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With China Plastic Machinery
With China Plastic Machinery
The single screw extruder is composed of an Archimedean screw rotating in a heated barrel. Due to its simple structure, easy manufacturing, high processing efficiency and low price, it is widely used and is currently the most mature and most used type of extruder.
At present, the single screw extruder has developed from the initial basic spiral structure to various structural types such as damping screw block, exhaust screw, slotted barrel, pin barrel, building block structure, etc. At the same time, due to the small space occupied by the single screw extruder, it has become the main equipment used in the field of composite processing and plastic blown film.
As a common extruder equipment, the single screw extruder is used in the plastic processing industry. What is the principle and structure? The following is an analysis of the principle of the single screw extruder from the conveying section, compression section and metering section of the extruder.
The single screw extruder is generally divided into three sections in terms of effective length. The three effective lengths are determined by the screw diameter, pitch and screw depth, and are generally divided into one-third each.
The high-efficiency single-screw extruder adopts a two-stage overall design to strengthen the plasticizing function, ensuring high-speed, high-performance and stable extrusion. The special barrier comprehensive mixing design ensures the mixing effect of the material. The high shear and low melt plasticizing temperature ensures the high-performance, low-temperature and low-pressure metering extrusion of the material. Design concept and features: high-speed and high-yield extrusion on the basis of high flatness.
The single-screw extruder is mainly composed of three parts: extrusion system, transmission system and heating and cooling system. Its basic structure is shown in Figure 1.
The main function of the extrusion system is to melt and plasticize the polymer material to form a uniform melt, realizing the transition from the glass state to the viscous flow state. In this process, a certain pressure is established, which is continuously extruded and transported to the die head by the screw. Therefore, the extrusion system plays an important role in the molding quality and output of the extrusion process.
The extrusion system mainly includes the feeding device, screw and barrel. It is the most critical part of the extruder. The screw is the heart of the extruder. The material can move in the barrel and get pressurized and partially heated only through the rotation of the screw.
The transmission system is usually composed of a motor, a reducer and bearings. Its main function is to drive the screw and provide the torque and torque required by the screw during the extrusion process. During the extrusion process, the screw speed is required to be stable and not change with the change of the screw load to ensure uniform quality of the product. However, in different occasions, the screw is required to be able to change speed so that one device can adapt to the requirements of extruding different materials or different shapes of products. In most extruders, the change of screw speed is achieved by adjusting the motor speed. The transmission system is also equipped with a good lubrication system and a rapid braking device.
The heating and cooling system of the extruder consists of a heating device and a cooling device, which is a necessary condition for the extrusion process to proceed smoothly. The heating device and the cooling device must ensure that the temperature conditions of the polymer material melt plasticization and the molding process meet the process requirements.
The cooling device is generally installed in the barrel, screw and the bottom of the hopper of the extruder. The barrel cooling can be water-cooled or air-cooled. Generally, small and medium-sized extruders mostly use air cooling; large extruders mostly use water cooling or a combination of the two forms. The screw cooling mainly uses central water cooling, the purpose is to increase the solid conveying rate of the material, stabilize the discharge amount, and improve the product quality. The cooling device at the bottom of the hopper is mainly to strengthen the conveying effect of the solid material, to prevent the material particles from becoming sticky due to the temperature rise, blocking the material port and affecting the feeding. Generally, for extruders with a screw diameter of more than 90mm and high-speed extruders, a cooling device must be installed at the bottom of the hopper.
The last thread of the material port is called the conveying section. The material here is not required to be plasticized, but it must be preheated and squeezed under pressure. In the past, the old extrusion theory believed that the material here was a loose body. Later, it was proved that the material here is actually a solid plug, that is, the material here is a solid like a plug after being squeezed. Therefore, as long as it completes the conveying task, it is its function.
Single screw extruder principle: The second section is called the compression section. The volume of the screw groove gradually decreases from large to small, and the temperature must reach the degree of material plasticization. The compression here is from the conveying section three, and here it is compressed to one. This is called the compression ratio of the screw - 3:1. Some machines also have changes. The plasticized material enters the third section.
Single screw extruder principle: The third section is the metering section. The material here maintains the plasticizing temperature, just like a metering pump, accurately and quantitatively conveying the melt material to supply the head. At this time, the temperature cannot be lower than the plasticizing temperature, and is generally slightly higher.
The single screw extruder is mainly used for extruding soft and hard polyvinyl chloride, polyethylene and other thermoplastics. It can be used with the corresponding auxiliary machines (including the molding head) to process a variety of plastic products, such as films, tubes, plates, ribbons, etc., and can also be used for granulation.
The plastic extruder has advanced design, high quality, good plasticization, low energy consumption, and adopts involute gear transmission. It has the characteristics of low noise, stable operation, large bearing capacity, and long life.
Pipe extrusion: suitable for PP-R pipes, PE gas pipes, PEX cross-linked pipes, aluminum-plastic composite pipes, ABS pipes, PVC pipes, HDPE silicon core pipes and various co-extruded composite pipes.
Plate and sheet extrusion: suitable for the extrusion of profiles and plates such as PVC, PET, PS, PP, PC, etc. Extrusion of various other plastics such as wires, rods, etc.
Profile extrusion: adjusting the speed of the extruder and changing the structure of the extrusion screw can be applied to the production of various plastic profiles such as PVC and polyolefins. Modified granulation: suitable for blending, modification and enhanced granulation of various plastics.
¡òHigh-speed and high-yield extrusion based on high quality.
¡òThe design concept of low-temperature plasticization ensures the extrusion of high-quality products.
¡òTwo-stage overall design strengthens the plasticization function and ensures the adjustment of high-performance extrusion.
¡òSpecial barrier and comprehensive mixing design ensure the mixing effect of materials.
¡òHigh torque output and extra-large thrust bearing.
¡òGears and shafts are made of high-strength alloy steel, carburized and ground.
¡òHigh hardness, high finish and ultra-low noise.
¡òPLC intelligent control can realize the linkage between the main and auxiliary machines.
¡òEasy-to-monitor human-machine interface, convenient for understanding the processing and machine status.
¡òThe control method (temperature control instrument) can be replaced according to needs.
¡òMaterial is 38CrMoAL/A nitrided, wear-resistant.
¡òStrict temperature control accuracy, cooling combined with air cooling and water cooling.
¡òUnique inlet design, with perfect water cooling device.
¡òThe barrel with grooved feeding bottom sleeve has enhanced feeding function, which provides guarantee for high-speed and high-yield extrusion.
Single screw extruder is a type of machine in plastic extrusion production line. Its technical parameters and models are as follows:
1. Technical parameters of single screw extruder:
1) Extruder production capacity Q: the amount of plastic extruded per hour
2) Specific flow rate per hour per revolution of the extruder production capacity
3) Nominal specific power per hour processing kg of plastic required motor power
4) Screw length-diameter ratio L/Db: the ratio of the length of the working part of the screw to the screw diameter
5) Screw diameter Db: refers to the large diameter, series standards 20, 30, 45, 65, 90, 120, 150, 165, 200, 250, 300
6) Drive screw motor power P: KW
7) Screw speed range: nmin-nmaxr/min
2. Model
150/20 means the screw diameter is 150mm, and the aspect ratio is 20:1Plastic extrusion
Application range: all thermoplastic extrusion molding, extrusion granulation.
Hard tooth surface gearbox, AC or DC stepless transmission speed regulation.
New screw structure, uniform melting and mixing, ensuring low melting temperature and high output
The screw barrel material is nitrided steel 38CrMoAIA nitrided, and the surface alloy treatment has higher hardness.
Cast copper and cast aluminum heaters are cooled by air or water as required.
Advanced electrical control system
Advantages: Single screw extruders are simple in design and cheap, so they are widely used.
Disadvantages:
(1) The material conveying of single screw extruders mainly relies on friction, which limits their feeding performance. Powders, pastes, glass fibers and inorganic fillers are difficult to add.
(2) When the head pressure is high, the backflow increases, reducing productivity.
(3) The surface renewal effect of the material in the exhaust zone of the single screw exhaust extruder is small, so the exhaust effect is poor.
(4) Single screw extruders are not suitable for certain processes, such as polymer coloring and thermosetting powder processing.
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