Now Fig. 177 is a sketch-plan of an endless band rope, such as may be seen at many collieries in Great Britain. A is the driving sheave on the engine at bank, round which the rope passes three or four times, and leads off to the overhead pulley B. Then it goes down the shaft, perhaps a very considerable distance, under the pulley C, and so on to D, whence it passes round the tightening sheave E, which is movable and contrived with weights to keep the rope always tight, and so prevent surging round the pulleys and sheaves and consequent loss of power. The rope then passes round D′ to the sheave F, the driving of which is the object aimed at, since that sheave in turn may work either one or two hauling ropes, as at G and H, working into the interior of the pit, in addition, perhaps, to a pump. The load on this rope may amount to several tons, and such a rope will therefore require a splice from 60 ft. to 100 ft. long.
Further, no matter what kind of a splice it may be, it must be made well. If it is a ship’s hawser, at times the safety of the vessel and all it contains may depend on a splice. Again, an awful disaster might be the result if the splice in a crane rope were to draw.
Fig. 177.—Colliery Band Rope Driving System.
There are three kinds of wire rope splices, the short splice, eye splice, and long splice.
A short splice is a bulky splice, and is used only for block straps, slings, etc. It is not suitable for driving ropes or for running tackle, and should never be put into a crane or hoist rope. It is made by unlaying the two ends of the rope to a sufficient length, from 1 ft. to 2 ft., according to size, and interlaying them together as in Fig. 178. Draw them close, and tuck the strands of one under the strands of the other several times. It is only a case of “over and under” as in splicing a hemp rope. After the ends have been tucked a sufficient number of times, about twice, each strand will stand in most cases. Hammer all down snug, and either cut off the ends with a hammer and chisel or twist the wires off one or two at a time, which makes a much neater job.
An eye splice may be made in two different ways—namely, left-handed, or “over and under,” and right-handed.
Fig. 178.—“Marrying” a Wire Rope Splice.
Left-handed splicing is undoubtedly stronger, tuck for tuck, than the right-handed method, for the “bite” on the strands is greater and the frictional adhesion is more acute. The strands and ends are practically plaited, and consequently locked together, and, no matter how the rope unlays itself, the splice is immovable. A splice like this should be put into every crane rope, for frequently the load when lifted from the ground spins round and unlays the rope to a certain extent.