MIL-HDBK-1110
(8)
Gun body and handle designed for easy
handling.
(9)
Air inlet from the air hose.
(10) Fluid inlet from fluid hose.
c) Air Nozzle. Two general types of air nozzles are
available: external atomization and internal atomization. In
both types, outer jets of air atomize the wet paint (see Figure
12). In the external type, paint is atomized outside the nozzle,
while in the internal type paint is atomized just inside the
nozzle opening. The type selected depends on the type of paint
to be sprayed and the volume of air available. The external type
is the more widely used. It can be used with paints and most
production work. The spray pattern can be adjusted. A fine mist
can be obtained which can result in a smooth even finish. Nozzle
wear and buildup of dry material are not major problems. The
internal-mix air nozzle requires a smaller volume of air and
produces less overspray and rebound than the external type. The
size and shape of the spray pattern of the internal-mix nozzle
cannot be adjusted. Catalyzed and fast drying paints tend to
clog the openings of internal-air nozzles. These coatings should
be sprayed with an external-mix nozzle.
d) Setting-Up, Adjusting Equipment, and Shutting-Down
Procedures. Both the pressure on the paint and the air pressure
at the gun must be properly regulated to obtain the optimum in
film performance. A properly adjusted nozzle will produce a fan
that is about 8 inches wide, 10 inches from the gun. The shape
of the spray pattern produced may vary from round to oval. The
pattern must have well defined edges with no dry spray at the
ends or heavy film buildup in the middle (Figure 13). Coating
manufacturers provide guidance on appropriate equipment and
pressures for application of their coatings. Additional job-site
adjustments may be necessary. The aim is to obtain a wet looking
film that is properly atomized with as little overspray as
possible. To minimize bounce back and dry spray, the atomizing
air pressure should be kept as low as possible. Common spray
pattern problems and their cause and remedy are listed in Table
12. The gun should be taken apart and cleaned at the end of each
day and the air cap and fluid tip should be cleaned with solvent.
Pivot points and packing should be lubricated with lightweight
oil. Leaving a gun in a bucket of solvent overnight will likely
cause the gun to become plugged and lead to premature failure of
the gun. The shutting-down procedure is detailed in the
instructions supplied by the manufacturer of the spray equipment
and these instructions should be followed. Other worker safety
issues are discussed in the section on safety.
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