What influence does mold temperature have on injection molding?

Mold temperature is the most important variable in injection molding - for any plastic, it is essential to ensure that the basic wetting of the mold surface is achieved. A hot mold surface keeps the plastic surface in a liquid state for a long time, which is sufficient to form pressure within the cavity. 

If the cavity is filled and the soft plastic is pressed against the metal before the hardened skin forms, the replication of the cavity surface will be high. On the other hand, if the plastic entering the cavity at low pressure pauses, no matter how short the time, the slight contact with the metal will cause spots, sometimes called gate stains. 

For each type of plastic and plastic part, there is a limit to the mold surface temperature. Exceeding this limit may result in one or more adverse effects (for example: the component may overflow with flash). 

Higher mold temperature means less flow resistance. On many injection molding machines, this naturally means that higher effective pressure will be generated in the runner and cavity more quickly. Flashing may occur. Since a hotter mold does not freeze the plastic that enters the flashing area before high pressure is formed, the melt can flash around the ejector pin and overflow into the parting line gap. This indicates that good injection speed rate control is needed, and some modern flow control programmers can indeed achieve this.

Generally, an increase in mold temperature reduces the solidified layer of plastic in the cavity, making the molten material flow more easily within the cavity and resulting in a greater part weight and better surface quality. At the same time, a higher mold temperature also increases the tensile strength of the part. 

The heat preservation methods for molds: 

Many molds, especially those for engineering thermoplastics, operate at relatively high temperatures, such as 80 degrees Celsius or 176 degrees Fahrenheit. If the mold is not insulated, the heat lost to the air and the injection molding machine can be as much as that lost from the injection cylinder. 

Therefore, it is necessary to insulate the mold from the machine plate. If possible, insulate the surface of the mold. If a hot runner mold is considered, try to reduce the heat exchange between the hot runner part and the cooled injection molded part. Such methods can reduce the preheating time and energy loss.