At that time, the extruder was a plunger type, and the operation mode was improved from manual to mechanical to hydraulic. However, in this period, no matter what form, it only reflects the difference in operation difficulty and labor intensity, as well as the essence of the production process: intermittent, which is also the same feature of the extruder at that time.
1879, Englishman M. Gray obtained the first patent of Archimedes screw extruder. In the same year, another Englishman, F. Shaw, also developed a screw extruder. Two years later, he turned his screw extruder into a product for sale. 1880, American J.Royle also developed a screw extruder. In recent years, several different types of extruders have appeared.
Paul. Troester, a German machinery manufacturer, took the lead in mass production and sales of screw extruders. During the 20 years from L892 to 19 12, he produced and sold more than 500 screw extruders. The same manufacturer developed and produced a thermoplastic extruder in 1935. Prior to this, the length-diameter ratio of extruder screw was about 3-5. Obviously, extruding rubber is not a problem, but for thermoplastics, it is impossible to meet the requirements of plasticization. This company not only increased the length-diameter ratio of extruder screw, but also made many improvements in heating mode, feeding device and transmission device. 1939, they developed the plastic extruder to a new stage, which can be called "modern single screw extruder stage". The characteristics of this stage are direct electric heating, air cooling, automatic temperature control device, nitriding treatment of lining cylinder and screw surface, screw length-diameter ratio 10, stepless speed change transmission device and so on.
In the decades since the emergence of modern single-screw extruder, the types of polymers that can be processed, the structure and forms of products have been continuously expanded, which has promoted the research and development of extrusion molding technology, molding equipment, new products and new technologies. As one of polymer processing technologies, extrusion molding technology develops with the development of polymer processing industry technology.
In 1950s, the development of petrochemical industry made the polymer industry mature rapidly. In 1960s, the production of plastics, rubber and chemical fibers turned to scale. In 1970s, the total amount of synthetic polymer materials in the world has surpassed that of metal materials. Only by molding can polymers become valuable products. Molding is an indispensable production link of polymer materials.
As an important technology in polymer processing industry, extrusion molding has developed in two aspects: polymer resin application engineering technology and extrusion production equipment development technology, which promote each other and depend on each other. Various extrusion products: early rigid PVC pipes, covered wires, polystyrene, polypropylene and ABS sheets and plates, polyethylene blown films and coated films, etc. Nowadays, PVC profiles, cross-linked polyethylene, aluminum-plastic composites, PPR pipes, biaxially oriented polypropylene, multilayer extruded composite films, films with special properties such as high barrier, air permeability, self-adhesion, heat shrinkage and self-extinguishing, functional master batches and color master batches. Prepare a modified polymer material through extrusion processing; * * * Some new modification technologies such as hybrid reinforcement and toughening technology, radiation modification technology and nano-composite technology; Extruders and production lines with various structures and functions; Mixing screws, exhaust extruders, twin-screw extruders, multi-screw extruders, reaction extruders, combined extruders, the molding devices established to adapt to the physical and chemical characteristics of polymer materials, have special functions required by various products, can be used as auxiliary equipment for extrusion production lines, and are new types of equipment that are constantly improved in pursuit of the goals of simple operation, accurate control, energy saving, high efficiency and clean production.
At present, the extrusion molding technology of many products has developed into a complete set of specialized technologies including production technology and production line equipment. The product quality is high, and good economic benefits can be obtained in production. Although the period of rapid development of new processing methods and theories of extrusion molding has passed, it is now much higher than the past and the development tends to be flat, but in the application of these technologies, we can still innovate, develop new products, manufacture new materials and form new technologies. Compared with other polymer molding methods, extrusion molding has many outstanding advantages.
(1) continuous production can produce tubes, plates, rods, profiles, films, cables and monofilaments of any length required.
(2) A single extruder with high production efficiency has high output, such as an extruder with a diameter of 65mm, with an annual output of more than 450t t of PVC film. ..
(3) Wide scope of application This processing method is widely used in the processing of rubber, plastics and fibers, especially plastic products. Almost all thermoplastics and some thermosetting plastics can be processed in this way. In addition to directly molding products, extrusion can also be used for mixing, plasticizing, granulating, coloring, blank molding and so on. For example, if an extruder is matched with a calender, a calendered film can be produced; Cooperate with press to produce various stamping parts; Combined with blow molding machine, hollow products can be produced. In the production process of rubber products, extrusion method is used to manufacture treads, inner tubes, hoses, products with various complex sections and semi-finished products such as hollow, solid and capsule rubber, and can also be used for continuous mixing, plasticization and granulation of rubber filters and raw rubber. In the process of producing resin in petrochemical plant, water in resin can be removed by extrusion, and additives and modifiers in various brands of resin can be mixed by extrusion to complete the granulation process of resin.
(4) One machine and one extruder can process various materials and products. As long as different screws and dies are replaced according to the performance characteristics of materials and the shape and size of products, different products can be produced.
(5) Simple equipment and low investment. Compared with injection molding and calendering, extrusion equipment is simpler, easier to manufacture, lower in equipment cost and more convenient to install and debug. The equipment occupies a small area, and the requirements for the workshop and supporting facilities are relatively simple.
The above advantages determine the important position of extrusion molding in polymer processing. Plastic products that are completely used in the production process or contain extrusion process account for about half of the total thermoplastic products. The products molded by this method have applications in agriculture, construction, petrochemical industry, machinery manufacturing, medical devices, automobiles, electronics, aerospace and other industrial sectors.