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Effect Of Mold Temperature On Injection Molding
Nov 29, 2018

A hot die surface keeps the plastic surface liquid for long enough to create pressure inside the cavity. If the cavity is filled and before the frozen epidermis becomes hardened, the cavity pressure can push soft plastic onto the metal, and the surface of the cavity is copied high. On the other hand, if the plastic that enters the cavity is suspended at low pressure, no matter how short, the slight contact with the metal can cause stains, sometimes called gate blotches

For each type of plastic and plastic part, there is a limit on the mold surface temperature beyond which one or more adverse effects may occur (e.g., components may overflow the flash). Higher mold temperature means less flow resistance. In many injection molding machines, this naturally means faster flow through the sprue, gate and cavity, as the injection flow control valve used does not correct this change and faster filling causes higher effective pressure in the sprue and cavity

May cause flash. Since the hotter model does not freeze the plastics that enter the spill side area before the high pressure builds up, the melt can spill the flash around the ejector and spill into the dividing line gap. This suggests that good injection rate control is required, and some modern flow control programmers can do just that.

In general, higher mold temperatures will reduce the amount of plastic in the mold cavity, making it easier for molten material to flow in the mold cavity, resulting in greater part weight and better surface quality. At the same time, the mold temperature will increase the tension strength of the parts. Many molds, especially engineering thermoplastic, operate at relatively high temperatures, and if the molds are not insulated, the heat lost to the air and injection molding machine can easily be as much as the ejector cylinder

Temperature control is necessary

(1) purpose and action of temperature control on formability

Shape appearance, physical properties of material, forming cycle, etc. Generally, the mold temperature is kept low, which can improve the injection rate, but the forming cycle related to the shape (mold structure) and the type of finished material is also dependent on the necessary increase in the temperature of mold filling.

(2) temperature control should be done to prevent stress

This is the problem of forming material. The only requirement is cooling speed. The cooling time is short, and the stress caused by uneven contraction can be avoided even in cases where some of the hardening is still soft. That is, proper temperature control can improve the cooling stress properties.

(3) temperature control for adjustment of crystallization degree of forming materials

Polythiamine (nylon), polyacetate, polypropylene and other crystalline materials regulate crystallization degree and improve mechanical properties, generally requiring higher mold temperature.