Compensating Quadrant Crane.

Progress, Volume VII, Issue 4, 1 February 1912, Page 991

Compensating Quadrant Crane.

There is a certain type of machine now in common use that has been handed down to us, with little change, from the very earliest days of history. The crane as employed by the Egyptians in building the Pyramids was not radically different from the derrick of the present day. It consisted then, as it does now, essentially of upright mast with a boom or gaff. Practically the only advances made in this type of machinery have been in the manipulation of the crane or the motive power utilized. Recently, a patent has been granted on a crane which is a decided innovation. The crane has no mast, but consists merely of a beam mounted on a frame in such a way that it can swing forward like the boom of a derrick while the load it carries moves on a virtually horizontal line as the beam is raised to the vertical position. The beam is built up of rolled steel and is secured to a pair of quadrants of east steel formed with teeth, to engage racks at the foot of the frame. The frame is mounted on a swivel base. The beam is raised or lowered by means of a horizontal screw which passes through a nut journaled to the quadrants. As the screw is operated, the quadrants roll on the

toothed foot of the frame. Hence, the fulcrum, which is the point of contact of the quadrant with the frame, moves outward as the beam moves toward the horizontal and at the same time the length of the lever from load to fulcrum is reduced, owing to the bell-crank form of the beam and quadrants. The compensating mechanism consists of a pair of arms hinged to the beam near the upper end, and secured to one end of a cable, which passes over a sheave at the top of the beam, and then runs to a point on the frame where it is permanently secured. As the beam is moved backward or forward, the arms are correspondingly swung on their hinges, so that their outer ends trace a practically horizontal line. At these outer ends the arms_ support the upper blocks of the hoisting tackle over which the hoisting cables run to a pair of winding drums. As a result of this “parallel motion” the load is not materially lifted as the crane is swung upward, and the bending moment on the beam is greatly reduced. The accompanying illustrations show a model of a full-sized 4-ton crane, which has a lifting capacity 0f2 22y 2 tons. In this crane the actual reduction in bending moment of the beam due to the compensating device is five-sixths that, is, a load of 120 foot-tons is reduced to 20 foot-tons, while the maximum thrust on the screw is less than 2% tons. The screw may thus be regarded as a simple controlling device rather than a means for shifting the load, the load being practically balanced. There is no bending moment on the screw, the thrust being exerted in line with its axis. In ise the crane is provided with separate motors for actuating the screw and the winding drums, and the gear by which the crane is swivelled on its base. Thus the crane is self-contained, making it a very serviceable piece of machinery for docks, ships, wrecking cars, etc. It is the present practice in the constructions of buildings to operate the cranes from a plant on the ground floor. Greater facility of operation would be afforded by the use of self-contained cranes, particularly in tall buildings.“ Scientific American.”