GB946196A - Jack device - Google Patents

Abstract

946,196. Jack devices. PROCEDES ET MATERIELS INDUSTRIELS S.A. June 6, 1962 [June 7, 1961; Feb. 2, 1962], No. 21914/62. Heading B8J. A jack device for hoisting a load, e.g. sliding shuttering, in incremental steps along a vertical bar includes a body, spring means for urging clamping jaws into gripping relationship with the bar, and means for abutting the spring means relative to the body, the abutting means being arranged for ready insertion and removal into and out of fixed relationship with the body. The arrangement facilitates bar extracting operations, e.g. after the shuttering has reached the top of a concrete wall being erected. As shown in Figs. 1, 2, a body 1 positioned around a vertical bar B is provided with a fixed, upper blocking unit 8 and a movable, lower blocking unit 24. The upper unit includes jaws 11 removably mounted in holders 9 which are pivoted about pins 10 extending through a flat, cylindrical member of the blocking unit 8. A spring 13 urges the three jaws 11 into gripping engagement with the bar B when the spring is seated on a removable wedging member 14 which rests on seating members 15, 16 secured to the body 1. The lower blocking unit has pivoted jaw holders 27 and is slidable vertically in the body 1 by a lever 21 connected to it by a link 22 and a cylindrical part 23 eccentrically related to a pivot 18 in the body. A spring 26 urges the jaws 28 upwardly, pressure against the jaws being adjustable by screws 7 which engage a cross member 5 on which the spring seats. With the wedging member 14 removed and the cross member 5 disengaged from the spring 26 no biasing force is applied to the clamping jaws, and initial insertion of the jack on a bar is facilitated. By removing the jaws from their holders, tilting the latter upwardly and reinserting the jaws in inverted position the jack may be operated in reverse for withdrawing the bar B. Fig. 8 shows a modified jack with its jaws reversed in the " bar-withdrawing " condition, the spring 13 being urged against the upper jaws by a flange 4 secured by screws 34 to the upper blocking member. Additional springs 13a, 13b exert downward pressure on the lower jaws 30. To place the lower jaws 30 to " jacking " condition after reversal, the screws 7 are screwed tight and vertical fingers on a spacer 31 compress the springs 13a, 13b, thus allowing the jaws 30 to be re-inverted. To fit the lower jaws 30 in the withdrawing position shown, the screws 7 are screwed tight and vertical fingers on a spacer 31 compress the springs 13a, 13b, thus allowing the jaws to be reinserted in their holders. To reposition the upper jaws after inversion, the cover flange 4 is removed, the spring 13 is shifted upwards through the cylindrical member of the blocking unit 8 and the jaws re-inserted from above. The cover 4 is then re-secured using elongated screws 34. A further modification, Fig. 9, is operated by an hydraulic ram 37 having a piston rod pivoted at 41 to one end of a two armed lever 38 the other end of which is pivoted to the body 1 at a bearing 39. The ram is non-manually operated by the selective operation of a valve. A feeler member 45 limits the effective jacking stroke to control the climb rates of a number of jacks used together.