Basic parameters of extruder screw
1, screw diameter Ds screw diameter is the diameter of the thread, the extruder production capacity (extrusion amount) is approximately proportional to the square of the diameter of the screw and, under the same other conditions, the screw diameter increases a little, significant increase will cause extrusion amount, the effect was even greater than the effect of the increase of screw speed on the extrusion rate is high. Therefore, the screw diameter is used to characterize the specifications of the extruder.
3, compression ratio epsilon, also known as the geometric compression ratio of screw, is the ratio of the volume of the first screw groove to the volume of the last screw groove at the homogenization section. It is determined by the physical compression ratio of plastics - that is, the density of the product and the density of the performance of the feed. The extruder is relatively compressed, the purpose is to make granular plastics fully plasticized and compacted. The selection of compression ratio should be different when different kinds of processing plastics are used. According to the compression ratio, the types of screw can be divided into three types: equidistant, unequal depth, equal depth, unequal distance, unequal depth, unequal distance. Among them, equidistant and unequal depth is the most common one. This kind of screw is easy to process, the contact area of plastic and cylinder is large, and the effect of heat transfer is good.
2. The ratio of the length to diameter of the screw, the length of the screw L/Ds and the ratio of L to the diameter of the screw Ds is called the ratio of length to diameter. When the other conditions are constant (such as the diameter of the screw), increasing the ratio of length to diameter means increasing the length of the screw. The L/Ds value is large and the temperature distribution is reasonable, which is beneficial to the mixing and plasticizing of plastics. At the same time, the heating time of the plastic in the barrel is longer, and the plasticization of the plastic will be sufficient and more uniform. So as to improve the quality of machine plastics. If the plastic quality requirement is constant, the rotation speed of the screw can be increased after the ratio of length to diameter increases, thereby increasing the extrusion amount of the plastic. However, too large length diameter ratio, power consumption will increase the screw, and the screw and barrel of the processing and assembly of chicken more difficult; the possibility of screw bending will increase, will cause the abrasion of the screw and the inner wall of the cylinder, reduce the service life. In addition, the heat sensitive plastic, large diameter and long retention time than thermal decomposition, the plasticizing and impact plastic extrusion quality. Therefore, in the full use of the advantages of increasing the ratio of length to diameter, the selection should be based on the physical properties of the processed plastics and the quality requirements of the products.
