This trial version can use only a part of item.

Runner System

In this chapter, you will learn about the functions, characteristics, and shapes of the sprue, runner, and gate.
The molten plastic injected from the injector nozzle will go through a sprue (sprue bush), a runner, and a gate and fill up in the cavity.
As the temperature of molten plastic is lowered while going through the sprue and runner, the viscosity will rise; therefore, the viscosity is lowered by shear heat generated when going through the gate to fill the cavity.

The sprue, the runner, and the gate will be discarded after a part is complete. However, the runner and the gate are important items that affect the quality or the cost of parts.


The gate is categorized into restrictive gate, which narrows the entrance, and nonrestrictive gate, which does not narrow the entrance.

The gate has the following functions: