What should I do if there are black spots in the granulation machine? During the granulation process, encountering black spots on the extracted particles is a common problem. How to solve this problem? Is this phenomenon caused by problems with the granulator, raw materials, or other factors? Below, we will analyze and analyze for everyone



The occurrence of black spots during the granulation process is a common fault phenomenon, especially on colored and light colored products. Often, in the final production process, it is found that the product performance and color are not a problem, but after a period of time, customers complain about "the product qualification rate is too low, there are black spots, and they request returns". At this time, many friends are struggling with why black spots appear, which makes them headache.



In order to avoid the harm of carbonization to plastic products as much as possible, the key is to effectively prevent and minimize losses. To gain a deeper understanding of the essence of carbonization, we must also be adept at using effective solutions. In every aspect of solving and preventing carbonization of plastic products, we need to strictly control it.

To quickly clean the carbides inside the machine, it is necessary to use harder plastics or their recycled materials mixed with white mineral oil for cleaning, and the temperature should be appropriately raised by 10-15 ° C. At this point, it is necessary to consider the plasticizing ability of the small extruder on the plastic. For large and medium-sized extruders capable of plasticizing ultra-high molecular weight plastics, ultra-high molecular weight plastics or their recycled materials can be cleaned with white mineral oil. Because ultra-high molecular weight plastics have good hardness, and when the temperature is high, the cleaning object will be softened, making it easy to fall off, which is beneficial for carbides to be carried out by the plastic melt. During the cleaning process, the speed of the extruder is repeatedly switched between low and high speeds. If there is still excess load on the motor, the extruder can be repeatedly stopped and restarted multiple times during operation to further improve the cleaning effect. When the carbides (black spots) in the melt are significantly reduced, replace the commonly used plastic and clean it until it is clean, gradually adjust to the appropriate temperature, and then normal production can be achieved.



In the actual production of plastic products, the feeding port is generally isolated before the plastic granulator is shut down, the plastic melt in the extruder and head is removed, the temperature in each area is turned off, and then the power is turned off. Due to the strong adhesion of plastic melt to metal, it is impossible to completely eliminate it every time the machine is stopped. In the end, a thin layer of plastic melt will firmly adhere to the inner wall of the extruder barrel, head, and screw. After the machine is stopped, it will naturally cool down and remain in a high temperature state for a long time during the next heating process, resulting in significant thermal degradation, gradually turning yellow and transforming into carbides. According to the conventional shutdown method, effective sealing measures were not taken at both ends of the die and feed ports of the machine head, resulting in air entering the machine and causing oxidation, which exacerbated the thermal degradation of residual plastic inside the machine and provided favorable conditions for carbonization.   



Due to the metal structure of the equipment, there is a significant difference in its thermal expansion rate compared to plastic. Carbonized plastic has reduced adhesion to metal and is prone to detachment from the inner walls of the plastic granulator's barrel, head, and screw, mixing into the plastic melt. This results in numerous black spots on the inner and outer walls of the product, making it prone to quality issues such as perforation or leakage. After prolonged shutdown and subsequent heating, many large and small black spots are likely to appear on the plastic product, which cannot meet the quality requirements of the product. These black spots are the carbides of residual plastic that have deteriorated due to thermal degradation inside the machine. Usually, the washing method of continuous extrusion of plastic and elimination of plastic melt with black spots is adopted for cleaning, with a washing time of up to 3-5 hours. If the original ultra-high molecular weight plastic cup is carbonized and the original color products are produced, it will greatly increase the difficulty of washing the machine, make the washing time longer, and increase the washing cost.