Technical data

CHAPTER 4
PAINTING APPLICATION METHODS
4.1 GENERAL.
Spray application is the standard for painting Air Force
aircraft and most other equipment. It is fast, and in the hands
of skilled operators, produces films of good uniformity and
quality. When application is described in this technical
manual without specifying the method, High Volume Low
Pressure (HVLP) spray application is implied. Methods other
than spraying are useful in special cases, particularly in
non-aeronautical or less critical applications. Brush or roller
applications have their place and should be considered as
alternate methods when used with suitable materials. The
painters discretionary use of brush or roller for painting
aerospace equipment should be based on local circumstances
such as health or fire hazards. Additionally, there are some
requirements which demand brush application, such as paint-
ing porous surfaces which require brushing-in for adequate
coverage and penetration.
4.2 SPRAY METHODS.
The Air Force uses several hand-operated spray methods: hot
spray, cold and/or hot airless, air assisted airless, HVLP spray,
and any of these methods in conjunction with electrostatics.
The HVLP method is now the standard spray method used in
the Air Force and meets the requirements of environmental
regulations.
4.2.1 HVLP Spray. In this method, the coating material
is atomized by a high volume of low pressure air through the
spray gun nozzle. The HVLP spray equipment generally
utilizes low pressure (below 20 PSIG) gun cups to assist in
delivery of the coating material to the gun nozzle. Low
pressure air between 1.0 and 10 PSIG is used to atomize the
coating material at the spray head. A high volume of air is
used to push the coating material and form a very soft,
low-velocity pattern. This soft spray generally provides more
consistent coverage and a better overall finish. The HVLP
gun should be held closer to the surface (6 to 10 inches) than
a conventional air spray gun because of the lower speed of the
paint particles. The film thickness generated in a single coat
is often greater than that of conventional air spray systems.
This equipment shall not be used above 10 PSIG at the
nozzle. Pressure should be checked regularly with a nozzle
pressure gauge (see Figure 4-1).
4.2.1.1 HVLP Touch-Up Spray Gun. For minor
touch-up and application of insignias and markings, a small
HVLP spray gun may be used. While designed for applying
quantities less than a quart, it has all of the advantages of the
full size HVLP. It is also preferred over other aerosol power
pack spray units for touch-up if an air source is available.
4.2.2 Hot Spray. Hot spraying is the application of
coatings with HVLP, or airless spraying equipment, using
heat as a substitute for all or a portion of the thinner ordinarily
used to reduce coating materials to spraying viscosity. Hot
spray is most frequently and effectively used with the airless
spray system. Also, the hot paint, while cooled rapidly when
atomized, retains sufficient heat to still be close to the ambient
air temperature when it reaches the work surface. This
reduces the possibility of blushing due to moisture conden-
sation and allows spraying under conditions of relatively high
humidity. However, a disadvantage is that heating the paint
reduces its pot life.
Figure 4-1. Nozzle Pressure Gauge
TO 1-1-8
Change 2 4-1