Mixing type single screw extruder
DATE：2021/3/10 9:32:25 / READ： / SOURCE：This station
Mixing type single screw extruder
Air permeable membrane equipment
Single screw extruder is one of the most important extruders in polymer processing industry. Its characteristics are simple structure, low cost, is the key part of the extruder; 2 transmission system: its role is to drive the screw, to ensure the screw in the working process of the required torque and speed; 3 heating and cooling system: it ensures the temperature control requirements of the plastic and extrusion system in the processing process. Air permeable membrane equipment www.handern.comScrew structure of single screw extruder
The screw of conventional single screw extruder is generally divided into three sections, namely, the feeding section with deep spiral groove and constant groove depth, the compression section (melting section) with shallow spiral groove and constant groove depth along the discharge direction, and the metering section (homogenization section) with shallow spiral groove and constant groove depth. The tail of the screw is a cylinder, the size should be selected according to the national standard, and the tail is connected with the transmission device by one or several keyways or splines. The unit of screw diameter is mm, and the diameter standard series are 30, 45, 65, 90, 120, 150, 200. When the extruder is working, the screw may bear a very high torque load, especially in the feeding section, the groove depth of the screw is deep, and the cross-sectional area of the screw is small. Sometimes the screw needs to be cooled by cooling water, which further reduces the cross-sectional area of the feeding section. Therefore, in order to bear high load, high strength material must be used. 38CrMoAl is often used to make screw in China, and its surface is nitrided to enhance its wear resistance and corrosion resistance. Air permeable membrane equipment www.handern.com
The determination of screw diameter and structure mainly depends on the output, specification, material type and screw characteristics. The screw of common single screw extruder belongs to the screw with full thread from feeding section to homogenizing section. The change of thread lift and groove depth can be divided into three forms, namely equidistant deepening screw, equidistant deepening screw and variable deepening screw.
The conventional single screw extruder, on the one hand, is difficult to provide high shear rate and large shear stress due to the deep screw groove; on the other hand, when the melt is transported forward in the screw groove, it is difficult to continuously adjust the interface orientation to make it in the best angle (45 "or 135) with the shear direction, so it is difficult to obtain large interface growth, which is unfavorable to mixing. In addition, in order to obtain a well mixed mixture, it is hoped that the extruder can not only provide good transverse mixing (that is, the mixing on the section perpendicular to the material flow direction is caused by transverse flow), but also provide good longitudinal mixing (mixing in the material flow direction). The radial mixing effect of conventional single screw extruder is poor, the residence time distribution of material in extruder is narrow, and good longitudinal mixing can not be achieved. The effect of dispersion and mixing mainly depends on the shear stress. In order to increase the shear stress, the shear rate must be increased. For conventional single screw extruders, there are two ways to increase the shear rate, one is to reduce the screw groove depth in the melt conveying area, the other is to increase the screw speed. But in fact, the groove depth of the melt conveying section of single screw extruder can not be very small, so it is difficult to provide high shear; the screw speed can not be too high, especially for those shear sensitive materials www.handern.com
Author：admin