GB814504A - A slewing and luffing jib crane - Google Patents

Abstract

814,504. Tower cranes. LIEBHERR, H. April 8, 1957 [April 6, 1956], No. 11389/57. Class 78 (4). A slewing and luffing jib crane in which the jib is mounted on a mast, and substantially level luffing is achieved by inserting a tackle in the load-hoisting line between the mast-head and the jib-head, has means to prevent the jib being accidentally over-luffed by the tension in the load-hoisting line. As shown the jib 12, Fig. 1, is luffed by a cable 13, and the load cable 25 has three runs between the jib head and the head of a tower 10 on the mast 7. A cable 30 is attached to the jib head and to a truss 31 pivoted at 11, and passes over pulleys 32, 33 before being attached to a pivoted counter-jib 34 carrying ballast 35 and supported by cables 36. The cable 30 is slack until the jib approaches a dangerous inclination, after which the ballast 35 counterbalances the jib as shown in dotted outline in Fig. 1. Alternatively the same effect may be achieved by spring means between the jib and the tower 10. Speed of movement of load.-The horizontal speed of the load is made substantially constant during luffing by using a conical or conical differential luffing drum. In the latter case the luffing cable 58, Fig. 6, passes from the drum 57 to the jib head via the top of the tower 10, then back to the drum by the same route, and is wound in the opposite direction round the other end of the conical drum, as at 59, Fig. 6. A constant linear speed of the load during slewing is obtained by an infinitely variable gear 63, controlled from the luffing shaft 65 through a belt or chain 64, in the drive to the slewing pinion 81. Since the variable gear is of a type which must be continuously rotated while varying, a magnetic clutch 80 is included in the slewing drive so that the slewing motor can be rotated, without necessarily slewing the crane, whenever the luffing motor is operated. Instead of the conical differential luffing drum 57 a cylindrical drum may be used, driven through an infinitely variable gear such as that shown at 63. Erection of the crane.-Erection about a pivot 68, Fig. 7, is achieved by a cable 74 which passes from the hoisting drum 73 and several times between pulley blocks 71 on a pivoted truss 70 and 72 anchored to the ground. Cables 77 connect the truss 70 to an anchorage 75 on the mast. The crane may be made mobile by mounting the mast sections 1, 2, 3, Fig. 1, above the rotating part 7, the whole being supported on a trolley.