The extruder originated in the 18th century and is one of the types of plastic machinery. Based on the direction of the material flow of the die and the angle between the center line of the screw, the die of the extruder can be divided into a right-angle die and an oblique die. . The screw extruder uses the pressure and shear force generated by the rotation of the screw to fully plasticize and uniformly mix the material, relying on die for molding. Single screw extruder, twin screw extruder, screwless extruder and multi-screw extruder are the basic classifications of plastic extruders.
The screw, barrel, hopper, machine and die are all components of the extrusion system. 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 by the head .
1. Machine head and mold
The machine head is composed of an alloy steel inner sleeve and a carbon steel outer sleeve, which transforms the rotating plastic melt into parallel linear motion. The function of the machine head is to transform the rotating plastic melt into parallel linear motion and move into the mold sleeve. It is introduced evenly and smoothly, and the necessary molding pressure is given to the plastic. The plastic is plasticized and compacted in the barrel, and the porous filter plate is used to pass through the neck of the machine head along a certain flow path, and flow toward the molding die of the machine head. The core and die sleeves are properly matched to make the annular gap of the continuously reduced cross-section. The plastic melt is formed by a continuous and dense tubular coating around the core wire. Generally, a shunt sleeve is installed to ensure a reasonable plastic flow path in the machine head, and it is convenient to eliminate the dead angle of the accumulated plastic. A pressure equalizing ring will also be set to eliminate pressure fluctuations during plastic extrusion. In order to adjust and correct the concentricity of the mold core and the mold sleeve, a mold correction and adjustment device is usually installed on the machine head.
According to the angle between the material flow direction of the die head and the center line of the screw, the extruder divides the die head into an oblique die head (with an angle of 120o) and a right angle die head. The shell of the machine head is fixed on the machine body by bolts. The core seat is located in the mold inside the machine head, and the wire inlet port of the machine head is fixed with a nut. The core is installed in front of the core seat and has a hole. Located in the center of the mold core and the mold core seat. Used to pass the core wire, there is a pressure equalizing ring installed in the front of the machine head to balance the pressure. The extrusion molding part is composed of the die sleeve seat and the die sleeve. The position of the die sleeve can be adjusted by the bolts to support. The relative position of the die sleeve to the die core is adjusted to facilitate the uniform adjustment of the thickness of the extruded layer. A heating device and a temperature measuring device are installed outside the machine head.
The barrel is a metal cylinder, usually made of alloy steel or composite steel pipe lined with alloy steel that is heat-resistant, high-pressure-resistant, strong, wear-resistant, and corrosion-resistant. The barrel and screw cooperate to realize the crushing, softening, melting, plasticizing, exhaust and compaction of the plastic, and the rubber material is continuously and uniformly delivered to the molding system. Usually the length of the barrel is 15-30 times its diameter, and its principle is to fully heat and fully plasticize the plastic.
A cutting device is installed at the bottom of the hopper. In order to facilitate the adjustment and cutting of the material flow, a sight hole and a calibration metering device are installed on the side of the hopper.
The screw is the main component of the extruder, which has a very direct relationship with the application range and productivity of the extruder. It is made of high-strength corrosion-resistant alloy steel.