ABC's of Spray Finishing

ABC’s of Spray Finishing $10.00 1-239-C 11/01

ABC’s of Spray Finishing Forward Table of Contents While this book examines the About this book..... Forward...... 2 spray finishing operation and its This book has been updated equipment from many viewpoints, several times from “The ABC’s of 1. Introduction...... 3 there is still much more to be Spray Equipment,” originally learned to become truly proficient Surface Preparation ...... 3 published by The DeVilbiss at spray finishing. Company in 1954. It focuses on Paint Preparation ...... 3 equipment and techniques for spray finishing. The best way to become proficient 2. Air Atomizing Spray Guns...... 4 at spray finishing is to just do it! Many trade technical and The format of the original book was Spray Gun Types ...... 4 community colleges offer courses question-and-answer. We have in spray finishing, a great way to retained that format in this edition. Part Identification and improve your skills. Function...... 6

This book is organized around the Operation...... 9 Many of the “tricks” of the major components of an air spray professional spray finisher involve Maintenance ...... 11 system… spray guns, material paints and coatings. The containers, hose, air control manufacturers of these materials Troubleshooting ...... 13 equipment, compressors, spray routinely publish complete books booths, respirators and a short on these subjects. These section on general cleanliness and publications are available in 3. Material Containers ...... 16 other sources of information. A specialty paint stores and will thorough understanding of the provide you with considerable material in this book - plus a lot of detail. Many of these books also 4. Hose and Connections...... 18 actual spray painting practice - contain information on techniques should enable you to handle just for surface preparation. about any spray painting situation. 5. Air Control Equipment...... 20

Another important source of Although we have made an effort Respirators information, particularly on 6...... 22 to make this book as detailed and equipment use and selection is as complete as possible, be aware your local spray finishing that the equipment and product 7. Air Compressors ...... 23 equipment distributor. No book systems used to illustrate points could ever completely cover a are entirely based on DeVilbiss specialist’s in-depth knowledge of technology. DeVilbiss is the world’s 8. Spray Booths ...... 25 equipment, techniques, oldest and largest manufacturer of maintenance and troubleshooting. spray painting equipment, and has maintained this leadership since its founding in 1888. Information is available from many resources on the subject of spray finishing. It is our hope that this book will provide you with a start toward perfecting your finishing skills.

A recent addition to resources available to the spray finisher is the World Wide Web. Many manufactures are represented and question and answer forums are available. Please visit our website at www.devilbiss.com.

2 1. Introduction This book is about the selection, Plastic parts may contain static and how much film may be applied use and maintenance of finishing electricity from the molding is its viscosity…or consistency. equipment: spray guns, tanks, process. This static attracts Following the paint manufacturer’s cups, hoses, compressors, particles of dust and dirt. Eliminate instructions will get you close, but regulators, spray booths, them by treating with “destatisiz- for professional results, use a respirators, etc. It presumes that ing” air using a special blow-off viscosity cup. It is a simple but very you are familiar with standard gun that imparts a neutral charge accurate way to measure the surface preparation techniques that to the airflow. A chemical anti-static thickness of paint. With the cup, may be required before finishing treatment is also available. you can thin or reduce the paint to actually begins. It also presumes a the precise consistency required by basic knowledge of the many the manufacturer. different types of paints and Paint Preparation Always prepare paint in a clean, coatings available. Today’s finishes are extremely dust-free environment. Paint has a Creating a perfect finish requires a complex chemical formulations. remarkable ability to pick up dirt. solid knowledge of surface They include both solvent and Dirty paint will not only clog your preparation, finishes and spray waterborne types. Some may spray gun, but it will also ruin your painting equipment. The first two require the addition of solvents to paint job. Get in the habit of always are extensively covered in many form the proper spraying viscosity. pouring paint into the cup or tank other books. The manufacturers of Others may simply require the through a paint strainer. Paint is paints and coatings have gone to addition of a second component at never as clean as it looks. great length to publish information a prescribed ratio to obtain on their new and existing products. sprayable consistency. Many of them also have hardeners or other But, even an extensive knowledge chemicals, added to them to insure of surface preparation techniques correct color match, gloss, and paint chemistry is not enough hardness, drying time or other to assure a professional finish. The characteristics necessary to finish must be applied by a spray produce a first class finish. Make gun, and all the variables of its use sure you are familiar with the must be mastered. specific finish material data sheets The equipment necessary to apply accompanying each material. Do the finish – the spray gun, tank, not mix materials from various cup, regulator, hoses, compressor, manufacturers. Read and follow etc. – must all be matched to the directions carefully. job as well as to each other. That All finish materials must also be equipment must be used and supplied with a Material Safety maintained properly, with an Data Sheet (MSDS). This data appreciation of how and why it provides information on proper works the way it does. handling and disposal of materials. The moment of truth for any finish Many states require that MSDS be happens when the trigger is pulled. kept on file by the user. This book focuses on that moment. The first step is knowing the type and color of paint the project requires. With this determined, Surface Preparation follow the manufacturer’s The surface to be finished should instruction for preparing it exactly. be well cleaned before painting. If If you have any doubts about how the paint manufacturer’s to proceed, don’t guess! Contact instructions call for it, the surface your paint supplier for help. should be chemically treated. Use Improperly prepared paint will a blow-off gun and tack rag to never produce a good finish! remove all dust and dirt. No The chief characteristic that amount of primer or paint will cover determines the sprayablility of paint up a badly prepared surface.

3 2. Air Atomizing Spray Guns Introduction Figure 4 shows a material container Suction feed is easily identified some distance away from its by the fluid tip extending slightly The spray gun is the key pressure feed gun. beyond the face of the air cap, component in a finishing system. It see figure 2. is a precision engineered and The type of material feed system is manufactured instrument. Each also a way of classifying guns: type and size is specifically Suction Feed...draws material to designed to perform a certain, the gun by suction as in Figure 1. defined range of tasks. Gravity Feed...the material travels As in most other areas of finishing down, carried by its own weight work, having the right tool for the and gravity as in Figure 3. job goes a long way toward get- ting professional results. Pressure Feed...the material is fed by positive pressure as in Figure 4. This chapter will help you know which is the proper gun by review- Guns may also be classified as Figure 2 - Suction Feed Air Cap ing the Conventional Air and High either external or internal mix Volume/Low Pressure spray gun depending upon the type of air Suction feed guns are suited to designs commonly used in finish- cap. many color changes and to small ing – suction feed, gravity feed and amounts of material, such as in pressure feed. It will also review the touchup or lower production different types of guns and 3. What is a suction feed gun? operations. components within each design. A spray gun design in which a A thorough understanding of the stream of compressed air creates a 4. What is a gravity feed gun? differences between systems will vacuum at the air cap, providing a allow you to select the right gun, to siphoning action. Atmospheric This design uses gravity to flow the use it properly to produce a high pressure on the material in the suc- material from the cup, which is quality finish and to contribute tion cup forces it up the suction mounted above the gun, into the toward a profitable finishing tube, into the gun and out the fluid gun for spraying. No fluid pick-up operation. tip, where it is atomized by the air tube is used, since the fluid outlet cap. The vent holes in the cup lid is at the bottom of the cup. must be open. This type gun is This cup has a vent hole at the top SPRAY GUN TYPES usually limited to a one-quart, or of the cup that must remain open. smaller, capacity container and low 1. What is an air spray gun? It is limited to 32 ounce capacities to medium viscosity materials. due to weight and balance. An air spray gun is a tool which uses compressed air to atomize Gravity feed guns are ideal for paint, or other sprayable material, small applications such as spot and to apply it to a surface. repair, detail finishing or for finishing in a limited space. They require Air and material enter the gun less air than a suction feed gun, through separate passages and are and usually have less overspray. mixed at the air cap in a controlled pattern.

2. What are the types of air spray guns? Air spray guns may be classified in various ways. One way is by the location of the material container: Figure 1 shows a gun with a cup attached below it. Figure 1- Suction Feed Gun with Figure 3 shows a gun with a cup attached cup Figure 3 - Gravity Feed Gun with attached above it. attached cup

4 2. Air Atomizing Spray Guns (Cont’d) 8. What is HVLP? A DeVilbiss Pro Tip: Type Viscosity Fluid Atomizing Type Feed (#2 Zahn) Oz/Minute Pressure Production When using a gravity feed system, Suction up to 24 10-12 40-50 Low HVLP, or High-Volume/Low downsize the tip one size from suction. Gravity up to 24 10-12 30-50 Low Pressure, uses a high volume of air If the suction system calls for a .070", Pressure up to 29 30-Oct 50-60 High (typically between 10-26 CFM) use a .055" or .063" HVLP up to 29 14-16 10 High delivered at low pressure (10 PSI or Table 1 less at the air cap) to atomize paint 5. What is a pressure feed gun? into a soft, low-velocity pattern of In this design, the fluid tip is flush 6. What is an external mix air particles. with the face of the air cap (see cap? In many cases, less than 10 psi is Figure 5). The material is This gun mixes and atomizes air needed in order to atomize. pressurized in a separate cup, tank and fluid outside the air cap. or pump. The pressure forces the Proper setup utilizes no more fluid material through the fluid tip and to It can be used for applying all and air pressure than is needed to the air cap for atomization. types of materials, and it is produce the required quality and a particularly desirable when flow rate that will meet production spraying fast drying paints such requirements. as lacquer. It is also used when a As a result, far less material is lost high quality finish is desired. in overspray, bounceback and blowback than with conventional air spray. This is why HVLP delivers a dramatically higher transfer efficiency (the amount of paint that adheres to the substrate compared to the amount of paint sprayed) than spray systems using a higher atomizing pressure. Figure 6 - External Mix Gun The HVLP spray gun resembles a standard spray gun in shape and operation. Models that use high 7. What is an internal mix cap? inlet pressure (20-80 psi) and This cap mixes air and material convert to low pressure internally inside the air cap, before expelling within the spray gun are called Figure 4 - Typical Pressure Feed them. HVLP conversion guns. Gun with remote pot It is normally used where low air Some HVLP models, particularly This system is normally used when pressures and volumes are those using turbines to generate large quantities of material are to available, or where slow-drying air, bleed air continuously to be applied, when the material is materials are being sprayed. minimize back-pressure against too heavy to be siphoned from a the air flow of the turbine. container or when fast application A typical example is spraying flat is required. Production spraying in wall paint, or outside house paint, The air cap design is similar to that a manufacturing plant is a typical with a small compressor. of a standard spray gun, with a use of a pressure feed system. variety of air jets directing the Internal mix caps are rarely used atomizing air into the fluid stream, for finishing when a fast-drying atomizing it as it leaves the tip. material is being sprayed, or when a high quality finish is required. HVLP is growing in popularity and new environmental regulations are requiring it for many applications. HVLP can be used with a wide variety of materials, including two-component paints, urethanes, acrylics, epoxies, enamels, Figure 5 - Pressure Feed Air Cap lacquers, stains, primers, etc.

Figure 7 - Internal Mix Air Cap

5 2. Air Atomizing Spray Guns (Cont’d) PART IDENTIFICATION There are various styles of caps to c) material feed system used FUNCTION produce different sizes and shapes (pressure, suction or gravity) of patterns for many applications. 9. What are the principal parts of d) size of fluid tip to be used (most a spray gun? air caps work best with certain fluid tip/needle combinations) 12. What are the advantages of the multiple jet cap? e) volume of air in cubic feet per minute (cfm) and pressure in This cap design provides better pounds per square inch (psi) atomization of more viscous available. materials. See the DeVilbiss spray gun It allows higher atomization catalog for proper selection of pressures to be used on more air cap / fluid tip / needle viscous materials with less danger combinations and typical uses. of split spray pattern. It provides greater uniformity in pattern due to better equalization 14. What is the function of the Figure 8 - Spray Gun Anatomy of air volume and pressure from the fluid tip and needle? cap. They restrict and direct the flow of 10. What happens when the It also provides better atomization material from the gun into the air trigger is pulled? for materials that can be sprayed stream. The fluid tip includes an with lower pressures. internal seat for the tapered fluid The trigger operates in two stages. needle, which reduces the flow of Initial trigger movement opens the material as it closes. air valve, allowing air to flow (see Figure 11). through the gun. The amount of material that leaves Further movement of the trigger the front of the gun depends upon pulls the fluid needle from its seat the viscosity of the material, the at the fluid tip, allowing fluid material fluid pressure and the size material to flow. When the trigger is of the fluid tip opening provided released, the fluid flow stops before when the needle is unseated from the air flow. the tip. This lead/lag time in the trigger Figure 10 - Multiple Jet External Mix Fluid tips are available in a variety operation assures a full spray Air Cap of sizes to properly handle pattern when the fluid flow starts. materials of various types, flow It also assures a full pattern until rates and viscosity. the fluid flow stops, so there is no 13. How should an air cap be coarse atomization. selected? The following factors must be 11. What is the function of the considered: air cap? a) type, viscosity and volume of The air cap (see figure 10) directs material to be sprayed compressed air into the fluid b) size and nature of object, or stream to atomize it and form the surface to be sprayed (multiple, or spray pattern. (see Figure 9) larger, orifices increase ability to Round Tapered Blunt atomize more material for faster painting of large objects). Figure 11 - The Fluid Tip and Fewer, or smaller orifices usually Needle require less air, produce smaller spray patterns and deliver less material. (These caps are designed for painting smaller objects and/or using slower speeds) Figure 9 - Types of Spray Patterns 6 2. Air Atomizing Spray Guns (Cont’d) 15. What is the nozzle Rule of thumb Rule of thumb combination? Optimum fluid pressures are 8-20 The lower the viscosity of the In practice, the air cap, fluid tip, psi. Pressures greater than this material, the smaller the I.D. of needle and baffle are selected as a generally indicate the need for a the fluid tip. unit, since they all work together to larger fluid tip size. produce the quality of the spray pattern and finish. These four items, as a unit, are referred to as 17. How are fluid tip and needle Material Production Tip Viscosity Rate Size the nozzle combination. sizes identified? #2 Zahn DeVilbiss fluid tips and needles are up to 23 sec Low FX(.042) 16. What are standard fluid tip identified by the letters stamped on 23-28 sec Med FF(.055) sizes and flow rates? the tip and the needle. 28-48 sec High E(.070) over 48 sec High D(.086) The standard sizes, corresponding The identification letters on these components should match. See fluid tip opening dimensions and Table 4 flow rates are: the appropriate DeVilbiss spray gun catalog for the proper selection of NOTE: Viscosity conversion charts Conventional Air Spray fluid tip and needle combinations. are available to convert one Tip ID Flow Rate viscosity cup reading to another Pressure Feed Systems from any material or equipment G .028"/.7mm up to 12 oz/min 18. What fluid tip and needle supplier. combination sizes are most FX .0425"/1.1mm up to 20 oz/min (2) The physical size of the object common? FF .055"/1.4mm up to 30 oz/min to be painted must also be E .070"/1.8mm over 30 oz/min E, EX, FF and FX are most considered. As a general rule, use EE .070"/1.8mm porcelain enamel generally used. The EX the largest possible spray pattern D .086"/2.2mm heavy body mtls combination is used for suction consistent with the object size. AC .110"/2.75mm heavy body mtls feed, while FF and FW are used for Remember that different air caps Suction Feed Systems gravity Feed. For pressure feed the deliver various pattern characteris- EX .070"/1.8mm up to 12 oz/min most common tips are FX, FF tics. This can reduce both spraying FW .062"/1.6mm up to 10 oz/min and E. time and the number of gun Gravity Feed Systems passes. FF .055"/1.4mm up to 30 oz/min (3) The next consideration in FW .062"/1.6mm up to 30 oz/min 19. How are nozzle combinations evaluating nozzle combinations is selected? Table 2 the speed with which the finish will Five basic considerations are be applied and the desired level of HVLP involved in selecting the nozzle quality. com-bination: Tip ID Flow Rate For speed and coverage, choose a Pressure Feed Systems • type and viscosity of material nozzle combination which FX .0425"/1.1mm up to 10 oz/min being sprayed produces a pattern as wide as FF .055"/1.4mm up to 14 oz/min possible. E .070"/1.8mm up to 20 oz/min • physical size of object being D .086"/2.2mm over 20 oz/min finished/fan pattern size When quality is the deciding factor, choose a nozzle combination Suction Feed Systems • desired speed/finish quality D .086"/2.2mm up to 9 oz/min which produces fine atomization DE .070"/1.8mm up to 8 oz/min • gun model being used and a smaller pattern size, thereby giving greater application control. Gravity Feed Systems • available air volume (cfm) and FF .055"/1.4mm up to 12 oz/min pressure (psi) from compressor (4) The model of the gun itself will FW .062"/1.6mm up to 12 oz/min limit the selection of nozzle (1) The type and viscosity of the combination. Table 3 material being sprayed is the first factor to consider. For a DeVilbiss suction feed gun, there are several nozzle types available which are suitable for finishing operations. These nozzles

7 2. Air Atomizing Spray Guns (Cont’d) have fluid tip openings ranging air cap, will not be able to atomize Viscosity recommendations may from .062" to.086", and are it properly causing a center-heavy be given in poise and centipoise designed to handle viscosities up pattern. (1 poise=100 centipoise). Viscosity to 28 seconds in a No. 2 Zahn conversion may be accomplished If the fluid tip opening is too large, Viscosity Cup. by consulting a viscosity material discharge control will conversion chart. For a DeVilbiss pressure feed gun, be lost. the amount of material discharged The fluid tip/air cap combination depends upon material viscosity, must be matched to each other 23. What is the spreader adjust- inside diameter of the fluid tip, and to the job at hand. Spray gun ment valve? length and size of hose, and catalogs include charts to help pressure on the material container A valve for controlling the air to the you match them properly. or pump. horn holes which regulate the spray pattern from maximum width down If the fluid tip opening is too small, to a narrow or round pattern the paint stream velocity will be too 21. Of what metals are fluid tips (see figure 8). high. If the fluid tip opening is too made? large, you will lose control over the Tips are made of the following material discharging from the gun. metals: 24. What is the fluid needle For most HVLP guns, the paint adjustment? a) 300-400 grade stainless steel for flow shouldn't exceed 16 oz. per both non-corrosive and corrosive This adjustment controls the minute. For higher flow rates, materials distance the fluid needle is allowed consult the DeVilbiss HVLP Spray to retract from its seat in the fluid Gun catalog. c) Carboloy inserts for extremely tip, which allows more or less abrasive materials (5) Available air supply is the last material through the fluid tip factor to consider. (see figure 14). Pressure feed air caps consume 22. What is viscosity? With pressure feed systems, the fluid delivery rate should be between 7.0 and 25.0 CFM, The viscosity of a liquid is its body, adjusted by varying the fluid depending on design. If your air or thickness, and it is a measure pressure at the pressure pot. Use supply is limited, because of an of its internal resistance to flow. the fluid adjustment knob for minor undersize compressor, or many Viscosity varies with the type and and/or temporary flow control. This other air tools are in use at once, temperature of the liquid. Any will extend the life of the fluid the gun will be starved for air, reference to a specific viscosity needle and tip. producing incomplete atomization measurement must be and a poor finish. accompanied by a corresponding temperature specification. 25. What are the components of 20. What are the criteria for The most common measurement suction and gravity feed selecting a pressure feed nozzle? used to determine viscosity in systems? finishing is flow rate (measured in While the fluid discharge in ounces Typical suction and gravity feed seconds from a Zahn, Ford, Fisher per minute from a suction feed gun systems consist of: a suction feed or other viscosity cup). is relatively stable (largely because or gravity feed spray gun with cup, it is determined by atmospheric Different viscosity cup sizes are an air compressor (not shown), a pressure), the fluid discharge from available. Each cup has a hole at combination filter/air regulator and a pressure feed gun depends more the bottom, specified to an exact air hoses (see figure 12). upon the size of the inside size. Use a viscosity cup that is diameter of the fluid tip and the designed to handle the time range pressure on the paint container or of the materials in use. Viscosity pump. The larger the opening, the control is an extremely important more fluid is discharged at a given and effective method to maintain pressure. application efficiency and quality consistency. Always measure If the fluid tip ID is too small for the viscosity after each batch of amount of material flowing from the material is mixed and make sure gun, the discharge velocity will be material temperature is the same, too high. The air, coming from the normally 70° to 80° F.

8 2. Air Atomizing Spray Guns (Cont’d) the Troubleshooting Section for (4) If the paint is not atomizing examples of faulty patterns to help properly, increase the air pressure diagnose your problem. slightly and make another test pass. Continue this sequence until the paint particle size is relatively uniform.

Uneven Distribution

Figure 12 – Suction Feed and Gravity Feed System Components

OPERATION 26. How is suction and gravity feed equipment hooked up for Figure 13 - Horizontal Test Pattern operation? (2) If the pattern produced by the Connect the air supply from the above test appears normal, rotate Even Distribution compressor outlet to the filter/air the air cap back to a normal Figure 15- Test Patterns regulator inlet. spraying position and begin spray- Connect the air supply hose from ing. (Example - a normal pattern (5) If the pattern seems starved for the air regulator outlet to the air with a #30 air cap will be about 9" material, and the fluid adjustment inlet on the spray gun. long when the gun is held 8" from screw allows full needle travel, the the surface). fluid tip may be too small or the After the material has been mater-ial may be too heavy. reduced to proper consistency, Recheck the viscosity or increase thoroughly mixed and strained into the size of the fluid tip and needle the cup, attach the gun to the cup (suction feed) or pour material into (6) If the material is spraying too attached cup (gravity feed). heavily and sagging, reduce the material flow by turning in the fluid adjusting screw (clockwise). 27. How are suction and gravity Remember, proper setup utilizes no feed systems initially adjusted for Figure 14 – Fluid Adjustment Screw more fluid and air pressure than is spraying? needed to produce the required (1) Spray a horizontal test pattern quality and a flow rate that will (air cap horns in a vertical position). (3) With the fluid adjusting screw meet production requirements. Hold the trigger open until the paint open to the first thread,(see figure begins to run. There should be 14) and the air pressure set at relatively even distribution of the approximately 30 psi, make a test paint across the full width of the pass (move the spray gun 3 times pattern. (see Figure 13). Adjust the the normal speed) with the gun on pattern width with the spreader some clean paper, cardboard or adjustment valve. If distribution is wood. If there are variations in not even, there is a problem with particle size- specks and/or large either the air cap or the fluid tip globs - the paint is not atomizing that must be corrected. Refer to properly (see figure 15).

9 2. Air Atomizing Spray Guns (Cont’d) 28. What are the components of Open fluid adjustment screw until a pressure feed system? the first thread is visible (see figure 14). A pressure feed system consists of: a pressure feed spray gun, a pressure feed tank, cup or pump, an air 31. How is the pressure feed filter/regulator, appropriate air and gun balanced for spraying? fluid hoses, and an air com-pressor (see figure 16). 1) Using control knob on fluid regulator, set fluid pressure at 5 to 10 psi. 2) Using control knob on air Figure 17 – Air Cap Test Kit regulator, set air atomization pressure at 25-35 psi. After establishing the operating 3) Spray a test pattern (fast pass) pressures required for production on a piece of paper, cardboard, or and finish quality, develop a wood. From that test pattern, Pressure Standardization program determine if the particle size is for your finish room to follow. small enough and relatively uniform throughout the pattern to achieve the required finish quality (see 32. What is a Pressure figure 15). If particle size is too Standardization Program? large or is giving too much texture in the finish, turn the atomization After establishing air and fluid pressure up in 3 to 5 psi pressures that meet required qual- increments until particle size and ity and production, record the data texture of finish is acceptable. to be used for that application for future reference. (see figure 18) 4) Spray a part with these settings. If you are not able to keep up with Booth #: ______the production rate required or if the finish is starved for material, Material Sprayed ______increase the fluid pressure with the Figure 16 - Pressure Feed System Application ______fluid regulator control knob in 2 to Components 4 psi increments until required wet Viscosity ______coverage is accomplished. Fluid Temperature ______29. How is equipment hooked up Note: A larger capacity fluid tip Spray Gun ______for pressure feed spraying? may be required. Air Cap ______Fluid Tip ___ Connect the air hose from the air 5) Remember, as you turn up the fluid pressure the particle size will regulator to the air inlet on the gun. Air Pressure ______increase. Once the coverage Connect the mainline air hose to required is obtained, it will be Fluid Pressure ______the air inlet on the tank. CAUTION: necessary to re-adjust the Do not exceed the container's atomization pressure in 3 to 5 psi Figure 18 – Pressure maximum working pressure. increments as explained in step 3 Standardization Chart Connect the fluid hose from the to insure required particle size and finish texture is achieved. fluid outlet on the tank to the fluid 33. How should the spray gun be inlet on the gun. 6) If using HVLP, using an “Air Cap held? Test Kit”, verify that the air cap pressure in not above 10 psi if It should be held so the pattern is 30. How is the pressure feed gun required by a regulatory agency. perpendicular to the surface at all adjusted for spraying? times. Open spreader adjustment valve Keep the gun tip 8-10 inches (air for maximum pattern size (see spray guns) or 6-8 inches (HVLP figure 8). guns) from the surface being sprayed. 10 2. Air Atomizing Spray Guns (Cont’d) 34. What is the proper technique flat, or nearly flat, surfaces should for spray gun stroke and be sprayed. triggering? Remember to overlap the The stroke is made with a free arm previously sprayed areas by 50% motion, keeping the gun at a right to avoid streaking. angle to the surface at all points of When painting very narrow the stroke. surfaces, you can switch to a Triggering should begin just before smaller gun, or cap with a smaller the edge of the surface to be spray pattern, to avoid readjusting sprayed. The trigger should be held the full size gun. The smaller guns fully depressed, and the gun are usually easier to handle in moved in one continuous motion, restricted areas. until the other edge of the object is A full size gun could be used, reached. The trigger is then however, by reducing the air released, shutting off the fluid flow, pressure and fluid delivery and but the motion is continued for a trigger-ing properly. few inches until it is reversed for the return stroke. When the edge of the sprayed MAINTENANCE object is reached on the return 37. How should the air cap be stroke, the trigger is again fully cleaned? depressed and the motion continued across the object. Figure 19 - Spray Techniques Remove the air cap from the gun and immerse it in clean solvent. If Lap each stroke 50% over the 36. What is the proper spraying necessary, use a bristle brush to preceding one. Less than 50% sequence and technique for clean dried paint. Blow it dry with overlap will result in streaks on the finishing applications? compressed air. finished surface. Move the gun at a constant speed while the trigger is Difficult areas, such as corners and If the small holes become clogged, pulled, since the material flows at a edges, should be sprayed first. Aim soak the cap in clean solvent. If constant rate. directly at the area so that half of reaming the holes is necessary, use the spray covers each side of the a toothpick, a broom straw, or Another technique of triggering is edge or corner. some other soft implement (see referred to as “feathering.” figure 20). Feathering allows the operator to Hold the gun an inch or two closer limit fluid flow by applying only than normal, or screw the spreader Cleaning holes with a wire, a nail or partial trigger travel. adjustment control in a few turns. a similar hard object could Needle travel should be only partial permanently damage the cap by by utilizing the “feathering” enlarging the jets, resulting in a 35. What happens when the gun technique. Either technique will defective spray pattern. is arced? reduce the pattern size. Arcing the stroke results in uneven If the gun is just held closer, the application and excessive over- stroke will have to be faster to spray at each end of the stroke. compensate for a normal amount When the tip is arced at an angle of of material being applied to smaller 45 degrees from the surface (see areas. figure 19), approximately 65% of When spraying a curved surface, the sprayed material is lost. keep the gun at a right angle to that surface at all times. Follow the curve. While not always physically possible, this is the ideal Figure 20 - Cleaning the Air Cap technique to produce a better, more uniform, finish. After the edges, flanges and corners have been sprayed, the

11 2. Air Atomizing Spray Guns (Cont’d) 38. How should guns be cleaned? The solvent is contained, and must Clean the container and add clean be disposed of properly. solvent. Atomization air should be A suction or pressure feed gun with turned off during this procedure. attached cup should be cleaned as Some states’ codes require the use Pressurize the system and run follows: of a gun cleaner, and it is un-lawful the solvent through until clean. to discharge solvent into the Turn off the air to the gun, loosen (Be sure to comply with local atmosphere. the cup cover and remove the fluid codes regarding solvent dispersion tube from the paint. Holding the After cleaning a spray gun in a gun and disposal.) tube over the cup, pull the trigger cleaner, be sure to lubricate as Clean the air cap, fluid tip and tank. to allow the paint to drain back into indicated in Figure 22. Reassemble for future use. the cup. Empty the cup and wash it with clean solvent and a clean cloth. Fill 39. What parts of the gun require it halfway with clean solvent and lubrication? (Figure 22) spray it through the gun to flush The fluid needle packing A, the air out the fluid passages by directing valve packing B and the trigger stream into an approved, closed bearing screw C require daily container. All containers used to lubrication with a non-silicone/ transfer flammable materials should non-petroleum gun lube. be grounded. (Be sure to comply with local codes regarding solvent The fluid needle spring D should disposal). be coated lightly with petroleum jelly or a non-silicone grease Then, remove the air cap, clean (ie. Lithium). it as previously explained, and replace it on the gun. Lubricate each of these points after every cleaning in a gun washer! Wipe off the gun with a solvent- soaked rag, or if necessary, brush the air cap and gun with a fiber brush using clean-up liquid or thinner.

To clean a pressure feed gun with Figure 21 - Using a Hose Cleaner remote cup or tank, turn off air sup-ply to cup or tank. Release Use a hose cleaner to clean materi-al pressure from the system internal passages of spray guns by opening relief valve. and fluid hose. This device incorporates a highly efficient fluid Material in hoses may be blown header, which meters a precise back. The lid must be loose and solvent/air mixture. The cleaner fluid pressure off. Keep gun higher operates with compressed air and than container, loosen air cap and sends a finely - atomized blast of trigger gun until atomizing air solvent through the fluid passages forces all material back into the of the hose, the spray gun, etc. pressure vessel. This simple, easy to use cleaner A gun cleaner may be used for speeds up equipment cleaning and Figure 22 - Lubrication Points either type of gun. This is an saves solvent. Savings may be as enclosed box-like structure much as 80%. It also reduces VOC (vented) with an array of cleaning emissions. (Be sure that both the nozzles inside. hose cleaner and gun are Guns and cups are placed over the properly grounded.) nozzles, the lid is closed, the valve Where local codes prohibit the use is energized, and the pneumatically of a hose cleaner, manually controlled solvent sprays through backflush the hose into the cup or the nozzles to clean the equipment. tank with solvent until clean and dry with compressed air.

12 2. Air Atomizing Spray Guns (Cont’d) Problem Cause Correction

Fluid leaking from packing nut 1. Packing nut loose 1. Tighten, do not bind needle 2. Packing worn or dry 2. Replace or lubricate

Air leaking from front of gun 1. Sticking air valve stem 1. Lubricate 2. Foreign matter on air valve 2. Clean or seat 3. Worn or damaged air valve 3. Replace or seat 4. Broken air valve spring 4. Replace 5. Bent valve stem 5. Replace 6. Air valve gasket damaged 6. Replace or missing

Fluid leaking or dripping from 1. Dry packing 1. Lubricate front of pressure feed gun 2. Packing nut too tight 2. Adjust 3. Fluid tip or needle worn 3. Replace tip and needle with or damaged lapped set 4. Foreign matter in tip 4. Clean 5. Fluid needle spring broken 5. Replace 6. Wrong size needle or tip 6. Replace

All Feed Systems Jerky, fluttering spray 1. Loose or damaged fluid 1. Tighten or replace tip/seat 2. Lubricate packing or tighten 2. Dry packing or loose fluid packing nut needle packing nut 3. Refill 3. Material level too low 4. Hold more upright 4. Container tipped too far 5. Backflush with solvent 5. Obstruction in fluid passage 6. Loose or broken fluid tube 6. Tighten or replace or fluid inlet nipple

Suction Feed Only 7. Material too heavy 7. Thin or reduce 8. Air vent clogged 8. Clear vent passage 9. Loose, damaged or dirty lid 9. Tighten, replace or clean coupling nut 10. Fluid tube resting on cup 10. Tighten or shorten bottom 11. Damaged gasket behind 11. Replace gasket fluid tip

13 2. Air Atomizing Spray Guns (Cont’d) Problem Cause Correction

Top or bottom-heavy spray 1. Horn holes plugged 1. Clean, ream with non-metallic pattern* point (ie. toothpick) 2. Obstruction on top or bottom 2. Clean of fluid tip 3. Cap and/or tip seat dirty 3. Clean

Right or left-heavy spray 1. Horn holes plugged 1. Clean, ream with non-metallic pattern* point (ie. toothpick) 2. Dirt on left or right side of 2. Clean fluid tip

*Remedies for the top, bottom, right, left heavy patterns are: 1. Determine if the obstruction is on the air cap or fluid tip. Do this by making a solid test spray pattern. Then, rotate the cap one-half turn and spray another pattern. If the defect is inverted, obstruction is on the air cap. Clean the air cap as previously instructed. 2. If the defect is not inverted, it is on the fluid tip. Check for a fine burr on the edge of the fluid tip. Remove with #600 wet or dry sand paper. 3. Check for dried paint just inside the opening. Remove paint by washing with solvent.

Center-heavy spray pattern 1. Fluid pressure too high for 1. Balance air and fluid pressure atomization air (pressure feed) Increase spray pattern width 2. Material flow exceeds air 2. Thin or reduce fluid flow cap’s capacity 3. Spreader adjustment valve set 3. Adjust too low 4. Atomizing pressure too low 4. Increase pressure 5. Material too thick 5. Thin to proper consistency

Split spray pattern 1. Fluid adjusting knob turned 1. Back out counter-clockwise to in too far increase flow 2. Atomization air pressure too 2. Reduce at regulator high 3. Fluid pressure too low 3. Increase fluid pressure (pressure feed) 4. Fluid tip too small 4. Change to larger tip

14 2. Air Atomizing Spray Guns (Cont’d) Problem Cause Correction

Starved spray pattern 1. Inadequate material flow 1. Back fluid adjusting screw out to first thread or increase fluid pressure 2. Low atomization air pressure 2. Increase air pressure and (suction feed) rebalance gun

Unable to form round 1. Fan adjustment stem not 1. Clean or replace spray pattern seating properly

Dry spray 1. Air pressure too high 1. Lower air pressure 2. Material not properly reduced 2. Reduce to proper consistency (suction feed) and temperature 3. Gun too far from surface 3. Adjust to proper distance 4. Gun motion too fast 4. Slow down

Excessive overspray 1. Too much atomization air 1. Reduce pressure pressure 2. Gun too far from surface 2. Use proper gun distance 3. Improper technique (arcing, 3. Use moderate pace, keeping gun speed too fast) gun parallel to work surface

Excessive fog 1. Too much, or too fast-drying 1. Remix with proper reducer thinner and temperature 2. Too much atomization air 2. Reduce pressure pressure

Will not spray 1. Pressure feed cap/tip used 1. Use suction feed cap/tip with suction feed 2. No pressure at gun 2. Check air lines 3. Fluid needle not retracting 3. Open fluid adjusting screw 4. Fluid too heavy (suction feed) 4. Lower fluid viscosity or change to pressure feed

15 3. Material Containers Introduction The tank is pressurized with clean, regulated, compressed air, which All spray painting systems - from forces the fluid out of the tank the smallest brush to the most through the fluid hose to the gun. sophisticated finishing system- must have containers to hold the The rate of fluid flow is controlled material being applied. by increasing or decreasing the air pressure in the tank. Material container types and sizes vary considerably, depending on A typical pressure feed tank the kind of spraying system being consists of: the shell A, clamp-on used. lid B, fluid tube C, fluid outlet D, regulator E, gauge F, safety relief This chapter will discuss these valve G, and agitator H (see containers, their particular applica- AB figure 3). tions, their construction and Figure 1 - Cup Attachment Styles maintenance. Pressure feed tanks are available with either top or bottom fluid outlets, and with various 5. What capacity does a pressure 1. What are material containers? accessories. feed cup have? Any container which serves as a A pressure feed cup can have a material supply reservoir for the one or two quart capacity. spray gun. These containers are usually made of metal or plastic Anything larger is considered a with capacities of 1/2 pint or more. pressure feed tank, which may be positioned some distance from the gun. 2. What are the types of material containers? There are three common types of cups which attach to the gun itself: Siphon, Gravity and Pressure. There are also remote pressure cups and tanks, which are located away from the gun. See Page 4 for types of guns and systems.

Figure 3 - Pressure Feed Tank 3. Where are cup containers used? 7. Where are pressure feed tanks Cup containers are typically one recommended? quart or less, and are used where relatively small quantities of Pressure feed tanks provide a material are being sprayed. practical, economical method of Figure 2 - Regulated 2 Qt. Pressure feeding material to the gun over Cup extended periods of time. 4. How are material feed cups 6. How do pressure feed tanks They are mostly used in continuous attached to lid assemblies? work? production situations, because the Cups are attached using a lid Pressure feed tanks are closed material flow is positive, uniform assembly (sometimes called a cup containers, ranging in size from and constant. attachment) that either clamps A or about two gallons to 60 gallons. Tanks can be equipped with screws B onto the cup container. They provide a constant flow of agitators (see Figure 3) that keep (see Figure 1) Some lid assemblies material, under constant pressure, the material mixed and in are detachable from the gun, while to the spray gun. suspension. others are integral parts and do not detach from less expensive models.

16 3. Material Containers (Cont’d) 8. When is an agitator used in a 12. What materials are used to pressure feed tank? construct pressure feed tanks? When the material being used has The smaller, non-code, light-duty filler or pigment that must be kept tanks are made of plated steel and in motion to keep its particles in have lower inlet pressure proper suspension. An agitator can restrictions. be hand, air or electrically driven. The heavy-duty, ASME-code tanks are made of galvanized or 300 series stainless steel. They also 9. What is a single regulated have plated or stainless steel lids tank? with forged steel clamps. This is a pressure feed tank with When abrasive or corrosive one air regulator controlling only materials are being sprayed, the the pressure on the material in the tank shell is coated or lined with a tank (see figure 4). special material, or a container insert is used.

13. What are container liners? They are inserts that are placed inside the tank to hold the material, keeping it from direct contact with the tank walls. They are made of disposable polyethylene. Figure 5 - Double Regulated Tank Using liners reduces tank cleaning time and makes color changeover easier. 11. What are code and non-code pressure tanks? Code tanks are manufactured to 14. When would you use a rigid standards as specified by the bottom outlet tank? American Society of Mechanical 1) When you are using very viscous Engineers. (ASME) Each step of materials. manufacture is closely controlled, and welding of the shell is certified. 2) When continuous, steady Code tanks are designed to pressure is required, such as when withstand pressures up to 110 psi. feeding plural component Figure 4 - Single Regulated Tank proportioning equipment. Non-code tanks are normally restricted to 3 gallons in size or 3) When you wish to use all the less. Due to the type of material in the tank and you are not 10. What is a double regulated using an insert. tank? construction, non-code tanks are rated at 80 psi or less. Regulations This is a pressure feed tank may restrict the type of materials 15. What would I use if I have equipped with two air regulators and pressures used with a non- difficulty accurately setting lower (see figure 5). code pressure tank. fluid pressures? One provides regulation for the air pressure on the material in the tank An extra-sensitive regulator is (thereby controlling fluid flow). The available for use with lower fluid other controls atomization air flow and/or lower viscosity pressure to the spray gun. materials where precise control is needed.

17 4. Hoses & Connections Introduction The tube is the interior flexible 5. What sizes of air hose are artery that carries air or fluid recommended? The various types of hose used to material from one end of the hose carry compressed air and fluid The hose from the regulator to a to the other. material to the spray gun are gun or tank should be a minimum important parts of the system. The reinforcement adds strength to of 5/16" ID. Tools requiring more air Improperly selected or maintained the hose. It is located between the may need 3/8" I.D. hose or larger. hose can create a number of tube and cover, and it can be many problems. This chapter will review combinations of materials and the different kinds of hose and reinforcement design. Its design Type Length Size fittings in use, provide guidance in determines pressure rating, selecting the proper types for the flexibility, kink and stretch 0' - 10' 1/4" ID job and cover the maintenance of resistance and coupling retention. General 10' - 20' 5/16" ID hose. The cover is the outer skin of the Purpose 20' - 50' 3/8" ID hose. It protects the reinforcement from contact with oils, moisture, 50' - 100' 1/2" ID 1. What types of hose are used in solvents and abrasive objects. The spray painting? 0' to 20' 5/16" ID cover protects the reinforcement, There are two types: air hose – but does not contribute to hose HVLP 20' - 50' 3/8" ID used to transfer compressed air performance. 50' - 100' 1/2" ID from the air source to the gun, and fluid hose – used only in pressure DeVilbiss hose is color-coded: Figure 3 - Recommended air feed systems to transfer the hose sizes RED or TAN ...... air and water material from its container to the spray gun. GREY...... air w/static ground 6. What is pressure drop? (NOTE: Do not use air hose for BLACK ...... low pressure fluid solvent-based materials.) This is the loss of air pressure due to friction (caused by air flow) 3. What type of tube is used in between the source of the air and fluid hose? the point of use. As the air travels Since the solvents in coatings through the hose or pipe, it rubs would readily attack and destroy against the walls. It loses energy, ordinary rubber compounds, fluid pressure and volume as it goes. hose is lined with special solvent- resistant nylon material that is impervious to common solvents. 7. How can this pressure drop be determined? At low pressure, with short lengths 4. What sizes of fluid hose are of hose, pressure drop is not recommended? particularly significant. As pressure Type Length Size increases, and hose is lengthened, the pressure rapidly drops and General 0' - 20' 1/4" ID must be adjusted. Purpose 10' - 35' 3/8" ID All air hose is subject to pressure 35' - 100' 1/2" ID loss or drop. For example, 1/4" pressure drop is 1 psi per foot and 100' - 200' 3/4" ID 5/16" is 1/2 psi per foot. This pressure loss may result in poor Figure 1 - Basic Hose Construction Figure 2 - Recommended fluid hose atomization. sizes Too often, a tool is blamed for 2. How is hose constructed? malfunctioning, when the real DeVilbiss hose is a performance cause is an inadequate supply of designed combination of three compressed air due to an com-ponents: Tube A, undersized I.D. hose. Reinforcement B and Cover C.

18 4. Hoses & Connections (Cont’d) For optimum spray gun results, 11. What is a threaded- type Care should be taken when the following is recommended: connection? selecting a quick-disconnect air up to 20 ft - 5/16" I.D., over connection. Due to design, most This is a common swivel-fitting 20 ft - 3/8" I.D. Q.D. connections result in type that is tightened with a significant pressure drop. This can wrench.(see figure 4). adversely affect spray guns with 8. How are hoses maintained? higher consumption air caps such as HVLP. Hoses will last a long time if they are properly maintained. Be careful when dragging hose across the floor. It should never be pulled around sharp objects, run over by vehicles, kinked or otherwise abused. Hose that ruptures in the middle of a job can ruin or delay the work. Proper hose cleaning techniques are covered on Pages 11 and 12. The outside of both air and fluid hose should be occasionally wiped down with solvent. At the end of Figure 4 - Threaded-Type every job, they should be stored Connection by hanging up in coils. 12. What is a quick-disconnect type connection? 9. What kinds of hose fittings are This is a spring-loaded, available? male/ female connection system Permanent, crimp type or reusable that readily attaches and detaches fittings are used to connect hoses by hand. No tools are required to air sources or to spray (see figure 5). equipment.

10. What kinds of hose connections are available? Although there are many different styles, the two most common are the threaded and the quick- disconnect types. Remember that elements added to any hose, such as elbows, connectors, extra lengths of hose, etc., will cause a pressure drop. On HVLP systems, quick- disconnects must have larger, ported openings (high flow) to deliver proper pressure for atomization. Because of normal pressure drop in these devices, most are not recommended for use with HVLP. Figure 5 - Quick-Disconnect Type Connection

19 5. Air Control Equipment Introduction 3. What are the types of air Regulators are used in lines already control equipment? equipped with an air filtration The control of volume, pressure device. and cleanliness of the air entering a Air control equipment comes in a spray gun are of critical importance wide variety of types, but it Air regulators are available in a to the performance of the system. basically all performs one or more wide range of cfm and psi of the following functions; air capacities, with and without Following some key installation filtering/cleaning, air pressure pressure gauges and in different principles will help decrease the regulation/indication and air degrees of sensitivity and accuracy. risk of contaminants. For example, distribution through multiple it’s important to use the right size They have main line air inlets and outlets. air compressor for your application. regulated or non-regulated air An overworked air compressor can outlets. produce a significant amount of dirt 4. How does an air filter work? and oil. Additionally, proper piping is very important to help prevent It filters out water, oil, dust and dirt 6. How is an air filter/regulator condensation from forming within before they get on your paint job. installed? Air entering the filter is swirled to the line and contaminating the air Bolt the air filter/regulator A remove moisture that collects in supply. securely to the spray booth wall the baffled quiet zone. This chapter examines the various near the operator. (see Figure 2) Smaller impurities are filtered out types of equipment available to This location makes it convenient by a filter. Accumulated liquid is perform these control functions. to read the gauges and operate the carried away through either a valves. Install the filter/regulator at manual or automatic drain. least 25 feet from the B 1. What is air control equipment? compressed air source. Install the Any piece of equipment installed C takeoff elbow on top of the D between the air source and the main air supply line. point of use that modifies the Piping should slope back toward nature of the air. the compressor, and a E drain leg should be installed at the end of each branch, to drain moisture 2. Why is air control equipment from the main air line. necessary? Use piping of sufficient I.D. for the Raw air, piped directly from an air volume of air being passed, and source to a spray gun, is of little the length of pipe being used. use in spray finishing. Raw air contains small, but harmful, quantities of water, oil, dirt and Minimum Pipe Size Recommendations* other contaminants that will alter Compressor Main Air Line the quality of the sprayed finish. Raw air will likely vary in pressure HP CFM LENGTH SIZE and volume during the job. 1 1/2-2 6-9 Over 50' 3/4" There will probably be a need for 3-5 12-20 Up to 200' 3/4" multiple compressed air outlets to run various pieces of equipment. Over 200' 1" Any device, installed in the air line, Figure 1 - Air Filter 5-10 20-40 Up to 100' 3/4" which performs one or more of 100' - 200' 1" these functions, is considered to 5. What is an air regulator? be air control equipment. Over 200' 1 1/4" This is a device for reducing the 10-15 40-60 Up to 100' 1" main line air pressure as it comes from the compressor. Once set, it 100' - 200' 1 1/4" maintains the required air pressure Over 200' 1 1/2" with minimum fluctuations. Table 1

20 5. Air Control Equipment (Cont’d) *Piping should be as direct as Check the following: possible. If a large number of a) Drain transformer, air receiver fittings are used, larger I.D. pipe and air line of accumulated should be installed to help moisture. overcome excessive pressure drop. b) Be sure the transformer is located at least 25 feet from the air source. c) Main air line should not run adjacent to steam or hot water piping. d) Compressor air intake should not be located near steam outlets or other moisture- producing areas. e) Outlet on the air receiver should be near the top of the tank. f) Check for damaged cylinder head or leaking head gasket, if the air compressor is water cooled. Figure 2 – Air/Filter Regulator Installation g) Intake air should be as cool as possible. 7. How often should the filter/regulator be drained of accumulated moisture and dirt? 9. What causes excessive pres- It depends largely on the level of sure drop on the main line gauge system use, the type of filtration in of the filter/regulator? the air system, and the amount of a) The compressor is too small humidity in the air. to deliver the required air For average use, once-a-day volume and pressure for all drainage is probably sufficient. tools in use. For heavily-used systems, or in b) The compressor is not high humidity, drainage should functioning properly. occur several times daily. c) There is leakage in the air Some units drain automatically line or fittings. when moisture reaches a d) Valves are partially opened. predetermined level. e) The air line, or piping system, is too small for the volume 8. What steps should be taken if of air required. Refer to Table 1, moisture passes through the Page 20. filter/regulator? Since moisture in the spray gun atomization air will ruin a paint job, it must be removed from the air supply. When the compressed air temperature is above its dew point temperature, oil and water vapor will not condense out into solid particles. 21 6. Respirators Introduction 4. What is an air-supplied air before it passes through the respirator? chemical cartridge. Consult with appropriate safety personnel or “Industrial Hygienist” This type is available in both mask The organic vapor respirator is if in doubt as to the suitability of a and visor/hood styles. Both provide normally used in finishing particular respirator before using it. the necessary respiratory operations with standard materials Respirators may not provide protection when using materials (not suited for paints containing protection against eye and skin that are not suitable for organic isocyanates). absorption of chemicals. vapor respirators. Spray finishing creates a certain The visor/hood style provides a amount of overspray, hazardous greater degree of coverage to the vapors and toxic fumes. This is head and neck of the operator. true, even under ideal conditions. Both styles require a positive Anyone near a spray finishing supply of clean, breathable air as operation should use some type of defined by OSHA (Grade D). respirator, or breathing apparatus. This chapter covers various types Figure 3 - Organic Vapor Respirator of equipment for this use.

6. What is a dust respirator and 1. What is a respirator? where is it used? A respirator is a mask that is worn Dust respirators are sometimes over the mouth and nose to used in spray finishing but, in prevent the inhalation of overspray most applications, they are fumes and vapor. unsatisfactory. (see Figure 4)

Figure 1 – Positive Pressure 2. Why is a respirator necessary? Visor/Hood For two reasons: First...some type of respiratory protection is required by OSHA/ NIOSH regulations. Second...even if it wasn't a require- ment, common sense tells you that Figure 4 - Dust Respirator inhaling overspray is not healthy. These respirators are equipped Overspray contains toxic particles with cartridges that remove only of paint pigments, harmful dust solid particles from the air. They and, in some cases, vapor fumes have no ability to remove vapors. which can be harmful to your health. They are effective, however, in preliminary operations such as Depending on design, a respirator Figure 2 – Positive Pressure Mask sanding, grinding and buffing. can remove some, or all, of these Respirator dangerous elements from the air 5. What is an organic vapor around a spray finishing operator. respirator and where is it used? NOTE: This type of respirator, which 3. What types of respirators are covers the nose and mouth, Before using any respirator, used by spray finishing (see Figure 3) is equipped with carefully read the manufacturer’s operators? replaceable cartridges that remove Safety Precautions, Warnings and organic vapors by chemical Instructions. Many respirators are There are three primary types; the absorption. not suitable for use with air-supplied respirator, the organic isocyanates, asbestos, ammonia, Some are designed with pre-filters vapor respirator and the dust pesticides, etc. respirator. to remove solid particles from the

22 7. Air Compressors Introduction relatively high pressures, the piston 5. What is a single stage type compressor is the more compressor? All air tools, spray guns, sanders, commonly used. etc., must be supplied with air This is a piston-type compressor which is elevated to higher with one or more cylinders, in which air is drawn from the pressures and delivered in 3. How does a piston-type atmosphere and compressed to its sufficient volume. The air compressor work? compressor compresses air for final pressure with a single stroke. use in this equipment and is a This design elevates air pressure All pistons are the same size, and major component of a spray through the action of a they can produce up to 125 psi. painting system. This chapter reciprocating piston. As the piston will examine the various types moves down, air is drawn in through an intake valve. As the available. 6. Where are single stage piston travels upward, that air is Compressed air is measured on compressors used? compressed. Then, the now- the basis of volume supplied per compressed air is discharged The application of this compressor unit of time (cubic feet per minute, through an exhaust valve into the is usually limited to a maximum or cfm) at a given pressure per air tank or regulator. pressure of 125 psi. It can be used square inch (psi), referred to as above 125 psi, but above this Piston type compressors are delivery. pressure, two stage compressors available with single or multiple Displacement is the output of air are more efficient. cylinders in one or two-stage by a compressor at zero pressure, models, depending on the volume or free air delivery. and pressure required. 7. What is a two-stage compressor? 1. What is an air compressor? A compressor with two or more An air compressor is a machine cylinders of unequal size in which designed to raise the pressure of air is compressed in two separate air from normal atmospheric steps. pressure to some higher pressure, The first (the largest) cylinder as measured in pounds per square compresses the air to an inch (psi). While normal intermediate pressure. It then atmospheric pressure is about Figure 1 - Piston Type Air Compressor exhausts it into a connecting tube 14.7 pounds per square inch, a called an intercooler. compressor will typically deliver air at pressures up to 200 psi. From there, the intermediate 4. How does a rotary screw pressurized air enters the smaller When selecting a compressor: compressor work? cylinder, is compressed even more Rule of thumb Rotary screw compressors utilize and is delivered to a storage tank or to the main air line. The cubic feet per minute delivered two intermeshing helical rotors in a by an electrically powered 2 stage twin bore case. Air is compressed Two-stage compressors can deliver industrial air compressor is 4 times between one convex and one air to over 175 psi. concave rotor. Trapped volume of the motor's horse power rating. They are normally found in (CFM=4xHP) air is decreased and the pressure is increased. operations requiring compressed air of 125 psi or greater. 2. What types of compressors are most common in spray finishing 8. What are the benefits of two- operations? stage compressors? There are two common types; the Two-stage compressors are usually piston-type design and the rotary more efficient. They run cooler and screw design. deliver more air for the power Because most commercial spray consumed, particularly in the finishing operations consume large Figure 2 – Rotary Screw Air over-100 psi pressure range. quantities of compressed air at Compressor

23 7. Air Compressors (Cont’d) 9. Is there anything else to know, about air compressors? Because this book mainly focuses on spray guns, it provides only basic coverage of air compressors and how they operate. There is much more to know: How to select the proper equipment in terms of size, delivery, etc. Compressors may be portable or stationary and there are different models to meet a variety of needs.

24 8. Spray Booths Introduction 4. What is a dry filter type spray booth? Containing the overspray and keeping it out of the air and off This booth draws overspray- other objects is an important contaminated air through consideration in a spray finishing replaceable filters and vents the operation. This chapter discusses filtered air to the outside. various types of booths and details It is the most common type of periodic maintenance. booth for most industrial and automotive applications. 1. What is a spray booth? It is used for spraying low-volume, slower-drying materials, and is not A compartment, room or enclosure affected by color changes. of fireproof construction; built to confine and exhaust overspray and fumes from the operator and finishing system. Figure 2 - Waterwash Industrial There are various models available, Type Spray Booth designed for particular spray applications. Spray booths may be partially enclosed (figures 1 & 2) or totally enclosed (figure 3). Consult the National Fire Protection Association (NFPA) pamphlet #33 and the O.S.H.A. requirements for construction specifications.

2. What are the benefits of a Figure 1 - Dry Filter Type Booth spray booth? Figure 3 – Automotive Downdraft Dry Filter Booth A well-designed and maintained 5. What is a waterwash type spray booth provides important booth? advantages: A waterwash booth actually 6. What is an exhaust fan? It separates the spraying operation washes the contaminated A typical exhaust fan consists of a from other shop activities, making overspray air with a cascade of motor, a multiple blade fan, pulleys the spraying, as well as the other water and traps the paint solids. and belts. It removes overspray operations, cleaner and safer. Fewer paint particles reach the from the spray booth area It reduces fire and health hazards outside atmosphere to harm the (see figure 4). environment. by containing the overspray. Contemporary exhaust fans are It provides an area that contains Waterwash booths are generally carefully designed to prevent residue, making it easier to keep used when spraying high volumes overspray from coming into contact clean. It also keeps both the of paint. with the drive mechanism. operator and the object being Blades are made of non-sparking sprayed cleaner. metal, and they move the In a booth equipped with adequate maximum volume of air- and approved lighting, it provides per-horsepower against resistance better control of the finish quality. such as exhaust stacks, filters, etc. (See NFPA pamphlet #33.)

3. What types of spray booths are there? There are two; the dry filter type and the waterwash type.

25 8. Spray Booths (Cont’d) multi-stage filters, designed for spray booth use. Single-stage furnace filters will not do the job. (b) Monitor the manometer reading daily, and know what a normal reading should be. (c) Keep the booth free of dirt and overspray. Floors and walls Figure 5 - Manometer should be wiped down after every job. Pick up scrap, 10. What does an air replacement newspapers, rags, etc. unit do? (d) Coat the inside of the booth Figure 4 – Exhaust fan The volume of air exhausted from a with a strippable, spray-on spray booth is often equal to three 7. What is air velocity? covering. When the overspray or more complete air changes per on it becomes too thick, strip Air velocity in a finishing operation hour. and recoat. is the term used to describe the Under such conditions, the speed of air moving through the (e) Periodically check the lighting temperature may become irregular empty spray booth. inside the booth, and replace and uncomfortable. Excessive dust weak or burned out bulbs. may become a problem. Improper lighting can cause 8. What effect does air velocity To prevent these conditions, the operator to apply a poor have on spray booth efficiency? sufficient “make-up” air must be finish. introduced to compensate for the Air must move through the booth exhausted air. with sufficient velocity to carry 12. What routine maintenance away overspray. The air replacement unit does a waterwash type booth automatically supplies this Too low a velocity causes poor, require? “makeup” air - both filtered and even potentially dangerous working heated - to eliminate the problems (a) Compounding of the water in conditions, especially when the of air deficiency and airborne this type unit is essential. material contains toxic elements. It contaminants. Employ only booth treatment also increases maintenance costs. chemicals in accordance with Too high a velocity wastes power suppliers’ recommendations. and the energy required to heat The ph of the water should be make-up air. between 8 and 9. (b) Maintain the water level at the proper setting per 9. What is a manometer? manufacturers’ specifications. It is a draft gauge that indicates (c) Check the tank for paint when paint arrestor filters or intake buildup on the bottom, check filters are overloaded. (see figure 5) the pump strainer to keep it Some states and local codes clean and clear, check the air require a manometer gauge on Figure 6 - Air Replacement Unit washer chamber and the each bank of filters to comply with nozzles in the header pipe. If OSHA regulations. the nozzles are plugged, the 11. What routine maintenance overspray will encroach on the does a dry type spray booth wash baffle section, fan require? and stack. (a) The continuous flow of air (d) Periodically check the float through the booth eventually valve for proper operation. loads the filters with dirt and Flood the sheet to be sure overspray. Periodically, inspect there is a uniform flow over and replacethem with the entire surface. 26 8. Spray Booths (Cont’d)

(e) Keep the booth interior and exhaust stack free from overspray and dirt accumulation.

13. What checks can be used to assure good results from a spray booth? (a) Keep the interior of the booth clean. (b) Maintain and replace intake and exhaust filters when necessary. (c) Caulk all seams and cracks where dirt might enter. (d) Maintain and clean all equipment used in the booth. (e) Keep operators’ clothing clean and lint-free. (f) Perform routine maintenance above on a scheduled basis.

27 NOTES

28 NOTES

29 Sales and Service Through a Nationwide Network of Industrial Distributors

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