Extruder screw design
Bausano Twin screw extrusion is used extensively for mixing, compounding, or reacting polymeric materials. In addition, the configurations of the screws themselves may be changed by Bausano’s design department achieving particular mixing characteristics for customized projects. The personalization of the screw is one of Bausano’s point of strengths, because every project needs special attention. Almost always, twin screw extruders also include the provision for degassing ports. Twin screw extruders are used for bulk polymerisation, processing (pipes, sheet…) or compounding. Twin screw extruder have better mixing capability and so more material is saved because twins generally mix with less energy input.
Direction of the screw
Twin screw extruders can be co-rotating or counter-rotating. Into the co -rotating, one screw wipes the other without creating high shear against the walls of the barrel. They are designed as mass-transfer devices, with the main applications being mixing, devolatilization and reactive extrusion. Both types of twin-screw extruders have distinct advantages that lead to their use in specific applications.
The Bausano counter-rotating machine has very good material feed and conveying characteristics. The residence time and material temperature control in the machine are also uniform. Fully intermeshing, counter rotating twin screw extruders are essentially positive displacement pumps independent of frictional criterion and are designed for thermally sensitive polymers such as PVC or C-PVC. During twin screw extrusion raw material is conveyed, compressed, degassed, plasticated, sheared, kneaded, fused at optimum level and homogenized before it enters the die.
Parallel Counter-rotating Twin Screw Extruder, like the one manufactured in Bausano, are the better solution for working for example PVC+100 p.h.r CaCO3. Parallel Screw are longer than the conical one, in fact with a L/D ratio of 1/30 the former is well suggested to guarantee a good jellification of the material. The shape of parallel screw gives more time to the plasticization process, to better coat and amalgamate the high quantity of carbonate. The carbonate is a high corrosion material, and this is a key point in terms of screw and barrel lifetime. With this type of application parallel screw has a higher resistance capacity against the corrosion action of carbonate filler due to the bigger and more resistant heart. This also guarantees a longer life of the barrel.
