Plastic parts are easy to crack under what conditions
Cracking, including surface cracks, cracks, cracks, cracks, cracks and cracks caused by mold sticking and flow passage, and cracking and cracking in cracking time. The main reasons are as follows:1. processing:(1) the pressure is too large, the speed is too fast, the more charge, the injection and the holding time are too long, and it will cause the internal stress to be too big and crack.(2) adjust the mold opening speed and pressure to prevent the rapid and strong pulling.(3) adjust the mold temperature properly, make the parts easy to release, reduce the material temperature properly and prevent decomposition.(4) prevention of cracking due to weld line and lower mechanical strength caused by degradation of plastics.(5) the appropriate use of release agent, pay attention to often remove the mold surface attached to aerosol and other substances.(6) the residual stress of the workpiece can eliminate the internal stress and reduce the formation of the crack by annealing immediately after molding.
Plastic parts itself is the disadvantage of resistance to internal stress is not good, easy to crack. Cracking reason:1, low temperature cracking.2. Contact chemicals are subject to corrosion and easy to crack.3, aging, easy to crack.4, the product design is unreasonable, easy to crack.
Mold aspects:(1) the top should be balanced, such as the number of the top and the section area to be enough, the mold slope should be enough, the cavity surface should be smooth enough, so as to prevent the external force caused by the residual stress concentration and cracking.(2) the structure of the parts can not be too thin, and the transition part should use the arc transition as far as possible to avoid the stress concentration caused by sharp corners and chamfering.(3) as far as possible less metal inserts, in order to prevent the inlay and parts shrinkage rate, resulting in increased internal stress.(4) deep parts shall be provided with proper release air inlet holes to prevent vacuum negative pressure.(5) the main runner is enough to release the sprue when the sprue is not ready to be cured so that it can be easily removed.(6) the main runner shall be joined with the nozzle to prevent the delay of the chill material and cause the parts to adhere to the fixed die.
Material aspects:(1) the content of recycled material is too high, which leads to the low strength of the parts.(2) excessive humidity results in chemical reaction between some plastics and water vapor and reduces the strength.(3) the material itself is not suitable for the processing environment, or the quality is poor, and the pollution will cause cracking.4. machine: injection molding machine plasticizing capacity should be appropriate, too small, plasticizing is not sufficient, can not be completely mixed and become brittle, too large will degrade.
