Conventional single screw extruder is not suitable for WPC forming operation, because it processes the weak ability for material transmission and plasticization. The transmission affection of single screw extruder mainly depends on the role of friction. The wood structure is too fluffy to feed, and the filling of wood structure make the polymer melt viscosity increase which makes extruding more difficult? so that the material has a longer residence time in the cylinder ,and at the same time it cannot operate to the plant fiber with high water percentage for its poor exhausting affection. Therefore, conventional single screw extruder will be greatly restricted in the extruding process of wood-plastic composite materials.
The single screw extruder, which can be applied to the WPC forming operation, should use the specially designed screw. This kind of screw should has strong ability for material transmission and mixing material plasticization, and it can often mix and pelletize materials before extruding.
Nowadays the main operation of WPC is twin screw extruder, because it delivers materials relying on the principle of positive displacement and having no pressure returning ,easy feeding ,good exhausting affection. Thus the volatile components in wood flour can be fully ruled out. The meshing of screws with each other and the strong shearing can make the material have better mixing and plasticization affection. The wood flour cannot be charred because the less amount of wood flour is, the shorter time the material will stay in twin screw extruder.
Thus, the flour can be used in WPC product for the twin screw extruder having a good material adding and mixing affection.
Twin screw extruders have two types: parallel co-rotating twin screw extruder and parallel counter-rotating twin screw extruder.
About the Author:
by Xiangsu twin screw extruder
Article Source: ArticlesBase.com - Single Screw Extruder and Twin Screw Extruder
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