Twin screw extrusion is used extensively for mixing, compounding, or reacting polymeric materials. The flexibility of twin screw plastic extruder allows this operation to be designed specifically for the formulation being processed. For example, the two screws may be corotating or counterrotating, intermeshing, or non intermeshing. Besides, the configurations of the screws themselves may be varied using forward conveying elements, reverse conveying elements, kneading blocks, and other designs to achieve particular mixing characteristics.

Twin screw compounding extruders are used for compounding when special colors or different properties need to be added to the plastic materials. This type of plastic extrusion machinery allows the mixing of different materials to create a certain color or property of the plastics.

Twin Screw Extruders Types

Co-Rotating Extruders

Co-Rotating machines indicated that the screws turn in the same direction. Often these intermeshing screws turn at higher RPMs than counter rotating machines. The material moves over one screw to the other and passes underneath. This flow provides consistent shear and dispersion. These machines are often used in compounding and mixing applications. The screw elements are modular and can be changed relatively easily to give a desired effect inside the barrel segments.

Co-Rotating double screw extruder machines have a lot of customization ability due to their modular nature. Many of these machines seen in the market can have multiple venting ports, screw fed material feed sections, and liquid additive sections along the barrel. The customization continues upstream as well. Because the machines are starve fed most extruders will have extensive feed systems with gravimetric or volumetric blending systems upstream. 

Counter Rotating Extruders

Counter-Rotating twin screw compounding extruders have two screws that spin in the opposite direction. Also often intermeshing this style of machine is usually found in the profile, PVC, or wood composite industry. 

These machines typically have a much lower screw RPM and generally have much smaller l/d ratios. The screw direction allows for less shear than a single or co rotating two screw machine. 

The two styles of extrusion machines within the counter-rotating extruder category known as parallel twin screw extruder machine and conical twin screw extruder. A parallel twin screw extrusion has a consistent barrel diameter through the entire barrel. A conical twin screw extruder has a taper. The feed section is much larger than the end of the barrel. Both counter rotating machines often have barrel venting. The barrels and screws of these machines are not modular so they may need to be changed for your specific application.  Air cooling and water cooling are both common.

How Does Extrusion Work?

Extrusion processing aims to physicochemically transform continuously viscous polymeric media and produce high-quality structured products thanks to the accurate control of processing conditions.

Chuangbo twin-screw extruders consist of two intermeshings, co-rotating screws mounted on splined shafts in a closed barrel. Due to a wide range of screw and barrel designs, various screw profiles and process functions can be set up according to process requirements. Hence, a double screw extruder machine can ensure transporting, compressing, mixing, shearing, heating, cooling, pumping, shaping, etc. With a high level of flexibility. The major advantage of intermeshing co-rotating twin-screw extruders is their remarkable mixing capability which confers exceptional characteristics to extruded products and adds significant value to processing units.

In twin screw extrusion processing, the raw materials may be solids (powders, granulates), liquids, and possibly gases. Extruded products are plastics compounds, chemically modified polymers, etc.

Twin Screw Extruder Parts

Screw Element

Extrusion Barrels

Extrusion Screw Shaft

Conical Feeder

Side Feeder

Liquid Feeder

Loss in Weight Feeder

Gearbox

Advantages of Twin Screw Compounding Extrusion