Knit line

Where it comes up

• Plastic injection moldingMolten thermoplastic injected into a steel or aluminum mold. Lowest piece price for plastic parts at 5,000+ a year.

Related terms

Gate

A gate is the opening where molten plastic or metal enters the mold cavity from the runner. Gate type, size, and location affect fill, knit lines, sink, and the mark left on the part. Common types include edge, submarine, pin point, and valve gates.

Cold shut

A cold shut is a casting defect where two streams of molten metal meet but fail to fuse, leaving a visible seam or weak line. It comes from low metal temperature, slow fill, or poor gating. In die casting, cold shuts often appear far from the gate on thin sections.

Short shot

A short shot is an injection molded part that is incomplete because plastic froze before filling the whole cavity. Causes include low shot size or pressure, blocked vents, thin walls, and long flow lengths. Molders often run short shots on purpose during mold trials to study fill.