Screw plasticator frictional heat

Time, pressure, and temperature controls indicate whether the performance requirements of a molded product are being met. The time factors include the rate of injection, duration of ram pressure, time of cooling, time of piastication, and screw RPM. Pressure requirement factors relate to injection high and low pressure cycles, back pressure on the extruder screw, and pressure loss before the plastic enters the cavity which can be caused by a variety of restrictions in the mold. The temperature control factors are in the mold (cavity and core), barrel, and nozzle, as well as the melt temperature from back pressure, screw speed, frictional heat, and so on in the plasticator. 

Heat to soften the plastic compound is supplied in two ways by external barrel heating and internal fiictional forces brought about on the plastic compound due to the action of the metal screw in the metal barrel. The amount of such frictional heat supplied in the plasticator is appreciable. In many extrusion operations, it represents most of the total heat supplied to the plastic. 

Pre-plasticising is the term given to the conversion of uncured rubber to a hot, soft (relative), and homogeneous, plastic mass. This is achieved by the rotation of a metal screw within a heater-jacketed barrel. The relationship between the temperature of the pre-plasticised rubber and that of the jacketed barrel is dynamic, as the hot rubber exchanges frictional heat to the barrel walls or, depending on the heater setting, gains more heat. Rubber strip is fed to the throat, or inlet to the screw where it is sheared... 

The screw does work on the material and generates frictional heat. At the present level of technology there is no good way to measure the temperature of the accumulated shot. It is either the same temperature as the barrel or it is not, and, if it is not, then it must be either hotter or colder than the barrel. The same statements hold true with respect to the screw. If there is a significant residence time in the barrel after the shot is accumulated, any temperature difference between the plastic and the surrounding metal wiU be the driving force for heat transfer. This in turn will lead to nonuniform temperature within... 

To create frictional heat to plasticize efficiently, bnt keep the temperature within a range that is controllable by heating and cooling of screws and barrel... 

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