Quality defects and treatment methods in extrusion process
1, plastic scorch
Plastic scorch is a common quality defect in plastic extrusion process. Its attention is as follows: the temperature is super high; the die has a large amount of smoke, strong irritating odor, and there is a bursting sound when it is severe; the extruded plastic layer has coke particles; There are continuous bubbles at the joints; the main reasons for the injection 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 scorch 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 material shear friction to overheat.
Therefore, during the extrusion process, it should be checked 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, poor plasticization of the extrudate
In the above, the plasticization problem has been mentioned in the temperature control requirements. The general plasticization failure is mainly as follows: the extrusion layer has a suede-like sample; the plastic surface is black, dull, and has small cracks; the extrusion layer is combined There are obvious seams at the glue; the main reasons for this 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.
4. The size of the extrusion package is unqualified, mainly manifested as eccentricity; the thickness or outer diameter of the sheath is out of tolerance; the main reasons for its formation are:
Extrusion and traction speed is unstable;
1) The outer diameter of the cable core changes too much;
2) The extrusion temperature is too high to cause a decrease in the amount of extrusion;
3) too much impurities in the plastic are blocked in the filter to reduce the plastic flow rate;
4) The tension of the retracting line is unstable;
5) The core selection is too large (squeeze type) or the length of the core carrier area is too short and the core is off;
6) The mode spacing is not suitable;
7) The temperature of the extruder head is not uniform;
8) The concentricity of the extrusion die is not adjusted well;
9) The temperature of the feed inlet is too high to make the feed difficult to affect the flow;
For the above reasons, the outer diameter of the sheath should be measured frequently; the extrusion mold should be properly matched and adjusted; the tension change of the retracting line should be adjusted in time; the temperature control should be consistent with the specified requirements;
5, the vertical bond belt bond strength is not qualified, the main reasons are:
1) the extrudate temperature is too low;
2) excessive filling of the grease;
3) The production line is too fast, so that the jacket is rapidly cooled;
4) The temperature of the hot water tank is too low and is close to the die;
5) The stretching ratio of the mold is too small, or the mold is unreasonable, so that it forms a loose bag;
6) The longitudinal melting zone of the composite film is too high;
According to the above reasons, attention should be paid to the mold matching requirements, if necessary, according to the core adjustment; the jacket should not be cooled rapidly to improve the bonding ability; the jacket setting temperature cannot be increased to excessively reduce the head temperature; The amount, in order to use a finger to touch the core can scrape a thin layer as well.
6, the appearance of the extrusion package is unqualified, the appearance of the unsatisfactory package is mainly caused by scratches on the surface of the extrusion layer; there are trachoma or micro-cracks on the rough; any defects caused by plasticization. The main reasons are:
1) The selection of the extrusion die set is unreasonable. Too small to cause hemp pattern; too large cause disjointed or squeezed loose;
2) Impurities in the extrusion die sleeve get stuck on the surface of the scratched jacket.
3) The heating temperature of the extruder head is too high to cause roughness, or the temperature is too low to cause microcracks;
4) There is damage to the sizing area of the mold sleeve;
5) The sheath is scratched in the sink;
Defects can be excluded or prevented in production for the above reasons.
In actual production, in addition to the above-mentioned defects and causes, there are problems such as the wiring problem, the vertical overlap width problem, and the shape of the bamboo joint. We observe and summarize more in production, and grasp the main and essence of the problem, we will solve it and make the cable quality level better.