Patent GB-646423-A (GB)
Title: Improvements in or relating to a paper making apparatus
IPC: D21F1/06
Filed: 1946-07-29
Abstract: 646,423. Automatic control systems for paper-making apparatus. BLACK-CLAWSON CO. July 29, 1946, No. 22490. Convention date, July 30, 1945. [Class 38 (iv)] [Also in Group VIII] In paper-making apparatus having a sheet-forming member, stock in liquid suspension is supplied to the forming member and the liquid level is maintained constant automatically by means detecting the level in a compartment communicating with the liquid at the forming member and correcting it through motor - operated means. A paper forming vat 10, Fig. 1, having a rotary forming member 12 therein, is supplied with stock through an inlet 15. The level of liquid in an overflow compartment 20 is detected by a pair of electrodes 63, 64, Fig. 2, at slightly different levels in a chamber 46 communicating with compartment 20. The position of the electrode assembly relative to the liquid is adjusted, under automatic control, by the threaded shaft 55 of a reversible electric servomotor 50 to reduce hunting. The position of the electrode assembly and motor 50 combined is adjustable relative to the liquid by a manually-operated screw 52 for setting the level of liquid desired. A slight flow of clean water through an inlet 68 prevents accumulation of stock fibres in chamber 46. The level of liquid in compartment 20 is maintained between the levels of electrodes 63 and 64 by a butterfly valve 70, Fig. 1, in an overflow discharge conduit 37, automatically controlled by a reversible electric servomotor 71. With the liquid level correct as in Fig. 3, three-phase servomotors 50 and 71 are disconnected from A.C. source 80 and control is quiescent. Rise of liquid to the level of electrode 64, however, causes short circuit of a winding 105 of a relay 99 which thereupon operates to energize the operating coil of a switch 82 to run motor 71 in the appropriate direction to increase the opening of valve 70. At the same time, to reduce hunting, the operating coil of a switch 84 is energized to run motor 50 in the appropriate direction to raise the electrode assembly until electrode 64 breaks contact with the liquid and the servomotors are stopped. Fall of liquid below the level of electrode 63 causes removal of a short circuit of a winding 104 of a relay 98 resulting in closure of switches 83 and 85 to operate the servomotors in the reverse direction. Switches 86 and 87, operated at the limits of travel of valve 70, de-energize both servomotors, and switches 66 and 67, operated at the limits of travel of the electrode assembly de-energize servomotor 50 only. Push buttons 91 and 92 are provided for manual control. The following modifications are described : Fig. 4 (not shown). The electrode assembly is operated through a slipping clutch from the servomotor operating valve 70 instead of by a separate servomotor. Figs. 5-7 (not shown). Servomotor 50 is replaced by a fluid-pressure servomotor, controlled by a pump driven by the servomotor operating valve 70, of the type which slowly returns to a central position after operation to give a level liquid-level/flow characteristic. Fig. 8 (not shown). Servomotor 71 is replaced by an electromagnetically-controlled fluid pressure servomotor. Fig. 9 (not shown). Servomotor 50 is replaced by a lever, moved in opposite directions by electromagnets, which is dashpot controlled to return slowly to a central position. Specification 646,435, [Group VIII], is referred to.