Plastic parts Name: raw materials: Terluran
& reg; GP-22 type ABS + high concentration of black masterbatch problem:
plastic parts intact when out of the mold in the air for 2 to 3 days, have
vertical section surrounding parts of the copper insert crack, some have even
been completely split. Reason analysis and improvement program: plastic parts
do not have any problem during the molding process, the problem does not lie in
molding equipment and technology, according to our understanding of the
analysis, the problem is caused by environmental stress cracking. Cause
environmental stress cracking might have the following areas:
First, the raw materials
(1) raw materials mixed with other
impurities or doped with inappropriate or excessive solvents or other
additives. Environmental stress cracking is a unique phenomenon polyolefin
plastic, which refers to the product when there is stress, and some active
media exposure, there will be a brittle crack, crack growth resulting in
product damage. Such active substances may be detergents, soaps, water, oil,
acids, alkalis, salts and no significant swelling effect of organic solvent
materials. A necessary condition for environmental stress cracking is a pattern
or part of memory in stress and stress concentration factors such as the
existence of a gap, surface scratches and so on. The ABS contains a polyolefin
component, and impurities contained in the starting material or solvent
indirectly provides these active substances, when the ABS plastics during
storage due to the emergence of a variety of causal factors surface chipped or
scratched, so there will be cracks .
(2) Some plastics such as ABS, etc., in the
damp heat condition can occur with moisture catalytic cracking reaction, the
occurrence of large parts of the strain thus cracking.
(3) plastic barrel heating time is too long
will cause brittle parts.
Second, product design
Such as polystyrene and plastic containing
this ingredient as little as possible because the metal insert, because these
plastic brittle cold specific volume. If the order to assemble and strength
requirements must be added inserts, as inserts made of metal copper, while
copper insert cooling dimensional change with heat-shrinkable plastic ABS
values vary greatly, resulting in a greater around the insert within stress,
thus resulting in cracking products. Specific improvements are as follows:
(1) Replace the insert of the materials
used to make the insert and the ABS product line expansion coefficient should
be as close as possible;
(2) increase the insert sharp parts of each
fillet, fillet products may cause stress concentration is too small, resulting
in product cracking;
(3) increase the thickness of the insert
around the plastic layer.
Third, preheat aspects inserts
With inserts in plastic products, around
the insert easily crack or cause product strength decline, which is made of
metal and plastic inserts for thermal and shrinkage caused by large
differences. Therefore, in designing parts, should increase the wall thickness
around the insert, in order to overcome this difficulty, preheated before
molding is an effective measure to carry out metal inserts. Because the
temperature difference between the warm-up can reduce the melt and insert in
molding can melt cooling inserts around slowly, more uniform shrinkage occurs
some hot material feeding action to prevent exerted around the insert large
internal stress. Fourth, since the annealing processing plasticized plastic in
the cylinder uneven or different cooling rate in the mold cavity, so often
produce uneven crystal orientation and contraction, resulting in product there
internal stress, which produces thick-walled or tape more pronounced when metal
inserts products. There are parts of internal stress occurs in the storage and
use of the Central Standing Committee mechanical performance, optical
performance deterioration, surface crazing, cracking or deformation. Production
of solving these problems is the power of a law article annealing. The method
of the article is annealed in the constant temperature liquid heating medium (e.g.
hot water, hot mineral oil, glycerin, ethylene glycol, and liquid paraffin,
etc.) or a hot-air circulating oven was allowed to stand for some time. For ABS
plastic parts plus insert, refer to the following: annealing treatment medium:
water annealing temperature: 10 ~ 20 ℃ low i.e. 60 ~ 70 ℃ annealed
heat distortion temperature than ABS time (85 ~ 100 ℃): 2 hours
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