Page 340 - Injection Molding Advanced Troubleshooting Guide
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336 34 Jetting
34.3.2.3 Mold: Gate Land Length
The land length of the gate is the distance that the actual gate thickness is ma-
chined into the steel. This distance is from the cavity to where the runner or gate
geometry chokes down to its final thickness.
Excessive land length on a gate can impact the likelihood of jetting occurring. The
longer the land becomes the more the material is restricted as it enters the cavity
and builds up pressure behind the material resulting in a burst into the cavity.
Typically land lengths should be kept to a maximum of 0.030 in.
If the land length of the gate is excessive, have a qualified mold maker reduce the
land length. This may improve the jetting as well as other issues due to the restric-
tive land length.
34.3.3 Jetting Troubleshooting Machine Issues
Most causes of jetting are not machine related; however, if the machine is not func-
tioning correctly jetting could be the outcome.
See Chapter 8 on machine performance.
34.3.4 Jetting Troubleshooting Material Issues
Given the wrong gate and molding process almost all materials can be made to jet.
