Recycling And Regeneration Of Waste Plastic

- Aug 16, 2019-


The main engine of recycling waste plastic is extrusion machine, which consists of extrusion system, transmission system and heating and cooling system.

Extrusion system

The extrusion system includes screw, barrel, hopper, head, and die. The plastic is molded into a uniform melt through the extrusion system, and the head is extruded continuously by screw under the pressure established in the process.

(1) recycled recycled plastic screw: it is the most important part of the extruder, which is directly related to the application range and productivity of the extruder. It is made of alloy steel with high strength and corrosion resistance.

(2) waste plastic recycling machine barrel: it is a metal cylinder, generally made of alloy steel with high heat resistance, compression strength, strong wear resistance and corrosion resistance or composite steel pipe lined with alloy steel. The barrel and screw coordinate to achieve the crushing, softening, melting, plasticizing, exhaust and compaction of plastics, and continuous and uniform delivery of rubber to the molding system. Generally, the length of the barrel is 15 ~ 30 times of its diameter, so that the plastic is fully heated and fully plasticized into the principle.

(3) recycling and reactivation of waste plastics hopper: the bottom of the hopper is equipped with a cutting device to adjust and cut off the material flow, and the side of the hopper is equipped with a viewing hole and calibration and metering device.

(4) recycling and recycling of waste plastic head and die: the head is composed of an alloy steel inner sleeve and a carbon steel jacket, and the head is equipped with a molding mold. The function of the head is to transform the rotating plastic melt into parallel linear motion, evenly and smoothly into the mold sleeve, and give the plastic the necessary molding pressure. The plastic is plasticized and compacted in the machine barrel, and flows into the machine head molding mold through the head neck along a certain flow path through the porous filter plate, and the mold core and die sleeve are properly matched to form the annular gap with decreasing cross section, so that the plastic melt forms a continuous and dense tubular cladding layer around the core wire. In order to ensure the reasonable plastic flow channel in the machine head and eliminate the dead Angle of accumulated plastic, there are often shunt sleeve installed. In order to eliminate the pressure fluctuation during plastic extrusion, there is also a pressure equalizing ring. The head is also equipped with a device for mold correction and adjustment, which is convenient to adjust and correct the concentricity of the mold core and sleeve.

The transmission system

The role of the drive system is to drive the screw, supply screw in the extrusion process required torque and speed, usually by the motor, reducer and bearing composition.

Heating and cooling unit

Heating and cooling are necessary conditions for plastic extrusion.

(1) recycling and recycling of waste plastics. Now extruders usually use electric heating, which can be divided into resistance heating and induction heating. Heating sheets are installed in the body, neck and head. The heating device heats the plastic inside the cylinder externally to reach the temperature required for the operation of the process.

(2) the recycling and regeneration cooling device of waste plastics is set to ensure that the plastics are in the temperature range required by the process. Specifically, the purpose is to eliminate the excess heat generated by the shear friction of screw rotation, so as to avoid the difficulty of plastic decomposition, burning or shaping due to too high temperature. Barrel cooling is divided into two types: water cooling and air cooling. Generally, small and medium-sized extruders are more suitable for air cooling, while large extruders are more suitable for water cooling or combined cooling in two forms. Screw cooling mainly adopts central water cooling, the purpose is to increase the material solid transport rate, stabilize the amount of glue, and improve product quality; But the cooling in the hopper, one is to strengthen the transport of solid materials, to prevent plastic particles from heating up and blocking the material mouth, two is to ensure the normal work of the transmission part.

Auxiliary equipment

The auxiliary machines of waste plastic recycling unit mainly include setting device, straightening device, preheating device, cooling device, traction device, meter counter, spark testing machine, and winding device. The different USES of the extruder unit and its auxiliary equipment are not the same. Such as cutting off device, blow-drying device, printing device and so on.

Straightening device

Eccentricity is one of the most common types of plastic extrusion waste products, and the bending of wire core is one of the important reasons of insulation eccentricity. In the sheath extrusion, the surface of the sheath is often scratched by the bending of the cable core. Therefore, the straightening device in various extruders is essential. The main types of straightening device are: drum type (divided into horizontal and vertical); Pulley type (divided into single pulley and pulley group); Pulley type, and play a drag, alignment, stability of tension and other functions; Pressure wheel (divided into horizontal and vertical) and so on.

Preheating device

Core preheating is necessary for both insulation extrusion and sheath extrusion. For the insulation layer, especially the thin layer insulation, do not allow the existence of pores, the core before squeezing the product package through high temperature preheating can completely remove the surface of water, oil. For jacket extrusion, its main function is to dry the cable core and prevent the possibility of air holes in the jacket due to moisture (or moisture around the coating). Preheating can also prevent the residual pressure of plastics during extrusion due to quench. In the extrusion process, preheating can eliminate the cold line into the high temperature machine head, in contact with the plastic at the die mouth, the difference in temperature, avoid the plastic temperature fluctuations caused by the extrusion pressure fluctuations, so as to stabilize the extrusion quantity and ensure the quality of extrusion. The electric heating device of hot wire core is used in the extruder group, which requires enough capacity and fast heating, so that the preheating of wire core and drying of cable core are high. Preheating temperature is limited by the speed of wire release, generally similar to the head temperature.

Cooling device

The plastic extrusion coating should be cooled and shaped immediately after leaving the head, or it will be deformed under the action of gravity. The cooling method is usually water cooling, and according to the different water temperature, divided into quench and slow cooling. Quench is direct cooling of cold water, quench on plastic extrusion coating design is beneficial, but for crystalline high polymer, because of sudden heat cooling, easy in the extrusion coating organization internal residual internal stress, resulting in the use of crack, general PVC plastic layer using quench. Slow cooling is to reduce the internal stress of products, in the section of the cooling trough to place the water of different temperatures, make products gradually drop in temperature to finalize the design, the extrusion of PE, PP with slow cooling, that is, through hot water, warm water, cold water three sections of cooling.

Control system


The control system of waste plastic recycling and regeneration includes heating system, cooling system and process parameter measurement system, which is mainly composed of electrical appliances, instruments and actuators (namely, control panel and operating table).

The main role

Control and adjust the driving motor of the main and auxiliary machines, output the speed and power in line with the process requirements, and make the main and auxiliary machines work in coordination; Test and adjust the temperature, pressure and flow of plastics in the extruder; Realize the control or automatic control of the whole unit.

Extrusion unit electrical control is roughly divided into drive control and temperature control of two parts, realize the extrusion process including temperature, pressure, screw revolution, cooling, cooling, machine barrel screw products control, cooling and diameter and drawing speed, neat row line and ensure the line plate from the line in empty plate to a plateful of constant tension control.