Understanding Wire Rope Construction
Three Factors to Ensure You Choose the Right Wire Rope
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| Wire rope consists of individual wires laid together in strands, which are, in turn, laid around a central core. |
All ground equipment operators want to get the highest reliability and the longest service life possible from the wire rope used with their cranes or hoists. Selecting the most suitable rope for a specific application requires a fundamental knowledge of the materials and types of construction that may be used.
In simple terms, wire rope consists of individual wires laid together in strands, which are, in turn, laid around a central core. The size of the wires, the number of wires in the strands, the direction in which the wire is wound and the core material are all factors that contribute to the characteristics of a particular wire rope. Each variation in these factors has both benefits and shortcomings, and no single wire rope product can provide 100% of all desirable properties for all applications. During service, a rope's wires, strands and core constantly interact, determining how well the rope performs when subjected to a variety of destructive forces such as tensile loading, abrasive wear, bending fatigue, lateral crushing and corrosion.
Factor One: The Wire Commonly used steel wire grades are:
IPS (improved plow steel) – with a high degree of strength, toughness and wear resistance.
EIP (extra improved plow steel) – with an approximate 15% higher minimum breaking force than IPS.
EEIP (extra extra improved plow steel) – with a minimum breaking force that is 10% higher than EIP.
It should be noted here that flexibility generally declines as wire strength increases.
In addition, special applications may call for stainless steel or other special grade wires.
Factor Two: The Core The core is the central foundation of a wire rope. It may be made from fibers or steel, and it supports the strands, keeping them in proper position under normal bending and loading conditions. Cores are normally designated in one of three ways:
Fiber (FC) – made from natural fibers such as sisal, or from synthetic fibers such as polypropylene. They are more resilient than steel cores and are best suited for applications that involve shock loads.
Independent Wire Rope Core (IWRC) – uses a separate wire rope as the core to increase the rope's strength, provide longer support under heavy loads and give more resistance to heat.
Wire Strand Core (WSC) – a single strand of wire is used as the core. This type of core is limited to standing ropes and small-diameter running ropes.
Factor Three: The Strands To resist fatigue and abrasion, the strands in a wire rope may consist of various combinations of wire quantities and sizes. A small number of large wires will, in general, make a more abrasive-resistant strand, but also one that is less fatigue-resistant than a strand consisting of a large number of small wires.
The lay of a wire rope refers to both the direction in which the wires in a strand are wound and the direction in which the strands are helically wound around the core. The chart below illustrates the five types of wire rope lay and includes brief descriptions of their characteristics.
Although this article has provided you with a fundamental knowledge of wire rope, the experts at Cableworks are always available to supplement this knowledge so that the rope you choose will be the best one to meet the requirements of your application.
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