 Problem |
Possible causes |
Possible solution |
| Problem at PS Injection |
| Black spots |
| Melt and/or mold temperature too high
|
| Decrease melt/ mold temperature |
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| Screw speeds too High
|
| Decrease the screw speed. High screw speeds may cause the material to degrade |
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| Material may have too much regrind content
|
| Reduce percentage of regrind |
|
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| Incompleted filling of mold |
| Insufficient pressure
|
| Increase injection pressure |
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| Material and mold too cold
|
| Reduce flow of cold water through mold |
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| Injection forward/boost time too short
|
| Increase injection forward and boost time |
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| Fill speed to slow
|
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| Runners/gates/nozzle too small
|
| Check runners, gates and/or nozzle |
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| Insufficient number of gates
|
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| Back pressure of entrapped air in mold
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| Incorporate or increase venting |
|
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| Surface defect |
| Material/mold too cold
|
| Increase material/mold temperature |
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| Too much mold surface lubricant
|
| Use less mold surface lubricant |
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| Insufficient injection speed
|
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| Material degraded in cylinder
|
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| Poor mold surface
|
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| Dimensional Inconsistency |
| Non-uniform feeding of material
|
| Adjust temperature for optimum filling |
| Increase shot size to maintain proper cushion |
|
| Insufficient packing of part
|
| Increase injection forward time and pressure to ensure gate freeze off |
|
| Regrind levels inconsistent
|
| Review regrind blending procedures or decrease level of regrind |
|
| Melt pressure variations
|
| Increase fill pressure to maintain the selected velocity of most runs |
| Increase holding pressure to maximum |
| Increase injection rate |
|
| Unbalanced runner system
|
| Balance runner and gate sizes to provide balanced filling |
|
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| Flow lines / Flow mark |
| Melt temperature to low
|
| Increase melt temperature |
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| Mold Temperature to low
|
| Increase mold temperature |
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| Gate size to small
|
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| Non- uniform wall thickness
|
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| Redesign part for more uniform wall thickness to provide for optimum filling
|
|
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| Surface of Part Orange-peeled |
| Mold closed too fast under too high pressure
|
| Close mold slowly (Punch and Cavity) |
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| Mold improperly polished
|
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| Material contain excessive moisture
|
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| Part Blistered |
| Mold too hot
|
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| Insufficient pressure
|
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| Molding cycle too short
|
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| Surface of piece dull |
| Mold too hot or too cool
|
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| Mold improperly polished
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| Part do not eject from mold |
| Poor mold finish
|
| Polish out undercuts in cavity |
| Check any damaged surfaces |
| Use mold-release agent |
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| Pressure too high / too long
|
| Lower injection forward time and boost time |
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| Cycle time too short
|
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| Part to hot for ejection
|
| Increase cooling time |
| Decrease melt temperature |
| Decrease mold temperature |
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| Too much packing
|
| Lower injection pressure, screw forward time or the injection boost time |
|
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| Flashing |
| Injection speed too high
|
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| Injection pressure too high
|
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| Melt temperature too high
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