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Possibilities of discoloration of black spots on injection moulds

Plastic Injection moulds are also one of the common types of moulds.During the manufacturing process, we often find black spots, or cause discoloration and coking of injection moulded products.This is a common problem in the manufacture of injection moulds. The added ultraviolet absorber, antistatic agent, etc. decompose in the barrel due to overheating, or stay in the barrel for too long, so as to decompose, coking, and form into the cavity with the molten material injected into the cavity. In order to avoid these problems, we can analyze from the following four aspects:

1. Machine aspect:

(1) As the heating control system is out of control, the barrel is overheated and the decomposition becomes black.

(2) 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 to cause decomposition. Should check whether the plastic head kit is worn or there is no foreign metal in it.

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

2. mould aspect:

(1) The exhaust of the mould is not smooth, easy to scorch, or the size of the pouring system is too small, and the shear is too strong to cause coking.

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

3. Plastic:

Too much plastic volatiles, too much humidity, too many impurities, too much recycled materials, and pollution.

4. Processing:

(1) Excessive pressure, excessive speed, excessive back pressure, and excessive rotational speed will cause the material temperature to decompose.

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

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