Plastics Cracking Analysis and Countermeasures

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

Abstract: The cracking plastic products often fatal flaw; cracking, including filamentous workpiece surface cracks, crazing, top white, sticky parts due to cracking and mold, stick-runner or trauma caused by the crisis, by cracking time points cracking cracking and stripping applications. Causes cracking aspect relates to a mold, molding process, plastic material or the like. This paper discusses the cracking of the plastic material selection angle.

Keywords: plastic material selection plastic cracking hot ductility balance
1: Summary of plastics defect
Plastics can be divided into external manifestation of defects defects (such as appearance, size, etc.) and internal defects (such as cracks, brittleness, etc.). The nature of the causes of defects of plastic products can be summarized as P (power), V (fill volume), T (temperature). The ultimate cause of plastic cracking is due to P (power) caused.
2: plastic cracking
Stripping cracking: plastic product from the mold stripping out or cracking in the machining process; the causes and consequences of this cracking to produce relatively easy to estimate. Applications cracking: cracking plastic products appear in the post-period of time or use. This cracking is often more difficult to predict, the consequences can be fatal. As some time before the emergence of 3G iPhone Mobile white version cover cracking phenomenon for Apple to bring in big trouble. (Battery heating up the plastic cover cause thermal expansion and contraction caused by uneven)
3: Cracking products analysis
Whatever plastics, eventually cracking because of the nature of the force (internal stress, external force, etc.) caused. Thus we must better understand the source of power. Currently some customers some errors in the plastic of choice, resulting in a large number of plastic cracking. Now some typical case analysis

4: plastic plastic cracking prevent cracking prevention

Ways to improve the plastic cracking foreign counterparts summed up a lot of valuable experience, now from plastic material selection point of view to explore how to effectively solve the plastic cracking. In terms of product selection, we should take full account of the way the plastic molding material, component structure, heat transfer and other operational issues the actual process; for some hollow structure, should take full account of the thickness, size and so hollow. Such as thin-walled, large hollow core member should try to use good ductility (elongation at break), good thermal conductivity of plastic, and use plastic rods processed into plastic pipe will have to fully take into account the heat balance, as far as possible choose ductile plastic rods, for some ductility bad plastic pipe, as far as possible avoid using bar processed into pipe (pipe general factory has been heat-treated residual stress). For some ductility bad plastic, plastic pipes and plastic rod effect is not the same. Cracking satisfy the conditions: μl / hßΨ≥ ξ μ- empirical process factor, h- wall thickness, l- hollow perimeter, ß- plastic shrinkage, Ψ- plastic thermal conductivity, ξ- breaking elongation 5. Conclusion prevent cracking of the most difficult point of plastic products is how to prevent the plastic products in different parts of the apparent thermal equilibrium, and the use of carbon fiber or metal filled plastic, because the strong heat conduction capability, so a relatively small chance of cracking. From the viewpoint of a plastic material, products related to cracking the wall thickness, volume hollow products, plastic ductility.
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Last Updated May 26, 2015