The main unit of a plastic granulator is an extruder, which consists of an extrusion system, a transmission system, and a heating and cooling system. Vigorously develop renewable resources and turn waste into treasure.
1. The extrusion system includes a hopper and a machine head. Plastic is plasticized into a uniform melt through the extrusion system, and under the established pressure in this process, it is continuously extruded by the screw from the machine head.
(1) Screw: It is the most important component of the extruder, which directly affects the application range and productivity of the extruder. It is made of high-strength and corrosion-resistant alloy steel.
⑵ Machine cylinder: It is a metal cylinder, generally made of heat-resistant, high compressive strength, sturdy, wear-resistant, and corrosion-resistant alloy steel or composite steel pipes lined with alloy steel. The combination of the barrel and screw enables the crushing, softening, melting, plasticization, exhaust, and compaction of plastics, and continuously and uniformly delivers the rubber material to the molding system. The length of the general machine barrel is 15-30 times its diameter, in order to ensure that the plastic is fully heated and plasticized.
⑶ Hopper: 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 measuring device.
(4) Machine head and mold: The machine head is composed of an alloy steel inner sleeve and a carbon steel outer sleeve, and a forming mold is installed inside the machine head. The function of the machine head is to transform the rotating plastic melt into parallel linear motion, evenly and smoothly guide it into the mold sleeve, and give the plastic the necessary molding pressure. Plastic is plasticized and compacted inside the machine barrel, and then flows through a certain flow channel through the neck of the machine head through a porous filter plate into the molding mold. The core and sleeve of the mold are appropriately matched to form a continuously decreasing circular gap, allowing the plastic melt to form a continuous and dense tubular coating layer around the core wire. To ensure the rationality of the plastic flow channel inside the machine head and eliminate dead corners of accumulated plastic, a diversion sleeve is often installed. To eliminate pressure fluctuations during plastic extrusion, a pressure equalizing ring is also installed. There is also a device for mold calibration and adjustment on the machine head, which facilitates the adjustment and correction of the concentricity of the mold core and sleeve.
The function of the transmission system is to drive the screw, supply the torque and speed required by the screw during the extrusion process, usually composed of an electric motor, reducer, and bearings.
Heating and cooling devices are necessary conditions for the plastic extrusion process to proceed.
In 2013, electric heating was commonly used in extrusion machines, which can be divided into resistance heating and induction heating. Heating plates were installed in the body, neck, and nose of the machine. The heating device is composed of plastic inside an external heating cylinder, which is heated to reach the temperature required for the process operation.
The cooling device 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 screw rotation, in order to avoid the difficulty of plastic decomposition, scorching, or shaping due to high temperature. Machine barrel cooling can be divided into two types: water cooling and air cooling. Generally, air cooling is more suitable for small and medium-sized extrusion machines, while water cooling or a combination of the two forms of cooling are more commonly used for large machines; The screw cooling mainly adopts central water cooling, with the aim of increasing the solid conveying rate of materials, stabilizing the glue output, and improving product quality; But the cooling at the hopper is to strengthen the conveying effect of solid materials, prevent plastic particles from sticking and blocking the material outlet due to temperature rise, and ensure the normal operation of the transmission part.