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How to solve the black spots in the granulation extruder of plastic granulation

How to solve the black spots in the granulation extruder of plastic granulation

In the process of granulating the plastic granulation extruder, it is a common problem to find black spots on the granulated particles. How to deal with the black spots in the plastic granulation process? What caused this phenomenon?

The problem of black spots in the granulation process of plastic granulation extruder is a common failure phenomenon, especially in color and light color products, often in the final large production process, feeling the performance and color of the product. There is no problem, but after a period of time, we will receive customer complaints and request a return. At this time, it is a headache to carry out the problem of black spots.

In order to effectively avoid the harm of plastic products to carbonization, the most important thing is how to prevent it effectively and minimize the loss. We need to understand the nature of carbonization and be good at using effective methods to solve and prevent the carbonization of plastic products, which requires our strict control.

To quickly clean the carbide in the plastic granulation extruder, it is necessary to use a harder plastic, or to return it with white mineral oil, and the temperature is appropriately increased by 10 to 15 °C. At the same time, the plasticizing ability of the plastic by a small plastic pelletizing extruder should be considered. For large and medium-sized plastic pelletizing extruders, ultra-high molecular weight plastics or their recycled materials plus white mineral oil can be used for cleaning. Ultra high molecular weight plastic large and medium extruder plasticized, ultra-high molecular plastic or recycled material and white mineral oil cleaning. Since the ultrahigh molecular weight plastic is hard, when the temperature is high, the cleaning object is softened and becomes easy to fall off, which is favorable for the carbide to be taken out by the plastic melt. During the cleaning process, the plastic pelletizing extruder repeatedly switches between low speed and high speed. If the motor load has a margin, during the operation, it can be repeatedly stopped and restarted several times to further improve the cleaning effect. When the carbides (black spots) in the melt are significantly reduced, they can be cleaned with plastics commonly used for flattening until they are clean, and gradually adjusted to the appropriate temperature for normal production.

In the actual production process, plastic products usually separate the feed port before the plastic granulation extruder, discharge the plastic melt in the extruder and the machine head, then turn off the temperature of each zone, and then turn off the power. Because the plastic melt has strong adhesion to the metal, it is impossible to completely eliminate it when the machine is stopped. Finally, there is always a layer of plastic melt firmly adhered to the extruded barrel and the inner wall of the machine head and the screw. On the other hand, after the device is turned off, the natural cooling and cooling, and the long-term retention of high temperature during the next heating process, significant thermal degradation occurs, gradually turning yellow and zooming into carbide. According to the conventional shutdown method, the die and the inlet of the machine head do not take effective measures to seal, so that the air enters the machine to generate oxidation, which causes the thermal deterioration of the residual plastic in the machine to increase, which provides favorable conditions for carbonization.

Because the equipment is a metal structure, the thermal expansion rate of the plastic is very different, and the adhesion of the carbonized plastic to the metal is lowered, and it is easy to be separated from the inner wall of the inner wall of the barrel of the plastic granulator, the inner wall of the machine head, and the screw. Mixing into the plastic melt, making the inner and outer walls of the product more black spots, prone to quality problems such as perforation or leakage. After a long period of time after shutdown, after heating and then turning on, plastic products are prone to many black spots of different sizes. The quality requirements of the products cannot be met, and the carbides after the thermal deterioration of the residual plastic in the machine are these black spots. It is usually washed by continuously extruding plastic and removing the plastic melt. The washing time is up to 3-5 hours. If the original ultra-high molecular weight plastic is carbonized and the original color products are produced, the difficulty of washing the machine will be increased, resulting in longer washing time and higher cost.

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