Fine machine Association equipment
DATE：2022/8/4 9:15:26 / READ： / SOURCE：This station
Fine machine Association equipment
3.1.5.4 structure and main partsThe structural composition of single screw extruder and the location of main parts are shown in Figure 34, including single heating and cooling system and electric control system. The structure of Screw Extruder mainly includes transmission system, compression molding system and feeding system. (1) The main components of the extrusion system the extrusion system of the extruder is the main part of the extruder equipment. Its function is to transform the raw materials from solid state to plasticized and molten state through extrusion and heating, and then evenly extrude them from the splitter plate (also known as porous plate) at the front end of the machine in equal quantity and equal pressure, and enter the molded product mold. Screw a Screw structure screw is an important part of extruder, and its diameter represents the specification of extruder; The selection and application of its structural form is one of the main conditions to ensure the plasticization quality of plastics. The structural forms of commonly used screws are gradual change screw and abrupt gradual change screw. The structural characteristics of gradual change screw are: the thread pitch of the screw is equal, and the depth of the thread groove gradually becomes shallow from the feeding section to the homogenization section. There is also a gradual change screw. The depth of the thread groove in the feeding section and homogenizing section remains the same, while the depth of the thread groove in the plasticizing section gradually becomes shallow from deep. This screw structure is suitable for extrusion and plasticization of PVC and polyethylene explosive car plastics. Mutant screw the depth of the screw groove in the feeding section and homogenization section of the mutant screw remains unchanged, The plasticizing section of the screw (also known as the length of the compression molding section is very short, and the thread groove depth of this section suddenly changes from deep to shallow. This structural screw is suitable for the extrusion molding of crystalline plastics such as polyolefin. The separation screw is widely used in the release type pphdpe pipe. The difference from the above screw structure is that an auxiliary screw is added to the screw part, thereby improving the plasticization speed of raw materials and increasing the output of the extruder. B. the size of the screw, the diameter of the screw refers to the size of the screw The diameter of the outer circle of the threaded part. It is expressed in D, and the unit is mm. The screw diameter can not only represent the size of the extruder, but also related to the size of the plastic products produced by the extruder. Table 37 lists the relationship between the screw diameter and the molding size of plastic products. Length diameter ratio refers to the ratio of the length of the screw thread to the diameter, i.e. l/d. Jb/t8061-1996 stipulates that the length diameter ratio of the screw is within the range of 20-30. So as to ensure the smooth progress of extrusion production. ① Heating extruder production time simple heating methods include resistance heating method, electric induction heating method and heat carrier heating method. At present, the most widely used heating method is resistance heating method. The cast aluminum heater structure as shown in Figure 3-16 is adopted. The resistance wire is installed in the metal tube, and then the tube is filled with magnesium oxide powder and other insulating materials, and then the metal tube is cast in the aluminum figure 3-16 cast aluminum heater structural alloy. Aluminum alloy sleeve and 1-terminal outside the barrel; 2-Metal pipe; 3-resistance wire: large circular contact surface, good heat transfer, metal 4-magnesium oxide powder; 5-The resistance wire in the cast aluminum alloy bushing is filled with magnesium oxide insulating powder, which has good sealing performance, prevents the resistance wire from oxidation, and extends the service life. ② The cooling parts of the cooling Extruder mainly refer to the sectional cooling of the barrel, the cooling of the feeding bucket seat, the cooling of the screw, and the cooling of the thrust bearing parts of the reducer and screw. Generally, air cooling is used for barrel cooling. When it is necessary to cool the barrel, the blower starts, and the flowing air takes away the heat on the surface of the barrel. The cooling of the charging bucket seat is to let the cooling water flow through the cavity cast in the hopper seat and take away the heat here to achieve the purpose of cooling. The purpose of cooling the feeding bucket seat is to prevent the heat generated by forced feeding in the hopper and the temperature rise of the screw feeding section from causing the material temperature to rise and become sticky. As a result, it sticks to the screw and rotates with it. In this way, the raw materials are pushed forward on the screw, so that the extrusion production cannot be carried out smoothly. Screw cooling is to pass heat-conducting medium (water or oil) into the screw drilled with axial hole, and the heat-conducting medium circularly input should be thermostatically controlled into the homogenization section of the screw to cool it. Because the molten material in this section is subject to greater extrusion, friction and shear, it generates more heat and has a fast temperature rise. In order to prevent the decomposition of molten material, it needs to be cooled. The cooling of the reduction gearbox and thrust bearing is to drive the lubricating oil with a pump, so that it can strongly circulate and take away heat, so as to achieve the purpose of cooling. (4) Screen changing device in the extrusion and plasticization system of the extruder, generally there are perforated plates and filter screens on the barrel at the front end of the screw. It can be changed according to the needs of products to ensure the smooth progress of extrusion production. Mesh filter screen and orifice plate; Some products can also be extruded without perforated plates and counting nets. At present, when filter nets are used to extrude products, there are quick screen changing devices, and the structure is shown in 3-17. When the screen needs to be changed, the hydraulic cylinder drives the sliding plate to quickly promote the movement of the commercial plate to complete the replacement of the positions of the old and new nets. At this time, some molten materials will be extruded from the gap of the sliding plate, and cooled and solidified in the gap to form a layer of thin sheets with a thickness of about 0.1mm, which plays a sealing role.
(5) Control system the control system in the extruder equipment is mainly used to control the screw speed, the heating temperature of each part and the melt pressure of plasticized material during the production process of the extruder. At present, the control system of extruder mostly adopts instrument control: PLC programmable control system is also beginning to be applied. Compared with the two control systems, PLC programmable control system is more suitable for the intelligent, automatic and digital control of the extrusion process.
3.1.6 twin screw extruder
In the barrel of the extruder, there are two screws rotating at the same time, that is, a twin-screw extruder. When working, the two screws work together at the same speed to jointly complete the forced advance, transportation and plasticization of plastic.
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