Auxiliary equipment
The auxiliary machine of the plastic granulating 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 for its optional auxiliary equipment. For example, there are also cutters, blowers, printing devices, and the like.
Straightening device: The most common type of plastic extrusion waste type is an eccentricity, and the bending of various types of wire core 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).
Preheating device
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.
Cooling device
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 cooled by water 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 the crystalline high polymer, due to rapid cooling, it is easy to residual internal stress in the extrusion layer, resulting in cracks during use. PVC is generally used. 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.
Control System
The control system of the plastic granulator includes a heating system, a cooling system and a process parameter measurement system, and is mainly composed of an electric appliance, a meter and an actuator (ie, a control panel and an operation console). Its main function is: control and adjust the drag motor of the main and auxiliary machines, output the speed and power according to the process requirements, and enable the main and auxiliary machines to coordinate work; detect and adjust the temperature, pressure and flow of the plastic in the extruder; Control or automatic control of the entire unit.
The electrical control of the extrusion unit is roughly divided into two parts: transmission control and temperature control, which realizes the control of the extrusion process including temperature, pressure, screw revolution, screw cooling, barrel cooling, product cooling and outer diameter, and traction speed. , neatly arranging the line and ensuring constant tension take-up control from the empty plate to the full plate on the take-up reel.
1. Temperature control of the extruder mainframe
The plastic extrusion of the wire and cable insulation and the sheath is based on the deformation characteristics of the thermoplastic, making it in a viscous flow state. In addition to the external heating of the screw and the barrel, it is transferred to the plastic to melt and extrude. It also considers the heat generated by the screw when extruding the plastic. Therefore, the temperature of the main unit should be considered from the whole, considering the heating and opening of the heater. Close, it is necessary to consider the factors of the extrusion head of the screw to cool, and to have effective cooling facilities. It is required to correctly and reasonably determine the position and installation method of the thermocouple of the measuring component, and accurately reflect the actual temperature of each segment of the host from the reading of the temperature control meter. And the accuracy of the temperature control instrument is required to cooperate with the system so that the fluctuation stability of the whole host temperature control system reaches the extrusion temperature requirements of various plastics.
2. Pressure control of the extruder
In order to reflect the extrusion of the machine head, it is necessary to check the head pressure during extrusion. Since the domestic extruder does not have a head pressure sensor, it is generally used to measure the thrust of the screw after extrusion, instead of the head pressure measurement, the screw load table (Electrometer or voltmeter) correctly reflects the extrusion pressure. The fluctuation of extrusion pressure is also one of the important factors causing the instability of extrusion quality. The fluctuation of extrusion pressure is closely related to the extrusion temperature, the use of a cooling device, and the length of continuous operation time. When an abnormal phenomenon occurs, the rapid elimination that can be eliminated, the reorganization of production must be decisively stopped, not only can avoid the increase of waste, but also prevent accidents. By detecting the pressure gauge reading, it is possible to know the pressure state of the plastic during extrusion, and generally, take the back pressure limit value alarm control.
3. Control of screw speed
The adjustment and stability of the screw speed is one of the important process requirements of the main drive. The screw speed directly determines the amount of glue and the extrusion speed. The normal production always wants to achieve the highest speed and achieve high output. When the extruder requires the screw speed from starting to the required working speed, the available speed range is large. . Moreover, the stability of the rotational speed is required to be high, because the fluctuation of the rotational speed will cause the fluctuation of the extrusion amount and affect the extrusion quality so that the change of the outer diameter of the cable will occur if the traction linear velocity does not change. Similarly, if the linear velocity of the traction device fluctuates greatly, the outer diameter of the cable will change. The speed of the screw and the traction wire can be reflected by the corresponding instrument on the console. The extrusion should be closely observed to ensure high quality and high yield.
4. Control of the outer diameter
As mentioned above, in order to ensure the size of the outer diameter of the product cable, in addition to the dimensional tolerance of the control core (core), the extrusion temperature, the screw speed, the linear speed of the traction device, etc. should be controlled, and the outer diameter The measurement control comprehensively reflects the accuracy and level of the above control. In the extrusion unit equipment, especially the high-speed extrusion production line, the online outer diameter detector should be used to detect the outer diameter of the cable at any time, and the over-range signal is fed back to adjust the speed of the traction or screw to correct the outer diameter. Very bad.
5. Tension control required for winding
In order to ensure the wire take-up at different line speeds, the constant tension requirement from the empty plate to the full plate operation, it is desirable to have the wire tension adjusting mechanism for the wire receiving device or to electrically consider the winding of the constant linear speed system and the constant tension system. and many more.
6. Electrical automation control of the whole machine
This is the process control requirement for high-speed extrusion production line, mainly: start-up temperature interlocking; working pressure protection and interlocking; proportional synchronous control of extrusion and traction two major components; synchronous control of take-up and traction; On-line detection and feedback control of the outer diameter; control of the single machine and the whole machine tracking of the components according to various needs.
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