Patent GB-1528053-A (GB)
Title: Controlling pressure in extrusion dies
IPC: B30B11/22
Filed: 1975-10-27
Abstract: 1528053 Fluid-pressure servomotors GENERAL ELECTRIC CO 27 Oct 1975 [18 Nov 1974] 44148/75 Heading G3P [Also in Division B5] Powdered coal, with binder, is compacted into a rod of solid or tubular section, by extrusion of the rod by a screw (12), Fig. 1 (not shown), from the outlet of a die 17, downstream of which it may be cut into briquettes by a guillotine, and the density of the rod is maintained constant by varying the resistance to passage of the coal through the die, by automatically varying the inward force applied by manually, or automatically, actuated means, to a number e.g. four or six, of inwardly and outwardly pivotable portions 28a, 28d of the die, Fig. 2, which are circumferentially spaced at its outlet. The force is applied to each die portion e.g. 28d, Fig. 3, by the piston 59d of a double acting hydraulic cylinder and piston motor 31d, 59d, to each side of which the admission and exhaust of fluid is respectively controlled by valves 51, 52 and 53, 54 which are either manually, or automatically actuable through a control circuit switch 62, with the force being varied by altering the pressure of the fluid supplied from a pump 56, by manual or automatic adjustment of a metering valve 58 which alters the return flow to a reservoir 66 and is brought into action through a manual opening valve 57. Extrusion is commenced by manually operating valves 51, 54, and 52, 53 and setting valve 58, and, at the desired density of the rod, the switch 62 is actuated to change to automatic control effected, with valves 51, 54 open and valves 52, 53 closed, from a meter relay 61 which measures the current consumption of a motor 11  driving the screw 12, and which has high and low set points at which electrical signals act respectively to actuate the valve 58 towards a more open or a more closed position, in a stepwise manner which prevents "hunting", and which is effected by a timer 63 delivering the signal from the meter relay 61 for pre-selected times. Pump 56 may operate continuously, or automatically, and is provided with a pressure relief valve 67. Where the die adjustment of Fig. 2 is insufficient to maintain the required density, it may be employed, Fig. 4, in conjunction with the apparatus of Specification 1528052 in which constant density is maintained by increasing or decreasing the length of the die passage respectively to increase or decrease the density, effected by a downstream portion 17 of the die being telescopically slidable around an upstream part under the action of a double acting and cylinder and piston motors, each having the cylinder 21 and pistons 22 respectively coupled to the die parts 17, 16. At the commencement of extrusion, the pistons 59d and cylinders 21 are manually respectively rendered operative and inoperative by respectively opening valves 73 and 74, and closing valves 76 and 77. The pressure of fluid on the side 24 of piston 22 measures the frictional resistance to passage of the coal through the die, and is transmitted by electrical signals from a transducer 81 to a recorder 82 and a meter relay 83 having adjustable high and low points. Automatic control of the die portions 28d is initiated from switch 78, and double pole double throw switches 71, 72 are actuated so that signals from the meter relay 83 pass, via timer 63, to actuate metering valve 58 as in the Fig. 2 embodiment. When the resistance to passage of the coal through the die is indicated as being too high on the recorder 82, the control is changed from the die portions 28d to the die part 17, by manually actuating the switches 71, 72 and closing the valves 57, 73 and 74, and opening the valves 76, 77, the control thereafter functioning in the manner of Specification 1528052 to increase or decrease the length of the die stepwise, via valves 51, 54 and 52, 53, until the desired reading on meter 83 is obtained when control is manually changed to the die portions 28d by the switches 71, 72. Alternatively, the control of the die portions 28d in conjunction with that of the die portion 17, may be effected by sensing the current consumed by the motor driving the screw, Fig. 5 (not shown).