Mold Venting: Depth, Placement, and Common Mistakes in Ejector Venting

Trapped air and gas in a mold cavity cause short shots, burn marks, and weak weld lines. Venting gives that gas a path out of the cavity during injection.

Vent Depth

Vent depth is set by the resin. Thin, low-viscosity materials need shallower vents to avoid flash; thicker materials can use deeper vents. Depth is typically measured in thousandths of an inch and matched to the material being molded.

Placement

Vents belong at the last point of the cavity to fill, along parting lines, and around ejector pins and inserts where gas naturally collects. Placing them at the flow end lets air escape ahead of the melt front.

Common Mistakes

• Vents too deep for the resin, causing flash.
• Vents too shallow, leaving gas trapped and causing burn marks.
• No venting at ejector pins, where gas collects around the pin.

Tooling Components supplies ejector pins, sleeves, and mold components engineered for reliable venting and long service life.