It mainly includes pay-off device, straightening device, preheating device, cooling device, traction device, length counter, spark tester and take-up device. The auxiliary equipment used for dual screw extruder varies according to its different purposes, such as cutters, dryers, printers, etc.
Straightening device
One of the most common types of plastic extrusion waste is eccentricity, and various types of bending of the conductor are important reasons for the generation of insulation eccentricity. In sheathing extrusion, scratches on the surface of the sheath are often caused by the bending of the cable core. Therefore, the straightening device is essential in various extrusion units. Twin screw extruder manufacturers must take extra efforts to implement straightening devices in their extrusion units and ensure that they are of high quality to offer cost-effective solutions for their clients.
The main types of straightening device include: drum type (divided into horizontal and vertical); pulley type (single pulley and pulley group); winding wheel type, serving multiple functions such as dragging, straightening, stabilizing tension, etc.; pressure roller type (divided into horizontal and vertical) and so on.
Preheating device
Cable core preheating is necessary for both insulation extrusion and sheathing extrusion. For insulation layers, especially thin ones, the existence of pores cannot be allowed. Preheating the wire core before extrusion can remove the surface moisture and oil stains.
For sheathing extrusion, its main function is to dry the cable core and prevent the possibility of pores in the sheath due to moisture (or the moisture in the winding layer). Preheating can also prevent the residual internal pressure of plastics due to sudden cooling during extrusion.
During plastic extrusion, preheating can eliminate the significant temperature difference caused by the cold wire entering the high-temperature head and making contact with the plastic at the mold mouth, avoiding the fluctuation of plastic temperature, stabilizing the extrusion output, and ensuring the extrusion quality. This process is particularly essential when using a small plastic extrusion machine, where small deviations in temperature can impact the extruded product quality. Therefore, it is vital to ensure consistent and uniform heating throughout the extrusion process.
All extrusion units use electric heating core preheating devices, which require sufficient capacity and rapid temperature rise to achieve high efficiency in preheating wires and drying cables. The preheating temperature is restricted by the pay-off speed and is generally similar to the temperature of the dual screw extruder head.
Cooling device
The formed plastic extruded layer should be cooled and set immediately after leaving the head; otherwise, it will deform under the influence of gravity. Cooling is usually achieved by water cooling and is divided into fast cooling and slow cooling according to the water temperature.
Fast cooling directly cools with cold water, which is beneficial to the shaping and setting of plastic extruded layers. However, for highly crystalline polymers, abrupt cooling can easily cause residual internal stress in the extruded layer structure, leading to cracking during use. Fast cooling is generally used for PVC plastic layers.
Slow cooling is to reduce the internal stress of the final product. Different temperature water is placed in the cooling tank at different sections to gradually cool and set the product. Slow cooling is used for the extrusion of PE and PP, which is done through three-stage cooling with hot water, warm water, and cold water.
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