Single-screw extruder has a long history, the application of basic research is quite adequate and mature, by contrast, the twin-screw extruder has only about 60 years of history, publicly published on the twin-screw extrusion literature far less than the single Screw. Twin-screw extruders can be categorized by a variety of features, so a wide variety. Their structural and operational characteristics are quite complex and vary greatly. Based on the literature on the twin-screw extrusion that has appeared so far, there are divergent opinions. Based on the classification and working principle of the parallel twin-screw mechanism, , The application of parallel twin screw mechanism in twin screw pump, twin screw compressor, twin screw extruder, twin screw extruder and twin screw refiner is emphatically expounded, and the differences, characteristics and Working conditions.
Twin Screw Profile
Originally produced in food and plastic processing, twin-screw machines have expanded their use in recent decades to include rubber, coatings, petrochemicals, building materials, pulp, food, feed processing and fluid machinery. Twin-screw machine is the core of double-screw mechanism. The twin-screw mechanism has been widely used because it has the advantages of simple conveying, high mixing capacity, good self-cleaning performance, high efficiency and simple structure than the three-screw and above multi-screw mechanism. Twin-screw mechanism by its screw axis position can be divided into parallel and non-parallel two categories. As the parallel twin-screw machine manufacturing, easy installation, lower cost, so a wide range of applications. This article mainly discusses the main features of parallel twin-screw mechanism and its application.
Parallel twin-screw mechanism
The construction of the parallel twin-screw system varies depending on the application area and operating characteristics. According to the steering is divided into different directions and the same direction of rotation, according to the form of engagement is divided into meshing and non-meshing, meshing is divided into fully meshed and partially meshed. As a wedge screw like a wedge into the same screw into the other screw slot, the material can not basically continue from the screw into the adjacent groove to go, but can only be forced by a screw The screw thread goes to the screw groove of the other screw. As the screw continues to rotate and forced the material to be turned, the result of the material by a better shear mixing, this structure has a good self-cleaning ability. Geometrically, the groove in the engagement area is closed in the transverse direction, but it can also be open, but it can not be closed in the longitudinal direction, otherwise interference will occur. That is, the width of the screw groove must be designed to be larger than the width of the screw thread, and the road is blocked by the other screw. Materials in the threaded push, through the part of the gap and do circular motion, but also to do axial movement. Material through the radial gap between the screw as if the material through the roller nip, subject to intense shear agitation. Due to the unique structure and working principle of twin-screw mechanism, it has many functions such as extrusion conveying, mixing or cutting, reaction and extrusion. Can be made into a closed material with the role of sealing, but also to the pressure of the place to feed, easy to add in any position or discharge; also because of its shell and rotating shaft made of water-cooled structure, it can be used for high temperature Occasions such as material handling. A variety of agencies in the performance and application of the existence of a rotating twin screw, screw edge and screw groove of the opposite direction of speed, the relative speed of rotation than the reverse, so the meshing material shear rate, shear force is also large , The mixing effect is better than the reverse rotation of the twin screw. The co-rotating twin screw extruder has no pressure at the helical engagement, no high shear zone, low wear of the screw and barrel, suitable for high speed operation. While the opposite twin screw at the top of the mesh to form a higher pressure, resulting in a larger shear rate, with the screw speed increases, the screw and cylinder wear increased, suitable for low speed operation. In addition, co-rotating twin-screw devices, because of their own mechanism, have good self-cleaning to avoid blockage problems and feeding problems, whereas cross-biaxial devices have only a degree of self-cleaning. As far as the number of screw heads is concerned, the co-rotating twin screw has the maximum positive displacement conveying capacity in the single head, which can prevent the material from accumulating in the feeding port because it is too late to move forward, affecting the normal feeding. The cross-sectional area of the helical groove of the double-headed forward threaded element is a little smaller and the shearing action is softer. It is currently used most frequently in applications where good mixing and conveying are required. Three positive thread components of the smallest cross-sectional area of the screw groove, the shearing strong, but the conveying capacity is low, and more for high shear needs to open the occasion to ensure vertical.
Application of parallel twin-screw mechanism
For cylindrical helical gears, counter-rotating twin-screw and twin-rotor, we can see that there is a great similarity whether in the meshing process, the working principle, or its manufacturing. Instead of thinking of a cylindrical helical gear as the primary of a counter-rotating twin-screw, the counter-rotating twin rotor is a higher order form of counter-rotating twin-screw that rotates the driver-driven follower. As for the co-rotating twin-screw, two screws need to be powered, the principle of engagement and gear meshing principle is different. Due to the large difference in mechanical properties of materials, the structure and operating parameters of twin-screw machines are also different. According to the structure and characteristics of its use, the twin-screw pump is divided into two categories: one is directly driven by the main rod from the rod; the other is the outer support type, from the rod by the main rod with synchronous gear transmission to non-contact operation between the working profile.
