In the injection molding process, the melt is guided from the machine nozzle into the sprue bushing and further into the runner system or the cavity.
The machine nozzle is pressed against the sprue bushing. In order to avoid leakage it is important that the radii of the machine nozzle and the sprue bushing are the same.
Sprue bushings are available with no radius, a radius of 15,5 mm or 40,0 mm.
The sprue bushing needs to be fixed against rotation, if a contour giving area has been incorporated. This can be done by flattening a side or inserting a pin.

Sprue Bushing in Plastic Industry

Injection Molding: A sprue bushing with a drilled hole to secure against rotation.

Related topics:

Mold Design

This glossary of plastic industry is provided by PLEXPERT Canada Inc.