Burn marks
Description
Changing color of plastic (from yellow to black), usually appeared in runner tails or compressed areas.
Preview
Causes
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Possible causes
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Suggested solution
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Injection molding machine |
1.Plastic is so hot. |
Reduced melt temperature.
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| 2.Mold filling speed is too fast. |
Reduce the injection speed
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| 3.Back pressure is too high. |
1.Reduced back pressure.
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2. Check a screw surface speeds are correct.
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| 4.Melting volatile in excess. |
1. Ensure that the air not incident with tank and plastic.
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2. Check the hopper is always filled with plastic to a stable height
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| 5.Using too much clamping force. |
Slightly reduced clamping force.
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6. In the previous production operation with an incorrect machine clearance procedures therefore the plastic cooked in cylinder.
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Strict customs clearance procedures.
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7.Plastic injection cylinders in heated for too long.
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Reduce cycle times.
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| Mold |
1. Mold exhausted or is closed |
Check and clean exhaust.
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2. Surrounded by molten plastic mold in the air and air trapped in it. Formation of trapped air is compressed and combustion burn marks.
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1. On the mold using vacuum exhaust.
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2.By reducing injection part walls or injection molded parts to increase mobile guide on changing the way mold filling
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| 3.Gate size too small. |
Increasing the depth or width of the gate, or increase the gate area area.
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| Plastic |
Incomplete drying of plastic, so left a trace of water.
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1. Drying plastic according to correct procedures.
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2. Use a vacuum or with desiccant dryers.
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