How to prevent and address carbonization issues in blow molded products in Shanghai (Part 1)

Carbonization of plastic products can have serious adverse effects on product quality and production costs. For Shanghai blow molding product manufacturers, it is of great significance to effectively prevent and solve the carbonization problem of plastic products.

1. Reasons and processes of carbonization

In the actual production of blow molded products in Shanghai, it is generally necessary to isolate the feed inlet before shutdown, remove the plastic melt from the extruder and head, turn off the temperature in each area, and then turn off the power.

Due to the strong adhesion of plastic melt to metal, it is impossible to completely eliminate it during each shutdown. In the end, a thin layer of plastic melt will firmly adhere to the inner wall of the extruder barrel, head, and screw. After shutdown, the equipment 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 equipment'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.

2. Carbonization solution

2.1 Cleaning inside the machine

After a long shutdown, heating and restarting can easily cause many large and small black spots on Shanghai blow molded products, which cannot meet the quality requirements of the products. These black spots are the carbides of residual plastic after thermal degradation inside the machine. Usually, a washing method is adopted to clean the machine by continuously extruding plastic and removing plastic melt with black spots, with a washing time of up to 3-5 hours. If the original ultra-high molecular weight plastic 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.

To quickly clean the carbides inside the machine, it is necessary to use harder plastics or their recycled materials with white mineral oil for cleaning, and increase the temperature by 10-15 ℃ appropriately.

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.