A SUMMER TRAINING REPORT ON

“WORKSHOP PRACTICES & RELATED MECHANICAL ACTIVITIES IN CENTRAL WORKSHOP, GEVRA”

By:-KHAGENDRA KUMAR DEWANGAN,13119040 MECH(7TH SEM) NIT RAIPUR, C.G.

TABLE OF CONTENTS

ACKNOWLEDGEMENT............................................................................................................................................

DECLARATION............................................................................................................................................................

INTRODUCTION..........................................................................................................................................................

ELECTRICAL REPAIR SHOP..................................................................................................................... ..............

ENGINE SHOP..............................................................................................................................................................

TRANSMISSION SHOP........................................................................................................................... ....................

HEAVY REPAIR SHOP..............................................................................................................................................

MACHINE AND HT SHOP........................................................................................................................... .............

RECLAMATION SHOP...............................................................................................................................................

DOZER SHOP........................................................................................................................... .....................................

ACKNOWLEDGEMENT

It gives me immense pleasure to come up with this report at the end of my training. This training involved the collection and analysis of information from a wide variety of sources and the efforts of many people beyond me. Thus it would not have been possible to achieve the results reported in this document without their help, support and encouragement. I would like to express my gratitude to the different dignitaries of CEWS GEVRA for their co-operation and valuable help during my Training Period. I am equally grateful to all the employees of Mechanical

Department & Processing units who had provided me with adequate

data/information and support in spite of their hectic schedule.

I am thankful to my Institute “National Institute of Technology,

RAIPUR” for allowing me to do my summer training at COAL INDIA

(CEWS, S.E.C.L. GEVRA).

Regards,

KHAGENDRA KUMAR DEWANGAN

Mechanical Engg.

NIT RAIPUR, C.G.

DECLARATION

I KHAGENDRA KUMAR DEWANGAN, hereby declare that this project report is the record of authentic work carried out by me during of 31days period from 17/05/2015 onwards and has not been submitted to any other University or Institute for the award of any degree/diploma etc.

Signature of student

Name of the student: KHAGENDRA KUMAR DEWANGAN

Roll No. : 13119040

Branch : Mechanical

Semester : 7th

Institute : National Institute of Technology, Raipur

Course : Bachelor of Technology

CERTIFICATE

This is to certify that Mr. KHAGENDRA KUMAR DEWANGAN, S/O

RAMDAYAL DEWANGAN, a student of “National Institute of Technology,

Raipur” has successfully completed his summer training from 18/05/2016 to

17/06/2016 at CEWS, S.E.C.L. GEVRA.

During the period of his training program with us he was found punctual,

hardworking and inquisitive.

We wish him every success in life.

…………………………………..

GM (HRD CEWS, GEVRA)

PREFACE

This report is the work done during the summer training at CEWS,

S.E.C.L. GEVRA under the supervision of Mr. R. Prasad, GM (HRD CEWS, GEVRA).

The report shall give an overview of the different places that are visited

by me during my summer training with technical details.

I have tried my best to keep report yet technically correct. I hope I have

succeeded in my attempt.

KHAGENDRA KUMAR DEWANGAN

NIT RAIPUR, C.G.

ELECTRICAL REPAIR SHOP

INTRODUCTION- In this shop AC/DC machines and Transformers are repaired and tested.

First inspection is to be done using various instruments and devices and after

that maintenance work are to be done. Then assembly of various parts and

components are done. Then delivery is done after the testing.

In the shop following machines are repaired-

1. AC/DC motors

2. AC/DC Generators

3. Transformers

MOTOR-

A motor is an electric device which converts

electrical energy to mechanical work.

Motor works on the phenomenon of

Fleming’s left hand rule.

Fig- A type of AC motor

On the basis of current we have two types of motors-

1. AC motor

2. DC motor

Types of AC motors we visited there are-

1. Induction motor

2. Slip ring motor

INDUCTION MOTORS-

In this motor stator winding is done and it is used for low load

applications.

SLIP RING MOTORS-

In this motors stator and rotor both winding is done and used for high

load applications and quick start.

Parts of motors-

Yoke:

It is made up of cast iron (small machines) and cast steel (heavy

machines).

The functions of yoke are:

1. To carry main flux

2. To support the field poles

3. To give the mechanical support

Field coils:

Enameled wire is used to do the coiling on the poles attached to yoke

to generate field-magnet .

Armature core :

It is made up of silicon steel and its function is to accommodate the

conductors which offers low reluctance.

Brush:

The function of brush is to make the electrical contact with the

commutator which moves with the rotating part.

Fig- Armature with Commutator used in DC machines

Types of DC motors- 1. Series motors

2. Shunt motors

3. Compound motors

Series motors-

The field winding is connected in series with the armature.

Shunt motors-

The field winding is connected in parallel with armature.

Compound motors-

It is subdivided into two types according to connection of field

windings. They are-

1. Short shunt

2. Long shunt

Testing of motor- 1. Pole testing

2. Meggar test

3. Load test

4. Core balance test

Fig- Motor testing we did during training at CEWS, GEVRA

Pole testing-

In this testing we use a small magnet to check the polarity. After

supply of power we bring near poles of motor a small magnet and see

whether it is attracting or repelling.

Meggar test-

We check the insulation by the help of meggar testing machine. If it

indicates a non zero reading then there will be perfect insulation.

Load test-

In delta connection of circuit we supply the required voltage and check

the current between two phases.

Fig-Tongue tester

Core balance test-

In star connection we supply current in two phases and keep open the

third phase and check the voltage drop among the phases and phase –neutral

voltages.

Fig- Tachometer for speed testing of rotor

Transformer- It may be defined as the static electric device that converts one level

of voltage or current to other level without changing in frequency. There

are two types of winding- primary and secondary in transformers.

There are two types of transformer-

1. Step up

2. Step down

Fig- Transformer

Step up Transformer-

In this transformer the secondary will have more no. of turns or

windings than the primary.

Step down Transformer-

In this transformer the primary will have more no. of turns than the

secondary.

Testing of transformer- Except pole testing all other are done same as in motors and one

more test-ratio test is done to ensure the perfect turn ratio.

Ratio test-

To ensure the turn ratio we provide the primary voltage and check

the voltage in secondary winding.

GENERATOR-

Generator is the Machine which convert mechanical energy into electrical

energy.

Types of Generator:-

1.AC Generator

2.DC Generator

Parts of Generator:-

Rotor arm Armature Commutator Pole.

ENGINE SHOP

Here mainly the maintenance of various engine parts and components are

done.

There are mostly three types of engine used in whole area of Gevra project

mines.

1. KOMATSU-

S6D170

S6D140

S6D125

S6D110

Where,

S- supercharger

6- no. of cylinders used

D- direct injector type

170- bore diameter (in mm)

2. CUMMINS

KTA38C

KT1150

NT855

NTA855

Where,

K- series symbol

T- turbocharger

A- aftercooler

38C- cubic in displacement

855- cubic in displacement

3. DDC (DETROIT DIESEL CONTROLLED)-

SAAE-140

SAAE3-140

Where,

S- supercharger

A- air to air

A- aftercooler

E- Emission

140- CID

SYSTEMS IN ENGINE

1. IGNITION SYSTEM

2. FUEL SYSTEM

3. AIR INTAKE OR EXHAUST SYSTEM

4. COOLING SYSTEM

5. LUBRICATION SYSTEM

IGNITION SYSTEM

Different types of ignition system used in various machine are

Battery system

Alternator

Rectifier (current changer)

Dynamo system

Self starter electrical energy mechanical

energy

FUEL SYSTEM

Types of fuel system-

Gravity system-

we can use gravitational force for fuel feeding.

Exa.- bike system

Forced feed system-

we can use a pump for feeding the fuel.

Exa.- P.T. pump system, F.I.P. pump system

Engine types on the basis of fuel-

Petrol engine

Diesel engine

Kerosene engine

CNG engine

AIR INTAKE OR EXHAUST SYSTEM

Natural aspirated-

Simply atmospheric air comes in engine.

Turbocharger-

It absorbs fresh air and send it to inlet. It works on the exhaust gas

temperature.

Supercharger-

Works same as turbocharger except it uses engine power.

Aftercooler-

Hot air is cooled and made dense.

Fig- Turbo-charger

Fig- Connecting Rod

COOLING SYSTEM

Air cooling system-

we can use fins.

Water cooling-

we can use radiator.

LUBRICATION SYSTEM

Liquid system

Solid system

Semi solid system

Method of lubrication-

Air type pump-

For simple oil requirement.

Plunger type pump-

For less oil requirement.

Splash type pump-

By crankshaft in oil sump.

SMOKES IN ENGINE

Due to unburnt hydrocarbon.

When oil and water and fuel mixes

When oil burns (due to damage of oil ring)

TYP

ES O

F SM

OK

E

BLACK

WHITE

BLUE

Fig- Piston connected with small end of Connecting Rod

Fig- Injectors

HEAVY REPAIR SHOP In this shop magnetorque, wheel motor, idler, roller, compressor and

motors are repaired.

Magnetorque –

It is used in shovel for hoisting (moving the bucket in upward and

downward direction). It consists 2 outer member, rotor and shaft (one outer

hollow and one inner solid shaft having independent rotation).

Outer hollow shaft connected to rotor and inner solid shaft connected to

outer member. In this machine the upper portion of magnetorque rotate when

we pass AC current through the slip ring. Due to magnetic induction the inner

part of this (armature) rotate with upper portion and in this way the torque is

produced and transmit to gears.

Fig-Magnetorque

Air compressor-

mainly reciprocating and screw compressor are used with different types

of machines. for high pressure requirement screw compressor (3kgf to 5kgf)

are used.

Fig- Screw Compressor

Screw compressor-

It consists of two rotors (male and female rotor) in a housing. Air from air

cleaner is pass through housing. Oil is used for lubrication. Compressed mixture

of oil and air is passed through separator, In which oil and compressed air get

separated.

This compressed air is used for different purpose. Bearing is used with

rotors to provide balance and smooth rotation.

Two types of clearance are provided between bearing and housing-

1. Discharge end clearance 2. Bearing end clearance

Fig-Compressor Housing

Inner diameter welding-

This type of welding is used to provide for refitting of idler, roller and

sprockets. Due to regular use of these, inner diameter get damaged so, MAG

(metal active gas) welding is used for refilling of materials. Carbon dioxide is

used as active gas which protects the welding zone from oxidation. Anti-spatter

spray is used to prevent the material from sticking on the workpiece.

Fig-Inner Diameter Welding

Outer diameter welding-

This type of welding is used to provide for refitting of idler, roller and

sprockets. Due to regular use of these, outer diameter get damaged so, this

welding is used for refilling of materials. flux is used to protects the welding

zone from oxidation. Anti-spatter spray is used to prevent the material from

sticking on the workpiece.

Fig- Outer Diameter Welding

MACHINE & HT SHOP This chapter describes machining processes with the capability of producing parts that basically are round in shape. Typical products made are as small as miniatures crews for the hinges of eyeglass frames and as large as turbine shafts for hydroelectric power plants, rolls for rolling mills, and gun barrels. One of the most basic machining processes is turning, meaning that the part is rotated while it is being machined. The starting material is generally a work piece that has been made by other processes, such as casting, forging, extrusion, drawing, or powder metallurgy. The machines used in the shop are discussed below:

LATHE MACHINE :

FIGURE: LATHE MACHINE

The operations performed on lathe machine are:

Turning: To produce straight, conical, curved, or grooved work pieces such as shafts, spindles, and pins.

Facing: To produce a flat surface at the end of the part and perpendicular to its axis, useful for parts that are assembled with other components. Face grooving produces grooves for applications such as O-ring seats.

Boring: To enlarge a hole or cylindrical cavity made by a previous process or to produce circular internal grooves.

Drilling: To produce a hole (Fig. 23.1i), which may be followed by boring to improve its dimensional accuracy and surface finish.

Threading: To produce external or internal threads.

Knurling: To produce a regularly shaped roughness on cylindrical surfaces, as in making knobs and handles.

. FIGURE: Miscellaneous cutting operations that can be performed on a lathe.

The cutting operations just summarized typically are performed on a lathe, which is available in a variety of designs, sizes, capacities, and computer controlled features. As shown in Fig, turning is performed at various (1) rotational speeds, N, of the work piece clamped in a spindle, (2) depths of cut, d, and (3) feeds depending on the work piece materials, cutting-tool materials, surface finish and dimensional accuracy required, and characteristics of the machine tool.

Tool Geometry: The various angles in a single-point cutting tool have important functions in machining operations. These angles are measured in a coordinate system consisting of the three major axes of the tool shank, as can be seen in Fig. Note, however, that these angles may be different, with respect to the work piece after the tool is installed in the tool holder. Rake angle is important in controlling both the direction of chip flow and the strength of the tool tip. Positive rake angles improve the cutting operation by reducing forces and temperatures. However, positive angles also result in a small included angle of the tool tip, possibly leading to premature tool chipping and failure, depending on the toughness of the tool material. Side rake angle is more important than the back rake angle, although the latter usually controls the direction of chip flow. For machining metals and using carbide inserts, these angles typically are in the range from -5° to 5°. Cutting-edge angle affects chip formation, tool strength, and cutting forces to various degrees. Typically, the cutting-edge angle is around 15°. Relief angle controls interference and rubbing at the tool-workpiece interface. If it is too large, the tool tip may chip off; if it is too small, flank wear may be excessive. Relief angles typically are 5 °. Nose radius affects surface finish and tool-tip strength. The smaller the nose radius (sharp tool), the rougher the surface finish of the workpiece and

the lower the strength of the tool. However, large nose radii can lead to tool chatter.

SHAPER MACHINE: Shaper is a reciprocating type of machine tool in which the ram moves the cutting tool backwards and forwards in a straight line. The basic components of shaper are shown in Fig. It is intended primarily to produce flat surfaces. These surfaces may be horizontal, vertical, or inclined. In general, the shaper can produce any surface composed of straight-line elements. The principal of shaping operation is shown in Fig. Modern shapers can also generate contoured surface as shown in Fig. 23.3. A shaper is used to generate flat (plane) surfaces by means of a single point cutting tool similar to a lathe tool.

FIGURE: SHAPER MACHINE

FIGURE: PARTS OF SHAPER MACHINE

SHAPER MECHANISM: Crank and Slotted Link Mechanism- In crank and slotted link mechanism (Fig. 23.6), the pinion receives its motion from an individual motor or overhead line shaft and transmits the motion or power to the bull gear. Bull gear is a large gear mounted within the column. Speed of the bull gear may be changed by different combination of gearing or by simply shifting the belt on the step cone pulley. A radial slide is bolted to the centre of the bull gear. This radial slide carries a sliding block into which the crank pin is fitted. Rotation of the bull gear will cause the bush pin to revolve at a uniform speed. Sliding block, which is mounted upon the crank pin is fitted within the slotted link. This slotted link is also known as the rocker arm. It is pivoted at its bottom end attached to the frame of the column. The upper end of the rocker arm is forked and connected to the ram block by a pin. With the rotation of bull gear, crank pin will rotate on the crank pin circle, and simultaneously move up and down the slot in the slotted link giving it a rocking movement, which is communicated to the ram. Thus the rotary motion of the bull gear is converted to reciprocating motion of the ram.

FIGURE: SHAPER MECHANISM

SLOTTER MACHINE: The slotter or slotting machine is also a reciprocating type of machine tool similar to a shaper or a planer. It may be considered as a vertical shaper. The chief difference between a shaper and a slotter is the direction of the cutting action. The machine operates in a manner similar to the shaper, however, the tool moves vertically rather than in a horizontal direction. The job is held stationary. The slotter has a vertical ram and a hand or power operated rotary table.

Fig-Slotter

MILLING MACHINE: A milling machine is a machine tool that removes metal as the work is fed against a rotating multipoint cutter. The milling cutter rotates at high speed and it removes metal at a very fast rate with the help of multiple cutting edges. One or more number of cutters canbe mounted simultaneously on the arbor of milling machine. This is the reason that a milling machine finds wide application in production work. Milling machine is used for machining flat surfaces, contoured surfaces, surfaces of revolution, external and internal threads, and helical surfaces of various cross-sections.

In milling machine, the metal is cut by means of a rotating cutter having multiple cutting edges. For cutting operation, the workpiece is fed against the rotary cutter. As the workpiece moves against the cutting edges of milling cutter, metal is removed in form chips of trochoid shape. Machined surface is formed in one or more passes of the work. The work to be machined is held in a vice, a rotary table, a three jaw chuck, an index head, between centres, in a special fixture or bolted to machine table. The rotatory speed of the cutting tool and the feed rate of the workpiece depend upon the type of material being machined.

Types of milling machine: (a) Hand milling machine (b) Horizontal milling machine (c) Universal milling machine (d) Vertical milling machine Types of milling cutters:

HEAT TREATMENT SHOP The various microstructures described thus far can be modified by heat-treatment techniques-that is, by controlled heating and cooling of the alloys at various rates. These treatments induce phase transformations that greatly influence such mechanical properties as the strength, hardness, ductility, toughness, and wear resistance of the alloys. The effects of thermal treatment depend on the particular alloy, its composition and microstructure, the degree of prior cold work, and the rates of heating and cooling during heat treatment. The processes of recovery, recrystallization, and grain growth are examples of thermal treatment, involving changes in the grain structure of the alloy. The following processes are done in this shop: Hardening: The structure can be made stronger by precipitation hardening. In this process, the alloy is reheated to an intermediate temperature and then held there for a period of time, during which precipitation takes place. The copper atoms diffuse to nucleation sites and combine with aluminium atoms; this process produces the theta phase, which forms as sub microscopic precipitates. The increase in strength is due to increased resistance to dislocation movement in the region of the precipitates. Tempering: If steels are hardened by heat treatment, then tempering or drawing is used in order to reduce brittleness, increase ductility and toughness, and reduce residual stresses. In tempering, the steel is heated to a specific temperature, de- pending on its composition, and then cooled at a prescribed rate. Alloy steels may undergo temper embrittlement, which is caused by the segregation of impurities along the grain boundaries at temperatures between 480° and 590°C . Annealing: Annealing is a general term used to describe the restoration of a cold-worked or heat-treated alloy to its original properties-for instance, to increase ductility (and hence formability) and reduce hardness and strength, or to

modify the microstructure of the alloy. The annealing process is also used to relieve residual stresses in a manufactured part, as well as to improve machinability and dimensional stability. The annealing process consists of the following steps: I. Heating the work piece to a specific range of temperature in a furnace; 2. Holding it at that temperature for a period of time (soaking), and 3. Cooling the work piece, in air or in a furnace. Normalizing: In this process the metal is softenedby heating upto 850 degree(for steel) i.e. temperature above critical temperature. Case Hardening: The heat-treatment processes described thus far involve microstructural alterations and property changes in the hulk of the material or component by means of through hardening. It is not desirable to through harden parts, because a hard part lacks the necessary toughness for these applications; a small surface crack could propagate rapidly through such a part and cause total failure. In many cases, however, alteration of only the surface properties of a part (hence, the term surface or case hardening) is desirable. This method is particularly useful for improving resistance to surface indentation, fatigue, and wear. Typical applications for case hardening are gear teeth, cams, shafts, bearings, fasteners, pins, automotive clutch plates ,tools, and dies. Types of furnace: Batch Furnaces: In a batch furnace, the parts to be heat treated are loaded into and unloaded from the furnace in individual batches. This includes:

a. A box furnace is a horizontal rectangular chamber with one or two access doors through which parts are loaded.

b. A pit furnace is a vertical pit below ground level into which the parts are lowered. This type of furnace is particularly suitable for long parts, such as rods, shafts, and tubing.

Continuous Furnace: In this type of furnace, the parts to be heat treated move continuously through the furnace on conveyors of various designs that use trays, belts, chains, and other mechanisms. Continuous furnaces are suitable for high production runs and can be designed and programmed so that complete heat-treating cycles can be performed under tight control.

RECLAMATION SHOP

DESCRIPTION OF SHOP WORKING-

INTRODUCTION-

In this shop various types of maintenance works are performed-

1. Repair and treatment of shovel bucket and welding of these wear parts 2. Repairing of dozer bucket, shovel dragline shovel body. 3. Fitting of new plate in dragline to improvement of loading capacity. 4. Removal of corrosion particle attached to the body while stick in the

equipment and removal of soil and moisture content. 5. Welding of plate and attaching of plate in dragline, shovel bucket

Figure-Shovel dragline

DOZER SHOP

Parts which are used to repair in shop are followings-

1. Dozer wheel – D355, D155, D475, Wheel dozer 834B

2. Arm blade- D355, D155, D475

3. EK446/5 arm

4. Hydraulic excavation- ex300, BE1000, BE220,Bucket

5. Lift cylinder repair-

6. Tilt cylinder

7. Cutting edge joining-motor, Grader825 CAT 2GM

8. Track frame- D355, D155

9. Spray painting of all repaired sub assemblies.

Dozer wheel/Sprocket –D355,D155,D475, Wheel dozer 834B

Fig-sprocket wheel

Arm blade- D355, D155, D475 Dozers

Figure-dozer blade

Excavation- ex300, BE1000,BE220,Bucket

Figure- dozer arm

Figure-dumper arm

Track frame- D355, D155 Dozers

figure-Dozer bucket

In both Reclamation and Dozer shops welding is the major process for repairing and maintenance.

The various welding processes, types, components and functions are detailed below-

ARC WELDING- Gas metal arc welding- Arc welding is a type of welding that uses a welding power supply to create an electric arc between an electrode and the base material to melt the metals at the welding point. They can use either direct (DC) or alternating (AC) current, and consumable or non-consumable electrodes. The welding region is usually protected by some type of shielding gas, vapor, and/or slag. Power supplies Engine driven welder capable of AC/DC welding. To supply the electrical energy necessary for arc welding processes, a number of different power supplies can be used. The most common classification is constant current power supplies and constant voltage power supplies. In arc welding, the voltage is directly related to the length of the arc, and the current is related to the amount of heat input. Constant current power supplies are most often used for manual welding processes such as gas tungsten arc welding and shielded metal arc welding, because they maintain a relatively constant current even as the voltage varies. This is important because in manual welding, it can be difficult to hold the electrode perfectly steady, and as a result, the arc length and thus voltage tend to fluctuate. Constant voltage power supplies hold the voltage constant and vary the current, and as a result, are most often used for automated welding processes such as gas metal arc welding, flux cored arc welding, and submerged arc welding. In these processes, arc length is kept constant, since any

fluctuation in the distance between the wire and the base material is quickly rectified by a large change in current. For example, if the wire and the base material get too close, the current will rapidly increase, which in turn causes the heat to increase and the tip of the wire to melt, returning it to its original separation distance. The direction of current used in arc welding also plays an important role in welding. Consumable electrode processes such as shielded metal arc welding and gas metal arc welding generally use direct current, but the electrode can be charged either positively or negatively. In welding, the positively charged anode will have a greater heat concentration and, as a result, changing the polarity of the electrode has an impact on weld properties. If the electrode is positively charged, it will melt more quickly, increasing weld penetration and welding speed. Alternatively, a negatively charged electrode results in more shallow welds. Non-consumable electrode processes, such as gas tungsten arc welding, can use either type of direct current (DC), as well as alternating current (AC). With direct current however, because the electrode only creates the arc and does not provide filler material, a positively charged electrode causes shallow welds, while a negatively charged electrode makes deeper welds. WELDING ELECTRODE- In arc welding an electrode is used to conduct current through a workpiece to fuse two pieces together. Depending upon the process, the electrode is either consumable, in the case of gas metal arc welding or shielded metal arc welding, or non-consumable, such as in gas tungsten arc welding. For a direct current system the weld rod or stick may be a cathode for a filling type weld or an anode for other welding processes. For an alternating current arc welder the welding electrode would not be considered an anode or cathode.

Alternating current electrodes- For electrical systems which use alternating current the electrodes are the connections from the circuitry to the object to be acted upon by the electric current but are not designated anode or cathode since the direction of flow of the electrons changes periodically, usually many times per second. Uses- Electrodes are used to provide current through nonmetal objects to alter them in numerous ways and to measure conductivity for numerous purposes.

Examples include:

• Electrodes for medical purposes, such as EEG, ECG, ECT, defibrillator • Electrodes for electrophysiology techniques in biomedical research • Electrodes for execution by the electric chair • Electrodes for electroplating • Electrodes for arc welding • Electrodes for cathodic protection • Electrodes for grounding • Electrodes for chemical analysis using electrochemical methods • Inert electrodes for electrolysis (made of platinum)

• Membrane electrode assembly SUBMERGED ARC WELDING- Submerged arc welding (SAW) is a common arc welding process.

Originally developed by the Linde - Union Carbide Company. It requires a non-

continuously fed consumable solid or tubular (flux cored) electrode. The

molten weld and the arc zone are protected from atmospheric contamination

by being “submerged” under a blanket of granular fusible flux consisting of

lime, silica, manganese oxide, calcium fluoride, and other compounds.

When molten, the flux becomes conductive, and provides a current path

between the electrode and the work. This thick layer of flux completely covers

the molten metal thus preventing spatter and sparks as well as suppressing

the intense ultraviolet radiation and fumes that are a part of the shielded

metal arc welding (SMAW) process.

SAW is normally operated in the automatic or mechanized mode, however, semi-automatic (hand-held) SAW guns with pressurized or gravity flux feed delivery are available. The process is normally limited to the flat or horizontal-fillet welding positions (although horizontal groove position welds have been done with a special arrangement to support the flux).

Single or multiple (2 to 5) electrode wire variations of the process exist. SAW strip-cladding utilizes a flat strip electrode (e.g. 60 mm wide x 0.5 mm thick). DC or AC power can be used, and combinations of DC and AC are common on multiple electrode systems. Constant voltage welding power supplies are most commonly used; however, constant current systems in combination with a voltage sensing wire-feeder are available. OXY-FUEL WELDING AND CUTTING- Oxy-fuel welding (commonly called oxyacetylene welding, oxy welding, or gas welding in the U.S.) and oxy-fuel cutting are processes that use fuel gases and oxygen to weld and cut metals, respectively. French engineers Edmond Fouché and Charles Picard became the first to develop oxygen-acetylene welding in 1903. Pure oxygen, instead of air (20% oxygen/80% nitrogen), is used to increase the flame temperature to allow localized melting of the workpiece material (e.g. steel) in a room environment. A common propane/air flame burns at about 3,630 °F (2,000 °C), a propane/oxygen flame burns at about 4,530 °F (2,500 °C), and an acetylene/oxygen flame burns at about 6,330 °F (3,500 °C). Oxy-fuel is one of the oldest welding processes. Still used in industry, in recent decades it has been less widely utilized in industrial applications as other specifically devised technologies have been adopted. It is still widely used for welding pipes and tubes, as well as repair work. It is also frequently well-suited, and favored, for fabricating some types of metal-based artwork.

In oxy-fuel welding, a welding torch is used to weld metals. Welding metal results when two pieces are heated to a temperature that produces a shared pool of molten metal. The molten pool is generally supplied with additional metal called filler. Filler material depends upon the metals to be welded. In oxy-fuel cutting, a torch is used to heat metal to its kindling temperature. A stream of oxygen is then trained on the metal, burning it into a metal oxide that flows out of the kerf as slag. Torches that do not mix fuel with oxygen (combining, instead, atmospheric

air) are not considered oxy-fuel torches and can typically be identified by a

single tank (Oxy-fuel cutting requires two isolated supplies, fuel and oxygen).

Most metals cannot be melted with a single-tank torch. As such, single-tank

torches are typically used only for soldering and brazing rather than welding.