The extruder screw is the most important part of the plastic extruder equipment, which is directly related to the plasticizing effect and output of the plastic machine. The rotation of the extruder screw in the barrel is carried out under the high temperature and high pressure and large twist. Because it strongly pushes the material forward during the rotation, it also has to withstand the strong friction and the plastic to decompose the corrosive gas. Erosion, the material of the extruder screw must have high mechanical strength, withstand large torques and non-deformation under high temperature and high pressure conditions.
   During the rotation of the extruder screw, the plastic is mainly sheared and plasticized by the screw edge, and the plastic is pushed forward. Therefore, the screw edge is subjected to huge shear stress and friction force, and the screw edge is operated due to long-term operation under severe conditions. Wear, the screw edge becomes smaller, and the gap with the barrel increases, which leads to a decrease in the amount of plastic extrusion. In severe cases, plastic reflow occurs, and the plasticizing effect is reduced, and the grain and productivity are seriously degraded.
   The process of melt extrusion is to take the premixed material from the feeding port into the extruder barrel. The first section of the barrel is the feeding section. The material will not melt at this stage. The material is taken along with the screw drive of the extruder. The second section is the compression section. The section is the heating stage, the material begins to melt, the friction between the materials increases, and a high-viscosity is formed. The third section that continues to drive with the screw of the extruder into the high shear is the homogenization section. It is very effective in separating pigment aggregates for the purpose of full dispersion. At present, the extruder equipment used in powder coatings is used in twin extruder screw extruders, single extruder screw extruders, and star extruder screw extruders, although the type of extruder, The internal structure is different, but the design is consistent, that is, the material is evenly dispersed. Therefore, Qingdao Guohao Plastic Machinery believes that the quality of the extruder directly determines the degree of dispersion of the material.
The main body of the plastic extruder is an extruder consisting of an extrusion system, a transmission system and a heating and cooling system.
1. Extrusion system The extrusion system includes a screw, a barrel, a hopper, a machine head, and a mold. The plastic is plasticized into a uniform melt by an extrusion system, and is continuously continuous by the screw under the pressure established in the process. Extruder head.
(1) Screw: It is the main 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: It is a metal cylinder. It is generally made of alloy steel with high heat resistance, high compressive strength, strong wear resistance and corrosion resistance or composite steel pipe lined with alloy steel. The barrel is matched with the screw to realize pulverization, softening, melting, plasticizing, venting and compacting of the plastic, and continuously and uniformly conveying the rubber to the molding system. The length of the general barrel is 15 to 30 times its diameter, so that the plastic is fully heated and fully plasticized.
(3) Hopper: The bottom of the hopper is equipped with a cutting device to adjust and cut the flow. The side of the hopper is equipped with a sight hole and a calibration metering device.
(4) Handpiece and mold: The machine head consists of an alloy steel inner sleeve and a carbon steel jacket, and a molding die is mounted in the machine head. The function of the machine head is to transform the rotating plastic melt into a parallel linear motion, which is evenly and smoothly introduced into the mold sleeve and imparts the necessary molding pressure to the plastic. The plastic is plasticized and compacted in the barrel, and flows into the head forming mold through the neck of the neck through a porous filter plate along a certain flow path. The mold core sleeve is properly matched to form an annular gap with a decreasing cross section, so that the plastic melt is in the A continuous dense tubular coating is formed around the core. In order to ensure the plastic flow path in the machine head is reasonable and eliminate the dead angle of the accumulated plastic, a shunt sleeve is often placed. In order to eliminate the pressure fluctuation during plastic extrusion, a pressure equalizing ring is also provided. A mold correction and adjustment device is also mounted on the handpiece to facilitate adjustment and correction of the concentricity of the core and the mold sleeve.
The extruder divides the machine head into a bevel head (120o angle) and a right angle head according to the angle between the flow direction of the head and the center line of the screw. The outer casing of the machine head is bolted to the fuselage. The mold in the machine head has a core sitting and is fixed to the inlet port of the machine head with a nut. The front of the core seat is equipped with a core, a core and a core holder. The center has a hole for passing the core wire; a pressure equalizing ring is arranged at the front of the machine head for equalizing the pressure; the extrusion molding part is composed of a die sleeve seat and a mold sleeve, and the position of the mold sleeve can be adjusted by the bolt through the support In order to adjust the relative position of the die sleeve to the core, it is convenient to adjust the uniformity of the thickness of the extrusion layer. The outside of the machine head is equipped with a heating device and a temperature measuring device.
2. Transmission system The function of the transmission system is to drive the screw. The torque and speed required by the supply screw during the extrusion process are usually composed of a motor, a reducer and a bearing.
3. Heating and cooling device Heating and cooling are necessary conditions for the plastic extrusion process.
(1) Nowadays, extruders usually use electric heating, which is divided into resistance heating and induction heating. The heating sheets are installed in the fuselage, neck and machine parts. The heating device heats the plastic in the cylinder from the outside to raise the temperature to achieve the temperature required for the process operation.
(2) 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 the screw rotation, so as to avoid the temperature being too high, so that the plastic is decomposed, scorched or shaped. The barrel cooling is divided into two types: water cooling and air cooling. Generally, small and medium-sized extruders are suitable for air cooling, while large ones are mostly water-cooled or combined with two forms of cooling. The screw cooling mainly uses central water cooling to increase the material solids conveying rate. Stabilize the amount of glue and improve the quality of the product; however, the cooling at the hopper is to strengthen the conveying effect on the solid material, prevent the plastic particles from sticking and blocking the material due to the temperature rise, and the second is to ensure the normal operation of the transmission part.