Twin Screw Extruder VS. Triple Screw Extruder

Extrusion technology plays a vital role in various industries, enabling the efficient processing of materials. Twin screw extruders and triple screw extruders are commonly employed for their distinct capabilities among the various types of extrusion machines. This article aims to provide a comparative analysis of these two extruder types, highlighting their differences and applications.

1. Product Design

The most prominent design distinction lies in the number of screws. Twin screw extruders are equipped with two parallel screws that rotate in the same direction, whereas triple screw extruders are designed with three screws, which can rotate either co-rotating or counter-rotating. This difference in screw count fundamentally shapes their design and operation.

Twin Screw Extruder: The twin screw extruder comprises two screws that intermesh and rotate within the barrel. These screws can be co-rotating or counter-rotating, depending on the desired processing requirements. The design allows for better mixing, melting, and conveying of materials, making it suitable for a wide range of applications.

Twin Screw

Triple Screw Extruder: On the other hand, the triple screw extruder incorporates three intermeshing screws that rotate within the barrel. This design offers enhanced material processing capabilities, particularly in terms of mixing, dispersion, and devolatilization. The additional screw provides increased surface area for heat transfer, making it ideal for applications requiring precise temperature control.

Triple Screw

2. Operation

  • Mixing Efficiency: The additional screw in triple screw extruders significantly enhances their mixing efficiency. The three screws work in tandem to provide intensive mixing, making them particularly suitable for applications where thorough blending and dispersion are essential.
  • Throughput Capacity: The presence of an extra screw in triple screw extruders allows them to handle larger material volumes and achieve higher throughput rates compared to twin screw extruders. This makes triple screw extruders ideal for high-volume production processes.
  • Exhaust Performance: The triple-screw extruder’s exhaust port remains free from material accumulation, ensuring no material leakage or blockage. This is primarily because nearly all the material is drawn into the central honey refining area within the screw. The mixing area functions like a melt pump, resulting in a consistently high vacuum level. As a result, the machine can attain a superior vacuum, thereby enhancing product quality.
  • Specialized Applications: While twin screw extruders are versatile and adaptable to a wide range of materials and applications, triple screw extruders are often chosen for more specialized tasks. These include processing high-viscosity materials, polymer compounding, masterbatch production, and chemical processes demanding intensive mixing and reaction.

3. The quality of the manufactured product

Firstly, the twin-screw extruder produces 50% conductive carbon black masterbatch, which must go through banburying. However, the three-screw extruder does not need an internal mixer, and the material can directly enter the triple-screw extruder to produce 50% carbon black masterbatch. If the masterbatch is bitten with teeth, it will be flat, cracked and not broken, indicating that the produced masterbatch Granular toughness.

Because the three-screw extruder is fully plasticized and the components are evenly dispersed, it is used to blow a 0.005mm film, and the test results are very uniform. With the help of stirring, the three-screw extruder can produce more concentrated carbon black masterbatches, and the particles have better toughness.

The 85% calcium carbonate produced by the twin-screw machine is used to fill the PE or PP masterbatch, and it will be broken with a pinch of your fingers.

The masterbatch with the same ratio produced by the three-screw machine cannot be pinched with fingers, and it cannot be broken by dehydration and drying with a centrifugal dehydrator.

In the manufacturing of flame-retardant PP cable materials, the product obtained from the twin-screw extruder, following the banburying process with an aspect ratio of 40, exhibits a tensile strength of 13 MPa and an elongation of 185%. Conversely, the material produced by the three-screw extruder without internal mixing boasts a tensile strength of 14 MPa and an elongation of 237%. Furthermore, the three-screw extruder has the capability to process masterbatch with aluminum powder or antimony trioxide filling up to 70%, whereas the twin-screw extruder cannot achieve this level of processing.

4. Molecular Grafting Function

Triple Screw Extruder: Everyone knows that high melt strength polypropylene (HMS-PP) must be used for PP foaming, which requires molecular grafting of ordinary PP, and its price is much more expensive than ordinary PP. The molecules have branches and have sufficient melt strength and ductility to be suitable for PP foaming.

However, after our tests, ordinary PP (both homopolymerized and copolymerized PP can be used) can be directly used to produce good EPP beads after being extruded by a three-screw machine, and the expansion ratio can reach 70 times. This is because ordinary PP has been molecularly grafted during the flow process in the three-screw machine and has become polypropylene with high melt strength.

Twin Screw Extruder: A twin screw extruder can be used for various material processing applications, including compounding and blending, but it does not possess inherent molecular grafting capabilities. Molecular grafting typically involves the chemical modification of polymer chains by introducing new functional groups onto the polymer backbone. This process typically requires specialized equipment and chemical reactions beyond the capabilities of a standard twin screw extruder.

5. Processing Capabilities

Twin Screw Extruder: The twin screw extruder stands out in a multitude of processing functions, such as compounding, blending, and reactive extrusion. Its adept mixing capabilities facilitate the integration of additives, fillers, and reinforcements into the base material, leading to enhancements in product characteristics. Furthermore, the twin screw extruder is versatile, capable of handling materials spanning a broad viscosity spectrum, from low to high viscosity.

Triple Screw Extruder: In a triple screw extruder, the processed materials undergo three shearing actions with each revolution of the screws. Additionally, the trefoil configuration within the barrel creates three cutting points, a notable contrast to the single cutting point in a standard twin screw extruder. Consequently, the triple screw extruder offers exceptional processing capabilities, especially in applications that necessitate high shear rates and thorough mixing. Its capacity to achieve superior dispersion and devolatilization makes it particularly well-suited for demanding processes like reactive extrusion, reactive blending, and reactive foaming. Furthermore, the triple screw extruder excels in handling highly viscous materials with remarkable ease.

6. Advantages and Applications

Twin Screw Extruder: The twin screw extruder’s versatility and efficiency make it a popular choice in industries such as plastics, food processing, pharmaceuticals, and chemical manufacturing. Its ability to handle a wide range of materials and achieve excellent mixing and compounding results in improved product quality and reduced production costs.

Twin Screw Extruder Application

Triple Screw Extruder: The triple screw extruder’s advanced processing capabilities make it indispensable in industries requiring precise control over material properties. Its applications include polymer modification, reactive extrusion of polymers, devolatilization of polymers, and specialty chemical production. The triple screw extruder’s ability to achieve superior dispersion and devolatilization results in enhanced product performance.

Triple Screw Extruder Application

7. Technological Formulas And After-Sales

With the long-term emergence of twin-screw extruders, various related technical formulas are more stable than those of three-screw extruders.

In addition, because the twin-screw extrusion appeared earlier and has a long history, there are many twin-screw manufacturers, and the after-sales is relatively more secure than the three-screw extruder.

Both twin screw extruders and triple screw extruders offer unique advantages and cater to different processing requirements. The twin screw extruder excels in versatility and efficient mixing, while the triple screw extruder provides advanced processing capabilities for demanding applications. Understanding the differences between these extruder types allows industries to choose the most suitable option based on their specific needs, ultimately leading to improved product quality and process efficiency.

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