In the plastic extrusion molding equipment, the plastic extruder is usually called the main machine, and the subsequent equipment plastic extrusion molding machine is called the auxiliary machine. After the development of 100 years, the plastic extruder has been derived from the original single screw into various models, such as twin-screw, multi-screw, and even no screw. The plastic extruder (main engine) can be matched with various plastic molding auxiliary machines, such as pipes, films, holding materials, monofilaments, flat wires, packing belts, net extrusion, sheets, profiles, granulation, cable coating and so on. , forming various plastic extrusion molding production lines to produce various plastic products. Therefore, whether now or in the future, plastic extrusion molding machinery is one of the widely used models in plastic processing industry.
2. Development
The plastic extruder originated from18th century. 1795, the manual piston extruder made by JoseghBramah in England for manufacturing seamless lead pipes is considered as the first extruder in the world. From then on, in the first 50 years of the19th century, the extruder was basically only used for the production of lead pipes, the processing of macaroni and other foods, brick making and ceramic industry.
In the process of developing a manufacturing method, R.Brooman applied for a patent on 1845 to produce Gutterbug glue line with an extruder, which was clearly recorded in 1 time. H.Bewlgy of Gutenberg Company subsequently improved the extruder and used it in 185 1 to cover the copper wire of 1 submarine cable between Dover and Calais Company. In the next 25 years, extrusion 13 became more and more important, and manual extruder was quickly replaced by electric extruder. At the beginning, the mechanically operated plunger extruder produced thousands of kilometers of insulated wires and cables, thus firmly establishing the position of extrusion method in cable production. In the early days, the extruders for producing cables were all plunger type, whether manual, mechanical or hydraulic. In this production process, the plunger presses hot gutta percha into the mold through which the copper wire passes, and the gutta percha is extruded from the mold, thus covering the copper wire to form an insulating layer.
Step 3 write a composition
The main engine of plastic extruder is extruder, which consists of extrusion system, transmission system and heating and cooling system.
4. Classification description
1. Extrusion system The extrusion system includes screw, barrel, hopper, die and die head. Plastic is plasticized into a uniform melt by an extrusion system, and is continuously extruded by a screw under the pressure established in the process.
Screw (1): It is the most important part of the extruder, which is directly related to the application scope and productivity of the extruder. It is made of high-strength corrosion-resistant alloy steel.
(2) Machine barrel: it is a metal cylinder, 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 and the screw cooperate to realize the crushing, softening, melting, plasticizing, exhausting and compacting of the plastic, and continuously and evenly convey the rubber to the molding system. Generally, the length of the barrel is 15 ~ 30 times of its diameter, and the principle is to fully heat and plasticize the plastic.
(3) 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 an observation hole and a calibration metering device.
(4) Mold: The mold consists of an alloy steel inner sleeve and a carbon steel outer sleeve, and a molding mold is installed in the mold. The function of the mold is to transform the rotating plastic melt into parallel linear motion, introduce it into the mold sleeve evenly and smoothly, and give the plastic the necessary molding pressure. Plastic is plasticized and compacted in the machine barrel, and flows into the molding die of the machine head through the neck of the machine head and the porous filter plate along a certain flow path. The core sleeve is properly matched to form an annular gap with gradually decreasing cross section, so that the plastic melt forms a continuous and dense tubular coating around the core wire. In order to ensure the reasonable plastic flow channel in the mold and eliminate the dead angle of plastic accumulation, a shunt sleeve and a pressure equalizing ring are often installed to eliminate the pressure fluctuation during plastic extrusion. The die head is also equipped with a device for correcting and adjusting the die, which is convenient for adjusting and correcting the concentricity of the die core and the die sleeve.
According to the angle between the material flow direction of the die and the center line of the screw, the extruder can divide the die into oblique die (angle 120o) and right-angle die. The shell of the machine head is fixed on the machine body through bolts, and the die in the machine head has a die core seat, which is fixed on the wire inlet of the machine head through nuts. The mold core is installed in front of the mold core seat, and the centers of the mold core and the mold core seat are provided with holes for the core wire to pass through; An equalizing ring is installed in front of the machine head to equalize the pressure; The extrusion molding part consists of a die sleeve seat and a die sleeve, and the position of the die sleeve can be adjusted through bolt support, so that the relative position of the die sleeve and the die core can be adjusted, and the thickness uniformity of the extrusion layer can be adjusted conveniently. A heating device and a temperature measuring device are installed outside the machine head.
2. Transmission system 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 device Heating and cooling are necessary conditions for plastic extrusion process.
(1) At present, extruders usually adopt electric heating, which can be divided into resistance heating and induction heating. The heating plate is installed on the fuselage, neck and head. The heating device heats the plastic in the cylinder from the outside to raise the temperature to the temperature required by the process operation.
(2) Set a cooling device 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 rotating shear friction of the screw, and to avoid the decomposition, scorching or difficult setting of plastics caused by too high temperature. Barrel cooling can be divided into water cooling and air cooling. Generally speaking, air cooling is more suitable for small and medium-sized extruders, and water cooling or a combination of the two forms is used for large extruders. Screw cooling mainly adopts central water cooling, aiming at increasing the solid conveying rate of materials, stabilizing the glue output and improving the product quality; However, the cooling at the hopper is to strengthen the conveying function of solid materials, prevent plastic particles from sticking and blocking the material opening due to temperature rise, and ensure the normal operation of the transmission part.
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