In the process of blow molding production, the carbonization of plastic products is a problem that cannot be ignored. Carbonization not only affects the appearance and quality of the product, but can also lead to downtime of the production line and increase production costs. In this article, GREAT will discuss the causes of carbonization of plastic products and the corresponding coping strategies from the perspective of blow molding professionalism. When blow molding manufacturers actually produce plastic products, they usually take measures to isolate the feed port before stopping the machine to ensure that the plastic melt in the extruder and machine head can be completely removed. However, due to the strong adhesion of the plastic melt to the metal, it is difficult to completely remove it every time the machine is stopped, and there is always a thin layer of plastic melt that adheres tightly to the barrel of the extruder, the inner wall of the machine head and the screw. In the process of natural cooling and cooling of the equipment and the next start of heating, the residual plastic melt will be in a high temperature state for a long time, resulting in obvious thermal deterioration, gradually turning yellow, zooming, and finally forming carbides.
Causes of carbonization of plastic products
The processing temperature is too high
During the cleaning process, the speed of the extruder can be switched between low and high speed several times. If the motor load allows, the extruder can also be stopped and restarted repeatedly during operation to further improve the cleaning effect. When the carbides (black spots) in the melt are significantly reduced, they can be replaced with plastic for daily use and continue cleaning until the machine is clean. Subsequently, gradually adjust to the right temperature and normal production can be resumed.
Improper setting of process parameters
The setting of blow molding process parameters, such as injection pressure, injection speed, holding time, etc., will affect the filling and cooling process of the plastic in the mold. If the parameters are not set properly, it may lead to uneven heating of the plastic in the mold, and the temperature in some areas is too high, resulting in carbonization.
The coping strategy of carbonization of plastic products
In-machine cleaning
After a long time of shutdown, when the machine is heated again, there are often many black spots of different sizes on the plastic products, which are actually carbides formed after the thermal deterioration of the residual plastic in the machine, which seriously affects the quality of the products. In order to remove these carbides, the method of continuous extrusion of plastic is usually employed, and the plastic melt with black spots is discharged to achieve the purpose of cleaning the machine, which often takes 3-5 hours. If the machine originally used ultra-high molecular weight plastic and has been carbonized, and the original color products are produced at the same time, the difficulty and cost of cleaning will be greatly increased.
In order to remove carbides from the machine quickly and efficiently, we can choose to use relatively hard plastic or its recycled material and add white mineral oil for cleaning. For large and medium-sized extruders that can plasticize ultra-high molecular weight plastics, they can directly use ultra-high molecular weight plastics or their recycled materials and white mineral oil for cleaning. This is because ultra-high molecular weight plastics are harder, and at higher temperatures, the object to be cleaned will be softened, making it easier to fall off, helping the carbides to be carried out by the plastic melt.
During the cleaning process, the speed of the extruder can be switched between low and high speed several times. If the motor load allows, the extruder can also be stopped and restarted repeatedly during operation to further improve the cleaning effect. When the carbides (black spots) in the melt are significantly reduced, they can be replaced with plastic for daily use and continue cleaning until the machine is clean. Subsequently, gradually adjust to the right temperature and normal production can be resumed.products is a complex issue, which needs to be comprehensively considered and responded to from multiple aspects. By optimizing the processing temperature, correct cleaning methods, and strengthening equipment maintenance and management, the risk of carbonization of plastic products can be effectively reduced, and the quality and production efficiency of products can be improved.
Disassemble and clean
It is relatively easy to clean the carbide in the extruder using the in-machine cleaning method, but it becomes much more tricky to clean the carbide in the storage head of the hollow blow molding equipment. This is mainly due to the relatively intuitive and simple internal structure of the extruder, while the storage head of the hollow blow molding equipment has a complex internal structure, and the equipment is running for a long time, which naturally makes it more difficult to clean.
In this context, disassembly and cleaning become an indispensable solution. For specific operation, the head needs to be heated to a suitable temperature, then the power supply should be cut off, and all components of the head should be removed one by one. Next, the remaining plastic melt in the machine head is carefully cleaned with a copper sheet, and the charred carbide is completely removed with a metal brush. Finally, the components are carefully polished with sandpaper or a leaf wheel to ensure that the surface is as clean as new, and then reassembled and put back into place.
Although the results of dismantling and cleaning are remarkable, the process is time-consuming and physically demanding.
Optimize the processing temperature
According to the characteristics of plastic raw materials and the requirements of blow molded products, the processing temperature is set reasonably. Avoid excessively high processing temperatures and reduce the residence time of plastics at high temperatures to reduce the risk of carbonization.
Adjust the process parameters
According to the characteristics and production requirements of blow molding products, the process parameters such as injection pressure, injection speed, and holding time are reasonably set. Ensure that the plastic can be fully filled and evenly cooled in the mold to reduce the occurrence of carbonization.
Strengthen equipment maintenance and management
Regularly inspect and maintain the blow molding equipment to ensure the normal operation of the equipment. Clean up the carbon deposits and impurities in the mold in time to keep the mold clean and smooth. At the same time, strengthen the training and management of operators, and improve the standardization and accuracy of production operations.
To sum up, the carbonization of plastic products is a complex issue, which needs to be comprehensively considered and responded to from multiple aspects. By optimizing the processing temperature, correct cleaning methods, and strengthening equipment maintenance and management, the risk of carbonization of plastic products can be effectively reduced, and the quality and production efficiency of products can be improved.