英语翻译ExtrusionIn the extrusion process,polymer is propelled c

英语翻译
Extrusion
In the extrusion process,polymer is propelled continuously along a screw through region of high temperature where it is melted and compacted,and finally forced through a die shaped to give the final object.
Extrusion is used to make three main types of products:
1 Standard profile such as rod,pipe,sheet,and irregular cross sections.
2 Extrusion around wire and cable as a protective coating.
3 Film to be used along and as coatings for paper,cloth,and other surfaces.
Each of these types can be made in varying sizes depending upon the size of the machine.Extruders are designated as to size by the diameter of the rotating screw.They range from large industrial extruders with screw diameters up to 6 in or 8 in,down to the laboratory model with a 3/4 in diameter screw.Extrusion is used only for the processing of thermoplastic resins.
The screw of an extruder is divided into several sections,each with a specific purpose (Chung 1977 ).The feed section picks up the finely divided polymer from a hopper and propels it into the main part of the extruder.In the compression section,the loosely packed feed is compacted,melted,and formed into a continuous stream of molten plastic.Some external heat must be applied,but much is generated by friction.The metering section contributes to uniform flow rate ,required to produce uniform dimensions in the finished product,and builds up sufficient pressure in the polymer melt to force the plastic through the rest of the extruder and out of the die.Since viscous polymer melts can be mixed only by the application of shearing forces (their viscosity is too high to allow turbulence or diffusion of contribute appreciably to mixing),an additional working section may be needed before the die.