In considering pneumatic painting equipment, the most important thing to be kept in mind is the proper application of materials. This can be successfully accomplished only thru the use of compressed air at low pressures. By this is meant using only sufficient main-line air to lay the paint, enamel, varnish or whatever finish may be used, on the object. Excessive pressure results in fumes, waste of material and air reduction taking place. By air reduction is meant the removal of the more volatile solvents, thinners, binders, etc., thru evaporation, and the material thus loses its adherent and coherent properties.
Both types of air-brush equipment illustrated here require three cubic feet of air per minute to operate and the pressure necessary depends on the density, consistency or viscosity of the material used. For example, undercoaters, japans, etc.; require from twelve to fifteen pounds of pressure to apply perfectly; while enamels and varnishes take from eighteen to twenty-five pounds. Water stains require about five pounds of pressure.
35. Construction of Pneumatic Painting Outfit.—A pneumatic painting outfit for finishing work consists essentially of an air brush, either of the attached-container type or the gun-type with separate paint tank, and a small compressor of sufficient capacity to operate the air brush, which can be belt-driven from shafting or direct connected. An exhaust hood with fan, for the removal of fumes, is advisable where the operation is reasonably continuous and especially where lacquers are used. The paint, ready for application, is poured into the tank; and the compressed air line leads to the tank with a branch line for air and paint from the tank to the nozzle of the gun type of machine; while only the air line is required with the attached-container type.
The air hose used is 5/16" in diameter while the paint or fluid hose is the same size. The paint hose is made of a special compound to resist the action of the thinners, solvents, etc., used in the paint; and it is important to have this correct, so that the lining will not disintegrate and clog the air brush or gun.
Fig. 11 shows a five-gallon container type. It will be noticed that the fluid connection is nearest the nozzle and that the air connection is at the bottom of the grip.
Fig. 11. A five-gallon air brush outfit
36. Special Attachments for Different Surfaces.—A cone nozzle is furnished for painting irregular surfaces and a fan nozzle for wide, flat work. Adjusting and locking the nozzle regulates the degree of atomization. The jets of the fan nozzle are depressed to prevent being knocked out of alignment. Final regulation of the flow of material is made on the back of the gun, independent of the pressure on the material container. A wide variety of adjustment is possible with this positive regulation.
The first pull on the trigger gives air only, which can be used for dusting ahead of the work; and as the trigger is released, the air valve closes last, which prevents clogging and dripping. When adjustments have been made the trigger action is the only moving part of the machine. Figs. 12 and 13 show the five-gallon container type in actual use.
Fig. 12. Using pneumatic paint sprayers