Warm Global Customers
With China Plastic Machinery
With China Plastic Machinery
The main machine of the waste plastic recycling machine is an extruder, which consists of an extrusion system, a transmission system, and a heating and cooling system.
The extrusion system includes a screw, a barrel, a hopper, a die, and a mold. The plastic is plasticized into a uniform melt through the extrusion system, and is continuously extruded out of the die under the pressure established in this process.
(1) Screw of waste plastic recycling machine: It is the most important component of the extruder. It is directly related to the application range and productivity of the extruder. It is made of high-strength and corrosion-resistant alloy steel.
(2) Barrel of waste plastic recycling machine: It is a metal cylinder, generally made of heat-resistant, high-compression strength, strong, wear-resistant, and corrosion-resistant alloy steel or a composite steel pipe lined with alloy steel. The barrel and the screw cooperate to achieve the crushing, softening, melting, plasticizing, exhausting and compacting of the plastic, and continuously and evenly transport the rubber material to the molding system. Generally, the length of the barrel is 15 to 30 times its diameter, so that the plastic can be fully heated and fully plasticized.
(3) Hopper of waste plastic recycling machine: The bottom of the hopper is equipped with a cut-off device to adjust and cut off the material flow, and the side of the hopper is equipped with a sight hole and a calibration metering device. Product
(4) Head and mold of waste plastic recycling machine: The head is composed of an alloy steel inner sleeve and a carbon steel outer sleeve, and a molding mold is installed in the head. The function of the head is to convert the rotating plastic melt into parallel linear motion, evenly and smoothly introduce it into the mold sleeve, and give the plastic the necessary molding pressure. The plastic is plasticized and compacted in the barrel, and flows into the head molding mold through the porous filter plate along a certain flow channel through the neck of the head. The mold core and mold sleeve are properly matched to form an annular gap with a continuously decreasing cross-section, so that the plastic melt forms a continuous and dense tubular coating around the core wire. In order to ensure the reasonable flow of plastic in the die and eliminate the dead corners of accumulated plastic, a diverter sleeve is often installed. In order to eliminate pressure fluctuations during plastic extrusion, an equalizing ring is also installed. The die is also equipped with a mold correction and adjustment device to facilitate the adjustment and correction of the concentricity of the mold core and the die sleeve.
According to the angle between the die flow direction and the center line of the screw, the extruder divides the die into an angled die (angle 120o) and a right-angle die. The shell of the die is fixed to the body with bolts. The mold in the die has a core seat and is fixed to the die inlet port with nuts. The front of the core seat is equipped with a core. There is a hole in the center of the core and the core seat for passing the core wire; an equalizing ring is installed at the front of the die for equalizing pressure; the extrusion molding part consists of a die sleeve seat and a die sleeve. The position of the die sleeve can be adjusted by bolts through the support to adjust the relative position of the die sleeve to the die core, so as to facilitate the adjustment of the uniformity of the thickness of the extruded layer. A heating device and a temperature measuring device are installed on the outside of the die.
The function of the transmission system is to drive the screw and provide the torque and speed required by the screw during the extrusion process. It is usually composed of an electric motor, a reducer and bearings.
Heating and cooling are necessary conditions for the plastic extrusion process to proceed.
(1) Waste plastic recycling machine Extruders now usually use electric heating, which is divided into resistance heating and induction heating. The heating plate is installed on the body, neck and head of the machine. The heating device heats the plastic in the cylinder from the outside to raise its temperature to the temperature required for the process operation.
(2) The cooling device of the waste plastic recycling machine is set to ensure that the plastic is within the temperature range required by the process. Specifically, it is to eliminate the excess heat generated by the shear friction of the screw rotation to avoid excessive temperature causing the plastic to decompose, burn or become difficult to shape. Barrel cooling is divided into water cooling and air cooling. Generally, air cooling is more suitable for small and medium-sized extruders, while large ones are mostly water cooling or a combination of the two forms of cooling; screw cooling mainly adopts central water cooling, the purpose is to increase the solid material conveying rate, stabilize the amount of glue, and improve product quality; but the cooling at the hopper is to strengthen the conveying effect of solid materials, prevent the plastic particles from becoming sticky and blocking the material port due to temperature rise, and to ensure the normal operation of the transmission part.
The auxiliary equipment of the waste plastic recycling unit mainly includes wire release device, straightening device, preheating device, cooling device, traction device, meter counter, spark test machine, and wire take-up device. The auxiliary equipment selected for the extruder unit is different for different purposes. For example, there are also cutters, blow dryers, printing devices, etc.
The most common type of plastic extrusion waste is eccentricity, and various types of bending of the wire core are one of the important reasons for insulation eccentricity. In sheath extrusion, scratches on the sheath surface are often caused by the bending of the cable core. Therefore, straightening devices in various extruders are indispensable. The main types of straightening devices are: roller type (divided into horizontal and vertical types); pulley type (divided into single pulley and pulley group); winch type, which has multiple functions such as dragging, straightening, and stabilizing tension; pressure wheel type (divided into horizontal and vertical types), etc.
Cable core preheating is necessary for both insulation extrusion and sheath extrusion. For the insulation layer, especially the thin layer insulation, the existence of pores cannot be allowed. The wire core can be completely cleaned of surface moisture and oil by high temperature preheating before extruding the product package. For sheath extrusion, its main function is to dry the cable core to prevent the possibility of pores in the sheath due to moisture (or moisture in the wrapping cushion layer). Preheating can also prevent the residual internal pressure of the plastic due to sudden cooling during extrusion. In the process of extruding plastic, preheating can eliminate the large temperature difference formed when the cold wire enters the high-temperature die and contacts the plastic at the die mouth, avoid the fluctuation of plastic temperature and cause the fluctuation of extrusion pressure, so as to stabilize the extrusion volume and ensure the extrusion quality. Electric heating wire core preheating device is used in the extrusion unit, which requires sufficient capacity and rapid temperature rise to make the wire core preheating and cable core drying efficient. The preheating temperature is restricted by the wire release speed and is generally similar to the die temperature.
The formed plastic extrusion layer should be cooled and shaped immediately after leaving the die, otherwise it will deform under the action of gravity. The cooling method usually adopts water cooling, and it is divided into rapid cooling and slow cooling according to the water temperature. Rapid cooling is direct cooling with cold water. Rapid cooling is beneficial to the shaping of the plastic extrusion layer, but for crystalline polymers, due to sudden heating and cooling, it is easy to leave internal stress inside the extrusion layer, resulting in cracking during use. Generally, PVC plastic layer adopts rapid cooling. Slow cooling is to reduce the internal stress of the product. Water of different temperatures is placed in the cooling water tank in sections to gradually cool the product down and set the shape. Slow cooling is used for the extrusion of PE and PP, that is, hot water, warm water and cold water.
The control system of the waste plastic recycling machine includes a heating system, a cooling system and a process parameter measurement system, which is mainly composed of electrical appliances, instruments and actuators (i.e., control panels and operating tables).
Control and adjust the traction motors of the main and auxiliary machines, output the speed and power that meet the process requirements, and enable the main and auxiliary machines to work in coordination; detect and adjust the temperature, pressure and flow of the plastic in the extruder; realize the control or automatic control of the entire unit.
The electrical control of the extruder unit is roughly divided into two parts: transmission control and temperature control, which realizes the control of the extrusion process including temperature, pressure, screw speed, screw cooling, barrel cooling, product cooling and outer diameter, as well as the pulling speed, neat wire arrangement and constant tension wire take-up control from empty to full on the take-up reel.
The plastic extrusion of wire and cable insulation and sheath is carried out according to the deformation characteristics of thermoplastics, making them in a viscous flow state. In addition to requiring external heating of the screw and barrel to transfer to the plastic to melt and extrude it, the heat generated by the screw itself when extruding the plastic must also be considered. Therefore, the temperature of the main machine should be considered as a whole, considering both the on and off of the heater heating, and the factors of the extrusion heat overflow of the screw to be cooled, and effective cooling facilities should be available. It is also required to correctly and reasonably determine the position and installation method of the thermocouple measuring element, which can be used from the temperature control instrument.
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