Patent GB-559154-A (GB)
Title: Improvements in or relating to extrusion machines
IPC: B29C48/395
Filed: 1942-07-31
Abstract: 559,154. Extrusion machines. HENLEY'S TELEGRAPH WORKS CO., Ltd., W. T., and GRIFFITHS, F. T. July 31, 1942, No. 10784. [Class 87 (ii)] [Also in Groups XI and XXII] The output of the screw-thread impelling device is controlled automatically by the axial position of one of the two relatively rotatable parts, e.g. the screw, which is permitted to move axially to a limited extent without positive restraint under the influence of a change in the thrust exerted upon it by the plastic material which is being extruded. Thus, if the pressure of the material at the delivery end of the screw rises, the screw is pushed back towards the feed end, and if the pressure falls at the delivery end the screw moves towards the delivery end, e.g. under the action of a spring. Three ways are described of controlling the output by means of the axial position of the screw : (1) The effective length of the impeller is varied. (2) Movement of the screw operates an electric switch or a valve controlling the supply of heat to, or the abstraction of heat from, an appropriate part of the impelling device. (3) Movement of the screw reduces the rate at which stock is fed in, either by adjusting the speed of an automatic feed device or, when the stock is fed in as a strip, by varying the width of the strip. (1) and (2) may be combined. Fig. 1. shows a lead extrusion machine constructed according to Specification 559,153, comprising two pairs of screws 131, 132 and 133, 134, the members of each pair being integrally united at their delivery ends. Molten metal is fed in at 14 and discharged through chambers 19 and ports 20 to the extrusion chamber 2. Electric heaters 16, 27, 22 (or induction coils) heat the metal at the feed and delivery ends, but midway the metal is cooled, by water passages 17, in order to make the metal plastic so that the screws may grip it. Each screw shaft 12 is supported in spaced bearings 30 between which a gear wheel 33 is secured on the shaft by screwed collars 34 having extensions 36. Between the extensions 36 and fixed thrust bearings 37 are clearances which determine the extent to which the shaft may float axially. If pressure increases at the delivery end of the screw 131, the upper shaft 12 will move to the left, thus diminishing the effective length of the screw 131, since the left-hand part thereof will move nearer to the hot feed chamber where its grip is ineffective. The output of the screw 131 is thus reduced. The output of screw 132 will increase. An additional corrective is applied by a toothed quadrant 42 pivoted at 40 and moved by a collar 38 on the shaft 12. The quadrant engages a pinion 43 which operates a temperature-control device 44 including (a) a rheostat which controls the heaters 21 and certain of the heaters 22, or (b) a valve controlling the flow of cooling liquid through the passages 17, or (c) both (a) and (b). The device may operate differentially on both screws of a pair, so that the slip or shear of one screw is increased and that of the other screw is decreased. Fig. 3 shows a modification in which the inner part 54 of a screw device is stationary and the outer part 52 rotates and floats to an extent determined by clearances at 67. Burners 62 heat the feed end of the rotor 52, and jets of air or water 63 cool the adjacent parts. A lever 69 pivoted in a groove in the rotor controls water valves 71 or gas valves 72 or both. Induction coils may replace the burners 62. A circumferential groove 64 in the rotor isolates the heated part from the cooled part as described in Specification 559,155. Material is delivered from both ends through a chamber 61 to the inner and outer dies 58, 59 which are coaxial with the screw device. In a further modification, a tubular impelling member having screw threads on its internal and external surfaces is disposed between a central stationary tubular die-carrying member and a hollow casing which is heated by spaced induction coils or resistance heaters between which cooling means is disposed. The impeller moves back, under pressure, against a spring, whereby the effective length of the impeller is reduced : additionally, the backward movement may control the supply of current to the induction coils or resistance heaters. In the embodiment shown in Fig. 4, heat is applied to the impelling device in the region of the fuel chamber 91 and also at the delivery end of the device by a pair of induction heating coils 92, 93 between which suitable cooling means may be provided. The impelling device, which comprises a tubular member 80 screw-threaded on both faces and mounted for rotation, by means of a gear 88, within fixed concentric parts 81, 82, is movable axially under control of a spring 94 and the pressure of the material at the front end of the machine and this movement may be used to control the supply of current to either or both of the heating coils.