Analysis of the causes of stress cracking in ABS

The general injection-grade ABS rubber content is about 18%. ABS is an amorphous polymer, and the internal stress mostly comes from the different degrees of orientation and cold and heat shrinkage. Product cracking in the processing of injection molded products includes filamentary cracks, microcracks, whitening, cracks, and cracks caused by mold sticking and runner sticking on the part. According to the cracking time, it is divided into mold release cracking and stress cracking. The main reasons are as follows.

ABS internal stress cracking analysis mainly includes:

(1) Excessive processing pressure, too fast speed, too much filling, too long injection and pressure holding time will cause excessive internal stress and cracking;

(2) Adjust the speed and pressure of mold opening to prevent mold release and cracking caused by rapid forced drawing;

(3) Properly increase the mold temperature to make the parts easy to demold; appropriately lower the material temperature to prevent decomposition;

(4) Prevent cracking due to deterioration of mechanical properties due to weld marks and plastic degradation;

(5) The residual stress of the workpiece can be eliminated by annealing and heat treatment immediately after forming to reduce the generation of cracks.

ABS internal stress cracking analysis mainly includes:

(1) The ejection should be balanced, such as the number of ejector pins, the cross-sectional area should be enough, the demolding slope should be enough, and the cavity surface should be smooth enough, so as to prevent the residual stress concentration caused by the external force.

Cracking

(2) The structure of the part should not be too thin, and the transition part should adopt arc transition as far as possible to avoid stress concentration caused by sharp corners and chamfers;

(3) Minimize the use of metal inserts to prevent the internal stress from increasing due to the difference in shrinkage between the insert and the workpiece;

(4) Appropriate demolding air inlets should be provided for deep-bottomed parts to prevent the formation of vacuum negative pressure;

(5) The main runner is large enough to allow the gate material to be demolded when it is cured in the future, so that it is easy to demold.

Polyrocks Chemical's environmentally friendly flame-retardant ABS uses environmentally-friendly bromine-antimony flame-retardant system and adopts advanced processing technology to highlight the mechanical properties and surface gloss of the material while ensuring the flame-retardant effect. It has passed the UL certification of the United States and meets the requirements of RoHS, SVHC, PFOS&PFOA, 17P, PAHs and other regulations for products.

Polyrocks Chemical specializes in the production of modified flame-retardant plastic materials, and attaches great importance to providing customers with fast pre-sales/after-sales services. It has professional injection molding engineers and technical service engineers to provide customers all over the world with accurate information consultation and timely services.