the authority since 1990 august troubleshooting … · shown in figure 1, stage one uses 140°f...

TROUBLESHOOTING GUIDE:PROBLEMS & SOLUTIONS

T H E A U T H O R I T Y S I N C E 1 9 9 0

SUPPLEMENT TO

AUGUST 2009

PRETREATMENT

49 Using reverse-osmosis systems to recycle used rinse water

54 Keppel Seghers case histories

APPLICATION AND RECOVERY

58 First pass transfer efficiency: How to get it, how to keep it

63 Custom coating: Powder coating process control

CURING

68 The 12 most common questions asked about oven temperature profiling

74 Oven design and maintenance

a-AugTSG_cover:PC0205_C1 8/5/09 10:15 AM Page i1

a-AugTSG_cover:PC0205_C1 8/5/09 10:15 AM Page i2

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Although powder coatings are dry, companies that applythem require large amounts of water to expedite the finishingprocess. Despite the fact that water was cheap and plentifulat one time, finishers now know it’s not an infinite resourcethat can be squandered. By using reverse osmosis (RO) anddeionization (DI) technologies, finishers have found ways toreduce their water consumption. This article focuses on ROtechnology to recycle used rinse water. It also discusses thehistory of water use in the powder coating industry. It thenexplains how RO and DI technologies came to play a role inwater treatment and how RO can be used to recycle as muchas 90 percent of the rinse water used in surface preparation.

The powder coating industry demands a high volumeof purified water to support production. Finishers

use purified water to clean and rinse parts. Simultane-ously, finishers face the need to reduce the total volume ofwastewater from their plants. As companies begin to findout that many of their waters can be reused internally bycontaining them and then repurifying them, finishers arealso finding that the process involved is so simple, it’s oftencost-effective for them to reclaim the water. This is partic-ularly true when membrane processes are used to treatwater because the water recovery for reuse is extremelyhigh, typically around 80 to 95 percent.

Water use reduction is becoming essential to the powdercoating industry. Finishers have reduced their water con-sumption through reuse and reclaim processes that haveresulted in a lowered total amount of water used. Wateruse reduction, if implemented correctly, translates to areduction in cost. However, this cost saving is only onereason to reduce water use. A growing customer demandfor industrial environmental responsibility has promptedseveral companies to develop environmental managementsystems (EMS) and to become International StandardsOrganization (ISO)1 14001 certified.

Certification in the ISO 14001 standard is partly basedon the requirements of a company’s EMS to identify theenvironmental aspects derived from their operations, setobjectives and targets to minimize significant aspects, andto commit to continual improvement. By reducing waterconsumption, companies have reaped many benefits. Forinstance, companies have been able to reduce costs,increase the efficiency of their operations, and reduce theconsumption of natural resources in today’s environmen-tally conscious community. Finishers can make significantreductions in wastewater discharge by eliminating anunneeded prerinse step or by counterflowing rinse bathsand then reclaiming the used rinse water.

Finishing businesses take water availabilityfor granted

With regard to water and related issues, the powdercoating industry is just emerging from its infancy. Pow-der coaters began by using water as a utility. They usedwater for

• Coolant

• Heat transfer

• Rinsing purposes

• Cleaning purposes

• Chemical solution preparation

During the industry’s infancy, water was relatively abun-dant and inexpensive. Because water was plentiful andcheap, finishers took it for granted. As the industry devel-oped during the past 2 decades, relatively large quantitiesof water were used on a once-through basis. Even high-purity final rinse water wasn’t conserved, recycled, orreused in the same application. Industrial times weren’tonly good, they were great. The use of water in the powdercoating industry continued to grow; simultaneously, thereuse and conservation of water continued to be neglected.

POWDER COATING Troubleshooting Guide | August 2009 49

Using reverse-osmosis systems torecycle used rinse water

Thomas Borcherding TB Sales

PRETREATMENT

a-PT-TBOsmosisArt-49-53:Masters 8/5/09 9:19 AM Page 49

Then, a change took place. Water became the target ofthe public eye. In addition, two other interesting resultsput pressure on water-related issues. First, because theindustry grew rapidly and because corrosion science hada tendency to be widely misunderstood, older plants andequipment, such as washers, began to leak. Bear in mindthat some of these plants were built rapidly and often withless than the most sophisticated engineering. Multiplematerials came in contact with each other, corrosionresulted, and leaks occurred. Leaks, sludge, scalebuildup, and plugged nozzles all caused downtime. Down-time threatened to ruin the economical aspect of powdercoating.

Second, a related and even more misunderstood issueoccurred with water. The amount and type of contami-nants found in raw water supplies throughout the coun-try varied considerably2. Mineral hardness, bicarbonatealkalinity, and total dissolved solids (TDS) content beganto affect washer chemistry. That, in turn, affected powderadhesion.

Finishers had a tendency to overlook water problemsbecause they considered water a utility rather than aproduct. An industry that started out by taking water forgranted had now grown to where water had become amajor problem. Now, the management of water promisesto dominate the next 2 decades of changes in the powdercoating industry. The use of water in washers is compli-cated by the wide variety of materials finishers have usedthrough the years in their water-transporting systems andby the chemicals finishers have been adding to the water tocontrol unwanted water-formed scale or debris, biologicalfouling, and many types of corrosion. By adding chemi-cals, cleaners, phosphates, and sealers, along with the nat-ural chemical concentration that occurs when water isevaporated, the powder coating industry is finding it nec-essary to staff its plants with personnel who can managewater or to outsource the job to companies capable of ful-filling this function as service vendors.

Whatever the case, powder coating operations generatewater and wastewater that must be contained, managed,and disposed of appropriately. The costs associated withthese processes are no longer trivial; they’re significantproduction expenses. Finishers can no longer make theassumption that water is an inexpensive commodity.

The first step in water and wastewater management isawareness. As companies become aware of ways to reusetheir water internally by containing and repurifying it,they’re also discovering that the process is so simple, it’soften cost-effective for them to reclaim the water. This isparticularly true when membrane processes are used totreat water because the recovery rate of water for reuse isextremely high, typically 80 to 95 percent. Conservationpractices may be new to the industry, but they’re becom-ing a way of life. Companies constructing new plants areinstructing their engineers to keep water conservation,reuse, and recycling in mind when drawing up designs.This trend is likely to continue.

Reverse osmosis replaces deionization systemsMany pretreatment systems used in the powder coating

industry rely on reverse osmosis (RO) and deionization(DI) technologies for water treatment. [See “Replacingdeionizers with reverse osmosis technology to purify waterfor multistage washers” Powder Coating, vol. 11, no. 3(April 2000), p. 23.] However, RO is replacing DI as thetechnology of choice for many coaters. Although the tech-nological advances in powder coating chemistry andrelated equipment are significant, the pretreatmentprocess, where parts are prepared for coating, can’t beoverlooked. This includes, as a minimum, spot-free finalrinsing of the product before powder application. In addi-tion, with many newer washers, pretreatment alsoincludes purification of the water used in the entirewasher.

RO is a relatively new technological development. Thefirst RO systems date back to the 1970’s. In the years sincethen, the technology has matured. Today’s systems repre-sent viable methods for reducing the concentration ofmaterials dissolved in water. The technology has becomeapplicable in widely diversified fields, including drinkingwater, fruit juices, waste treatment, and the productionof highly pure process water for use in numerous indus-trial applications. RO technology uses a high-pressurepump to force water through a semipermeable membranemade of plastics. The water molecules are small enough topass through the membrane, leaving behind the largermetal ions and mineral salts. In this manner, an ROmachine can remove 97 to 98 percent of the TDS found inincoming feed water.

Early attempts to introduce RO for industrial use metwith reliability and performance problems mainly associ-ated with the high pressure required to achieve reason-able fluxes, the limits of membrane service life, the lack ofoperating experience, and the lack of guidelines. Followingthis rather questionable introduction, viable RO technol-ogy, based on a new generation of membranes and a betterunderstanding of operating requirements, was eventuallyintroduced in the 1980’s. The commercial introduction ofRO then rapidly evolved so that today, most new andmany retrofit water systems use RO instead of the tradi-tional ion-exchange systems. Furthermore, by using spe-cific and newly developed membranes, RO technology hasworked successfully in other applications, including waste-water treatment.

In a typical five-stage washer system, such as the oneshown in Figure 1, stage one uses 140°F water and alkalinecleaner to remove cutting oils and to degrease the parts.Stage two is an ambient-temperature city water rinse thatcontinuously overflows to drain. Stage three is a surfacepreparation cycle using 130°F chemical solution containingiron phosphate. Stage four is another ambient-temperaturecity water rinse, also overflowing continuously to drain.Stage five uses a traditional deionizer for fresh DI water toachieve a spot-free final rinse. Many improvements havebeen made to this system design in recent years, including

50 POWDER COATING Troubleshooting Guide | August 2009



replacing the final rinse water with an RO system (see Fig-ure 2) that not only provides spot-free rinse water qualitybut also does this more efficiently and less expensively thanthe deionizer. Moreover, the continuous overflow to drainfrom the rinse stages can be reduced and sometimes elimi-nated when using RO water for the rinse baths.

Recycling rinse water requires separationHow do you recycle the used rinse water without over-

flowing it? To recycle the rinse water, you need to sepa-rate the used rinse water into a bulk storage tank so that

Five-stage washer system

Powder booth

Five-stage washer

Oven

Cleaner Ironphosphate

140ºF 130ºFRinse RinseRecirculating

deionizedwater rinse

End-product exit

Conveyor entrance

City water

Deionized water

1 2 3 4 5

FIGURE 1

you can repurify it. This stored water can now be contin-uously circulated through a series of filters, each specifi-cally designed to remove certain impurities such as iron,mineral hardness, chlorine, organics, turbidity, sus-pended colloidal particulates, and dissolved salts. Figure3 shows the whole washer RO system design. The systemis similar to the RO system discussed previously, but withthe addition of two more storage tanks, you can now sep-arate the used rinse water returned from the washer andcollect the concentrate waste stream from the ROmachine for reuse.

FIGURE 2

Reverse osmosis water system

Pump

Levelcontrol

Flowcontrol

Vent filter

Sof

tene

r

Car

bon

Reverse-osmosis waterto washers

City waterReverseosmosis

Reverse-osmosiswater storage tank

a-PT-TBOsmosisArt-49-53:Masters 8/5/09 9:19 AM 1


your five-stage washer. Typically, the final 10 percent issent to an evaporator or other means of disposal whenyou need to meet zero-discharge requirements. This sys-tem works well when the TDS of the used rinse watercan’t exceed a concentration of 200 milligrams per liter(mg/L). The final concentrate to the evaporator will thenstay below 800 to 1,000 mg/L, which in many instances isstill cleaner than the raw water (city water) that youstarted with.

Figure 4 shows an RO reclaim system at Tuthill Trans-port Technologies, Brookston, Ind. The system includesfour 1,500-gallon storage tanks, an activated carbon fil-ter, duplex water softener, and a 10,000-gallon-per-dayRO machine. The used rinse water is continuously circu-lated through the equipment. Purified water is then sentback to the washer. This allows the company to recycle90 percent of its used rinse water with the remaining 10percent going to the evaporator. The system meets zero-discharge regulations.

In summary

This article has discussed the advantages of RO technol-ogy as well as the advantages of incorporating RO into anew system design. The concept of having a whole washerRO with reclaim offers several advantages. For example,the whole washer RO system

• Recycles as much as 90 percent of used rinse water

• Reduces dumping and the need to recharge chemicalstages with more chemicals

• Eliminates scale buildup on heat exchangers

In this manner, water going out to the washer is purifiedRO water (Tank 1) and all of the used rinse water (Tank2) returned from the washer must pass through the ROequipment. The concentrated salts from the RO rejectstream are also collected (Tank 3) and passed throughthe RO machine one more time. By adjusting the recov-ery rate of the RO machine, you can recycle and reuseas much as 90 percent of the rinse water being used in

Whole washer reverse-osmosis system design

Sump Carbon filter

Water softener

Rev

erse

osm

osis

Washer

Purified reverse-osmosis water

Used rinse water

Final concentrate

3Tank 3

4 51Tank 1

2Tank 2

FIGURE 3

FIGURE 4

Used rinse water in the large storage tank, right,is purified as it goes through the reverse osmosis(RO) machine at the entrance to this washer,taking on a clear blue color in the other largestorage tank.


• Reduces sludge buildup

• Provides a spot-free final rinse

• Increases finish quality by increasing powder adhesion

Consider these benefits and find ways to incorporateRO technology into your finishing process. This way,you’ll be making economical as well as ecologically wisedecisions. PC

Endnotes1. International Standards Organization, located at 1, rue de Varembé, Case

postale 56, CH-1211 Geneva 20, Switzerland; 011-4122-749-0111, fax011-4122-733-3430; Web site is at [www.iso.ch]. ISO 14001 is the interna-tional standard for environmental management systems.

2. The Water Quality Association (WQA) provides detailed information aboutthe quality of water supplied by municipal water systems in the US. Formore information, contact the organization at: WQA, International

Headquarters and Laboratory, 4151 Naperville Rd., Lisle, IL 60532;630/505-0160; Web site is at [www.wqa.org]; E-mail address is[[email protected]].

Editor’s noteFor further reading, see articles listed under the Surface prepara-tion headings in the “Index to Articles and Authors 1990-2008,”Reference and Buyer’s Issue, Powder Coating, vol. 19, no. 9(December 2008) and check the Powder Coating Web site at[www.pcoating.com].

Thomas Borcherding is president of TB Sales, PO Box 99,Slinger, WI 53086; 414/333-1807. He is a distributor forOsmonics RO machines and specializes in designing andinstalling custom built industrial RO systems. He studiedchemical engineering at the University of Wisconsin-Mil-waukee, is the author of several articles for trade publi-cations, and speaks at seminars and other educationalprograms.



www.peridiumpowder.com

Metal Rehab Technologies sees rapidgrowth with Keppel Seghers’ help

quickly proved to be all that wasexpected. This system rapidly andcompletely removed plastics, rubber,paint and an array of coatings frommetal surfaces with no damage to themetal substrates. Because of a sophis-ticated control system for controllingtemperature, it even cleaned springsteel with no degradation to physicalcharacteristics. Short cycle timesallowed pick up and delivery of paintline fixtures within a wide radius andled to servicing many other industrialapplications.

Keppel Seghers’ Fluidized Sand Bedpromoted rapid growth for MetalRehab, and as a result a secondlarger system was recently purchased,adding increased capabilities and newmarkets to service.

1235 Kennestone Circle, Suite FMarietta, Georgia 30066

Tel: 770-421-1181

Fax: 770-421-8611

[email protected]


KEPPEL SEGHERS CASE HISTORIES

PRETREATMENT

Metal Rehab Technologies, Inc.is a custom metal cleaning

service dedicated to environmentallycompliant cleaning technologies. ATexas based company, located inArlington, Texas; Metal Rehab beganbusiness by developing new and envi-ronmentally responsible chemicalsystems to remove organic coatingsand rust from metals and rapidlybecame a premier service provider inthe antique and classic car marketnationally.

As the company grew, it became evi-dent that other technologies must beadded in order to meet additionalmarket demands. Requirements fora new technology were:

1) must meet all local, state, and fed-eral mandates and guidelines

2) must have a short cycle time

3) must be able to remove a widearray of coatings

4) must handle large numbers of smallitems in addition to larger ones

5) must be safe and relatively easy tooperate

6) must be reliable.

After a great deal of research intovarious thermal and non-thermalprocesses and devices, Marietta,Georgia, based Keppel Seghers’ Flu-idized Bed Technology became theobvious choice for meeting all crite-ria. A system was purchased and

— Submitted by the advertiser—

b-PT-KeppelSeghersCH-52-57:Masters 8/5/09 9:23 AM Page 54

In 2006, Jerry Croy, ValmontIndustries Elkhart Indiana's

powder coat supervisor, was awarethat grounding problems wereaffecting the efficiency of his powdercoating operation. The weight of theproduct required tempered steelhooks. Environmental issues elimi-nated chemical stripping and con-cerns over losing temper preventedthermal cleaning methods. Valmont

resorted to using a hammer to phys-ically clean the hooks by chippingpowder from grounding points.

Jerry's search led to KeppelSeghers Inc. to determine if theirfluidized bed was the answer to hishook cleaning. He found their Flu-idClean offered a quick, efficientand environmentally friendly solu-tion to Valmont's stripping needs.With a temperature differential of


less than 10º F throughout bed, theFluidClean was able precisely con-trol to cleaning temperature. Thecleaning cycle was less than onehour and hooks could go directlyfrom the fluidized bed back to thepaint line.

Upon purchasing the FluidCleanand new paint guns, Valmont docu-mented reject rates and powderwastage before and after installation

of the FluidClean andwas surprised by theresults. The estimateddecrease in powderwastage would yield anannual savings of over$160,000 with a signifi-cant decrease in paintrelated rejects.

An additional benefitwas the elimination of thelabor intensive hammer-ing a grounding point.According to CharlieGray, the group leaderwhose job it was to createthe grounding point, "asfar as I'm concerned, thisis the best money we everspent."

[email protected]

Keppel Seghers’ fluidized bed savesmoney for Valmont Industries


The Boss just told me thatour fixture stripping is

not keeping up with our linespeed and he wants a cleaningsolution that is quick, econom-ical, and environmentallyfriendly. Did I mention it needsto have low labor, operational,and maintenance cost?

IMPOSSIBLE

Not really.The Keppel SeghersFluidClean meets all thoserequirements.

The Environmental friendly Fluid-Clean has an average cycle time ofless than 45 minutes for powder coatstripping giving our customers theopportunity to strip every 2-3 passesthrough the line. Labor and opera-tional costs are minimal and theoperation is low maintenance.

As the organics are destroyed inthe flame zone, there is no wastestream and this product meets strictemission standards for both hydro-carbons and particulate matter. Thehot fluidized sand not only removesand destroys the organics but alsoremoves most of the ash residue.Have us prove the above by callingus for a free test cleaning.

[email protected]

www.keppelseghersusa.com


Paint Stripping with Keppel Seghers



In 2006, The Toyota MotorsMalaysia Special Projects

Department of Assembly Servicesneeded to find a single cleaning unitthat could handle all their strippingneeds. The size and number of fix-tures to be cleaned presented a realchallenge. The method chosen hadto be able to clean several types ofpaint from skids, grates, and a widevariety of paint fixtures. The systemchosen also needed to have lowoperating costs and be environmen-tally friendly.

After careful consideration ofavailable cleaning methods, thechoice became clear, the ArenaScirocco. The Scirocco (A) 127 Dselected by Toyota Malaysia was thelargest Suspended Solids Reactor inthe world used for stripping, withan internal size 6 m x 1.75 m x 1.1 m.This size and the efficiency of theScirocco allowed them to provide asingle cleaning system for all theirneeds: paint booth grids, produc-tion tools, and body skids. To opti-mize the efficiency of loading anextra automatic loading system was

delivered which gives the ability toprepare several loads in advancewhich are automatically loaded insequence reducing idle time of theequipment.

The quick cycle times, 45 minutesfor grates (120 @ 2 kg of cured painton each), 60 minutes for skids (3skids per load), and 40 minutes perload for over 1,000 assorted fixturesallow the cleaning to keep up withthe production schedule and notbecome the production bottleneck.

Strip Search uncovers the Arena Scirocco

[email protected] www.keppelseghersusa.com


www.keppelseghersusa.com

How’s your first-pass transfer efficiency (FPTE) these days?If it’s poor, or worse yet, you don’t know what FPTE is, thenyou need to read this article. It discusses factors that limitor reduce FPTE in powder coating systems and focuses onways to improve it.

Sometimes, you read an article and it’s so familiar—asthough you’re the one that the story was written about

because your situation is identical to the one in the story.Well, this is one of those articles, and now is the time whensome light can be shed on improving first-pass transferefficiency (FPTE) in your powder coating operation.

The basics need to be thoroughly understood firstUnderstanding what FPTE is and how it affects your over-

all paint operation and bottom line is important, especiallyin these days of lean manufacturing. Usually powder coat-ing involves a one-coat application, and overall transfer effi-ciency (TE) is high (90 to 95 percent) when reclaiming thepowder. This is impressive compared with the reclaimabilityof other types of coatings. Compared with liquid systems,the cost savings when using powder coating systems are con-siderable in both TE and waste production.

Powder coatings are generally applied electrostatically.The powder is given a + or - charge when it passes througha charged corona field. As the powder passes through thischarged field, it picks up the charge and is attracted to theclosest ground—the part. Most of the powder will beattracted to the part, and the rest will fall into a collectionhopper where it can then be resieved and reused.

The specific gravity of powder is actually the ratio of theweight of a given volume of powder to the weight of anequal volume of water. FPTE is the ratio of the amount of

powder coating actually deposited on the substrate thefirst pass by the spray guns compared with the amount ofpowder coating directed at the parts to be coated that isn’tdeposited on the part. Your powder coatings manufac-turer should have provided you with the specific gravityinformation for your powder coating on a product specifi-cations worksheet. Table 1 shows you how many squarefeet (sq ft) of coverage you’ll get with certain specific grav-ities and mil thicknesses.


First-pass transfer efficiency: How to getit, how to keep it

Bob Utech Powder Visions

APPLICATON & RECOVERY

TABLE 1

Specific 1 2 3 4gravity mil mils mils mils

1.0 193.2 96.6 64.4 48.3

1.1 175.6 87.8 58.5 43.9

1.2 161.0 80.5 53.7 40.3

1.3 148.6 74.3 49.5 37.2

1.4 138.0 69.0 46.0 34.5

1.5 128.8 64.4 42.9 32.2

1.6 120.8 60.4 40.3 30.2

1.7 113.6 56.8 37.9 28.4

1.8 107.3 53.7 35.8 26.8

1.9 101.7 50.9 33.9 25.4

2.0 96.6 48.3 32.2 24.2

2.1 92.0 46.0 30.7 23.0

2.2 87.8 43.9 29.3 22.0

Square feet of coverage by mils and specific gravitycalculated at 100% transfer efficiency

c-AR-UtechFPTEArt-58-62:Masters 8/5/09 9:27 AM Page 58


Powder coverage. To calculate how much it will cost youto coat parts, use the following formulas:

Formula 1:192.3 (fixed)

(Specific gravity of the powder) (mil thickness) = Sq ft ofcoverage at 100% TE

Actual TE will be less than 100 percent. Use your esti-mated efficiency.

Formula 2:

Sq ft of coverage at 100% � TE = Actual coverage

To calculate the total cost of the powder needed for a job,use the following formula.

Formula 3:

Total sq ft to be covered � Actual coverage = Total pounds(lb) of powder needed

Total lb of powder needed � Price per lb = Cost for job

Example 1:

If the specific gravity of a powder is 1.5 and you plan toput 3 mils of powder onto a part at 70 percent FPTE, you

will cover 29.91 sq ft for each pound of powder you spray.Calculate the amount of sq ft you need to coat, divide by29.91 sq ft, and you’ll get the amount of powder you need touse for the job. Simply multiply that number by the costper lb.

Example 2:

If the specific gravity of your powder is 1.6 and you planto apply the powder at 2 mils, the chart says that you willcoat 60.1 sq ft at 100 percent FPTE. At 50 percent FPTE,only 30.05 sq ft will be coated.

Many factors can affect FPTEOf all the strategies available for reducing pollution (air,

water, and waste) and costs from a coatings shop, TEprobably provides the most benefits. Several factors affectTE to a smaller or greater extent. (See Table 2.) We’ll dis-cuss the more important factors. Keep in mind that pow-der spray booths are designed to effectively contain over-sprayed powder, efficiently reclaim oversprayed powder,improve TE, and create a safe, clean, and comfortableoperating environment.

Electrostatic corona. High- or low-voltage cables are twobasic ways that the voltage source is currently applied tothe tip of the corona-charged powder spray gun. The typeof cable depends on whether the high-voltage generatoris an external or internal power supply gun. Both come innegative or positive polarity. Generally, coronacharginguses a negative polarity on the electrode as negative polar-ity produces more ions and is less prone to arcing thanpositive polarity. Positive polarity guns are generally usedwhen spraying nylons or touching up with a tribochargingsystem.

Powder spray guns. The two major gun categories aremanual and automatic. Manual guns can be used in stand-alone units, in applications not requiring automatic guns,or with automatic systems that are generally used for dif-ficult-to-reach part areas, complex parts, or both.Because the hand painter uses the spray gun for long peri-ods of time, the flexibility, weight, efficiency, and durabil-ity of the spray gun are important. When considering theadded mass of the hose and cable, keep in mind that mostapplicators will hold the hose and cable with the otherhand so that only 3 or 4 feet of hose and cable weight areadded to the gun.

In addition, depending on where the hose and cable areattached to the gun, the added weight may or may notimprove or degrade the overall balance of the gun. Thiscan be important when considering TE because thecoater’s arm may tire due to the extra weight carried by aninternal gun system, which may degrade efficiencies asthe day progresses. The external corona gun is by far themost common type in use today. It provides good unifor-mity and TE.

If you feel your equipment is not performing adequately,ask your equipment supplier to bring a DC-voltage test

TABLE 2

GroundCoating conductivity (or resistivity)Voltage potential between electrode and ground Spray-gun proximity to other grounded objectsPart sizePart geometryGun-target distanceCoating viscosityCoating atomization easeSpray-gun design and atomization methodFeed pressureAtomizing air pressureFan sizeSpray-gun-cap deflector diameterSpray-booth air velocitySpray-booth air balanceCoater application technique (spray-gun stroke overlapping)Lead- and lag-triggering timesConveyor line speedSpray-gun travel speedPainter fatigueSpray-booth lightingSpray-booth space constraintsManagement attitudeCoater attitude

Factors affecting transfer efficiency in powdercoating systems


meter (Figure 1). This meter can provide a high-voltagetest of your electrostatic output. This test equipment isreally inexpensive and could prevent shutdown by moni-toring your output from time to time. Problems from pooroutput can cause poor TE.

Nozzle design. The gun and nozzle design is a majorinfluence in achieving FPTE. This comes into play wherethe air velocities are low and where the powder is well-dis-persed. This is when the nozzle design matters. The twomost widely used nozzles are the deflector-pattern and theflat-spray nozzles. Both are available in various patternsand shapes. The flat-spray nozzle is more directional thanthe deflector type and has a well-defined pattern. Thedeflector-pattern nozzle has a soft well-dispersed patternand has the appearance of a liquid bell. Many other typesof nozzles are available, but these two types account for90 percent of them in today’s powder coating systems.

Hoppers. A fluidizing hopper-feeder with level control isprobably the most overlooked and underrated device of anypowder system. These systems have three key features:

• Level control

• Fluidizing plenum

• Venting

Level control. A good level control will enable the flu-idizing feeder to maintain a consistent powder and feedheight.

Fluidizing plenum. The fluidizing plenum distributes theair uniformly across the fluidizing membrane, which inturn provides uniform fluidization throughout the exte-rior of the feed hopper. More fluidizing airflow is not bet-ter when dealing with TE. Too much air or nonuniformdistribution of air will result in extremely violent fluidiza-tion in certain areas. As a result, efficiency of the powderpump will be reduced causing the powder pump to drawair and reduce the proper powder flow rate. The fluidiza-tion needs to be carefully monitored for each type of pow-der introduced within the hopper. Too little or too muchair introduced will potentially give surges within the sys-tem, defeating the efficiency.

Venting. A powder feed hopper is like a pressure vessel.The feed hopper can receive powder from three to four ormore venturi transfer pumps. These pumps are a simpleair-transfer type, and the air pressure from these pumpsand the fluidizing bed below must be relieved from the hop-per feeder. The best way to remove the excess air is througha direct vent design. This design relieves internal pressure.

Powder pump and fluidizing flow rate. The purpose ofthe pump is to supply powder to the gun at a uniform andconstant rate. Powder pumps use a venturi principal todeliver powder from a supply hopper to the powder spraygun. The lowest flow rate possible is the ideal condition forFPTE while still maintaining coverage through each gun.Consistent high-charging efficiency is controlled by thegun output. The more powder passing by the gun elec-trode, the less chance each powder particle has to pick upthe maximum charge. More powder flow is not betterwhen dealing with TE. Adding additional guns to keep out-puts low is better than reducing the number of guns andincreasing the output of each gun. Remember, TE isachieved through proper charging of the powder appliedto the part.

Process controls and monitoring devices. Process con-trols and monitoring devices can enhance the operatingefficiency of your powder coating system. When you lookat FPTE, consider a system in which the guns are trig-gered on at all times and the space between the parts isequal to the part size. The highest achievable FPTE will beno more than 50 percent because 50 percent of the powdersprayed goes into the air.

System history has shown that the FPTE will vary from 20to 60 percent of the times the guns are spraying with knownparts in front of the guns. Depending on gun triggering,however, your overall FPTE could improve from 20 to 60percent. An added benefit of automatic gun triggering is thecapability to adjust the spray duration to either reduceheavy edges on parts or increase wrap on parts.

Booth canopy design. The design of the powder coatingbooth contains oversprayed powder within the booth.Because the powder is applied via an electrostatic charge,and our goal is high FPTE, we want the powder to beattracted to the part and not to the booth. To achieve this,the booth canopy or the area around the automatic gunsshould be constructed with a low or nonconductive mater-ial. This will allow the electrostatic field emitted by the gunsto attract the powder to the part and not to the booth wall.

Airflow factors. The spray zone, defined as the areawhere the powder is applied, can be disrupted in manyways, disturbing TE. Some sources of disruption includethe air-make-up units, open doors, and outside weatherconditions. The parts in a powder booth require a consis-tent air velocity enveloping them. If the conditions men-tioned previously exist, disruption of the air envelopecould occur and contamination would result. The airmovement within powder spray booths is much moreimportant than it is in liquid coating booths. This is due tothe powder particle make-up. It takes very little outsideair disruption (and sometimes inside disruption) to dis-


FIGURE 1

Gun test kit



turb the proper airflow within a powder booth. Planningand placement of equipment is a top priority for control-ling contamination.

Gun-to-booth-wall distance. One canopy issue that willaffect FPTE and good housekeeping is the distance of thegun tip to the booth canopy behind the gun. The powdergun should be at least 12 inches inside the booth so thatthe electrostatic field is attracted to the part and not thebooth canopy.

Gun-to-part distance. The distance between the partsyou’re coating and the gun tip will affect your TE. Manyvariables with gun placement depend on line speed andpart specification. Generally, start at 8inches to 12 inches away from the part.

Booth airflow. Uniformity in spraybooth airflow is one key applicationvariable. Again, you must rememberthat more powder flow is not betterwhen dealing with TE. In any boothtype, you’re looking for powder con-tainment. Too much airflow will drawthe powder away from the parts beingcoated. Many coaters try to overcom-pensate with a higher powder flow rateand less FPTE.

Humidity. Both humidity and tem-perature can affect the performance ofa powder coating system. The powdersystem should be installed within anenvironmental room if possible to giveyou application consistency becauseany change in temperature and hu -midity may affect fluidization, filterefficiency, filter service life, and pow-der charging capabilities. The temper-ature of the environmental roomshould remain at 68°F to 80°F. Rela-tive humidity should remain at 45 to 60percent.

Water and powder do not mix whenthe intent is to spray as a dry powder.Exposure to excessive humidity cancause the powder to absorb either sur-face moisture or bulk moisture. Thiscauses poor handling, such as poor flu-idization or poor gun feeding, whichcan lead to gun spitting, surging, andeventually feed-hose blocking. Highmoisture content will certainly causeerratic electrostatic behavior, whichcan result in changed or reduced TEand, in extreme conditions, alteredappearance or performance of thecured coating.

Maintaining proper humidity is alsocritical in controlling contaminationand film thickness within a powder sys-

tem. Maintaining a clean environment should be of theutmost importance. Fibers and dust that float around anarea need to be controlled, and the best way to do this iswith humidification. Attaching moisture (humidity) to theparticles will help make them heavy so that they drop outof the air. In fact, it has been observed in many shops, thatwhen it rains, dirt levels are usually lower.

Employing several methods, which include spray coils,spray nozzles, rigid media humidification, steam injection,atomizing nozzles at the burner, and ultrasonic humidifi-cation, can control humidity. It should be noted that to acertain degree, each of these methods could contribute to

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particulate contamination. This should really be consid-ered when choosing a method to control humidity.

In addition, dry air increases static electricity. The dryerthe air, the higher the static charge. Maintaining properhumidity levels will reduce the static electricity that cancause a part to act as a magnet to attract and hold conta-mination. This is similar to electrostatic painting when acharge is used to apply powder to a part for better TE.Contamination will do the same thing when it is chargedwith static electricity. It will attach itself to the part to bepowder-coated and once attached, will be difficult toremove. Increasing the humidity in the air reduces staticcharge and thus reduces particulate contamination. In apowder coating application area, this is even more criticalbecause of negative airflow to the booth, which pulls inoutside air thereby producing a cloud that will hang in theapplication area. Low relative humidity will decrease theattraction of powder, yielding low film thickness andrequiring a voltage increase to maintain the appropriatecoating. Fluctuations in humidity will also affect the film-thickness consistency.

Ground. Part grounding is extremely important. Anungrounded substrate will attract the charged powder to acertain point. Eventually, it begins to repel the chargedmaterial, which affects your FPTE.

Many shops continue to allow their racks, hooks, orboth to remain within the powder coating system longafter they have lost the capability to properly ground theparts being coated. Usually, this is done for the followingreasons:

• It involves more personnel to actually clean or take offhooks and racks.

• It costs more to send out the racks for cleaning.

• Employees aren’t trained to identify problem racks andhooks.

• Management thinks that production output outweighsthe time necessary to clean racks and hooks.

Grounding rods should be placed at both ends of allbooths and be attached at the conveyor if used. Manybooths use grounding copper, or rub bars, within thebooths themselves, and while this can help ensure thatyou have an optimal ground system, it usually producesmore debris from them than they are worth, and theytake more time to clean. In some instances, the groundisn’t any better with these rub bars than without them.Again, properly cleaned hooks and racks will efficientlyprovide adequate ground for the powder system.

Powder coatings. Some of the physical and chemicalproperties of the powder coating you use can affectFPTE. Not all powders are the same. Some powders workbetter with some gun brands than others.

Reclaim powder. The larger the powder particle on themetal surface and the higher its charge, the stronger theelectric field between the particle and its mirror image.

The fact that larger particles experience a stronger attrac -tion to grounded metal provides one explanation for anorange-peel effect on thicker layers of powder coatings.

The lower charges of smaller particles may not be suffi-cient to create an attraction force strong enough to retainthe particles on top of the already deposited powder coat-ing layer. The result will be lost efficiency within the sys-tem and reduced appearance to the part being coated.Powder fines don’t charge well. This is why you shoulduse at least a 50-to-50 ratio of virgin-to-reclaim powder inyour feed hopper.

Totally integrated systems produce thegreatest efficiency

You can achieve the greatest application efficiency if youapply powder at the highest TE possible at all times. Itmay even be economical to spray to waste by increasingthe TE of the application equipment.

The value of FPTE can’t be underestimated. Achievingthe highest TE involves more than a powder gun. In fact, itinvolves a totally integrated system. In some cases, a piece-meal system may look like a powder coating system; how-ever, its overall performance, operating cost, quality, andsystem efficiency may fall short of a totally integrated pow-der system’s efficiency. PC

ReferencesNordson Powder Coating Systems, Technical Library, 1994

R. Joseph, Transfer efficiency 1999

B. Utech, A Guide to High-performance Powder Coatings (Dearborn,Mich.: Society of Manufacturing Engineers (SME)/Association forFinishing Processes/SME, 2002)

Bob Utech is owner of a consulting company called PowderVisions and is a former member of the magazine’s EditorialAdvisory Board. The former Minneapolis area resident hasdesigned and installed numerous coating systems for busi-nesses large and small during his years in the powder coat-ing industry. He also was a powder coating instructor atDunwoody Institute in Minneapolis and is author of A Guideto High-performance Powder Coatings. He attended Nor-mandale College, Minneapolis, and has an associate degreein criminal justice.



This article outlines some of the most effective methods and

techniques to track and control the powder coating applica-

tion process, and reduce the reject rate through continuous

improvement. The article analyzes control variables on a

typical conveyorized powder coating system.

Process control in a powder coating shop begins with ageneral understanding of the overall process and the

variables that can affect the overall system and its perfor-mance. A number of control techniques can be used byline operators to keep the powder coating system in check.

A powder coating system includes separate processesworking in sequence to achieve a common goal—a qual-ity, cost-effective finish. A successful powder coating com-pany is made up of various processing components func-tioning together in harmony much like organs within thehuman body. Like the human body, the health of the over-all finishing operation depends on the quality of the com-ponents that operate within it. Following is a breakdownof the components in a powder coating system and theircontrol features.

Compressed airClean, dry air is essential for overall quality in the pow-

der coating system. The air compressor breathes life intothe equipment, allowing the powder to flow through thepowder feed and recovery equipment. Compressors sim-ply take air and compress it, moisture and all. As a result,the moisture must be removed before the air can be usedin the powder coating system.

Poor air quality causes clogged equipment, wet powder,and a contaminated finish. A properly designed and well-

maintained air filtration system ensures good air qualityand helps maintain healthy powder delivery and recov-ery. As a final safeguard, you should place a filter at theair-supply hookup to the powder gun. Generally, this is a5.0-micron filter in a glass canister that can be easilychecked visually for moisture, oil, or other contaminants.

Conveyor and racksA well-maintained conveyor and racking system is also an

important part of maintaining control in the powder coatingsystem. Materials handling by racking represents the circu-latory system of the powder coating process. Periodic clean-ing and proper lubricating can’t be overemphasized.

The efficiency of the overall system is greatly affected byproper electrostatic ground and smooth delivery of partsfrom one process to another. Automatic lubricators areavailable for conveyor systems and are worth the invest-ment for new system construction.

Surface preparationThe leading cause of rejects in the finishing industry

today is inadequate surface preparation before coating.Unbalanced chemical concentrations, bad rinse water,clogged or misdirected nozzles, and other factors left unat-tended will certainly cause rejects, regardless of topcoatquality. If allowed to operate unchecked, the surfacepreparation system would turn from a valuable asset to ahuge liability in a short time.

A properly done control and maintenance program dra-matically reduces rejects caused by failures in surface prepa-ration. System control variables include the following:

•Time

•Temperature

•Concentration


Custom coating: Powder coatingprocess control

Michael W. Cravens Powder Finishing Consultants

IKON Powder Coating

APPLICATION & RECOVERY

d-AR-CravenCoatingArt-63-67:Masters 8/5/09 9:30 AM Page 63

•Impingement

•Rinse-water quality

You can titrate your pretreatment solution to determineconcentration strength and easily keep track of it throughstatistical process control. Regular testing and immediaterecording of results allow the system to operate in a tightrange of parameters as determined by your pretreatmentchemical supplier.

Surface preparation systems require a good deal of main-tenance for a variety of reasons, including extended equip-ment life, quality performance, and efficient operation. Ineach stage, the pumps, nozzles, and burners also needproper attention. The objective is to deliver parts withclean, dry surfaces and proper phosphate coating weights tothe powder coating booth as quickly as possible.

To meet this objective, a few guidelines should be fol-lowed. A maintenance schedule and logbook should bekept to track the regularity of additions of make-up water,chemicals, and replacement parts. This helps the systemsmanager determine when the next chemical change ortank cleaning is needed. Following is a list of maintenancechecks for your surface preparation system:

•Check regularly for spray nozzles that are out of posi-tion, damaged, or missing as a result of fallen parts fromimproper racking. A misdirected nozzle from a rinsestage can overflow a chemical stage, diluting the chemicalconcentration in a matter of minutes.

•Check regularly for clogged nozzle orifices. Cloggingincreases the pressure of the unclogged nozzles. Toomuch pressure is undesirable. In some cases, excessivepressure causes spotting and uneven phosphate coatingweights. It can also blow parts from the racking system.

•Inspect and grease the pumps regularly to ensure properpressure to the nozzles.

•Clean pump screens daily to prevent lint from gloves,rags, and other materials from entering and clogging thepump, header pipes, and nozzles.

•Keep drains free of scale and foreign matter to preventoverflow of wastewater into the work area.

•Install interior grids to prevent falling parts from enter-ing the holding tanks. This allows the systems operator tore trieve the parts easily between breaks. We affectionatelyrefer to an unprotected solution tank as the Bermuda rec-tangle. Parts fall in and are never seen again.

•Replace air-intake filters on burners regularly to ensureclean efficient fuel consumption and maximum controlof solution temperature in the holding tanks. Filter air-borne contaminants from the intake air stream; other-wise, the contaminants will burn and create excessivebuildup inside the burner tube, which causes inefficientheat exchange.

Most custom powder coaters process a variety of sub-strates. Shops that don’t have the necessary surfacepreparation equipment typically find surface preparation

control difficult to impossible, as well as costly, laborintense, messy, inconvenient, time consuming, and trou-blesome. As a result, these shops often take shortcuts andsacrifice quality.

In any quality metal finishing operation, proper surfacepreparation isn’t optional. Historically, surface prepara-tion has caused more premature field failures than anyother segment of the finishing process. Suppliers of surfacepreparation chemicals and equipment offer options andsolutions to many of today’s surface preparation and sub-strate requirements. Consult these suppliers at the time ofsystem design and keep them in the loop throughout thestart-up and service life of the system. Surface preparationis the area where most shops get into trouble at one time oranother. Keep it organized, clean, and in control.

Dry-off and preheat. After cleaning and phosphatizing,parts must be dried. A postheat oven or a cure-oven sec-tion dries the substrate before powder application. Sub-strate temperature control at the application booth affectsthe transfer efficiency of the overall system. The control ofpart surface temperature at the time of powder applica-tion will become even more important as progress in woodand other nonmetallic applications develops.

Powder applicationAnother crucial part of the powder coating process is

powder application. This involves four key areas: the pow-der material, powder delivery system, powder chargingsystem, and powder collection booth.

The powder material.Most applicators assumethat all powder is fresh,new, and ready to be in -tro duced into the pro cessas soon as it’s receivedfrom the supplier. Un for -tunately, many on-lineproblems occur because ofim proper transportation,handling, and storage of the powder material. In addition,powder that has been in house for a time may lose some ofits desired properties. For example, powder that has passedits expiration date, or has been exposed to heat for a time,may exhibit some or all of the following:

•Poor fluidization

•Agglomerated particles

•Reduced gloss

•Excessive orange peel or textured appearance

•Pinhole formation

To ensure that all materials received are of good quality,the applicator should check the date of manufacture at thetime of delivery. It’s also a great idea to do first-in first-out, or FIFO, inventory control. The manufacturing date,lot, and box numbers are clearly marked on each powderbox (sometimes in code) and should be included with jobprocessing information for each order processed. This

We affectionately refer to an

unprotected solution tank as

the Bermuda rectangle.

Parts fall in and are never

seen again.




information is valuable when tracing a powder-relatedproblem.

Powder received near its expiration date should bechecked for quality before introducing it to the finishingsystem. A simple preproduction check can give finishingline personnel valuable insight to possible powder-relatedproblems before on-line rejects occur.

Powder delivery system. Powder delivery is the processby which clean, dry air is carefully mixed with the properratio of powder and delivered to the gun tip via the feedpump and hose at just the right velocity. Adjusting the flu-idizing air, the flow-rate air, and the atomizing air at thegun control console determines powder delivery. Each airsource affects the air-to-powder ratio at the gun tip. Forexample, the fluidizing air mixes the air and powder in thefeed hopper.

To ensure proper powder dispersion without clumping,screen powder into the hopper. The flow-rate air adjust-ment uses venturi air to create a vacuum in the feed pump,which forces air and powder from the feed hopper into thefeed hose. The atomizing-air control introduces more airdirectly into the feed hose at the pump to increase air vol-ume and velocity and change the powder cloud pattern atthe gun tip. Each of these controls plays an important rolein the transfer efficiency of the powder delivery system.

Powder charging system. This system depends on theproper delivery of the powder coating.To understand the powder chargingsystem, you need to have a basic under-standing of electrostatics. Many articlesare available on this topic (see the Edi-tor’s note at the end of this article). It’sa good idea to develop a good under-standing of how electrostatic attractiondiffers from other forms of electricity.

Powder applicators should be trainedby application equipment suppliers inthe proper use of the control variablesand maintenance details required tokeep the guns operating at their peak.Applicators should also understandthat more isn’t always better when itcomes to powder charging and delivery.

The charging of powder particles isn’tmagic. Some people find the electrosta-tic attraction of powder particles tometallic and nonmetallic surfaces assomewhat mysterious. In the negativecoronacharging system, an electrostaticgenerator creates a charging field. Theintensity of the electrostatic charge isrelated to the control console settingthat reads in kilovolts (kV). Properadjustment and control of the chargingsystem and adequate grounding areessential for the highest first passtransfer efficiency. You need to con-

sider substrate composition and geometry when setting thekV controls.

Often, the powder charging system will be overwhelmed.For tribocharging, or friction charging, systems, the pow-der flow rate and velocity directly affect the amount offriction the powder has in the charging tubes. Too muchvelocity may blow powder off the parts. This happenswhen the amount of energy produced by the airflow over-whelms the positive electrostatic attraction of the powderparticle to the neutral substrate. Proper control of thepowder application equipment makes the differencebetween profit and loss—it pays to be in control.

Powder collection booth. Powder containment duringapplication isn’t optional. It’s the law. In Southern Cali-fornia, for example, the South Coast Air Quality Manage-ment District is serious about powder containment. Pow-der materials must not be allowed to escape into theenvironment. Several powder coating companies have hadto detail automobiles that were contaminated by powderescaping from their plants and fusing onto the finish of thevehicles.

The purpose of the powder booth is to contain the pow-der in a controlled environment under conditions thatallow for the highest first pass transfer efficiency. The col-lection booth must be designed, installed, and maintainedto contain the powder within the booth away from appli-

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cation personnel and to keep the powder and air ratiosafely below the lower explosive limits.

The objective is for the operator to control the environ-ment in the application booth in such a way that the pow-der is efficiently attracted to the part. To do this, opera-tors must be trained to properly operate and maintainthe collection equipment (and all other powder coatingequipment).

Powder containment for reuse is optional and highlyrecommended whenever possible. Many powder usersare now realizing the financial benefits of collecting pow-der for reuse. With the advanced technology in the de -sign of collection booths, equipment manufacturers havegiven operators controls with which to increase or de -crease the air draft. This is useful for tasks such as boothcleanup.

Powder curingThermosetting powder coatings must reach a certain

temperature for a determined amount of time for the pow-der to properly cure. Your suppliers should give you therecommended time and temperature for curing each pow-der coating. Different powder formulations require dif-ferent cure temperature and oven dwell time.

When exposed to heat, the powder melts, flows, gels, andfinally cures. The dwell time in each of the four stages ofcure can be altered by controlling the atmo s pheric tem-perature of the oven, the surface temperature of the sub-strate by preheating, or both. If the time in the oven isdecreased, the temperature may be increased to ensurecomplete cure. Proper control of the substrate time attemperature is important. Testing should be done to findthe most appropriate cure window, or time at tempera-ture. Surface and atmospheric temperature recordingdevices are available to eliminate the guesswork related tosubstrate time and temperature.

Following are some factors to consider when determiningand controlling the cure schedule for a powder coating ona part:

•Powder manufacturer’s cure recommendations (time attemperature)

•Total oven dwell time

•Atmospheric oven temperature

•Oven parameters (airflow and other heat-related ovenconditions)

•Substrate composition

•Substrate mass

•Substrate geometry

Line operators, under pressure to increase productivity,occasionally increase line speeds without considering thereduced time at temperature. As a result, they are at riskof undercuring the powder coating. Undercured powderdoesn’t perform to the formulator’s standards and leadsto rejects or premature field failures.

Individual job settings and controlsOnce line operators determine the system control para-

meters and clearly understand the system control vari-ables, they can focus on individual jobs and applicablelimitations.

One of the first issues a good line manager should focuson is determining the limiting factor. This is a single factorthat will limit the rate at which a job is processed. Forexample, a 12-inch by 12-inch, flat, 22-gauge, cold-rolledsteel part cures at a faster rate than a 6-inch by 6-inch by6-inch block of solid steel.

The limiting factor in this case is the oven dwell time asopposed to the rate at which the parts could be cleaned orproperly coated. When setting line speeds, all too oftenthe powder application time is the only consideration. Ifthe total process can’t perform all the necessary functionscompletely, quality suffers.

Job process trackingEach job and part number should have a job process

work sheet. For original equipment manufacturers, thisis generally an important cost accounting considerationand is almost always a part of the total manufacturingprocess flow. OEMs record and track job processing stan-dards for processing and scheduling purposes as well ascosting. Custom coaters can use this same technique whenprocessing repeat orders and similar parts.

Job process tracking may not be a difficult task for thecustom coater with a single line. However, shops that haveseveral lines or have systems at various locations must beable to track the status of orders in house throughout theprocess to effectively communicate key issues to the cus-tomers in real time.

Computers are great for job process tracking whenmany jobs need to be tracked simultaneously. Qualitystandards can be checked at various intervals and docu-mented as the process progresses, not just when the jobis complete. Often, the customer calls to find out the sta-tus of an order in process and wants the informationimmediately. The customer who receives accurate infor-mation regarding the progress of an order in a timelymanner is much more likely to be comfortable with thefinisher’s capabilities and impressed with the finisher’sprofessionalism.

Job process recordingThe recording of jobs is simply a matter of developing a

detailed history of jobs completed. This information is valu-able to the cost accounting department and the job estima-tor. Job-history details can be reviewed and discussed withline personnel, thus eliminating much of the guesswork indetermining the cost to process similar new jobs.

A good job estimator will review in-process data after ajob to determine if the estimated production rates andmaterial use were correct. Proper documentation, track-ing, and review ensures that the company is making money


job after job. Don’t let the profitable jobs carry the non-profitable ones. This sends a false message to the customerand doesn’t help you, the customer, or the industry in thelong run.

Job process recording is also necessary when the cus-tomers require a certification of conformance. These doc-ument and certify processing details as they’re completedand accurately list all quality control documentation. Cus-tomers are comfortable with custom coaters who canprove that predetermined quality standards are beingchecked throughout the process.

ConclusionProcess control in any powder coating system is a full-

time job. The ever-changing variables in the system makeprocess control a continuous challenge for the finishingline manager and system operators. Variables in sub-strates, equipment, powder coatings, and people requirecontinuous monitoring to ensure quality daily.

Employees must be trained to first understand and iden-tify the variables within the system and continue to learnabout all other factors that influence quality. The equip-ment doesn’t run itself—an investment in education for

all employees is an investment in the future success of yourbusiness. Keep your system safe, keep your system clean,and keep your system in total control. PC

Editor’s noteFor further reading on topics in this article, see the “Index to Arti-cles and Authors 1990-2008,” Powder Coating, vol. 19, no. 9December 2008.

Michael Cravens is president of Powder Finishing Consul-tants, Inc., Yorba Linda, Calif., and president of IKON Pow-der Coating, Inc., Anaheim, Calif. With more than 3 decadesof experience in the powder coating industry, he has writtennumerous articles and a training series. He is also a videoproducer, a seminar leader, and a member of many finish-ing industry organizations, including the Powder CoatingInstitute.



www.rapidindustries.com

Temperature profiling allows you to record and interpret thetemperatures of your products and oven air through a con-veyorized or batch oven. The data collected by a tempera-ture profiler tells you how hot your products became and forhow long, and what temperatures your products reachedand at what point. This article answers the most commonquestions coaters have about temperature profiling andexplains how analyzing profile data enables you to increaseproduction and solve production problems.

QMy oven is practically brand new and has thelatest facilities in oven control. Why should Iprofile my oven?

AYou want to profile your product, not your oven.A quality cure depends on the temperature thesubstrate experiences through out the oven.

Although it’s important to control the exact oven tem per -ature, knowing the oven temperature doesn’t mean youknow the product temperature. This is the informationyou get from temperature profiling.

Temperature profiling allows you to measure producttemperature in differentregions of the oven and dif-ferent locations on the sameworkpiece. Frequently,products hung at the top ofthe oven cure significantlymore than those placed atthe bottom. Thermal massalso impacts heating rates.Taking readings from vari-ous segments of a complexproduct or one of mixedcomponents verifies eachsection has been success-fully cured.

In Figure 1, two steelplates, one twice as thick asthe other, are profiled

through identical powder coating ovens. The resultsclearly show that the thicker plate—the one with higherthermal mass—heats at a much slower rate. In fact, themetal never reaches the target cure temperature of 360°F.

QI’m trying to compare two ovens that havetotally different temperature profiles. How can Ibest quantify cure? Simple time-at-temperature

calculations at 400°F in one oven indicate severe under-cure, yet physical test results show good cure.

AIdeally, you want to match the powder coatingssupplier’s cure schedule. It guarantees optimumphysical and cosmetic properties of the product.

This time-at-temperature specification has been providedafter extensive testing of powder-coated metal panels in acontrolled laboratory batch oven under differing condi-tions. In a perfect world, lab oratory conditions would sim-ply need to be replicated. In practice, this is impossible.Calculating the duration at a specific temperature ignoresthe fact that crosslinking occurs at other temperatures. Ittakes time for a product to heat up and cool down, andmatching exact cure temperatures can’t be done in a large-scale conveyorized oven.

The example in Figure 2illustrates this point. Twoprofiles from differentovens have very differentprofile shapes. Becauseneither of them shows adwell time of 6 minutes at400°F, it might be as -sumed that the product issignificantly undercured.To get an accurate analy-sis, the cure contributionsof all temperatures mustbe calculated.

The most accurate way toquantify cure is to use anindex-of-cure calculation.Working from cure sched-


The 12 most common questions askedabout oven temperature profiling

Steve Offley, Ph.D. Datapaq

CURING

FIGURE 1Oven temperature profile

Note: Blue trace indicates oven temperature; red trace indicates 0.079”steel plate; green trace indicates 0.157” steel plate.

Tem

pera

ture

(°F

)

00:00:00 00:02:00 00:04:00 00:06:00 00:08:00 00:10:00Time (hours:minutes:seconds)

400

350

300

250

200

150

100

e-Cure-12QDatapaq-68-73:Masters 8/5/09 9:36 AM Page 68

them a color printout of the run but that can take days. Isthere a quicker and easier way to send them the data?

ATo help share data between powder suppliers andend users freely, download software availablefrom some profile equipment suppliers’ web sites.

This software allows profile data to be viewed by a cus-tomer who doesn’t have a profiler or operating software.The raw data file can be e-mailed to the customer whoopens the file with the viewer software and prints a basicreport.

Alternatively, many commercial packages are availablethat can generate a PDF (Portable Document Format) ofthe profile report, which can be e-mailed directly to the cus-tomer and opened with an appropriate reader package.

QMy powder coatings supplier visits with a profil-ing system, so why should I invest in a unit of myown?

ARoutine temperature profiling does much morethan verify that a specific run on a specific day iswithin specification. By profiling regularly, you

can see when variables are changing and when oven per-formance is deteriorating. As a result, you canidentify the source of faults before they impactproduct quality. It is, simply put, problem pre-vention. The information from temperature pro-filing allows you to plan routine maintenance atyour convenience rather than having to fix aproblem at the worst possible moment during acatastrophic failure.

Don’t forget your powder supplier is interestedin getting the best out of the coating, which mightnot be best for your process in terms of produc-tivity or fuel consumption. How would your fuelbill change if you reduced the oven set-point by5°F? Low cost, easy-to-use profiling systems arean excellent investment. They give you control ofyour process and information when you need it—with no waiting.

QI supply automotive parts to a high-vol-ume automotive original equipmentmanufacturer (OEM) who requires that

I supply documentary proof from every shift thatmy part is cured correctly. Is there any way I canvalidate my process and provide documentaryevidence of QA without having to send up to 60profile reports each month?

AAn excellent way of collating profile datacollected over a period of time is by usingstatistical process control (SPC) strategies.

A single one-page SPC chart (Figure 3) summarizesthe variation in key process parameters bothgraphically and numerically with SPC indicatorssuch as Cp, Cpk, Pp, and Ppk1. Your OEM canimmediately see the cure is in control for a particu-


ule data at different temperatures, a temperature-time rela-tion can be derived based around first order Arrheniusreaction kinetics. Having derived this relation, it’s possibleto sum all time and temperature contributions from the pro-file and calculate a single cure index value. A value of 100indicates that the cure contribution exactly matches thepowder supplier cure schedule. Higher than 100 illustratesovercure, and lower than 100 indicates undercure. In mostsituations, customers use physical tests to determine anacceptable tolerance range for cure index values.

In the example in Figure 2, the index values for each ofthe files was 101, showing that both of the ovens achieveda successful cure even though the profile shapes are totallydifferent. The value of 101 confirms cure performanceand agrees with physical test data.

Employing the index of cure simplifies life because itworks independently of product size, product mass, oroven operating temperatures and is ideal for both accu-rate process development and quality assurance (QA)activities.

QI’m a powder supplier, and I use my oven profilingsystem to prove that our product is within specifi-cations. Customers frequently ask me to send

FIGURE 2

Product temperature profile traces from two ovens with powdercure schedule for 6 minutes at 400°F

Note: Profile 1: Time at 400°F = 2.51 minutes.Profile 2: Time at 400°F = 3.00 minutes.

Tem

pera

ture

(°F)

00:00:00 00:02:00 00:04:00 00:06:00 00:08:00 00:10:00 00:12:00 00:14:00

Time (hours:minutes:seconds)

450

400

350

300

250

200

150

100

FIGURE 3

SPC chart created with process data over a month’s production

Dat

apaq

val

ue

02/11/1993 07/11/1993 12/11/1993 17/11/1993 22/11/1993 27/11/1993

Date (day/month/year)

140.00

120.00

100.00

80.00

Upper limit

Target value

Lower limit



lar process because the index of cure is shown to be in tol-erance for the entire evaluation period. (Editor’s note: Foran article series on SPC, go to [www.pcoating.com] andclick on Article Index and then Testing.)

QBeing a high-volume architectural aluminumextrusion manufacturer, I’m processing thesame size and profile extrusion on one line 6

days a week. How can I make system setup easy for lineoperators and guarantee consistency of data run to run?Currently, I can’t always guarantee whether probes arealways put in the same position.

AWhen powder coating the same product shiftafter shift, day after day, you might considerusing a test piece. If designed with care to simu-

late production items (thermal mass and position), the testpiece allows test data to be collected repeatedly withoutdamaging production items. And repeatability is guaran-teed because the thermocouples areattached to the same point on the testpiece. This can save both materialand time, especially if you use a two-part data logger (Figure 4). Thermo-couples remain attached to the testpiece and to the second half of thedata logger, which stays inside thethermal barrier. At the start of a shift,the QA manager plugs the loggertogether. The system and test piececan then be sent through the processat the convenience of the line opera-tor without any other setup. Trigger-ing of the logger can be programmedto occur when the system enters theoven.

QI’ve successfully profiledconvection ovens for yearsbut have just installed an

infrared (IR) oven for a new productline. Can I use my system to monitorIR? What thermocouple type shouldI use?

AProfiling IR ovens is possi-ble, but care must be takento consider the factors affect-

ing the heat transfer mechanism. Adesirable feature of IR technology isthe very rapid heat transfer possiblewhen the metal substrate absorbselectromagnetic radiation. The degreeof absorption (heating rate) is con-trolled by the emissivity of the sur-face. It’s essential that the productbeing tested is coated with the samepowder type and color used in theproduction run. Exposed junction orpatch probes will accurately measurethe temperature experienced by the

coating. They respond very rapidly to temperature changeand can be coated easily. One word of warning: Gas-firedIR emitter temperatures can be very high. If polytetraflu-oroethylene (PTFE) cables get too close or touch the safetycages, they can melt. Fiberglass cables can help eliminatethis problem. (See Figure 5.) Stainless steel thermal barri-ers work well in IR ovens because they reflect IR well. Ifusing a barrier of an alternative material, wrap it in alu-minum foil (shiny side out) to get the same effect.

QHistorically, we used trailing thermocouples tomeasure product temperature as it traveledthrough the oven. Although difficult, it provided

real-time temperature data. Can oven profilers be usedwith trailing thermocouples to do real-time analysis?

AMany profile systems can be connected directlyto a personal computer (PC) to provide hard-wired profile data live. This creates issues of

FIGURE 4

Profile test piece designed for routine profiling of aluminum extrusion, left,used with a two-piece logger designed for quick-and-easy operation, right

FIGURE 5

Light-duty patch probe in polytetrafluoroethylene (PTFE), left, and heavy-dutyfiberglass exposed junction probe, right


safety, and using long thermocouples becomes expensiveand troublesome. Telemetry is a recent development thatovercomes these problems. It’s now possible to transmitdata back to the monitoring PC during the process via aradio frequency signal so that data review and analysis canbe done live. Data transmission efficiency varies fromprocess to process, so you should first determine the feasi-bility of telemetry for your process and plant.

QMy automotive customer wants me to comparemy powder cure against a cure-chart specifica-tion. This is labor intensive, and I can’t archive

the results digitally without scanning the hard copy. Isthere an alternative?

ARecent software2 innovations make it possible togenerate cure-chart specifications digitally withcommercial profiling software (Figure 6). Thechart is a graphical cure schedule provided by thepowder supplier. The green area in Figure 6 showsthe acceptable cure region for a specified powder.Any point (time at temperature) within this areawill satisfy cure. Profile data is automatically ana-lyzed against this specification, requiring that atleast one time-at-temperature value calculatedfrom the profile graph falls within the cure win-dow. All such data can be customized by the userand archived for routine analysis.

QTime-at-temperature data is importantfor QA in my company, but I don’t wantmy line operators spending hours enter-

ing and interpreting data in order to give me a passor fail for each run. Can this be simplified or auto-mated for my specific requirements?


FIGURE 6Basic cure chart specification against which time-at-temperaturedata from the oven profile is assessed

Tem

pera

ture

(°F)

00:00:00 00:10:00 00:20:00 00:30:00

Time (hours:minutes:seconds)

450

400

350

300

From ISO cure functionMinimum Datapaq value= 100

Target Datapaq value= 341Maximum Datapaq value= 955

Bake window-Acceptable cure

Datapaq values - ISO cure lines

POWDER TARGET CURE

When you call

our advertisers

tell them you saw

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www.armaturecoil.com


ARecent software innovations make it easy to getsophisticated and detailed analysis quickly. Anexample is the two-tiered software with dual-

operating levels. The QA manager has access to all soft-ware functionality, and it’s the manager’s job to define andcreate the test and analysis parameters to be used. Thisdata is stored as a template, which can be used but notchanged by operators. Line operators with passwordaccess use the software on a basic level, which tracks whodid what test when. If necessary, the profile action can besimplified to checking for a green pass light. If problemsare experienced, alarms go off and give the reason for fail-ure. At this point, the QA manager steps in and uses thefull functionality of the software to fault-find and providethe data to rectify the problem highlighted.

QHow frequently should I monitor my process?

AIf I were to survey the powder coating industryabout this question, the answers could range fromas high as six times a day to as low as only when

there’s a problem.

Obviously, there are a lot of factors that influence thelevel of profiling needed by a user. Process engineers oftenprofile frequently when an oven is being set up for a newproduct or process. Temperature profiling is a valuabletool for optimizing oven settings for optimum productivity,efficiency, and quality. Subsequent routine profiling pro-vides process control data. Frequency is then governed bythe value of the product and the desire to know that theprocess is in control.

After-sales service and attention to detail can be key fac-tors in winning contracts in the competitive world of powercoating. Profile data, often in the form of a one-pagereport, can assure customers that you’re meeting qualityand process specifications.

QAre there any guidelines on howmany probes I should use andwhere they should be placed?

AThe number of probes and theirplacement will vary significantlyfrom process to process depending

on oven size and complexity of the part beingpowder-coated.

In general, it’s important that you profilecuring over the working area of the oven.When using an overhead conveyor, I recom-mend placing a probe on the highest and low-est rack positions, then at points in between.For the product itself, place probes at loca-tions you believe will heat up at differentrates. Select the heaviest and thinnest sec-tions to check process extremes. When pro-filing is done for QA purposes, it’s beneficial

to collect product data as well as environmental tempera-ture. When failure occurs, it will be due to oven problemsin most situations.

Probes positioned to monitor air temperatures can easilylocate hot or cold spots. With an eight-channel system, youcan measure four product and four air temperatures. Ifyour process uses a flat-bed conveyor, it’s useful to do anoven survey across the width of the oven. Monitoring onlythe air temperature is an ideal way to check oven balanceas seen in the oven thermal contour map in Figure 7. PC

Endnotes1. Cp equals process capability; Cpk equals process capability index; Pp

equals process performance; and Ppk equals process performance index.

2. BakeChart software by Datapaq

Editor’s note

For further reading on the topics discussed in this arti-cle, see Powder Coating magazine’s Web site at [www.pcoating.com]. Click on Article Index and search by sub-ject category. Have a question? Click on Problem Solvingto submit one.

Steve Offley, Ph.D., is oven product manager, Datapaq, 187Ballardvale St., Wilmington, MA 01887; 978/988-9000; e-mail[[email protected]]; Web site is [www.datapaq.com]. He isresponsible for specifying and developing oven-temperature-profiling equipment. He holds a BSc (Hons) in applied chem-istry from Coventry Polytechnic, Coventry, UK, and a Ph.D.in analytical chemistry from Loughborough University ofTechnology, Loughborough, UK, with postdoctoral researchat the University of Massachusetts-Amherst. In 1992, he waselected as a member of the Royal Society of Chemistry(CChem MRSC).

FIGURE 7

Thermal contour map of a mesh belt cure oven showing the clearidentification of a cold spot located midway through the oven

00:00:00 00:05:00 00:10:00 00:15:00

Time (hours:minutes:seconds)R

ange 490(top) to 110

(bottom) in 10° increm

ents

Thermograph (full zoom)°F key


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This article discusses how oven design contributes to mainte-

nance efficiency and gives specific design criteria. The article

discusses the importance of oven controls and includes a list

of yearly, quarterly, and monthly maintenance tasks for gas-

fired and electric convection and infrared ovens.

An oven is a critical component in any finishing sys-tem. Getting the best results from an oven for a par-

ticular system depends on several factors:

•The parts

•The line speed

•The plant space available

A wide variety of ovens are available today, includinggas-fired or electric convection ovens, gas-fired or electricinfrared (IR) ovens such as those shown in figures 1 and 2,combination IR and convection ovens, and combinationdry-off and cure convection ovens. When determining theoven for your application, you need to talk with a varietyof equipment suppliers.

You also need to seek recommendations from the suppli-ers of your powder coatings and pretreatment chemicals.These suppliers can point out areas that you need to con-sider when making your oven selection. For example, doyou run parts that are difficult to drain after a powerwash? Do you coat parts with multiple metal thicknessesthat may be a challenge to cure? The suppliers can let youknow what the minimum requirements are for their prod-ucts to perform as expected.


Oven design and maintenance

Bob Anderson Powder Spray Technologies

CURING

FIGURE 1

Gas-fired infrared oven

Phot

o co

urte

sy In

fra-

Red

Tec

hnol

ogie

s, N

. Kan

sas

City

, Mo.

FIGURE 2

Electric infrared oven

Phot

o co

urte

sy B

lasd

el E

nter

pris

es, G

reen

sbur

g, In

d.

f-Cure-Maintenance Series-74-79:Masters 8/5/09 9:38 AM Page 74

fail after several hours, or minutes, of operation. Some-times, the burner may not light at all.

In an electric convection oven with an adjustable fresh-air vent in the heating chamber, airborne particles canenter through the vent and build up on heater elementsand the recirculation fan. This reduces heating efficiencyand increases operation costs.

With electric IR ovens, airborne particles that reach theemitters reduce the amount of reflection in the oven andreduce efficiency. Gas-fired-IR oven efficiency can alsobe greatly reduced by particles adhering to the face of theemitter.

If layout constraints force you to place the oven andburner-box components near dust-producing processes,you need to consider isolating the oven, the burner box,or the powder recovery and application areas.

You also need to make sure that the oven is as accessibleas possible. For instance, if you have a flat-belt electricor gas-fired IR oven with emitters 12 to 18 inches off thetop of the belt, how easily can you service the emitters?Will the belt conveyor or oven need to be disassembled toaccess the interior emitters? Will maintenance personnelneed yoga lessons to change or service interior oven com-ponents? What can the manufacturer do to make themaintenance procedure easy and quick?


Input from all sources will help you determine the rightoven for your application. You also should test the partsto be doubly sure that the oven you selected performs toyour expectations.

Design criteria

Cleanliness of the oven and the surrounding area is soimportant that this article starts with that topic ratherthan ends with it. Poor housekeeping creates about 50percent of oven maintenance problems and downtime.Location is everything when it comes to your oven. Whendesigning your system, therefore, you need to considerhow the location of the oven is going to affect the amountof maintenance required. Interior as well as exterioroven cleanliness is extremely important regardless ofyour oven type.

Locating a convection oven heater, or burner, box (seeFigure 3) near the powder booth area creates manyproblems. For example, if the oven is gas-fired, airbornepowder particles can float into the combustion air blowerand burner. These particles can come from sweeping upthe area around the booth or from adding powder to thehopper. Eventually, the buildup of particles restricts thedelivery of fan air to the burner, the quality of the flamein the burner, or both. Placing an oven near dust-gener-ating processes, open doorways, or outside drafts createsthe same burner problems. This can cause the burner to

FIGURE 4

Flame safety controls

Phot

o co

urte

sy E

clip

se C

ombu

stio

n, R

ockf

ord,

Ill.

Interlocks closedSystem errorFlame failureAir failure

FIGURE 3

Gas-fired convection oven burner box

Phot

o co

urte

sy P

owde

r Sp

ray

Tech

nolo

gies

, Arli

ngto

n, T

ex.



You also need to consider many other areas of ovendesign. If you select a convection oven, for example, youneed to consider the number of air changes per minuteoffered by the recirculating fan to get an even tempera-ture throughout the oven. You also need to review thedesign of the outlet ductwork, the number and type ofadjustable air outlets in the ductwork to eliminate hotand cold spots, and the location of the ductwork (flooror ceiling).

If you choose electric IR, you need to determine properemitter wavelength, watt size, and amp load. If you

choose gas-fired IR, you need to consider the number ofemitters, Btu’s per hour, and controls. You also need todetermine whether or not your application requires zon-ing for the greatest efficiency.

Furthermore, parts may have been tested successfullyon two different types of IR ovens. One oven may belonger than the other because of the wavelength used. Youneed to take that into consideration if floor space is tightat your plant.

In addition, one oven may be more costly to install andoperate than the other. The cost and availability of utili-

TABLE 1

Preventive maintenance program for convection ovens

Gas-fired

Annually�� Leak test safety shut-off valves for tightness.�� Test pressure-switch settings by checking switch movements against pressure setting and comparing with actual impulse

pressure.�� Visually check ignition cable and connectors.�� Make sure the following components aren’t damaged or distorted:

� Burner nozzle� Spark plugs� Flame sensors� Flame tube or combustion block of burner

�� Test oven temperature profiler. Make necessary adjustments to balance oven temperature.

Quarterly�� Lubricate fan-bearing points on the oven.�� Inspect belts for tension, and adjust as needed. Check belts for separation or cracks, and replace as needed.�� Blow out fan motors, and remove residue buildup.

Monthly�� Inspect flame-sensing devices for condition and cleanliness. Keep the glass lens of scanners clean with a soft, damp

cloth because small amounts of dust can measurably reduce the flame signal. Wash the flame-rod electrode andinsulator with soap and water, and then rinse and dry them thoroughly.

�� Test the alarm systems for proper signals.�� Check ignition spark electrodes, and check proper gap.�� Test interlock sequence of safety equipment. Manually make each interlock fail, noting what related equipment closes or

stops as specified by the manufacturer (check your manufacturer’s test procedures).�� Inspect combustion air blower on burner, and clean residue from fan. If residue buildup is found in fan, inspect burner

outlet ports, and remove residue.�� Blow out combustion air blower fan motor, and clean off residue buildup.�� Sweep oven interior.

Electric

Annually�� Test pressure-switch settings by checking switch movements against pressure setting and comparing with actual impulse

pressure.�� Visually inspect electrical heating elements for cleanliness, damage, or deterioration. Replace elements or insulators as

needed.�� Test oven temperature profiler. Make necessary adjustments to balance oven temperature.


Monthly�� Sweep oven interior.

f-Cure-Maintenance Series-74-79:Masters 8/6/09 3:15 PM Page 76

ties in your area will be a factor in selecting gas or electric.You expect your oven to reach the design temperatureand maintain that temperature. However, you need toknow how long it will take the oven to reach operationaltemperature every morning.

Oven controls

In the past, locating a problem with an oven could be adifficult and time-consuming process, especially with gas-fired ovens. Thank goodness technology is moving for-ward to make everyone’s life a little easier.

Flame safety controls now indicate a problem in theoven (see Figure 4). If an oven with flame safety controlfails, an indicator light tells the operator that the problemis in a certain part of the oven. For instance, an air fail-ure light indicates a fan problem or an airflow switchproblem. Sometimes, hours or entire shifts have beenspent tracking down a problem without these indicators,only to find that an airflow switch needed adjustment.

Flame safety controls can also indicate when an inter-lock is open, when a pilot or main flame fails, and whena system error occurs. System errors can include aproblem with wiring or welded contacts, a malfunction

of the flame safety, the failure of the main fuel, a faultwith the scanner, electrical interference on sensor leads,or an out-of-sequence flame.

If your oven is operating with a flame safety control thatdoesn’t offer troubleshooting indicators, you shouldreplace it. You can get payback for the price of the sys-tem with the first problem by indication of where theproblem is and the quick repair, adjustment, or replace-ment of the component.

A preventive maintenance program

Have a preventive maintenance program in placebefore oven delivery. Review the necessary maintenanceprocedures with the oven manufacturer. Compile a com-plete maintenance program. This should include a dailystart-up sheet that has a dedicated section for produc-tion personnel comments. If an employee observes some-thing out of the ordinary, it can be noted and followedup on by maintenance personnel.

A written schedule for preventive maintenance that istied to hours, weeks, or months of production is impor-tant. As you complete the tasks, compile the reports, orwork orders, along with any other nonpreventive main-


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tenance tasks performed. You can use these completedwork orders to build a history of the oven and to formthe basis for a predictive maintenance program.

Several computerized maintenance programs auto-matically generate work orders for preventive mainte-nance tasks. The programs automatically generate a his-tory of the oven from these orders. Many of theprograms include areas for CAD drawings, part lists,spare parts inventory, purchase orders, and taskdescriptions. Whether your preventive maintenanceprogram is on a computer or in a notebook, recordkeeping is a must.

Tables 1 and 2 include suggestions for maintenanceschedules. You can adjust these lists to fit your particu-lar situation. You may need to do some tasks more fre-quently, or you may need to add some tasks. Remem-

ber, though, maintenance and cleanliness need to becultivated and emphasized from the first day of ovenoperation. PC

Bob Anderson is vice president of marketing at Powder

Spray Technologies, P.O. Box 201464, Arlington, TX

76006; 972/606-2727. He has more than 20 years of experi-

ence in the finishing industry, primarily in powder coating

systems, including washers, dry-off and cure ovens, over-

head conveyors, and powder application and recovery

systems.


TABLE 2

Preventive maintenance program for infrared ovens

Gas-fired

Annually�� Leak test safety shut-off valves for tightness.�� Test pressure-switch settings by checking switch movements against pressure setting and comparing with actual

impulse pressure.


Monthly�� Visually inspect emitters for cleanliness.�� Clean emitters with a soft paint brush only.�� Run oven as hot as possible to burn off powder buildup if evident on heater.�� Cover emitters with plastic when cleaning oven interior or sweeping out. This will prevent dust and other materials

from collecting on the catalyst surface.�� Inspect blower, and remove residue buildup if combustion air blower is used. Blow off motor, and remove residue

buildup.

Electric

Quarterly�� Clean reflectors with warm, soapy water, wipe dry, and rebuff.�� Lubricate fan-bearing points on the oven.�� Inspect belts for tension, and adjust as needed. Check belts for separation or cracks, and replace as needed.�� Blow out fan motors, and remove residue buildup.�� Check output amperage to emitters with amp probe at contactor in electrical control panel.�� Check for excessive heat from back of emitters. This will indicate an efficiency loss and reflector uncleanliness.

Monthly

�� Clean reflectors with warm, soapy water.

Weekly

�� Wipe reflectors with a soft rag.�� Visually inspect emitters for proper functioning.


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