Introduction to the working principle of screw plastic pelletizing extruder

Screw plastic granulating extruder is one of the most important equipment for plastic molding processing. It uses solid power transportation, compaction, melting, shear mixing extrusion molding of plastics through external power transmission and heat transfer from external heating elements. Since the birth of the screw extruder, after nearly a century of development, it has developed from an ordinary screw extruder to a new type of screw plastic pelletizing extruder. Although there are many types of new screw extruders, they are basically the same in terms of the extrusion mechanism. The extrusion process of the traditional screw plastic pelletizing extruder is realized by the external heating of the barrel, the friction between the solid materials and the barrel, the screw friction force and the melt shear force. "Friction coefficient" and "friction force", "viscosity" and "shear stress" are the main factors affecting the working performance of traditional screw extruders. Because the factors affecting "friction" and "viscosity" are very complex, therefore, traditional screw extrusion The extrusion process is an unstable state, which is difficult to control. It is particularly prominent for some thermally sensitive plastics with poor thermal stability and high viscosity. Since the 1960s, scholars from various countries around the world have done a lot of research on the mechanism of screw extrusion, and have made significant achievements, but because their research is mostly limited to traditional plastic extrusion molding mechanisms, mechanical structural forms and energy conversion methods, There has been no major breakthrough. A series of shortcomings of the traditional screw extruder, such as large volume, high energy consumption, high noise, and difficult to improve product quality, have not been fundamentally solved.

In 1979, after many years of teaching, scientific research and practice, Professor Qu Jinping, after long-term observation, thinking, and theoretical research, on the basis of summing up previous studies, he boldly proposed the concept of introducing vibration fields into the entire process of extrusion molding. The screw extruder structure is completely changed. After two years of hard work, the first prototype of a plastic electromagnetic dynamic plasticizing extruder was finally developed in 1990. The principle prototype uses a direct energy conversion method to introduce the vibration field into the entire plasticization extrusion process, from principle to mechanical structure. They are completely different from traditional screw extruders and overcome many of the shortcomings of traditional equipment. They have the advantages of small size, light weight, low manufacturing cost, low energy consumption, low noise, and good plasticizing and mixing effects. At the end of 1990, experts from the Torch High-tech Industrial Development Center of the National Science and Technology Commission, after inspection and defense, included it in the 1991 National Torch Plan preparation project for research and development. In July 1991, one of a series of studies, "Research on the Electromechanical Integration of Plastic Blending Extrusion Equipment" was supported by the "Huo Yingdong Youth Education Fund". With the support of this fund, the in-depth study of the co-extrusion compounding mechanism of plastic electromagnetic dynamic plasticization extrusion mechanism was firstly put forward at home and abroad for the first time. The mathematical models of conveying, melting and melt conveying clarify and quantitatively describe the basic laws of dynamic plasticization and extrusion of polymers. Based on the new principle, the "electromagnetic dynamic plasticizing and extruding equipment for plastics", which was pioneered at home and abroad, was developed.

Innovative technology trends in the twin-screw market: Twin-screw processing technology has become a very common processing method used in the plastic processing industry, and the corresponding competition is extremely fierce. How to be invincible in the fierce competition? Different suppliers have launched their own innovative technologies to win the market. High-speed, high-output High-speed, high-efficiency, energy-saving has been the main theme of continuous improvement of international plastic machinery in recent years. High speed and high output allow investors to obtain high returns with lower investment. However, the high speed of the screw speed brings a series of problems to be solved: if the material stays in the screw for a short time, it is easy to cause uneven mixing and plasticization of the material; too high shear may cause the material to heat up rapidly and thermally decompose; Extrusion stability issues; the need for high-performance auxiliary machines and precision control systems to support them; wear problems of screws and barrels; and design issues of reduction gearboxes. Therefore, providing solutions to the problems caused by high speed is one of the important directions for technical innovation of twin screw suppliers.

In order to meet the needs of high speed and high output, the plastic pelletizing extruder needs to have multiple improvements. Equipped with a barrel heater, which can complete the heating of the extruder in a very short time, the maximum heating temperature can reach 450 ℃; the cooling channel design truly realizes reverse flow cooling and optimizes the cooling system; "Tightening device", the replacement time of the barrel can be faster than the traditional bolt connection type; the barrel uses a patented high-frequency quench hardening process, which gives excellent wear resistance, thereby eliminating expensive wear-resistant bushings; It is also equipped with the company's advanced process control system. In terms of function, the twin-screw extruder is no longer limited to the molding and mixing of high-molecular materials, and its use has expanded to the fields of food, feed, explosives, building materials, packaging, pulp and ceramics. In addition, the "one-step direct extrusion process", which combines kneading and granulation with extrusion molding, is also very attractive.