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  • 25 May 2020
  • 343 Comment

A hot mold surface keeps the plastic surface liquid for a long time, enough to form pressure in the cavity.

A hot mold surface keeps the plastic surface liquid for a long time, enough to form pressure in the cavity. If the cavity is filled and before the frozen skin hardens, the cavity pressure can press the soft plastic onto the metal, the replication of the cavity surface is high. On the other hand, if the plastic entering the cavity at low pressure is suspended, no matter how short the time is, the slight contact with the metal will cause stains, sometimes referred to as gate stains.

For each plastic and plastic part, there is a limit of mold surface temperature, beyond which one or more adverse effects may occur. Higher mold temperature means less flow resistance. The flow valve of injection molding machine can not correct this change. Faster filling will cause higher effective pressure in sprue and cavity, which may cause overflow burr. Since the hotter model does not freeze the plastic that enters the overflow edge area before high pressure is formed, the melt can overflow the burr around the ejector pin and overflow into the gap of the split line. This shows that good injection rate control is needed, and some modern flow control programmers can do this.