Analysis of the causes of black spots in the discoloration and coking of TPE injection molded products

  • Time of issue:2021-09-01
  • Views:739

Analysis of the causes of black spots in the discoloration and coking of TPE injection molded products

  • Categories:Elastomer knowledge
  • Author:SPP
  • Time of issue:2021-09-01
  • Views:739

The main reason for the discoloration and coking of the injection molded product when the TPE elastomer material is injected is that the plastic or the added ultraviolet absorber, antistatic agent, etc. are overheated and decomposed in the barrel, or decomposed and coked after staying in the barrel for too long. , And then inject the molten material into the cavity to form. analyse as below:

   1. For the machine:

   (1) Due to the out-of-control heating control system, the barrel is overheated, which causes decomposition and blackening.

   (2) Due to the defects of the screw or barrel, the melt is stuck in and accumulated, and it is decomposed by long-term fixed heating. It should be checked whether the rubber head kit is worn or whether there are metal foreign objects in it.

   (3) Some plastics such as ABS are cross-linked and coked by high heat in the barrel. It is difficult to melt under the condition of almost maintaining the original particle shape, and it is entrained into the workpiece after being crushed by the screw.

  2. Mould aspect:

   (1) The mold is not well ventilated, it is easy to scorch, or the size of the pouring system is too small, and the shearing is too severe to cause coking.

   (2) There are inappropriate oil lubricants and mold release agents in the mold.

  3. Plastic aspect:

   Too much volatile plastics, too much humidity, too much impurities, too much recycled materials, and contaminated.

  4. Processing aspects:

   (1) Too much pressure, too high speed, too much back pressure, and too fast speed will decompose the material temperature.

   (2) The barrel should be cleaned regularly to remove additives that are less resistant than plastic.

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