Wire rope, also called wire cable, is an assembly of wire strands formed helically around a central core. It is used for pulling, lifting, rigging, hoisting, and in motion-control applications most commonly in the manufacturing, marine, oil, mining, fiber-optics, aircraft, automotive accessory, and construction industries. A combination of characteristics including material, finish, construction, diameter, length, and breaking strength give each rope its performance ability.
When selecting wire rope, there are several things to consider. One feature is material. Carbon (C) steel, also called plain steel, or plow steel, has one of the highest breaking strengths for wire rope, and comes in several grades of different strengths. Stainless steel resists corrosion and scaling and also comes in various grades for specific performance. Other commonly used materials are galvanized steel or iron, and Monel. Materials are selected for properties such as strength, elasticity, conductivity, and chemical- and weather-resistance.
Most wire rope is made of bright (uncoated or bare) wire, for strength. Wire rope is also produced in a variety of finishes, such as polypropylene (PE), vinyl (PVC), or nylon. These coatings can increase overall durability, strength, and allow for specific use, such as ease of movement over sheaths and pulleys, and/or resistance to substances and environmental conditions. Wire rope can be coated, or insulated and/or uncoated. A protective and insulating plastic filling can be used to increase performance, and reduce internal wear. Wire rope lubrication is essential to maintain functionality, and can be useful as a corrosion preventative, especially in crane operations.
Another wire rope characteristic is construction, which is expressed in the number of strands and the number of wires in each strand. For example, a 7 x 19 wire rope has seven strands, and 19 wires within each strand. The strands are formed helically around a core, which is typically made from Wire Strand Core (WSC), Independent Wire Rope Core (IWRC) or Fiber Core (FC). A fiber core can be made of natural material such as sisal or cotton, or synthetic material such as polypropylene (PE). A fiber wire core is typically more elastic, and holds lubrication better than a WSC or IWRC, but is not as crush-resistant, and may enable the wire rope to rotate under load. IWRC and strand cores are stronger, and more crush-resistant than fiber core, but less flexible.
The number of wires, strands and their design determine standard construction. There are also common rope constructions known as class constructions. Within these classifications, the number of strands can vary. For example, wire ropes with a 6x19 classification may have 15 to 26 wires in one strand. It is common practice to refer to rope either by its specific construction, or its classification.
Depending on its specific construction, wear, and use, wire rope can demonstrate fatigue and/or abrasion resistance. Wire rope fatigue refers to the process of progressive fracture, resulting from the bending of individual wires. These fractures can occur at bending stresses well below the breaking strength of the wire rope. Fatigue resistance increases with more, smaller outside wires, per strand. Fatigue-resistant wire rope must be capable of bending repeatedly with use, and under stress, without incurring damage that would impact its ability to function safely and correctly. Abrasion-resistance is wire rope's ability to withstand outer metal surface wear. A wire rope's abrasion-resistance increases with fewer, larger outside wires. Its metal strength, the load carried by the wire rope, and the running speed also affect its abrasion rate. A wire rope can be both abrasion-, and fatigue-resistant. However, generally, the more abrasion-resistant a wire rope is, the less fatigue-resistant it is.
The outer diameter of a wire rope is important in determining performance ability and expected life, and in calculating breaking strength. Wire rope outer diameter is commonly measured in inches, or centimeters, and is taken from the crowns of two opposing strands. A wire rope's diameter affects its bendability, and is a factor in determining use with pulleys, drums, or sheaths.
To function for its intended use, wire rope must be of an appropriate length. Wire rope length is commonly measured in imperial measurements, and is expressed by the foot, and possibly further by the inch. It can also be measured using metric meters or centimeters.
Breaking strength, also called tensile strength or breaking force, is the strength at which new wire rope will fail under a stationary load. Breaking strength is not considered safe working load (SWL) limit. Nominal strength refers to the published acceptable breaking strength figures that have been calculated by a standard procedure, and accepted by the wire rope industry. A wire rope should not operate at or near its nominal strength.