In the Material Processing, Why Are Single-Screw Extruders Chosen in Some Cases While Twin-Screw Extruders Are Chosen in Others?

Ningbo Fangli Technology Co., Ltd. is a mechanical equipment manufacturer with more than 30 years’ experiences of plastic pipe extrusion equipment, new environmental protection and new materials equipment. Since its establishment Fangli has been developed based on user’s demands. Through continuous improvement, independent R&D on the core technology and digestion & absorption of advanced technology and other means, we have developed PVC pipe extrusion line, PP-R pipe extrusion line, PE water supply / gas pipe extrusion line, which was recommended by the Chinese Ministry of Construction to replace imported products. We have gained the title of “First-class Brand in Zhejiang Province”.

In the field of polymer material processing, extruders are undoubtedly a type of extremely critical equipment. Single-screw extruders and twin-screw extruders, as the two main types, each play important roles in different application scenarios relying on their unique performance characteristics. Today, let's discuss why in the polymer material production process, single-screw extruders are chosen in some situations, while twin-screw extruders are preferred in others.

Differences in Structural Design

Single-Screw Extruder: The structure of a single-screw extruder is relatively simple, mainly consisting of a single screw rotating within a heated barrel. It has gradually evolved from the initial basic helical structure into various types including mixing blocks, vented screws, grooved barrels, pin barrels, and modular structures. This simple structure gives the single-screw extruder a smaller footprint, making it highly favored in areas like compounding processing and plastic blown film.

Twin-Screw Extruder: The twin-screw extruder is equipped with two parallel screws housed in a barrel with a "∞"-shaped cross-section. Based on the relative position of the screws, they can be classified as intermeshing or non-intermeshing; based on the degree of meshing, there are partially intermeshing and fully intermeshing types; based on the rotation direction, they can also be divided into co-rotating and counter-rotating categories. The complexity of its structure grants it some unique performance advantages.

Performance Comparison

Mixing Capability

-   Single-Screw Extruder: The mixing effect is relatively weak. Material primarily relies on the friction and pressure generated by the screw rotation to be conveyed forward and mixed. This can suffice for materials that do not require high mixing homogeneity.

-   Twin-Screw Extruder: The mixing effect is excellent. The two intermeshing screws provide higher shear forces to the material during operation, achieving more uniform mixing. It is particularly suitable for processes with high mixing requirements, such as blending modification of multiple materials.

Shear Intensity

-   Single-Screw Extruder: The shear intensity is limited. It may face challenges when processing high-viscosity materials, struggling to provide sufficient shear force for adequate plasticization and uniform mixing.

-  Twin-Screw Extruder: Capable of generating higher shear intensity. Whether for high-viscosity materials or those with high filler loadings, good plasticization and mixing can be achieved through the special design and interaction of the screws.

Conveying Mechanism

-   Single-Screw Extruder: Primarily relies on the frictional drag force between the material and the screw/barrel to convey the material. This conveying method can sometimes lead to unstable material feeding, especially for materials with poor flowability.

-  Twin-Screw Extruder: Particularly intermeshing twin-screw extruders, utilize a positive displacement conveying mechanism. As the screws rotate, the intermeshing screw flights, similar to gears, forcibly push the material forward, resulting in a stable and reliable conveying process.

Self-Cleaning Capability

-   Single-Screw Extruder: Lacks good self-cleaning functionality. During processing, material can easily adhere to the screw and barrel wall. After prolonged use, this may affect product quality and cleaning is relatively troublesome.

-   Twin-Screw Extruder: Due to the opposite velocity directions in the intermeshing zones of the screw flights and channels, the relative speed is high, which can scrape off accumulated material adhering to the screws. This provides good self-cleaning, short material residence time, reducing the risk of localized degradation, and making material changeover more convenient.

Energy Consumption and Cost

-   Single-Screw Extruder: The simple structure requires relatively less driving power, and its energy consumption is typically lower than that of twin-screw extruders. Moreover, its manufacturing and maintenance costs are also relatively lower, making the equipment price more affordable.

-   Twin-Screw Extruder: Due to the complex structure, a higher power drive unit is required, leading to higher energy consumption. Simultaneously, its manufacturing process is complex, requiring high precision for components, resulting in relatively higher equipment costs and maintenance costs.

How to Choose?

Applicable Scenarios for Single-Screw Extruders:

When the material does not require high mixing homogeneity, such as in the production of ordinary plastic pipes, sheets, blown film, etc.; when the material has good flowability and is easy to plasticize and convey; when the processing environment is cost-sensitive, pursuing low-cost, high-volume production; in these cases, the single-screw extruder is an ideal choice.

Applicable Scenarios for Twin-Screw Extruders:

When blending modification of multiple components is required for the material, preparing high-performance composite materials; when processing high-viscosity, high-filling materials; when product quality requirements are high, requiring precise control over the material's mixing, plasticization, and conveying processes; in these cases, the twin-screw extruder can better meet the demands.

Both single-screw and twin-screw extruders have their own advantages and disadvantages in polymer material processing. To summarize in one sentence:

For thermally sensitive, highly filled, or materials requiring modification, we generally choose twin-screw extruders; whereas for stable, single-component, general-purpose materials, we generally choose single-screw extruders.

In terms of process complexity, if multi-stage venting or shear-reactive extrusion is needed, we generally choose twin-screw extruders; for materials requiring only simple plasticization, we choose single-screw extruders.

If you need more information, Ningbo Fangli Technology Co., Ltd. welcomes you to contact for a detailed inquiry, we will provide you with professional technical guidance or equipment procurement suggestions.