It is important to trigger the gun in order to avoid
an uneven coat at the beginning and end of a stroke.
Triggering is the technique of starting the gun moving
toward the area to be sprayed before the trigger is
pulled and continuing the motion of the gun after the
trigger has been released.
You should avoid too much overlapping on each
pass of the gun because an uneven coat will result.
The rate of the stroke should produce a full, wet, even
coat. Once the job is started, it must be completed
Spray Gun Adjustments
Figure 14-42 shows the principal parts of a typical
spray gun. The spreader adjustment dial is used to
adjust the width of the spray pattern. When you turn
the dial to the right, a round pattern is obtained. When
you turn to the left, a fan-shaped pattern results.
As the width of the spray is increased, more
material must be allowed to pass through the gun to
get the same coverage on the increased area. To apply
more material to the area, you should turn the fluid
needle adjustment to the left. If too much material is
applied to the surface, turn the fluid needle
adjustment to the right.
In normal operation, the
wings on the air cap are adjusted to the horizontal
position, as shown in figure 14-43. This provides a
vertical fan-shaped pattern.
Normally, you will be concerned about spray
painting lacquer, enamel, and epoxy materials. The
correct air and fluid pressures used with these
materials vary. There are several pitfalls of incorrect
pressures, some of which are as follows:
Excessive air pressure may cause dusting and
rippling of the finish.
Too little air pressure, coupled with excessive
fluid pressure, causes orange peel.
Excessive fluid pressure causes orange peel
Too little fluid pressure causes dusting.
SEALANTS AND SEALING PRACTICES
Learning Objective: Recognize the types of
sealants and the procedures used for
Sealants are used to prevent the movement of
liquid or gas from one point to another. They are used
in an aircraft to maintain pressurization in cabin areas,
to retain fuel in storage areas, to achieve exterior
surface aerodynamic smoothness, and to weather-
proof the airframe. Sealants are used in general repair
work to maintain and restore seam integrity in critical
areas where structural damage or paint remover has
loosened existing sealants.
TYPES OF SEALANTS
The physical conditions surrounding the seal
govern the type of sealant to be used. Some sealants
are exposed to extremely high or low temperatures.
Other sealants contact fuels and lubricants. There-
fore, it is necessary to use a sealant that has been
compounded for the particular condition. Sealants
are supplied in different consistencies and cure rates.
Basic sealants are classified in three general
categoriespliable, drying, and curing.
Pliable sealants are referred to as one-part
sealants and are supplied ready for use as packaged.
They are solids and change very little during or after
application. Solvent is not used with pliable sealants.
Therefore, drying is not necessary. Except for normal
aging, they remain virtually the same as when they
were packaged. They easily adhere to metal, glass,
and plastic surfaces. Pliable sealants are used around
access panels and doors and in areas where
pressurization cavities must be maintained.
Drying sealants set and cure by evaporation of the
solvent. Solvents are used in these sealants to provide
the desired application consistency. Consistency or
hardness may change when this type of sealant dries,
depending on the amount of solvent it contains.
Shrinkage during the drying process is an important
consideration. The degree of shrinkage also depends
upon the amount of solvent it contains.