PAINTING
CLINIC
B.R. said, "ABS will be much more likely to crack if not
molded at the correct temperature and pressure. The cracks
do not show up in the molding process, but later when
parts are processed or stressed (often this is when they are
painted). They need to slow the process down a little, increase
the pressure or time under pressure, and/or increase the
temperature at which the part is molded. Molders process
parts at as low a temperature as they can, and at as low a
pressure as they can, for as short a period of time as possible.
Often the problems do not show up until the solvents in the
painting process stress the plastic. The cracks are a sign their
process is not under control."
C.S. said, "You are correct that paint will not improve the
crack resistance of ABS. Different kinds of paints degrade
plastic impact resistance to one degree or another. The
question doesn't address when the cracking occurs. It could be
that some environmental exposure like sunlight or chemical
resistance is contributing to the cracking. If so, painting would
help by protecting the surface.
"Other solutions might be to change the gas venting in
the mold. Gas trapping can contribute to cracking or poorer
impact resistance. Designing the mold itself with ribs might
be a solution. Finally they might look at changing materials
to a glass-filled ABS or an ABS/PC blend, or go to PC."
Thanks for the input, B.R. and C.S. Responses such as
yours are always welcome at Painting Clinic.
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