Single screwThe extruder is composed of an Archimedean screw rotating in a heated barrel. It is widely used due to its simple structure, easy manufacturing, high processing efficiency and low price. It is the most mature and most used type of extruder.
Single-screw extruders have evolved from the original basic spiral structure to various structural types such as damping screw blocks, venting screws, slotted barrels, pin barrels, and building block structures. At the same time, due to the small space occupied by single-screw extruders, they have become the main equipment used in composite processing and plastic blown film fields.
Basic structure
- Connecting flange
- Porous plate
- Cooling water pipe
- heater
- screw
- Material cylinder
- Oil pump
- Speed motor
- Ball bearings
- Feeding hopper
- Gear reducer
- Screw cooling device
The single screw extruder is mainly composed of three parts: extrusion system, transmission system and heating and cooling system.
Extrusion system
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, and the screw is continuously extruded and transported to the die head. 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 through the rotation of the screw and obtain pressurization and partial heat.
Drivetrain
The transmission system is usually composed of an electric 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 the 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.
Heating and Cooling Systems
The heating and cooling system of the extruder consists of a heating device and a cooling device. It 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 usually installed in the barrel, screw and the bottom of the hopper of the extruder. The barrel can be cooled by water or air. Generally, small and medium-sized extruders use air cooling, while large extruders use water cooling or a combination of the two. The screw cooling mainly uses central water cooling, the purpose of which is to increase the solid material conveying rate, stabilize the output, and improve product quality. The cooling device at the bottom of the hopper is mainly to enhance the conveying effect of solid materials and prevent the material particles from becoming sticky due to temperature rise, blocking the material port and affecting the feeding. Generally, for extruders with a screw diameter of more than 90 mm and high-speed extruders, a cooling device must be installed at the bottom of the hopper.
Applications
1. Pipe extrusion: suitable for PP-R pipe, PE gas pipe, PEX cross-linked pipe, aluminum-plastic composite pipe, ABS pipe, PVC pipe, HDPESilicone core tubes and various co-extruded composite tubes.
2. Plate and sheet extrusion: Suitable for the extrusion of PVC, PET, PS, PP, PC and other profiles and plates. Extrusion of other plastics such as wire, rod, etc.
3. Extrusion of profiles: 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. Modification granulation: Applicable to the blending, modification and enhancement granulation of various plastics.
Machine design
- High-speed and high-yield extrusion based on high quality.
- The design concept of low temperature plasticization ensures the extrusion of high-quality products.
- Two-stage overall design strengthens the plasticizing function and ensures high-performance extrusion.
- Special barrier and comprehensive mixing design ensure the mixing effect of materials.
- High torque output, extra large thrust bearing.
- Gears and shafts are made of high-strength alloy steel, carburized and ground.
- High hardness, high finish, ultra-low noise.
- PLC intelligent control can realize the linkage between main and auxiliary machines.
- Easy-to-monitor human-machine interface, convenient for understanding processing and machine status.
- The control mode (temperature control instrument) can be changed according to needs.
- The material is 38CrMoAL /A nitrided, wear-resistant.
- Strict temperature control accuracy, combined cooling of air cooling and water cooling.
- Unique feeding port design with perfect water cooling device.
- The screw barrel with grooved feeding bottom sleeve has enhanced feeding function and provides guarantee for high-speed and high-yield extrusion.
Single screw extruder is a type of machine in plastic extrusion production line. The explanation of its technical parameters is as follows:
Technical parameters of single screw extruder
ExtruderProduction capacity Q: the amount of plastic extruded per hour
Extruder production capacity per hour per revolution
Nominal specific power: The motor power required to process kg of plastic per hour
Screw aspect ratio L/Db: ratio of the length of the working part of the screw to the screw diameter
Screw diameter Db: refers to the large diameter
Driving screw motor power P: KW
Screw speed range: nmin-nmax r/min
Features
1. Hardened gearbox, AC or DC stepless transmission speed regulation.
2. New screw structure, uniform melting and mixing, ensuring low melting temperature and high output
3. The screw barrel material is made of nitrided steel 38CrMoAIA, and the surface alloy treatment has higher hardness.
4. Cast copper and cast aluminum heaters can be cooled by air or water according to requirements.
5. Advanced electrical control system
Advantages and disadvantages
1. Advantages: Single screw extruder is simple in design and cheap in price, so it is widely used.
2. Disadvantages:
(1) The material conveying of the single-screw extruder mainly relies on friction, which limits its feeding performance. It is difficult to add powder, paste, glass fiber and inorganic filler.
(2) When the head pressure is high, the backflow increases, which reduces 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 process steps, such as polymer coloring, thermosetting powder processing, etc.
