1. Extrusion systemThe extrusion system includes a screw, a barrel, a hopper, a head, and a mold, and the plastic is plasticized into a uniform melt through the extrusion system, and under the pressure established in this process, the screw is continuously extruded out of the head.
(1) Screw: It is the main component of the extruder, which is directly related to the application range and productivity of the extruder, and is made of etched alloy steel.
(2) Barrel: It is a metal cylinder, which is generally made of alloy steel or composite steel pipe lined with alloy steel that is not afraid of heat and compressive strength, strong and not easy to corrode. The barrel cooperates with the screw to crush, soften, melt, plasticize, vent and compact the plastic, and continuously and evenly conveys the rubber material to the molding system. Generally, the length of the barrel is 15~30 times of its diameter, so that the plastic can be sufficiently heated and plasticized as the principle.
(3) Hopper: The bottom of the hopper is equipped with a cut-off device in order 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.
(4) Machine head and mold: The machine head is composed of alloy steel inner sleeve and carbon steel outer jacket, and the machine head is equipped with a forming mold. The function of the machine head is to convert the rotating moving plastic melt into parallel linear motion, which is evenly and smoothly introduced into the mold sleeve, and gives the plastic the required molding pressure. The plastic is plasticized and compacted in the barrel, and flows into the head forming mold through the corresponding flow channel along the corresponding flow channel through the porous filter plate, and the mold core sleeve is properly matched to form an annular void with decreasing cross-section, so that the plastic melt forms a continuous and dense tubular coating layer around the core line. In order to determine the correctness of the plastic flow channel in the machine head and remove the dead angle of the accumulated plastic, a shunt sleeve is often placed, and a pressure equalizing ring is also set to remove the pressure fluctuation during plastic extrusion. The machine head is also equipped with a device for mold correction and adjustment, which is convenient for adjusting and correcting the concentricity of the mold core and mold sleeve.
2. The function of the transmission system is to drive the screw and supply the torque and speed required by the screw in the extrusion process, which is usually composed of a motor, a reducer and a bearing.
3. Heating and cooling deviceHeating and cooling are the necessary conditions for the plastic extrusion process.
(1) At present, the extruder usually uses electric heating, which is divided into resistance heating and induction heating, and the heating sheet is installed in the body, neck, and head. The heating device heats up the plastic inside the external cylinder to the temperature required for the process operation.
(2) The cooling device is set up to determine the temperature range of the plastic in the process requirements. Specifically, it is to eliminate the excess heat generated by the shear friction of the screw rotation, so as to avoid the high temperature that makes it difficult for the plastic to decompose, scorch, or set. Barrel cooling is divided into two types: water-cooled and air-cooled, generally small and medium-sized extruders use air cooling, and large extruders mostly use water-cooled or two forms of combined cooling; The screw cooling mainly adopts central water cooling, which aims to increase the solid conveying rate of materials, stabilize the amount of glue, and improve product quality. However, the cooling at the hopper is to increase the conveying effect of solid materials and prevent the plastic particles from sticking and blocking the material port due to rising temperature, and the second is to ensure that the transmission part works normally.
