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ABCs of Spray PaintingABCs of Spray Painting$10.00 A-2928-AForward Table of Contents2While 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 tojust 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 materialsroutinely 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 isyour 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 finishingskills.A recent addition to resourcesavailable to the spray finisher isthe World Wide Web. Manymanufactures are represented andquestion and answer forums areavailable. Please visit our .t andAbout this book.This book has been updatedseveral times from “The ABCs ofSpray Equipment,” originallypublished by The DeVilbissCompany in 1954. It focuses onequipment and techniques forspray 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 controlequipment, 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 andas 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 .21. Introduction .3Surface Preparation.3Paint Preparation32. Air Atomizing SprayGuns.4Spray Gun Types .4Part Identification andFunction.6Operation .9Maintenance .11Troubleshooting .133. Material Containers.164. Hose and Connections 185. Air Control Equipment.206. Respirators .227. Air Compressors.238. Spray Booths .25.1. Introduction3This 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 standardsurface 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 togreat 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 PreparationThe 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 PreparationTodays 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 ata 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 getyou 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.32. Air Atomizing Spray Guns4IntroductionThe spray gun is the keycomponent in a finishing system. Itis a precision engineered andmanufactured instrument. Eachtype and size is specificallydesigned to perform a certain,defined range of tasks.As in most other areas of finishingwork, having the right tool for thejob 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 TYPES1. 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 tothe 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 cupSuction feed is easily identified bythe fluid tip extending slightly be-yond the face of the air cap, seefigure 2.Figure 2 - Suction Feed Air CapSuction feed guns are suited tomany color changes and to smallamounts of material, such as inautomotive panel/bumper repairsand completes, touchup, orlower 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 suctionfeed gun, and usually have lessoverspray.Figure 3- Gravity Feed Gun withattached cup2. Air Atomizing Spray Guns (Contd)55. 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 potThis 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 fleetrefinishing operation is a typicaluse of a pressure feed systemFigure 5 - Pressure Feed Air CapType Viscosity Fluid Atomizing TypeFeed (#2 Zahn) Oz/Minute Pressure ProductionSuction up to 24 10-12 40-50 LowGravity up to 24 10-1212-2430-50 LowPressure up to 29 50-60 High6. 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 Gun7. 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-dryingmaterial is being sprayed, or whena high quality finish is required.Figure 7 - Internal Mix Air Cap8. 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-velocitypattern 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 calledHVLP 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 andnew 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”52. Air Atomizing Spray Guns (Contd)6PART IDENTIFICATIONFUNCTION9. What are the principal partsof a spray gun?Figure 8 - Spray Gun Anatomy10. 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, the fluid 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 BluntFigure 9 - Types of Spray PatternsThere are various styles of caps toproduce different sizes andshapes of patterns for manyapplications.12. What are the advantages ofthe 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 Cap13. How should an air cap beselected?The following factors must be con-sidered:a) type, viscosity and volume ofmaterial to be sprayedb) 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 theneedle 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 andNeedleAirCapFluidTipFluidNeedleNeedlePackingAirValveSpreaderAdjustmentValveFluidAdjustmentScrew2. Air Atomizing Spray Guns (Contd)715. What is the nozzlecombination?In practice, the air cap, fluid tip,needle and baffle are selected asa unit, since they all work togetherto 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 feedthe 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 sprayedphysical size of object beingfinished/fan pattern sizedesired speed/finish qualitygun model being usedavailable air volume (cfm) andpressure (psi) fromcompressor(1) The type and viscosity of thematerial being sp