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MIXING THE PAINT Paint must be thoroughly stirred to obtain
uniform pigment distribution. When pressure feed tanks are used,
they should be equipped with continuous airoperated
stirrers to prevent pigment settling which can cause high pigment
volume concentration in the paint film and lead to failure of
the paint. It is important to use the proper type and amount
of thinner. Too much thinner can reduce the durability of the
paint. The paint suppliers' instructions for mixing should be
followed. For spray application, the viscosity of the
paint should be controlled on each batch of paint after mixing
and before spraying. Manufacturers' recommendations may vary
slightly but are usually based on measurement with a No. 4 Ford
viscosity cup. Viscosity cups are available from most chemical
supply houses. Viscosity is affected by temperature and should be
adjusted for a standard temperature of 73°F. The acrylic based
paints are usually sprayed at a viscosity of 15 to 17 seconds as
measured by a No. 4 Ford cup. Other viscosity cups may be used,
but the time will be different. The corresponding time on a No. 1
Zahn cup, for example, is 24 to 26 seconds. The color fastness of the paint film depends on
the quality of the paint. I n some cases, however, poor color
stability will result from mixing or reducing two normally stable
colors. Before making production parts, therefore, consult the
paint manufacturer for an opinion on the color stability of
specific mixtures of paints. |
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Copyright © Plastiglas de Mexico 1999
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