Twin screw extruder is an industrial equipment that uses two interlocking (or non interlocking) screws as the core working components, and achieves continuous processing of materials such as “conveying, melting, mixing, shearing, exhaust, plasticizing” through the synergistic effect of screw rotation and barrel heating. It is widely used in the modification, granulation, and molding processing of plastics, rubber, food, medicine, and other fields. Its essence is to solve the limitations of single screw extruders in mixing efficiency and material adaptability through “screw forced conveying+multi zone process control”, and meet the requirements of high complexity material processing.

Origin and development

Origin stage: As early as 1869, French mining engineer Jean Francisc Cognet proposed a material transportation and processing equipment similar to a twin-screw structure and obtained a US patent, but it was not applied to polymer processing. Until 1938, Roberto Colombo, the founder of the Italian LMP company, manufactured the first twin-screw extruder for polymer processing, which was used to manufacture PVC pipes. In 1939, it was improved to a diameter of 109mm and received its first customer, beginning to gain market recognition.

Theoretical and Technical Systematization Stage: In the 1940s, IG Farben’s factory in Saxony Anhalt, Germany organized mathematicians, physicists, and engineers to systematically study the meshing co rotating twin-screw extruder, aiming to develop equipment suitable for high viscosity product chemical processes. Walter Meskat and Rudolf Erdmenger jointly applied for a basic configuration patent for threaded screws in 1944, and Erdmenger also applied for a modular twin-screw extruder patent. Later, Werner&Pfleiderer obtained permission from Bayer to name the tightly coupled co rotating extruder “ZSK System Erdenger”. The first prototype was manufactured in 1955 and put into production in 1957.

Commercial and diversified development stage: After the expiration of ZSK technology license in the 1970s, the manufacturing technology of modular co rotating twin-screw extruders was diffused, and more than 50 manufacturers such as Berstoff from Germany, Farrel from the United States, and JSW from Japan began producing related equipment. Different manufacturers develop multiple models based on technology introduction or independent exploration. For example, Farrel Company in the United States developed FCM continuous mixers based on the principle of internal mixers, and JSW Hiroshima Factory in Japan began producing non meshing counter rotating twin-screw extruders in the 1970s to increase production capacity.

Domestic development stage: China’s twin-screw extruder started later than foreign countries. In the 1980s, Nanjing Rubber and Plastic Machinery Factory produced the first domestically produced SHJ-30 co rotating parallel twin-screw extruder, and at the same time, the Chemical Machinery Research Institute of the Ministry of Chemical Industry developed the SHL-60 co rotating twin-screw extruder. In the 1990s, some of the engineers involved in research and development moved to Nanjing, helping it become the core distribution center for parallel twin-screw extruders in China. In recent years, Sichuan Zhongzhuang Technology has mastered the core technology of symmetrical and asymmetrical high torque gearboxes, breaking some of the foreign monopolies in high-end technology.

Current development trend: The current twin-screw extruder is developing towards high torque, high speed, and low energy consumption to improve productivity. The split twin-screw extruder can reach a speed of 500 revolutions per minute, suitable for processing high viscosity and heat sensitive materials. At the same time, with the upgrading of downstream industries and the increasing demand for environmental protection, intelligent automation control and equipment adapted for processing recyclable materials have also become important exploration and innovation directions at home and abroad.

Applications

Twin screw extruders are widely used in various industrial fields due to their excellent material mixing, plasticization, and reaction efficiency. Their core value lies in adapting to different material characteristics (such as high viscosity, thermal sensitivity, and multi-component mixing requirements) and achieving continuous and efficient production.

1. Plastic processing industry (core application areas)

Twin screw extruder is a key equipment for plastic modification, compounding and molding, which can solve the problems of uneven mixing and low plasticization efficiency of single screw extruder. Specific applications include:

Plastic modification: By adding fillers (such as calcium carbonate and talcum powder), reinforcing agents (such as glass fiber and carbon fiber), or functional additives (such as antioxidants and flame retardants), the mechanical properties (strength, toughness), heat resistance, or functionality of plastics can be improved. For example, mixing glass fiber with polypropylene (PP) to produce high-strength modified plastics for automobiles; Add flame retardant to polyethylene (PE) to manufacture flame-retardant wire and cable materials.

Preparation of plastic alloys: To achieve the blending of two or more incompatible plastics to form alloy materials with complementary properties. Typical cases include blending polycarbonate (PC) with acrylonitrile butadiene styrene copolymer (ABS) to prepare PC/ABS alloy that combines PC heat resistance and ABS processability, which is used for electronic and electrical casings and automotive interior parts.

Recycling plastic processing: For the recycling processing of waste plastics (such as PET bottles and PP films), cleaning, melting, and impurity separation are completed through extruders, and they are remade into particles (recycled materials) for the production of pipes, sheets, or low-end plastic products, which meets the requirements of environmental recycling.

Special plastic molding: When processing heat sensitive plastics such as PVC and polyamide PA, the forced conveying and rapid plasticizing ability of twin-screw can reduce material retention time and avoid high-temperature degradation; At the same time, it can be used for the processing of high filling plastics (such as calcium plastic materials with a filling amount exceeding 50%), ensuring uniform dispersion of fillers.

2. Rubber and elastomer industry

In the processing of rubber and thermoplastic elastomers (TPE/TPR), twin-screw extruders are mainly used for mixing, vulcanization, and molding, replacing traditional open rubber mixing machines to achieve continuous production:

Rubber mixing: Efficient mixing of raw rubber, vulcanizing agents, reinforcing agents (such as carbon black) and other components to form a uniform rubber compound for subsequent molding of tires and seals; Compared to traditional intermittent mixing, it can improve production efficiency by more than 30%, and the quality of the rubber material is more stable.

Preparation of thermoplastic elastomers (TPE): Through dynamic vulcanization technology, rubber and plastic are blended and vulcanized in a twin-screw extruder to produce TPE materials that combine rubber elasticity and plastic processability. They are widely used in daily products such as toothbrush handles and sealing strips, as well as medical consumables such as infusion tube fittings.

3. Food and Feed Industry

Twin screw extruders are widely used in food and feed processing due to their characteristics of “low-temperature extrusion, efficient mixing, and sterilization”, especially suitable for functional and expanded products

Food processing: used for producing puffed foods (such as potato chips and rice cakes), which are puffed by the high temperature and high pressure environment inside the extruder, and then cut and dried into finished products; It can also produce nutritious Rice noodles, cereal bars, etc., and ensure the taste and nutrition retention rate of food by precisely controlling the temperature and screw speed; In addition, it can process modified starch (such as cross-linked starch, esterified starch) for use as a food thickener and stabilizer.

Feed production: For the granulation processing of livestock, poultry, and aquatic feed, corn, soybean meal, vitamins, minerals, and other raw materials are mixed and melted by an extruder to form pellet feed. During the process, high temperatures can kill harmful microorganisms (such as Salmonella) in the raw materials and improve the digestion and absorption rate of the feed.

4. Pharmaceutical and Biomaterials Industry

The pharmaceutical industry has extremely high requirements for equipment cleanliness, accuracy, and material compatibility. Twin screw extruders (usually made of stainless steel and designed with no dead corners) can meet these needs, and their main applications include:

Preparation of pharmaceutical excipients: Production of pharmaceutical grade polymer particles (such as hydroxypropyl methylcellulose HPMC, polyvinylpyrrolidone PVP) for tablet coating and capsule shell raw materials. The extrusion process requires strict control of temperature and speed to avoid degradation of excipients or introduction of impurities.

Manufacturing of sustained-release/controlled release formulations: By using extrusion rolling technology, drugs are mixed with polymer carriers (such as polylactic acid PLA) and extruded into pellets or skeleton tablets to achieve slow drug release and prolong efficacy (such as long-acting drugs for cardiovascular diseases).

Biodegradable material processing: Production of absorbable medical materials, such as polylactic acid (PLA) surgical sutures and fracture fixation screws. The twin-screw extruder can accurately control the molecular weight distribution of the materials, ensuring that their degradation rate in vivo matches the pace of tissue healing.

5. Composite and specialty materials industry

With the increasing demand for high-end manufacturing, the application of twin-screw extruders in special fields such as composite materials and new energy materials is gradually expanding

Composite material forming: used for the preparation of carbon fiber reinforced composites (CFRP) and glass fiber reinforced thermoplastic composites (GMT), by mixing fibers with resin matrix (such as epoxy resin, PP) and extruding them to make prepreg or profiles, which are used in aerospace (such as aircraft fuselage components) and new energy vehicles (such as battery casings).

Functional film/sheet production: Through extrusion casting process, special functional films are produced, such as EVA adhesive film for photovoltaic cells (requiring high transparency and aging resistance), and barrier film for packaging (such as EVOH barrier film, preventing oxygen penetration). The uniform plasticizing ability of twin-screw ensures uniform film thickness and stable performance.

6. Chemical and New Material Synthesis

Twin screw extruders can also be used as “continuous reaction equipment” for polymerization and modification reactions of chemical raw materials, replacing traditional batch reactors, improving efficiency and reducing pollution:

Aggregation reaction: used for solid-phase thickening reaction of polyamide (PA) and polyester (PET), removing reaction by-products (such as moisture) through the vacuum exhaust system of the extruder, and increasing the molecular weight and viscosity of the polymer; It can also be used for ring opening polymerization of polylactic acid (PLA), directly converting monomers into polymers and extruding them into granules.

Production of special chemical additives: such as preparing polymer flame retardants and anti-static agents, achieving monomer polymerization and functional group grafting through extruders, ensuring the molecular weight and dispersibility of additives, and improving their application effect in plastics.

Common practical applications

1. Glass fiber reinforcement, flame retardant material granulation (such as: PA6, PA66, PET, PBT, PP. PC reinforced flame retardant, etc.)
2. Granulation of high-filling materials (such as PE and PP filled with 75% CaCO3.)
3. Granulation of heat-sensitive materials (such as PVC, XLPE cable materials)
4. Concentrated masterbatch (e.g. filled with 50% color powder)
5. Antistatic masterbatch, alloy, coloring, low filling blending granulation
6. Granulation of cable materials (such as sheath materials, insulation materials)
7. Granulation of XLPE pipe materials (e.g. masterbatch for hot water cross-linking)
8. Compounding and extrusion of thermosetting plastics (such as phenolic resin, epoxy resin, powder coating )
9. Hot melt adhesive, PU reaction extrusion granulation (such as: EVA hot melt adhesive, polyurethane)
10. K resin, SBS devolatilization granulation

Structure

The twin-screw extruder consists of several parts, such as a transmission device, a feeding device, a barrel and a screw. The functions of each part are similar to those of a single-screw extruder. Its structure is shown in the “Structural Schematic Diagram of a Twin-Screw Extruder”. The difference from a single-screw extruder is that a twin-screw extruder has two parallel screws placed in a barrel with an “∞” shaped cross section.

Twin-screw extruders used for profile extrusion are usually tightly meshed and counter-rotating, although a few use co-rotating twin screws. They are generally operated at relatively low screw speeds, around 10 r/min. High-speed intermeshing co-rotating twin screw extruders are used for compounding, venting, or as continuous chemical reactors. The maximum screw speed of these extruders ranges from 300-600 r/min. Non-meshing extruders are used for mixing, venting, and chemical reactions. Their conveying mechanism is very different from that of intermeshing extruders and is closer to that of single-screw extruders, although there are essential differences between the two.

Auxiliary equipment

Straightening device

The most common type of plastic extrusion waste is eccentricity, and various types of bending of the core are one of the important reasons for insulation eccentricity. In sheath extrusion, scratches on the sheath surface are often caused by the bending of the cable core. Therefore, straightening devices in various extrusion units are indispensable. The main types of straightening devices are: drum type (divided into horizontal and vertical types); pulley type (divided into single pulley and pulley group); winch type, which has multiple functions such as dragging, straightening, and stabilizing tension; pressure wheel type (divided into horizontal and vertical types), etc.

Preheating device

Cable core preheating is necessary for both insulation extrusion and sheath extrusion. For the insulation layer, especially the thin layer insulation, the existence of pores is not allowed. The surface moisture and oil can be completely removed by high temperature preheating of the core before extrusion. For sheath extrusion, its main function is to dry the cable core to prevent the possibility of pores in the sheath due to moisture (or moisture in the wrapping cushion layer). Preheating can also prevent the residual internal pressure of the plastic due to sudden cooling during extrusion. In the process of extruding plastic, preheating can eliminate the large temperature difference formed when the cold wire enters the high-temperature die and contacts the plastic at the die mouth, avoid the fluctuation of the extrusion pressure caused by the fluctuation of the plastic temperature, thereby stabilizing the extrusion volume and ensuring the extrusion quality. Electric heating core preheating devices are used in extrusion units, which are required to have sufficient capacity and ensure rapid heating, so that the core preheating and cable core drying efficiency are high. The preheating temperature is restricted by the pay-off speed, and is generally similar to the die temperature.

Cooling device

The formed plastic extruded layer should be cooled and shaped immediately after leaving the die, otherwise it will deform under the action of gravity. Water cooling is usually used for cooling, and it is divided into rapid cooling and slow cooling according to the water temperature. Rapid cooling is direct cooling with cold water. Rapid cooling is beneficial to the shaping of the plastic extruded layer, but for crystalline polymers, due to sudden cooling, internal stress is easily left inside the extruded layer, resulting in cracking during use. Generally, PVC plastic layer adopts rapid cooling. Slow cooling is to reduce the internal stress of the product. Water of different temperatures is placed in the cooling water tank in sections to gradually cool down the product and shape it. Slow cooling is used for the extrusion of PE and PP, that is, it is cooled in three stages: hot water, warm water, and cold water.

Principles

1. Structural principles

The basic mechanism of the extrusion process is simply that a screw rotates in the barrel and pushes the plastic forward. The screw structure is an inclined plane or slope wrapped around the center layer, the purpose of which is to increase pressure in order to overcome greater resistance. As far as the extruder is concerned, there are three kinds of resistance that need to be overcome during operation: one is friction, which includes the friction of solid particles (feed) on the barrel wall and the mutual friction between them during the first few turns of the screw (feed zone); the second is the adhesion of the melt on the barrel wall; the third is the internal logistics resistance of the melt when it is pushed forward.

According to Newton’s law, if an object is stationary in a certain direction, then the force on the object in this direction is balanced. For a screw that moves in a circumferential direction, it has no axial movement, that is, the axial force on the screw is in a state of equilibrium. So if the screw applies a large forward thrust to the plastic melt, it also applies a thrust of the same magnitude but in the same direction to another object. Obviously, the thrust it applies is acting on the thrust bearing behind the feed port. Most single screws are right-handed threads. If you look at it from the back, they rotate in opposite directions. They rotate backward out of the barrel through rotational motion. In some twin-screw extruders, the two screws rotate in opposite directions in the two barrels and cross each other, so one must be right-handed and the other left-handed. For interlocking twin screws, the two screws rotate in the same direction and must have the same orientation. However, in either case, there is a thrust bearing that bears the backward force, which still conforms to Newton’s law.

2. Temperature principle

Extrudable plastics are thermoplastics, they melt when heated and solidify again when cooled. Therefore, heat is required during the extrusion process to ensure that the plastic can reach the melting temperature. So where does the heat for molten plastic come from? First of all, the preheating of the feed and the barrel/ die heater may play a role and is very important at startup. In addition, the motor input energy, that is, the friction heat generated in the barrel when the motor turns the screw against the resistance of the viscous melt, is also the most important heat source for all plastics, of course, small systems, slow screw speeds, high melt temperature plastics and extrusion coating applications are the exceptions. In operation, it is important to realize that the barrel heater is not actually the main heat source, and its effect on extrusion may be smaller than we expect. The rear barrel temperature is more important because it affects the meshing or solids conveying speed in the feed. In general, except for some specific purposes (such as glazing, fluid distribution or pressure control), the die and mold temperature should reach the required melt temperature or close to this temperature.

3. Deceleration principle

In most extruders, the screw speed is varied by adjusting the motor speed. The drive motor usually runs at a full speed of about 1750 rpm, which is too fast for an extruder screw. If it runs at such a fast speed, too much friction heat will be generated, and the residence time of the plastic will be too short to produce a uniform, well-mixed melt. The typical reduction ratio should be between 10:1 and 20:1. The first stage can be either gear or pulley, but it is better to use gears for the second stage and position the screw in the center of the last large gear. For some slow-running machines (such as twin screws for UPVC), there may be three reduction stages, and the maximum speed may be as low as 30 rpm or less (ratio up to 60:1). On the other hand, some very long twin screws used for mixing can run at 600 rpm or faster, so a very low reduction ratio and more deep cooling are required. If the reduction ratio is not matched to the work, too much energy will be wasted. It may be necessary to add a pulley set between the motor and the first reduction stage to change the maximum speed, which either increases the screw speed even beyond the previous limit, or reduces the maximum speed. This increases the available energy, reduces the current value and avoids motor failure. In both cases, the output may increase due to the material and its cooling needs.

Classification

There are various classification methods for twin-screw extruders, which can be classified based on key dimensions such as screw meshing state, rotation direction, and structural form. Different types of equipment have significant differences in working principles and applicable scenarios.

Classification by screw engagement status (core classification dimension)

According to whether the teeth of two screws are embedded (engaged) with each other during operation, they can be divided into meshing and non meshing types. The mixing and conveying capabilities of the two types differ greatly, and they are the primary reference for selecting equipment.

1. Mesh type twin-screw extruder

The teeth of two screws mesh with each other (similar to gear meshing), and the material is forcibly squeezed and sheared in the gap between the screws, resulting in high mixing efficiency and uniform residence time of the material. It is currently the mainstream type of polymer material modification and mixing.

According to the degree of meshing, it can be further divided into:

Full meshing type: The top of the screw tooth is completely aligned with the root of another screw tooth, with no obvious gap. The material has almost no “reflux”, high conveying efficiency, strong shearing effect, and is suitable for scenarios that require high-intensity mixing (such as plastic filling modification and color masterbatch preparation).

Partial meshing type: There is a certain gap between the top of the screw tooth and the root of another screw tooth (not completely fitting), which has a certain mixing ability and conveying flexibility, suitable for materials that are sensitive to shear and need to avoid excessive processing (such as certain elastomers and heat sensitive plastics).

2. Non meshing twin-screw extruder

The two screws are independent of each other and do not mesh, with a large distance between them. The material is mainly transported by the screw’s spiral thrust, and the mixing effect is weak, leaning more towards the function of “conveying+preliminary plasticization”.

Applicable scenarios: Material handling with low mixing requirements (such as initial conveying for plastic recycling granulation, feeding section assistance for large pipe extrusion), extrusion of high viscosity materials (such as rubber), or scenarios where excessive material shearing needs to be avoided.

Classified by screw rotation direction

In the meshing type twin-screw, the direction of rotation directly affects the force state and mixing effect of the material, and is an important indicator for distinguishing equipment functions.

1. Co rotating twin-screw extruder (most widely used)

Two screws rotate in the same direction (such as clockwise or counterclockwise), and after the material is “bitten” in the meshing area, it is subjected to strong shear, compression, and stretching effects (similar to the “kneading” effect), while being transported forward along the axial direction of the screw.

Core advantages: good mixing uniformity, short material retention time (reducing thermal sensitive material degradation), high yield, and wide adaptability (adjustable process by replacing screw components).

Typical applications: plastic modification (such as fiberglass reinforced PP, flame-retardant ABS), preparation of color masterbatch/functional masterbatch, granulation of biodegradable plastics, high uniformity mixing of food/feed.

Representative structure: “Building block” screw (the screw is composed of different functional components such as conveying blocks, shearing blocks, and kneading blocks, which can be flexibly replaced according to process requirements and is currently the mainstream design).

2. Counter rotating twin-screw extruder

Two screws rotate in opposite directions (clockwise and counterclockwise), and the material is “squeezed” forward in the meshing area, with relatively gentle shear and high conveying pressure (similar to the forced conveying effect of a “gear pump”).

According to the details of the rotation direction, it can be further divided into:

Internal and opposite rotation: The rotation direction of the screw engagement area is “inward” (such as clockwise for the upper screw and counterclockwise for the lower screw, causing the material in the engagement area to gather towards the center), and the material is forced towards the center of the screw, resulting in concentrated shear force, suitable for plasticizing high viscosity materials (such as hard PVC pipe/profile extrusion).

Outward rotation: The rotation direction of the screw engagement area is “outward”, and the material is pushed towards the inner wall of the barrel, with weak shear effect. It is mainly used for conveying or forming low viscosity materials (such as some soft PVC products).

Core advantages: High conveying pressure, suitable for molding processing (rather than simple mixing), relatively gentle cutting of materials, reducing material degradation.

Typical applications: Extrusion molding of PVC pipes/profiles/sheets, extrusion of high filling materials (such as calcium powder filled PVC), preliminary plasticization of rubber products.

Classified by screw structure form

Mainly based on whether the screw is detachable and has functional adjustability, it is divided into “integral” and “block” types, which directly affect the flexibility and applicability of the equipment.

1. Integrated twin-screw extruder

The screw is an integrated structure (non separable), and the spiral groove and functional sections (such as the conveying section, compression section, and homogenization section) are machined on one shaft.

Advantages: Simple structure, low cost, high screw strength (suitable for high torque scenarios).

Disadvantage: Fixed function, unable to adjust mixing strength or process, can only adapt to a single or a few similar materials (such as PVC extrusion with fixed formula), poor flexibility.

Applicable scenarios: Production of single products with large batches and stable processes (such as long-term continuous production of conventional PVC pipes).

2. Building block twin-screw extruder (modern mainstream design)

The screw is composed of multiple independent functional components (such as conveying block, shearing block, kneading block, anti threading block) and the screw core shaft, which are connected by key slots or splines and can be freely combined or replaced according to material characteristics and process requirements.

Advantages: Extremely flexible – by replacing different components (such as adding shear blocks to improve mixing strength, adding anti threading blocks to extend material retention time), it can adapt to different materials (from thermosensitive plastics to high filling materials) without the need to replace the entire screw, reducing equipment investment and production time.

Disadvantages: The structure is relatively complex, the precision requirements for component processing are high, and the cost is higher than that of a monolithic structure.

Applicable scenarios: multi variety, small batch production (such as modified plastic enterprises producing different grades of reinforcing/blocking fuels), R&D scenarios (exploring new formulation processes), and fields that require frequent process adjustments.

Classified by purpose/application scenario

According to the specific processing requirements of the equipment, it can be subdivided into specialized twin-screw extruders, which are usually customized in terms of structure and parameters:

1. Mixing modified twin-screw extruder: The core function is “mixing+granulation”, mostly in the same direction of rotation and building block structure. The screw length to diameter ratio (L/D) is relatively large (usually 28-48) to ensure sufficient mixing time and uniformity. It is commonly used for plastic reinforcement, filling, flame retardancy, and toughening modification.

2. Reactive twin-screw extruder: used for chemical reaction processes of polymer materials (such as polymerization, grafting, crosslinking), requiring precise temperature control (to avoid reaction runaway), inert gas protection system (to prevent material oxidation), vacuum exhaust system (to eliminate reaction by-products), commonly used in PA6 polymerization, PP grafting maleic anhydride, rubber crosslinking, etc.

3. Recycling special twin-screw extruder: For the recycling of waste plastics (such as waste film, waste wire, and nozzle materials), it is usually equipped with strong shear elements (crushing and plasticizing waste materials), filtration systems (removing impurities), and some models have a two-stage structure (first-order twin-screw plasticization+second-order single screw granulation) to improve the quality of recycled materials.

4. Food/pharmaceutical grade twin-screw extruder: The material should meet food grade (such as 316L stainless steel) and pharmaceutical grade standards, with high surface polishing accuracy (to avoid material residue), equipped with a sanitary sealing and cleaning system, used for processing food extrusion (such as breakfast grains, pet food particles) and pharmaceutical excipients (such as sustained-release pellets).

5. Double screw extruders for profile/pipe extrusion: mostly of the opposite rotation type, focusing on “stable conveying+uniform plasticization”, and cooperating with subsequent molds to achieve continuous extrusion of profiles (such as PVC window frames) and pipes (such as PE water supply pipes). The screw length to diameter ratio is relatively small (usually 20-30), and the conveying pressure is high.

Other special types

1. Conical twin-screw extruder: The screw has a conical shape (with a diameter gradually increasing from the feed end to the discharge end), rather than a cylindrical shape with parallel twin-screw, and is mainly used for extruding PVC profiles/pipes. The advantage is that the screw groove volume at the feeding end is large (suitable for PVC powder feeding), and the pressure at the discharging end is high (to ensure the compactness of the profile), but the flexibility is lower than that of parallel twin-screw.

2. Double stage twin-screw extruder: composed of “first stage twin-screw” and “second stage single screw”, the first stage is responsible for mixing and plasticizing, and the second stage is responsible for further homogenization, pressure building, and granulation (or extrusion molding), suitable for high filling, high viscosity materials (such as plastic materials with calcium carbonate filling content>60%) or scenarios that require secondary homogenization, reducing the risk of material degradation.

The approximate price of the machine

The price of twin-screw extruders varies depending on the model, specifications, functions, and applicable industries. According to wholesale information from Made in China, the approximate price range is between $500 and $2.5 million. The detailed introduction is as follows:

Laboratory small twin-screw extruder: usually used for experimental research and development, with small processing capacity and relatively simple configuration. Its price is often between $8950 and $15800 per set.

Food industry twin-screw extruder: equipment used for producing snack food, aquatic feed, etc., with a price range of $7000 to $50000 per set.

Conventional plastic processing twin-screw extruder: commonly used for granulation or extrusion of PVC, PP and other conventional plastics, with prices ranging from $10000 to $120000 per set. Among them, commonly used plastic twin-screw extruders such as 65/120 may cost up to $50000 per set; If it is a plastic extrusion production line equipped with automated auxiliary equipment, its price may reach 200000 to 500000 US dollars per set.

High configuration or large professional twin-screw extruders: Large professional twin-screw extruders designed for special material processing, high output requirements, or advanced functions such as special mixing often have higher prices. For example, some high-speed and high torque machines used for special engineering plastic processing may cost between 150000 to 600000 US dollars per set; A few ultra large and highly automated top configuration extrusion production lines can cost over 1 million US dollars, and even reach 2 to 2.5 million US dollars per set.

Working principle

From the perspective of movement principle, the co-rotating meshing, counter-rotating meshing and non-meshing types in twin-screw extruders are different.

1. Co-rotating intermeshing twin screw extruder

These extruders are available in both low-speed and high-speed versions, the former primarily used for profile extrusion and the latter for specialty polymer processing operations.

(1) Closely meshing extruder. Low-speed extruders have a closely meshing screw geometry, in which the flight shape of one screw closely matches the flight shape of the other screw, i.e., a conjugate screw shape.

(2) Self-cleaning extruder. High-speed co-rotating extruders have closely matched screw flight shapes. This type of screw can be designed to have a relatively small screw gap, so that the screw has a closed self-cleaning effect. This type of twin-screw extruder is called a tightly self-cleaning co-rotating twin-screw extruder.

2. Counter-rotating intermeshing twin screw extruder

The gap between the two screw grooves of the tightly meshed counter-rotating twin-screw extruder is very small (much smaller than the gap in the same-direction meshing twin-screw extruder), so positive conveying characteristics can be achieved.

3. Non-intermeshing twin-screw extruder

The center distance between the two screws of a non-intermeshing twin-screw extruder is greater than the sum of the two screw radii.

Advantages

Wear

Since it is easy to open, the degree of wear of the threaded components and the barrel liner can be found at any time, so that effective repair or replacement can be carried out, so as not to find out the problem when the extruded product has a problem, causing unnecessary waste.

Reduce manufacturing cost

When manufacturing masterbatches, it is often necessary to change colors. If it is necessary to change products, the open processing area can be opened within a few minutes. In addition, the mixing process can be analyzed by observing the melt profile on the entire screw. When changing colors, ordinary twin-screw extruders need to use a large amount of cleaning materials to clean the machine, which is time-consuming, power-consuming, and wasteful of raw materials. The split twin-screw extruder can solve this problem. When changing colors, it only takes a few minutes to quickly open the barrel and perform manual cleaning, so that no or less cleaning materials are used, saving costs.

Improve labor efficiency

When repairing the equipment, ordinary twin-screw extruders often need to remove the heating and cooling systems first, and then pull out the screw as a whole. However, this is not necessary for split twin-screw extruders. You only need to loosen a few bolts, turn the worm gear box handle device to lift the upper part of the barrel, and then open the entire barrel for repair. This not only shortens the repair time, but also reduces labor intensity.

High torque, high speed

The development trend of twin-screw extruders in the world is towards high torque, high speed and low energy consumption. The effect of high speed is high productivity. Split twin-screw extruders belong to this category, and their speed can reach 500 rpm. Therefore, they have unique advantages in processing high-viscosity and heat-sensitive materials.

In terms of the core technology of high speed and high torque, only German and Japanese manufacturers have mastered the core technology of asymmetric and symmetric high torque gearboxes, and the maximum speed can reach more than 1,800 revolutions. In China, only Sichuan Zhongzhuang Technology has mastered this core technology, which is also one of the main choices for domestic high-end material processing manufacturers and is a national encouragement project for domestic independent innovation.

Wide range of applications

Wide range of applications, suitable for processing a variety of materials

High yield, high quality

It has other advantages of ordinary twin-screw extruders and can achieve high output, high quality and high efficiency.

Comparison

The core difference between twin-screw extruders, single screw extruders, and triple screw extruders lies in the differentiation of material conveying mechanisms, mixing capabilities, and applicable scenarios brought about by the number of screws and meshing structures. Each of the three has its own positioning in industrial applications. The following comparison is made from dimensions such as structural principles, core performance, and applicable scenarios to help clearly distinguish their differences and adaptability:

1. Core positioning and structural foundation

The core difference between the three lies in the “number of screws+meshing relationship”, which directly determines their functional orientation – single screw focuses on “simple conveying molding”, twin-screw focuses on “efficient mixing modification”, and triple screw is an advanced solution for “ultimate uniform mixing”.

Single screw extruder: With only one screw, the structure is the simplest. The screw forms a single material channel with the barrel, relying on the “screw rotation friction force+barrel inner wall friction force” to push the material forward, without meshing effect;

Twin screw extruder: Two parallel or conical screws (divided into “same direction meshing” and “opposite direction meshing”), forming a “forced conveying” channel through the mutual meshing of screw teeth. The material is forcibly grasped and sheared by the screw meshing area, and the mixing and conveying efficiency is much higher than that of a single screw;

Three screw extruder: Three screws mesh in a “V” shape or a “triangular arrangement”, and an additional screw is added to the twin-screw to form more “meshing shear zones” and more complex material flow channels. The mixing uniformity and shear controllability are further improved, but the structural complexity and cost also significantly increase.

2. Key performance comparison

1. Material conveying capacity

Single screw: relying on the friction between the material and the screw or barrel, the conveying efficiency is low and unstable – if the material has low viscosity (such as some plastic particles) or is prone to slipping, it may result in “idling without feeding”; Only suitable for materials with low viscosity and good fluidity, with significant fluctuations in conveying pressure.

Twin screw: Through “meshing forced conveying”, the material is forcibly pushed forward by the screw teeth, unaffected by material viscosity, with high conveying efficiency and stable pressure; Even materials with high viscosity and filling rate (such as plastics with added fiberglass) can be transported stably with higher precision in adjusting the conveying volume.

Three screws: The meshing of three screws forms a “multi-point forced grasping”, which ensures a more uniform residence time of materials in the flow channel and reduces pressure fluctuations during transportation; However, due to the more complex flow channels, the conveying capacity is slightly lower than that of twin-screw with the same screw diameter (priority is given to ensuring mixing uniformity).

2. Mixing and shearing performance

Single screw: The mixing ability is extremely weak, and relying solely on the “drag and drop mixing” of the screw edges cannot achieve uniform dispersion of materials (such as the occurrence of “color spots” when mixing color masterbatch particles with plastic particles); The shear strength is low and uncontrollable, only suitable for simple extrusion without mixing requirements (such as extrusion of pure plastic pipes).

Twin screw: Excellent mixing performance – Same direction meshing twin screw (commonly used) achieves material dispersion through “shearing and stretching in the screw meshing area”, while opposite direction meshing twin screw (such as used for profile extrusion) focuses on “extrusion molding”; The shear strength can be flexibly controlled by adjusting the screw combination (such as adding shear blocks, mixing blocks) to meet most modification requirements (such as plastic filling, reinforcement, alloying).

Three screws: Mixing uniformity is the best among the three – the “cross shear zone” formed by three screws can break the material into smaller units, and the “residence time distribution” of the material in the barrel is narrower (to avoid local overheating or uneven mixing); Suitable for scenarios that require extremely high mixing accuracy, such as micro powder mixing of pharmaceutical excipients and preparation of precision composite materials, but the difficulty of adjusting shear strength is higher than that of twin-screw.

3. Production and energy consumption

Single screw: low output (under the same screw diameter, the output is only 1/3~1/2 of twin-screw), and low energy efficiency – in order to meet the conveying requirements, higher screw speed is required, resulting in higher energy consumption per unit output.

Twin screw: High production capacity (such as the production capacity of 200~300kg/h for a Φ 65mm twin screw, far exceeding that of a single screw of the same specification), excellent energy efficiency – forced conveying reduces energy loss caused by material slippage, and unit production energy consumption is 20%~30% lower than that of a single screw.

Triple screw: The output is lower than that of twin-screw of the same specification (due to greater flow resistance), but the energy consumption per unit output is similar to that of twin-screw; To achieve the same output as twin-screw, it is necessary to increase the screw diameter or speed, which will result in slightly higher energy consumption.

4. Scope of applicable materials

Single screw: limited to materials with “low viscosity, no mixing requirements, pure or simple blending”, such as:

Extrusion of pure plastic pipes, sheets, and films (such as PE pipes and PP sheets);

Simple modification with low filling amount (such as coloring with a small amount of color masterbatch).

Twin screw: The most widely applicable, covering materials with high viscosity, high filling, and complex mixing requirements, such as:

Plastic modification (glass fiber reinforced PP, talc filled PE, plastic alloy);

Extrusion of biodegradable plastics and bioplastics (requiring devolatilization, twin-screw can be equipped with multiple exhaust ports);

Screw extrusion granulation of rubber, coatings, and adhesives.

Triple screw: focusing on special materials with “high precision and high uniformity requirements”, such as:

Pharmaceutical grade excipients (such as mixed extrusion of sustained-release drug carriers, with no dead corners or residues);

Nanocomposite materials (such as uniform dispersion of nanoparticles and plastics to avoid agglomeration);

High value-added functional materials (such as conductive plastics, optical grade plastics).

3. Comparison of Operation, Maintenance, and Cost

1. Difficulty of operation

Single screw: simple structure, few parameter adjustments (only need to control the speed and barrel temperature), low difficulty to operate, suitable for small and medium-sized production or novice operation.

Twin screw: It is necessary to adjust the screw combination (replace the shear block and mixing block according to material requirements), meshing clearance, exhaust port vacuum degree, etc. There are more operating parameters that require professional personnel to debug, but currently most equipment has achieved automated control with controllable difficulty.

Triple screw: The screw arrangement is complex, and the precision of adjusting the meshing clearance is extremely high (a deviation of 0.1mm may affect the mixing effect). In addition, the material flow channel is difficult to clean, and the operation threshold is the highest, requiring a professional technical team for maintenance.

2. Maintenance costs

Single screw: with few vulnerable parts (only screws and barrel liners), simple maintenance, low replacement cost (such as the cost of replacing a single screw with a diameter of 65mm, which is about thousands of yuan), and low failure rate.

Twin screw: The vulnerable parts are the meshing teeth and material cylinder of two screws, and the replacement cost is 2-3 times that of a single screw (such as the replacement cost of a Φ 65mm twin screw, which is about 10000 to 20000 yuan); And due to the meshing structure, it is necessary to regularly check the parallelism of the screw, and the maintenance frequency is higher than that of a single screw.

Three screws: Three screws need to be replaced synchronously (with strict meshing requirements), and the cost of vulnerable parts is 1.5 to 2 times that of twin-screw; Moreover, the equipment structure is complex, and troubleshooting is difficult (such as a worn screw that may cause abnormal overall engagement), resulting in the highest maintenance cost.

3. Equipment cost

Single screw: The lowest price, typically ranging from tens of thousands to tens of thousands of yuan for small and medium-sized (Φ 30~80mm) equipment, suitable for scenarios with limited budget and simple demand.

Twin screw: The price is moderate, with equipment of the same specifications (Φ 30~80mm) priced at 3~5 times that of a single screw (about 200000~1 million yuan), but due to its wide range of applications, it is the most cost-effective choice in industry.

Triple screw: The highest price, with equipment of the same specifications priced 2-3 times higher than twin-screw (approximately 500000 to 300000 yuan), only used in high-precision demand scenarios (such as pharmaceuticals and high-end materials).

Summary

1. Menu screw: If the demand is “simple extrusion molding, no mixing requirements, limited budget”, such as pure plastic pipe/sheet extrusion, small-scale low value-added product production, priority should be given to menu screw, which has the highest cost-effectiveness.

2. Choose twin-screw: If the demand is for “plastic modification, high filling/reinforcement, multi material mixing”, or for stable production and volatilization function (such as degradable plastic granulation), twin-screw is the optimal solution – balancing performance, cost, and applicability, and is currently the most widely used type in industrial applications.

3. Choose three screws: Only when the demand is for “extreme mixing uniformity, high-precision material processing” (such as pharmaceutical grade materials, nanocomposites), and the budget is sufficient and there is a professional maintenance team, should three screws be considered to avoid cost waste caused by “excessive performance”.

Manufacturers and brands of twin-screw extruders

Chinese manufacturers

Nanjing Kerke Extrusion Equipment Co., Ltd.: It mainly engages in the design, manufacturing, and sales of co directional block type parallel twin-screw extruders and spare parts. The product can be used in many fields such as plastics, rubber, food, pet food, etc. It is suitable for polymer material blending, homogenization, plasticization, coloring, filling, reinforcement, and recycling operations.

Dalian Rubber and Plastic Machinery Co., Ltd.: It has the ability to independently design and manufacture twin-screw extruders, and has corresponding achievements in the field of extrusion granulation equipment for large-scale polyolefin plants in China. It is a well-known enterprise in the field of rubber and plastic machinery in China.

Nanjing Keya Chemical Equipment Co., Ltd.: It was founded by Mr. Liu Guangzhi, the founder of Chinese twin-screw extruders, in 1993. We have over 100 nationally authorized patented technologies and have undertaken the drafting of national and group standards for the twin-screw extruder industry multiple times. Our HK/SK/ZK MT series ultra-high torque twin-screw extruders and other complete machines have performance comparable to international leading levels.

Changzhou Jinwei Intelligent Chemical Equipment Co., Ltd.: It focuses on the research and manufacturing of twin-screw extruders. With 30 years of technical accumulation and a professional R&D team, it has developed various products such as biodegradable plastic granulation lines, which are exported to over 100 countries and regions such as Russia and India.

Nanjing Ruiya Extrusion Machinery Manufacturing Co., Ltd.: a wholly-owned subsidiary of CPM Group in the United States, with over 25 years of experience in manufacturing twin-screw extruders. By integrating advantageous technologies from the United States, Germany, and China, it has developed into a well-known production and installation base for extrusion machinery equipment in Asia.

Jiangsu Yuesheng Technology Co., Ltd.: Established in 2008, it is committed to the development of new technologies and equipment for polymer material processing equipment. It has delivered domestically produced high torque twin-screw extruders with a torque of 10.3 Nm/cm ³ at that time, and has also launched various characteristic models such as cylindrical heating and dual cooling twin-screw extruders for engineering blending granulation.

Jiangsu Chengmeng Equipment Co., Ltd.: Established in Nanjing in 2005, it has the ability to manufacture twin-screw extruders and reciprocating single screw mixing extruders on a large scale. The annual output of the 240 models produced by it reaches 150000 tons, which can meet the domestic demand for large-scale equipment.

Nanjing Jieya Extrusion Equipment Co., Ltd.: focuses on the research and manufacturing of production lines with co rotating twin-screw extruders and high-efficiency single screw extruders as the core. Our products cover many fields such as compounding modified granulation and polymerization reactions, with an annual production and sales capacity of over 350 sets.

Dongguan Jiewei Machinery Manufacturing Co., Ltd.: supplies twin-screw extruders and peripheral equipment for applications such as PET, PP, EVA, etc., with reliable quality and high-quality after-sales service, and customers all over the world.

Manufacturers from other countries

Troester, Germany: Established in 1892, focuses on the research and development of mechanical equipment related to tires, cables, and other related fields. Its spiral rubber extruder is favored by major rubber processing factories in Europe and other regions. Its QSM pin type cold feed extruder has excellent plasticizing effect and can adapt to a variety of rubber materials.

Lesterz, Germany (List): A family owned enterprise with an extrusion technology department that provides precise, efficient, and flexible twin-screw extruders. With advanced technology, it has significant advantages in meeting the complex processing needs of modern manufacturing.

Davis Standard: With a long history, its twin-screw extruders are renowned for their high quality, reliability, and innovation, meeting the diverse production requirements of various industries such as packaging and construction.

ICMA San Giorgio SpA in Italy: Since its establishment in 1907, it has accumulated a hundred years of experience and combined new technologies to launch high-performance twin-screw extruders, especially suitable for specific scenarios such as wood plastic composite material processing.

Steer, founded in Bangalore in 1993, is a pioneer in the manufacturing of twin-screw extruders in India. It focuses on fields such as plastics, pharmaceuticals, and biomaterials, emphasizing innovation and sustainable development, and continuously improving its product technology level.

Coperion, a pioneer in blending and processing technology, formerly known as Werner&Pfleiderer, has been producing ZSK series co rotating twin-screw extruders since 1957. These extruders are widely used in granulation scenarios for polyolefins such as PP, HDPE, and LDPE, helping users save on related costs such as spare parts.

JSW: Established in 1907, its Hiroshima factory began producing non meshing counter rotating twin-screw extruders in the 1970s, and subsequently launched the CMP-X series of meshing counter rotating twin-screw extruders, with a maximum production capacity of several tens of tons per hour.

Kobe Steel Co., Ltd., founded in 1905, is a large steel conglomerate. Its twin-screw extruder technology originated from the opposite rotation type, and with advanced technology solutions, it occupies an important position in applications such as twin-screw mixing and granulation in the plastic and chemical industries.

Battenfeld Cincinnati, Austria: Founded in the 1940s, Battenfeld Cincinnati is a leading global custom extrusion production line design and manufacturing enterprise. Twin screw extruders are known for their high automation and energy efficiency, and can customize specialized extrusion production lines for industries such as pipes and sheets according to user needs.

Milacron: Since entering the field in 1968, it has always been at the forefront of plastic processing machinery manufacturing. Products such as twin-screw extruders have high efficiency and stability, and are commonly used in plastic processing in packaging, construction, automotive and other fields.

Common faults and troubleshooting methods

During long-term operation, twin-screw extruders are susceptible to various faults due to factors such as material characteristics, operating standards, and equipment aging. The following are common faults and their corresponding cause analysis and basic treatment directions:

1. Abnormal extrusion volume (decreased or fluctuating production)

1. Production continues to decline

Core reasons: blockage of the feeding system, severe screw wear, abnormal cylinder temperature (too high or too low), and vacuum system leakage.

Blockage of feed is often caused by moisture absorption and agglomeration of materials (such as PA and PET with strong moisture absorption), or foreign objects (such as metal impurities) getting stuck in the feeding screw;

Screw wear can lead to a decrease in the volume of the screw groove, especially the wear of the thread edges in the conveying and measuring sections, which makes it difficult to effectively push materials;

When the temperature is too low, the material does not melt sufficiently, resulting in poor fluidity in the screw groove and high pushing resistance; If the temperature is too high, the material may stick to the wall and carbonize, blocking the flow channel.

Basic treatment: First check the feeding hopper of the feeder, clean up clumped materials or foreign objects; If the feeding is normal, observe the appearance of the screw (stop the machine for disassembly). If the wear is severe, replace the screw components; Re calibrate the temperature control of each section of the cylinder to ensure compliance with the material melting curve; Finally, check the vacuum pipeline interface, replace the aging sealing ring, and eliminate the leakage problem.

2. Frequent fluctuations in production

Core reasons: unstable feeding amount (abnormal feeding motor speed, fluctuating hopper level), fluctuation of screw speed, uneven material particle size or humidity.

Basic treatment: Adjust the speed of the feeder to a stable range and maintain the material level in the hopper at more than 1/2 (to avoid a sudden decrease in feeding volume due to low material level); Check the frequency converter of the screw drive motor to eliminate voltage fluctuations or parameter drift issues; Pre dry materials (such as plastics with excessive humidity) and screen for materials with uniform particle size.

2. Melt quality issues (melt fracture, carbonization, uneven dispersion)

1. Melt fracture (cracks and ripples appearing on the surface of extruded products)

Core reasons: high shear rate (too fast screw speed), low cylinder temperature (incomplete melting of material), unreasonable die design (sudden shrinkage of flow channel).

High shear can lead to the breakage of material molecular chains, especially for low viscosity plastics such as PE and PP;

When the temperature is insufficient, there are unmelted particles in the molten material, which cause uneven force when passing through the mold and lead to surface fracture.

Basic treatment: Reduce the screw speed appropriately, gradually increase the cylinder temperature (especially in the measuring section and mouth mold section), and observe the appearance of the melt; If there is still no improvement, it is necessary to evaluate the mouth mold flow channel and replace it with a suitable mouth mold if necessary (such as using a gradient flow channel design).

2. Melt carbonization (black spots and coke particles appearing on the product)

Core reasons: Local high temperature of the cylinder or screw (temperature controller failure, heating coil damage), excessive material retention time in the equipment (low production, slow screw speed), carbonization of residual old materials in the equipment (not thoroughly cleaned during material replacement).

Basic treatment: Immediately shut down and inspect each heating coil section, replace faulty temperature control components; If producing low yield products, it is necessary to adjust the screw speed (to avoid material retention in the cylinder for more than 15 minutes, depending on the material’s thermal stability); Before replacing the material, thoroughly clean the screw, cylinder, and mouth mold with cleaning material (such as specialized screw cleaning material) to eliminate residual old materials.

3. Uneven dispersion of materials (there are unmixed fillers or masterbatch particles in the product)

Core reasons: Unreasonable screw configuration (insufficient dispersing and mixing components, such as lack of kneading blocks and toothed discs), low screw speed (insufficient shear mixing strength), high filler addition ratio (such as failure to match specialized dispersing configuration when the proportion of glass fiber and carbon black exceeds 30%).

Basic processing: If it is a new equipment, it is necessary to confirm whether the screw configuration is suitable for the material (such as for composite materials with high dispersion requirements, the number of kneading blocks needs to be increased); Appropriately increase the screw speed (but avoid causing melt fracture due to excessive speed); For high filling materials, feeding can be done in stages (such as adding the main material from the main feeding port and adding the filler from the lateral feeding port to reduce agglomeration).

3. Abnormal noise and vibration during equipment operation

1. Abnormal noise from the transmission system (such as a “buzzing” or “clanging” sound from the gearbox)

Core reasons: Insufficient or deteriorated lubricating oil in the gearbox (lubricating oil has been used for more than 12 months without replacement or mixed with impurities), gear wear (long-term overload operation leading to tooth surface peeling), bearing damage (excessive axial or radial clearance).

Basic treatment: Stop the machine to check the gearbox oil level, replenish or replace lubricating oil that meets the model (such as industrial gear oil CKD 220); If the abnormal noise persists, disassemble the gearbox and observe the gears and bearings. If the wear is severe, replace the parts to avoid further damage to the transmission structure.

2. Friction noise between screw and cylinder (“metal friction” sound)

Core reasons: coaxiality deviation between the screw and the cylinder (not calibrated during installation, or bearing deformation after long-term operation), loose screw components (loose connection bolts of modular screws), and metal foreign objects in the cylinder (such as screws and debris mixed in during feeding).

Basic treatment: Immediately stop the machine to avoid further wear of the screw and cylinder; First, check the bolts of the screw components and tighten the loose parts again; If the bolt is normal, disassemble the equipment and calibrate the coaxiality between the screw and the cylinder; Finally, clean the foreign objects inside the cylinder and check the filtering device of the feeding system (such as installing a magnetic separator) to prevent impurities from being mixed in again in the future.

4. Temperature control system malfunction (temperature out of control, abnormal display)

1. High temperature (actual temperature far exceeds the set value)

Core reasons: Short circuit of the heating coil (continuous heating of a single section of the heating coil cannot be disconnected), malfunction of the temperature controller (abnormal feedback signal from the sensor, causing the controller to misjudge the temperature), cooling system failure (such as blockage of the cooling water circuit of the cylinder, unable to dissipate heat in a timely manner).

Basic treatment: Disconnect the power supply of the faulty heating coil and replace the short circuited heating coil; Calibrate the temperature controller sensor (such as thermocouple), and replace it if the sensor is damaged; Clean the cooling water circuit (use descaling agent to clear the scale inside the pipeline), ensuring that the cooling water flow is normal (generally requiring a water pressure of 0.2-0.4MPa).

2. The temperature cannot reach the set value

Core reasons: Insufficient power of heating coils (some heating coils are damaged, such as broken carbon fiber heating coils), incorrect parameter settings of temperature controllers (such as PID parameter drift, resulting in slow heating response), low ambient temperature (workshop temperature in winter is below 5 ℃, heat dissipation is too fast).

Basic treatment: Use a multimeter to check the resistance value of each heating coil and replace damaged heating coils; Reset the PID parameters of the thermostat (refer to the recommended values in the equipment manual or calibrate through the “self-tuning” function); Install insulation cotton on the outside of the cylinder to reduce heat loss, especially in low-temperature environments.

5. Vacuum system malfunction (insufficient vacuum degree or inability to evacuate)

Core reasons: Vacuum pipeline blockage (material volatiles condense into oil or solid impurities, blocking the pipeline), vacuum pump failure (low oil level in the pump, blade wear), aging of vacuum seals (such as O-ring and flange gasket damage in the cylinder’s vacuum port).

Basic treatment: First, turn off the vacuum pump, disassemble the vacuum pipeline, and clean the condensation on the inner wall with a solvent (such as acetone); Check the oil level of the vacuum pump, replenish or replace the vacuum pump oil (such as special mineral oil for vacuum pumps), and replace the pump core if the blades are worn; Finally, replace the aging seals to ensure that there is no leakage at the vacuum port (a small amount of vacuum sealing grease can be applied to enhance sealing).

6. Feeding system malfunction (feeding interruption or insufficient feeding amount)

Core reasons: Wear of feeding screw (unable to effectively push materials), hopper bridging (materials forming an “arch bridge” at the hopper outlet due to static electricity or viscous agglomeration, hindering feeding), feeding motor failure (motor stalling or insufficient speed).

Basic treatment: Clean the clumped materials in the hopper, install anti-static coating on the inner wall of the hopper (for materials that are prone to static electricity, such as PVC), or install a vibrator to break the bridge; Check the thread of the feeding screw and replace it if it is severely worn; If the motor is stuck, check if it is due to foreign objects getting stuck in the feeding screw or if the motor bearings are damaged. If necessary, repair or replace the motor.

Daily maintenance

The daily maintenance of twin-screw extruders is the key to ensuring stable operation, extending service life, and avoiding sudden failures. It is necessary to focus on the principle of “prevention first, precise maintenance”, covering the core components of the equipment (screws, barrels, transmission systems, etc.) and auxiliary systems (heating, cooling, lubrication, etc.), which can be specifically divided into the following types of maintenance:

1. Pre startup inspection and preparation (core purpose: to eliminate startup risks and ensure compliance with equipment status)

1. Appearance and connection inspection

Firstly, observe the overall appearance of the equipment to confirm that there is no obvious deformation or damage to the barrel and screw, and that the shell is not loose or damaged; Check the key connection parts one by one, including the coupling bolts between the screw and the transmission box, the flange connection bolts of the barrel, and the fixing buckles between the heating ring and the barrel, to ensure that all fasteners are not loose (if loose bolts are found, they should be tightened according to the torque requirements in the equipment manual to avoid component displacement caused by vibration during operation).

At the same time, check the electrical circuits and pipelines to confirm that the power lines, heating control lines, and cooling water/oil pipes are not aging, damaged, or leaking, and that the interface is well sealed (if there is water leakage at the cooling water pipe joint, the sealing ring should be replaced in a timely manner to prevent moisture from seeping into the electrical box or affecting the cooling efficiency of the machine barrel).

2. Lubrication system inspection

The lubrication system is a “protective barrier” for transmission components such as gearboxes and bearings, and requires special inspection:

Gearbox lubricating oil: Check if the oil level is within the range of the oil gauge (usually 1/2-2/3 height). If the oil level is too low, add the corresponding type of lubricating oil (do not mix different brands or models to avoid a decrease in lubrication performance); Observe the color of the oil. If it appears dark brown, turbid, or contains impurities, it should be replaced in a timely manner (usually after 100 hours of operation of new equipment, the oil should be changed for the first time, and then replaced according to the 2000-3000 hour cycle, as specified in the equipment manual).

Bearing lubrication: Check whether the lubricating grease of each rotating bearing (such as screw support bearings, motor bearings) is sufficient. If the lubricating grease dries up or there are signs of abnormal noise, it is necessary to supplement with high-temperature resistant and wear-resistant special lubricating grease (to avoid using ordinary lubricating grease that may cause bearing overheating and damage).

3. Heating and cooling system inspection

Heating system: Turn on the power supply of the heating control cabinet and test the temperature rise of each section of the barrel heating ring and the head heating ring one by one to see if it is normal (after setting the target temperature, observe whether the temperature display is stable and meets the standard, without obvious fluctuations or no temperature rise); If a certain section of the heating coil does not work, it is necessary to check whether the heating wire is blown or the wiring terminal is loose, and replace or repair it in a timely manner.

Cooling system: Check whether the cooling water pump starts normally and whether the cooling water pipeline is unobstructed (you can feel the water flow by touching the water pipe or observe the flow meter to confirm that the flow rate meets the standard); Clean the impurities and scale in the cooling water tank (if the water quality is poor, regular addition of rust inhibitors or replacement of purified water is necessary to prevent pipeline blockage or corrosion of the engine barrel); At the same time, check the cooling system of the screw core (if any) to ensure normal circulation of coolant and avoid overheating and deformation of the screw.

4. Material and mold inspection

Confirm that the material to be processed is free of impurities and clumps (if the material is damp, it needs to be dried in advance to avoid bubbles or blockage of the screw during extrusion); Check whether the mold installation is firm, whether the mold mouth is deformed or damaged, and whether the sealing gasket between the mold and the machine head is aging (if the sealing gasket is damaged, it needs to be replaced in a timely manner to prevent melt leakage); If changing the material variety, it is necessary to clean the residual materials in the screw and barrel in advance (especially heat sensitive materials, to avoid high-temperature degradation of residual materials affecting product quality).

2. Real time monitoring and maintenance during operation (core purpose: to detect anomalies in a timely manner and avoid the expansion of faults)

1. Monitoring of equipment operating parameters

Pay full attention to the key operating parameters of the extruder, record data and compare it with the normal range. If any abnormalities are found, handle them immediately:

Temperature parameters: The temperature of each section of the machine barrel, machine head, and mold should be stable within the set value ± 5 ℃ range. If the temperature suddenly rises or drops, it is necessary to check whether the heating system and cooling system are faulty (such as short circuit of the heating coil or blockage of the cooling water pipe).

Pressure parameters: The head pressure should be controlled within the rated pressure range of the equipment (usually monitored by a pressure gauge or pressure sensor). If the pressure suddenly increases, it may be due to poor material melting, mold blockage, or excessive screw speed. It is necessary to reduce the speed, clean the mold, or adjust the material formula; If the pressure drops sharply, it is necessary to check whether the material supply is interrupted or whether the clearance between the screw and the barrel is too large (which may be caused by screw wear).

Speed and current parameters: The screw speed should be stable without fluctuations, and the motor working current should be within the range of 80% -90% of the rated current. If the current suddenly exceeds the standard, it may be due to excessive material load (such as high material viscosity or excessive filling) or transmission system blockage. The speed should be immediately reduced and the transmission components (such as the gearbox for abnormal noise) should be checked.

2. Abnormal sound and vibration monitoring

During operation, it is necessary to carefully listen to the sound of the equipment, which should be a uniform “buzzing” sound under normal conditions, without sharp abnormal sounds (such as metal friction sound, impact sound) or periodic noise:

If there is a “piercing friction sound”, it may be due to insufficient clearance between the screw and the barrel, bearing wear, or foreign objects entering the screw. It is necessary to immediately stop the machine for inspection to avoid scratching the screw and barrel.

If the vibration of the equipment significantly increases, it is necessary to check whether the anchor bolts are loose and whether the coupling is aligned (if the coupling is offset, it needs to be recalibrated to prevent component damage caused by transmission imbalance).

3. Melt quality and product appearance monitoring

Observe the state of the extruded melt (such as color, uniformity) and the appearance of the final product (such as particles, profiles, films):

If black spots or coke particles appear in the melt, it may be due to excessive heating temperature, prolonged material residence time, or degradation of residual materials inside the screw. It is necessary to lower the temperature, shorten the material residence time, or clean the screw.

If the product has bubbles, uneven surface, or dimensional deviation, it is necessary to check the drying condition of the material, whether the mold temperature meets the standard, or whether the cooling system is normal (such as insufficient cooling leading to poor product shaping).

4. Regular inspections and simple maintenance

Conduct on-site inspections every 1-2 hours, with a focus on:

Check if the connecting parts are loose (such as heating ring fixing bolts and mold bolts) and tighten them in a timely manner.

Check if the cooling system is leaking (such as water pipe joints, water tank seals). If there is a leak, immediately shut down for treatment to prevent moisture from affecting electrical components or causing equipment corrosion.

Whether the material conveying system (such as feeder) is normal, ensuring uniform supply of materials without interruption or excessive feeding.

3. Comprehensive cleaning and maintenance after shutdown (core purpose: to protect equipment components and prepare for the next startup)

1. Material cleaning and maintenance of screws and barrels

Before stopping the machine, stop feeding and continue running the screw for 5-10 minutes (the idle time should not be too long to avoid dry grinding caused by lack of material lubrication of the screw and barrel). Squeeze out the residual material in the barrel as much as possible to reduce residue.

If processing heat sensitive materials (such as PVC, PA) or easily colored materials, it is necessary to thoroughly clean the screw and barrel with cleaning materials (such as special screw cleaning materials, PE cleaning materials) until the extruded cleaning materials have no residual color or impurities, and then stop the machine to disassemble the screw and barrel (special tools should be used during disassembly to avoid forced tapping causing screw deformation).

After cleaning, the screw and barrel need to be dried or blown dry with compressed air. Check whether the screw edges are worn or deformed, and whether there are scratches on the inner wall of the barrel (if the wear is minor, it can be repaired by polishing; if the wear is severe, the screw or barrel needs to be replaced to avoid affecting the plasticization and mixing effect of the material).

2. Maintenance of molds and machine heads

After disassembling the mold, use a copper scraper (to avoid scratching the mold surface) to clean the residual melt in the mold mouth and flow channel, and then wipe the mold surface with alcohol or special cleaning agent to check whether there is any damage to the mold cavity and mouth (if there are small scratches, they can be repaired by polishing with fine sandpaper); After cleaning the mold, apply anti rust oil and store it properly (to avoid mold rusting or deformation due to collision); At the same time, clean the sealing gasket and filter screen (if any) inside the machine head, replace the damaged filter screen, and ensure the melt filtration effect for the next use.

3. Auxiliary system maintenance

Heating system: After turning off the heating power, check whether there is any residual melt on the surface of the heating ring, wipe it clean with a cloth, and avoid the residual melt from sticking to the heating ring after cooling, which will affect the heating efficiency next time; If there is oil stains on the surface of the heating coil, it should be cleaned with a neutral cleaner and corrosive solvents should not be used.

Cooling system: After turning off the cooling water pump, drain the accumulated water in the cooling water tank (especially during winter or long-term shutdown, to prevent the water tank from freezing and cracking), and clean the scale and impurities on the inner wall of the water tank; Check the valves and joints of the cooling water pipeline. If there is any leakage, replace the sealing ring or valve.

Electrical system: After turning off the main power, clean the dust inside the electrical box with compressed air (to avoid dust accumulation and short circuit of electrical components), check whether the wiring terminals of electrical components (such as contactors, relays, temperature controllers) are loose, and if there are oxidation marks, use sandpaper to polish to ensure good contact.

4. Overall cleaning and recording of equipment

Wipe the dust and oil stains on the surface of the equipment casing, operating table, and control cabinet with a cloth to keep the equipment clean; Clean up material debris and debris around the equipment to ensure a safe operating environment; Finally, fill in the equipment maintenance record, detailing the daily start-up time, operating parameters, abnormal situations, and handling measures, to provide reference for subsequent maintenance (such as analyzing the wear pattern of screws and developing more reasonable replacement cycles through records).

4. Regular special maintenance (core purpose: to prevent failures in advance for consumable components)

In addition to daily maintenance, special maintenance needs to be carried out according to a fixed cycle. The specific cycle can refer to the equipment manual. Common items include:

Screw and barrel wear inspection: Every 3000-5000 hours (or adjusted according to the degree of material wear), disassemble the screw and barrel, measure the thickness of the screw edge and the inner diameter of the barrel. If the wear exceeds the allowable range specified by the equipment (usually 5% -10% of the initial size), replace the screw or barrel to avoid affecting the extrusion volume and product quality.

Gearbox maintenance: Replace the gearbox lubricating oil every 2000-3000 hours and clean the impurities inside the gearbox (the degree of gear wear can be determined by observing the impurities in the oil when draining); Check the meshing condition of the gears inside the gearbox. If there is tooth wear or pitting, the gears should be repaired or replaced in a timely manner to prevent gearbox failure.

Motor maintenance: Check the insulation performance of the motor every 5000 hours (measure the insulation resistance with a megohmmeter, which should be ≥ 0.5M Ω), clean the dust on the motor fan and heat sink, and ensure good heat dissipation of the motor; Check the motor bearings. If there is any abnormal noise or axial movement, replace the bearings to prevent the motor from overheating and burning out.

Sensor and instrument calibration: Calibrate temperature sensors, pressure sensors, speed sensors, and related instruments (such as ammeters and voltmeters) every 6 months to ensure accurate measurement data and avoid improper parameter control due to instrument errors, which may affect product quality or equipment safety.

Purchase suggestions

The selection of twin-screw extruders should be comprehensively judged based on core factors such as production needs, material characteristics, and long-term costs, to avoid blindly pursuing “high configuration” or “low price”. The following provides systematic purchasing recommendations from 7 key dimensions, covering the entire process from demand analysis to after-sales support:

1. First, clarify the core requirement: to avoid making the wrong purchase

The first step in purchasing is to accurately define one’s own needs, which is the foundation for all subsequent choices. Four key points need to be confirmed:

1. Processing materials and process objectives

The material type directly determines the equipment configuration:

Ordinary plastics (PVC, PP, PE): Conventional screw material (38CrMoAlA nitriding treatment), basic temperature control is sufficient;

Special materials (PEEK, LCP, carbon fiber reinforced plastic): require high torque drive, wear-resistant screws (such as dual alloy coating), precise temperature control (within ± 1 ℃), and consider the number of exhaust ports (to avoid material degradation);

Food/pharmaceutical industry (starch, protein, pharmaceutical excipients): requires hygiene grade configuration (stainless steel 316L body, no dead corner design, compliant with FDA/CE certification) to avoid lubricant contamination.

Process objective: Is it “granulation”, “extrusion of profiles” or “blending modification”? For example, granulation needs to focus on yield stability, while blending modification needs to focus on the flexibility of screw combination (to facilitate adjusting mixing strength).

2. Production requirements (key indicators)

Select equipment based on “actual demand output+10% -20% redundancy”: for example, if 100kg/h is actually required, equipment with a capacity of around 120kg/h can be selected (to avoid shortening the lifespan due to full load operation).

The output is directly related to the screw diameter (reference: Φ 35mm screw ≈ 10-30kg/h, Φ 65mm ≈ 50-120kg/h, Φ 95mm ≈ 150-300kg/h), and needs to be combined with the aspect ratio (L/D) – the larger the aspect ratio, the better the mixing and plasticizing effect, but the output will be slightly lower (under the same diameter).

3. Application scenarios (industry/scale)

Laboratory research and development: Select a small twin-screw extruder (Φ 16-30mm, L/D=20-40), focusing on “high-precision control (such as micro feeding), rapid material change, and data recording function”, with a price usually ranging from 10000 to 50000 US dollars;

Small and medium-sized production: Choose conventional models with a diameter of 40-65mm to balance “output, cost, and footprint”, suitable for plastic modification and small-scale food production;

Large scale industrialization: For models with a diameter of over 75mm, automated auxiliary machines (such as automatic feeding, cutting, and sorting systems) are required, with a focus on “high stability, low failure rate, and continuous operation capability”.

4. Product quality standards

If high-precision products (such as electronic wires and medical tubing) need to be produced, attention should be paid to the “extrusion stability” of the equipment (such as screw speed fluctuation ≤± 0.5rpm) and the “melt pressure control accuracy” (within ± 0.5MPa);

If there are requirements for environmental protection (such as VOCs emissions), an additional “exhaust gas recovery system” or “exhaust gas treatment module” needs to be configured.

2. Evaluate core parameters: Ensure ‘usability’

Screw diameter: commonly used in laboratories ranging from 27 to 58mm; Industrial production often uses equipment with screw diameters ranging from 70 to 133mm. It is closely related to yield, with a 10mm increase in diameter resulting in a theoretical yield increase of approximately 30%.

Length to diameter ratio (L/D): typically ranging from 32:1 to 60:1, with high-end applications reaching up to 72:1. A high aspect ratio is beneficial for the stable molding of heat sensitive materials such as PC, PA, etc. The filling formula system for PP products often requires an aspect ratio of 48:1 to 52:1.

Screw configuration: Modular design is preferred for customized combinations according to different production needs.

Maximum speed: Typically 600 to 1200rpm, some high-end models exceed 1500rpm. PP products often require a high speed of around 1000rpm, while nylon products are mostly within 600rpm.

Pay attention to core systems and advanced functions

Drive system: It is recommended to use a servo motor with a precision gearbox, and the torque density is recommended to be ≥ 11Nm/cm ³. The appropriate torque should be matched according to the production volume and material viscosity.

Cylinder design: Building block cylinder for easy maintenance and configuration adjustment; If dealing with highly viscous or difficult to feed materials, slotting the feeding section cylinder is better. Meanwhile, multi-stage temperature control helps to achieve precise temperature control.

Screw components: Screw components should be made of special alloy steel and undergo surface treatments such as nitriding and spraying to extend their wear resistance life.

Online monitoring system: If producing precision products, a machine model that can monitor melt pressure, temperature, and viscosity in real time is required to ensure stable product quality.

Automatic control system: A system with PLC and touch screen can achieve automated production, supporting formula management and data recording for easy production control.

Auxiliary system: equipped with automatic feeding, lateral feeding system or melt pump according to production needs. When processing fiberglass reinforced materials, the precise feeding system can improve the uniformity of fiber dispersion.

3. Configuration matching: Reject ‘excessive configuration’ or ‘insufficient configuration’

Select necessary configurations based on requirements to avoid additional costs or missing features:

Required configurations: Basic screw combination (default combination provided according to the process), main motor, temperature control system, simple operation interface;

Optional configurations (add as needed):

Exhaust ports: 1-3 (for handling volatile materials such as PVC and ABS);

Screen changer: manual screen changer (for small batches and low impurity materials), automatic screen changer (for continuous production and high impurity materials to avoid downtime);

Melt pump: Improve extrusion pressure stability (used for precision profile and pipe extrusion);

Underwater granulation system: high granulation efficiency and uniform particle size (suitable for thermosensitive materials to avoid particle adhesion);

Material drying system: Used in conjunction with moisture absorbing materials such as PA and PET to avoid the generation of bubbles during processing.

4. Select manufacturers: prioritize “technical strength+after-sales support”

The stability of the equipment and subsequent services are highly dependent on the manufacturer, and need to be examined from four dimensions:

1. Industry experience: Prioritize manufacturers that focus on the target industry (such as manufacturers of plastic modification equipment, who understand material characteristics better than general equipment manufacturers);

2. Customization capability: If there are special requirements (such as non-standard screws, special temperature control), it is necessary to confirm whether the manufacturer has the ability to “screw design and machining” (some small manufacturers rely on purchased screws, which have long customization cycles and high costs);

3. Case reference: The manufacturer is required to provide customer cases in the same industry (such as “providing PEEK processing equipment for a certain automotive parts enterprise”), and can conduct on-site inspections of the equipment operation;

4. After sales response: Confirm the “warranty period” (industry standard 1-2 years, core components such as motors and reducers can strive for 3 years), “vulnerable parts supply cycle” (such as screws and barrels need to be shipped within 1 week), and “on-site service capability” (whether there is a localized after-sales team, fault response time ≤ 24 hours).

>Attention: Avoid choosing “three no small factories” – although the price is low (possibly 30% -50% lower than regular manufacturers), there are risks such as “poor screw accuracy (leading to unstable product quality), false motor power standards (actual production cannot be achieved), and lack of after-sales guarantee”.

5. Cost accounting: Focus on “full lifecycle cost” rather than just purchase price

The cost of twin-screw extruders is divided into “short-term procurement cost” and “long-term operating cost”, which need to be calculated comprehensively:

1. Procurement cost: Refer to the price range mentioned earlier (laboratory type 100000-50000 US dollars, conventional production type 100000-120000 US dollars, large-scale production line 200000-2.5 million US dollars), but pay attention to whether the quotation includes auxiliary equipment (such as feeders, pelletizers, dryers – some manufacturers quote “bare machine prices”, and additional fees will be required for adding auxiliary equipment in the future);

2. Operating costs:

Energy consumption: The main motor power (such as the motor power of the Φ 65mm model, which is about 37-55kW), heating power (about 20-30kW), calculated based on 300 days of operation per year, the difference in electricity bills may reach tens of thousands of dollars per year;

Maintenance cost: Replacement frequency of vulnerable parts (screws, barrels, seals) – ordinary screws have a lifespan of about 1-2 years (special material processing may take 6-12 months), and double alloy screws have a lifespan of 3-5 years, with a single replacement cost of about 10000 to 50000 US dollars;

3. Residual value rate: The residual value rate of well-known brand equipment is higher (such as imported brands or domestic top brands, the transfer price can reach 40% -60% of the original price after 3 years of use, and small factory equipment may be less than 20%).

6. Test validation: final “check”

Before signing the contract, it is essential to request the manufacturer to conduct on-site machine testing (or send samples for trial production) to verify the following three points:

1. Product quality: Whether it meets expectations (such as particle uniformity, profile size accuracy, material dispersion);

2. Equipment stability: Run continuously for 4-8 hours and observe whether the speed, temperature, and pressure fluctuate (the smaller the fluctuation, the better);

3. Convenience of operation: Whether material replacement, cleaning, and parameter adjustment are convenient (affecting subsequent production efficiency).

If conditions permit, the manufacturer may be requested to provide “equipment operating noise and energy consumption data” (noise ≤ 85dB is qualified, and energy consumption must be consistent with the quoted parameters).

7. Contract and after-sales: Clarify the “responsibility boundary”

When signing a contract, it is important to clearly specify the following terms to avoid future disputes:

1. Configuration list: Detailed list of main engine, auxiliary engine, and vulnerable parts models and quantities (to avoid manufacturers’ “reduction of configuration”);

2. Acceptance criteria: Clearly define the acceptance indicators for product quality, output, and equipment parameters (such as “output ≥ 100kg/h, particle qualification rate ≥ 99%”);

3. After sales guarantee: Free maintenance scope during the warranty period (such as motor and reducer failures), number of on-site services, and discounted prices for vulnerable parts;

4. Training services: Manufacturers are required to provide “operation+maintenance” training (to ensure that employees can operate independently and reduce malfunctions caused by misoperation).