Pollution Prevention for Painting and Coating Compliance Enhancement is a cooperative effortof the Design for the Environment (U.S. Environmental Protection Agency) and the Iowa WasteReduction Center at the University of Northern Iowa.

Assessing the Efficiency of Liquid ApplicationSystems - Keep it Simple

There is no question that measuring efficiency is an important step toward improving it. However, this does notnecessarily require something as elaborate or intrusive as a transfer efficiency determination. As depicted in thisarticle, measuring efficiency is better and more easily accomplished by focusing on finish quality, film build and

material consumption.

The Effect of Air Restrictions on Spray FinishingJust when you think 1/4-inch air hoses are a thing of the past, you visit a manufacturing facility that is running

over 100 feet of it from their main air line to their spray booth. The purpose of this article is offer someinsight on how common air restrictions might affect your air spray finishing operation.

News BriefsThe Minnesota Paint and Powder Coating Exposition, Mississippi On-Site Reviews, and the Environmental

Management Service are all ways the IWRC staff reaches small businesses.

Recoating Powder Coated Parts and Methods ofReducing or Eliminating Out-Gassing:

DuPont Powder CoatingsDuPont Powder Coatings addresses problems often encountered with recoating and coating porous cast-

ings

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any case, an inability to meet fin-ish quality objectives means lostproductivity, excessive materialusage and high production costs.It also contributes to a deteriorat-ing customer base.

Film Build EfficiencyAlthough the definition of trans-fer efficiency is well known, theconcept of film build efficiency(FBE) is not. The purpose ofspray finishing is to apply anorganic film onto a substrate fordecorative and functional purpos-es. The suggested thickness of thefilm is typically specified by thebusiness, its customers and/or thecoating manufacturer. FBE is sim-ply a measure of film thickness,uniformity and consistency acrossa part relative to a specified (ortargeted) film thickness.

Unfortunately, the significance offilm build efficiency is often lostin the transfer efficiency hype.From a production standpoint,

Figure 1.A mechanical (gear-type) flow meter manufactured by Graco Incorporated.

This in-line fluid monitor accurately measures fluid flow rate, batch totals andcumulative totals of material that passes through the fluid line. A softwarepackage is also available that allows the meter to send material usage data to astandard PC for reporting purposes. It is intrinsically safe and can be mountedin hazardous locations.

by Brian GedlinskeIWRC Environmental Specialistgedlinske@uni.edu AA good number of businesses

that perform spray finishingoften get caught up in assessingthe transfer efficiency (TE) oftheir process. TE, after all, is the“buzz-word” in spray finishingwhether you’re from industry, aregulatory agency or a pollutionprevention program.Consequently, a great deal oftime and energy are often spentdevising schemes to assess TEfor a particular spray gun or fin-ishing process.

TE means much less to me nowthan it once did. Anymore, TEnumbers are readily disregardedwhen brought to my attention –especially spray gun TE ratings.In regard to spray finishing effi-ciency, experience shows that thetype of spray equipment used isless important than the mannerin which it is setup, operated andmaintained. Knowing the processand the equipment are key

aspects of any efficient spray fin-ishing process.

There is no question that meas-uring efficiency is an importantstep toward improving it.However, this does not necessar-ily require something as elaborateor intrusive as a TE determina-tion. Measuring efficiency is bet-ter and more easily accomplishedby focusing on finish quality, filmbuild and material consumption.

Finish Quality The primary objective of anyspray finishing operation is tomeet finish quality objectives ona consistent basis. Finish qualityis, of course, site dependentsince every business has its ownstandard of quality. This typicallyincludes appearance characteris-tics such as color, gloss and tex-ture. Oftentimes, it also includescoating performance criteriarelated to weatherability, corro-sion resistance and durability. In

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FBE is more important thantransfer efficiency simplybecause FBE is related to finishquality while transfer efficiency isnot. If the film build applied to asubstrate is too heavy or light,finish quality objectives (thenumber one finishing priority)may not be met.

FBE is also more importantfrom an environmental perspec-tive. For example, if finish quali-ty objectives are not met becauseof film build problems, theworkpiece must be reworked orscraped out. This means morespray finishing work, higher airemissions, and increased wastegeneration rates.

In cases where excessive filmbuilds still meets finish qualityrequirements, room for improve-ment opportunities exist fromenvironmental and productionperspectives. For example, apply-ing four mils of coating whentwo mils would suffice (in termsof finish quality) means you arespraying twice what you need.This is equivalent to doublingyour air emissions and coatingmaterial costs. It also meansmore spray booth maintenance,equipment wear and materialhandling.

As you should now realize, a dryfilm thickness gauge is an indis-pensable quality control tool inthe spray finishing industry. Itallows you to monitor film buildsapplied to your product anddiagnose finish quality problemsthat are oftentimes related toFBE. Another important note –in order to be effective, filmbuild monitoring results need tobe shared with spray operators

on a continual basis. Withoutfeedback, spray operators do notknow if they are applying toomuch or not enough coating.Feedback is also utilized to iden-tify problem areas on certainparts.

Material ConsumptionMeasuring material usage is oftenrequired for environmental com-pliance and reporting purposes.It’s also an important part ofassessing and improving the effi-ciency of an existing spray fin-ishing process. In many cases,material usage is determinedthrough inventory tracking.However, for purposes ofprocess improvement, a paintmetering system may be the bestinvestment. Meters are usefultools for monitoring and opti-mizing a spray finishing process.They are also useful for employ-ee training, quoting costs andsimplifying environmental com-pliance duties.

A number of fluid-metering sys-tems (rated for various operatingpressures and flow rates) areavailable for liquid applicationsystems (see Figures 1 and 2).These are typically portable, easyto install and user friendly.Although cost is a function offeatures, basic metering systemsare available in the $1,500 to$2,500 range. This may seemexpensive at first, but the poten-tial payback is considerable.Experience suggests that it is notuncommon to reduce coatingmaterial consumption by 20 to50 percent through employeetraining and proper equipmentsetup. Therefore, in many cases,a spray finishing operation couldrecoup the cost of a meteringsystem in a relatively short peri-od of time through material sav-ings. An even faster paybackwould be realized if the meteringsystem improves environmentalcompliance productivity.

Process ImprovementDocumentationBefore implementing anychanges toward improving theefficiency of a spray finishingprocess, it is a good idea to gath-er some data on existing condi-tions. This baseline informationis useful for assessing and docu-menting progress. It also plays animportant role in justifyingprocess changes to managementand employees. Some basic infor-mation that should be collectedand recorded as part of the base-line process includes:v Spray gun setup and operating

parameters. This wouldinclude the make and model ofspray gun, fluid nozzle/tip sizeinformation, air cap informa-tion, atomizing air pressure,and fluid pressure.

v Coating characteristics information such as application vis-cosity, percent solids and rec-ommended dry film thickness.Some coating suppliers pro-vide product informationsheets for their coatings(please note: I am nnoott refer-ring to material safety datasheets [MSDS]). These prod-uct information sheets providesome very useful informationon the coating and how itshould be applied for best per-formance.

v Dry film build measurements across the part or parts thatwill be finished during theprocess evaluation (for assess-ing FBE).

v Coating usage (per part or batch of parts) and fluid deliv-ery rate of the spray gun

should be measured with theuse of the paint metering sys-tem.

v Finish quality of the parts fin-ished during the process eval-uation. Here it is important toidentify existing finish qualityproblems and determine rejectrates.

v Identify the spray operatorsperforming the work. Sprayoperators vary greatly inregard to spray finishing effi-ciency. So, in order to make afair “before-after” compari-son, its best to use the samepeople.

v Production rate considerations must be taken into account.Production rate is a functionof more than just line speed.It is also dependent on the sizeand complexity of the partbeing finished.

Once sufficient background datahas been obtained, processchanges may be implemented (ina systematic fashion) to evaluatetheir effect on spray finishingefficiency. How detailed thisneeds to be is somewhat subjec-tive. However, do not make itharder than it has to be (a com-mon vice for many people).Again, finish quality, FBE andcoating consumption should bethe focal points of process opti-mization. Consistency with finishquality objectives and optimizingFBE should receive top priority.Accomplishing these objectiveswhile reducing coating usage isan improvement on all fronts andhas much more significance thanany TE number.

Figure 2. A mass flowme-tering systemmanufactured byMicro Motion,Incorporated.These metersprovide accuratedirect mass flow,volume flow, den-sity and tempera-ture measure-ments whileexhibiting anexceptionally lowpressure drop.

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JJust when you think 1/4-inch airhoses are a thing of the past, youvisit a manufacturing facility thatis running over 100 feet of itfrom their main air line to theirspray booth. At the spray booth,the line is plumbed throughnumerous fittings and quick-dis-connects on its way to some sortof air filtration system. The airmight then be plumbed through

some sort of air regulator fittedwith a pressure gauge that iseither dysfunctional or is coveredwith so much overspray that youcan’t tell its dysfunctional. Doesany part of this (or all of it)sound familiar? The purpose ofthis article is offer some insighton how common air restrictionsmight affect your air spray finish-ing operation.

Air Spray Atomizationand Air RestrictionsWith conventional or high vol-ume-low pressure (HVLP) airspray, atomization energy impart-ed by compressed air from the aircap is used to break up the fluidstream from the spray gun. Inregard to atomization energy,conventional air spray guns relymore on air velocity to break upthe fluid stream. HVLP atomiza-tion energy, on the other hand,relies more heavily on the massof air from the air cap. In anycase, air restrictions reduce atom-ization energy and may cause dis-appointing results with respect tofinish quality, particularly whenusing HVLP equipment.

The following are some commonsources of air restrictions:

Small Diameter Air HosesSmall diameter air hoses shouldbe a thing of the past. However,it is not unusual to find 1/4-inchhoses being used to supply atom-izing air to a spray gun. Smalldiameter hoses starve the spraygun of air. For air spray equip-

ment, 3/8-inch hoses are best(particularly for HVLP sprayguns) although 5/16-inch may bejust fine for short hose runs (seeFigure 1).

Excessive Hose LengthsUsing a 50-foot length of air hosein a spray booth where a 10-footlength would suffice does not

Figure 2. Various fittings and plumbing arrangements.

Figure 1. Large vs. small capacity quick-disconnects (above) and 1/4-inch vs. 3/8-inch air hose diameters.

(continued on page 15)

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by Brian GedlinskeIWRC Environmental Specialist

gedlinske@uni.edu

Minnesota Paint andPowder Coating ExpoThe Twin Cities Chapter of Chemical CoatersAssociation International and the MinnesotaTechnical Assistance Program (MnTAP) hostedthe 5th Minnesota Paint and Powder Coating Expoon Thursday, October 17, 2002. Approximately 280people attended the event that included 15 techni-cal seminars, a vendor show featuring 50 exhibits,and a variety of hands-on demonstrations. Expopresentations addressed new technologies andprocesses, powder coating, liquid application sys-tems, pretreatment, efficiency and environmentalissues.

The IWRC Establishes anEnvironmental ManagementSystem Service Centerby Marci CarterIWRC Waste Reduction Specialistcarterm@uni.edu

An Environmental Management System (EMS)is a systematic approach for managing a busi-ness’ environmental activities. The ISO 14001

standard defines EMS as part of an overall man-agement system for developing, implementing,achieving, reviewing and maintaining an organi-zation’s environmental policy. Every level of theorganization is involved in meeting the goals andobjectives of the EMS. As a result, an EMS pro-motes organizational communication. It alsopromotes trust building between the businessand external shareholders (e.g., neighbors, cus-tomers and regulators) by offering pollution pre-vention techniques to reduce waste, create finan-cial gain, and reduce environmental liability.

Most companies have some EMS componentsalready in place. For example, an EMS can beintegrated with a business’ OSHA or RCRA pro-gram because of shared components (e.g., train-ing, emergency response, monitoring and meas-urement). Additionally, an effective EMS doesnot have to be completed over night. It can bedeveloped in segments over time and remainsvalid as long as the facility does not undergo amajor operational change.

Unfortunately, EMS development and imple-mentation remains an overwhelming task formany small businesses because of lack ofresources and cost. The estimated cost of imple-mentation for small and medium-sized businessvaries from $10,000 to $50,000. Of these costs,50 to 90 percent are internal. Consequently, theIWRC’s EMS Service Center was established tofacilitate EMS development and implementationfor Iowa small business. Services offeredthrough the Center include EMS presentations,training, and implementation assistance. Foradditional information, contact Marci Carter orLisa Hurban at 800/422-3109.

John Heckman, Director of the JohnsonCenter for Virtual Reality at Pine Technical

College in Pine City, Minnesota [heck-manj@ptc.tec.mn.us] offers Jim Olson

(IWRC Waste Management Specialist)some advice with virtual reality spray fin-ishing. The Johnson Center specializes in

virtual reality industrial and technicaltraining development.

Mississippi On-SiteVisitsIn October, Process Training staffpartnered with Mississippi’s TechnicalAssistance Program (MISSTAP) toperform on-site visits at threeMississippi businesses. Mary JeanGates (MISSTAP Waste ReductionEngineer [mjhg1@tecinfo.com]) coor-dinated the effort. The site visitsfocused on an OEM’s metal finishingline, an OEM’s wood finishing opera-tion and an auto body repair shop.The manufacturing site visits includeda review of each facility’s spray finish-ing operation. As part of each review,problem areas were identified, recom-mendations toward improving appli-cation efficiency were provided, andsome equipment changes were imple-mented. The body shop visit includedone-on-one training with a refinishingtechnician. Training results showedthe technician could complete a jobusing 25 percent less basecoat simplyby practicing good spray techniqueand spray gun setup.

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fFor a variety of reasons, it issometimes necessary to applyone coat of powder overanother. Re-coating, also calleddouble-coating, can be donewith most powders but thereare some common problemsthat usually have to beaddressed. These include elec-trostatic deposition problemsand inner-coat adhesion (i.e.,adhesion between two coats ofpowder).

Before attempting a re-coatproject, it is always a good ideato check with your manufactur-er for advice on the powdersyou are using. Keep in mind,however, that major powderproducers may formulate hun-dreds of products and may nothave double-coat test data foryour powders. Even so, it isstill worth the price of a phonecall to see what information isavailable. Regardless of whatyou learn from your supplier, it

is still important to perform in-house testing with your equip-ment, parts and applicationmethods to determine whatworks.

Powder DepositionCommon deposition problemsencountered with double-coatapplications include light areasaround holes and part edges, orjust poor powder depositionoverall. The cause is fairlystraightforward. To some

degree, the film formed on thesubstrate from the first powdercoating application insulatesthe substrate. This insulatinglayer reduces the electrostaticattraction between the powderand work piece during subse-quent applications. As a result,the second coat of powdermay not deposit as quickly oreffectively on the part (as com-pared to the first coat), requir-ing more application time.With double-coat applications,it is important that the secondcoat of powder covers the partcompletely and is applied atthe recommended film thick-ness. Otherwise, the final layerof powder will have a roughappearance - similar to liquidpaint dry spray. Other appear-ance problems may manifestthemselves as star-burst pat-terns (i.e., backionization) andpitting on the surface of thedry powder as well as in theunderlying cured film. Herethe first powder layer reducespart grounding, causing elec-trostatic rejection of the sec-ond powder application.

The following techniques maybe used to resolve depositionproblems:

GroundingBy now it should be apparentthat proper grounding is morecritical than ever with double-coating. One of the first thingsto inspect are the contactpoints between the part, thehanging fixture (or fixtures)and conveyor. Each hangingpoint must have good metal-to-metal contact. In somecases, it may be necessary toscrape away some cured filmon the part and/or hooks.

This is especially true if oneset of hooks is used for thefirst coat and then the parts aretransferred to another hookfor the second. When partsare re-hung, the bare area ofthe part (i.e., the first coathook mark) may not contactthe new hook, resulting in agrounding problem.

For safety and efficiency, theresistance between the work-piece and true earth groundshould be maintained below 1megohm (i.e., 1,000,000ohms). In regard to depositionefficiency, 0.5 megohms or lessis even better. A megohmmeter should be used to meas-ure resistance and assess sys-tem ground. When checkingcontinuity to ground, be sureto test the entire path at thebooth (where the coating isapplied) and check a numberof parts to determine if inter-mittent grounding problemsexist. If not already done, agrounding rod installed adja-cent to the booth and wired tothe conveyor provides greatercontinuity-to-ground assur-ance in the area where it ismost important.

Voltage Output or CurrentThe voltage output of thespray gun affects the size andshape of the electrostatic fieldbetween the grounded partand the gun’s electrode. It alsoaffects the current output fromthe gun. Lowering the gun’svoltage output reduces the sizeof the electrostatic field andthe rate at which ions are trans-ferred to the grounded work-piece. Therefore, lowering thevoltage output of the gun

should reduce back-ionizationproblems while improvingpenetration in Faraday Cageareas. If you have the capabili-ty, limiting the gun’s currentoutput should also reducebackionization problems.Additionally, newer modelpowder coating systems nowinclude “recipes” for specificapplications such as re-coating,applying metallic powders orfinishing parts with difficultFaraday Cage areas. Withthese systems, the operatorsimply pushes a button toselect a recipe of voltage andcurrent settings suitable forthat particular application.

Preheat the PartIf attempts to double-coat apart at room temperature donot work, then preheating thepart will. With this method,the high part temperaturecauses the powder to melt andstick without the aid of elec-trostatics. Although parts thatare slightly hot (150-200degrees Fahrenheit) will pro-vide some improvement, thebest performance is accom-plished when the part is hotenough to melt the powder asit is applied (generally 300-400degrees Fahrenheit). Keep inmind that higher part tempera-tures cause faster film buildsand make film thickness con-trol more difficult. High filmbuilds may create fat lips (pic-ture framing) at part edges.Thicker films also havereduced impact resistance andflexibility.

Avoid coating work pieces attemperatures of 225 to 275degrees Fahrenheit. At these

Edited for print by

Brian Gedlinske

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temperatures, the cure of thepowder may advance justenough to prevent normal flowand “wetting” of the substratesurface when baked. This cre-ates high orange peel in thetopcoat and may possiblyreduce inner-coat adhesion.Higher temperatures do nothave this problem since thepowder melts and flows.

Adhesion ProblemsAs with any substrate, surfacesoils present on a cured pow-der coating film may interferewith adhesion of the next coat.If the surface of the first coatis clean, most powders willhave good inner-coat adhesion.Additional surface preparationsteps may not be needed if thesecond coat is applied soonafter the first coat bake cycle(i.e., less time on the linemeans fewer contaminantproblems). The customer willhave to evaluate this possibility.A word of caution - once fullproduction begins, an ovenloaded with numerous partsmay allow volatiles to con-dense back onto the surface ofthe parts, causing adhesionproblems. So testing with justa few parts may not be repre-sentative of the results that willoccur during a production run.

If some type of surface prepa-ration is required to achievegood inner-coat adhesion,close monitoring with a goodquality-control (QC) programis needed to insure consistentpart preparation. Any untestedchanges in an establishedpreparation process (intendedor not) may reduce adhesionbetween coatings and causedelamination. Therefore,

cross-hatch adhesion testing isan important QC monitoringtool.

The following are some poten-tial techniques used to combatinner-coat adhesion problems:

v A power washer or dip tank system may be used to cleanthe part before the secondcoat application. However,it is critical that no residues(e.g., water spotting, streaksor drip-lines) remain on thepart surface.

v Windex or isopropyl alcohol work well when cleaning asmall number of parts.These solvents are effective,cheap and easily obtained.Additionally, isopropyl alco-hol has low flammability.

v For stubborn cases, strong solvents like acetone ormethyl-ethyl-ketone (MEK)may be used with care.Surfaces receive a quick sol-vent wipe followed by a vir-gin solvent flowing rinse (toflush soils from the surface)and ample flash-off timebefore recoating (otherwisesolvent popping may occurthrough the topcoat).Disadvantages with usingthese solvents include theirhigh cost and flammability.Additionally, any spent sol-vent and, possibly, the dis-posable rags generated fromthe process are hazardouswaste.

v Sanding or other means ofabrasion may be used. Anycontaminants present on thecoating surface need to beremoved prior to any abra-sion process, otherwise con-taminants may becomeembedded in the coating.

Care must also be taken toensure the abrasive mediaand any contaminants leftbehind from the process(such as the binder used onsand paper) are completelyremoved prior to re-coating.Coarse abrasive media mayalso create a physical profilein the first coating that man-ifests itself as an undesirableappearance in the topcoat.

v Preheating the part may be used to improve adhesion.The reduced melt-viscosityof the powder, caused byraising the part temperature,improves the “wetting” ofthe substrate. This, in turn,improves adhesion betweencoatings and produces asmoother cured film. Again,with part preheating, caremust be taken to avoidproblems with excessivefilm builds.

v Under-curing the first coatis another technique usedsuccessfully to provide goodbonding between two coats.The first coat should becured enough to withstandany necessary handling -usually 50-75 percent. If thefirst coat is a urethane, besure to cure it enough toeliminate any further releaseof volatiles. Otherwise,volatiles from the base coatcould “pop” through thesecond coat.

As with any new coating job orprocedure, always do adequatetesting to work out applicationtechniques and problemsbefore attempting production.And remember - Q.C., Q.C.,Q.C.!

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METHODS OF REDUCING ORELIMINATING OUT-GASSING

From Cast Aluminum, Magnesium, Zinc and Other Porous MetalsDuPont Powder Coatings

Method Advantages / DisadvantagesPurchase higher ADVANTAGESquality castings 4 Good, long-term solutionMold casting (best) 4 Highly effectiveDie casting (good) 4 Consistent resultsSand casting (worst)

DISADVANTAGES4 May increase cost (however, this could be off-set by savings in

rejects, lost production, etc.)4 Poor short term solution - requires time to investigate and specify

Change alloy composition ADVANTAGESIf an effective alloy is found, then:4 Good, long-term solution4 Highly effective4 Consistent results

DISADVANTAGES4 May increase cost (however, this could be off-set by savings in

rejects, lost production, etc.)4 Poor short term solution - requires time to investigate and specify

Pre-bake parts to ADVANTAGES

de-gas before coating 4 Good, short-term solution for small quantities or batch processes

DISADVANTAGES4 May burn soils into the casting4 Results may be inconsistent4 Some castings may require very high temperatures and/or long

treatment time4 May affect temper of some alloys4 Generally too time consuming for long-term use or mass production

Use anti-gassing powder ADVANTAGES4 Good, long-term solution4 Relatively inexpensive

DISADVANTAGES4 Poor short-term solution if a new product must be designed (R/D

and powder production usually require time)4 May not totally eliminate problem

Method Advantages / Disadvantages

Method Advantages / DisadvantagesUse I.R. cure to prevent ADVANTAGES

part heat-up 4 Good, long-term solution4 Can be highly effective

DISADVANTAGES4 May be expensive to purchase and install equipment

(however, costs could be offset by savings in rejects, lost production, etc.)

4 Poor short-term solution - requires time to investigate,purchase equipment and install

Grit blast parts to open ADVANTAGES

pores near surface of casting 4 If this works, then this is a good short term solution for small quantities or batch processes

4 Improves adhesion, corrosion performance and physical properties of the powder coating

DISADVANTAGES4 Can introduce soils onto the casting4 Results may be inconsistent4 May make out-gassing worse in some cases4 Cannot be used on light gage metal4 Labor and time intensive - not easily adapted for mass

production

Surface vacuum impregnation ADVANTAGES4 Good long term solution4 Can be highly effective

DISADVANTAGES4 Poor short term solution if process must be performed by

another vendor or if equipment must be purchased for in-house processing

4 Use of an outside service will increase costs and process turn-around time

METHODS OF REDUCING OR ELIMINATING OUT-GASSINGFrom Cast Aluminum, Magnesium, Zinc and Other Porous Metals

DuPont Powder Coatings(continued)

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Method Advantages / DisadvantagesRe-cast parts ADVANTAGES

4 May be an effective short-term solution

DISADVANTAGES4 Increased cost and time4 Poor long term solution

Coat parts hot ADVANTAGES4 Can be a good short term solution4 If production line is setup for it, can be a good long term

solution4 Has added advantage of improved adhesion and coating

appearance4 Thicker films may improve corrosion resistance

DISADVANTAGES4 Time and labor intensive if shop is not set up for pre-heating4 Film control may be difficult4 Thicker films will increase powder usage while reducing impact

and chip resistance4 Any out-gassing may be exaggerated due to large bubble

formation in thicker films4 Good timing required to prevent parts from cooling before coating

Apply two coats of powder ADVANTAGES4 Can be an effective short term or long term solution

DISADVANTAGES4 Doubles time and cost4 May not be totally effective4 Thicker films will increase powder usage while reducing impact

and chip resistance4 May experience inner-coat adhesion and deposition problems

Note: A combination of two or more of the above methods may prove best for difficult parts.

make sense from an air supplyperspective. The excess hoselength also makes for some inter-esting ergonomics and challeng-ing footwork.

Low Capacity QDsSpray guns are often fitted withquick disconnects for conven-ience and ergonomics. In regardto flow capacity, QDs are not allthe same. Most spray finishingfacilities use small diameter QDsthat contribute to their existingair restriction problems. For bestperformance, small diameterQDs should be replaced withhigh capacity QDs (see Figure 1).

Piecemeal PlumbingCreativity is often reflected in afacility’s air plumbing work.Examples of piecemeal plumb-ing include 1/4-inch coil hose,small inside diameter 90 degreegalvanized pipe elbows, air linesplices, and a series of fittingsthat oscillate from 3/16- to 1-inch inside diameter (see Figure2).

Effect of Air RestrictionsTable 1 illustrates how some ofthe above scenarios affect air-flow and atomizing energy (interms of air cap pressures) for avariety of HVLP spray guns. Foreach trial, the flow meter outletpressure was maintained at 50 psiand the spray gun’s shaping airvalve was fully open. The lengthof air hose used was also kept at25 feet. Variables included inTable 1 include the inside diame-ter of the air hose, the size of theQDs used at each end of the airhose, and variations in theplumbing from the flow meteroutlet (i.e., a straight plumbingrun vs. a 90 degree bend). Figure3 illustrates the various scenariosincluded in the measurements.

ResultsAs indicated in Table 1, the useof 1/4-inch air hose, small diam-eter QDs and indirect plumbinghave an adverse effect on HVLPair output and air cap pressures.Reducing the inside diameter ofa 25-foot air hose from 3/8 to1/4 of an inch reduced the spraygun’s air output by approximate-ly 30 to 44 percent. It also

reduced atomizing air cap pres-sures by approximately 44 to 63percent.

Use of small QDs and indirectpiping for each hose diametershowed similar results. As shownin Table 1, airflow output andatomizing pressure (at the aircap) using the 3/8-inch hose and90 degree plumbing were 28 and45 percent less, respectively, thanthat obtained for the same hosediameter, large QDs and astraight plumbing run. Similar(but less dramatic) results wereobtained for the 1/4-inch airhose.

In short, lower airflow outputand air cap pressures mean lessatomization energy. As a result,restrictive plumbing may preventair spray guns (particularlyHVLP) from producing anacceptable finish. This may causethe operator to become discour-aged with the spray gun orreduce the viscosity of the coat-ing through increased solventadditions. Fortunately, thesetypes of air restrictions are easilyremedied once recognized.

Spray Finishing(continued from page 5

Figure 3. The best and worst case scenariosused for measuring the effect of airrestrictions. The left photographshows 3/8-inch air hose fitted withlarge capacity QDs and a straightplumbing run from the meter outlet.The photograph to the right shows1/4-inch air hose being used withsmall diameter QDs and a 90degree plumbing bend.

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Is this the first time you received AAhheeaadd ooff tthhee PPAACC22EE??

The AAhheeaadd ooff tthhee PPAACC22EE newsletter is an educational and outreach component of the IWRC’s Painting and Coating Compliance Enhancement (PAC2E)program. The PAC2E program’s focus is to improve efficiency and pollution prevention in the painting and coating industry. The intent of the newsletteris to: 1) provide the spray finishing industry with technical information aimed at improving product quality and process efficiency; 2) inform industry ofpertinent environmental compliance issues; and 3) keep readers informed of PAC2E activities through case study write-ups, research articles and news briefs.The following is a list of past newsletter articles (available at www.iwrc.org/pubs/pace.cfm).October 1999 Articles

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• Editor’s Welcome • The Cost of Inefficiency • Benefits of Proper Gun Setup • Process Training Begins • News Briefs

May 2000 Articles• Wastewater Management • Pretreatment System Maintenance • Case Study: Energy Costs of Wastewater Evaporation • Troubleshooting Basics for Powder Coatings • News Briefs

December 2000 Articles• Editor’s Note: Process Training • PAC2E Case Study I: Wisconsin • How Spray Operators Impact Application Efficiency • Troubleshooting Basics for Powder Coatings-Cure • PAC2E Case Study II: The Arkansas Experience

Summer 2001 Articles

• Editor’s Note • Applying Powder Efficiently • Trouble-Shooting Basics for Powder Coatings-Adhesion • Wood Finishing-Case Study • Application Equipment Selection Considerations • More Efficient Autobody OperationsWinter 2001 Articles• Editor’s Note • Coatings Removal Options • Auto Refinishing: Solvent Selection, Dirt Control & a Quality Finish • Process Training Case Study 1: Pretreatment Efficiency & Water Quality • Metal Finishing, Wastewater, & the Proposed MP&M Regulations • News Briefs • Process Training Case Study 2: Wastewater ReductionSummer 2002 Articles• Editor’s Note • Process Training Case Study: Pretreatment Alternatives • Auto Refinishing: Proper Surface Preparation • Case Study 1: Automotive Refinishing HVLP and Conventional Air Spray • Case Study 2: Pressure Feed HVLP vs. Conventional Air Spray • News Brief• Case Study 3: Industrial FinishingIf this is the first time you have received AAhheeaadd ooff tthhee PPAACC22EE and wish to

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PAC2EPainting & Coating Compliance Enhancement

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PAC2EPainting & Coating Compliance Enhancement

Iowa Waste Reduction CenterUniversity of Northern Iowa

1005 Technology ParkwayCedar Falls, IA 50613-6951

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