MIL-HDBK-1110
in a variety of environments. For more severe service such as
very acid or alkaline conditions, or fresh or salt water spray,
splash, or immersion, the coating may be sealed with a thin
conventional organic coating or silicone. A white-metal blasted
surface is required. Metal spray coatings are normally very
abrasion resistant and provide excellent corrosion control.
Thermal spraying of metals is best accomplished in a
shop environment, but can also be done in the field.
DOD-STD-2138(SH) describes the wire flame spraying of aluminum
using oxygen-fuel gas. SSPC Guide 23, Coating Systems describes
thermal spray metallic coating systems.
7.5.4.9
Application Technique. Proper application technique is
essential for obtaining quality films. Poor technique can result
in variations in paint thickness, holidays (small holes), and
other film defects, and wasted time and materials. The same
basic techniques described below are used for both conventional
and airless spraying:
a) Stroking. With the spray gun at a right angle to
the work, the wrist, arm, and shoulder are moved at a constant
speed parallel to the surface. Holding the gun at an upward or
downward angle to the surface will result in a non-uniform
coating thickness and may increase the problem with dry spray or
overspray. Also, changing the distance between the gun and the
surface, arcing, as illustrated in Figure 14, will result in a
non-uniform coating thickness. For large flat surfaces, each
stroke should overlap the previous one by 50 percent as shown in
Figure 15. This produces a relatively uniform coating thickness.
The stroke length should be from 18 to 36 inches, depending upon
the sprayer's arm length and comfort. Surfaces of greater length
should be divided into smaller sections of appropriate length
(Figure 16). Each section should slightly overlap the previous
one along the lines where they are joined.
b) Triggering. The spray gun should be in motion
before triggering and continue briefly after releasing at the end
of a stroke. This is illustrated in Figure 17. Proper
triggering also keeps the fluid nozzle clean, reduces paint loss,
prevents heavy buildup of paint at corners and edges, and
prevents runs and sags at the start and end of each stroke.
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