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Knowledge Exploration

September 8, 2023

In recent years, co-rotating twin-screw extruders have developed rapidly. Their output, torque and speed have greatly improved, and their use has become increasingly widespread. Improving the production efficiency of co-rotating twin-screw extruders, improving product quality and achieving multi-functionality of equipment are the basic requirements for achieving high performance, and are also the difficulties in research and development. Twin screw extruder manufacturer

  • Improve production efficiency

    Improving production efficiency is one of the primary goals in the development of new co-rotating twin-screw extruders. It can be achieved by increasing screw speed, enhancing plasticizing and mixing capabilities.

Under the same screw speed, increasing the depth of the screw groove can greatly increase the transportation volume. Correspondingly, the plasticizing and mixing capabilities of the screw are required to increase, which requires the screw to withstand greater torque. At high screw speeds, the residence time of the material in the extruder is reduced, which may result in insufficient plasticization, melting, and mixing of the material. For this reason, the screw length needs to be appropriately increased, which in turn will inevitably lead to an increase in the actual carrying torque and power of the twin-screw extruder.

Increasing the free volume of the screw channel is also an important factor. In the feeding section and devolatilization section, it is very necessary for the threaded element to have a large free

volume. For bulk materials, increasing the free volume of the feeding section and the filling degree of the material in the screw groove can greatly improve the production of the extruder. Talent.

To increase torque and speed, careful planning of the reduction distribution box is required. To greatly improve the torque index of the equipment, higher requirements will be placed on the design and manufacturing level of the transmission box. The higher the torque, the higher the design, manufacturing accuracy, material strength and heat treatment requirements for gears, output shafts, bearings and other parts in the transmission box. At the same time, the design and manufacturing accuracy requirements for parts such as the screw mandrel, threaded elements and kneading discs are also higher. higher. Since the free volume of the threaded element needs to be increased, the base distance between the two screws will decrease while the outer diameter of the screw remains unchanged, which will inevitably make the problem of insufficient installation space for the proportioning gear and thrust bearing more prominent.

  • Improve product quality

    To obtain high product quality, the core component of the extruder – the planning of the plasticizing system is closely related.

The plasticizing system mainly includes a screw and a barrel. In order to meet various processing requirements, the screw and barrel are usually designed as a building block structure. According to the function of each section, the screw can be divided into feeding section, plasticizing section, mixing section, exhaust section and extrusion section. These sections have different functions in the extrusion process, their structures are different, and the corresponding screw element geometric parameters are also different. Therefore, how to determine the screw element geometric parameters has become the key to plasticizing system planning.

    For co-rotating twin screws, there is a certain relationship between the pitch diameter ratio (i.e. the ratio of the base distance of the two screws to the radius of the screw), the number of thread heads and the thread top angle. It cannot be designed arbitrarily, otherwise there will be a gap between the two screws. interfere. In order to solve this problem, the author obtained the theoretical end face curve of the screw based on the motion trajectory of the two screws. Using the three-dimensional solid modeling function of large-scale computer-aided design (CAD) software, the author compiled a twin-screw geometric modeling program and completed the three-dimensional twin-screw Entity graphics display, get the geometric parameters of various standard self-cleaning thread elements, and check the meshing status of the two screws. In addition, combined with engineering practice, with the help of computers, a three-dimensional solid shape of a twin-screw with a gap was completed, which can be used to check whether the gap between the two screws is uniform, so that the material has no dead ends in the screw movement, that is, to ensure that the screw has a strong The self-cleaning ability can effectively prevent materials from degradation due to staying in the machine for too long, which undoubtedly provides a good processing method for the production of high-end and excellent plastic products.

    As the screw speed increases, the residence time of the material in the extruder is shortened. In order to make the material more fully plasticized and mixed, and to ease the temperature rise of the material and obtain high-quality products, in addition to the need for In addition to the optimized combination of screw elements, it is also necessary to increase the aspect ratio of the screw. However, as L/D increases, the requirements for the manufacturing accuracy and driving power of the machine as well as the load-bearing torque of the screw core shaft increase, requiring a higher level of manufacturing technology and structural design.

In addition, optimizing the combination of threaded components in the exhaust section, establishing pressure-building components in front of the exhaust port, and using large-lead threaded components can improve devolatilization efficiency; in addition, use melt between the machine head and the extruder. The gear pump builds pressure, which reduces the end pressure of the metering section of the extruder, shortens the effective filling length of the screw, and lengthens the effective exhaust length, which can also improve the exhaust effect to a certain extent. Twin screw extruder manufacturer

Complete multi-functionality

    As the technical uses of twin-screw extruders become more and more widespread, in addition to completing the usual feeding, transportation, compression, plasticizing, mixing, exhausting, homogenizing and other processes in the extruder, dehydration is also usually required. , drying, degradation, reaction extrusion and other technologies, and requires the twin-screw extruder to have functions such as multi-channel feeding and multi-stage exhaust. In order to meet the different technologies of users and the requirements for rapid product updates, the design process of the plasticizing system should focus on the development of different threaded components, barrels and feeding systems. In addition to developing four types of screw elements for different combinations, it is also necessary to design different types of barrels. In addition to the usual closed barrels used in the plasticizing, melting and homogenizing sections, there are also charging barrels with upper openings. barrels, side-feed barrels with side openings and fiberglass, vacuumed barrels.

    The feeding barrel is designed with a wedge-shaped gap at the feeding port. A wedge-shaped gap is formed between the side wall of the feeding port and the surface of the screw to the base of the bottom of the feeding port, so that the material can be smoothly rotated and brought into the extruder. The side feeding barrel is designed for adding difficult-to-add materials such as carbon black or easily decomposed additives that should not stay in the screw for too long, while the auxiliary feeding barrel is designed for adding additives such as glass fiber. On the exhaust barrel, the exhaust port is straight upward, and the base line of the exhaust port is offset from the base line of the barrel by a certain distance along the screw rotation direction, thereby reducing the material being thrown away from the exhaust port by the rotating screw due to centrifugal force. out possibility.

    Designed as a self-cleaning, high-volume co-rotating twin-screw dosing feeder, it cooperates with the side feeder liquid writer to obtain pre-mixing through the stirrer than conventionally used, and then adds it together with the base material through the main feeding port The technology of twin-screw extruders results in better mixing quality and can increase output value to a certain extent.

    Multiple exhaust devices can also be designed, such as natural exhaust and vacuum exhaust systems, to discharge evaporated components during the mixing process. The use of multi-stage exhaust ports can discharge a large amount of evaporated components, which can save the intermediate process of polymerization and mixing and improve production efficiency.

    For extruders with multi-channel feeding and multi-stage exhaust, the length-to-diameter ratio of the equipment should be larger, ranging from 36 to 48, and can be freely adjusted according to the user’s processing technology requirements. Twin screw extruder manufacturer

Barrel and screw have high wear resistance. Threaded components and kneading components need to be made of highly wear-resistant carbide. When used for glass fiber reinforced processing, the service life is 6 to 8 times longer than commonly used nitrided steel. The barrel uses a bimetal bushing to improve wear resistance and extend the service life of the barrel. The bimetal bushing is made of a layer of SL100 high wear-resistant alloy with a thickness of 1.5~2.0mm on the inner wall of the cylinder of ordinary steel or low alloy steel, and then processed by special machinery. The hardness of the alloy layer reaches HRC58~64.