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The Working Principle Of Plastic Screw Extruder May 25, 2018

Screw extruder is one of the most important equipments for plastic molding processing. It transfers solid plastics, compaction, melting, shear mixing, and extrusion molding through external power transmission and heat transfer of external heating elements. Since the birth of the screw extruder, after nearly one hundred years of development, it has developed from a common screw extruder to a new type of screw extruder. Despite the wide variety of new screw extruders, they are basically the same in terms of the extrusion mechanism.

The extrusion process of traditional screw extruder is achieved by heating outside barrel, solid material and barrel, screw friction and melt shear force. "Friction coefficient" and "friction force", "viscosity" and "shear stress" are the main factors affecting the performance of conventional screw extruders. Because the factors that affect "friction" and "viscosity" are very complex, traditional screw extruders The extruder extrusion process is a non-steady state, difficult to control, and it is particularly prominent for some heat-sensitive plastics with poor thermal stability and high viscosity.

Since the 1960s, scholars around the world have conducted a lot of research on the screw extrusion mechanism, and have also made remarkable achievements, but because most of their research is limited to the traditional plastic extrusion molding mechanism, mechanical structure and energy conversion methods, Has not been able to make major breakthroughs. Traditional screw extruders have a series of disadvantages such as large volume, high energy consumption, large noise, and difficult product quality improvement that have not been fundamentally resolved.

In 1979, after years of observation and theoretical research, Prof. Jinping Jin boldly proposed the idea of introducing the vibration field into the entire extrusion process after summarizing the previous studies and the traditional research. The screw extruder structure has undergone a complete revolution.

After two years of hard work, in 1990 it finally developed the first plastic electrodynamic dynamic plasticizing extruder prototype. The principle prototype used direct transduction and introduced the vibration field into the plastic extrusion process, from the principle to the mechanical structure. All are completely different from conventional screw extruders, which overcome many of the shortcomings of traditional equipment, and 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 Industry Development Center of the State Science and Technology Commission examined and responded to the plan and listed it in the 1991 National Torch Program Preparation Project for research and development.

In July 1991, one of the series of researches on “Electromagnetic Integration of Plastic Coextrusion Devices” was funded by the “Fok Ying Tung Youth Education Fund”.

Under the support of the fund, the coextrusion and compounding mechanism of the plastic electro-magnetic dynamic plasticizing extrusion mechanism was studied in depth. The principle of the polymer electro-magnetic dynamic plasticizing extrusion engineering was first proposed at home and abroad, and a relatively perfect polymer dynamic solid was established. The mathematical model of conveying, melting, and melt conveying clarifies and quantitatively describes the basic laws of the dynamic plasticizing extrusion process of polymers. Based on the new principle, we have developed the first "Dynamic Plastic Dynamic Plasticizing Extrusion Equipment" at home and abroad.

Twin-screw market innovation technology trends: twin-screw processing technology has become a widely used processing method in the plastics processing industry, and the corresponding competition is extremely fierce. How to be invincible in the fierce competition? Different suppliers have introduced their own unique and innovative technologies to win the market.

High-speed, high-output High-speed, high-efficiency, and energy-saving have been the main theme of the continuous improvement of international plastics 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 will easily cause uneven mixing and plasticization of the material; excessive shear may cause rapid temperature rise and thermal decomposition of the material; Extrusion stability problems; need high-performance auxiliary machinery and precision control system to match; screw and barrel wear problems and gearbox design issues.

Therefore, it is one of the important directions for the twin screw supplier's technological innovation to provide solutions to the problems that may arise due to high speed. The new Zeux series, a new twin-screw extruder introduced by Berstorff, Germany, is distinguished by its excellent screw diameter/productivity ratio. The maximum speed of the screw design is 1200rpm, and the torque is large. The extrusion capacity is between 100 and 3500kg/h. At the same time, materials can be mixed, reacted, and exhausted.

The barrel and screw are modularly designed to meet a variety of special process requirements with excellent process flexibility. ZSEF side feeders are also available to achieve a high solids delivery rate. Match different yields and material processing.

In order to meet the needs of high speed and high production, the extruder has many improvements. Equipped with a cartridge heater, the temperature rise of the extruder can be completed in a very short time. The maximum heating temperature is up to 450°C. The cooling flow channel design actually realizes reverse flow cooling and the cooling system is optimized. The bow clip is equipped. "Tightening device" can replace the barrel faster than the traditional bolted type; the barrel uses a patented high-frequency quenching process, giving excellent wear resistance, eliminating the need for expensive wear sleeves; In addition, the company's advanced process control system is also equipped.

Multi-functionality In terms of function, twin-screw extruders are no longer limited to the molding and mixing of polymer materials, and their use has expanded to food, feed, fried yao, building materials, packaging, pulp and ceramics and other fields. In addition, the "one-step direct extrusion process" in which the kneading granulation and the extrusion molding process are integrated is also very attractive.

WPC (wood plastic composites) has been used for outdoor applications such as decking and fences for a long time, especially in the United States. The Cincinnati company specially developed the Fiberex series and continues to optimize it for WPC molding. The fourth-generation Fiberex, with an extended, wear-resistant processing unit, can fully meet the different requirements of customers and achieve high output. At last year's NPE show, Cincinnati demonstrated the entire Fiberex pilot production line with a Fiberex T58 extruder with a production capacity of 200 kg/h (440 lb/h) for 75% molding processing. Wood powder filling amount of PP compound. The production line manufactures a profile for the furniture industry with a wall thickness of 2.5 mm and an extrusion setting speed of 2 m/min.

Large-scale and precision The large-scale extrusion equipment can reduce production costs, especially for large twin-screw granulation units, blown film units, and pipe groups. In China, large-scale equipment has long relied on imports, and large-scale twin-screw granulators are now being researched in China. Precision can improve the gold content of products, such as multi-layer co-extruded film. Melt gear pump as an important means to achieve precision extrusion should increase efforts to develop research. Internationally renowned suppliers have a large number of mature technologies in the development of large extruders. To meet the needs of different customers, JSW offers twin-screw extruders with different specifications from TEX30 to TEX400.

Its largest twin-screw extruder TEX400 barrel diameter 443mm, a total length of 35m, a total weight of 320 tons. Yanbu National Petroleum recently ordered a large twin-screw ZSK320 extruder from W&P, including motors, pelletizers, and water-cooled systems, worth more than 20 million euros. According to different polymer varieties and viscosities, its output reaches 25-50 tons per hour.

Cincinnati Extrusion Co., Ltd., Vienna, Austria, was shipped to a customer in the United States in 2006 as the world's largest counter-rotating parallel twin screw extruder to date. The output of this 30t giant machine can reach 2000kg/h, which is the ideal equipment for high-speed production of pvc sheet.

Domestic research institutes have also done a lot of work in the research and development of melt gear pumps. Beijing University of Chemical Technology has developed several series of melt gear pump products. Krauss-Maffei's 36D series twin-screw extruders are specially designed for PVC processing. Modularization and specialization Modular production can meet the special requirements of different users, shorten the development cycle of new products, gain greater market share, and specialization. Production can arrange fixed-point production of each system module component of extrusion molding equipment and even purchase it globally, which is very beneficial to ensure the quality of the entire machine, reduce costs, and accelerate the turnover of funds.

Manufacturers will significantly reduce the cost of PVC pipe raw materials by increasing the amount of filler. The engineering challenge is to ensure the stability of the process and the quality of the product. The Krauss-Maffei 36D parallel twin-screw extruder is designed for ideal PVC processing. They achieve the unity of high-yield and high-product mechanical properties. In addition, these extruders can provide high quality and stable quality pipes.

In the processing of highly filled formulations, the use of a 36D twin-screw extruder developed by Krauss-Maffei for the processing of PVC sewer pipes with a loading capacity of up to 65 parts (approximately 40%) of CaCO3 is also feasible. Highly filled tubes with a diameter of 50-500mm are mainly used for the transport of sewage. To make processing of highly filled formulations easier, the extruder is equipped with special material addition, weighing and metering systems. With the help of a screw feed screw, the PVC dry mix and CaCO3 are conveyed from the storage silo to the hopper of the weighing and metering device. Mixers and stirrers are installed in the hopper to prevent bridging.

In addition, all surfaces of the metering device in contact with the material have a special coating to prevent the flow of material from being blocked. From the metering device, the material is fed to a feed device located at the feed port of the extruder under the action of a stirrer and a special twin screw feeder. Intelligentization and Networking In addition to the technological transformation of the equipment itself, advanced twin-screw extruders have generally adopted microcomputer control, and the process parameters such as melt pressure and temperature, various sections of the fuselage temperature, and main screws for the entire extrusion process have been adopted. The on-line monitoring and control of parameters such as feed screw speed, feeding amount, ratio of raw materials, and current and voltage of the motor are extremely beneficial for ensuring the stability of the process conditions and improving the accuracy of the product.