GB971874A - Apparatus for controlling longitudinal tension - Google Patents

Abstract

971,874. Feeding webs. KEELAVITE HYDRAULICS Ltd. June 13, 1962 [May 4, 1961], No. 16261/61. Heading B6B. [Also in Division D1] Apparatus for controlling the longitudinal tension in a web, filament or the like 2 and wherein the tension is applied by an hydraulic motor 5 of the type which applies a torque determined by the pressure of the working fluid to e.g. a winding reel 4, comprises a device for sensing the web tension e.g. a roller 1, means for applying an adjustable hydraulic pressure to the sensing device in opposition to the force exerted by the web tension, a valve device 21 controlling the pressure of the working fluid in a passage 7 from a pump 6 to the motor 5, and means whereby the movement of the sensing device controls the valve device to maintain the web tension substantially constant. The web tension tends to move the roller 1, carried on a pivoted arm 8, downwardly against hydraulic pressure in a chamber 15 and against the pressure of a spring 14 which biases upwardly to open position a valve 13 controlling the admission of hydraulic pressure from a line 25 to a chamber 47 communicating with an outlet passage 16. During normal operation of the apparatus, the passage 16 is connected via a change-over device 17 referred to later, with a chamber 18 in the valve 21, and pressure therein acting on a plunger 30A tends to maintain a pilot valve 28 closed. A chamber 40 below the valve 28 is in communication with a chamber 38 below a main valve 27, and a chamber 41 above the valve 28 communicates via a passage 42 with an outlet chamber 32 of the main valve. The main valve 27 controls a passage 34 between an inlet chamber 31 connected to the passage 7 and the chamber 32, and has a transverse opening 35, and a restricted passage 37 communicating with the chamber 38. The passage 37 maintains the pressures in the chambers 31, 38 at equal values, so that if the pressure in chamber 31 rises, the pilot valve 28 opens, and the main valve 27 moves downwardly causing the chambers 31, 32 to communicate via the passage 34 and maintain the pressure in the line 7 constant. The pressure at which the pilot valve 28 opens depends on the pressure in the chamber 18 and thus on the web tension. The pressure in the line 25 is supplied by an auxiliary pump 26 and is controlled by a valve structure 24 identical with that of valve 21 except that the chamber 18 and plunger 30A are replaced by a manually adjustable member 30 which controls the opening pressure of its pilot valve 28. Hydraulic pressure is applied to the chamber 15 from the line 25 via a reducing valve 22. This valve is very similar to the valve 24, but differs in that the chamber 41 is connected directly to the reservoir 6A via a line 45, and the main valve 27 has no transverse passage but has a cut-away part 35A connecting the two sides of the passage 34 when in the position shown; furthermore, the inlet and outlet chambers 31, 32 are reversed. The action of the valve 22 is similar to that of the valve 24 so that adjustment of its member 30 adjusts the pressure in the chamber 15. When starting up the apparatus, the change-over device 17 is actuated manually to disconnect the chamber 18 from the passage 16 and to connect it to a passage 20 connected to the outlet 32 of a reducing valve structure 23 identically with the valve 22. The inlet side 31 of the valve 23 is connected to line 25. At this stage, pressure liquid in chamber 47 passes through a restricted opening 48 to a chamber communicating with the reservoir 6A. The members 30 of the valves 24, 23, 22 are first set so that respectively (a) the pressure in the line 25 will be maintained at a predetermined value higher than that required in chamber 15 or passage 20 (b) the pressures in chamber 18 and passage 7 are such that substantially no torque is applied to the reel 4 and there is no tension in the web 2 and (c) the pressure in the chamber 15 is in accordance with the tension it is desired to maintain in the web. The member 30 of valve 23 is then adjusted to raise the pressure in the chamber 18 and hence in the passage 7, to increase the torque until the web tension is sufficient to move the valve 13 downwardly to a point where the pressure in the chamber 47 as read by a gauge 50 decreases to a value equal to that in the chamber 18. The change-over device 17 is now operated to connect the chamber 47 via passage 16 to the chamber 18, and to disconnect the passage 20, thus bringing into operation the automatic control and rendering the valve 23 inoperative. Gauges 49, 51 are provided to indicate the pressures in the chamber 15 and passage 20 respectively.