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Principles of Extrusion


1.Continuous process
2.In principle, the plastic raw material is plasticated by means of a screw plastications unit and the molten material is continuously pumped out of through a standard orifice (die) in order to take the shape and then the shape is set by cooling/sizing system.
3.The required materials (Polymers,  Additives, Re-inforcements, etc.) are fed through a feed hopper into a barrel. 

4.The polymeric material soften by the heat from the external heaters and generated by frictional  force. 
5.The energy needed to convert the cold particle into a hot viscous melt depends on the specific heat, heat of melting (crystalline polymers), the maximum temperature of the extrusion. 
6.The transfer of heat into individual pellets by thermal conductivity. 
Thermal conductions is important in removing the heat from the melt in order to solidify it. 

7.The pressure required for the continuous extrusion can be generated by the extruder alone,  or by attached pump, viz, gear or screw type. 
  
8.The pressure for economic production depends on the material properties (especially  the melt rheology), type of restriction (filter pack,  die,  post-die equipment), the screw geometry,  and the required  throughput. 
9.The forward flow of the material is achieved due to the drag flow in the screw channel. 

 Example: Film, pipe,Tube,Sheet,Monofilament,
Extrusion coating/Lamination, Box Strapping, Tape/Woven sack, Wire Coating/Covering,
Profiles (Door & Window) etc.



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