Patent GB-736022-A (GB)
Title: Improvements in or relating to screw extrusion machines
Inventor: RICHARDS ARTHUR BRUCE FRASER G
IPC: B29C48/85
Filed: 1952-10-23
Abstract: 736,022. Screw extrusion machines. BRITISH INSULATED CALLENDER'S CABLES, Ltd. Oct. 22, 1953 [Oct. 23, 1952], No. 26632/52. Class 87 (2). A screw extrusion machine of the type in which the material is subjected to a milling action at the rear and to pressure build up at the front comprises a feed screw with a threaded rear portion of large diameter compared with that of a threaded front portion from which it is separated by a threaded tapered intermediate portion, the front and rear portions each being of cylindrical form or tapering in the same sense as, but to a smaller degree than, the intermediate portion, the screw working within a correspondingly shaped barrel and the tapered intermediate portion being axially adjustable within the barrel to a limited extent to vary the clearance between it and the surrounding tapering wall of the barrel. The barrel is in three portions, a cylindrical front portion 3 with a renewable liner 7, an intermediate conical portion 5, about a quarter the length of the front portion, and a cylindrical rear portion 4, about the same length as the front portion and about two and a half times its diameter, with a renewable liner 8. The three barrel portions have jackets 15, 17, 16 for heating or cooling fluids. The feed screw is in two separate sections, a front section 18 in the barrel portion 3 and a rear section 20, 19 in the barrel portions 5, 4. In the embodiment described the threads 21 are the same hand and pitch on the three portions of the feed screw, that on the portion 20 being a continuation of the thread on the portion 19, but the threads may differ on the three portions in various ways. At the rear of the machine are a main housing 2 and an inner housing 27, the front wall of the main housing carrying a ball bearing 33 and the front wall of the inner housing having screwed into it a sleeve 43 which has a multi-start thread. A spigot 37 projects from the rear of the feed screw portion 19, 20 and is splined to a sleeve 35 which is rotatable in the bearing 33 and in a ball bearing 34 mounted in the sleeve 43, which also houses a roller thrust bearing 42. The sleeve 35 carries a worm wheel 38 which is driven by a worm 39 on a shaft 40 which projects sideways from the housing. The threaded sleeve 43 enables axial adjustment to be given to the intermediate and rear portions of the feed screw by turning the sleeve through an angular distance by means of a spoke 47 which projects through the housing and has a handle 49, the multi-start thread giving a relatively large axial movement. To drive the front portion 18 of the feed screw a torque tube 51 extends rearwards from it through a bore in the rear portions of the feed screw and is keyed, with clearance to allow for thermal expansion, to a sleeve 52 supported by a ball bearing 53 in the rear wall of the inner housing 27 and by a coned roller bearing 55 in the rear wall of the outer housing 2. The sleeve 52 carries a worm wheel 57 which is driven by a worm 58 on a shaft 59 which projects sideways from the housing on the same side as, or the opposite side to, the shaft 40. The shafts 40, 59 are driven by a motor through hydraulic variable gearing which enables their relative speeds to be varied, as through mechanically variable gearing, as by two separate variable speed motors. For heating or cooling the feed screw 19 a tube 67 extends from an enlargement 68 in the bore of the feed screw 20 to the spigot 37, forming an annular chamber in the feed screw 19, and a pipe 70 passes through the wall of the spigot into this chamber and along its .length to introduce heating or cooling fluid to the front of the feed screw which is supplied from a pipe 80 through a gland 74 and a channel 72 in the driving sleeve 35. The fluid, after circulating in the feed screw, returns through a pipe 71, channel 73 and passage 81 in the wall of the gland 74 to the inside of the housing 27, from which it is drained by a pipe 82. The interior of the front portion 18 of the feed screw is heated or cooled by fluid sent through a pipe 83 which extends through the torque tube 51, returning through the clearance between the pipe and the tube. In place of, or in addition to, heating by circulating fluid, electric heating elements may be incorporated in' the wall of the feed screw, connected to clip rings on the driving sleeve 35. The connection may be through plug and socket couplings to permit the feed screw to be withdrawn without disconnecting the leads. In view of the different speeds at which the front portion 18 and the rear portions 19, 20 of the feed screw may be driven, leakage of material between the two must be guarded against, and one way in which this may be done is to provide helical grooves on the front end of the circumferential surface of the torque tube 51 and/or the internal surface of the feed screw portion 20, the helices being of opposite hands when both surfaces are grooved, material leaking through being impelled back by the action of these grooves. Any material not so repelled is allowed to flow to the rear of the portion 19, whence it escapes through an inclined passage 95. Fig. 3 shows alternative sealing means in which carbon rings 85, 86 are seated in recesses in the intermediate feed screw portion 20 and in the torque tube 51 with a space between them occupied by a U-shaped ring 87 of beryllium copper alloy with its sides pressed against the carbon rings by the pressure of material which is allowed to pass through a small gap 88 between the front and intermediate feed screw portions 18, 20. To prevent fluid from reaching the seal from the tube 67 a sealing ring 89 is fitted. In another modification the sealing means comprises a beryllium copper alloy ring,between two carbon rings, of U-secfion with the opening facing towards the axis, oil under pressure entering the U through the clearance between the tube 67 and the torque tube 51 and forcing its sides against the carbon rings. Granular material is fed to the machine from a hopper 96 fitted with a vibrator 99, the granules passing from the hopper to the inlet through a flexible tube 97. Pasty material is fed from the hopper by a spiral screw, or by a pair of feed rollers at the bottom of the hopper. To adapt the machine to various purposes different delivery heads may be bolted to the front flange 107, Fig. 1A, showing a construction in which. a head 108, for extruding a coating about wire fed transversely, is clamped by a screw carried by a yoke 109, as described in Specification 660,249. Fig. 8 shows an attachment by which pellets are produced, the material being forced through perforations in a cylinder 111 and the extruding filaments being cut by blades 116, 117 rotated by a motor 115, the pellets so formed being collected by a hood 118 and leaving by a shoot 119. The cutters may be rotary, 121, Fig. 9, each with a pinion engaging a ring of teeth carried on the inside of the hood. The liners of the barrels may be internally ribbed or grooved. Oil is contained in the lower part of the housing 2 to form an oil bath, and is kept cool by a coil through which cold liquid is circulated.