One of the most common types of plastic extrusion waste is eccentricity, and the bending of various types of wire core is one of the important reasons for producing insulation eccentricity. In the sheath extrusion, the scratches on the surface of the sheath are often caused by the bending of the core. Therefore, the straightening device in all kinds of extruding units is essential. The main forms of straightening device are: drum type (divided into horizontal and vertical); pulley type (divided into single pulley and pulley block); winch type, and drag, straightening, stabilizing tension and other functions; roller type (divided into horizontal and vertical).
The preheating of the cable core is necessary for the extrusion of insulation and the extrusion of the sheath. For insulating layer, especially thin layer insulation, the existence of pores can not be allowed. The core of the wire can thoroughly remove the water and oil from the surface before preheating through the high temperature before squeezing. For the jacket extrusion, its main function is to dry the cable core and prevent the possibility of stoma in the jacket due to the effect of moisture (or the moisture of the wrapped cushion). Preheating can also prevent the effect of internal pressure remaining in the extrusion of plastics in the extrusion. In the process of extruding plastic, preheating can eliminate the difference between the cold line entering the high temperature head and the contact with the plastic when the die is in place, so as to avoid the fluctuation of the plastic temperature and lead to the fluctuation of extrusion pressure, so as to stabilize the volume of extrusion and ensure the extrusion quality. The preheating device of electric heating wire core is used in the extruding unit, which requires enough capacity and ensures rapid heating up, so that the preheating of wire core and the drying efficiency of cable core are high. The preheating temperature is restricted by the speed of the discharge line, which is generally similar to the temperature of the head.
The molded plastic pack layer should be cooled immediately after leaving the machine head, otherwise it will be deformed under the action of gravity. The cooling method is usually cooled by water and is divided into quick and slow cooling according to the different water temperature. Quench is the direct cooling of cold water. Quench is beneficial to the shaping of plastic extrusion. But for crystalline polymers, because of sudden cooling, it is easy to remain internal stress in the extrusion layer, resulting in cracking in the use process. Generally, the PVC plastic layer is used for quench. Slow cooling is aimed at reducing the internal stress of products, and placing different temperature water in the cooling tank to make the products gradually cool down. The extrusion of PE and PP is carried out by slow cooling, that is, the three stage cooling is hot water, warm water and cold water.
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