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Cold Slugs / Unmelted Lumps:
Unmelted or insufficiently plasticized material enters the mold cavity along with the melt flow, causing hard plastic lumps to become embedded inside or on the surface of the molded part.
| 20.1 Causes | 20.2 Solutions |
|---|---|
| 20.1.1 Material temperature, mold temperature, and nozzle temperature are too low, or injection speed is too slow. | 20.2.1 Properly increase the material, mold, and nozzle temperatures, and raise the injection speed. |
| 20.1.2 Back pressure too low, resulting in uneven plasticization. | 20.2.2 Increase back pressure appropriately and adjust screw speed to ensure uniform plasticization. |
| 20.1.3 Insufficient plasticizing capacity of the injection machine; machine capacity is close to the part weight; molding cycle too short. | 20.2.3 Use an injection molding machine with higher plasticizing capacity. |
| 20.1.4 Contamination or mixing of materials of different grades. | 20.2.4 Replace material and ensure it is free from impurities. |
| 20.1.5 Uneven or oversized pellets. | 20.2.5 Replace material with uniform and appropriately sized pellets. |
| 20.1.6 Absence of a main runner or cold slug well, or improper position of the cold slug well. | 20.2.6 Add a cold slug well in the mold and polish the runner. |
| 20.1.7 Poor fit between mold gate and nozzle. | 20.2.7 Repair or adjust nozzle radius or diameter. |
| 20.1.8 Low hot runner temperature or heater malfunction. | 20.2.8 Increase hot runner temperature or replace the heater. |
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