The Working Principle of Extruder
The extruder can turn solid plastic into a uniform melt through the heating, pressure and shear then the melt is conveyed to the next process. The melt includes mixing masterbatch and other additives, blending resin, and then smash in the production process. The finished melt must be homogeneous on the concentration and temperature. The pressure must be large enough to viscous polymer extrusion.
Extruder completes all of the above process through the barrel with a spiral track and a screw. The plastic pellets through a hopper at one end of the barrel into the barrel, and then transmitted to the other end of the barrel by the screw. The thread depth of screw starts to decrease with the increase distance of the hopper to ensure sufficient pressure. External heating and the internal heat generated by friction in the plastic and the screw make plastic soften and melt. Different polymers and applications have various design requirements of the extruder. Many options are related with the outlet, upper feed port, etc.
The extrusion machine is normally composed by at least three segments. The first paragraph is feeding zone near the hopper. This part can push the material into the extruder at a relatively steady rate, which will maintain relatively low temperature to avoid clogging of the feeding channel. The second part is divided into the compression zone which forms a melt and increases the pressure. The transition can be sudden or gradually (gentle) from the feed zone to the compression section. The last part is the metering zone close to the outlet of the extruder. The main function is to maintain uniform material from the outflow of the extruder. And the material should have a sufficient residence time to ensure the uniformity of the composition and temperature.
Another important part is the drive mechanism of the extruder. And the drive mechanism controls the rotational speed of the screw which determines the output of the extruder. The required power is determined by the viscosity of the polymer (flow resistance) which depends on the temperature and the flow rate. (End)
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