The auxiliary machine of the plastic extrusion unit mainly includes a pay-off device, a straightening device, a preheating device, a cooling device, a traction device, a metering device, a spark testing machine, and a wire take-up device. The use of the extrusion unit is different, and the auxiliary equipment used for the selection is not the same, such as cutters, blowers, printing devices, etc.
One of the most common types of plastic extrusion waste is eccentricity, and the bending of various types of cores is one of the important reasons for insulation eccentricity. In sheath extrusion, the scratch on the surface of the jacket is also often caused by the bending of the core. Therefore, alignment devices in various extrusion units are essential. The main types of straightening devices are: drum type (divided into horizontal and vertical); pulley type (divided into single pulley and pulley group); winch type, which combines dragging, straightening, and stable tension; Pressure roller type (divided into horizontal and vertical).
Core preheating is necessary for both insulation extrusion and jacket extrusion. For the insulating layer, especially the thin layer insulation, the existence of the pores cannot be allowed, and the core can completely remove the moisture and oil on the surface by preheating before high temperature. For sheath extrusion, its main function is to dry the core to prevent the possibility of voids in the jacket due to moisture (or moisture surrounding the cushion). Preheating also prevents the internal pressure of the plastic from being quenched during extrusion. In the process of squeezing plastic, preheating can eliminate the disparity temperature difference formed when the cold wire enters the high temperature machine head and contact with the plastic at the die mouth, avoiding the fluctuation of the plastic temperature and causing the fluctuation of the extrusion pressure, thereby stabilizing the extrusion amount and ensuring Extrusion quality. The electric heating core preheating device is used in the extrusion unit, which requires sufficient capacity and ensures rapid heating, so that the core preheating and core drying efficiency are high. The preheating temperature is limited by the speed of the line, and is generally similar to the temperature of the head.
After the formed plastic extrusion layer leaves the machine head, it should be cooled and shaped immediately, otherwise it will be deformed under the action of gravity. The cooling method is usually water-cooled and divided into quenching and slow cooling depending on the water temperature. Quenching is the direct cooling of cold water. Quenching is beneficial to the shaping of plastic extrusion coating. However, for crystalline high polymer, due to the rapid cooling, it is easy to residual internal stress in the extrusion layer, resulting in cracks during use. The plastic layer is quenched. Slow cooling is to reduce the internal stress of the product. Different temperatures of water are placed in the cooling water tank to gradually cool down the product. The extrusion of PE and PP is carried out by slow cooling, that is, through hot water, warm water and cold water. Three sections of cooling.