Parts (ABS plus copper insert) cracking existential analysis, improvement

Posted May 26, 2015 by cnmoulding

Cnmoulding plastic mould factory and injection molded plastic products maker in China. Manufactures and exports quality OEM plastic injection molding parts and plastic moulds for injection molding &mould making

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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Last Updated May 26, 2015