CHAPTER XIX. PIT-FRAMES, PULLEYS, CAGES, WATER-TANKS, CONDUCTORS, HYDRAULIC STAGES, DOUBLE STAGES, ROPES, ETC. THE pulleys for a winding-rope are generally of large diameter, sometimes reaching 20 feet for a steel rope about 1 or 1 inch in diameter. The diameter of a pulley ought to be in some way proportional to the diameter of the wires of which the rope is made, and also in some way proportional to the diameter of the rope. A rope may work round a pulley only 3 feet in diameter, but it will endure longer the greater the diameter of the pulley. For a winding-rope only 1 inch in diameter, a pulley 10 feet in diameter may give satisfactory results; but for large collieries, with steel ropes 1 to 1 inch in diameter, the pulley is generally from 14 to 16 feet. It is generally made with a cast-iron grooved rim (see Fig. 526), with wrought-iron arms cast in, and also cast into a central cast-iron boss. The boss is cast in two halves, split across the diameter, so that the pulley-rim may freely contract when cooling. The two halves of the boss are afterwards united by wrought-iron collars shrunk on, and then bored and key-gated. Flat rope pulleys are constructed in a similar manner, merely altering the shape of the groove. Sometimes the rim is made of wrought-iron or steel plates riveted together, with wrought-iron or steel arms riveted on (see Fig. 527, of a 20-foot pulley for Harris's Navigation). FIG. 526.-Cast-iron pulley. The details of this pulley are given in Fig. 527. The shaft is of wrought iron, 10 inches in diameter, and 4 feet 10 inches long over all. The journals are about 8 inches in diameter, and 12 inches long. The boss is of cast iron, about 3 feet 6 inches in diameter, keyed on to the shaft, which is turned to fit. The rim is carried by forty-eight round steel arms, 1 inch in diameter. These arms are flattened at the end nearest the rim, to which they are attached by small steel plates riveted on to the arms and also on to the rim, as shown in the figure at a. The rim is made of two layers of curved steel plates, breaking joint with one another, and riveted together. The ends of the arms at the boss are screwed and fixed by nuts on both sides of the boss flange. The arms can thus be tightened to the extent requisite to bring the rim into a true circle. The curve of the rim is of just sufficient size to take the rope at the bottom, which is about I inch in diameter. The pedestals have under brasses, but no top brasses. Beneath the under brasses are three blocks of indiarubber, each two inches thick, separated by steel plates. These are intended to act as a spring to diminish the strains on the rope. Some pulleys 20 feet in diameter have been made with castiron rims, turned in the lathe to secure perfect smoothness and truth in running. A rule sometimes given for the diameter of pulleys is eight hundred times the diameter of the wires of which the rope is made. This rule may suffice for haulage and transmission of power, but gives an insufficient diameter for winding-rope pulleys. For haulage ropes of steel 1 inch diameter, pulleys 5 to 7 feet are commonly used with good results. Pit-frames. The pulleys are carried on a frame of timber or iron, so that the centre of the pulley is from 20 to 80 feet above the level of the bank. The height of the pulley above the bank depends, first, on the height of the cage (thus a four-decked cage may be 20 feet in height); next, on the length of the chains by which the cage is suspended from the rope; third, on the safety-hook and catch-plate, requiring, with the cage-chains, another height of 12 or 14 feet. There should also be room to raise the cage above the bank whilst the other cage is being lowered into the sump, say 6 feet; adding half the diameter of the (say 16-feet) pulley, 8 feet, gives a total minimum height from bank to centre of pulley, 48 feet. The height of pit-frames at large collieries is often from 60 to 80 feet above the bank. Wrought-iron pulleyframes are sometimes in the shape of a plate girder (see Fig. 528), and sometimes of a lattice girder (see Fig. 529), sometimes a box-girder and lattice-girder frame combined (see Fig. 530), and sometimes the upright and backstays are cylindrical plate-iron riveted columns, similar to ships' masts. Examples of wooden pit-frames are shown in Figs. 531, 531a. Rope-socket.-The attachment of the winding-rope to the cage may be done in several ways. The end of the rope is some times, in the case of flat ropes, turned round a grooved link and clamped, as shown in Fig. 532. is put into a socket made of wrought iron (see Fig. 533), which is larger at the bottom than the top. The socket is generally split, and has a loop at the bottom through which a shackle can be placed connecting it to the cage-chains; about 4 feet of the rope-end is untwisted, and the part above is bound tightly round with copper wire. The ends of the wires are now turned back, some of the wires for the whole 4 feet, others are cut off rather shorter, and in this way a lump is formed at the end of the rope where the wires are bent round. The wires so bent back are then closely bound round with wire; this is placed in the socket; Over this wrought-iron rings are tightly More often the end of the rope hammered down, closing the FIG. 529.-Pit-frame, lattice girder (Mansfeld). two sides of the socket, so that the rope cannot be drawn through. Sometimes the two sides of the socket are closed by rivets; a pricker is put through 53 FIG. 530.-Pit-frame, lattice girder (Harris's Navigation). the rope to open a way for the rivet. A solid socket is some A rope is more likely |