Cause Analysis and Solution of Black Spot in Plastic Granulation

In the process of processing the recycled materials, there are often mixed impurities and additives with different components due to the different sources of raw materials, and many problems will arise during the processing, such as products with black spots, strips easy to break, material particles have bubbles, granules with filaments …So how to solve these problems that have long plagued the recycling industry?

Black spot problem

Black spot problem is the most common problem in plastic recycling and pelletizing. For light color products, it will affect its use because of the existence of black spots. In addition to the raw material itself, there are several reasons why there are black spots in the product.

1. Part of the screw is overheated has storng shearing

The local overheating and shear strength of the screw can cause the local temperature of the material to be too high, which will lead to the carbonization of the material, and the carbides will be brought into the strip to form black spots.

2. Too much pressure on the diehead (including blockage, more filters, lower  temperature, etc.)

Heavy head pressure will cause material reflux aggravation, serious will lead to carbonation of the head materials, forming black spots.

3. The aging machine leads to an increase in the gap between screw and barrel

The gap between the screw and barrel will increase with the long service time of the machine, and a large amount of material will remain in the gap for a long time, resulting in carbonation and forming black spots.

4. Long time no cleaning of natural and vacuum vents

In the process of production, the exhaust holes gradually form the material accumulation, the accumulated material will be slowly carbonized, and then the material will be taken to the strip to form black spots during the subsequent extrusion granulation.

5. Diehead (including outlet and internal dead angle) is not clean

If the outlet is not smooth, there are shallow grooves and potholes, as well as parts of the original thread damage (lack of angle, wear and so on to form a dead angle) will cause material accumulation and carbonization, forming black spots.

6. Impurity mixing caused by external environment or human.

Pay attention to the production environment and operation process, avoid foreign impurities mixed into raw materials and finished products.