Common quality defects and treatment methods in extrusion process

1. Plastic scorch: Plastic scorch is a common quality defect in plastic extrusion process. Its main performance is: the temperature is super high; the die has a large amount of smoke, strong irritating smell, and bursting sound when it is severe; extrusion There are coke particles in the plastic layer; there are continuous bubbles in the rubber joint; the main reasons are:

1) The temperature control is too high to reach the thermal degradation temperature of the plastic;

2) The screw has not been cleaned for a long time, and the accumulated burnt material is extruded with the molten plastic;

3) Heating or downtime is too long, so that the plastic in the barrel is decomposed by heat for a long time;

4) The temperature control instrument is out of control or misaligned, causing pyrolysis;

5) The extruder cooling system is not opened, causing the material to shear friction and overheat. Therefore, during the extrusion process, it should be strengthened to check whether the heating and cooling system work normally; the setting of the extrusion temperature should be determined according to the process requirements and the rotation speed of the screw; the temperature is controlled reasonably, and the extrusion system is cleaned regularly.

2, the plasticization of the extrudate is poor. In the above, the plasticization problem has been mentioned in the temperature control requirements. The general plasticization is mainly manifested as: the extrusion layer has a suede-like shape; the plastic surface is black, dull, and Small cracks; the extruded layer has obvious seams at the glue; the main reasons are:

1) The temperature control is too low, especially the nose part;

2) Other plastic particles of different properties are mixed in the insulating or sheathing material;

3) The screw is too fast to plastic, and the plastic is not completely plasticized;

4) There are quality problems in the plastic itself. For the above reasons, attention should be paid to the rationality of extrusion temperature control; the quality of the materials to be used should be confirmed; the extrusion speed should not be pursued blindly; the storage of raw materials should be strengthened, especially in the plastic drying process; To enhance extrusion pressure and screw backflow.

3. There are pores or bubbles in the section of the extrusion layer, which are mainly caused by:

1) The temperature control is too high (especially the feed section);

2) The plastic is damp and has moisture;

3) Parking for a long time, the plastic is not excluded;

4) The natural environment has high humidity;

5) The water or vapor content in the core is too high.

For the above reasons, the temperature of each section of the screw should be reasonably controlled; the materials used should be pre-dried in advance; the requirements of strict process operation should be improved, and the ability to judge the plasticization degree of plastics should be improved; attention should be paid to the production environment and storage conditions of materials. Among them, the size of the extrusion is unqualified, mainly characterized by eccentricity; the thickness or outer diameter of the jacket is out of tolerance; the unqualified appearance of the extrusion is mainly caused by scratches on the surface of the extrusion layer; there are trachoma or microcracks on the rough; Any defects caused.