Black Spots on Injection Products | Possible Causes

This is an analysis of the possible causes of black spots on injection products.

Causes of black spots

1. Machine

  • As the heating control system is out of control, the barrel is overheated and becomes black after decomposition.
  • Due to the defect of the screw or the barrel, the molten material is stuck and hoarded, which is subject to long-term fixed heating, causing decomposition. Thus, we should check whether the plastic head kit is worn or whether there are metal foreign objects inside.
  • Some plastics such as ABS are subject to high heat in the barrel and are crosslinking coking. And it is difficult to melt under the condition of almost maintaining the original particle shape. Then, it is crushed by the screw and entrained into the part.

2. Mold

  • Mold exhaust is not smooth, easy to scorch.
  • The size of the pouring system is too small.
  • The shear is too strong, causing coking.
  • There are inappropriate oil lubricants and mold release agents in the mold.

3. Plastics

  • Too much plastic volatiles
  • Overly high humidity
  • Too many impurities
  • Too much recycled materials and contamination

4. Processing

Excessive pressure, excessively high speed, excessive back pressure, and excessively fast speed will cause the material temperature to decompose.

We should clean the barrel regularly to remove additives that are less resistant than plastic.

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