Control of extrusion temperatures
With a sheet production extruder having an elongated barrel, an extrusion orifice located at one end of the barrel, a feed inlet located toward the other end, and conveying means for forcing polymeric feed through the barrel and out of the orifice, there is additionally provided a heating means which is thermostatically controlled for regulated heating of the extruder barrel.
It will therefore be understood that the temperature to which the polymeric material is heated and maintained within the single screw extruder is not so high as to detrimentally degrade or devolatilize the material, but is nonetheless high enough to facilitate the extrusion and provide an excaudate having the desired bonding characteristics and/or viscosity.
By use of two thermostatically controlled heating means, the heating zone in the twin screw extruder barrel can have two sections, and the amount of heat supplied to each section can be independently regulated thermostatically. Accordingly, the thermal energy input to the polymeric material upon entering the extruder can be at a relatively high rate, thus permitting rapid heat-up and softening of the feed in the first section of the heating zone, and followed by input of an additional increment of thermal energy in the second section of the zone to heat the polymeric material to the temperature at which it is to be extruded. Superheated steam which is circulated through one or more jackets on the extruder barrel. Furthermore, the heat supplied by such means can also be regulated by readily available thermostatic control devices designed for use with fluids instead of electricity.
Should the extrusion operation be interrupted, thermostatic regulation of the heating remains in effect, thus preventing overheating of the extruder and its polymeric contents during the nonoperational period. Furthermore, the extruder and its contents are at the necessary temperature whenever extrusion is resumed, i.e. no preliminary heat-up is required. It will also be understood that while the invention set forth herein is particularly applicable to portable, hand-held twin screw extruder, it is equally applicable to control of extrusion temperatures in stationary extruders.
While the illustrated sheet production extruder gun is equipped with two heating elements with independent thermostatic switches for each, it will be understood that--provided the polymeric material being fed to the extruder is not too stiff--only one element need be employed for the extruder barrel in conjunction with one thermostatic switch located near the discharge end of the barrel, e.g. thermostatic control switch 50, while also providing the barrel with sufficient length to effect heat-up to extrusion temperature. However, the present invention permits use of a shorter and more manageable gun by affording a short barrel length which can be used even with highly viscous polymeric materials.