June 9, 2020

How to eliminate the ejector pins to break during injection molding of K material

At high temperatures, the friction between the K material (styrene-butadiene copolymer, SB in English, commonly known as “K material”) and the surface of the metal mold is very large, so the release resistance of the K material injection molded parts will be quite large, resulting in production It often happens that the ejector pin and ejector sleeve are broken, sometimes even severe enough to break a few pieces a day, which prevents the production from proceeding normally.

Usually, spraying release agent will be considered to reduce the friction between the product and the mold. However, spraying the release agent can easily cause obvious oil stains on transparent plastic parts, and it is not easy to control, and the scrap rate is high. If the injection molded parts need to be sprayed with paint, they can not be produced with release agent, otherwise there will be problems such as poor oil spray (oil sticking), spots, and matt color. Therefore, the use of release agent is not a good way to solve the problem of easy broken ejector pin and ejector sleeve of the mold.

In fact, as long as the injection molded parts are not deformed, not shrunk, and the demolding is smooth, try to shorten the cooling time and let the injection molded parts demold early, which can solve this problem well.

Because the cooling time of the injection molded part is shortened, the friction between the injection molded part and the mold surface can be reduced because the shrinkage is not large, the injection molded part becomes smoother, and the number of broken needles will naturally decrease. If possible, reducing the injection pressure as much as possible can also help reduce ejector pin breakage.

In addition, a ejector pin can also be used to replace the ejector sleeve. When the injection part is ejected from the mold core and the ejector pin is retracted again, the injection part is automatically pulled out of the ejector pin when it is stuck outside the mold. This can not only reduce the number of mold losses, but also save some ejector sleeve.

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Injection Molding, Plastic Mold Case, Plastic Molding Design, Plastic Parts
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