cutting fluid management in small machine shop operations - world1

Cutting Fluid Managementin Small Machine Shop

Operations

Iowa Waste Reduction CenterUniversity of Northern Iowa

Cedar Falls, Iowa50614-0185

(319) 273-2079

1990,Iowa Waste Reduction Center,University of Northern Iowa

This manual was developed by DebbyYetter and Douglas Feil of theEnvironmental Training Center,Kirkwood Community College, CedarRapids, Iowa under contract to theIowa Waste Reduction Center,University of Northern Iowa. Reviewand editing of the manual was done bythe staff of the Iowa Waste ReductionCenter.

Any trade names of commercialproducts referenced in this manual arenot endorsed or recommended by theIowa Waste Reduction Center orKirkwood Community College.

Table of Contents

I. Introduction .................................................................. 1II. Functions of a Cutting Fluid .......................................... 4

Cooling .......................................................................... 4Lubricating....................................................................4Rust Control .................................................................. 5Rancidity Control .......................................................... 5

III. Cutting and Grinding Fluid Selection ............................. 7Straight Oils (100% petroleum oil) ..............................7Soluble Oils (60-90% petroleum oil) ...........................8Introduction of Chemical Cutting Fluids ................... .9Synthetics (0% petroleum oil) .....................................9Semisynthetics (2-30% petroleum oil) ..................... . l lApplication .................................................................. 11

IV. Fluid Maintenance........................................................ 13Water Quality .............................................................. 13Coolant Concentration ............................................... 14Refractometers ............................................................ 15Titration Methods ....................................................... 18pH, Acidity ................................................................... 19pH Monitoring ............................................................ 19Biological Growth Monitoring ...................................20Fluid Controls ............................................................. 20Tramp Oil Removal ..................................................... 21Control of Microbial Growth ......................................23

Fluid Recycling ........................................................... 25Fluid Change Procedure .............................................27

V. Fluid Disposal.............................................................. 28Hazardous Waste Regulations ....................................29Heavy Metals ............................................................... 36Disposal of Waste Cutting Fluids ...............................36Contract Hauling ........................................................ 37Chemical Treatment ...................................................37Ultrafiltration Systems ............................................... 37Evaporators ................................................................. 38Centrifugation ............................................................. 39Disposal As Wastewater............................................... 39

VI. Health Concerns .......................................................... 40VII. Summary..................................................................... 41

VIII. Index ........................................................................... 42

I. Introduction

Machine shops and manufacturers with machiningoperations use and dispose of a significant amount ofcutting and grinding fluid. The fluid is used as a coolantand lubricant in the cutting operations, as well as thevehicle to carry away chips and fines produced in themachining and cutting operations. There are severaltypes of cutting and grinding fluids on the market,including both water soluble and non-soluble petroleumbased oils. When these fluids lose their efficiency, theyare generally disposed of, and the methods used fordisposal are often environmentally unsound.

Significant potential exists at the smaller machiningand manufacturing operations to extend cutting andgrinding fluid life, There is also a possibility ofreclaiming, or recycling, spent fluids and possibilitiesfor biological treatment and disposal.

Proper management of cutting and grinding fluids willalso prevent them from being declared a hazardouswaste at the end of their useful life.

The majority of cutting and grinding fluids in use todayare water soluble. Over time, these fluids can becomerancid or contaminated with microbiological growth.With use, fluids lose their rust control capabilities, aswell as their anti-foam characteristics. In addition, thefluids contain the chips and “fines” from thecutting/grinding operations. Oils called “tramp oil”accumulate from coatings on the metal and use ofspecial petroleum based cutting and lubricating fluids.The fluid is disposed of once its efficiency is lost.

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Cutting Fluid Management in Small Machine Shop Operations

Many times this disposal is done in a manner that isdamaging to the environment. Across the nationnewspaper headlines have shown public and governmentconcern for improper disposal.

Federal Jurors Indict Firm on Dumping Count

Judge Hauls in Chief Exec for Pollution Plea

Judge Reprimands Firm’s Chief forPolluting Tacoma Waters

Official Found Guilty In Ohio Waste Case

The following is a newspaper article found in the CedarRapids Gazette on April 2, 1990. The unknown fluid waslater identified as waste cutting fluid.

Sewer Substance StillUnidentifiedby Jeff Burham

Whoever dumped an oily substance into a southeast-side stormsewer may have to pay a tidy sum to clean it up.

The still unidentified milky-white substance presents no dangerto the water supply near 32nd Street Drive and Emerald AvenueSE, according to District Fire Chief Robert Reynolds.

“But I sure wouldn’t want my kids playing in it,” saidReynolds, who inspected the scene for more than five hoursSaturday night.

Neighbors spotted the substance through an opening in thestorm sewer and called the Fire Department.

Reynolds said it may be “something like soluble oil.” HealthDepartment officials are testing the substance in hopes of makinga positive identification.

If it is a soluble oil, Reynolds said, the substance will mix withwater in Indian Creek and “eventually go away.”

But he still wants to find out who dumped the substancebecause city ordinance would require the responsible party to payto remove the mess. “And that could get into some reallyhorrendous costs,” Reynolds added, declining to estimate.

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Through discussion with small machine shop operatorswe have learned that “backdoor” and “parking lot dump-ings” appear to be common methods of disposal. Evenwhen fluids are properly managed, fluid associated withchip removal can create problems. The chips and finesfound in the machine coolant fluids are removed toadequately maintain the cutting fluid. Machine shopsusing improper removal techniques will end up withsignificant amounts of cutting fluid in the chips and“fines”. This fluid often ends up in the ground or washedinto nearby waterways.

This manual will address three major areas of cuttingand grinding fluid management. Selection of fluids,maintenance of fluids to obtain maximum fluid life ex-pectancy, and disposal alternatives.

Good coolant management practices can go a long waytoward solving coolant problems and making the mostcost-effective use of your coolant.

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Il. Functions of a Cutting Fluid

Cutting fluids used in machine shops help to improvethe life and function of cutting tools. The two mostimportant functions of a cutting fluid are to providecooling and lubrication. A good cutting fluid, in additionto prolonging cutting-tool life, should resist rancidityand provide rust control.

Cooling

Laboratory tests have proved that the heat producedduring machining has a definite bearing on cutting-toolwear. Reducing cutting-tool temperature is important totool life. Even a small reduction in temperature willgreatly extend the life of a cutting tool. For example, iftool temperature were reduced only 500 F from 9500 to9000 F, cutting tool life would be increased by five times,from 19.5 to 99 minutes. Water is the most effectiveagent for reducing the heat generated during ma-chining. Since water alone causes rusting, soluble oilsor chemicals which prevent rust and provide otheressential qualities are added to make it a good cuttingfluid.

Lubricating

The lubricating function of a cutting fluid is asimportant as its cooling function. The effective life of acutting tool can be greatly lengthened if the heat andfriction generated by the cutting process are reduced.

When cutting fluids are used, faster speeds and feeds canbe used in the machining process resulting in increasedproduction and a reduction in the cost per piece.


Rust Control

Cutting fluids used on machine tools should inhibit rustfrom forming; otherwise machine parts and work will bedamaged. Cutting oil prevents rust from forming butdoes not cool as effectively as water. Water is the bestand most economical coolant but causes parts to rustunless rust inhibitors are added. All chemical cuttingfluids now contain rust inhibitors, which inhibit orprevent the process of rusting.

Rancidity Control

In the early days of the industrial revolution lard oil wasthe only cutting fluid used. After a few days lard oilwould start to spoil and give off an offensive odor. Thisrancidity is caused by bacteria and other microscopicorganisms that grow and multiply. Modern syntheticfluids are susceptible to the same problem, therefore,most cutting fluids contain some type of bactericidewhich controls the growth of bacteria and makes thefluid more resistant to rancidity. Bactericides too high inconcentration can be harmful to the skin.

No matter how good the engineering qualities of acoolant, if it develops an offensive odor, it can causeproblems for management. The material may become ahazardous waste and may create disposal costs greaterthan the fluid’s worth.


The following is a list of characteristics a cutting fluidshould posses to function effectively.

l l Good cooling capacityl l Good lubricating qualitiesl l Rust resistancel l Stability - for long lifel l Resistance to rancidityl l Nontoxicl l Transparent - to allow the operator to see

the work clearly during machiningl l Relatively low viscosity- to permit the chips

and dirt to settle quicklyl l Nonflammable- to avoid burning easily and

should be noncombustible.

In addition, it should not smoke excessively,form gummy deposits which may causemachine s/ides to become sticky, or clog thecirculating system.

Ill. Cutting and GrindingFluid Selection

Most machining operations are performed with the aidof some fluid or lubricant to prolong tool life. Of themultitude that are available, the most common typescan be classified into four groups:

Cutting and Grinding Fluids1. straight oils2. Soluble oils3. Synthetics4. Semisynthetics

Some are suitable for many operations; others are bestfor a select few.

Straight Oils (100% petroleum oil)

Straight oils, so called because they don’t contain water,are basically petroleum or mineral oils with or withoutadditives designed to improve specific properties. Noadditives are necessary for the easiest tasks-moderatecuts on free-cutting metals such as brass, for example.For more severe applications, straight oils are typicallycombined with up to 20% fatty oils, sulfur, chlorine,phosphorus or combinations of these ingredients. Forextreme conditions, additives (primarily with chlorineand sulfurized fatty oils) exceed 20%.

The straight oils have not changed much since theirintroduction around the turn of the century, althoughsome modifications have been made in recent years.Sulfur is now added in such a way that it won’t staincopper, for example. The major advantage of straight oilsis the lubricity or cushioning effect that they providebetween the workpiece and cutting tool. On the other

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hand, they are not especially effective in dissipating theheat generated by cutting and, thus, are usually limitedto low-speed operations.

Products of different viscosities are available for eachduty class. Viscosity can be thought of as a lubricantfactor: the higher the oil’s viscosity the greater itslubricity.

Highly viscous fluids, however, cling to the workpieceand tool, increasing coolant loss by dragout andnecessitating lengthier and more costly cleanupprocedures. Therefore, it can be more efficient to choosea low-viscosity oil that has been compounded to providethe same lubricity as a highly viscous one.

Soluble Oils (60-90% petroleum oil)

Emulsifiable, or soluble, oils are mineral oils containinga soaplike material (emulsifier) which makes themsoluble in water and causes them to cling to theworkpiece during machining. Soluble oils are suitablefor light-and medium-duty operations. Although they donot match the straight oils in lubricity, they, like water-based fluids in general, are better at cooling. Because oftheir water content, however, they are usuallyformulated with additives for additional workpiececorrosion prevention and to resist microbial degradationand souring. Maintenance costs to retain thesecharacteristics are relatively high.

The heavy-duty soluble oils are suitable for most of thecutting operations that the straight oils can handle. Forexample, broaching, trepanning, tapping, and of course,

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light- and medium-duty operations. Soluble oils havebeen replaced in most operations with chemicalsynthetics.

Introduction of Chemical Cutting Fluids

Chemical cutting fluids, called synthetic orsemisynthetics fluids, have been widely accepted sincethey were first introduced in about 1945. They arestable, preformed emulsions which contain very little oiland mix easily with water. Chemical cutting fluids de-pend on chemical agents for lubrication and frictionreduction. Some types of chemical cutting fluids containextreme-pressure (EP) lubricants, which react withfreshly machined metal under the heat and pressure of acut to form a solid lubricant. Fluids containing EPlubricants significantly reduce the heat generatedduring the cutting and grinding operations.

Synthetics (0% petroleum oil)

Synthetics were introduced in the late ‘50s and weremuch like soluble oils without the oil. These water-dilutable systems are designed for high cooling capacity,lubricity, corrosion prevention, and easy maintenance ofcomposition. Synthetics tend to be preferred whenclarity is important and less lubrication is needed. Onedrawback is that the synthetics tend to defat human skinand cause dermatitis.


The chemical agents found in most synthetic fluidsinclude:

1.2.3.4.5.

Amines and nitrites for rust preventionNitrates for nitrite stabilizationPhosphates and borates for water softeningSoaps and wetting agents for lubricationPhosphorus, chlorine, and sulfur compounds forchemical lubrication

6. Glycols to act as blending agents7. Germicides to control bacteria growth

As a result of the chemical agents which are added toenhance the cooling qualities of water, synthetic fluidsprovide the following advantages.

1.2.

3.

4.5.6.7.8.

9.

10.

Good rust controlResistance to rancidity for long periods oftimeReduction of the amount of heat generatedduring cuttingExcellent cooling qualitiesLonger durability than cutting or soluble oilsNonflammable, nonsmokingNontoxicEasy separation from the work and chips, whichmakes them clean to handleQuick setting of grit and fine chips so they arenot recirculated in the cooling systemPrevents clogging of the machine cooling system

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Semisynthetics (2-30% petroleum oil)

Semisynthetics contain small dispersions of oil in anotherwise organic water-dilutable system. Unlike mostoil-in-water emulsions, which are milky and opaque, thesemisynthetics are almost transparent, having only aslight haze. Most are also heat sensitive: unlike truesolutions, they become less soluble in heated water astheir extremely small molecules tend to gather aroundthe cutting tool and provide more lubricity. As thesolution cools, the molecules disperse again.

Application

Synthetics and semisynthetics are more broadly appli-cable than soluble oils and substantially easier tomaintain. Like the straight oils and soluble oils, theymay contain sulfur, chlorine and/or phosphorus. Overall,they offer cleanliness with less tendency to foam, goodcorrosion protection, and low cost.

Highly compounded straight oils are still preferred forsevere cutting operations; crush grinding, severebroaching and tapping, and deep-hole drilling, forexample; and for the more difficult-to-cut metals, suchas certain stainless steels and many superalloys. Theircost is high, but, under such conditions, they providethe longest tool life. They are also easier to maintain,less likely to cause corrosion, and less likely to causeproblems if misapplied.

At one time it was a common perception that syntheticswere primarily for grinding, but heavy-duty syntheticshave been introduced in the last few years that canhandle most machining operations. Both synthetics and

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semisynthetics have greater longevity and better coolingthan straight oils. Yet straight oils are stillrecommended for some operations because they providea better lubricating film.

Choosing the right cutting fluid for your operation canbe confusing and time consuming. Testing coolants inyour operation is an important process to improveproducts and manufacturing efficiency. Suppliers can behelpful by recommending fluids and thereby narrowingthe choices. One thing that must be remembered whenchoosing fluids, in today’s world you generally get whatyou pay for. Don’t choose a fluid just on its initial costbut on the cost per gallon divided by its life expectancy.

Fluid Cost Per Day Example

One 55 gallon drum $230Life expectancy 60 days

$230 / 55 gal = $4.18 per gal$4.18 / 60 day life = $0.07

$0.07 per gal per day

One 55 gallon drum $450Life expectancy 180 days

$450 / 55 gal = $8.18 per gal$8.18 / 180 day life = $0.045

$0.045 per gal per day

The lower priced fluid is close to twice the costof the higher priced fluid.

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IV. Fluid Maintenance

The key to extending fluid usefulness is proper fluidmaintenance. To maintain a fluid it must be monitoredto predict or anticipate problems. Monitoring includesdetermination of concentration using a refractometer ortitration kits, and control of rancidity with pH mea-surement and/or dip slides.

Monitoring is only the firststep in fluid maintenance.

It must be followed with maintenance in the form offluid concentration adjustments, tramp oil removal,chips and fines removal through sump cleaning, biocideaddition, and pH adjustment.

Water Quality

The quality of the water used to dilute fluid concentrateis important to the performance of the fluid. Fluid life,tool life, foam characteristics, product residue, corrosioncontrol and stability are all affected by water quality.

During normal fluid use, evaporation of water increasesthe concentration of the working fluid. As new water isadded to make up for evaporation loss additionalminerals from the water are also added, minerals thatare left in the fluid by evaporation. Hard water has moreminerals or total dissolved solids than soft water and thehigher the initial hardness of the water the faster thesolids will increase in the working fluid.

Certain dissolved solids or minerals contribute more toproblems with working fluids than others. Chloride

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salts and sulfates contribute to corrosion at levelsgreater then 100 parts per million. Sulfates also pro-mote growth of sulfate reducing bacteria that causefluids to become rancid. In many areas drinking watermay have sulfate concentrations of 50 to 100 ppm.Chloride levels are generally less then 10 ppm inuntreated water but are greatly increased by commonwater softening.

If fluid life is a problem, it is important to have a wateranalysis completed. If the shop is served by a publicwater supply, the local supplier of water can provide theneeded data. The fluid manufacturer may recommendsome form of water treatment based on the wateranalysis. This may be use of deionized water from aninline tank much like a water softener, or a reverseosmosis unit. With some waters, distillation units are anoption. Reverse osmosis may be a problem with highsulfate waters. Both types of units may need a commonwater softener preceding the treatment unit. Under nocircumstances should water from a common home typewater softener be used to treat make-up water formetalworking fluids.

Coolant Concentration

The concentration of your coolant must be monitoredregularly. Weekly monitoring is the minimum, dailymonitoring is suggested for small sumps or stand alonemachines. Concentration is important because it is themeasure of the amount of active ingredients present inthe coolant. Rich concentrations can result inincreased coolant cost and foam.

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Dilute concentrations can result in shorter tool life,increased biological activity, and increased risk of ruston newly machined parts. Concentration is measuredusing a refractometer or by doing a chemical titration.Using a refractometer is fast, using a titration kit fromthe fluid supplier is more accurate.

Refractometers

Refractometers have recently found their way into themetal working industry. They are being used indetermining total solubles in aqueous solutions ofcutting fluids and quenching solutions used in heattreating. The term refractometer is principally applied toinstruments used for determining the index of refractionof a liquid. The index of refraction is a measurement ofhow much light is bent as it passes through a liquid.With cutting fluids, as the refractometer readingincreases so has the product’s concentration. Bymeasuring the concentration of a cutting fluid with arefractometer, water lost in the cooling process can bereplaced, maintaining an optimum dilution of the fluid.Optimum dilution improves fluid life and maintainsproper cooling and fluid characteristics.

Refractometer

One small machine shop uses an all-purpose cutting andgrinding fluid that advertises to be a water dilutablesemi-synthetic fluid used for ferrous and non-ferrous

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metals. This product’s benefits include: outstandingcleanliness, rust control, trouble-free performance on awide variety of metals and operations, peak efficiency,long fluid life and low maintenance expense. Oneproblem with the fluid is that it loses water as it is usedand becomes more and more concentrated. This hindersits cooling capacity and shortens its life. The shop alsofound that if it tried to redilute the fluid it often overcompensated leaving the fluid too dilute. The resultingfluid contained few of the desired characteristics of agood cutting fluid. This shop now uses refractometers todetermine and maintain the proper dilution of theircutting fluids.

Optimum dilutions improve fluid life and maintainproper cooling and fluid characteristics.

Manufacturers recommend dilutions and correspondingrefractometer readings for specific operations. Forexample, the fluid used for the above mentioned shop isused in a 2O:l to 3O:l dilution. The shop maintainsthe 2O:l to 3O:l dilution using a refractometerkeeping the readings between 1.8 and 3.0.

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Refractometer Operating Instructions

1. Hold the instrument in a horizontal position. Lift the cover plate toexpose the prism and, using the dipstick, place a few drops of thesample on the face of the prism. It is preferable to obtain the samplefrom the work area rather than from a reservoir so that anycontaminants in the liquid will be better dispersed. To preventscratching the prism face, always use the dipstick which is provided.In the absence of the dipstick, do not use glass, metal or the fingers.A common plastic stirring rod is a good substitute. Unfinished woodis not suitable since it may absorb some of the water in the specimenand give an incorrect reading. To reduce evaporation to a minimum,close the cover plate over the prism without delay.

2. To hold the instrument for reading, keep the cover plate in contactwith the prism and point the instrument toward a window or otherilluminating source. Look through the eyepiece and take thereading at the point where the dividing line between light and darkcrosses the scale.

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Until one has had sufficient experience to immediately recognize theoptimum contrast obtainable between light and dark boundary, theinstrument should be tilted with respect to the light source untilbest results are obtained. Good daylight or artificial light is adequateto illuminate the scale. Distant fluorescent light is sometimesinadequate.

3. Use a soft cloth or soft tissue paper moistened with water for wipingthe prism and cover plate. Dry the prism and cover plate with a softcloth or tissue. If the prism and cover plate is not well cleanedbefore the next sample is loaded an erroneous or fuzzy reading willresult. Do not use hot water and never use gritty cleaningcompounds to clean the prism.

NEVER EXPOSE THE INSTRUMENT TOTEMPERATURES ABOVE 1500F.

All instruments are factory calibrated and the adjustments are sealed. Youmay check the accuracy of your instrument by using distilled water as asample. This should give you a reading of zero.

Titration Methods

Refractometer methods are fast but become lessaccurate when the fluid is contaminated with tramp oils.To overcome this problem vendors of fluids havedeveloped titration kits to determine fluidconcentration. The titration measures a specificchemical or group of chemicals and is less affected byinterferences due to tramp oil or water quality.

The titration may be done by taking a measured volumeof fluid, adding an indicator and then adding the titrant,drop by drop until a color change is noted. The coolantconcentration is determined from the number of dropsof titrant added.

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pH, Acidity

The pH is the measurement of hydrogen ionconcentration. The higher the pH the more alkaline thesolution. Coolants should be maintained within alimited range of alkalinity, between 8.5 and 9.5. If pH ofcoolant in a sump falls below 8.5, the coolant losesefficiency, is prone to rusting, and biological activity willincrease significantly. The pH usually remains constantand any rapid change in pH should be investigated andaction taken to prevent damage to the coolant. Suddendownshifts in pH are usually indicative of increasedbiological activity or a sudden change in coolantconcentration due to contamination. If coolantconcentration and pH both jump downwards, the sumphas been contaminated. If coolant concentrationremains fairly constant and pH falls off, biologicalactivity is more than likely increasing.

pH Monitoring

The pH or acidity can be measured in two ways. Lowcost test papers give a quick estimate of the pH of afluid. Test papers are accurate to plus or minus a full pHunit. Medium cost pH meters are accurate to plus orminus 0.2 pH units and high cost meters are accurate tohundredths of a pH unit. To determine the pH of a fluid,simple pH paper will do. To predict biocide failure amedium cost pH meter kit will be needed. pH meter kitscan be obtained for one hundred to two hundred dollars.High cost pH meters that are highly accurate are of littleuse in fluid management.

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Tips on use of pH Meters and pH Testers1. pH electrodes must be kept wet and clean. If one

dries out, soak it in water for 24 hours.2. pH meters and testers must be calibrated with

buffer solutions. It is best to use two buffers suchas pH 7 and pH 4 to make sure the meter isworking properly.

3. Mix the solution, then let the meter readingstabilize for 10 to 20 seconds. Then take themeasurement by immersing the tip of theelectrode only 1 inch into the solution.

4. Do not be alarmed when white crystals form onthe electrode, just soak the electrode in buffer orwater.

5. When all else fails read the instructions that comewith the meter or tester.

Biological Growth Monitoring

Reliable microbial growth dip slides are available. Testscost less then ten dollars each and are useful in settingup biocide addition programs. When rancidity is aproblem, microbial growth dip slide monitoringprovides a chance to add biocide before problems arise.Dip slides are avalible from fluid suppliers and fromlaboratory supply houses.

Fluid Controls

For optimum fluid performance and life, fluidcontaminants must be controlled. These contaminantscan be minimized with good maintenance andhousekeeping programs. With many machineslubricating oils and greases cannot be isolated from thefluid. These contaminants, as well as metalcontaminants, are expected by-products.

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Many of the contaminants that cause fluids to bedisposed of frequently are foreign materials, such asffoor sweepings, cleaners, solvents, dirt, tobacco,food etc.

If improved fluid life is a goal, it must start witheducation and revised shop practices. The first step influid control is improved housekeeping and sanitation.Only then will control of natural contaminants of oil,chips and fines, and bacteria be effective in improvingfluid life.

Tramp Oil Removal

Machine shops use coolants to transfer heat generatedduring the machining process away from cutting toolsand parts being produced. The coolant is collected inand recirculated from a sump. During use the coolantcollects lubricating oil from the machine lubricatingsystem. This oil, called tramp oil, coats the coolantsurface, contributes to the growth of anaerobic bacteriaand makes-the material unsuitable for disposal througha sewer system. Anaerobic bacteria produce hydrogensulfide gas, which smells like rotten eggs and mayirritate the skin. Anaerobic bacteria will shorten coolantlife, and eventually force disposal of the coolant waste. Italso produces acidic conditions that may dissolve chipsand fines making the coolant a hazardous waste.

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Tramp Oil Removal1. Absorbent Blankets, Fabrics or Pillows2. Disk me Oil Wheels3. Belt me Skimmers4. Rope Type Skimmers5. Porous Media Separators or Coalescers6. Centrifuges

Belt and disc skimmers to remove tramp oil from thesurface of coolants are the most common and found tobe cost-effective in large and some small operations.

For small sumps, oil absorbent fabrics or pillows can beused. Choose a fabric or pillow treated to repel water butabsorb hydrocarbons. The fabric can be drawn across thesump pit removing tramp oil, or the pillows can float inthe sump while absorbing oils.

A coalescer is a porous media separater. As the fluidpasses through the coalescer media, the media attractsand separates the tramp oil from the fluid. The media isnormally made of polypropylene which attracts oil to itin preference to water. The coalescer has no movingparts and is generally self cleaning. The oil separates tothe top of the tank and is removed by a skimmer. Smallshop coalescing units run from $1,000 to $5,000.

Coolant sumps, depending on maintenance practices,may require oil removal monthly or even weekly. Theexact management scheme for waste oil is determinedby the type of coolant, level of contamination, presenceof regulated materials (metals, organic solvents) andavailability of treatment.

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Control of Microbial Growth

Since the introduction of water-based technology earlyin this century, microbial contamination of the fluidshas been of concern. As mentioned earlier the effects ofmicrobial growth in fluids can significantly reduce fluidlife. Successful control is a must.

Bacterial growth can be controlled by routinecleaning of the sump and the use of biocides.

Studies have been done on the effect of biocidetreatment patterns on antimicrobial efficacy inmetalworking fluids. Fouled fluids were treated with acommercial biocide at various concentrations andfrequencies, while microorganism populations weremonitored. For all biocide application rates tested, theefficiency of antimicrobial control was found to varywidely with treatment pattern. Less frequent doses withhigher concentrations of biocide were found to be muchmore effective than low-level, frequent doses. The rea-sons for this behavior were investigated, and found to berelated to biocide residual concentrations, biocide con-sumption by microorganisms, and changes in thepredominant species of bacteria which populated thefluids.

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COMPARISON OF BIOCIDE DOSE RATES

300 ppm per week

1 2 4 6 8Time in Weeks

Improper control of microbial growth will also alter thepH of the fluid. As the fluid becomes rancid or septic thepH drops; in other words, the solution becomes moreacidic.

This acid produced by the bacteria will dissolve metalchips and fines and possibly cause the material to meetthe Resource Conservation and Recovery Act (RCRA)definition of hazardous waste.

This is discussed in detail in the hazardous wasteregulation section.

Failure to remove chips and fines from the sumps alsopromotes microbial growth. Biocides do not reach thefluids mixed in the fines and this sludge in the bottom ofthe sump becomes septic or rancid. Even if the majorityof the fluid is free of bacteria the sludge in the bottomwill harbor the bacteria, creating a septic condition. Thispromotes the dissolving of metals and increases the

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toxicity of the fluid making disposal in the localwastewater treatment plants unacceptable.

Fluid Recycling

Self-contained recycling system units can be purchasedthat are specifically designed for smallermachine/grinding shops. These units provide a completesump maintenance, coolant recycling system in oneunit, portable and nonportable. It is recommended thatcoolants be recycled every two or three weeks on anaverage to keep coolants fresh and usable for extendedperiods of time. Use of fluid recycling units results in asignificant reduction in waste disposal and related costs.Problems associated with rancidity and operatordermatitis are usually eliminated with improved coolantcondition. Recycling equipment is usually easy tooperate and maintain. These units also provide effectiveconcentration control.

Facilities recycling fluidsreport fluid life of one to twoyears of more.

There is a wide variety of recycling systems or, as theyare sometimes called, “contaminant removal systems”.For small shops the most effective method to extendfluid life or to recycle fluid for individual machines is theuse of batch treatment systems. Such systems arecapable of removing contaminants such as tramp oil,dirt, bacteria; and can readjust the fluid concentrationbefore the fluid is returned to the individual machine.Batch treatment must be done on a frequent basis tominimize the contaminants in the fluid. Many shopsfind that, to keep fluid clean, batch treatment must be

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Fluid Change Procedure

The following is an example of a coolant change practiceused at one small machine shop and found to be themost efficient for extended coolant life.

1. Skim all tramp oil from coolant surface2. Pump coolant from sump3. Vacuum chips from sump4. Remove sump access covers5. Vacuum chips from sump6. Clean and vacuum sump (repeat until clean)7. Replace sump access covers8. Replace original coolant

The change practice was performed every 2-3 monthsand required an average of 5.21 hours to accomplish ona cast sump, 20-100 gallons. Sumps made of sheet metaltake several hours less because corners are generallyrounded and more easily cleaned. This coolant changepractice, when combined with improved ongoingcoolant maintenance, holds promise for extendingcoolant life;

With proper maintenance of fluids, proper addition ofbactericides and inhibitors, and maintenance of properdilution, cutting fluids can last almost indefinite/y.

SUMP CLEANER/FILTER27

V. Fluid Disposal

Proper care of cutting fluids is important if themaximum benefits of using water-based products are tobe obtained. Prolonging cutting fluid life is a sound,economically justifiable policy and certainly the firststep of any waste management program.

While prolonging the life of a cutting fluid is possible,extending it indefinitely is not. Eventually, it will have tobe treated and disposed of as a waste.

Cutting fluid wastes are as varied as they are numerous.Their chemical components reflect not only theiroriginal makeup, but also the operations and conditionsof their use. In fact, many cutting fluid wastes containhigher percentages of machine tool lubricating oilsand/or suspended solids (dirt) than they do cutting fluid.

If all tramp oil is removed, and waste fluid is not allowedto become septic, and chips and fines are removed, watersoluble and synthetic fluids can in many cases, with theapproval of local wastewater authorities, be disposed ofin the municipal sewer treatment system. If not treatedproperly waste can become toxic and will fall underhazardous waste regulations.

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Hazardous Waste Regulations

Congress defined the term “hazardous waste” in theResource Conservation and Recovery Act (RCRA) as a“solid waste, or combination of solid wastes, whichbecause of its quantity, concentration or physical,chemical or infectious characteristics may:

1. Cause, or significantly contribute to anincrease in mortality or an increase in seriousirreversible, or incapacitating reversible,illness.

2. Pose a substantial present or potential hazardto human health or the environment whenimproperly treated, stored, transported, ordisposed of, or otherwise managed.”

Note that hazardous wastes are defined in terms of properties of asolid waste. It should be stressed that a solid waste need not be asolid, it can also be a liquid, semisolid or a contained gaseousmaterial.

Hazardous Wastes May Be

SOLID LIQUID GAS

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A solid waste is hazardous if it meets one of three conditions:

1. Exhibits, on analysis, one or morecharacteristics (ignitability, corrosivity,reactivity or toxicity) of a hazardous waste.

2. Has been named as a hazardous waste andlisted.

3. Is a mixture containing a listed hazardouswaste and a non hazardous solid waste (unlessthe mixture is specifically excluded or nolonger exhibits any of the characteristics ofhazardous waste).

Four characteristics for hazardous wastes have beendelineated by the federal Environmental ProtectionAgency (EPA). Any solid waste that exhibits one ormore of them is classified as a hazardous waste. Thecharacteristics are: ignitability, corrosivity, reactivity,toxicity.

Hazardous Waste Classifications

Ignitable Corrosive Reactive Toxic

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IGNITABLE

Ignitability-

A solid waste exhibits the characteristic ofignitability if a representative sample ofthe waste has any of the followingproperties:

A. A liquid with a flash point less than 60°C(140” F), except for aqueous solutionscontaining less than 24 percent alcohol.

B. A non-liquid capable, under normalconditions, of spontaneous and sustainedcombustion.

C. An ignitable compressed gas perDepartment of Transportation (DOT)regulations.

D. An oxidizer per DOT regulations.

EPA included ignitability as a charac-teristic of wastes that could causefires during transport, storage, or dis-posal. Examples of ignitable wastesinclude many waste so/vents.

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CORROSIVE

2. Corrosivity -

A solid waste exhibits the characteristic ofcorrosivity if a representative sample of thewaste has any of the following properties:

A. An aqueous material with a pH less than2 or greater than 12.5 as determined bya pH meter using an EPA test method oran equivalent test method.

B. A liquid that corrodes steel at a rategreater than l/4 inch per year at a testtemperature of 550 C (1300 F).

EPA selected pH as an indicator of cor-rosivity because wastes with high or lowpH can directly affect human health orthe environment or react dangerouslywith other wastes or cause toxiccontaminants to migrate from certainwastes. Examples of corrosive wastesinclude acidic wastes and spent pickleliquor (used to clean steel duringmanufacture).

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REACTIVE

3. Reactivity -

A solid waste exhibits the characteristicof reactivity if a representative sample ofthe waste has any of the followingproperties:

A. Normally unstable and undergoesviolent change without detonating.

B. Reacts violently with water.

C. Forms a potentially explosive mixturewith water.

D. Generates toxic gases, vapor, or fumeswhen mixed with water.

E. Contains cyanide or sulfide andgenerates toxic gases, vapors, or fumesat a pH between 2 and 12.5.

E Listed by DOT as a forbidden explosiveor as a Class A explosive or a Class Bexplosive.

Reactivity is a characteristics that identifies unstable wastesthat can pose a problem, such as an explosion, at any stage ofthe waste management cycle. Examples of reactive wastesinclude water from TNT operations and used cyanide solutions.

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TOXIC

4. Toxicity -

A solid waste exhibits the characteristic oftoxicity if, by using designated testmethods, the liquid waste or extractfrom a representative sample contains anyof the contaminants listed below atconcentrations greater than the followingin milligrams per liter:

Contaminant

Arsenic ....................................... 5.0Barium .................................... 100.0Benzene ...................................... 0.5Cadmium .................................... 1.0Carbon tetrachloride ................ .0.5Chlorobenzene.. ..................... .lOO.OChloroform ................................. 6.0

. Chromium .................................. 5.0o-Cresol ................................... 200.0m-Cresol ................................. 200.0p-Cresol ................................... 200.0Cresols (total) ........................ .200.01,4-Dichlorobenzene ................. .7.51,2-Dichloroethane.. .................. .0.51,1-Dichloroethylene.. ............... .0.72,4-Dinitrotoluene.. ................... .0.13Hexachlorobenzene ................... .0.13Hexachloro-1,3-butadiene.. ...... .0.5Hexachloroethane ..................... .3.0

Conc EPA HW.mg/l No.

DO04DO05DO18DO06DO19DO21DO22DO07DO23DO24DO25DO26DO27DO28DO29DO30DO32DO33DO34

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Lead ............................................. 5.0Mercury .................................... 0.2Methyl ethyl ketone .............. 200.0Nitrobenzene .............................. 20.Pentachlorophenol ................ lOO.OPyridine ....................................... 5.0Selenium ..................................... 1.0Silver .......................................... 5.0Tetrachloroethylene .................. .0.7Trichlorethylene ........................ .0.52,4,5-Tkichlorophenol.............400.02,4,6-Trichlorophenol.................2.0Vinyl chloride.............................. 0.2

DO08DO09DO35DO36DO37DO38DO10DO11DO39DO40DO41DO42DO43

The list identifies wastes likely to leachhazardous concentrations of toxicconstituents into the ground water as aresult of improper management.

Generators are responsible for determining if aparticular solid waste is hazardous. They must eithertest the waste material using standard methods or havesufficient knowledge about the waste to assess whetherit exhibits any of the characteristics of a hazardouswaste.

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Heavy Metals

Heavy metal is a term commonly found in the jargon ofchemists and toxicologists and in environmentalregulation. Heavy metals are hazardous due to theirtoxic effects on various body systems. Most of thesematerials do not break down readily in the body, andthus can accumulate over time. Many small businesses,for example machine shops, can produce a fluidcontaining heavy metals.

A primary objective of cutting fluid management isto keep a fluid from becoming a hazardous waste.

Fluids and other wastes that may contain smallquantities of these metals have typically been consideredhazardous waste according to the toxicity testingprocedure.

Disposal of Waste Cutting Fluids

If the waste fluid is hazardous the major wastetreatment and disposal options are contract hauling,chemical treatment, ultrafiltration, and evaporation.Method of disposal depends on volume generated, wastecomposition, availability and cost of options. If thewaste is hazardous it can not be disposed of to awastewater treatment plant.

Dilution was once regarded as sufficient treatment andmost wastes were disposed of by emptying them directlyinto the nearest sewer or stream. With the advent of theClean Water Act and the Environmental ProtectionAgency, such practices are restricted. To understand the

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objectives of waste treatment it is important to realizethat there are few direct answers for every problem andeach situation demands individual attention.

Minimizing waste by practicing effective coolantmaintenance is the best approach to waste disposal.

Contract Hauling and Disposal Services

Contract disposal services and contract hauling costs arehigh and many large machine shops opt for in plantwaste treatment. Studies have shown that for smallvolumes of waste (less than 200 gallons), extremelycomplex or highly toxic wastes, it may be cheaper tohave it hauled away for chemical treatment or incin-eration.

Chemical Treatment

Chemical treatment is the addition of chemicals whichchange the nature of the liquid waste. Elementarychemical treatment methods work well on somewastewater. But, metalworking wastes are too complexfor most treatment processes . Chemical treatmentbeyond pH control is generally not an option for smallfacilities.

Ultrafiltration Systems

Ultrafiltration systems were created for themetalworking industry to treat such wastes as usedcutting fluids, detergents, parts-washer solutions, andother oily wastewaters . Strict environmental laws

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require proper treatment prior to discharge.Ultrafiltration systems provide effective treatment of thiswastewater by separating the water from the oily waste.The quality of water is then ready for sewer disposal.

The concentrate from ultrafiltration may be processedfor oil recovery or incinerated.

Ultrafiltration systems are usually better than chemicaltreatment, less expensive than incineration and contracthauling, easily operated and space efficient. Unitsprocess from 100 to 300 gallons per day and cost from$5,000 to $13,000.

Evaporators

Evaporators are generally considered suitable for lowvolumes of waste, due to the enormous amount ofenergy required to evaporate even a small volume ofmaterial.

Used coolants are normally 90 to 95% water.Evaporators can be used to remove the water from wasteliquids, reducing the volume of waste, thereforereducing disposal costs. The advantages of evaporatorsinclude; they require very little chemical knowledge tooperate, they use very little space, they are simple to op-erate, and the type of coolant used (synthetic, semisyn-thetic, or soluble oil) is not critical.

Evaporators do not eliminate waste, only reduce thevolume of waste. Evaporators are also labor intensivewhen it comes to cleaning the units. Evaporatorsshould be considered when other treatment systems do

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not meet a shop’s needs and waste must be disposed ofby contract.

Centrifugation

Centrifuges remove solids only and can be used forpretreatment. Centrifuges are expensive, and othermethods such as oil skimmers are more economical forsmall volumes of fluids.

Disposal As Wastewater

Small amounts of spent cutting fluid can be disposed ofas wastewater if it is not a hazardous waste.

Spent cutting fluids that:1. Are water soluble2. Receive regular biocide additions3. Have not become septic4. Have had the chips and fines removed5. Have had the tramp oil absorbed to less then

100 mg/l6. Have a pH between 6.0 and 9.07. Do-not contain toxic concentrations of heavy

metal ionscan be disposed of in a municipal sewer but the localwastewater treatment plant operator should becontacted for approval prior to any disposal.

The long-term goal of waste treatment legislation is thecomplete elimination of pollution. The cost of completecontrol is enormous and such control is rarely practiced.Yet, the benefit of exercising some control ofenvironmental contaminants is worthwhile, resulting ina cleaner environment.

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VI. Health Concerns

The machining of metals involves human exposure tomany chemicals. The biggest health concerns forcoolants are dermatitis and respiratory problems. Mostproblems come from the contaminants instead of theingredients of the coolant. Because human contact withcoolants in the workplace is unavoidable, ingredientsand potential health effects should be considered whenselecting a cutting fluid. Most producers avoid usingcorrosive and irritating ingredients.

The use of straight oils can cause health and safetyconcerns. They create fire hazards, slippery floors andharmful oil mist.

Under the Hazard Communication Standard, MaterialSafety Data Sheets (MSDS) on all fluids purchased arerequired. These MSDS’s contain important health andsafety information. Consult your MSDS if any questionsarise on toxicological components of the coolant.

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VII. Summary

The economics of fluid use is changing rapidly.Emerging issues include improved fluid productivity,health and safety, and environmental concerns. Thereare many components when considering overall fluiduse costs. As metalworking fluid needs change and costsincrease, it is imperative for plants to implement a fluidmanagement program.

Obtaining and maintaining a steady state condition ofyour cutting fluid are the most important parts of a fluidmanagement program. This is done by proper fluidselection, proper pH monitoring, concentration controland biological activity monitoring.

Through careful fluid management, metalworkingfacilities can substantially improve fluid life, per-formance and reduce overall costs.

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VIII. Index

1,1-Dichloroethylene 341,2-Dichloroethane 341,4-Dichlorobenzene 342,4,5-Trichlorophenol352,4,6Trichloropheno1352,4-Dinitrotoluene 34Advantages of synthetics 10Alkaline 19Arsenic 34Bactericide 5Barium 34Batch treatment 26Benzene 34Biocide 23Biocide doses 24BIOLOGICAL GROWTH

MONITORING 20Cadmium 34Carbon tetrachloride 34CENTRIFUGATION 39CHEMICAL CUTTING FLUIDS 9CHEMICAL TREATMENT 37Chloride salts 14Chlorobenzene 34Chloroform 34Chromium 34Coalescer 22Contaminant removal systems 25Contaminants 21CONTRACT HAULING 37CONTROL OF MICROBIAL GROWTH 23COOLANT CONCENTRATION 14COOLING 4Corrosivity 32Creso134

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Cutting and Grinding Fluids 7Cutting fluid 6Cyanide 33Deionized water 14Dermatitis 40DISPOSAL AS WASTEWATER 39DISPOSAL OF WASTE CUTTING FLUIDS

36DISPOSAL SERVICES 37Dissolved solids 14Emulsifiable 8Emulsifier 8EP lubricants 9Evaporation 13Evaporation loss 13EVAPORATORS 38Extended fluid life 1FLUID CHANGE PROCEDURE 27FLUID CONTROLS 20FLUID DISPOSAL 28Fluid life 25FLUID MAINTENANCE 13FLUID RECYCLING 25Generators 35Hard water 13Hazard Communication Standard, 40Hazardous waste classification 30HAZARDOUS WASTE REGULATIONS 29HEALTH CONCERNS 40Heat sensitive 11HEAVY METALS 36Hexachlorobenzene 34Hexachlorobutadiene 34Hexachloroethane 34Ignitability 31


Improved fluid life 21Lead 35LUBRICATING 4m-Creso134Material Safety Data Sheets (MSDS) 40Mercury 35Methyl ethyl ketone 35Monitoring 13MSDS 40Municipal sewer 39Nitrobenzene 35o-Creso134Objective of cutting fluid management 36Oil absorbent fabrics 22Optimum dilutions 18p-Creso134Pentachlorophenol35pH 19pH MONITORING 19Porous media separater 22Pyridine 35RANCIDITY CONTROL 5RCRA 29Reactivity 33Refractometers 15Resource Conservation and

Recovery Act 24Respiratory problems 40Reverse osmosis 14RUST CONTROL 5Selenium 35SEMISYNTHETICS

(2-30% petroleum oil) 11Silver 35

Skimmers 22Soft water 13Solid waste 29SOLUBLE OILS (60-90% petroleum oil) 8STRAIGHT OILS (100% petroleum oil) 7Sulfates 14Sulfide 33SYNTHETICS (0% petroleum oil) 9Tetrachloroethylene 35Titration kits 18Tool temperature 4Toxicity 34Tramp oil 1TRAMP OIL REMOVAL 21Trichlorethylene 35ULTRAFILTRATION SYSTEMS 37Vinyl chloride 35Viscosity 8Wastewater treatment plant operator 39WATER QUALITY 13Water softener 14

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cutting fluid management in small machine shop operations - world1

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