TROUBLESHOOTING

Generally burn marks at the gate are caused by an over-shearing of material. The melt flow will reach its highest shear rate while in the gate. Since the gate will also be the hottest area, over-shearing here will leave a burn mark at the gate.

Gate Size
Using smaller gates and higher shear rates keeps melt viscosity low, which improves melt flow of our TPV materials. We recommend using as small a gate as possible (too small of a gate will over-shear the material). A gate size no smaller than 0.5 mm (0.020") and no larger than 3.0 mm (0.120") is recommended. Refer to the Quick Processing References on our website for more information on gating using specific grades of our TPVs.

Restricted Gate
A restricted gate slows the flow of material around the gate area, which increases the shear of our TPV materials. Restrictions could be caused by a rapid wall thickness change in the part. We recommend wall thickness transitions of 15 percent or less. Burrs or sharp corners at the gate will also reduce flow at the gate. Polishing the gate area can reduce this restriction.

Injection Speed Too High
Most of our TPVs process using fast injection rates, achieving fill times ranging from 0.5 to 1.5 seconds. However, trying to inject too rapidly will increase the shear rate of melt flow in the gate.

Back Pressure Too High
A rapid withdraw of the screw will over-shear the material. The last place for melt flow to set up is around the gate, which increases the chance of a burn mark in this location.

Mold Temperature At Gate Too High
Reducing the temperatures around the gate will reduce burning at the gate.

Front Barrel Zone Temperature Too High
Reducing front barrel zone temperatures will reduce burning at the gate.

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