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Injection Moulds Often Appear Black Spots
May 30, 2018

Core Tip: Injection molds are also one of the common types of molds. During the manufacturing process, we often spot black spots or cause discoloration and coking during injection molding. This is a common problem during the manufacture of injection molds. The main cause of this problem is It is the plastic or the added ultraviolet absorber, antistatic agent, etc., that the inside of the barrel is overheated and decomposed, or that the inside of the barrel stays too long, so that it is decomposed and coking, and is formed along with the melt injection cavity. In order to avoid these problems, we can analyze the following four aspects:

 

    1, machine side:

 

    (1) As the heating control system loses control, the cartridge is overheated and the decomposition becomes black.

 

    (2) Defects due to prolonged fixed heating due to defects in the screw or barrel causing the melt to stick in and accumulate. The plastic head kit should be checked for wear or metal foreign objects inside.

 

    (3) Some plastics, such as ABS, are exposed to high heat and cross-linked coke in the barrel. When almost the original shape of the pellets is maintained, it is difficult to melt, and is broken into pieces by screw pressure.

 

    2, mold:

 

    (1) The mold is not exhausted smoothly, burns easily, or the size of the gating system is too small and the shear is too severe to cause coking.

 

    (2) Inappropriate oil lubricants and mold release agents in the mold.

 

    3. Plastics:

 

    Excessive plastic volatiles, excessive humidity, excessive impurities, too much recycled material, and contamination.

 

    4, processing:

 

    (1) The pressure is too high, the speed is too high, the back pressure is too large, and the speed is too fast to decompose the material temperature.

 

    (2) The barrel should be cleaned regularly to remove additives that are inferior to plastics.