What Is a Hot Runner Mold?

What Is a Hot Runner?
During the plastic injection process a “Hot Runner” ensures that the plastic passing through the runner stays molten by heating the runner. Temperatures along the entire runner, from the barrel outlet of the injection molding machine to the gate at the mold, are in a constant state of flux. By using heating rods and heating rings near the runner, a high-temperature state is maintained and the plastic in the runner is kept molten. Generally, between operation runs, it is not necessary to open the runner to take out the plastic after the machine is shut down. It is only necessary to heat the runner to the required temperature when the machine is turned on again. The production cycle of the hot runner mold is shorter than that of the traditional mold, which saves on raw materials. Today, hot runner molds have been widely used in industrial manufacturing.

What are Gates and Runners?
Runners are the tunnels molten plastic flow through to get to the mold. At the end of the runner is the gate which leads into the mold cavity. A hot runner mold is a mold in which the runners of a traditional three-plate mold are heated. Hot runner systems are divided into a fully hot runner and semi hot runner. The semi-hot runner has a simple hot runner structure on one side of the mold, is stable and easy to use, and has a low failure rate. Due to its simple structure, the maintenance cost is low, and the stability of production is more guaranteed.

The hot runner structure includes a manifold, a nozzle, and a temperature control box. A hot runner can be divided into open type (miniature semi-hot runner) and needle valve type (insulated runner). The hot nozzle directly determines the design of the hot runner system and how the mold is manufactured. A manifold is used when a mold has multiple cavities or multi-point feeding and is generally divided into standard and non-standard. Its structure is mainly determined by the distribution of cavities in the mold, the arrangement of the nozzles, and the position of the gates. The mold has a temperature control box for electronic control.

The Working Principle of the Hot Runner:
In the hot runner mold, the plastic raw material enters directly into the mold chamber rather than passing through a traditional cold runner which allows the runner to cool and solidify between each cycle.

Read more: What Is a Hot Runner Mold?

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