ABC of Spraying

8/3/2019 ABC of Spraying

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ABCs of Spray Painting

ABCs of Spray Painting$10.00 A-2928-A


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Forward Table of Contents

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While this book examines thespray finishing operation and itsequipment from many viewpoints,there is still much more to belearned to become truly proficientat spray finishing.

The best way to becomeproficient at spray finishing is to

just do it! Many trade technicaland community colleges offercourses in spray finishing, a greatway to improve your skills.

Many of the tricks of theprofessional spray finisher involvepaints and coatings. Themanufacturers of these materials

routinely publish complete bookson these subjects. Thesepublications are available inspecialty paint stores and willprovide you with considerabledetail. Many of these books alsocontain information on techniquesfor surface preparation.

Another important source ofinformation, particularly onequipment use and selection is

your local spray finishingequipment distributor. No bookcould ever completely cover aspecialists in-depth knowledge ofequipment, techniques,maintenance and troubleshooting.

Information is available from manyresources on the subject of sprayfinishing. It is our hope that thisbook will provide you with a starttoward perfecting your finishing

skills.

A recent addition to resourcesavailable to the spray finisher isthe World Wide Web. Manymanufactures are represented andquestion and answer forums areavailable. Please visit our websitesawww.binks.com.t www.devilbiss.com and

About this book..

This book has been updatedseveral times from The ABCs ofSpray Equipment, originallypublished by The DeVilbissCompany in 1954. It focuses onequipment and techniques for

spray finishing.

The format of the original bookwas question-and-answer. Wehave retained that format in thisedition.

This book is organized around themajor components of an air spraysystem spray guns, materialcontainers, hose, air control

equipment, compressors, spraybooths, respirators and a shortsection on general cleanliness andother sources of information. Athorough understanding of thematerial in this book - plus a lot ofactual spray painting practice -should enable you to handle justabout any spray painting situation.

Although we have made an effortto make this book as detailed and

as complete as possible, be awarethat the equipment and productsystems used to illustrate pointsare entirely based on DeVilbisstechnology. DeVilbiss is theworlds oldest and largestmanufacturer of spray paintingequipment, and has maintainedthis leadership since its foundingin 1888.

Forward .....2

1. Introduction ..3

Surface Preparation...3

Paint Preparation3

2. Air Atomizing SprayGuns....4

Spray Gun Types ..4

Part Identification and

Function...6

Operation ....9

Maintenance .11

Troubleshooting ...13

3. Material Containers...16

4. Hose and Connections 18

5. Air Control Equipment..20

6. Respirators ..22

7. Air Compressors.23

8. Spray Booths ..25

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1. Introduction

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This book is about the selection,use and maintenance of finishingequipment: spray guns, tanks,cups, hoses, compressors,regulators, spray booths,respirators, etc. It presumes thatyou are familiar with standard

surface preparation techniquesthat may be required beforefinishing actually begins. It alsopresumes a basic knowledge ofthe many different types of paintsand coatings available.

Creating a perfect finish requires asolid knowledge of surfacepreparation, finishes and spraypainting equipment. The first twoare extensively covered in manyother books. The manufacturers ofpaints and coatings have gone to

great length to publish informationon their new and existingproducts.

But, even an extensive knowledgeof surface preparation techniquesand paint chemistry is not enoughto assure a professional finish.The finish must be applied by aspray gun, and all the variables ofits use must be mastered.

The equipment necessary to applythe finish the spray gun, tank,

cup, regulator, hoses,compressor, etc. must all bematched to the job as well as toeach other. That equipment mustbe used and maintained properly,with an appreciation of how andwhy it works the way it does.

The moment of truth for any finishhappens when the trigger ispulled. This book focuses on thatmoment.

Surface Preparation

The surface to be finished shouldbe well cleaned before painting. Ifthe paint manufacturersinstructions call for it, the surfaceshould be chemically treated. Usea blow-off gun and tack rag toremove all dust and dirt. Noamount of primer or paint willcover up a badly preparedsurface.

Plastic parts may contain staticelectricity from the moldingprocess. This static attractsparticles of dust and dirt. Eliminatethem by treating with destatisiz-ing air using a special blow-offgun that imparts a neutral chargeto the airflow. A chemical anti-static treatment is also available.

Paint Preparation

Todays finishes are extremelycomplex chemical formulations.They include both solvent andwaterborne types. Some mayrequire the addition of solvents toform the proper spraying viscosity.Others may simply require theaddition of a second component at

a prescribed ratio to obtainsprayable consistency. Many ofthem also have hardeners or otherchemicals, added to them toinsure correct color match, gloss,hardness, drying time or othercharacteristics necessary toproduce a first class finish. Makesure you are familiar with thespecific finish material data sheetsaccompanying each material. Donot mix materials from variousmanufacturers. Read and followdirections carefully.

All finish materials must also besupplied with a Material SafetyData Sheet (MSDS). This dataprovides information on properhandling and disposal ofmaterials. Many states require thatMSDS be kept on file by the user.

The first step is knowing the typeand color of paint the projectrequires. With this determined,follow the manufacturersinstruction for preparing it exactly.

If you have any doubts about howto proceed, dont guess! Contactyour paint supplier for help.Improperly prepared paint willnever produce a good finish!

The chief characteristic thatdetermines the sprayablility ofpaint and how much film may beapplied is its viscosity orconsistency. Following the paintmanufacturers instructions will get

you close, but for professionalresults, use a viscosity cup. It is asimple but very accurate way tomeasure the thickness of paint.With the cup, you can thin orreduce the paint to the preciseconsistency required by themanufacturer.

Always prepare paint in a clean,dust-free environment. Paint has aremarkable ability to pick up dirt.Dirty paint will not only clog yourspray gun, but it will also ruin yourpaint job. Get in the habit ofalways pouring paint into the cupor tank through a paint strainer.Paint is never as clean as it looks.

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2. Air Atomizing Spray Guns

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Introduction

The spray gun is the keycomponent in a finishing system. Itis a precision engineered andmanufactured instrument. Eachtype and size is specifically

designed to perform a certain,defined range of tasks.

As in most other areas of finishingwork, having the right tool for the

job goes a long way toward get-ting professional results.

This chapter will help you knowwhich is the proper gun by review-ing the Conventional Air and HighVolume/Low Pressure spray gundesigns commonly used in finish-ing - suction feed, gravity feed andpressure feed. It will also reviewthe different types of guns andcomponents within each design.

A thorough understanding of thedifferences between systems willallow you to select the right gun,to use it properly to produce ahigh quality finish and to con-tribute toward a profitable finishingoperation.

SPRAY GUN TYPES

1. What is an air spray gun?

An air spray gun is a tool whichuses compressed air to atomizepaint, or other sprayable material,and to apply it to a surface.

Air and material enter the gunthrough separate passages andare mixed at the air cap in acontrolled pattern.

2. What are the types of airspray guns?

Air spray guns may be classifiedin various ways. One way is by thelocation of the material container:

Figure 1 shows a gun with a cupattached below it.

Figure 3 shows a gun with a cupattached above it.

Figure 4 shows a material con-tainer some distance away fromits pressure feed gun.

The type of material feed systemis also a way of classifying guns:

Suction Feed... draws material to

the gun by suction as in Figure 1.Gravity Feed... the material travelsdown, carried by its own weightand gravity as in Figure 3.

Pressure Feed... the material isfed by positive pressure as inFigure 4.

Guns may also be classified aseither external or internal mixdepending upon the type of aircap.

3. What is a suction feed gun?

A spray gun design in which astream of compressed air createsa vacuum at the air cap, providinga siphoning action. Atmosphericpressure on the material in thesuction cup forces it up the suctiontube, into the gun and out the fluidtip, where it is atomized by the aircap. The vent holes in the cup lidmust be open. This type gun isusually limited to a one-quart, orsmaller, capacity container andlow to medium viscosity materials.

Figure 1- Suction Feed Gun withattached cup

Suction feed is easily identified bythe fluid tip extending slightly be-yond the face of the air cap, seefigure 2.

Figure 2 - Suction Feed Air Cap

Suction feed guns are suited tomany color changes and to smallamounts of material, such as inautomotive panel/bumper repairsand "completes," touchup, or

lower production operations.

4. What is a gravity feed gun?

This design uses gravity to flowthe material from the cup, which ismounted above the gun, into thegun for spraying. No fluid pickuptube is used, since the fluid outletis at the bottom of the cup.

This cup has a vent hole at the topof the cup that must remain open.

It is limited to 34 ounce capacitiesdue to weight and balance.

Gravity feed guns are ideal forsmall applications such asautomotive panel/bumper repairsand "completes," spot repair,orfor finishing in a limited space.They require less air than a suction

feed gun, and usually have lessoverspray.

Figure 3- Gravity Feed Gun withattached cup


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2. Air Atomizing Spray Guns (Contd)

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5. What is a pressure feed gun?

In this design, the fluid tip is flushwith the face of the air cap (seeFigure 5). The material ispressurized in a separate cup,tank or pump. The pressure forcesthe material through the fluid tipand to the air cap for atomization.

Figure 4 - Typical Pressure Feed Gunwith remote pot

This system is normally usedwhen large quantities of materialare to be applied, when thematerial is too heavy to besiphoned from a container orwhen fast application is required.Production spraying in amanufacturing plant or fleet

refinishing operation is a typicaluse of a pressure feed system

Figure 5 - Pressure Feed Air Cap

Type Viscosity Fluid Atomizing Type

Feed (#2 Zahn) Oz/Minu te Pressure Production

Suction up to 24 10-12 40-50 Low

Gravity up to 24 10-12

12-24

30-50 Low

Pressure up to 29 50-60 High

6. What is an external mix aircap?

This gun mixes and atomizes airand fluid outside the air cap.

It can be used for applying alltypes of materials, and it isparticularly desirable whenspraying fast drying paints such asbasecoat and lacquer. It is alsoused when a high quality finish isdesired.

Figure 6 - External Mix Gun

7. What is an internal mix cap?

This cap mixes air and materialinside the air cap, before expellingthem.

It is normally used where low airpressures and volumes areavailable, or where slow-dryingmaterials are being sprayed.

A typical example is spraying flatwall paint, or outside house paint,with a small compressor.

Internal mix caps are rarely usedfor finishing when a fast-drying

material is being sprayed, or whena high quality finish is required.

Figure 7 - Internal Mix Air Cap

8. What is HVLP?

HVLP, or High-Volume/LowPressure, uses a high volume ofair (typically between 15-26 CFM)delivered at low pressure (10 PSIor less at the air cap) to atomizepaint into a soft, low-velocity

pattern of particles.

In many cases, less than 10 psi isneeded in order to atomize.

Proper setup utilizes no more fluidand air pressure than is needed toproduce the required quality and aflow rate that will meet productionrequirements.

As a result, far less material is lostin overspray, bounceback andblowback than with conventionalair spray. This is why HVLPdelivers a dramatically highertransfer efficiency (the amount ofpaint that adheres to the substratecompared to the amount of paintsprayed) than spray systemsusing a higher atomizing pressure.

The HVLP spray gun resembles astandard spray gun in shape andoperation. Models that use highinlet pressure (35-80 psi) andconvert to low pressure internallywithin the spray gun are called

HVLP conversion guns.Some HVLP models, particularlythose using turbines to generateair, bleed air continuously tominimize back- pressure againstthe air flow of the turbine.

The air cap design is similar tothat of a standard spray gun, witha variety of air jets directing theatomizing air into the fluid stream,atomizing it as it leaves the tip.

HVLP is growing in popularity and

new environmental regulations arerequiring it for many applications.

HVLP can be used with a widevariety of materials, includingtwo-component paints, urethanes,acrylics, epoxies, enamels,lacquers, stains, primers, etc.

A DeVilbiss Pro Tip:When using a gravity feed system,downsize the tip one size from suction.If the suction system calls for a .070,use a .055 or .063

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PART IDENTIFICATIONFUNCTION

9. What are the principal partsof a spray gun?

Figure 8 - Spray Gun Anatomy

10. What happens when thetrigger is pulled?

The trigger operates in twostages. Initial trigger movementopens the air valve, allowing air toflow through the gun.

Further movement of the triggerpulls the fluid needle from its seatat the fluid tip, allowing fluidmaterial to flow. When the triggeris released, thefluid flow stopsbefore the air flow.

This lead/lag time in the triggeroperation assures a full spraypattern when the fluid flow starts.It also assures a full pattern untilthe fluid flow stops, so there is nocoarse atomization.

11. What is the function of the aircap?

The air cap (see figure 10) directscompressed air into the fluidstream to atomize it and form thespray pattern. (see Figure 9)

Round Tapered Blunt

Figure 9 - Types of Spray Patterns

There are various styles of caps toproduce different sizes andshapes of patterns for manyapplications.

12. What are the advantages of

the multiple jet cap?This cap design provides betteratomization of more viscousmaterials.

It allows higher atomizationpressures to be used on moreviscous materials with less dangerof split spray pattern.

It provides greater uniformity inpattern due to better equalizationof air volume and pressure fromthe cap.

It also provides better atomizationfor materials that can be sprayedwith lower pressures.

Figure 10 - Multiple Jet External MixAir Cap

13. How should an air cap beselected?

The following factors must be con-sidered:

a) type, viscosity and volume ofmaterial to be sprayed

b) size and nature of object, orsurface to be sprayed (multiple, orlarger, orifices increase ability toatomize more material for fasterpainting of large objects).

Fewer, or smaller orifices usuallyrequire less air, produce smallerspray patterns and deliver lessmaterial. (These caps aredesigned for painting smallerobjects and/or using slowerspeeds)

c) material feed system used(pressure, suction or gravity)

d) size of fluid tip to be used(most air caps work best withcertain fluid tip/needlecombinations)

e) volume of air in cubic feet perminute (cfm) and pressure inpounds per square inch (psi) avail-able.

See the DeVilbiss spray guncatalog for proper selection of aircap / fluid tip / needlecombinations and typical uses.

14. What is the function of thefluid tip and needle?

They restrict and direct the flow ofmaterial from the gun into the airstream. The fluid tip includes aninternal seat for the tapered fluidneedle, which reduces the flow ofmaterial as it closes. (see Figure11).

The amount of material thatleaves the front of the gundepends upon the viscosity of thematerial, the material fluidpressure and the size of the fluidtip opening provided when the

needle is unseated from the tip.Fluid tips are available in a varietyof sizes to properly handlematerials of various types, flowrates and viscosity.

Figure 11 - The Fluid Tip andNeedle

AirCap

FluidTip

FluidNeedle

NeedlePacking

AirValve

SpreaderAdjustment

Valve

FluidAdjustment

Screw


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15. What is the nozzlecombination?

In practice, the air cap, fluid tip,needle and baffle are selected asa unit, since they all work together

to produce the quality of the spraypattern and finish. These fouritems, as a unit, are referred to asthe nozzle combination.

16. What are standard fluid tipsizes and flow rates?

The standard sizes, correspondingfluid tip opening dimensions andflow rates are:

Rule of thumbOptimum fluid pressure is 8-20 psi.Pressures greater than thisgenerally indicate the need for alarger fluid tip size.

17. How are fluid tip and needlesizes identified?

DeVilbiss fluid tips and needlesare identified by the lettersstamped on the tip and theneedle.

The identification letters on thesecomponents should match. Seethe appropriate DeVilbiss spraygun catalog for the properselection of fluid tip and needlecombinations.

18. What fluid tip and needlecombination sizes are mostcommon?

1.0, 1.1, 1.4 and 1.8 are mostgenerally used. The 1.4 and 1.6combination is used for gravityfeed, while 1.6 and 1.8 are usedfor suction feed. For pressure feed

the most common tips are 1.1mmand 1.4mm.

19.How are nozzlecombinations selected?

Five basic considerations are in-volved in selecting the nozzlecombination:

type and viscosity of materialbeing sprayed

physical size of object beingfinished/fan pattern size

desired speed/finish quality

gun model being used

available air volume (cfm) andpressure (psi) fromcompressor

(1) The type and viscosity of thematerial being sprayed is thefirst factor to consider.

Rule of thumbThe lower the viscosity of thematerial, the smaller the I.D. of thefluid tip.

Material Production Tip

Viscosity Rate Size

#2 Zahn

up to 23 sec Low 1.1 mm

1.4 mm

1.8 mm

2.2 mm

23-28 sec Med

28-48 sec High

over 48 sec High

NOTE: Viscosity conversioncharts are available to convert one

viscosity cup reading to anotherfrom any material or equipmentsupplier.

(2) The physical size of the objectto be painted must also beconsidered. As a general rule, usethe largest possible spray patternconsistent with the object size.Remember that different air capsdeliver various patterncharacteristics. This can reduceboth spraying time and thenumber of gun passes.

(3) The next consideration inevaluating nozzle combinations isthe speed with which the finish willbe applied and the desired level ofquality.

For speed and coverage, choosea nozzle combination whichproduces a pattern as wide aspossible.

When quality is the decidingfactor, choose a nozzle

combination which produces fineatomization and a smaller patternsize, thereby giving greaterapplication control.

(4) The model of the gun itself willlimit the selection of nozzlecombination.

For a DeVilbiss suction feed gun,there are several nozzle typesavailable which are suitable forfinishing operations. These

Plus Technology(High Efficiency)

Tip Size Max. Flow Rate

Gravity Feed1.2 mm/.047" 6 oz./min.1.3 mm/.051" 7 oz./min.1.4 mm/.055" 8 oz./min.1.5 mm/.059" 9 oz./min.1.6 mm/.062" 10 oz./min.1.8 mm/.070" heavy-bodied material

Suction Feed1.6 mm/.062" 9 oz./min.1.8 mm/.070" 12 oz./min.

Pressure Feed1.0 mm/.039" 10 oz./min.1.4 mm/.055" 16 oz./min.

or heavy-bodied material

HVLP Technology



Suction Feed1.8 mm/.070" 6 oz./min.2.0 mm/.078" 7 oz./min.2.2 mm/.086" 8 oz./min.



Conventional Air Spray



Suction Feed1.6 mm/.062" 9 oz./min.1.8 mm/.070" 12 oz./min.



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nozzles have fluid tip openingsranging from .062 to.086", andare designed to handle viscositiesup to 28 seconds in a No. 2 ZahnViscosity Cup.

For a DeVilbiss pressure feedgun, the amount of material

discharged depends upon materialviscosity, inside diameter of thefluid tip, length and size of hose,and pressure on the materialcontainer or pump.

If the fluid tip opening is too small,the paint stream velocity will betoo high. If the fluid tip opening istoo large, you will lose control overthe material discharging from thegun.

For most HVLP guns, the paint

flow shouldn't exceed 16 oz. perminute. For higher flow rates,consult the DeVilbiss HVLP SprayGun catalog.

(5) Available air supply is the lastfactor to consider.

Pressure feed air caps consumebetween 7.0 and 25.0 CFM,depending on design. If your airsupply is limited, because of anundersize compressor, or manyother air tools are in use at once,

the gun will be starved for air,producing incomplete atomizationand a poor finish.

20. What are the criteria forselecting a pressure feednozzle?

While the fluid discharge inounces per minute from a suctionfeed gun is relatively stable(largely because it is determinedby atmospheric pressure), the fluid

discharge from a pressure feedgun depends more upon the sizeof the inside diameter of the fluidtip and the pressure on the paintcontainer or pump. The larger theopening, the more fluid isdischarged at a given pressure.

If the fluid tip ID is too small for theamount of material flowing fromthe gun, the discharge velocity willbe too high. The air, coming fromthe air cap, will not be able to

atomize it properly causing acenter-heavy pattern.

If the fluid tip opening is too large,material discharge control will belost.

The fluid tip/air cap combination

must be matched to each otherand to the job at hand. Spray guncatalogs include charts to help youmatch them properly.

21. Of what metals are fluid tipsmade?

Tips are made of the followingmetals:

a) 300-400 grade stainless steelfor both non-corrosive andcorrosive materials

b) Carboloy inserts for extremelyabrasive materials

22. What is viscosity?

The viscosity of a liquid is its body,or thickness, and it is a measureof its internal resistance to flow.Viscosity varies with the type andtemperature of the liquid. Anyreference to a specific viscositymeasurement must beaccompanied by a correspondingtemperature specification.

The most common measurementused to determine viscosity infinishing is flowrate(measured inseconds from a Zahn, Ford, Fisheror other viscosity cup).

Different viscosity cup sizes areavailable. Each cup has a hole atthe bottom, specified to an exactsize. Use a viscosity cup that isdesigned to handle the time range

of the materials in use. Viscositycontrol is an extremely importantand effective method to maintainapplication efficiency and qualityconsistency. Always measureviscosity after each batch ofmaterial is mixed and make surematerial temperature is the same,normally 70 to 80 F.

Viscosity recommendations maybe given in poise and centipoise(1 poise=100 centipoise).

Viscosity conversion may beaccomplished by consulting aviscosity conversion chart.

23. What is the spreader adjust-ment valve?

A valve for controlling the air tothe horn holes which regulate thespray pattern from maximum widthdown to a narrow or round pattern(see figure 8).

24. What is the fluid needleadjustment?

This adjustment controls thedistance the fluid needle isallowed to retract from its seat in

the fluid tip, which allows more orless material through the fluid tip(see figure 14).

With pressure feed systems, thefluid delivery rate should beadjusted by varying the fluidpressure at the pressure pot. Usethe fluid adjustment knob for minorand/or temporary flow control.This will extend the life of the fluidneedle and tip.

25. What are the components ofsuction and gravity feedsystems?

Typical suction and gravity feedsystems consist of: a suction feedor gravity feed spray gun with cup,an air compressor (not shown), acombination filter/air regulator andair hoses (see figure 12).


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Figure 12 - Suction Feed and

Gravity Feed System Components

OPERATION

26. How is suction and gravityfeed equipment hooked up foroperation?

Connect the air supply from thecompressor outlet to the filter/airregulator inlet.

Connect the air supply hose fromthe air regulator outlet to the airinlet on the spray gun.

After the material has been re-duced to proper consistency, thor-oughly mixed and strained into thecup, attach the gun to the cup(suction feed) or pour material intoattached cup (gravity feed).

27. How are suction and gravityfeed systems initially adjustedfor spraying?

(1) Spray a horizontal test pattern(air cap horns in a verticalposition). Hold the trigger openuntil the paint begins to run. Thereshould be relatively evendistribution of the paint across thefull width of the pattern. (seeFigure 13). Adjust the patternwidth with the spreaderadjustment valve. If distribution isnot even, there is a problem witheither the air cap or the fluid tip

that must be corrected. Refer tothe Troubleshooting Section forexamples of faulty patterns to helpdiagnose your problem.

Figure 13 - Horizontal Test Pattern

(2) If the pattern produced by theabove test appears normal, rotatethe air cap back to a normalspraying position and begin spray-ing. (Example - a normal patternwith a conventional or #2000 HVLPair cap will be about 10-11" longwhen the gun is held 8" from thesurface).

Figure 14 Fluid AdjustmentScrew

(3) With the fluid adjusting screwopen to the first thread,(see figure14) and the air pressure set atapproximately 30 psi, or for HVLP10 psi at the air cap. Make a testpass (move the spray gun 3 timesthe normal speed) with the gun onsome clean paper, cardboard orwood. If there are varations in

particle size- specks and/or largeglobs - the paint is not atomizingproperly (see figure 15).

(4) If the paint is not atomizingproperly, increase the air pressureslightly and make another testpass. Continue this sequence until

the paint particle size is relativelyuniform.

Uneven distribution

Even Distribution

Figure 15- Test Patterns

(5) If the pattern seems starved formaterial, and the fluid adjustmentscrew allows full needle travel, thefluid tip may be too small or thematerial may be too heavy.Recheck the viscosity or increasethe size of the fluid tip and needle

(6) If the material is spraying tooheavily and sagging, reduce thematerial flow by turning in the fluidadjusting screw (clockwise).

Remember, proper setup utilizesno more fluid and air pressurethan is needed to produce therequired quality and a flow ratethat will meet productionrequirements.

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28. What are the components ofa pressure feed system?

A pressure feed system consistsof: a pressure feed spray gun, apressure feed tank, cup or pump,an air filter/regulator, appropriateair and fluid hoses, and an air

compressor (see figure 16).

Figure 16 - Pressure Feed SystemComponents

29. How is equipment hookedup for pressure feed spraying?

Connect the air hose from the airregulator to the air inlet on thegun.

Connect the mainline air hose to

the air inlet on the tank.CAUTION: Do not exceed thecontainer's maximum workingpressure.

Connect the fluid hose from thefluid outlet on the tank to the fluidinlet on the gun.

30. How is the pressure feedgun adjusted for spraying?

Open spreader adjustment valvefor maximum pattern size(seefigure 8).

Open fluid adjustment screw untilthe first thread is visible (seefigure 14).

31. How is the pressure feedgun balanced for spraying?

1) Using control knob on fluidregulator, set fluid pressure at 5 to10 psi.

2) Using control knob on air regulator,set air atomization pressure at 25-50psi or for HVLP 10 psi at the air cap.

3) Spray a test pattern (fast pass)on a piece of paper, cardboard, or

wood. From that test pattern,determine if the particle size issmall enough and relativelyuniform throughout the pattern toachieve the required finish quality(see figure 15). If particle size istoo large or is giving too muchtexture in the finish, turn theatomization pressure up in 3 to 5psi increments until particle sizeand texture of finish is acceptable.

4) Spray a part with thesesettings. If you are not able to

keep up with the production raterequired or if the finish is starvedfor material, increase the fluidpressure with the fluid regulatorcontrol knob in 2 to 4 psiincrements until required wetcoverage is accomplished. Note:A larger capacity fluid tip may berequired.

5) Remember, as you turn up thefluid pressure the particle size willincrease. Once the coveragerequired is obtained, it will be

necessary to re-adjust theatomization pressure in 3 to 5 psiincrements as explained in step 3to insure required particle size andfinish texture is achieved.

6) If using HVLP, using an AirCap Test Kit verify that the aircap pressure is not above 10 psi, ifr(see figure 17).equired by a regulatory agency

Figure 17 Air Cap Test Kit

After establishing the operatingpressures required for productionand finish quality, develop aPressure Standardization programfor your finish room to follow.

32. What is a PressureStandardization Program?After establishing air and fluidpressures that meet required qual-ity and production, record the datato be used for that application forfuture reference. (see figure 18)

Booth #: _______________

Material Sprayed ________

Application _____________

Viscosity _______________

Fluid Temperature ________

Spray Gun ______________

Air Cap ______ Fluid Tip ___

Air Pressure _____________

Fluid Pressure ____________

Figure 18 Pressure StandardizationChart

33. How should the spray gunbe held?

It should be held so the pattern isperpendicular to the surface at alltimes.

Keep the gun tip 8-10 inches (airspray guns) or 6-8 inches (HVLPguns) from the surface beingsprayed.


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34. What is the propertechnique for spray gun strokeand triggering?

The stroke is made with a freearm motion, keeping the gun at aright angle to the surface at allpoints of the stroke.

Triggering should begin justbefore the edge of the surface tobe sprayed. The trigger should beheld fully depressed, and the gunmoved in one continuous motion,until the other edge of the object isreached. The trigger is thenreleased, shutting off the fluidflow, but the motion is continuedfor a few inches until it is reversedfor the return stroke.

When the edge of the sprayed

object is reached on the returnstroke, the trigger is again fullydepressed and the motioncontinued across the object.

Lap each stroke 50% over thepreceding one. Less than 50%overlap will result in streaks on thefinished surface. Move the gun ata constant speed while the triggerispulled, since the material flowsat a constant rate.

Another technique of triggering is

referred to as "feathering."Feathering allows the operator tolimit fluid flow by applying onlypartial trigger travel.

35. What happens when the gunis arced?

Arcing the stroke results in unevenapplication and excessive over-spray at each end of the stroke.When the tip is arced at an angleof 45 degrees from the surface

(see figure 19), approximately65% of the sprayed material islost.

Figure 19 - Spray Techniques

36. What is the proper spraying

sequence and technique forfinishing applications?

Difficult areas, such as cornersand edges, should be sprayedfirst. Aim directly at the area sothat half of the spray covers eachside of the edge or corner.

Hold the gun an inch or two closerthan normal, or screw thespreader adjustment control in afew turns. Needle travel should beonly partial by utilizing the "feath-

ering" technique. Either techniquewill reduce the pattern size.

If the gun is just held closer, thestroke will have to be faster tocompensate for a normal amountof material being applied tosmaller areas.

When spraying a curved surface,keep the gun at a right angle tothat surface at all times. Followthe curve. While not always physi-cally possible, this is the ideal

technique to produce a better,more uniform, finish.

After the edges, flanges and cor-ners have been sprayed, the flat,or nearly flat, surfaces should besprayed.

Remember to overlap the previ-ously sprayed areas by 50% toavoid streaking.

When painting very narrow sur-faces, you can switch to a smallergun, or cap with a smaller spraypattern, to avoid readjusting thefull size gun. The smaller guns areusually easier to handle in restrict-ed areas.

A full size gun could be used,however, by reducing the air pres-sure and fluid delivery and trigger-ing properly.

MAINTENANCE

37. How should the air cap becleaned?

Remove the air cap from the gunand immerse it in clean solvent. Ifnecessary, use a bristle brush toclean dried paint. Blow it dry withcompressed air.

If the small holes becomeclogged, soak the cap in cleansolvent. If reaming the holes isnecessary, use a toothpick, abroom straw, or the speciallydesigned cleaning needle andhandle from a Professional SprayGun Cleaning Kit.

Cleaning holes with a wire, a nailor a similiar hard object couldpermanently damage the cap byenlarging the jets, resulting in adefective spray pattern.

Figure 20 - Cleaning the Air Cap

11


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12

38. How should guns becleaned?

A suction or pressure feed gunwith attached cup should becleaned as follows:

Turn off the air to the gun, loosen

the cup cover and remove the fluidtube from the paint. Holding thetube over the cup, pull the triggerto allow the paint to drain backinto the cup.

Empty the cup and wash it withclean solvent and a clean cloth.Fill it halfway with clean solventand spray it through the gun toflush out the fluid passages bydirecting stream into an approved,closed container. All containersused to transfer flammable

materials should be grounded. (Besure to comply with local codesregarding solvent disposal).

Then, remove the air cap, clean itaoutside of fluid tip and baffle area,and replace air cap on the gun.

Wipe off the gun with a solventsoaked rag, or if necessary, brushthe air cap and gun with a fiber brushusing clean-up liquid or thinner.

s previously explained. Clean

To clean a pressure feed gun withremote cup or tank, turn off airsupply to cup or tank. Releasematerial pressure from the systemby opening relief valve.

Material in hoses may be blownback. The lid must be loose andfluid pressure off. Keep gun higherthan container, loosen air cap andtrigger gun until atomizing airforces all material back into thepressure vessel.

A gun cleaner may be used foreither type of gun. This is an en-closed box-like structure (vented)with an array of cleaning nozzlesinside.

Guns and cups are placed overthe nozzles, the lid is closed, thevalve is energized, and thepneumatically controlled solventsprays through the nozzles toclean the equipment.

The solvent is contained, andmust be disposed of properly.

Some states' codes require theuse of a gun cleaner, and it is un-lawful to discharge solvent into theatmosphere.

After cleaning a spray gun in agun cleaner, be sure to lubricateas indicated in Figure 22.

Figure 21 - Using a Hose Cleaner

Use a hose cleaner to cleaninternal passages of spray gunsand fluid hose. This deviceincorporates a highly efficient fluidheader, which meters a precisesolvent/air mixture. The cleaneroperates with compressed air andsends a finely - atomized blast ofsolvent through the fluid passagesof the hose, the spray gun, etc.

This simple, easy to use cleaner

speeds up equipment cleaningand saves solvent. Savings maybe as much as 80%. It alsoreduces VOC emissions. (Be surethat both the hose cleaner andgun are properly grounded.)

Where local codes prohibit the useof a hose cleaner, manuallybackflush the hose into the cup ortank with solvent until clean anddry with compressed air.

Clean the container and add cleansolvent. Atomization air should beturned off during this procedure.Pressurize the system and run thesolvent through until clean. (Besure to comply with local codesregarding solvent dispersion and

disposal.)Clean the air cap, fluid tip andtank. Reassemble for future use.

39. What parts of the gunrequire lubrication? (Figure 22)

The fluid needle packing A, the airvalve packing B and the triggerbearing screw C require dailylubrication with a non-silicone/non-petroleum gun lube.

The fluid needle spring D shouldbe coated lightly with petroleum

jelly or a non-silicone grease (ie.Lithium).

Lubricate each of these pointsafter everycleaning in a gunwasher!

Figure 22 - Lubrication Points

C

D

B

A


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13

Problem

Fluid leaking from packing nut

Air leaking from front of gun

Fluid leaking or dripping fromfront of pressure feed gun

Jerky, fluttering spray

Cause

1. Packing nut loose2. Packing worn or dry

1. Sticking air valve stem

2. Foreign matter on air valve orseat

3. Worn or damaged air valve orseat

4. Broken air valve spring5. Bent valve stem6. Air valve gasket damaged or

missing

1. Dry packing2. Packing nut too tight3. Fluid tip or needle worn or

damaged

4. Foreign matter in tip5. Fluid needle spring broken6. Wrong size needle or tip

All Feed Systems1. Loose or damaged fluid

tip/seat2. Dry packing or loose fluid

needle packing nut3. Material level too low4. Container tipped too far5. Obstruction in fluid passage6. Loose or broken fluid tube or

fluid inlet nipple

Suction Feed Only7. Material too heavy8. Air vent clogged9. Loose, damaged or dirty lid

10. Fluid tube resting on cupbottom

11. Damaged gasket behind fluidtip

Correction

1. Tighten, do not bind needle2. Replace or lubricate

1. Lubricate

2. Clean

3. Replace

4. Replace5. Replace6. Replace

1. Lubricate2. Adjust3. Replace tip and needle with

lapped set

4. Clean5. Replace6. Replace

1. Tighten or replace

2. Lubricate packing or tightenpacking nut

3. Refill4. Hold more upright5. Backflush with solvent6. Tighten or replace

7. Thin or reduce8. Clear vent passage9. Tighten, replace or clean

coupling nut10. Tighten or shorten

11. Replace gasket

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14

ProblemTop or bottom-heavy spraypattern*

Right or left-heavy spraypattern*

Center-heavy spray pattern

Split spray pattern

Cause1. Horn holes plugged

2. Obstruction on top or bottomof fluid tip

3. Cap and/or tip seat dirty

1. Horn holes plugged2. Dirt on left or right side of fluid

tip

*Remedies for the top, bottom,right, left heavy patterns are:1. Determine if the obstruction is onthe air cap or fluid tip. Do this bymaking a solid test spray pattern.Then, rotate the cap one-half turn andspray another pattern. If the defect isinverted, obstruction is on the air cap.Clean the air cap as previouslyinstructed.2. If the defect is not inverted, it is onthe fluid tip. Check for a fine burr onthe edge of the fluid tip. Remove with

#600 wet or dry sand paper.3. Check for dried paint just insidethe opening. Remove paint bywashing with solvent.

1. Fluid pressure too high foratomization air (pressure feed)

2. Material flow exceeds aircaps capacity

3. Spreader adjustment valve settoo low

4. Atomizing pressure too low5. Material too thick

1. Fluid adjusting knob turned intoo far

2. Atomization air pressure toohigh

3. Fluid pressure too low(pressure feed)

4. Fluid tip too small

Correction1. C

straw or the specially designedcleaning needle and handle froProfessional Spray Gun Cleani

lean, ream with a toothpick, b

Cstraw or the specially designedcleaning needle and handle froProfessional Spray Gun Cleani

lean, ream with a toothpick, b

2. Clean

3. Clean

1.

2. Clean

1. Balance air and fluid pressureIncrease spray pattern width

2. Thin or reduce fluid flow

3. Adjust

4. Increase pressure5. Thin to proper consistency

1. Back out counter-clockwise toincrease flow

2. Reduce at regulator

3. Increase fluid pressure

4. Change to larger tip


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15

ProblemStarved spray pattern

Unable to form round spraypattern

Dry spray

Excessive overspray

Excessive fog

Will not spray

Cause1. Inadequate material flow

2. Low atomization air pressure(suction feed)

1. Fan adjustment stem notseating properly

1. Air pressure too high2. Material not properly reduced3. Gun too far from surface4. Gun motion too fast

1. Too much atomization airpressure

2. Gun too far from surface

3. Improper technique (arcing,gun speed too fast)

1. Too much, or too fast-dryingsolvent

2. Too much atomization airpressure

1. Pressure feed cap/tip usedwith suction feed

2. No pressure at gun

3. Fluid needle not retracting4. Fluid too heavy (suction feed)

Correction1. Back fluid adjusting screw out

to first thread or increase fluidpressure

2. Increase air pressure andrebalance gun

1. Clean or replace

1. Lower air pressure2. Reduce to proper consistency

andtemperature solvent

select correct

3. Adjust to proper distance4. Slow down

1. Reduce pressure

2. Use proper gun distance3. Use moderate pace, keeping

gun parallel to work surface

1. Remix with correcttemperature solvent

2. Reduce pressure

1. Use suction feed cap/tip

2. Check air lines3. Open fluid adjusting screw4. Lower fluid viscosity or

change to pressure feed

15


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3. Material Containers

16

Introduction

All spray painting systems - fromthe smallest brush to the mostsophisticated finishing system-must have containers to hold thematerial being applied.

Material container types and sizesvary considerably, depending onthe kind of spraying system beingused.

This chapter will discuss thesecontainers, their particular applica-tions, their construction and main-tenance.

1. What are materialcontainers?

Any container which serves as amaterial supply reservoir for thespray gun. These containers areusually made of metal or plasticwith capacities of 1/2 pint or more.

2. What are the types of materialcontainers?

There are three common types ofcups which attach to the gun itself:Siphon, Gravity and Pressure.

There are also remote pressurecups and tanks, which are locatedaway from the gun. See Page 4for types of guns and systems.

3. Where are cup containers

used?

Cup containers are typically onequart or less, and are used whererelatively small quantities ofmaterial are being sprayed.

4. How are material feed cups

attached to lid assemblies?

Cups are attached using a lidassembly (sometimes called a cupattachment) that either clamps Aor screws Bonto the cupcontainer. (see Figure 1) Some lidassemblies are detachable fromthe gun, while others are integral

parts and do not detach from lessexpensive models.

A B

Figure 1 - Cup Attachment Styles

5. What capacity does a

pressure feed cup have?A pressure feed cupcan have aone or two quart capacity.

Anything larger is considered apressure feed tank, which may bepositioned some distance from thegun.

Figure 2 - Regulated 2 Qt.Pressure Cup

6. How do pressure feed tankswork?

Pressure feed tanks are closedcontainers, ranging in size fromabout two gallons to 60 gallons.They provide a constant flow ofmaterial, under constant pressure,to the spray gun.

The tank is pressurized with clean,regulated, compressed air, whichforces the fluid out of the tankthrough the fluid hose to the gun.

The rate of fluid flow is controlledby increasing or decreasing the airpressure in the tank.

A typical pressure feed tankconsists of: the shell A, clamp-onlidB, fluid tube C, fluid outlet D,regulator E, gauge F, safety reliefvalve G, and optional agitator H(see figure 3).

Pressure feed tanks are availablewith a top fluid outlet and variousaccessories.

Figure 3 - Pressure Feed Tank

7. Where are pressure feedtanks recommended?

Pressure feed tanks provide apractical, economical method offeeding material to the gun overextended periods of time.

They are mostly used incontinuous production situations,because the material flow ispositive, uniform and constant.

Tanks can be equipped withagitators (see Figure 3) that keep

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3. Material Containers (Contd)

17

the material mixed and insuspension.

8. When is an agitator used in apressure feed tank?

When the material being used hasfiller or pigment that must be keptin motion to keep its particles inproper suspension. An agitatorcan be hand, air or electricallydriven.

9. What is a single regulatedtank?

This is a pressure feed tank withone air regulator controlling onlythe pressure on the material in the

tank (see figure 4).

Figure 4 - Single Regulated Tank

10. What is a double regulatedtank?

This is a pressure feed tankequipped with two air regulators(see figure 5).

One provides regulation for the airpressure on the material in thetank (thereby controlling fluidflow). The other controls

atomization air pressure to thespray gun.

Figure 5 - Double Regulated Tank

11. What are code and non-code

pressure tanks?

Code tanks are manufactured torigid standards as specified by theAmerican Society of MechanicalEngineers. (ASME) Each step ofmanufacture is closely controlled,and welding of the shell iscertified. Code tanks are designedto withstand pressures up to 110psi.

Non-code tanks are normallyrestricted to 3 gallons in size or

less. Due to the type ofconstruction, non-code tanks arerated at 80 psi or less.

12. What materials are used toconstruct pressure feed tanks?

The smaller, non-code, light-dutytanks are made of plated steel andhave lower inlet pressurerestrictions.

The heavy-duty, ASME-codetanks are made of galvanized or300 series stainless steel. Theyalso have plated or stainless steellids with forged steel clamps.

When abrasive or corrosivematerials are being sprayed, thetank shell is coated or lined with astank liner is used.pecial material, or a polyethylene

13. What are tank liners?

They are inserts that are placedinside the tank to hold thematerial, keeping it from directcontact with the tank walls. Theyare made of disposablepolyethylene.

Using liners reduces tank cleaningtime and makes color changeoverand cleanup easier.

Note:

The A.S.M.E. code, as it relates to pressure vesselsattached to spray gun nozzles, is primarily concerned

with the use of flammable materials and also covers

applications where a tank is used in an OSHA-regulatedenvironment. To comply with OSHA regulations, if you

are using a flammable material at greater than 15 PSI

and your local fire department has adopted NFPA 33,you must use an A.S.M.E. code tank. Refer to NFPA

33, standard for spray application using flammable orcombustible materials.

17


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4. Hoses & Connections

18

Introduction

The various types of hose used tocarry compressed air and fluidmaterial to the spray gun areimportant parts of the system.Improperly selected or maintainedhose can create a number of

problems. This chapter will reviewthe different kinds of hose andfittings in use, provide guidance inselecting the proper types for the

job and cover the maintenance ofhose.

1. What types of hose are usedin spray painting?

There are two types: air hose -used to transfer compressed air

from the air source to the gun, andfluid hose - used only in pressurefeed systems to transfer thematerial from its container to thespray gun.

(NOTE: Do notuse air hose forsolvent-based materials.)

Figure 1 - Basic HoseConstruction

2. How is hose constructed?

DeVilbiss hose is a performancedesigned combination of threecomponents: Tube A,Reinforcement B and Cover C.

The tube is the interior flexibleartery that carries air or fluidmaterial from one end of the hoseto the other.

The reinforcement adds strengthto the hose. It is located betweenthe tube and cover, and it can be

many combinations of materialsand reinforcement design. Itsdesign determines pressurerating, flexibility, kink and stretchresistance and coupling retention.

The cover is the outer skin of thehose. It protects the reinforcementfrom contact with oils, moisture,solvents and abrasive objects.The cover protects thereinforcement, but does notcontribute to hose performance.

DeVilbiss hose is color-coded:

RED or TAN..... air and water

GREY...............air w/static ground

BLACK ............ low pressure fluid

3. What type of tube is used influid hose?

Since the solvents in coatings

would readily attack and destroyordinary rubber compounds, fluidhose is lined with specialsolvent-resistant nylon materialthat is impervious to commonsolvents.

4. What sizes of fluid hose arerecommended?

Type Length Size

General 0' - 25' 1/4" ID

Purpose 25' - 50' 3/8" ID

50' - 100' 1/2" ID

Figure 2 - Recommended fluidhose sizes

5. What sizes of air hose arerecommended?

The hose from the regulator to agun or tank should be a minimumof 5/16" ID. Tools requiring moreair may need 3/8" I.D. hose orlarger.

Type Length Size

0' - 10' 1/4" ID

General 10' - 25' 5/16" ID

Purpose 25' - 50' 3/8" ID

50' - 100' 1/2" ID

0' to 25' 5/16" ID

HVLP 25' - 50' 3/8" ID

50' - 100' 1/2" ID

Figure 3 - Recommended airhose sizes

6. What is pressure drop?

This is the loss of air pressure dueto friction (caused by air flow)between the source of the air andthe point of use. As the air travelsthrough the hose or pipe, it rubsagainst the walls. It loses energy,pressure and volume as it goes.

7. How can this pressure dropbe determined?

At low pressure, with short lengthsof hose, pressure drop is notparticularly significant. Aspressure increases, and hose islengthened, the pressure rapidlydrops and must be adjusted.

All air hose is subject to pressureloss or drop. For example, 1/4"pressure drop is 1 psi per foot and5/16" is 1/2 psi per foot. Thispressure loss may result in pooratomization.

Too often, a tool is blamed formalfunctioning, when the realcause is an inadequate supply ofcompressed air due to anundersized I.D. hose.

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4. Hoses & Connections (Contd)

19

For optimum spray gun results,the following is recommended: upto 25 ft - 5/16" I.D., over 25 ft -3/8" I.D.

8. How are hoses maintained?

Hoses will last a long time if theyare properly maintained.

Be careful when dragging hoseacross the floor. It should never bepulled around sharp objects, runover by vehicles, kinked orotherwise abused. Hose thatruptures in the middle of a job canruin or delay the work.

Proper hose cleaning techniquesare covered on Pages 11 and 12.

The outside of both air and fluidhose should be occasionallywiped down with solvent. At theend of every job, they should bestored by hanging up in coils.

9. What types of hose fittings areavailable?

Permanent, crimp type or reusablefittings are used to connect hosesto air sources or to sprayequipment.

10. What types of hoseconnections are available?

Although there are many differentstyles, the two most common arethe threaded and thequick-disconnect types.

Remember that elements addedto any hose, such as elbows,connectors, extra lengths of hose,etc., will cause a pressure drop.

On HVLP systems,quick-disconnects must havelarger, ported openings (high flow)to deliver proper pressure foratomization. Because of normalpressure drop in these devices,most are not recommended foruse with HVLP.

11. What is a threaded- type

connection?

This is a common swivel-fittingtype that is tightened with awrench.(see figure 4).

Figure 4 - Threaded-TypeConnection

12. What is a quick-disconnecttype connection?

This is a spring-loaded, male/female connection system thatreadily attaches and detaches byhand. No tools are required (seefigure 5).

Figure 5 - Quick-Disconnect TypeConnection

Care should be taken whenselecting a quick-disconnect airconnection. Due to design, mostQ.D. connections result insignificant pressure drop. This canadversely affect spray guns withhigher consumption air caps suchas HVLP.

19


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5. Air Control Equipment

20

Introduction

The control of volume, pressureand cleanliness of the air enteringa spray gun are of criticalimportance to the performance ofthe system.

Following some key installationprinciples will help decrease therisk of contaminants. For example,its important to use the right sizeair compressor for yourapplication. An overworked aircompressor can produce asignificant amount of dirt and oil.Additionally, proper piping is veryimportant to help preventcondensation from forming withinthe line and contaminating the airsupply.

This chapter examines the varioustypes of equipment available toperform these control functions.

1. What is air controlequipment?

Any piece of equipment installedbetween the air source and thepoint of use that modifies thenature of the air.

2. Why is air control equipmentnecessary?

Raw air, piped directly from an airsource to a spray gun, is of littleuse in spray finishing. Raw aircontains small, but harmful,quantities of water, oil, dirt andother contaminants that will alterthe quality of the sprayed finish.Raw air will likely vary in pressureand volume during the job.

There will probably be a need for

multiple compressed air outlets torun various pieces of equipment.

Any device, installed in the air line,which performs one or more ofthese functions, is considered tobe air control equipment.

3. What are the types of aircontrol equipment?

Air control equipment comes in awide variety of types, but itbasically all performs one or moreof the following functions; airfiltering/cleaning, air pressureregulation/indication and airdistribution through multipleoutlets.

4. How does an air filter work?

It filters out water, oil, dust and dirtbefore they get on your paint job.Air entering the filter is swirled toremove moisture that collects inthe baffled quiet zone.

Smaller impurities are filtered outby a filter. Accumulated liquid iscarried away through either amanual or automatic drain.

Figure 1 - Air Filter

5. What is an air regulator?

This is a device for reducing themain line air pressure as it comesfrom the compressor. Once set, itmaintains the required airpressure with minimumfluctuations.

Regulators are used in linesalready equipped with an airfiltration device.

Air regulators are available in awide range of cfm and psicapacities, with and withoutpressure gauges and in differentdegrees of sensitivity andaccuracy.

They have main line air inlets andregulated or non-regulated airoutlets.

6. How is an air filter/regulatorinstalled?

Bolt the air filter/regulator Asecurely to the spray booth wallnear the operator. (see Figure 2)

This location makes it convenientto read the gauges and operatethe valves. Install the filter/regulator at least 25 feet from theB compressed air source. Installthe C takeoff elbow on top of theD main air supply line.

Piping should slope back towardthe compressor, and a E drain legshould be installed at the end ofeach branch, to drain moisturefrom the main air line.

Use piping of sufficient I.D. for thevolume of air being passed, andthe length of pipe being used.

Minimum Pipe Size Recommendatio

Compressor Main Air Lin

HP CFM LENGTH SIZ

1 1/2 - 2 6-9 Over 50' 3/4

3-5 12-20 Up to 200' 3/4

Over 200' 1"

5-10 20-40 Up to 100' 3/4

100' - 200' 1"

Over 200' 1 1/4

10-15 40-60 Up to 100' 1"

100' - 200' 1 1/4

Over 200' 1 1/2

Table 1

20


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5. Air Control Equipment (Contd)

21

*Piping should be as direct aspossible. If a large number offittings are used, larger I.D. pipeshould be installed to helpovercome excessive pressuredrop.

Figure 2 Air/Filter RegulatorInstallation

7. How often should thefilter/regulator be drained ofaccumulated moisture and dirt?

It depends largely on the level ofsystem use, the type of filtration inthe air system, and the amount ofhumidity in the air.

For average use, once-a-daydrainage is probably sufficient.

For heavily-used systems, or inhigh humidity, drainage shouldoccur several times daily.

Some units drain automaticallywhen moisture reaches apredetermined level.

8. What steps should be taken ifmoisture passes through the

filter/regulator?

Since moisture in the spray gunatomization air will ruin a paint job,it must be removed from the airsupply.

When the compressed airtemperature is above its dew pointtemperature, oil and water vaporwill not condense out into solidparticles.

Check the following:

a) Drain air filter, air compressortank, and air line of accumulatedmoisture.

b) Be sure the air filter islocated at least 25 feet from theair source.

c) Main air line should not runadjacent to steam or hot waterpiping.

d) Compressor air intake shouldnot be located near steam outletsor other moisture-producing areas.

e) Outlet on the air compressor tankshould be near the top of the tank.

f) Check for damaged cylinderhead or leaking head gasket, if theair compressor is water cooled.

g) Intake air should be as cool aspossible.

9. What causes excessive pres-sure drop on the main line

gauge of the filter/regulator?

a) The compressor is too smallto deliver the required airvolume and pressure for alltools in use.

b) The compressor is notfunctioning properly.

c) There is leakage in the air lineor fittings.

d) Valves are partially opened.

e) The air line, or piping system,is too small for the volume ofair required. Refer to Table 1,Page 20.

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6. Respirators

22

Introduction

Consult with appropriate safetypersonnel or Industrial Hygienistif in doubt as to the suitability of aparticular respirator before usingit. Respirators may not provideprotection against eye and skin

absorption of chemicals.

Spray finishing creates a certainamount of overspray, hazardousvapors and toxic fumes. This istrue, even under ideal conditions.

Anyone near a spray finishingoperation should use some type ofrespirator, or breathing apparatus.This chapter covers various typesof equipment for this use.

1. What is a respirator?A respirator is a mask that is wornover the mouth and nose toprevent the inhalation of oversprayfumes and vapor.

2. Why is a respiratornecessary?

For two reasons:

First...some type of respiratoryprotection is required by OSHA/

NIOSH regulations.

Second...even if it wasn't arequirement, common sense tellsyou that inhaling overspray is nothealthy.

Overspray contains toxic particlesof paint pigments, harmful dustand, in some cases, vapor fumeswhich can be harmful to yourhealth.

Depending on design, a respiratorcan remove some, or all, of thesedangerous elements from the airaround a spray finishing operator.

3. What types of respirators areused by spray finishingoperators?

There are three primary types; theair-supplied respirator, the organicvapor respirator and the dustrespirator.

4. What is an air-suppliedrespirator?

This type is available in both maskand visor/hood styles. Bothprovide the necessary respiratoryprotection when using materialsthat are not suitable for organic

vapor respirators.The visor/hood style provides agreater degree of coverage to thehead and neck of the operator.

Both styles require a positivesupply of clean, breathable air asdefined by OSHA (Grade D).

Figure 1 Positive PressureVisor/Hood

Figure 2 Positive PressureMask Respirator

5. What is an organic vaporrespirator and where is it used?

This type of respirator, whichcovers the nose and mouth, (seeFigure 3) is equipped withreplaceable cartridges thatremove organic vapors bychemical absorption.

Some are designed with pre-filtersto remove solid particles from the

air before it passes through thechemical cartridge.

The organic vapor respirator isnormally used in finishing opera-tions with standard materials (notsuited for paints containingisocyanates).

Figure 3 - Organic VaporRespirator

6. What is a dust respirator andwhere is it used?

Dust respirators are sometimesused in spray finishing but, in mostapplications, they areunsatisfactory. (see Figure 4)

Figure 4 - Dust Respirator

These respirators are equippedwith cartridges that remove onlysolid particles from the air. Theyhave no ability to remove vapors.

They are effective, however, inpreliminary operations such assanding, grinding and buffing.

NOTE:

Before using any respirator,carefully read the manufacturersSafety Precautions, Warnings andInstructions. Many respirators arenot suitable for use withisocyanates, asbestos, ammonia,pesticides, etc.

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7. Air Compressors

23

Introduction

All air tools, spray guns, sanders,etc., must be supplied with airwhich is elevated to higherpressures and delivered insufficient volume. The aircompressor compresses air for

use in this equipment and is amajor component of a spraypainting system. This chapter willexamine the various typesavailable.

Compressed air is measured onthe basis of volume supplied perunit of time (cubic feet per minute,or cfm) at a given pressure persquare inch (psi), referred to asdelivery.

Displacement is the output of air

by a compressor at zero pressure,or free air delivery.

1. What is an air compressor?

An air compressor is a machinedesigned to raise the pressure ofair from normal atmosphericpressure to some higher pressure,as measured in pounds persquare inch (psi). While normalatmospheric pressure is about14.7 pounds per square inch, a

compressor will typically deliver airat pressures up to 200 psi.

When selecting a compressor:

Rule of thumbThe cubic feet per minutedelivered by an electricallypowered 2 stage industrialaircompressor is 4 times the motor'shorse power rating. (CFM=4xHP)

2. What types of compressorsare most common in sprayfinishing operations?

There are two common types; thepiston-type design and the rotaryscrew design.

Because most commercial sprayfinishing operations consumelarge quantities of compressed airat relatively high pressures, the

piston type compressor is themore commonly used.

3. How does a piston-typecompressor work?

This design elevates air pressurethrough the action of areciprocating piston. As the pistonmoves down, air is drawn inthrough an intake valve. As thepiston travels upward, that air iscompressed. Then, thenow-compressed air is dischargedthrough an exhaust valve into theair tank or regulator.

Piston type compressors areavailable with single or multiplecylinders in one or two-stagemodels, depending on the volume

and pressure required.

Figure 1 - Piston Type AirCompressor

4. How does a rotary screwcompressor work?

Rotary screw compressors utilizetwo intermeshing helical rotors ina twin bore case. Air iscompressed between one convexand one concave rotor. Trappedvolume of air is decreased and thepressure is increased.

Figure 2 Rotary Screw AirCompressor

5. What is a single stagecompressor?

This is a piston-type compressorwith one or more cylinders, inwhich air is drawn from theatmosphere and compressed to itsfinal pressure with a single stroke.

All pistons are the same size, andthey can produce up to 125 psi.

6. Where are single stagecompressors used?

The application of this compressoris usually limited to a maximumpressure of 125 psi. It can be usedabove 125 psi, but above thispressure, two stage compressorsare more efficient.

7. What is a two-stagecompressor?

A compressor with two or morecylinders of unequal size in whichair is compressed in two separatesteps.

The first (the largest) cylindercompresses the air to anintermediate pressure. It thenexhausts it into a connecting tubecalled an intercooler.

From there, the intermediatepressurized air enters the smallercylinder, is compressed evenmore and is delivered to a storagetank or to the main air line.

Two-stage compressors candeliver air to over 175 psi.

They are normally found inoperations requiring compressedair of 125 psi or greater.

8. What are the benefits of two-stage compressors?

Two-stage compressors areusually more efficient. They runcooler and deliver more air for thepower consumed, particularly inthe over-100 psi pressure range.

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7. Air Compressors (contd)

24

9. Is there anything else toknow, about air compressors?

Because this book mainly focuseson spray guns, it provides onlybasic coverage of air compressorsand how they operate.

There is much more to know:How to select the properequipment in terms of size,delivery, etc.

Compressors may be portable orstationary and there are differentmodels to meet a variety of needs.

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8. Spray Booths

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Introduction

Containing the overspray andkeeping it out of the air and offother objects is an importantconsideration in a spray finishingoperation. This chapter discusses

various types of booths anddetails periodic maintenance.

1. What is a spray booth?

A compartment, room orenclosure of fireproof construction;built to confine and exhaustoverspray and fumes from theoperator and finishing system.

There are various modelsavailable, designed for particularspray applications. Spray boothsmay be partially enclosed (figures1 & 2) or totally enclosed (figure3).

Consult the National FireProtection Association (NFPA)pamphlet #33 and the O.S.H.A.requirements for constructionspecifications.

2. What are the benefits of aspray booth?

A well-designed and maintainedspray booth provides importantadvantages:

It separates the sprayingoperation from other shopactivities, making the spraying, aswell as the other operations,cleaner and safer.

It reduces fire and health hazardsby containing the overspray.

It provides an area that contains

residue, making it easier to keepclean. It also keeps both theoperator and the object beingsprayed cleaner.

In a booth equipped with adequateand approved lighting, it providesbetter control of the finish quality.

3. What types of spray boothsare there?

There are two; the dry filter typeand the waterwash type.

4. What is a dry filter type spraybooth?

This booth draws overspray-contaminated air throughreplaceable filters and vents thefiltered air to the outside.

It is the most common type ofbooth for most industrial andautomotive applications.

It is used for spraying low-volume,slower-drying materials, and is notaffected by color changes.

Figure 1 - Dry Filter Type Booth

5. What is a waterwash typebooth?

A waterwash booth actuallywashes the contaminatedoverspray air with a cascade ofwater and traps the paint solids.Fewer paint particles reach theoutside atmosphere to harm theenvironment.

Waterwash booths are generallyused when spraying high volumesof paint.

Figure 2 - Waterwash Industrial TypeSpray Booth

Figure 3 Automotive Downdraft DryFilter Booth

6. What is an exhaust fan?

A typical exhaust fan consists of amotor, a multiple blade fan,pulleys and belts. It removesoverspray from the spray bootharea (see figure 4).

Contemporary exhaust fans arecarefully designed to preventoverspray from coming intocontact with the drive mechanism.

Blades are made of non-sparkingmetal, and they move themaximum volume of

air-per-horsepower againstresistance such as exhauststacks, filters, etc. (See NFPApamphlet #33.)

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8. Spray Booths (Contd)

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Figure 4 Exhaust fan

7. What is air velocity?

Air velocity in a finishing operationis the term used to describe the

speed of air moving through theempty spray booth.

8. What effect does air velocityhave on spray booth efficiency?

Air must move through the boothwith sufficient velocity to carryaway overspray.

Too low a velocity causes poor,even potentially dangerousworking conditions, especially

when the material contains toxicelements. It also increasesmaintenance costs.

Too high a velocity wastes powerand the energy required to heatmake-up air.

9. What is a manometer?

It is a draft gauge that indicateswhen paint arrestor filters or intakefilters are overloaded. (see figure

5)Some states and local codesrequire a manometer gauge oneach bank of filters to comply withOSHA regulations.

Figure 5 - Manometer

10.What does an airreplacement unit do?

The volume of air exhausted froma spray booth is often equal tothree or more complete airchanges per hour.

Under such conditions, the

temperature may become irregularand uncomfortable. Excessivedust may become a problem.

To prevent these conditions,sufficient "make-up" air must beintroduced to compensate for theexhausted air.

The air replacement unitautomatically supplies this"makeup" air - both filtered andheated - to eliminate the problemsof air deficiency and airbornecontaminants.

Figure 6 - Air Replacement Unit

11. What routine maintenancedoes a dry type spray boothrequire?

(a) The continuous f low of airthrough the booth eventuallyloads the filters with dirt andoverspray. Periodically, inspectand replace them with multi-

stage filters, designed for spraybooth use. Single-stagefurnace filters will notdo the

job.

(b) Monitor the manometer readingdaily, and know what a normalreading should be.

(c) Keep the booth free of dirt andoverspray. Floors and wallsshould be wiped down afterevery job. Pick up scrap,newspapers, rags, etc.

(d) Coat the inside of the boothwith a strippable, spray-oncovering. When the oversprayon it becomes too thick, stripand recoat.

(e) Periodically check the lighting

inside the booth, and replaceweak or burned out bulbs.Improper lighting can cause theoperator to apply a poor finish.

12. What routine maintenancedoes a waterwash type boothrequire?

(a) Compounding of the water inthis type unit is essential.Employ only booth treatmentchemicals in accordance with

suppliers' recommendations.The ph of the water should bebetween 8 and 9.

(b) Maintain the water level at theproper setting permanufacturers' specifications.

(c) Check the tank for paintbuildup on the bottom, checkthe pump strainer to keep itclean and clear, check the airwasher chamber and thenozzles in the header pipe. If

the nozzles are plugged, theoverspray will encroach on thewash baffle section, fan andstack.

(d) Periodically check the floatvalve for proper operation.Flood the sheet to be surethere is a uniform flow overthe entire surface.

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8. Spray Booths (Contd)

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(e) Keep the booth interior andexhaust stack free fromoverspray and dirtaccumulation.

13. What checks can be used toassure good results from aspray booth?

(a) Keep the interior of the boothclean.

(b) Maintain and replace intakeand exhaust filters whennecessary.

(c) Caulk all seams and crackswhere dirt might enter.

(d) Maintain and clean allequipment used in the booth.

(e) Keep operators' clothing cleanand lint-free.

(f) Perform routine maintenanceabove on a scheduled basis.

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NOTES


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Documents

ABC of Spraying