Working principle of extruder screw On the whole, altho […]
Working principle of extruder screw
On the whole, although the theory of extruder screw is very mature now, there is still room for advancement. From the study of its extrusion process, the extruder screw is divided into three parts
1. In the process of extrusion, the change rules of physical state of polymer, the transport principle of solid melt, the phase and rule of solid melt transportation and exhaust are established. The mathematical and physical model is used to guide the planning of extruder screw and the optimization of extrusion process
2. It is necessary to find out the real state change of two or more polymers and materials in the extrusion process, the mixing shape, the process of structural change, and the relationship between the mixture and its function
3. As an extruder screw, the internal relationship among reaction process, speed and function, screw configuration and operating conditions during extrusion reaction molding is established to guide reaction molding extrusion.
Generally speaking, screw is the most important part of kneading machine extruder. It not only determines the curing and gelatinization function strength of kneading machine, but also determines the final product quality. Different screws have different kneading functions. The kneading function of screw depends on the planning parameters of screw. Various planning parameters of screw.
The pitch (T) of thread is the interval between the corresponding points on the summary of two adjacent threads; when the thread rotates for 1 cycle, the interval (pitch n) of the thread pushed in the axial direction is called the number of screw slots or the number of thread heads measured by the multiple of the thread pitch. For the screw with single head thread, the pitch is equal to the thread pitch; for the screw with double thread, the pitch is equal to twice the thread pitch; for the screw with three head thread, the pitch is equal to three times of the thread pitch. The screw with multi thread can increase the conveying ability and viscous flow (QD). In the process of continuous mixing and conveying materials, the screw will produce mechanical conflict effect and heat, and then the material will melt.
The screw sleeve wrapped outside the screw can be made into a whole structure, but it is usually equipped with a jacket for circulating heating of steam or superheated oil or for cooling of circulating water. The purpose is to enable kneading machine to accurately regulate the temperature of each operation section. Most screw sleeves are equipped with pressure sensors, temperature sensors and temperature control equipment. The internal and external surface of the screw sleeve is generally made into groove shape, some are linear groove, some are spiral groove. Spiral groove, boost the downstream flow, and linear groove, prevent the downstream flow. Therefore, the linear groove will lead to a lower flow rate, but its mechanical shear effect is greater. The clearance between the screw and its sleeve is generally kept to a minimum to reduce leakage flow.