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How to improve stress cracks of injectin molding?

Feb 26, 2020

What's stress cracks? It is external or internal crack caused by stresses, that are less than the ultimate tensile stresses.Local internal stresses, among other things, are responsible for the formation of stress cracks. The crack formation is initiated either by external tensile stress, or by the effect of aggressive solvents and chemicals. The magnitude of the internal stresses incorporated into the injection molded part is influenced by the processing. Process related internal stresses can be analyzed using solvents or chemicals, which initiate stress cracks. Contact IEC Mould to improve your injection molding quality level.

Stress crack injection molding

Causes Recommendations
The material is overloaded because the holding pressure is too high or the mold construction is not good enough. Reduce the back pressure, if applicable, set a decreasing back pressure profile.
Improve the mold construction.
The temperature selected for the mold is too low. Increase the mold temperature.
Cracks are formed during ejection owing to sever external forces, because of the forced removal from undercuts from the mold. This is due to not enough draft angle and the number of ejectors being insufficient, becasue the ejectors are positioned incorrectly. Reduce the undercut or avoid it through design measures.
Improve the removal from the mold by means of larger drafts.
Optimize the ejector system.
The molecular weight of the selected product is too low, this has to be taken into consideration when agressive solvents or chemicals are used. Use a material with a higher molecular weight.