Gate Vestige and Gate Blush: Reviewing the Mark the Gate Leaves Behind

Every gated part separates from its feed system and leaves a witness mark. The mark itself is unavoidable. Disputes usually center on height, location, and cosmetic impact. Separate the physical remnant (vestige) from the shear-induced disturbance around it (blush) so you demand the right tooling or process fix.

Gate Vestige: The Physical Remnant

Vestige is the stub, shear mark, or trimmed flat left where the gate left the part. Height and location matter most.

A peer-reviewed study of gate vestiges (Express Polymer Letters, 2015) makes two points buyers need:

1. Vestige is a safety finding, not only cosmetic. A sharp or protruding remnant on a handled surface is a product-safety defect. If a part is touched, gripped, or contacts skin, put a maximum vestige height in the drawing notes. “Keep it small” is not enough.
2. Cold-runner tools inherently produce vestige. Hot-runner valve gates shut off mechanically and leave a very clean witness. Cold-runner and three-plate tools rely on shearing or manual trimming. Vestige height then follows process and gate geometry (including short tapered regions). Buy a cold-runner tool and vestige is part of the deal. Negotiate size and placement.

Gate type sets the mark character: edge gates leave a trimmed edge, sub/tunnel gates shear below the surface, pin gates leave a small face vestige. Location sets impact. A large vestige on a hidden rib can be fine. A microscopic vestige in the center of a high-gloss A-surface is a reject because gloss amplifies it.

Gate Blush: The Shear Halo

Gate blush is not a physical remnant. It is a dull, hazy, or discolored zone radiating from the gate, caused by high shear as melt accelerates through a restriction. It often rides with splay or jetting.

Because blush is velocity-driven cosmetics, the wrong fix is common: slow injection until blush fades. That papers over a tooling problem and can create short shots or sink elsewhere.

Persistent blush is almost always geometry dressed up as process. If it survives reasonable tuning at T1, look upstream. An undersized sprue, a runner gated off its side rather than its center, or a gate land (the short jump from runner into the part) that is too long will all induce high shear.

A general industry rule: gate land length should be roughly half the gate depth. The fix is cutting steel (“getting the shear out of the gate”), not only slowing the machine. If a supplier proposes process-only fixes for stubborn blush, ask for gate, land, runner, and sprue dimensions and compare them to the resin manufacturer’s recommendations. Let the tooling math answer.

Establishing Criteria Before Tooling

Gate-mark disputes start from missing written standards. Define three criteria in the RFQ:

• Location: Agree gate positions against a marked drawing. Identify cosmetic and functional surfaces and restrict gating in those zones.
• Vestige: Define maximum height (for example flush, or < 0.5mm) and whether manual trimming is expected and priced into piece cost.
• Cosmetic zone: State whether blush, halo, or gloss variation around the gate is acceptable on specific faces, judged under the same lighting and distance as the rest of the cosmetic standard.

Reviewing at T1

Evaluate the gate area against the written criteria. If a cold-runner vestige is too tall, ask whether the cause is gate construction or process, and demand a correction plan. If blush is present and the supplier says it “improves when we slow injection,” recognize that tuning against poor geometry rarely stays stable in production. Demand the tooling dimensions.

Disclaimer

PlasticsTechnologyAlliance.com is an independent buyer resource. It does not manufacture parts or set acceptance standards. Gate marks are part-, tool-, and material-specific. Agree written criteria with your supplier before tooling and verify them at samples.