Counter-rotating twin-screw extruders are used for a variety of plastic products and processes. It is interesting to note that a closely intermeshing, counter-rotating twin-screw extruder can be designed to pump materials in a non-drag flow manner in locked C-shaped chambers. Only this device(and ram extruders) can convey via positive displacement, as compared to the drag flow single-screw extruder and semi drag flow co-rotating twin-screw extruder.

1. The Structures of Co-Rotating Twin-Screw Extruder

Forced conveying

Engage the same direction of rotation of the twin screws, at the engagement of the two screw movement in the opposite direction, a screw to pull the material into the engagement gap, while the other screw to push the material out of the gap, the result of the material from a screw groove to another screw groove, the material along the screw is “∞” shape to the head direction is forced to convey.

(a) Homogenisation and mixing

Isotropic twin-screw in the engagement gap is very small, screw prism and screw groove speed direction opposite, the relative speed, so the engagement area has a very high shear speed, the shear force is very large, mixing effect is much better than single-screw extruder and anisotropic rotary twin-screw extruder.

(b) Self-cleaning

Isotropic rotary twin-screw extruder, due to the engagement area screw prism and screw groove speed in the opposite direction, the relative speed is large, so has a fairly high shear speed, can scrape off any accumulation of material adhering to the screw, there is a very good self-cleaning effect so that the residence time of the material is very short, not easy to produce local degradation and deterioration.

(c) The participation of materials

The size of the screw gap has a great impact on the quality of material participation. The smaller the gap, the greater the shear force, but the amount of material through the reduction; the larger the gap, the amount of material through the increase, but the sheer force is reduced.

(d) The compression of the material

Isotropic twin-screw extruder compression of the material too much more methods, the comprehensive effect is good.

(e) the way to add material

Co-directional twin-screw extruder requires uniform quantitative feeding, using metering hunger feeding method.

(f) Exhaust

Due to the starvation feeding, the threaded conveying element with a large lead can be used, so that the screw groove is in a state of unfilled and zero pressure, which can set out the exhaust section.

Performance evaluation indicators and development

Increasing production efficiency is an important objective in the development of co-rotating twin-screw extruders, which can be achieved by increasing the screw speed and enhancing the plasticising and mixing capacity. At the same screw speed, increasing the degree of material filling in the screw groove can lead to a significant increase in conveying capacity. This allows the screw speed to be increased further without the material temperature rising too high and degrading it, thus increasing the extruder’s capacity while maintaining product quality. This increases the plasticising and mixing capacity of the screw, which requires it to be able to withstand a higher torque. At high screw speeds, the residence time of the material in the extruder is reduced, which may lead to insufficient plasticisation and mixing. For this reason, the screw length needs to be increased, which in turn leads to an increase in the actual torque and power of the twin-screw extruder. All these technical parameters are interlinked.

High drive power, high screw speeds and ultra-high torque extrusion have always been the goal of operators of co-rotating twin-screw extruders. In the case of the modular twin-screw extruder, the centre distance between the two screws is determined and the output is usually limited by the conveying capacity and the permissible torque that the screw arbour can withstand. For this reason, R. Erdmenger, the developer of the modular co-rotating twin-screw extruder, used two parameters to evaluate the performance of the co-rotating twin-screw extruder.

2. The Functions of Co-Rotating Twin-Screw Extruder

The co-rotating twin-screw extruder has the advantages of high conveying efficiency, strong dispersing and mixing ability, good self-cleaning performance, even distribution of material residence time in the machine and good adaptability, etc. It is widely used in the blending and modification of different plastics, plastics and rubber, blending of various additives with plastics, glass fibre, carbon fibre reinforced plastics, etc. It is the first choice of continuous mixing equipment for polymer modification.

3. The Application of Co-Rotating Twin-Screw Extruder

The twin-screw extruder can process different kinds of waste plastics into plastic pellets, which are now growing in price with a small investment and a large return. It is mainly used to process waste plastic film (industrial packaging film, agricultural film, greenhouse film, beer bags, handbags, etc.), woven bags, agricultural convenience bags, tubs, barrels, beverage bottles, furniture, daily necessities and most other common waste plastics, and is the most widely used and popular plastic recycling processing machine in the waste plastic recycling industry. It has a good development prospect both now and in the future.

4. The Features of Co-Rotating Twin-Screw Extruder

(1) Wear and tear

Thanks to the easy opening, the degree of wear of the threaded elements and barrel bushings can be detected at any time, so that they can be repaired or replaced effectively. It is not necessary to detect problems with the extruded product only when they occur, resulting in unnecessary waste.

(2) Reduced production costs

When manufacturing masterbatches, it is often necessary to change colours and if a product change is necessary, to open the open processing area within a few minutes and additionally to analyse the mixing process by looking at the melt profile on the entire screw. The current common twin-screw extruder requires a large amount of clearing material to clear the machine when changing the colour, which is time-consuming, power-consuming and a waste of raw material. The split twin-screw extruder, on the other hand, solves this problem by quickly opening the barrel for manual cleaning in just a few minutes when changing colours, thus saving costs by using no or less cleaning material.

(3) Improved labour efficiency

When servicing equipment, ordinary twin-screw extruders often require the heating and cooling system to be removed before the screw can be withdrawn in its entirety. The split twin screw does not need to be removed, as long as a few bolts are loosened and the upper half of the barrel is lifted by turning the worm gearbox handle device to open the entire barrel for maintenance. This shortens maintenance time and reduces labour intensity.

(4) High torque, high speed

The current trend in the world of twin-screw extruders is towards high torque, high rotation speed and low energy consumption, the effect of high rotation speed being high productivity. The split twin-screw extruder falls into this category, with a speed of up to plus 500 rpm. This gives it a unique advantage in the processing of highly viscous, heat-sensitive materials.

In terms of high speed and high torque core technology, asymmetric and symmetric high torque gearboxes are currently only available in Germany and Japan, where the core technology can reach a maximum speed of 1800 rpm or more.

(5) Wide range of applications

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

(6)High output, high quality

With the other advantages of a common twin-screw extruder, high output, high quality and high efficiency can be achieved.