How to solve the black spots of plastic granulating extruder?

The problem of black spots in the granulation process of plastic pelletizing extruder is a common failure phenomenon, especially in colored and light-colored products. It is often in the final large-scale production process that the performance and color of the product are felt. No problem at all, but after a period of time, I will receive customer complaints and requests for returns. At this time, the problem of tangled black spots is too headache.

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

    To quickly clean the carbides in the plastic pelletizing extruder, it is necessary to use a harder plastic or its return material plus white mineral oil to clean it. The temperature is appropriately increased by 10 to 15 ° C. At the same time, it is necessary to consider the plasticizing ability of the small plastic pelletizing extruder for the plastic. For large and medium-sized plastic pelletizing extruders, ultra-high molecular weight plastics or its feedstock plus white mineral oil can be used for cleaning. Ultra-high molecular weight plastic large and medium-sized extruder plasticizing, ultra-high molecular plastic or return material and white mineral oil cleaning. Because the ultra-high molecular weight plastic has good rigidity, when the temperature is high, the cleaning object will be softened and easily fall off, which is conducive to the carbide being carried out by the plastic melt. During the cleaning process, the plastic pelletizing extruder is repeatedly switched between low speed and high speed. If the motor load has a margin, during the operation, it can be repeatedly stopped and restarted multiple times to further improve the cleaning effect. When the carbides (black spots) in the melt are significantly reduced, they can be cleaned with plastic commonly used for flattening until they are clean, and gradually adjusted to the appropriate temperature, normal production can be achieved.

    In the actual production process, plastic products are usually isolated from the feed port in front of the plastic pelletizing extruder, discharging the plastic melt in the extruder and the head, then turning off the temperature in each zone, and then turning off the power. Because the plastic melt has strong adhesion to metal, it is impossible to completely exclude it when the machine is stopped. In the end, there will always be a layer of plastic melt firmly adhered to the inner wall of the extruded barrel and the head and the screw. On the other hand, after the equipment is naturally cooled down and left for a long period of time during the next heating process, significant thermal degradation occurs, which gradually turns yellow and zooms into carbides. According to the conventional shutdown method, effective measures are not taken at both ends of the die head and the feed port of the machine head to make the air enter the machine to be oxidized, which causes the thermal degradation 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 coefficient is very different from that of plastic. The adhesion of the carbonized plastic to the metal decreases, and it is easy to separate from the inner wall of the barrel, the inner wall of the head and the screw of the plastic granulator. Mixed 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 shutting down, turning on the machine after heating, plastic products are prone to many black spots of various sizes. The quality requirements of the products cannot be met, and the carbides remaining in the machine after thermal degradation are these black spots. Generally, the washing method is to continuously extrude the plastic and remove the plastic melt for washing, and the washing time is up to 3-5 hours. If the original ultra-high molecular weight plastic is carbonized, and the production of primary-color products, it will increase the difficulty of washing the machine, resulting in longer washing time and higher cost.