Common problems and solutions in the extrusion production line process
1. Plastic scorch is a common quality defect in the plastic extrusion process. Its attention is shown as follows: the temperature is extremely high; there is a lot of smoke in the die mouth of the machine head, strong irritating smell, and cracking in severe cases; plastic extrusion There are coke particles in the layer; there are continuous bubbles at the joint of the glue;
The main reasons are:
1) The temperature is controlled to be as high as the thermal degradation temperature of the plastic;
2) The screw has not been cleaned for a long time, and the accumulated scorch is extruded with the molten plastic;
3) The heating or shutdown time is too long, so that the plastic in the barrel will be decomposed by long-term heating;
4) The temperature control instrument is out of control or inaccurate, causing high temperature decomposition;
5) The cooling system of the extruder is not turned on, causing the material to be overheated by shear friction. Therefore, during the extrusion process, check whether the heating and cooling systems are working properly; the extrusion temperature should be set according to the process requirements and the speed of the screw; the heating time should be reasonably controlled, and the extrusion system should be cleaned regularly.
2. Poor plasticization of extrudates. The problem of plasticization has been mentioned in the temperature control requirements mentioned earlier. Generally, poor plasticization is mainly manifested as: the extruded layer has a toad skin; the plastic surface is black and dull, and there are Small cracks; the extruded layer has obvious seams at the glue; the main reasons are:
1) The temperature control is too low, especially the head part;
2) Other plastic particles of different properties are mixed in the insulating or sheathing material;
3) The screw rotates too fast and the plastic cannot be completely plasticized;
4) The plastic itself has quality problems. For the above reasons, attention should be paid to the reasonableness of extrusion temperature control; the quality and product name of the materials used should be confirmed; the extrusion speed cannot be increased in pursuit of output; the storage of raw materials should be strengthened, especially in the plastic drying process; reasonable mold allocation, To increase the extrusion pressure and screw backflow.
3. There are pores or bubbles in the section of the squeezed layer, and the main reasons are:
1) The temperature control is too high (especially the feed section);
2) The plastic is damp and has moisture;
3) When parking for a long time, decomposing the plastic but not removing it cleanly;
4) High humidity in natural environment;
5) The content of water or vapor in the cable core is too high. In view of the above reasons, the temperature of each section of the screw should be controlled reasonably; the materials used should be pre-dried in advance; the process operation requirements should be strict, and the ability to judge the degree of plasticization of the plastic should be improved; attention should be paid to the production environment and material storage and storage conditions.
4. The size of the extruded package is unqualified, which is mainly manifested as eccentricity; the thickness or outer diameter of the sheath is out of tolerance; the main reasons are: the extrusion and traction speed are unstable;
1) The outer diameter of the cable core changes too much;
2) Excessively high extrusion temperature causes a decrease in extrusion volume;
3) Excessive impurities in the plastic block the filter screen to reduce the plastic flow;
4) The tension of the take-up and take-up line is unstable;
5) The mold core is selected too large (extrusion type) or the length of the mold core wire-bearing area is too short and eccentric;
6) The mold spacing is inappropriate;
7) The temperature of the extruder head is uneven;
8) The concentricity of the extrusion die has not been adjusted well;
9) The temperature of the feed inlet is too high to make the feed difficult and affect the material flow;
For the above reasons, the outer diameter of the sheath should be measured frequently and adjusted in time; the extrusion die should be selected and adjusted reasonably; the tension of the take-up and take-up line should be adjusted in time; the temperature control should be consistent with the specified requirements;
5. The main reasons for the unqualified bonding strength of the longitudinal wrapping tape are:
1) The temperature of the extrudate is too low;
2) Excessive filling and overflow of ointment;
3) The production line speed is too fast, causing the sheath to be rapidly cooled;
4) The temperature of the hot water tank is too low and it is close to the mold opening;
5) The stretch ratio of the matching mold is too small, or the matching mold is unreasonable, causing it to form a loose package;
6) The melting point of the composite film of the longitudinal wrapping tape is too high; according to the above reasons, attention should be paid to the requirements of the mold and adjusted according to the cable core if necessary; the sheath cannot be rapidly cooled to improve the bonding ability; the sheath setting ability should not be improved. Reduce the temperature of the machine head excessively; pay attention to the filling amount of the ointment, and it is better to touch the cable core with your fingers to scrape a thin layer.
6. The appearance of the extruded package is unqualified. The unqualified appearance of the extruded package is mainly manifested as scratches on the surface of the extruded layer; roughness with trachoma or microcracks; any defects caused by inadequate plasticization. The main reasons are:
1) The selection of extrusion die sleeve is unreasonable. Too small will cause hemp pattern; too large will cause disjointed or squeezed looseness;
2) Impurities in the extrusion die sleeve are stuck and scratch the surface of the sheath.
3) Excessive heating temperature of the extruder head causes roughness, or too low temperature causes micro-cracks;
4) The die sleeve sizing area is damaged;
5) The sheath is scratched in the sink; the defects can be eliminated or prevented in production for the above reasons. In actual production, in addition to the above-mentioned defects and causes, there are also problems such as wiring problems, overlapping widths of longitudinal bags, and slub-shaped shapes. We observe and summarize more in production, grasp the main and essence of the problem, and we will solve it easily and make the quality level of the cable better.
Contact: Lily Peng
Phone: +86 13372130421
Email: [email protected]
Add: Tangqiao Town,Zhangjiagang City, Jiangsu Province, China