Extrusion process aims to transform plastic / polymeric materials in order to produce high quality products. Twin screw extruders consist of two screws mounted on splined shafts in a closed barrel. Those screws are co-rotating which allows different types of plastic to be mixed well together. Twin screw extruders have a remarkable mixing capability which adds significant value to the production unit.
Twin Screw Extruders
Twin screw extruders belong to Plastic / Rubber machine category on Exapro and are used for production of plastic pipes, tubes or sheets of plastic. Extrusion is actually the first stage of producing a sheet of plastic thermoforming being the second stage of this process. As opposed to single screw extruder, twin screw feature allows to better mix the materials together. Hence it is possible to use different types of plastic which will be mixed together during extrusion to create the final product.
Inside of the extruder, two screws are rotating and this rotary motion is pushing plastic up front and mixing it at the same time. What kinds of materials can be used in a twin screw extruder? Usually, it is plastic pellets with additional colorants to achieve a special color of plastic. On the other hand, twin screw extruders are perfect for production of compounds: 2 types of plastic pellets mixed together to create a final product.
To start the extrusion process, machine operator should set the screw rotation speed and the volume of material needed for the production of the final part. During production process, mixed plastic is going through the die which is giving the product it's final shape. Part of the extrusion machine could be a cooling tank which is needed to cool the final product down. The final stage of production is cutting - pipes/tubes generally need to be cut to a specific length.
Various types of plastic can be used for extrusion. The type of plastic depends on the material the screw is made of. Every screw is made of a special metal compatible with certain types of plastic. Among typical extrusion materials belong polyethylene (PE), polypropylene, polystyrene, polyvinyl chloride (PVC), acrylonitrile butadiene styrene (ABS), acetal, acrylic, nylon (polyamides) and polycarbonate.
Area of Use
Plastic products have a very wide range of use in everyday life and industrial environment. For instance, plastic sheets are used for further production of yogurts caps, lids, cling film, even plastic bags. Pipes and tubes can be implemented in many areas, starting from individual housing up to the industrial range of use. Extruders are also installed inside of blow moulding machines which are used for production of plastic (PET) bottles.
Mixing capability. Due to screw rotation and the diversity of available screw designs mixing intensity and quality can be remarkably high. On the other hand, single screw extruder mixing capability is quite limited.
Production process flexibility. Twin screw extruders are capable of handling multiple processing functions (such as melting, mixing, cooking, venting, cooling, etc.). It can be achieved thanks to independent screw speed.
Better control of production parameters: narrower residence time distribution, lower dispersion of shear rates and strain, higher convective heat transfer, accurate control of temperature profile.
Higher productivity. Twin screw extruders can handle wider variety of plastic materials and mix formulations including complex recipes in a shorter time-frame.
Most popular manufacturers of twin screw extruders are the following companies: Amut, Bandera, Krauss Maffei and Cincinatti. For a reliable twin screw extruder, also check out brand names like Battenfeld, Leistvitz, Weber, Werner & Pffeiderer.