GB739509A - Improvements relating to screw-presses - Google Patents

Abstract

739,509. Presses for separating liquids from solids. AKTIESELSKAPET STORD. Jan. 26, 1954, No. 2395/54. Class 46. [Also in Groups XXIX and XXXV] In screw-presses of the kind in which the thread volume gradually decreases from the inlet towards the outlet and comprising a screw member both rotatable and axially slidable within a perforate cylindrical casing, means operative to transmit hydraulic pressure to the screw member are provided to urge the latter axially towards the outlet opening of the casing. A screw 5 comprising a helical thread 11 mounted on a hollow shaft 10 increasing in diameter from inlet 7 to outlet 12 is rotated, in a perforate casing 2 which is surrounded by an outer casing 1, by an electric motor 23 acting through gears 21, 20. The gear 20 is mounted on a stub shaft 15 to which the shaft 10 is secured for both rotation and axial movement therewith. To the right-hand end of the shaft 10 is secured a piston 24 sliding in a cylinder 25 to which hydraulic fluid may be supplied by a pump 29 from a reservoir 31 and from which it may return to the reservoir through a choke valve 32. When valves 37a and 37b on inlet and return pipes 27 and 28 respectively are turned through 90 degrees clockwise and anticlockwise respectively from the positions shown, fluid is locked in the cylinder 25, and the output of pump 29 is returned to the reservoir via a by-pass pipe 37c. With the valves in the position shown, adjustment of the choke valve 32 to vary the resistance to return of fluid to the reservoir 31 effects adjustment of pressure in the cylinder 25 to move the screw axially. For any particular setting of the choke valve the hydraulic pressure in the cylinder is constant, and the screw will take up a position depending on the relation between that pressure and the backward thrust due to the material being treated. Thus, on increase in fluidity of incoming material the screw is urged to the left, such movement bringing a smaller diameter portion of the shaft 10 beneath the hopper 7 and increasing the difference in thread volumes between inlet and outlet, to cause in turn a corresponding increase in the amount of liquid expressed until the axial thrust is restored and the former position resumed. Where oil-containing materials are being treated the extracted oil may be used as the hydraulic fluid. The valve 32 may be rotated automatically in the opening direction to reduce the pressure in the cylinder 25 when resistance to rotation of the screw rises, that is, when resistance to compression rises, and vice versa. A wattmeter 35, measuring the power absorbed by the motor 23, rotationally positions the rotor R1 of a synchrogenerator 36a, the rotor and stator of which are electrically connected to the rotor and stator respectively of a synchro-motor 36b, the rotor of which is coupled by gearing to the valve 32. A hand-wheel 32b may also be provided. In Fig. 2 (not shown) the same servo-mechanism is used to perform the opposite function, that is, to increase the pressure in the cylinder 25 when resistance to compression rises, and vice versa, the (axial) screw position thus being maintained constant. The shaft 10 is hollow so that steam may be applied through stub-shaft 15 to heat the contents of the press.