Through different barrel and screw combination, the co rotating parallel twin-screw extruder can meet the mixing requirements of almost all kinds of plastics in the market. It has become a widely used blending technology with rapid market development.
 

At the same time, in order to meet the processing requirements of higher filling volume, domestic and foreign suppliers have developed various disc extruders, reciprocating screw extruders and different combinations of multi screw extruders. In recent years, multi-screw extruder has gradually become a force for the rapid development of blending market to meet the direct processing demand of sensitive materials.
 

New screw technologies emerge in endlessly
 

The traditional multi-screw extruders are planetary screw extruder, annular screw extruder, etc. in recent years, different manufacturers and research institutes have successively developed new models such as inverted triangle three-screw extruder, one line three-screw extruder, one word four-screw extruder, Mrs multi-screw extruder, as well as the combination of multi-screw extruder and single screw or twin-screw extruder The direct processing system plays a special role in different fields.
 

Beijing University of chemical technology independently developed a full mesh three screw extruder with inverted triangle arrangement. According to reports, the newly developed three screw extruder has the advantages of low energy consumption, high output, good mixing and dispersing quality, smaller aspect ratio, better dispersion effect than conventional twin-screw extruder, excellent exhaust performance and no overflow at the exhaust port, which can effectively reduce the loss of raw material and energy in the production process. In this project, the technology of end face combination error correction is proposed and adopted for the first time to realize the smooth transition in the process of different thread components combination, and ensure the interchangeability of thread components.
 

The National Engineering Research Center of new polymer molding equipment of South China University of technology has developed TDM series parallel three screw dynamic mixing extruder based on the national key scientific and technological research project and "863" project. Under the action of vibration force field, the axial meshing gap between the main screw and the two auxiliary screws changes periodically, which makes the material subject to strong shear, extrusion, kneading and grinding, so that the material is better homogenized and dispersed. Compared with the traditional co rotating parallel twin-screw dynamic mixing extruder, there is one more high shear zone, which can realize high-yield extrusion. The production capacity of the twin-screw extruder with the same screw diameter is nearly twice that of the twin-screw extruder with the same screw diameter. Due to the increase of specific surface area and surface renewal rate, the devolatilization efficiency is also greatly improved. This series of machines adopt the three screw structure of parallel combination in the same direction, and introduce the vibration force field into melting, plasticizing, mixing and mixing, with unique advantages of high filling, high dispersion, high output and low energy consumption.
 

The newly developed Mrs extruder with multi screw mixing system was introduced in k2007 and Chinaplas 2008. Mrs system consists of a single screw drum. According to different specifications, there are 8-10 screw barrel grooves on the screw drum. In these screw barrel grooves are respectively equipped with conveying screws parallel to the axis of the extruder. These small screws are driven by a set of planetary gear system and rotate reversely with the main screw. Using this system to achieve significant exchange effect. These small screw barrel grooves are opened on the screw drum, and 30% of the place is open, so that the melt can be optimized and discharged easily. In addition, since the temperature control of all parts in contact with the melt can be carried out independently, the extremely accurate melt temperature control can be realized.
 

Mrs extruder contains a single screw drum, which can achieve significant exchange effect
 

According to the introduction, Mrs's unique system components and structure make its possible devolatilization area much higher than that of the conventional extrusion system. For example, a Mrs system can produce 25 times more melt free surfaces per minute than a co rotating twin-screw extruder under vacuum conditions.
 

Compared with the traditional multi screw extruder, Mrs system has many obvious differences. In Mrs system, each screw has its own bearing support. This means that 8-10 small screws are running in parallel with each other. The annular extruder is usually composed of a plurality of screws which are meshed in pairs, while the planetary screw is meshed with the barrel and the main screw respectively. It is very sensitive to impurities in both materials. These impurities are often unavoidable in the processing of recycled materials.
 

Technovel, a Japanese extruder manufacturer, exhibited the full mesh rotary four screw extruder at k2007. The device is arranged in one word. It is not suitable for the processing of traditional twin-screw extruders, such as the single screw extruder developed by technovel. According to the introduction, the equipment can reduce the heat generation of materials, prolong the residence time of materials, improve the exhaust function and feed performance, and has good dispersion performance. It can realize stable precision extrusion, and save energy and space.
 

Pet direct processing becomes a hot spot
 

With the wide application of pet in packaging field, the application of recycled PET has become a hot spot in the market. The moisture content in the process of PET material processing is easy to cause thermal degradation of the material, resulting in the degradation of mechanical and optical properties. Different manufacturers have developed a variety of advanced molding processing schemes for pet direct processing and recycled PET direct processing. Among them, the multi screw extruder seems to become a high degree of concern in the industry.
 

It is superior to the traditional APET sheet direct processing technology
 

The transparent PET sheet used in packaging industry should not only eliminate the pollution of external substances and dust, but also ensure that the distribution of colorants should be highly uniform, the intrinsic viscosity should be at least 0.74g/dl, and the crystallinity should be more than 40%. To meet these stringent requirements, sheet manufacturers use a variety of processing methods.
 

The commonly used processing method is single screw extruder, which requires the raw materials to be completely dried. Due to the high energy consumption of pre drying equipment, processors have been looking for alternative methods. A feasible way is to use a single screw extruder combined with an infrared dryer, which can reduce the energy consumption by 60% compared with the traditional processing method. In contrast, the third way is single screw extruder with crystallizer. This way can also reduce energy consumption, but it is mainly recommended for recycled material processing, because the quality of the final product is poor. Traditional single screw extruders have proved unsuitable for this application without drying equipment because of their low surface area / volume ratio. From this point of view, the multi-screw extruder is very suitable, but due to its complexity, the market penetration is not high so far.
 

Pet without drying can be directly processed in co rotating twin screw extruder with high efficiency exhaust. When the initial moisture content of raw materials is below 4000ppm, this processing method can obtain excellent sheet quality. Especially for high-yield extrusion lines between 1500 and 3000 kg / h, it is advisable to use this equipment, despite the significant increase in equipment investment.
 

The modified planetary screw and single screw are used to produce high quality APET sheet
 

Pattenfeld extrusion technology company has introduced a new concept of economic single screw extruder to produce high quality APET sheet. This new processing equipment is not only suitable for extrusion lines with production capacity of 800 to 1000 kg / h, but also can retain the processing flexibility, that is, it can process not only pet, but also PS or PP. The novelty of the equipment lies in the combination of modified planetary screw and single screw with high efficiency melt exhaust function. Although the equipment investment is similar to that of single screw extruder with traditional pre drying equipment, the maintenance cost and energy consumption of this new technology are relatively lower.
 

Planetary screw has been used in PVC processing for a long time. According to the basic principle of involute screw rotation around its center, the meshing mode is similar. The melt is transported in the meshing process and new surface is formed continuously. Under the vacuum degree of about 5mbar, the exhaust can be completely carried out, and the effect is very ideal. At the same time, the self-cleaning characteristics of the planetary screw section can ensure a relatively short time, and the residence time of the melt can be predetermined, so the thermal decomposition of the polymer molecular chain can be greatly reduced. Through a large exhaust port, the multi-stage vacuum pump can completely remove water vapor and any by-products. The planetary screw is followed by a short single screw for pressure formation and conveying the polymer melt after venting to the melt pump and die head.
 

The first extruder of this type has been installed and operated at a well-known manufacturer of pet hot-formed sheet in Europe, with excellent production performance. This equipment can process raw APET with an initial moisture content of 3000 ppm and recover 100% bottle material.

Multi screw system for direct processing of PET film
 

Mkf folien and entex have jointly developed an optimized pet blending process, which can process different PET materials. The core of this technology is entex's patented technology, planetary extruder with vacuum system. As we all know, pet is easy to hydrolyze in the process of processing, so it is usually necessary to carry out complex pre drying treatment. Using planetary extruder, with its vacuum system and upstream processing, can realize continuous processing of materials. At this time, pre drying is not a necessary work.
 

Entex introduces that in the practical application of mkf, the overall net capacity can be increased to 600-1000kg / h (gross capacity 1200kg / h). The quality of the film produced is consistent with the traditional extrusion line using pre drying. At the same time, other devolatilization components can be discharged during the processing.
 

Mrs 110 extruder, especially suitable for recycling PET material.
 

In addition, this system can avoid pet thermal degradation or thermal oxidative degradation due to moisture in other processing methods, and will not reduce the mechanical and optical properties of materials. The test of IV value of the film shows that the performance of the two methods is similar to that of the traditional pre drying method and the optimized method.
 

Entex emphasizes that the materials used in the process of use can be easily controlled, and has more advantages when using recycled materials. Plant operators can use recycled materials to immediately reproduce the high quality of the end product and complete material replacement. Due to no pre drying and partial crystallization of materials, the energy consumption for PET film production is significantly reduced. According to reports, this technology can be used in all pet extrusion processing applications.
 

Innovative Mrs extruder for pet direct processing
 

The purpose of developing Mrs devolatilization system is to optimize the devolatilization of polymer melt. Due to its larger polymer melt area, Mrs equipment, or Mrs extruder, has a more efficient devolatilization capacity than existing devolatilization systems on the market. In addition, since the surface area is constantly changing, opening or renewing at a high speed can produce a larger free volume, which makes it easier to discharge gas when it is generated.
 

Mrs110 extruder, especially suitable for recycling PET material
 

Using the integrated Mrs exhaust zone, the recycled PET can be processed quickly and easily by single screw extruder without pre drying. In a specific processing application, a water ring pump can generate the required suction of 20-40mba. At the same time, the viscosity of the material can also be increased. This makes the Mrs extruder particularly suitable for making PET sheet or packing belt from recycled PET material, such as bottle sheet. Therefore, it is not surprising that the first Mrs extruder was sold to this field.
 

According to Gnos, because of the special advantages of Mrs system, it can be used to: dehydrate or remove residual monomer in PC processing; separate monomer and residual oligomer in nylon processing; increase molecular weight of pet, PBT and PTT by polycondensation; remove monomer styrene from ABS or San; reduce VOC of POM, PP, ABS used in automobile interior decoration materials. In addition, it can also be used to introduce chemical or physical foaming agent or other components in the manufacture of PS, PE, pet, PP and other foaming products. These are only a small part of the field that Mrs system can be applied to.