GB655950A - Improvements in or relating to jib cranes - Google Patents

Abstract

655,950. Jib cranes. CURRAN, Ltd., J., and WHITEHEAD, C. D. Nov. 18, 1947, No. 30526. [Class 78 (iv)] A jib crane is movable on a vehicle from a position in which it is wholly supported by the vehicle to a position in which the crane base rests on the surface which supports the vehicle, the vehicle serving as a counterpoise when the crane is supported by the surface. The crane shown serves for lifting aircraft on an aerodrome to permit transporting means to be inserted beneath and is supported by a lattice beam structure 2 pivoted at 3 to the vehicle, the beam withstanding all longitudinal stresses. The jib is in two parts 6, 7, hinged together at 8, the upper portion 7 comprising two lower members 7a and an upper member 7b, while the lower portion 6 comprises two laterally-spaced side-frames joined by suitable bracing, and terminating in plates 9 to which are universally pivoted a pair of transverse beams 14 (see especially Fig. 4) carrying at each end a swivelling foundation plate 10. During transport, the parts 6, 7 of the jib lie above one another, spaced by a closed telescopic link 20, with the crown block 19 and tackle 17, 18 disposed between the folded plates 10 and clamped by means not shown, the lower jib part 6 being pivoted to the beam 2 at 21 and being joined by links 22a to bell-crank levers 23 pivoted at 24 to the beam 2 and urged to the position shown by a spring 29. In erecting the crane the luffing drum 4 operating a rope 26 passing over a pulley 27 in a frame 28 pivoted to the jib part 7 is operated to raise the jib part 7 till the link 20 is fully extended, as shown in Fig. 2; if this process is continued too far the jib part 6 moves the bellcrank 23 against the action of the spring 29 to operate a switch or cut-out device which stops the winches. The links 22a are now disconnected and the winch 4 again operated so that the jib structure turns as a whole about the pivot 21 till the lug 22 is in position to be pinned at 30 to the upper end of the bell-crank 23. The beam 14 and foundation-plates 10 are then unclamped, and the pivot 21 released so that by paying out the luffing rope 26 and the lifting rope 25 by means of the winches 4, 5, the jib structure turns under its own weight about the pivot 30 to the position shown in Fig. 4, in which notches 31 (Fig. 2) in the plates 9 engage pivots 32 on the bell-cranks 23 to which they are then secured. The telescopic link 20 may now be disconnected, the lower half being swung down and secured, and the luffing rope 26 drawn in so that the jib part 7 turns about the pivot 8 to be secured by a triangular frame 33 to the lower jib part 6. The pivot 30 is now released and the rope 26 paid out to permit the jib to pivot about the point 32 so that the plates 10 rest on the ground, taking the weight of the crane and the beam 2 rocks on its pivot 3 and comes to rest on a stop 2a. A further vehicle carrying counterweights may be secured at 35 to the front of the beam 2. A jib comprising only a single part may be employed, and it is stated that instead of turning the jib about a series of pivots at 21, 30 and 31, it may be turned about a single pivot which is movable longitudinally of the vehicle.