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

Every gated part separates from its feed system, leaving a witness mark. Because the existence of the mark is unavoidable, disputes usually center on its height, its location, and its cosmetic impact. Buyers must differentiate between the physical remnant of the gate (vestige) and the shear-induced cosmetic disturbance around it (blush) to demand the correct tooling or process fix.

Gate Vestige: The Physical Remnant

Vestige is the physical stub, shear mark, or trimmed flat left where the gate separated from the part. The critical variables are height and location.

A peer-reviewed study of gate vestiges (Express Polymer Letters, 2015) highlights two points critical for buyers:

1. Vestige is a safety finding, not just a cosmetic one. A sharp or protruding remnant on a handled surface is a product-safety defect. If a part is touched, gripped, or contacts skin, a maximum vestige height must be specified in the drawing notes. A verbal request to “keep it small” is insufficient.
2. Cold-runner tools inherently produce vestige. While hot-runner valve gates shut off mechanically and leave an incredibly clean witness, cold-runner and three-plate tools rely on material shearing or manual trimming. In these tools, vestige height is a function of both processing parameters and gate geometry (specifically the short tapered regions). If you purchase a cold-runner tool, vestige is part of the agreement; the negotiation is strictly about its size and placement.

Gate type dictates the character of the mark: edge gates leave a trimmed edge, sub/tunnel gates shear off below the surface, and pin gates leave a small face vestige. Location dictates its impact. A large vestige on a hidden rib is acceptable; a microscopic vestige in the center of a high-gloss A-surface is a reject because gloss amplifies the defect.

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 molten plastic accelerates through a restriction. It frequently appears alongside splay or jetting.

Because blush is a cosmetic defect driven by velocity, it often triggers the wrong corrective action: slowing down the injection speed until the blush fades. This papers over a tooling problem and can induce short shots or sink elsewhere in the part.

Persistent blush is almost always a geometry problem masquerading as a process problem. If the defect survives reasonable process tuning at the T1 trial, the root cause lies upstream. An undersized sprue, a runner gated off its side rather than its center, or a gate land (the short jump from the runner into the part) that is too long will all induce massive shear.

A general industry rule is that the gate land length should be roughly half the gate depth. The fix requires cutting steel—“getting the shear out of the gate”—not simply slowing the machine down. If a supplier proposes process adjustments to fix a stubborn blush, buyers should request the gate, land, runner, and sprue dimensions, and compare them against the resin manufacturer’s recommendations. Let the tooling math answer the question.

Establishing Criteria Before Tooling

Gate-mark disputes stem from the lack of a written standard. Buyers can avoid this by defining three criteria in the RFQ:

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

Reviewing at T1

At first samples, evaluate the gate area against the written criteria. If a cold-runner vestige is too tall, ask the supplier whether the root cause is gate construction or process, and demand a correction plan. If blush is present and the supplier claims it “improves when we slow the injection down,” recognize that tuning against poor geometry rarely remains stable across a production run. 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.