• 2023-10-09
• 796
• 5 Comments

Reduce the impact of mold temperature difference on the injection molding process

Mold temperature is the most important variable in injection molding - no matter what kind of plastic is injected, it must ensure that the basic wetting of the surface of the mold is formed. A hot mold surface keeps the plastic surface liquid for long enough to build up pressure in the mold cavity. If the cavity is filled and the cavity pressure presses the soft plastic onto the metal before the frozen skin hardens, then the cavity surface replication is high.

On the other hand, if the plastic entering the cavity at low pressure is suspended, no matter how short the time, then its slight contact with the metal will cause a stain, sometimes called a gate stain.

For each type of plastic and plastic parts, there is a limit to the mold surface temperature beyond which one or more adverse effects may occur (e.g., components can spill raw edges). Higher mold temperature means less flow resistance.

On many injection moulding machines, this naturally means faster flow through the sprue and cavity because the injection moulding flow control valve used does not correct for this change, and faster filling causes higher effective pressure in the sprue and cavity.

May cause overflow raw edges. Since the hotter model does not freeze plastics that enter the overflow edge area before the high pressure builds up, the molten material can spill raw edges around the ejector rod and into the divider gap. This indicates the need for good injection rate control, and some modern flow control programmers can indeed do this.

Generally, the increase in mold temperature will reduce the condensation layer of the plastic in the mold cavity, making it easier for the molten material to flow in the mold cavity, resulting in greater part weight and better surface quality. At the same time, the increase of mold temperature will also increase the tensile strength of parts.

Heat preservation method of mold

Many molds, especially 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 injection machine can easily be as much as the heat lost to the injection cylinder.

Therefore, the mold should be insulated from the skeleton plate and, if possible, the surface of the mold should be insulated from the heat. If a hot runner mold is considered, try to reduce the heat exchange between the hot runner part and the cooled injection part. This method can reduce energy loss and warm-up time.