Structure and Characteristics of Hot Runners

Hot runners are a method of carrying out molding without generating scraps by heating and melting the runner part during plastic injection molding. Various types of structures have been realized for hot runners such as the method of heating or injecting. The major hot runner structures and their characteristics are as follows.

Open gate structure:

-	Controls the nozzle temperature to a constant value
-	The structure is simple and the number of constituent parts is small.
-	Know how is required for temperature control.
-	The gate part can become solidified easily.
-	Depending on the plastic, stringiness of the gate plastic can easily occur.

On-Off Control structure:

-	The gate is heated during injection, and at the end of injection the gate is left to cool
-	The structure is relatively simple.
-	The temperature control is simple.
-	The gate seal is good.
-	A special thermocouple is required.

Hot edge gate structure:

-	The gate part is sheared off at the time of opening the mold.
-	The structure is relatively simple.
-	The gate does not become hard easily.
-	There is no stringiness generated.
-	There are some restrictions on the applicability of the mold shape.

Valve gate structure:

-	The opening and closing of the gate is forcibly controlled by the valve pin.
-	The gate seal is definite because it is mechanical.
-	It is easy to control the molding conditions.
-	A source for driving the opening and closing of the valve pin will be required.
-	It is necessary to manage the maintenance of the sliding of the valve pin.
-	The structure is complex and know how is required even for the mold design.
-	The price is high.