Wire Rope and Mechanical Cable Information
Wire rope and mechanical cable is wound from high-strength metal strands for structural, mechanical actuation and motion control applications. Suppliers typically list the number of wires per strand followed by the number of strands per rope or cable. For example, products with a 7 x 19 designation have seven strands per cable and 19 wires per strand. Some wire rope and mechanical cable products are enclosed in a metal wrap or jacket to provide additional surface protection and abrasion resistance. Examples include swaged aluminum casing (lockclad), armored cable, flat wrap, round wrap, wire wrap or braiding, and solid metal conduits or tubing. Other products are encased in a plastic jacket, coating or conduit, or feature a protective plastic filling that is infused into the finished cable. Wire rope assemblies, mechanical control cables, and wire rope slings with attached clips, eyes, handles or other fittings are also commonly available.
Selecting Wire Rope and Mechanical Cable
Selecting wire rope and mechanical cable requires an analysis of wire materials. Aluminum is versatile, lightweight, and relatively corrosion-resistant. Titanium, another lightweight metal, provides high strength and superior corrosion resistance. Copper and copper alloys such as bronze and brass have very good corrosion resistance, high electrical and thermal conductivity, and moderate strength. Bronze and copper alloys are often used when additional electrical conductivity or grounding is required. Nickel and nickel alloys have excellent corrosion resistance and are available in specialized and proprietary forms. Steel, a commercial iron that contains carbon in any amount up to about 1.7 percent, is malleable under suitable conditions and distinguished from cast iron by both its malleability and lower carbon content. Steel wire is often brass-plated or copper-clad to improve its corrosion resistance, appearance, or friction characteristics. Wire rope made from zinc-galvanized steel is also available.
Physical specifications for wire rope and mechanical cable include diameter, length, breaking strength, and core type. The size of the pulley, sheave or drum determines the maximum diameter of the rope or cable that can be fed through the transit or fitting. With control cables, diameter usually refers to the overall, conduit or outer casing dimension. With bare wire rope, the largest outer diameter (OD) is listed because the rope’s diameter is not uniform in size. Diameter and length are measured in inches (in). Breaking strength is the maximum tensile load or force in pounds (lbs) that a rope or cable will hold before breaking. It is multiplied by a safety factor to determine the actual operating or working load. There are several core types for wire rope and mechanical cable. Plastic cores contain a solid, polyvinyl chloride (PVC) rod or a multi-filament rope made of polypropylene (PP), nylon or other synthetic material. Fiber core (FC) and hybrid products with metal and fiber strands are also available. Stranded metal wire core (SWC or SC) and independent wire rope core (IWRC) varieties are the strongest core types.
Approvals and Features
Wire rope and mechanical cable vary in terms of approvals, and features. Some products meet U.S. military specifications (MIL-SPEC) or comply with guidelines from the American Society of Testing Materials (ASTM). Other products are approved by the International Organization for Standardization (ISO) or Deutsches Institut für Normung (DIN). Cable-laid rope consists of several constituent wire ropes that are laid helically or wound over a core into a single cable. Compacted wire rope and mechanical cable is compressed using a swaging, rolling or other flattening or deformation processes. Spin resistant products consist of a large, wire rope core and strands that lay in the opposite direction. Guy wires support towers or antennas during high wind loads. Aircraft cables are used in tie-downs and fastener safety applications.
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