Single Screw Extruder vs Twin Screw Extruder

November 19, 2021

Single screw extruder and twin screw extruder have their own characteristics and applications. In some applications, you can choose either single screw or twin screw.

Extruder can be used in plastics industry, food & Pet food industry, chemicals industry, Pharmaceutical, Minerals and Nonwovens industry. This guide mainly introduces the plastic extruder.

Let’s introduce in detail what are the advantages and differences between single-screw and twin-screw extruders.

About Single Screw Extruder

1. What's Single Screw Extruder

Single screw extruder means that there is only one screw in the extruder barrel.

It is mainly composed of three parts: extrusion system, transmission system and heating and cooling system. Its basic structure is shown in Figure 1.

· Extrusion System

The main function of the extrusion system is to melt and plasticize the polymer material to form a uniform melt, and realize the transition from the glass state to the viscous fluid state.

The extrusion system mainly includes feeding system, screw and barrel. It is the core part of the extruder, and the screw is the key core component of the extruder.

· Transmission System

The transmission system is usually composed of a motor, a reducer and a bearing. Its function is mainly to drive the screw and supply the torque and torque required by the screw in the extrusion process.

During the extrusion process, the screw speed is required to be stable to ensure uniform product quality. However, under different circumstances, the screw speed needs to be adjustable so that the same equipment can be adapted to extrude different materials or different shapes products.

· Heating and Cooling System

The heating and cooling system of the extruder consists of a heating device and a cooling device, which is a necessary condition for the smooth operation of the extrusion process. The heating device and cooling device must ensure that the temperature conditions meet the process requirements.

2. Application of Single Screw Extruder

Single screw extruder is mainly used in:

Pipe extrusion: suitable for PP-R pipes, PE gas pipes, PEX cross-linked pipes, aluminum-plastic composite pipes, ABS pipes, PVC pipes, HDPE silicon core pipes and various co-extruded composite pipes.
Sheet and sheet extrusion: suitable for the extrusion of PVC, PET, PS, PP, PC and other profiles and sheets.
Profile extrusion: Adjusting the speed of the extruder and changing the structure of the extruder screw can be used to produce various plastic profiles such as PVC and polyolefins.
Modified compounding: It is suitable for compounding, modifying and enhancing compounding of various plastics.

About Twin Screw Extruder

1. What's Twin Screw Extruder

The twin-screw extruder is developed on the basis of the single-screw extruder. Due to its good feeding performance, mixing and plasticizing performance, exhaust performance, extrusion stability, etc., it has been widely used in extruded products. Forming processing.

There are two types of twin-screw extruders: intermeshing and non-intermeshing. And, Intermeshing twin screw extruders have two types: co-rotating and counter-rotating.

2. Segmentation of Twin Screw Extruder

The screw system of a parallel twin-screw extruder is generally divided into 4 sections: conveying section, melting section (exhaust port), plasticizing section (vacuum port), and discharging section.

Conveying section: The function is to transport materials and prevent backing.
Melting section: In this section, the materials are fully melted and mixed through heat conduction and frictional shearing.
Plasticizing section: further melt and mix the ingredients of the material, with the function of distributing and dispersing mixing.
Discharge section: conveying and pressurizing, forming a certain pressure, making the materials more compact, and at the same time further mixing, to achieve the purpose of extrusion and granulation.

3. Advantages of Twin Screw Extruder

· High torque, high speed

The development trend of twin-screw extruders in the world is toward high torque, high speed, and low energy consumption. The effect of high speed is high productivity. It has unique advantages in processing high-viscosity and heat-sensitive materials. At the same time, higher productivity can be achieved.

· Wide range of applications

Suitable for processing a variety of materials.

There are many types of twin-screw extruders, and the equipment under various applications has very different characteristics.

For example, the intermeshing counter-rotating twin-screw extruder is excellent in the main application areas of pipe and profile extrusion, especially for PVC materials.

For applications related to compounding and reactive extrusion, the building block self-cleaning co-rotating twin-screw extruder is more excellent and widely used.

4. Application of Twin Screw Extruder

In the plastic extrusion industry, twin screw extruders are widely used.

· Foam extrusion

XPS extruded board
Graphite EPS beads
PET foam
XLPE foam sheet
etc.

· PET extrusion

PET recycling
PET sheet / PET film
PET foam sheet/board
etc.

· Sheet direct extrusion

PP Compounding with Talc and Sheet Extrusion
PP Compounding with Wood Fiber and Sheet Extrusion
HDPE Waterproof Sheet
BOPP Film Extrusion
BOPET Film Extrusion
EVA Film for Solar Cell Encapsulation
PVB/SGP Film for Laminated Glass
etc.

· Compounding extrusion

Color masterbatchs
Filler masterbatchs
Additive masterbatchs
High filling material granulation (such as: PE, PP filled with 75% CaCO.)
Glass fiber reinforced, Flame retardant material pelletizing (such as: PA6, PA66, PET, PBT, PP. PC reinforced flame retardant, etc.)
HFFR/PVC/XLPE cable materials compounding
XLPE pipe material compounding
HDPE pipe coating material compounding
TPE/TPR/TPU/TPV compounding
Hot melt adhesive, PU reactive extrusion granulation (such as: EVA hot melt adhesive, polyurethane)
K resin and SBS devolatilization granulation
Rubber devolatilization compounding
etc.

Difference Between Single and Twin Screw Extruder

Single screw is relatively simpler and cheaper. For some applications, a single screw is sufficient
The twin screw is relatively efficient and energy-saving, and it is more excellent in blending and reactive extrusion
The structure principle is different, the applicable material range is not the same
Other than with a single screw extruder, the throughput rate can be chosen independently of screw speed

In general, the single screw extruder is developing in the direction of high speed, high efficiency and specialization. The twin-screw extruder has good feeding characteristics and is suitable for powder processing. It has better mixing, venting, reaction and self-cleaning functions than the single-screw extruder. When processing plastics and blends with poor thermal stability It also shows its superiority.

How to Choose Plastic Extruder

Although there are indeed many differences between single and twin screw extruders, they can also be used for some of the same applications, or they can be used in combination. So how should we choose a plastic extruder?

Generally speaking, within the budget, choose the most cost-effective equipment according to the application requirements.

Application requirements

According to the application direction that you want to put into production, communicate with experts what kind of solution should be adopted, whether it is a mature solution or a customized solution.

Budget range

Money does not fall from the sky. We hope to choose the best equipment within a reasonable budget to maximize the return on investment. Based on the results of communication with experts from multiple potential suppliers, we have to determine which ones are kept on the candidate list.

Brand selection

There are many large and small brands in the extruder industry, internationally known such as Coperion, Kraussmaffei, JSW, CPM and so on.

For most companies, the price of equipment from well-known brands is relatively high, so we have to select small and medium-sized brands with rich experience, enough cases, relatively cheap prices, and little difference in quality. Like us, USEON.