GB593901A - Improvements in and relating to high frequency electrostatic heating of plastics, especially in connection with the moulding thereof - Google Patents

Abstract

593,901. Heating by dielectric losses. MACMILLIN, H. F. Jan. 3, 1944, No. 46. Convention date, March 10, 1943. Drawings to Specification. [Class 39 (iii)] [Also in Group V] Consists in a method of heating plastic material such as thermoplastic or thermosetting resin, in which the material is subjected to high-frequency electrostatic heating in two successive stages, the material being first heated uniformly in a high-frequency field between electrodes and then transferred to and further heated in a second field of greater intensity. The method is particularly described in connection with injection-moulding machines (see Group V), in which the material is heated in a cylinder in the space between a central axially-disposed electrode and the wall of the cylinder, which forms the other electrode. High frequency current is impressed upon the electrodes to establish a first heating zone in which the material is uniformly heated, after which the central electrode, an end of which is tapered to conform to the conical shape of the end of the cylinder adjacent to the nozzle, is moved forward close to the said conical end ; a second heating zone of greater intensity than the first is thus set up near the nozzle, and the material is then forced through the second zone, from which it passes to the moulding dies. The temperature of the material may be controlled by a thermo-couple. The Specification as open to inspection under Sect. 91 also describes and illustrates (Fig. 13, Cancelled, not shown), an injection-moulding machine in which heating of material is effected in a uniform high-frequency field set up in a cylinder between the wall thereof and a fixed electrode passing through the injection plunger and extending axially into the cylinder. A thermo-couple, which is short-circuited until the plunger passes the feed-opening into the cylinder, prevents overheating. The Specification also describes (Fig. 14, Cancelled, not shown), an extrusion-moulding machine having similar means for high-frequency heating, comprising an electrode fixed axially within the cylinder. This subject-matter does not appear in the Specification as accepted.