Analysis and solution of black spots and broken bars of plastic granulation in injection molding

1. Black dot problem The black dot problem is the most common problem in the production of recycled materials. For light-colored products, the use of black dots will be affected due to the existence of black dots. We will not discuss the problem of black spots in the raw materials themselves. In addition to the raw materials themselves, there are generally the following reasons for the large number of black spots in products.

1. Partial overheating and excessive shearing of the screw Partial overheating and excessive shearing of the screw will cause the local temperature of the material to be too high, which will lead to carbonization of the material in severe cases, and the carbides will be brought into the strip to form black spots. 2. The pressure of the machine head is too high (including blockage, many filters, low temperature of the machine head, etc.). If the pressure of the machine head is high, it will cause the back flow of the head material to increase. In severe cases, the head material will be carbonized and form black spots. 3. The machine is old, and the gap between the screw and the sleeve increases. As the machine is used for a long time, the gap between the screw and the sleeve will increase, and a large amount of material will remain in the gap for a long time, causing carbonization and forming black spots.
4. The natural exhaust port and vacuum exhaust port are not cleaned for a long time. During the production process, the exhaust hole gradually forms a material accumulation, and the accumulated material will be slowly carbonized, and it is brought to the strip during the subsequent extrusion granulation , Forming black spots.
5. The die (including the discharge port and the internal dead corner) is not cleaned. If the discharge port is not smooth enough, there are shallow grooves and potholes, and the damage of some thread originals (dead corners, wear, etc. form dead corners) will cause material accumulation and then Carbonized to form black spots.
6. Impurities mixed into the external environment or artificially. It is necessary to pay attention to the production environment and operating procedures, and to prevent foreign impurities from being mixed into the raw materials and finished products.