Selecting the Right Wire RopeContent
All wire rope is not created equal. Every design is engineered for certain jobs and uses. When selecting wire rope, you should consider all its features, including strength, reserve strength, resistance to metal loss and deformation, crushing and fatigue resistance, bendability and stability.
Often, there’s an interrelationship between features. The better it performs in one area may have an inverse effect on another. For example, the greater a rope resists abrasion, the less resistant it is to fatigue, and vice-versa. Rope with fewer wires, such as a 6 X 19 design, better withstand abrasion, though its ability to resist bending, over sheaves and on to drums is reduced. The opposite is true of a 6 X 36 rope, which provides less abrasion resistance in exchange for more fatigue resistance.
The strength of wire rope is measured in tons (2000 pounds). It’s often referred to as tensile strength, because new rope is placed under tension on a pull test device to find its breaking point. Similarly, reserve strength is measured by the combined strength of all the inner wires inside a rope, accounting for the possibility that all outer wires have been worn away.
Abrasion resistance is a wire rope’s resistance to metal loss and deformation. Metal in individual surface wires can often be worn away, as if they had been subjected to filing or sanding, due to continued dragging across a surface, which ultimately reduces strength. In some cases, ropes appear as if someone hammered them, a condition known as peening. That typically occurs with wire to wire contact on drums and on sheaves. The result is reduced fatigue resistance. Ropes made of many wires have more fatigue resistance than the same size rope made of fewer wires.
While in use, wire ropes can be struck by hard objects, which can flatten or distort their shapes. A rope’s ability to withstand these forces is known as crush resistance. Generally, Independent Wire Rope Core (IWRC) ropes are more resistant than fiber core ropes; regular lay more crush resistant than lang lay; and the fewer the strands, the more crush resistant.
Bendability of a rope is determined by how easily it bends in an arc. Smaller ropes are more bendable than large ones and ropes with many wires are more bendable than the same size ropes with fewer wires. A final consideration is stability of the rope. No exact formulas exist, though ropes that unspool freely or don’t tangle are usually called stable. In general, the fewer wires per strand the more stable the rope.