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Discussion on PVC, PE and other plastic wire and cable extruders
- 2019-04-10-

1.    Extruder History of Forming


The electric air-cooled extruder was successfully developed in 1939, and in 1941 it was Successful development of PE has been extruded for more than 60 years.


II.    Production of cable extrusion


The conductor or core wire is supplied to the production line by the wire spool, and after passing preheating, passes through the die and eye mold of the extruder. Insulation or coating is carried out, and after a small period of air cooling, it is cooled into the water tank, and then it is detected by the spark test machine whether it is broken or not, and after inspection of the outer diameter, eccentricity, printing, etc., the coil is taken by the take-up device and the coiler. On the spool.


The extruder is usually expressed by the screw diameter or the inner diameter of the cylinder. For example, the screw diameter is 70MM, which is called 70M/M extruder.


Three.     In terms of the function of the extruder, it is more important to design the screw rod. If the design is improper, not only the operation efficiency is low, but also the quality of the finished product is difficult to control.


General screw can be divided into three parts: feeding section, compression section and metering section. The length of the feeding section is about 1/4 of the total length of the screw. The molten material obtains a good Kunming effect, and the air existing between the materials is pressed back, and is discharged from the feeding hopper. At present, both the PVC and the PE are extruded with a screw of a longer compression section, and the measuring section is a heavier screw. Where it is needed, it can force the molten material to be squeezed out and control the amount of extrusion.


Four.    L/D=effective length of screw


screw outer diameter            (General PVC foamed PE, Screw L/D is above 20)


Compression ratio (CR)=feeding section depth           (General PVC foamed PE, conductive PE extrusion uses a lower compression ratio,


Measuring section depth            screw thermal stability Good PE and PP extrusions use a higher compression ratio screw.)


V.    Gap between the screw and the inner wall of the cylinder


The smaller the clearance is, the better the mechanical manufacturing is. If the gap is large, the material will be very The large countercurrent reduces the amount of extrusion and reduces the efficiency of extrusion. At the same time, when the back pressure is large, the pressure fluctuation has a great influence on the amount of extrusion, which causes uneven material flow, which will affect the control of the outer diameter of the cable and the quality of the finished product. decline.


Six.    Checking method for the stagnation part of the extruder head


If the design of the machine head is improper or worn, the molten material will be burnt due to stagnant time, serious Affecting the quality of the cable, the inspection method can be carried out using materials with strong contrast colors. For example: first use white material for 5-10 minutes, then use the same type of black material for 10-30 minutes. After stopping the machine, look inside the machine head and check the stagnant and stagnant amount of white material.


VII.    The role of the honeycomb plate


Supports the filter group to change the flow direction of the molten material from the circumferential direction of the screw to the parallel direction and the connection screw cylinder and the head .


The purpose of the device filter group is to remove foreign matter and impurities in the molten material, improve the pressure inside the screw cylinder, and make the material knead well. The compounding agent and the filling agent are redispersed.


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