Injection Mold Insulation Methods You Should Know

Mold temperature is the most important variable in injection molding—regardless of the type of plastic being injected, it is essential to ensure basic wetting of the mold surface. A hot mold surface keeps the plastic surface in a molten state for a longer time, allowing pressure to build up inside the cavity. If the cavity is filled and the cavity pressure can press the soft plastic against the metal before the frozen skin hardens, then the replication of the cavity surface will be high.

On the other hand, if the plastic entering the cavity at low pressure is paused, even for a short period of time, its slight contact with the metal will cause blemishes, sometimes referred to as gate blush.

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, flash may occur on the component). A higher mold temperature means lower flow resistance.

On many injection molding machines, this naturally means faster flow through the gate and cavity, because the injection flow control valve used does not correct this change; faster filling will cause higher effective pressure in the runner and cavity.

This may cause flash and burrs. Since hotter models do not freeze the plastic that enters the flash area before high pressure is achieved, the melt can flash and form burrs around the ejector pins and leak into the parting line gap. This indicates the need for good injection rate control, which some modern flow control programmers are indeed capable of achieving.

Typically, an increase in mold temperature reduces the formation of a condensation layer inside the cavity, making it easier for the molten material to flow within the cavity. This results in greater part weight and better surface quality. At the same time, a higher mold temperature also increases the tensile strength of the parts.

The insulation method of the mold

Many molds, especially those used for engineering thermoplastics, operate at relatively high temperatures, such as 80 degrees Celsius or 176 degrees Fahrenheit. If the molds are not insulated, the heat lost to the air and the injection molding machine can easily be as much as the heat lost through the shot sleeve.

To insulate the mold's framework plate, if possible, insulate the surface of the mold as well. If considering using a hot runner mold, try to reduce the heat exchange between the hot runner section and the cooled injection-molded parts. This approach can reduce energy loss and preheating time.