TROUBLESHOOTING

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There are a few key reasons why flash appears on the parting line of a part. First, excessive injection pressures may be forcing the mold apart. Ensure that injection pressures are appropriate (under 70 MPa [10,000 psi]). Check that the machine is creating enough clamping force to keep the mold halves together. We recommend the machine be able to apply forces between 4.0 and 6.9 kN/cm² (3 and 5 tons/in²) of the projected area. Finally, the mold may be improperly aligned, damaged, worn or have over-sized vents.

Excessive Injection Pressure Causes Mold To Part
Flash will occur during fill when the injection pressures are greater than the clamping force. Using injection pressures meant for a lower viscosity material can flash the mold. It is important to note that a distinction must be made whether the flash is occurring during fill or during the pack and hold stage. This can be determined by doing a fill-only shot. Adjust the pack and hold pressures to zero and use velocity only to fill the mold (95%). If the part is flashing at this point, the problem is occurring during the fill. Decreasing injection speed, verifying injection fill time and moving the transfer point back are steps that can help alleviate this problem. Finally, increase pack and hold pressure to 50% of the injection pressure setting and pack and hold times to 2 to 3 seconds to ensure that the part is filled. Increase pack and hold time until the part weight does not change (refer to Start Up Procedures).

Melt Temperature Is Too High
Material viscosity can also cause flash. Temperature can affect the viscosity of our TPV materials, though not as significantly as shear. When temperatures are too high, viscosities may be too low. To increase viscosity, systematically reduce the temperature settings of the nozzle, front barrel zone and mold in 5 to 10° increments. Finally, if no reduction in flash is observed, reduce the screw RPM by 5 to 10% to decrease the shear, which in turn will increase the viscosity of the melt.

Mold Function Is Incorrect
The last, and many times the most expensive, remedy involves the mold. Before reworking the mold, check to make sure mold faces and machine platens are aligned properly. Make sure there is no foreign matter on the mold faces. We do not recommend using any release agent on the mold surface. Check for damage on the mold, wear or improper venting. For proper venting instruction, refer to the venting section in the Injection Molding Guide.

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