After the plastic bottle cap mold is installed, the mold must be preheated before mold trial. There are roughly two methods for mold preheating. It uses the cooling water hole of the mold itself to pass in hot water for heating. At present, there are a large number of mold heaters used at home and abroad, which is a good method for mold heating. The other is the external heating method. That is, the cast aluminum heating plate is installed on the outside of the mold, and the heating is carried out from the outside to the inside. This method heats quickly but consumes a lot of heat energy. It is more suitable for the cold winter in the north.

For plastic bottle cap molds, the heat of the injection material can be used to increase the temperature. The use of raw materials that are not difficult to inject does not require mold preheating. However, for large and medium-sized molds, the melt is forcibly injected into the cavity by using a temperature-relieving material and high pressure. Although it is also possible to obtain parts for trial molds, it actually damages the mold itself seriously and wastes energy. Due to the large internal stress and severe deformation, the size of the obtained product is very unstable, which brings trouble to the inspection of the product size. Therefore, this method should not be adopted.

When the mold is preheated after installation, the injection barrel is also heated. When both temperatures meet the requirements, that is, when the mold temperature reaches 30 to 60 ℃ or more. When the plastic in the barrel is in a molten state and is uniformly plasticized, it is deemed that the temperature is appropriate, that is, the test mold injection conditions are available, and the test mold can enter the test injection stage.