1. Plastic scorch
Plastic scorch is a common quality defect in the plastic extrusion process. Its attention is shown as follows: the temperature is too high; There is a large amount of smoke and strong irritating smell at the die mouth of the machine head, and there is a popping sound when it is serious; The extruded plastic layer has coke particles; There are continuous bubbles at the glue joint; The main reasons for the note are:
1. The temperature is controlled to reach the plastic thermal degradation temperature;
2. The screw has not been cleaned for a long time, and the accumulated coke is extruded with the molten plastic;
3. The heating or shutdown time is too long, which causes the plastic in the barrel to decompose due to 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 opened, resulting in overheating of the material due to shearing friction.
Therefore, during the extrusion process, it is necessary to strengthen the inspection of whether the heating and cooling systems work normally; Extrusion temperature shall be set according to process requirements and screw speed; The heating time shall be controlled reasonably, and the extrusion system shall be cleaned regularly.
2. Poor plasticization of extrudates
The plasticizing problem was mentioned in the temperature control requirements mentioned earlier. Generally, the poor plasticizing is mainly shown as follows: the extruded cladding has a frog skin; The plastic surface is black, dull, and has small cracks; The extruded cladding has obvious seam at the gluing position; The main causes are:
1. Temperature control is too low, especially at the machine head;
2. Other plastic particles of different properties are mixed in insulation or sheath materials;
3) The screw rotates too fast, and the plastic is not fully plasticized;
4) The plastic itself has quality problems.
In view of the above reasons, we should pay attention to the rationality of extrusion temperature control; The quality and product name of the received materials shall be confirmed; It is not allowed to increase the extrusion speed by blindly pursuing the output; Strengthen the storage of raw materials, especially in the plastic drying process; Reasonable die matching to enhance extrusion pressure and screw reflux.
3. There are air holes or bubbles on the extruded cladding section, which are mainly caused by:
1. Temperature control is too high (especially in the feeding section);
2. The plastic is affected with moisture;
3. Stop for a long time, and the decomposed plastic is not removed completely;
4. High humidity in natural environment;
5. There is water or too much gasified substance in the cable core.
For the above reasons, the temperature of each section of the screw should be reasonably controlled; Pre dry the materials used in advance; Strict process operation requirements, improve the judgment ability of plastic plasticization degree; Pay attention to production environment and material storage conditions.
4. The extruding size is unqualified, which is mainly manifested as eccentric core; Sheath thickness or outer diameter out of tolerance; The main reasons are: the extrusion and traction speed is unstable;
1) . The outer diameter of the cable core changes too much;
2. Too high extrusion temperature will reduce the extrusion amount;
3. Excessive impurities in the plastic block the filter screen to reduce the plastic flow;
4. Unstable tension of take-up and pay off;
5. The mold core is too large (extrusion type) or the length of the mold core wire bearing area is too short and the core is biased;
6. Improper selection of die spacing;
7. The temperature of the extrusion die is uneven;
8. The concentricity of the extrusion die is not well adjusted;
9. The high temperature at the feed inlet makes it difficult to feed and affects the material flow;
For the above reasons, the outer diameter of the sheath shall be measured frequently and adjusted in time; Reasonably select and adjust the extrusion die; Pay attention to the timely adjustment of the tension change of take-up and pay off; The temperature control shall be consistent with the specified requirements;
5. The main reasons for the unqualified bond strength of longitudinal wrapping tape are:
1. The extrudate temperature is too low;
2. Overfilling and overflow of ointment;
3. The speed of the production line is too fast, so that the sheath is rapidly cooled;
4. The temperature of hot water tank is too low and close to the die mouth;
5. The drawing ratio of the matching die is too small, or the matching die is unreasonable, which makes it loose
6. The melting point of the longitudinal clad strip composite film is too high;
According to the above reasons, attention should be paid to the requirements of mold matching, and if necessary, it should be adjusted according to the cable core; The sheath shall not be cooled rapidly to improve the bonding ability; It is not allowed to reduce the head temperature too much due to the improvement of sheath sizing capacity; Pay attention to the filling amount of the ointment. It is better to touch the cable core gently with your fingers to scrape off a thin layer.
6. The appearance of extrusion package is not qualified. The appearance of extrusion package is mainly characterized by scratches on the surface of extrusion coating; Rough with trachoma or microcrack; Any defect caused by plasticization. The main reasons are:
1. The selection of extrusion die sleeve is unreasonable. Too small causes fried dough twist lines; Too large to cause disconnection or extrusion looseness;
2. There are impurities in the extrusion die sleeve that jam and scratch the sheath surface.
3. The heating temperature of the extrusion die head is too high to cause roughness, or the temperature is too low to cause microcracks;
4. The sizing area of the die sleeve is damaged;
5. The sheath is scratched in the water tank; For the above reasons, defects can be eliminated or prevented in production. In actual production, in addition to the above defects and causes, there are also problems such as cable laying, overlapping width of longitudinal package, and bamboo shaped appearance. We should observe and summarize more in production, grasp the main and essence of the problem, and it will be solved easily, so as to improve the quality of the cable.
