Basic knowledge of screw combination-screw element


Shipping components   The transport element is threaded […]

Shipping components
  The transport element is threaded, and its function is to transport materials (including liquid materials). The shape of the screw groove can be rectangular or special shape (meshing type) generated according to the principle of relative motion. The threaded elements can be divided into two types, forward and reverse, and can be divided into single-head, double-head and three-head threaded elements.
  Single-head threaded element
   has the ability to efficiently transport solids, and is generally used in the feeding section to improve the extrusion volume that is restricted by the feeding volume and to transport materials with poor fluidity, such as low-density materials. It is generally used to transport materials with a particle size similar to water during the reaction process, and can also be used in the discharge section. The output of a single-threaded thread is greater than that of a multi-threaded thread, the torque is also greater than that of a multi-threaded thread, and its mixing characteristics are more than that of a multi-threaded thread.

Comparison of double-thread and triple-thread
   Under the same central moment, D/D. It is relatively large and the groove is deeper, so under the same screw speed, it can provide a lower shear rate, which is more suitable for processing powder materials, especially low bulk powder, glass fiber and other materials that are sensitive to shear . Compared with three-threaded components, under the same shear stress and torque, two-threaded components can be operated at a higher speed and have higher productivity. Under the same screw speed, the three-threaded element can exert a higher uniform shear rate and shear force on the material. In addition, due to the shallow screw groove, the material layer becomes thinner, and the three-threaded component has better heat transfer performance than the two-threaded component. Conducive to plasticization and melting of materials. However, due to the intense shearing, it is generally not easy to process materials that are sensitive to shearing, such as glass fiber and PVC.
   Lead changes and characteristics:
In the screw combination, for the output-oriented occasions, selecting a thread with a larger lead is beneficial to increase the output value. For the extrusion of heat-sensitive polymers, selecting a large lead can shorten the residence time of the material and reduce the thermal degradation of the material . The thread lead has a great influence on the extrusion volume, mixing characteristics, and torque. Generally speaking, the addition of the thread lead and the screw extrusion volume reduce the residence time of the material, and the mixing effect on the material is relatively reduced, and the torque is also Become smaller. Regarding the mixing-oriented occasions, select the middle-lead threads, and for the threads in different working areas of the screw 2, the lead is gradually reduced. Most of them are used for the output and pressurization of solid materials, and then improve the melting Speed ​​or mixing speed and extrusion stability.