GB732091A - Curved extrusion process and apparatus - Google Patents

Abstract

732,091. Making curved channel members from thermoplastic material. FISCH, R. A. Aug. 27, 1953, No. 23731/53. Class 87 (2). Curved strip of thermoplastic material channel-shaped in cross-section, is produced by extruding the material R downwards through a die 20 with a channelforming orifice, rotating a supporting member 30 having a flange 31 adapted to fit snugly into the channel of the extruded strip, cooling the strip along the path followed by the periphery of the supporting member and withdrawing the cooled, set and curved strip before it has completed more than three-quarters of a revolution on the supporting member. The strip leaves the die in a downward direction to minimize the tendency for the soft flanges of the channels to become disturbed by gravitational forces. The die is preferably heated, a suitable temperature being 250‹-300‹ F. The member 30 is mounted to rotate freely, and the strip is pulled round by a pair of rollers 41, 42 with peripheries which fit into one or more grooves in the strip. To retain the curvature the peripheral speed of the outer roller 42 must be slightly higher than that of the inner roller 41, either by rotating it faster or giving it a larger diameter. A suitable speed is one which draws off the strip at about 35 feet per minute. The channel in the extended strip is forced to straddle the rotating flange 31 by a jig 40, which may be stationary or may be a rotating wheel. The cooling is effected by passing the strip through water or other cooling liquid 65, with a thermostat heater to keep it at a constant temperature, suitably 110‹ F. Alternatively, jets of cooling gas may be used. The temperature of the material is such that any liquid on the flange 31 would vaporize and distort the product, and the level of the liquid must therefore be below the point where the strip meets the rotating flange and any liquid carried round by the flange must be removed, which may be done by forcing dry air through a jet 67. The configuration of the rotating member 30 may be other than circular, e.g. elliptical. The strip leaving the rollers 41, 42 may be led into a container which is rotated so that the strip is deposited in it in the form of a helix. The product finds use as a rim insulating shield in a cathode ray tube.