Twin Screw & Conical Extruders — Complete Guide

There are two kinds of twin screw extruders: parallel twin screw extruder and conical twin screw extruder. Parallel twin extruder can be divided into co-rotating and counter-rotating extruders. Recently, with the rapid development of domestic electrical machine, communication, and automobile industry, polymer modification and mixed substrate technology are on growth. Co-rotating twin screw mixed substrate extruder is the most popular extruder, so that it nearly becomes another name of twin screw. Nowadays, a change of its application has taken place from high-tech equipment to mass style. Although the difference of technology and strength is still existing in producers, admittedly, twin screw extruder has become more and more mature, especially in small and medium-sized extruder market.

Comparatively speaking, counter-rotating twin extruder is not so popular as co-rotating one in domestic market, and conical twin screw extruder is more widely used in formation, especially in processing of architecture.

Twin screw extruder has become the leading force in extrusion processing market, because of its high production, favorable mixing performance, and block structure, which is convenient for adjusting as per different materials.

Nowadays the main operation of WPC is twin screw extruder, because it delivers materials relying on the principle of positive displacement and having no pressure returning ,easy feeding ,good exhausting affection. Thus the volatile components in wood flour can be fully ruled out. The meshing of screws with each other and the strong shearing can make the material have better mixing and plasticization affection. The wood flour cannot be charred because the less amount of wood flour is, the shorter time the material will stay in twin screw extruder. Thus, the flour can be used in WPC product for the twin screw extruder having a good material adding and mixing affection. Twin screw extruders have two types: parallel co-rotating twin screw extruder and parallel counter-rotating twin screw extruder.

A theoretical model to determine the residence time distribution (RTD) in a co-rotating twin-screw extruder is proposed. The method consists of coupling a continuum mechanics approach with a chemical engineering one and allows us to obtain the RID without any adjustable parameter. The process parameters are obtained using Ludovic(R) twin-screw modeling software, and ideal reactors are chosen to depict the screw profile. The influence of screw speed, feed rate and viscosity on RTD are described on a fictive screw profile. The predictions of the model are in qualitative agreement with literature data. The key point of this procedure is obviously the correct association between an ideal reactor and a screw element.

Basically a twin screw extruder shares the same extrusion theory as a single screw extruder: solid polymer conveying, melting, pressurizing and pumping, mixing, stripping and devolatilizing, but it has more than this. Due to late theoretic study With many styles, the late study, complex screw geometry and the complex extrusion process, the study of Twin screw extrusion is difficult.
Generally speaking, the theoretical study of twin screw extruder is still in the initial stage, which is called “art than science.” From its study of the extrusion process, probably divided into two components:
1. It is apply to guide the design of twin screw extruder and extrusion process optimization, as physical state changes, Delivery Principle, Solid melt delivery,ect during the process of polymer extrusion.
2. It is necessary to find out the truth of polymers and materials physical state changes in the process of extrusion, mixed form, the process of structural change, and relationship between the final mixture and performance.

A twin screw extruder not only shares the common operation principles with a single screw extruder: solid conveying, melting, admixture of pressurizing and pumping up, etc., but also owns its distinct characteristics. There are several factors that tackle the study of basic principles of co-rotating twin screw extruder, such as the late research of extrusion theory, various types, complex screw geometry, and complicated extruding process.

Basically speaking, the study of twin screw extruding theory is still at the initial stage, which indicates that the study is still more art than science. There are three links of its operation principles according to the extruding process:

1.The design of twin screw extruder and optimization of extruding process could be improved by material change laws, conveying theory ,including convey of solid and melt, also gas filling and ejecting characteristics, which can form a mathematics and physical model in the extruding process.

2.Make sure to have a clear command of the change regulation of two or more polymers and materials in the extruding process, their mixing state, the process of their structural change, and the relationship between final mixtures and their functions.

3.A model that is helpful for the molding-filling process can be formed by the internal relationship among the reaction process, speed, function of extruding process and screw’s structure, as well as operation condition.

The development of twin screw extruders: it was first invented in 1930s in Italy, while in the late 1960s and early 1970s, it experienced a rapid development. With the development of RPVC products, counter-rotating twin screw extruder came into being; while co-rotating twin screw extruder appeared, companying with the polymer modification. It is useful to study the twin screw extruding theory, because it can not only be applied effectively, but also has become a consensus and a hot research in the world.

Plastic is melt into homogeneous melt plastics by a twin screw extruder, and can make the head of the extruder with constant temperature, constant quality and constant pressure under the pressure created in the process of plasticization. This is also the way which is used on most thermoplastic plastic. Extruders have different kinds of type and etalon,among which twin screw extruder is the most common one.

The technological requirement can be satisfied and the technological control index can be reached by the wheeling of the mainframe of twin screw extruder, which uses the kv2000 AC frequency converter.

From long stable practical operation of each place, it is obvious that twin screw extruder has a strong adaptability that can bring significant economic benefits to our society.

According to the direction of the rotation of the twin screws, extruders can be divided into two types: parallel co-rotating twin screw extruder and parallel counter-rotating twin screw extruder. The parallel co-rotating twin screw extruder means that the two screws of the extruder rotate to the same direction but the screws of the parallel counter-rotating twin screw extruder work in the opposite directions.

According to the axis lead of the twin screw extruder parallel or not, extruders can be divided into axis lead and intersecting twin screw extruder. The parallel axis lead is the twin screw extruder, while the intersecting is the conical twin screw extruder.

Twin screw extruder can also be divided into the meshing and non-meshing.

The first twin screw extruder was born in Italy in 1930s. During late 60s and early 70s, it got a rapid evolution. Intermeshing counter rotating twin screw extruder was developed with the progress of RPVC products while intermeshing co rotating twin screw extruder was developed with the modification process of polymers. It is a consensus all around the world that the extrusion theory is behind the actual application.

Screw extruder, including single screw extruder and twin screw extruder, is the most commonly used method of polymer processing, and it was in 1930s that twin screw extruder came into being era.

In accordance with the direction of the two screws’ relative rotation, an extruder can be divided into two broad categories: the rotation and varies with the rotating. In 1960s, appearing on behalf of the two axes is not parallel conical twin screw extruder machine, which belongs to the counter-rotation. With high stability, counter rotating twin screw extruder is mainly used for pipe, profile and so on, demanding cross-section size extrusion products and it is used as a host in the current window and door profile production. Co-rotating twin screw extruder is applied for mixing, and mixture occupies an important position in polymer processing (above the polymer need to be final products before going through the mixture screw). Nowadays, the extrusion system of co-rotating twin screw extruder mainly uses modular structure, the barrel assembly, and the screw components.

The twin screw extrusion technology in China has developed several decades of history. It is more and more popular with its application and development, but the understanding of the related basic research of twin screw extruder is still not prefunding enough, and applications have lagged behind. Complex movement and the geometric relationship of twin screw extruder generate various difficulties of qualitative and quantitative description of extruding process, but researches on have never stopped. Therefore, it is of both theoretical and practical significance to have in-depth understanding of the process of twin screw extruder, continuous production, the question of the actual case of theoretical analysis and summing up, and gradually build up the basic theory of application on the basis of reliable test, which is able to serve the production of twin screw extruder.

With excellent compounding, good self-cleaning, flexible modular composition, Parallel Co-rotating Screw Extruder could be applied in different kinds of processing. It can be widely applied in polymers processing, food processing, chemical product and all kinds of macromolecular materials processing.

Twin screw extruder is composed of drive part and extruder part.

The drive part includes gearbox and motor. As per the specification of machine, customer could choose AC motor or DC motor. Gearbox takes parallel triaxial structure with alarm functions when oil level too low or filter blocking overpressure.

The twin screw extruder system includes core bar, barrel and screws. It takes modular principles. With all kinds of common pressing elements include screw elements of different ditches, kneader panel of different stagger angle arrangement, reverse screw elements and some common compounding elements, the closing barrel with L/D 4, feeding barrel and discharging barrel. As per different techniques, customers could require non-standard specifications, for example, with new type compounding elements, side feeding barrel and all kinds of fittings.

Customer could choose different kinds of pelletizer, water cooling strand pelletizer, cool air hot cutter, water ring face cutter and underwater cutter.

HT series — HT25, HT30, HT37, HT47, HT60, HT75, HT95, total 7 types and 18 sub-types parallel co-rotating twin screw extruders. HT series extruders have the characteristics of high rotation, high torque and high output, which not only satisfy the market, but also shorten the quality and function gap from foreign equipments.

This parallel twin screw extruder specializes in a kind of special equipment for extruding of PVC powder. It features:
1. It can produce all sorts of PVC plastic pipe material, bar material and granulation with different kinds of molds and auxiliary machines.
2. The screw uses an oil system; barrel is cooled by a unique wind cooling system.
3. The screw is made up of high precision special digital screw miller; extruding property will be extremely precise.
4. It has a superior technique of producing screws with variable pitch and depth, so that the material can be more softly sheared and cut.
5. The control system is handled by computer.
6. The electrical system uses the imported parts, and it has multiple alarm systems.
7. The cooling system is of special design, the heat emission area is enlarged, and the cooling speed is very rapid.

The vertical flow channel of counter-rotating twin screw extruder is closed due to its geometric parameters, so materials are forced to move towards screw conveyor, which is the so-called positive displacement. This makes the stability of forming extrusion become the main feature of counter-rotating twin screw extruder. On the twin screw extruder, therefore, it should be specified in the direction of rotation.

Twin screw extruder is characterized as follows: higher speed and in the mating area (in the cross-section of the overlapping part of two screws) there is relative velocity, it can produce a strong uniform shear; Geometry determines that it must be open for its vertical flow channel, so that there is materials exchange between the two screws. In exchange, materials at the bottom of a screw slot will move to another screw at the top of the spiral groove. The opening up of the vertical flow make it possible for horizontal flow channel to be open,which is to achieve the exchange of materials between adjacent slot of the same screw. This makes the twin screw extruder with a good ability of distribution and mixture, so it is the most suitable machine for mixing operations.

As compared with a single screw machine, one of the chief advantages of a twin screw extruder, is that the twin screw equipment running more times in the manner of a positive displacement pump. In other words, with single screw extruders there is considerable fore and aft movement of the material when it progresses along the length of the barrel (such machines can be characterized as drag flow devices), and this can arouse inefficiencies, especially when extremely viscous materials are going through processing. As far as a twin screw machine though, this fore and aft “slippage” of material during processing is thoroughly reduced or washed out. Thus, in processing extremely viscous material such as synthetic resins or something similar, twin screw extruders are generally the apparatus of preference.

Twin screw extruder is widely used in mixing, compounding, or reacting polymeric materials. The flexibility of twin screw extrusion equipment is specifically designed in order to process formulation. For example, the two screws may be co-rotating or counter-rotating, intermeshing or non-intermeshing. Also, the configurations of the screws may be varied using forward conveying elements, reverse conveying elements, kneading blocks or other designs aimed to attain special mixing characteristics.

Twin Screw extruders have a controlled produced heat due to reduce screw speed and are able to have a constant or lower temperature than melting point. Because of the extruder length and thermostats can also be used to supply required heat to the melting Polymer. Twin screw extruders are applied in industries because of their high capacity. They are typically used for mixing powder with chemical additives as well as melting with thermal and mechanical energy in the 3 zones: feed, compression and metering. Twin-screw extruders with a short distance between screws are better than other types, due to their high capacity and good thermal and mechanical capacities.

Twin screw extruder Puffed food processing line is a new type of extruding food processing line. With working hard advance the basic technology so that its technical performance and quality become the most advanced in the world. This line specializes in mixing, extruding, shaping, core-filling, cutting, spraying and producing in a one-pass automatic operation. It also features many different configurations, flexible collocation, widely used materials, various products and easy operation.

There is three-dimensional flowfield of the melt conveying zone in an intermeshing counter-rotating twin screw extruder. Nowadays, the research about twin screw extrusive process main focus on the step of fuse-element output. This is because the output characteristics of materiel in this section clearly affect the performance characteristics of twin screw extruder and the solution of molten ingot flow process can take research achievements of hydrodynamics as reference. Rotational direction of screw must maintain a certain relationship with the rotational direction of thread in order to make sure that the materials can transfor from the charging hole to the head of extruder.

Screw combination is the key to the development of extruding process. Co-rotating twin screw extruder mainly with a mixing extrusion, screw combination need to take into account of the shape of the main performance and accessories, feeding sequence and location, the location of vents, barrel temperature settings and so on. At the same time, with the various categories of mixture, it is obvious that there is a variety of combinations. The current research mainly depends on a combination of design experience. Nevertheless, the screw combination of twin screw extruder has its own portfolio and basic laws to follow.

A twin screw extruder (10) including an elongated barrel (12), a pair of elongated rotatable screws (14) and (16) positioned within the barrel (12) for moving material therethrough, and a high-speed bearing support assembly (18) for supporting the screws (14, 16) against misalignment and wear. The bearing support assembly (18) includes a pair of rotors (42, 44) each operable coupled with corresponding extruder screws (14, 16) for rotation therewith and a stator member (46) coupled with the extruder barrel (12) for receiving the rotors (42, 44). The stator (46) includes a plurality of injection ports (62) for directing an edible lubricant such as liquid fat into the bearing assembly (18) during operation of extruder (10).

A two-stage extruder has a first, vertical stage and a second, separately driven, horizontal stage. The two stages are off-set from one another and lie at tangents to one another in the region of a connecting passage. The first stage has a rotatable single screw extruder with kneading blades off-set from one another and is located between conveying screw components of said member. A bearing is provided for the member at its upper end and a cylindrical sleeve surrounding the lower end of the member. It can be turned to control the effective size of the connecting passage or to eject material through a second outlet. A two-stage extruder features low consumption, high quality and output.

There are two types of a double stage extrusion. A double stage single screw apparatus and a composition of a twin screw extruder and a single screw extruder. The extruders are valuale in the extrusion of plastic resins. While in a highly viscous state with minimum blow-back, the first stage includes positively advancing the resinous material. With the use of a screw, the second stage encompasses mixing and the ultimate discharge of the resin. By providing precise metering and discharge of the molten resin, through the die over, there is a wide variation of die pressures.

Twin screw plastics processing technology has become very common in industrial applications, so that competition is extremely fierce. Different suppliers of twin screw extruder have been offering their own unique features and innovative technologies in order to win the twin screw extruder market.

1) High-speed, high-volume: high-speed, high efficiency, energy saving in recent years have been the main theme of the continuous improvement in international plastics industry. The potential for solving problems caused by high-speed is one of the major directions for suppliers of
technological innovation in twin screw extruder.

2) Multi-function: In the function, twin screw extruder is no longer limited to polymer materials and the mixing of the molding, and its use has been extended to food, feed, explosives, construction materials, packaging, paper and ceramics and other fields.

3) Large-scale and precision: the realization of large-scale extrusion equipment can reduce the production cost, and precision can improve the value of products.

4) Intelligent and networking: the technological transformation in the equipment itself, the advanced twin screw extruders have been widely used with computer control ,online monitoring and control process conditions in extrusion process s, which can ensure the stability, improve the accuracy of product.

A transmission for a twin-screw extruder with a housing that accommodates a take-off shaft driven by a gear and another take-off shaft driven by the first take-off shaft and two distributor shafts on each side. The housing is divided along a sectional joint into directly connected halves. The housing has only one sectional joint, which is vertical and extends along the second take-off shaft. The second take-off shaft and the distributor shafts are accommodated in the sectional joint, the first take-off shaft in one housing half, and the driveshaft in the other housing half.

conical twin-screw extruder is a highly efficient extruding equipment.Machines of this series feature even plasticization and agglomeration, low power consumption, reliable quality, wide application range and long service life. Using PVC powder as raw material for a direct forming, these extruders perform an excellent effectiveness. These machines have automatic temperature control, vacuum ventilation, oil cooled screws, stepless speed regulation, as well as a forced feeding and self-cleaning mechanism. Machines of this series have wide application. With appropriate extruding heads, screws and other downstream, they are able to directly convert plastic into pipes, bars, films, hollow cross-section products.

Compared with the parallel co-rotating twin screw extruder, conical counter-rotating twin screw extruder can be described “section-material-type”equipment with low speed and low power consumption. It normally uses the non-combination screw.

Compared with general conical twin screw extruder, the screw of conical counter-rotating twin screw extruder used of WPC production should have larger and longer material feeding part in order to fit the requirement of small percentage of wood flour and plant fiber but larger filling portfolio of them. Besides it can reduce the shearing of wood fiber and make the wood fiber distribute uniformly and material melt fully, so it would fit the wide range of production.

If the wood flour and plant fiber has a large feeding amount and the melted resin has a strong rigidity, it would have a requirement of a resistant high-pressure gear box, and use the screw which can compress fast, melt quickly and have a short metering part. Thus it can be ensured that the wood fiber has a short resident time and the screw cannot be broken away and has no degradation of performance.

The conical twin screw extruder when equipped with the suitable mould tools and downstream auxiliary device, can directly produce plastic pipes, plates, profiles and etc. from PVC power. This type of machinery can be controlled by two different of electric control systems: normal control and microcomputer control. There are also two kinds of main drive systems: direct-current speed control and frequency conversion speed control.

Similarities:
Both of parallel twin screw extruder and conical twin screw extruder have the transmission mechanism to push forward the plastic compulsorily. The two kinds of extruders also have the nicer ability of mixed plasticization and dehydration. In addition, they have the similar adaptability of molding process for the material and plastic.

Differences:
1. Diameter
Parallel twin screw extruder has the same diameters but there is a difference between diameters of the small end and big end of the conical twin screw extruder.
2. Concentric distance
Parallel twin screw extruder has the same concentric distance but there is an angle between the two axes of the conical twin screw extruder.
3. Length-diameter ratio (L/D)
The L/D of the parallel twin screw extruder means the ratio of the screw’s effective length to the outside cycle of the screws. But the L/D of the conical twin screw means the ratio of the screw’s effective length to the average value of the diameters of small and big end.

Conical twin screw extruder features :
Nice looking, newly designed, compact structure, room-saving.
World class frequency conversion system, sectional malfunction alarming brings easier troubleshooting.
High-performance reducing torque distribution system guarantees reliable and quiet running.
Flexible air cooling/oil cooling system reduces cost.
Optimized designed, carefully fabricated screw shafts and barrel bring an extremely good plasticization.
Under the prerequisite of keep a high melt quality, it realizes a maximum extruding ability.
World class DC/AC control system and sectional malfunction alarming make maintenance easy.

The conical twin screw extruder features:
1. Reduction torque distribution gear casing of high performance
2. High precision, wide range of adjustment, forced quantitative feeder
3. Reliable and effective vacuum exhaust unit
4. Screw core circulating oil heating device, convenient to control temperature
5. Air cooling system with high efficiency and low noise
6. Precise automatic temperature control system
7. Precise and stable speed control system

Twin Screw Extruder Designed to forcibly extrude and sheet compounded rubber, plastic, synthetic resin or nonmetallic material in continuous production, it has high efficiency and is ideal for working with mixers or dispersion mixers.

1. This machine is comprised of the two main parts, i. e. the double conical-screw extruder and the two-roll sheeter. The design is compact and rational, and makes the maintenance convenient.

2. The stepless speed regulation with the AC frequency control technology or the DC speed regulation technology is used for the feeder and the sheeter so that it can meet the technological requirement of the rubber or resin sheeting line.

3. It has the welded feeding barrel of jacket type and the bored sheeting roll where cooling water or hot oil/hot water/steam can be lead through to control the temperature and meet the technological requirements for different kinds of stock.

4. The sheeter, which is installed on the rack and the slide rail on the base plate, can be moved horizontally through operation of the manual or pneumatic mechanism so that it can be separated and clutched, which facilitates replacing or cleaning the feed head.

5. The working surfaces of all parts in contact with stock are plated with hard chrome to resist abrasion and corrosion.

6. The double conical screws for feeding are of the tapered convergent type with variable pitch, which raises the extruding capacity. Meanwhile, the flat die head improves the extrusion density and planeness.

7. The electrical control system incorporating the PLC technology can provide not only individual control of single machines but also gang control of the sheeting line.

A twin screw extruder which importantly cuts down on extruder wear through provision of separating, complementarities, inter fitted conical screw and barrel portions adjacent the outlet end of the extruder barrel which achieves an even, bearing-type support for the rotating screws as material passes through the apparatus. In preferred forms, the screws are intermeshed along the majority of the extruder barrel, but diverge at the section of the final conical screw sections and are accepted within respective complementary barrel sections; in this way the material which is processed is split into adjacency, non-communicating streams, and therefore equally flows around and supports the adjacent screw part to reduce the tendency of the screws to detach themselves and come into wearing contact with the surrounding barrel walls. The extruder can be utilized to deal with a great variety of plant-derived materials, but is especially benefical for viscous substances which can be difficult to handle with single screw extruders.

Series-SHR-High-Speed-Mixer Spring-Loader
Process consists on steady state melt extruding unfoamed extrudate of molten thermoplastic polymer, the aforementioned melt extruding being carried out wherein a polymer has foam cell nucleating agent incorporated therein and is made up from laminar flow of said polymer, this melt extruding being conveying out at a shear rate which is at least 1.2 times the shear rate at which the onset of surface roughness for said extrudate takes place in the lack of mentioned foam cell nucleating agent and laminar flow, said extrudate being unacted on surface roughness, the amount of said foam cell nucleating agent being effective to afford the surface free of surface roughness, the foam cell nucleating agent being thermally stable during said extruding, and gained said unformed extrudate as a result of it, whereas the articles obtained from said unfoamed extrudate are unfoamed also .

Pipe Extrusion:
It is applicable for PP R pipe, PE gas pipe, PEX cross-linked pipe, aluminum plastic composite pipe, ABS pipe, PVC pipe, HDPE silicon core pipe and all kinds of co-extruded composite pipes.
Board and sheet extrusion :
It is suitable for board and sheet extrusion from PVC, PET, PS, PP, PC and other products such as yarn and rod.
Profile Extrusion :
It is used for the production of PVC, polyolefin and other plastic profiles by adjusting screw speed and changing screw configuration.

The use of High Speed Energy Input (HSEI) co-rotating and counter-rotating twin screw extruders has become a good choice to process lots of bio-based polymer compounds. They are widely used in compounding, reactive processing, devolatilization, and foaming. The final product varies from pellets for subsequent forming processes or a direct extrusion of fiber, film, sheet or profile.

Recent design has enhanced the High Speed Energy Input (HSEI) twin screw extruder, it can offer the benefits of higher torque, improved heat transfer (cooling), more free volume and also with examples for processes limited by torque and feed volume, along with the corresponding melt-temperature ramifications when compared with the traditional one. It will also be presented with a variety of system configurations for PLA, TPS and other bio-based materials as part of pelletizing, profile, sheet, and foaming extrusion systems.