Extrusion twin screw barrel consist of two intermeshing, co-rotating screws mounted on splined shafts in a closed barrel. Due to a wide range of screw and barrel designs, various screw profiles and process functions can be set up according to process requirements. Hence, a extrusion twin screw barrel is able to ensure transporting, compressing, mixing, cooking, shearing, heating, cooling, pumping, shaping, etc. with high level of flexibility. The major advantage of intermeshing co-rotating twin screw extruders is their remarkable mixing capability which confers exceptional characteristics to extruded products and adds significant value to processing units.
Benefits of Extrusion Twin Screw Barrel
Intuitively understand the wear and tear of wearing parts
Due to the convenient opening, the degree of wear of the screw elements and the inner liner of the barrel can be found at any time, so that effective maintenance or replacement can be carried out. It will not be discovered when there is a problem with the extruded product, causing unnecessary waste.
Reduce production costs
When manufacturing masterbatch, it is often necessary to change the color. If it is necessary to change the product, open the open processing area within a few minutes. In addition, the mixing process can be analyzed by observing the melt profile on the entire screw.
Improve labor efficiency
During equipment maintenance, ordinary twin-screw extruders often have to remove the heating and cooling systems first, and then take out the screw as a whole. The split twin screw is not needed. Just loosen a few bolts and turn the worm gear box handle device to lift the upper half of the twin screw barrel to open the entire barrel and then perform maintenance. This not only shortens maintenance time, but also reduces labor intensity.
High torque and high speed
At present, the development trend of twin-screw extruders in the world is toward high torque, high speed, and low energy consumption. The effect of high speed is high productivity. The extrusion twin screw barrel belongs to this category, and its speed can be up to 500 rpm. So it has unique advantages in processing high viscosity and heat sensitive materials.
- The screw barrel material of 45 steel is relatively cheap, cost-effective, and has good processing functions. The only disadvantage is: Poor wear resistance and corrosion resistance. Heat treatment: quenching and tempering HB220-270; high frequency quenching HRC45-48.
- The screw barrel material of 40Cr has better functions than 45# steel, but we need to plate a layer of chromium frequently to improve its ability to resist corrosion and wear. However, there are higher requirements for the chrome plating layer. If the plating layer is too thin, it is easy to wear, and if it is too thick, it is easy to peel off. After peeling, it will accelerate corrosion, so the material is currently used less. The heat treatment method is: Quenching and tempering HB220-270; hard chrome plating HRC> 55.
- Nitrided steel and 38CrMoAl, which is also the materials of screw barrel, has relatively good comprehensive functions, and its application functions are also relatively wide. Generally, the nitride layer is 0.4 to 0.6 mm. However, this material has relatively low resistance to hydrogen chloride corrosion and is relatively expensive. The heat treatment method: Quenching and tempering HB220-270; nitriding HRC> 65.
Structural Forms of Hopper of Extrusion Twin Screw Barrel
Ordinary hopper with twin screw barrel
This simple structure and low cost hopper is mostly used in small extruders to feed the extruder barrel. The feeding method of this hopper is to rely on the weight of the pellets themselves to fall freely into the extruder barrel. Therefore, during work, pay attention to avoiding the phenomenon of "bridging" of raw materials in the hopper, which affects the continuous feeding of the extruder.
Forced hopper with twin screw barrel
Forced hopper feeding is mostly used in large extruders or when the extruded raw materials are powdered materials. The spiral motor is decelerated by a worm and worm wheel and then driven to rotate. A spring on the upper end applies a certain pressure to the spiral, so that the raw material is pressed into the twin screw barrel when the spiral rotates. When the material in the barrel is full, the back pressure of the pressed material will push up the screw and stop the barrel feeding. When there is no raw material in the barrel, the spiral is pressed down by the spring force and continues to rotate to feed the barrel.
This compulsory feeding method avoids the "bridging" phenomenon of raw materials in the hopper, and can ensure that the hopper continuously feeds the extruder barrel and ensures that the extruder continues to feed production.
Vibrating hopper with twin screw barrel
The structure of the vibrating feed hopper is relatively simple, except that an electromagnetic vibrator is added to the ordinary hopper. When the extruder barrel needs to be fed, start the vibrator to make the hopper shake in the horizontal direction, the raw material in the hopper overcomes the frictional resistance between the hopper wall and the material, and slides down in the shaking and enters the extrusion inside the machine barrel.
The vibrating hopper is suitable for powdery or granular materials. The structure is simple, and it is not easy to cause the phenomenon of "bridging" of raw materials. The cost is low and it is very practical.
Application and Structure of Extrusion Twin Screw Barrel
The use of twin screw extruder barrel
When the screw rotates and pushes the plastic to move forward in the barrel, the outside of the extruder barrel heats and conducts heat to the plastic in the barrel. In addition, the volume of the screw thread on the extruder is gradually reduced, so that the plastic in the screw groove is affected. After the action of various forces such as extrusion, turning and shearing, it is uniformly mixed and plasticized. As it moves to the front of the barrel, it gradually melts into a viscous fluid state to complete the plasticization of the plastic.
The normal cooperation of the extruder barrel and screw ensures the continuous extrusion of raw materials and molding production of the extruder screw.
The structure of the twin screw extruder barrel
The structure is relatively simple. In a large extruder, the structure of the twin-screw extruder barrel can be composed of several sections. Since the barrel is divided into several sections, the length of each section of the barrel is reduced, which brings convenience to the machining of the barrel.
However, for this type of extruder barrel composed of several sections, the inner diameter size after machining and the concentricity accuracy of the inner holes of the several sections of the barrel are difficult to be consistent.
In addition, the barrel of the segmented twin-screw extruder is connected by a flange, which will bring some difficulties to the layout of the heating and cooling equipment of the barrel, and the temperature control will not be too uniform.
In order to save more expensive alloy steel, the barrel of some large extruders adopts the method of inner hole lining or casting wear-resistant alloy layer. The outer casing of the extruder barrel can be cast from ordinary steel to achieve the purpose of reducing the manufacturing cost of the barrel.
Innovative Technology Trends in the Extrusion Twin Screw Barrel Market
High speed, high output of twin screw
High speed, high efficiency and energy saving have been the main theme of continuous improvement of international plastic machinery in recent years. High speed and high output allow investors to obtain high returns with lower investment. However, the high speed of the twin-screw speed brings a series of problems that need to be solved: if the material stays in the screw for a short time, it is easy to cause uneven mixing and plasticization of the material; excessive shear may cause the material to rise rapidly and thermally decompose; Extrusion stability problems occur; high-performance auxiliary machines and precision control systems are needed to match them; screw and barrel wear problems and reduction gear box design problems. Therefore, to provide solutions to the problems that may be brought about by high speed is one of the important directions of extruder screw manufacturers' technological innovation.
Multifunctional twin screw
In terms of function, the twin-screw extruder is no longer limited to the molding and mixing of polymer materials, and its use has expanded to the fields of food, feed, explosives, building materials, packaging, pulp and ceramics. In addition, the "one-step direct extrusion process" that combines the mixing and pelletizing and extrusion molding processes into one is also very attractive.
Large-scale and sophisticated twin screw
Realizing the large-scale extrusion molding equipment can reduce production costs, especially for large twin-screw pelletizing units, film blowing units, and pipe groups. In China, large-scale equipment has long relied on imports, and research on the localization of large-scale twin-screw pelletizing units is currently underway. Precision can increase the gold content of products, such as multi-layer composite co-extruded films. As an important means to realize precision extrusion, melt gear pump should be intensified for development and research.
Modularity and specialization of twin screw
Modular production can adapt to the special requirements of different users, shorten the research and development cycle of new products, and strive for a larger market share; while specialized production can arrange fixed-point production and even global procurement of various system module components of extrusion molding equipment. Ensuring the quality of the whole machine, reducing costs, and accelerating capital turnover are all very beneficial.
Intelligent and networked of twin screw
In addition to the technical transformation of the equipment itself, the advanced twin-screw extruder has generally adopted microcomputer control, the process parameters of the entire extrusion process such as melt pressure and temperature, the temperature of each section of the machine, the speed of the main screw and the feeding screw, the amount of feed, the ratio of various raw materials, the current and voltage of the motor and other parameters are monitored online and control, which is extremely beneficial to ensure the stability of the process conditions and improve the accuracy of the product.
Maintenance knowledge of twin screw extruder barrel
1.After the machine has been used for a period of time, a comprehensive inspection should be done to check the tightness of all screws.
2.In case of production interruption, the main drive and heating will stop. When the power supply is restored, each section of the twin screw barrel must be reheated to the specified temperature and kept for a period of time before the extruder can be started.
3.After the extruder is used for 500 hours, there will be iron filings or other impurities from the gears in the reduction box. Therefore, the gears should be cleaned and the reduction box lubricant should be replaced.
4.If the steering of the meter and pointer is found to be full, check whether the contact of the thermocouple is in good condition.
Daily maintenance of twin screw extruder barrel
1.No debris is allowed in the material of the screw and barrel, and it is strictly forbidden to enter the hopper and extruder with hard objects such as metal and sand.
2.When opening the extruder barrel cover or the air extraction cover, strictly prevent foreign matter from falling into the host.
3.The barrel of the twin-screw extruder should have enough preheating time, and the manual turning should be brisk before driving. Generally, the temperature should be kept constant for 2 hours after reaching the process set temperature.
4.The extruder feed screw can only be started at low speed, and the idling time should not exceed 3 minutes.
5.After the new machine is running in, all gear boxes should be replaced with new oil. After 3000 hours of operation, the lubricating oil should be replaced again. In the future, the lack of quality will be detected during the necessary maintenance and replaced if necessary.
6.Check the wear of the screw barrel and screw, gear box, bearing and oil seal every year.
7.When the main motor is a DC motor, check the carbon brushes of the motor every month, and make a record, and replace them if necessary.
8.When parking for a long time, take measures to prevent rust and pollution of the machine.
9.Daily inspection content: the lubrication status and oil level of each lubrication part, the temperature rise and noise of each rotating part bearing, the vibration of the unit; the current and voltage display of the motor; the temperature and pressure display of the lubricating oil and cooling water and The leakage of its pipeline.
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