BLOCK'S. Bait's Differential Pulley-Block. made by the Boston & Lockport Block Co., is shown in Fig. 1. The disk-pulley carrying the hand-chain has cast upon its side a scroll or spiral groove which meshes into the teeth of a wheel placed at right angles to it which carries upon its side the sprocket-wheel for the load chain. The angle of the spiral groove being low, it exerts a powerful purchase on the- hoisting wheel. The friction is sufficient to sustain the load.
Alfred Box (C. Co.'s Double-Sceew Hoist is shown m Fig. 2. The power is applied through the chain •q on the large sprocket-wheel E. seen at the left of the cut, which drives a, double worm, C D, geared right and left into two worm.wheels. A B. which also are geared into each other. One of these carries the sprocket-wheel for the hoisting chain f. Both chains are always kept in place by the guides.
The Detroit Sure-Grip nckle-Block is shown in Fig. 3. The brake which will hold the load at any point is simply a wedge that drops by gravity between the upper sheaves. The face of the wedge is fluted to the curve of the rope. The block is made of steel. The arrows in the cut show the direction of the rope through the. blocks. It will be noticed that the two center ropes that come in contact with the wedge both travel in the same direction at the same time.
Weston's Triplex Spur-Gear Block, made by the Yale & Towne Mfg. Co.. is shown in Figs. 4, 5, 6. and 7. Figs. 4 and 5 are external views of the block suspended as for use; Fig. 6 is a transverse view, the lower half being shown in section, and Fig. 7 a section show ing the hoisting mechanism. All of the mechanism is symmetrically grouped upon a single horizontal axis, and is so arranged as to occupy- as little vertical space as possible. Power is applied to an endless hand-chain passing over the pocketed chain-wheel on one end of the central shaft, and is transmitted thereby to the train or spur-gearing contained in the hous ing on the other side of the block. The main or load chain passes over a pocketed chain sheave in the center of the block, one of its ends being provided with a suitable hook for receiving the load, and the other being looped up and permanently secured to the frame of the block. Referring to Pig. 6, the hand-wheel at the left transmits power through the cen tral shaft to the steel pinion on its opposite end (seen best in Fig. 7), which in turn engages with the three planet-wheels surrounding it. These hitter are of hard bronze, and have east with them a smaller series of pinions, shown in Fig. Iii, which latter engage with the annular gear cast in the stationary frame of the block, as shown in Fig. 7. ']'he three double planet wheels are carried in a frame or cage which supports both ends of each of the pins forming the axis of the wheels. As the central shaft is turned, the whole cage and its three pinions thus rotate slowly within the housing of the block. The inner side of the pinion cage consists of
a disk keyed to one end of the steel sleeve forming part of and carrying the hoisting-chain sheave, so dolt the rotary motion of the pinion cage is thus transmitted to the chain-sheave. The two hubs of the bitter are prolonged to furor bearings on each side in the frame of the block, and are bored through the center to permit the shaft of the hand-chain wheel to pass through the sleeve just formed. The mechanism thus described constitutes the entire gear ing by which the load is hoisted, and is obviously not self-sustaining. The sustaining mechanism is placed at the hand-chain end of the block (the left of Fig. ffi, and consists of a set of brass friction disks, the disks being alternately attached to the central axis and to a ratchet check wheel. The hand-ehain wheel is screwed upon the central spindle, as shown, and the construction is such that it is clamped tightly by the friction disks to the shaft either if it is rotated in the direction for hoisting, or if the shaft attempts to revolve in the opposite direction under the pull of the load. The parts being thus clamped together act as one, and the ratchets offer no resistance to the effort of the operator in hoisting. When the direction of the hand-chain is reversed, the alternate disks are released, and the others being held by the ratchets, the load is lowered against their friction at a rate entirely controlled by the move ment of the hand-chain. while the stoppage of the hand-chain movement causes the disks to tighten at once and sustain the load. In another form of this tackle a double suspension is employed, two hooks being used, one to sustain the triplex block and the other to carry the chain-tackle, This form is well adapted for use in connection with trolleys for overhead tramrail. o• for permanent suspension from fixed eye-bolts, and in some cases its use en ables an increase in the available height of hoist to he obtained. In case a powerful block is needed for use on a single occasion, such as the erection of a large engine or other heavy machine. it possesses the advantage that it may be taken apart after the performance of the heavy duty, and the triplex block used alone for subsequent and lighter service.
Efficiency of Chain-Blocks.—Chain-blocks other than the Weston triplex depend upon the friction of the working parts to sustain the load, and for this reason their mechanical efficiency is very low. In the Weston triplex block, as above described, the mechanism is especially constructed so as to reduce friction to a minimum, and therefore it requires a separate attachment for sustaining the load. The following is a record of tests made by Prof. It H. Thurston, of the efficiency of different forms of chain-block found in the market as compared with the Weston triplex and the old Weston differential: