In injection molding production, it is often necessary to change the raw materials, change the color, or cause the decomposition of the raw materials due to the increase of temperature. When all these situations occur, the barrel of the plastic injection molding machine needs to be cleaned. There are several cleaning methods as follows.
1. For the cleaning of the barrel of the plunger injection molding machine, the assembly must be disassembled and then cleaned.
2. The cleaning of the barrel of the screw injection molding machine usually adopts direct refueling cleaning. In order to facilitate the cleaning of the barrel, generally the plastic injection molding products with light color, low melting temperature and poor thermal stability are processed first.
3. If the molding temperature of the new material is higher than the temperature of the remaining material in the barrel, the temperature of the barrel and nozzle should be raised to the minimum processing temperature of the new material, and then the new material (or its recycled material) should be added for continuous air injection until the After the remaining material in the barrel is exhausted, the temperature of the barrel is raised, and when the temperature of the nozzle reaches the required range, new raw materials can be added and transferred to production.
If the plastic injection molding temperature of the new raw material is lower than the temperature of the remaining material in the barrel, the temperature of the barrel and the nozzle should be raised to make the remaining material in the best flow state, then cut off the heating power of the barrel and the nozzle, and use a new The raw materials (or their recycled materials) are continuously injected into the air until the remaining materials in the barrel are exhausted. When the temperature drops to the processing temperature of the new materials, new raw materials are added for production.
4. For heat-sensitive residual materials such as polyvinyl chloride and polyoxymethylene, in order to prevent the plastics from decomposing during the cleaning process, the plastics with good thermal stability such as low-density polyethylene and polystyrene should be used for transition cleaning, and finally the processed The new material replaces the cleaning material.
5. In order to reduce the waste of raw materials, injection molding machine barrel cleaning agent can be used, which is suitable for cleaning injection molding machine barrels of various thermoplastics with a processing temperature range of 180-280 °C.
In plastic injection parts, some metal inserts are sometimes added to increase the working strength of the parts due to the work needs of the parts. Metal parts and plastics are welded into one body during injection molding. Due to the large difference in thermal performance and temperature between the two, a large stress concentration occurs around the plastic and metal contacts during curing, cracks appear, and the strength of the product is reduced.
In order to avoid these phenomena, the metal parts should be preheated before welding with the plastic. The preheating treatment of metal parts can be carried out in the range of 110-150°C according to different metal materials. For smaller metal parts, preheating may be omitted as appropriate.