In injection molding, mold temperature is a crucial variable. No matter what kind of plastic is processed, it is necessary to ensure the appropriate wettability of the mold surface. The thermal mold enables the plastic surface to remain liquid for a sufficient time to generate the required pressure in the cavity, thus achieving high surface reproduction accuracy.
On the contrary, if the plastic enters the cavity under low pressure conditions, even a short stay may lead to slight contact with the metal, resulting in stains, commonly known as gate stains. The mold surface temperature corresponding to each plastic and finished product has a critical value, beyond which a series of adverse consequences may result, such as burring on the part. Higher mold temperatures usually mean lower flow resistance, which speeds up the flow of plastic through the gate and cavity, increasing the effective pressure in the cavity.

This phenomenon can lead to the formation of a raw overflow edge, because the higher temperature mold fails to cure the plastic that enters the overflow edge area under high pressure, resulting in the possibility of molten material spilling around the ejector rod and into the gap of the divider. Therefore, effective injection rate control is particularly important, and modern flow control programmers have played a significant role in improving this.