Technical data
Table 4-1. Spray Coating Troubles, Possible Causes, and Remedies - Continued
Trouble Possible Causes Preventive Measures Or Remedies
Inconsistent Color-
ing
Pigment not evenly distributed as a result
of settling or insufficient mixing.
Apply additional coats after thoroughly
mixing the finish material.
Defective Spray
Patterns (Heavy
Center)
1. Setting too low on fan adjustment. 1. Adjust fan adjusting valve.
2. Air cap; atomizing pressure too low. 2. Adjust atomizing pressure.
3. Pressure feed: Fluid pressure too high for
normal capacity of air cap.
3. Adjust fluid pressure.
4. Nozzle too large for fluid used. 4. Replace nozzle with correct size.
Defective Spray
Patterns (Split
Spray)
Air and fluid feeds not properly balanced. Reduce width of spray pattern by means
of the spreader adjusting valve, and if
condition is not remedied, increase fluid
pressure. The latter increases rate of
material flow. Readjust atomizing pres-
sure, fluid pressure, and spray width
until desired spray is obtained.
Defective Spray
Patterns (Heavy
Top or Bottom)
(Heavy Right or
Left)
1. Horn holes partially clogged. Obstruction
on top or bottom side of nozzle.
1. Determine location of obstruction by rotat-
ing air cap one-half turn and spray a
new pattern. If defect is reversed, ob-
struction is in air cap; if not reversed, it
is on the nozzle of fluid tip.
2. Dirt on air-cap seat or nozzle fluid tip seat. 2. Clean. Check for burrs and dried paint in
opening.
Starving the Spray
Gun
1. Insufficient air because of waste filter in
transformer too tightly packed or
clogged.
1. Repack or replace filter.
2. Aircocks, hose or pipelines too small. 2. Replace with units of adequate size.
3. Inadequate air supplies from too small a
compressor or a break in the system.
3. Obtain a compressor of adequate size or
repair leakage.
Failure of Wet
Tape Test
Insufficient drying time for wash primer
and/or primer; insufficiently cleaned sur-
face; cleaning compound residue, etc. Oil
seepage through inspection doors or fas-
teners; entrapped oils and soil in shop
applied temporary primer; insufficient
removal of shop primer and/or previous
coatings; use of final finishes incorporat-
ing wax ingredients; use of laundered
rags instead of new lint free cotton rags;
seepage of water containing cleaning in
compound residues from between faying
surfaces.
Employ solvent wipe down, per Chapter
2; remove any shop primers to provide a
clean aluminum surface prior to any
painting; employ solvent-dampened
cloths in lieu of dry cloths for removal
of oil contamination (especially along
jet engine inspection doors); conduct
laboratory analysis to determine primer
a ceptability; allow aircraft to stand for
sufficient time to permit drainage of ef-
fluent before final cleaning; note the
type of failure, such as to bare metal
intercoat failure, and select the appli-
cable remedy according to the cause of
failure.
TO 1-1-8
4-17