The extrudable plastic is a thermoplastic - they melt upon heating and re-solidify upon cooling. Where does the heat of molten plastic come from? Feed preheat and cylinder / mold heater may work and are very important at start-up, however, the motor input energy - the motor to overcome the resistance of the viscous melt The friction heat generated in the cylinder when the screw is rotated - is all Plastic, the most important heat source, small system, low speed screw, high melt temperature plastic and extrusion coating applications except.
For all other operations, it is important to recognize that the cylinder heater is not the primary heat source in operation and that the effect of extrusion is less than we might expect (see Principle 11). The post-cylinder temperature may still be important because it affects the rate at which the solids are fed in the feed or in the feed. The die and die temperatures should normally be the desired melt temperature or close to this temperature unless they are used for a specific purpose like glazing, fluid distribution or pressure control.www.screwbarrel.co