What are the different types of steel wire ropes?

Wire rope identification is not only done by its component parts, but also by its construction, i.e., by the way the wires have been laid to form strands, and by the way the strands have been laid around the core.

In Figure 3, “a” and “c” show strands as normally laid into the rope to the right in a fashion similar to the threading in a right-hand bolt. Conversely, the “left lay” rope strands (illustrations “b” and “d”) are laid in the opposite direction.

Again in Figure 3, the first two (“a” and “b”) show regular lay ropes. Following these are the types known as lang lay ropes (“c” and “d”). Note that the wires in regular lay ropes appear to line up with the axis of the rope; in lang lay rope the wires form an angle with the axis of the rope. This difference in appearance is a result of variations in manufacturing techniques: regular lay ropes are made so that the direction of the wire lay in the strand is opposite to the direction of the strand lay in the rope; lang lay ropes are made with both strand lay and rope lay in the same direction. Finally, “e” called alternate lay consists of alternating regular and lang lay strands.

Effects of Bending

All wire ropes, except stationary ropes used as guys or supports, are subjected to bending around sheaves or drums. The service obtained from wire ropes is, to a large extent, dependent upon the proper choice and location of the sheaves and drums about which it operates.

A wire rope may be considered a machine in which the individual elements (wires and strands) slide upon each other when the rope is bent. Therefore, as a prerequisite to the satisfactory operation of wire rope over sheaves and drums, the rope must be properly lubricated.

With this in mind, the effects of bending may be classified as:

• Loss of strength due to bending.
• Fatigue effect of bending.

Loss of strength due to bending is caused by the inability of the individual strands and wires to adjust themselves to their changed position when the rope is bent. Tests made by the National Institute of Standards and Technology show that the rope strength decreases in a marked degree as the sheave diameter grows smaller with respect to the diameter of the rope. The loss of strength due to bending wire ropes over the sheaves found in common use will not exceed 6% and will usually be about 4%.

The bending of a wire rope is accompanied by readjustment in the positions of the strands and wires and results in actual bending of the wires. Repetitive flexing of the wires develops bending loads which, even though well within the elastic limit of the wires, set up points of stress concentration.

The fatigue effect of bending appears in the form of small cracks in the wires at these over-stressed foci. These cracks propagate under repeated stress cycles, until the remaining sound metal is inadequate to withstand the bending load. This results in broken wires showing no apparent contraction of cross section.

Experience has established the fact that from the service view-point, a very definite relationship exists between the size of the individual outer wires of a wire rope and the size of the sheave or drum about which it operates. Sheaves and drums smaller than 200 times the diameter of the outer wires will cause permanent set in a heavily loaded rope. Good practice requires the use of sheaves and drums with diameters 800 times the diameter of the outer wires in the rope for heavily loaded fast-moving ropes.

It is impossible to give a definite minimum size of sheave or drum about which a wire rope will operate with satisfactory results, because of the other factors affecting the useful life of the rope. If the loads are light or the speed slow, smaller sheaves and drums can be used without causing early fatigue of the wires than if the loads are heavy or the speed is fast. Reverse bends, where a rope is bent in one direction and then in the opposite direction, cause excessive fatigue and should be avoided whenever possible. When a reverse bend is necessary larger sheaves are required than would be the case if the rope were bent in one direction only.

All wire ropes, except stationary ropes used as guys or supports, are subjected to bending around sheaves or drums. The service obtained from wire ropes is, to a large extent, dependent upon the proper choice and location of the sheaves and drums about which it operates.A wire rope may be considered a machine in which the individual elements (wires and strands) slide upon each other when the rope is bent. Therefore, as a prerequisite to the satisfactory operation of wire rope over sheaves and drums, the rope must be properly lubricated.With this in mind, the effects of bending may be classified as:Loss of strength due to bending is caused by the inability of the individual strands and wires to adjust themselves to their changed position when the rope is bent. Tests made by the National Institute of Standards and Technology show that the rope strength decreases in a marked degree as the sheave diameter grows smaller with respect to the diameter of the rope. The loss of strength due to bending wire ropes over the sheaves found in common use will not exceed 6% and will usually be about 4%.The bending of a wire rope is accompanied by readjustment in the positions of the strands and wires and results in actual bending of the wires. Repetitive flexing of the wires develops bending loads which, even though well within the elastic limit of the wires, set up points of stress concentration.The fatigue effect of bending appears in the form of small cracks in the wires at these over-stressed foci. These cracks propagate under repeated stress cycles, until the remaining sound metal is inadequate to withstand the bending load. This results in broken wires showing no apparent contraction of cross section.Experience has established the fact that from the service view-point, a very definite relationship exists between the size of the individual outer wires of a wire rope and the size of the sheave or drum about which it operates. Sheaves and drums smaller than 200 times the diameter of the outer wires will cause permanent set in a heavily loaded rope. Good practice requires the use of sheaves and drums with diameters 800 times the diameter of the outer wires in the rope for heavily loaded fast-moving ropes.It is impossible to give a definite minimum size of sheave or drum about which a wire rope will operate with satisfactory results, because of the other factors affecting the useful life of the rope. If the loads are light or the speed slow, smaller sheaves and drums can be used without causing early fatigue of the wires than if the loads are heavy or the speed is fast. Reverse bends, where a rope is bent in one direction and then in the opposite direction, cause excessive fatigue and should be avoided whenever possible. When a reverse bend is necessary larger sheaves are required than would be the case if the rope were bent in one direction only.