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Defective Spray Patterns | Up
TM-43-0139 Painting Instructions for Army Material Manual | Next
Figure 5-9. Spray Painting Faults |
TM 43-0139
f.
Orange Peel Finish. A common cause of this effect is the use of an improper or inferior thinner. With some
thinners and paints, this condition may be noticed at certain times of the year due to atmospheric changes. Other causes
are:
(1)
Insufficient atomization.
(2)
The gun is held too far from the surface.
(3)
The gun is held too close to the surface, allowing air to ripple the surface.
(4)
The material is not thoroughly dissolved or agitated.
(5)
With synthetics and lacquers, drafts exist in the finishing room.
(6)
With synthetics, there is low humidity.
(7)
Improper (generally high) viscosity; the material should be reduced to specification requirements.
g.
Streaks in Finish. Streaks are caused by:
(1)
Tipping the gun, thereby causing one side of the pattern to deposit more material than the other. See figure
5-9.
(2)
An improper spraying pattern.
h.
Sags and Runs in Finish. Sags and runs are caused by:
(1)
Tipping the gun, resulting in an uneven deposit of material.
(2)
Too much material on the surface due to too much pressure, or gun travel that is too slow.
(3)
Improper (generally high) viscosity; the material should be reduced to specification requirements.
i.
Mist or Fog.
(1)
This condition is caused by high atomization due to:
(a)
An atomizing pressure that is too high.
(b)
The wrong air cap for the material used.
(c)
The wrong fluid tip for the material used.
(d)
In pressure-feed systems, the fluid pressure is too low.
(2)
It is also caused by improper use of the gun, specifically:
(a)
Incorrect stroking.
(b)
A gun that is held too far from the painting surface.
j.
Starving. This condition is caused by insufficient air reaching the spray gun due to:
(1)
The waste in the air transformer is packed too tightly or the air transformer is clogged with rust or dirt.
(2)
The air cocks are too small.
5-12
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