of equipment has an eccentric shaft that causes the frame of the

shaker to lurch at a given angle. This lurching action literally throws the material forward and up. As the machinereturns to its base state the material falls by gravity to physically lower level. This type of screening is used alsoin mining operations for large material with sizes that range from six inches to +20 mesh.[7]

• High frequency vibrating equipment - This type of equipment drives the screen cloth only. Unlike above theframe of the equipment is fixed and only the screen vibrates. However, this equipment is similar to the above suchthat it still throws material off of it and allows the particles to cascade down the screen cloth. These screens arefor sizes smaller than 1/8 of an inch to +150 mesh.[8]

• Gyratory equipment - This type of equipment differs from the above two such that the machine gyrates in acircular motion at a near level plane at low angles. The drive is an eccentric gear box or eccentric weights.[9][10]

•• Trommel screens - Does not require vibrations, instead, material is fed in to a horizontal rotating drum withscreen panels around the diameter of the drum.

Circle-throw vibrating equipmentCircle-throw vibrating equipment is a shaker or a series of shakers as to where the drive causes the whole structure tomove. The structure extends to a maximum throw or length and then contracts to a base state. A pattern of springsare situated below the structure to where there is vibration and shock absorption as the structure returns to the basestate.This type of equipment is used for very large particles, sizes that range from pebble size on up to boulder sizematerial. It is also designed for high volume output. As a scalper, this shaker will allow oversize material to passover and fall into a crusher such a cone crusher, jaw crusher, or hammer mill. The material that passes the screenby-passes the crusher and is conveyed and combined with the crush material.Also this equipment is used in washing processes, as material passes under spray bars, finer material and foreignmaterial is washed through the screen. This is one example of wet screening.

Mechanical screening 46

High frequency vibrating equipmentHigh frequency vibrating equipment is a shaker whose frame is fixed and the drive vibrates only the screen cloth.High frequency vibration equipment is for particles that are in this particle size range of an 1/8 in (3 mm) down to a+150 mesh.These shakers usually make a secondary cut for further processing or make a finished product cut.These shakers are usually set at a steep angle relative to the horizontal level plane. Angles range from 25 to 45degrees relative to the horizontal level plane.

Gyratory equipmentThis type of equipment has an eccentric drive or weights that causes the shaker to travel in an orbital path. Thematerial rolls over the screen and falls with the induction of gravity and directional shifts. Rubber balls and traysprovide an additional mechanical means to cause the material to fall through. The balls also provide a throwingaction for the material to find an open slot to fall through.The shaker is set a shallow angle relative to the horizontal level plane. Usually, no more than 2 to 5 degrees relativeto the horizontal level plane.These types of shakers are used for very clean cuts. Generally, a final material cut will not contain any oversize orany fines contamination.These shakers are designed for the highest attainable quality at the cost of a reduced feed rate.

Trommel ScreensTrommel screens have a rotating drum with screen panels around the diameter of the drum and is on a shall angle.The feed material always sits at the bottom of the drum and as it rotates, always comes in to contact with cleanscreen. The oversize travels to the end of the drum as it does not pass through the screen, while the undersize passesthrough the screen in to a launder below.

References[1] http:/ / www. rotex. com/ 02applications/ applications. aspx[2] Woven Wire Mesh Glossary of Terms (http:/ / www. screentg. com/ wiremesh. htm)[3] Woven wire (http:/ / www. wovenwire. com/ products. htm)[4] Soil Gradation (http:/ / tpub. com/ content/ engine/ 14081/ css/ 14081_454. htm)[5] Screening (http:/ / www. metsominerals. com/ inetMinerals/ mm_segments. nsf/ WebWID/ WTB-041223-2256F-10C45?OpenDocument)[6] The Complete Wire Mesh Glossary of Terms (http:/ / www. wovenwire. com/ reference/ glossary. htm)[7] WS Tyler » F-Class (http:/ / www. wstyler. on. ca/ 85. html)[8] RHEWUM WA- The original (http:/ / www. rhewum. comon)[9] Engelsmann Separators and Screeners (http:/ / www. engelsmann. com)[10] Sweco - Vibratory Screener, Sifters, Separators, Round Screen, Vibratory Separator (http:/ / www. sweco. com/ round. html)

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Filtration  Source: http://en.wikipedia.org/w/index.php?oldid=519096778  Contributors: A3RO, A8UDI, Access Denied, Achowat, Adelaineyeo, Adoniscik, Agne27, Aitias, Aleenf1,Alexandrov, Alfie66, AnnaFrance, Aushulz, Avnjay, Avoided, Ayudante, Bdiscoe, BendersGame, Bergmosis, Bob, Bongwarrior, Borgx, Budnick1, Caltas, Calvin 1998, Can't sleep, clown willeat me, CanisRufus, CardinalDan, CarlFink, Cffrost, Charles Matthews, ChrisGualtieri, Chriswaterguy, Conversion script, Crispmuncher, Curtis23, DFS454, DShantz, Dagordon01, Danimf,Davewho2, Deor, Dudtz, Edward, Eike Welk, Elvim, Epbr123, Erielhonan, Fanghong, Fetchcomms, FocalPoint, Forstafilters, Fourthgeek, Gauss, Geek302, Gentgeen, Gertdam, Giftlite, Gilliam,Gonoo, Gveret Tered, H8973jgf, HalfShadow, Hyacinth, Igoruha, Ike9898, Iohannes Animosus, ItsZippy, Ixfd64, J.delanoy, James086, Jasonbrotherton, JogyB, JohandteA, Jorge Stolfi,Josh3580, Juliancolton, K.murphy, KJS77, Karl2620, Karlhahn, Kashmyre, Katieh5584, Kevin S., Kevinomad, Kisiel1mk, KoshVorlon, Kyle Barbour, LadyofHats, Langbein Rise, Loren.wilton,LouisBB, Luca 1101, Luk, Luna Santin, Manu yadav, Marek69, Mark, Martarius, Materialscientist, Matey, MattieTK, Message From Xenu, Michael Hardy, Mikael Häggström, Mike Rosoft,Mion, Morel, MyopsToo, Names are hard to think of, Naois, Ojigiri, Oxymoron83, Physchim62, Piano non troppo, Pollystenberg, Priestx, Quantockgoblin, R'n'B, R19h72, Rama's Arrow,RexNL, Richard leics, Richard001, Rifleman 82, Ryanjunk, ST47, Saijc11, Samchafin, Sarindam7, Sckchui, Shanes, Shech736, Sicvolo, Simon D M, Slimydrip, Sluzzelin, Smalljim, Smokefoot,Sonja Diig, Steel Hybrid, Sxim, SzaboUK, TCO, THEN WHO WAS PHONE?, TUF-KAT, TVScott, Thatguyflint, The Thing That Should Not Be, ThePaper, Think outside the box, Tnxman307,Tobias Bergemann, Tomwilson16, Uncle Dick, Valar, Veinor, Velella, Vrenator, Vsmith, WLU, Wackywace, Walkerma, Wikiwayman, World Pumps, Xuneternal, Zad68, 345 anonymous edits

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Image Sources, Licenses and ContributorsImage:LOC MI0086 QuincyMine TIF 00027aS.png  Source: http://en.wikipedia.org/w/index.php?title=File:LOC_MI0086_QuincyMine_TIF_00027aS.png  License: Public Domain Contributors: User:LarFile:Compression test.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Compression_test.jpg  License: Creative Commons Attribution-Sharealike 3.0,2.5,2.0,1.0  Contributors: Cjp24File:Kafar na Odrze.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Kafar_na_Odrze.jpg  License: Public Domain  Contributors: Gepardenforellenfischer, JuloFile:Impact wrench 01.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Impact_wrench_01.jpg  License: GNU Free Documentation License  Contributors: Original uploader wasBushytails at en.wikipediaFile:Malibucrash.JPG  Source: http://en.wikipedia.org/w/index.php?title=File:Malibucrash.JPG  License: GNU Free Documentation License  Contributors: Analogue Kid, NrbelexFile:Impact-test.jpg  Source: 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Attribution-ShareAlike 3.0Unported  Contributors: User:Bryan DerksenFile:Simple Grinding Forces.png  Source: http://en.wikipedia.org/w/index.php?title=File:Simple_Grinding_Forces.png  License: Public Domain  Contributors: HandsclarkFile:Ball mill.gif  Source: http://en.wikipedia.org/w/index.php?title=File:Ball_mill.gif  License: Public Domain  Contributors: Lưu LyFile:Principle of SAG Mill operation.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Principle_of_SAG_Mill_operation.jpg  License: Public Domain  Contributors: QwertytamImage:Laboratory sieves BMK.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Laboratory_sieves_BMK.jpg  License: Creative Commons Attribution-Sharealike 2.0  Contributors:User:BMKFile:Laborsiebmaschine BMK.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Laborsiebmaschine_BMK.jpg  License: Creative Commons Attribution-Sharealike 2.0  Contributors:de:User:BMK Original uploader was BMK at de.wikipediaImage:Wurfbewegung.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Wurfbewegung.jpg  License: Creative Commons Attribution-Sharealike 3.0,2.5,2.0,1.0  Contributors: ParticlesImage:planbewegung.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Planbewegung.jpg  License: GNU Free Documentation License  Contributors: ParticlesImage:tapping.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Tapping.jpg  License: Creative Commons Attribution-Sharealike 3.0,2.5,2.0,1.0  Contributors: ParticlesFile:Retsch AS 200 jet.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Retsch_AS_200_jet.jpg  License: Creative Commons Attribution-Sharealike 3.0,2.5,2.0,1.0  Contributors:ParticlesImage:Momentum1.png  Source: http://en.wikipedia.org/w/index.php?title=File:Momentum1.png  License: Public Domain  Contributors: WipwareImage:Ball mill.gif  Source: http://en.wikipedia.org/w/index.php?title=File:Ball_mill.gif  License: Public Domain  Contributors: Lưu LyFile:Ballmill.jpg  Source: 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