Fig. 34
Springs are sometimes placed under the journals of the head-sheaves to lessen the strain on the rope while starting the load; the 15-foot head-sheaves of the Robinson deep mine at Johannesburg have locomotive springs under the journal boxes, the actual load on each spring due to the weight of the sheave, rope, skip, and rock being equal to about 20,000 pounds; it was estimated that the sheave would thus be lowered by the load on it, about 3 inches, which would be equal to an action of a spring giving motion of 6 inches at the cage. Springs can often be used both on the rope and under the sheave in the same plant to advantage.
Fig. 36
36. Square Type With Inclined Brace.—[Fig. 36] shows a very substantial frame with square tower and inclined brace.
Fig. 37
Its principal dimensions are as follows: height to sheave center 59 feet 6 inches; base of tower 15 feet 8 inches by 14 feet; distance of bottom of inclined leg from vertical post 48 feet. Each end post a is composed of two channels, double-latticed. The horizontal members b are I beams and each inclined member c is made up of two angles. The inclined leg d is trussed as shown and built of channel and angle beams, the main member being made of two channels, the incline and base members of the truss being made up of two angles, and the short vertical member of two channels. The center post of the tower is similar to the end posts, except that the uprights are I beams instead of channels. The frame is designed for a static weight of 16,000 pounds and for a maximum strain on the cable of 32,000 pounds.