Wire Rope

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As a versatile, high load capacity alternative to natural fiber ropes such as hemp and manila, wire rope provides motion transmission through nearly all angles, tie down, counterbalance, guidance, control or lift. Also referred to as stranded wire due to their multiple strand configuration, nearly all wire ropes, or cables, including control cables, are fabricated from strands of cold drawn carbon steel wires, although stainless steel cables are manufactured for highly corrosive environments. Galvanized cables are also popular for the increased strength and durability needed for specialized ropes such as aircraft cables. Specially treated steel cable and plastic coated cables are common to many application specific variations of wire robe such as push pull cable assemblies used in transferring motion between two points. Wire rope assemblies such as these are configurations of one or multiple ropes equipped with wire rope fittings for connecting to other cables, and wire rope slings or eye splices. Such applications extend the capabilities and applicability of wire ropes.

Obvious applications for wire rope include multi-ton hoisting and tie-down in industrial manufacturing, construction, ship rigging, oil rigging and mining, many other industries in the manufacturing and consumer sectors use wire rope. Additional applications abound, however, ranging from consumer goods to transportation. Fitness industries use plastic coated cable in most weight machines; theater industries use black powder coated cables for stage rigging; outdoor playground equipment often use plastic coated cables, and many types of electronic equipment, communications devices and medical devices use miniature wire rope and wire rope fittings. Each industrial, commercial or domestic application for wire rope requires the use of specialized cables best suited to that use. Suppliers typically identify wire cable by listing both the number of strands and the amount of wires per strand respectively, though stranded cable may alternatively be measured by their lay and length or pitch. Identification codes can also be extended to specifics which are abbreviated to quickly denote core type, work load limit and more. The connections, fasteners, fittings and other hardware are also listed by most suppliers as these offer differing degrees of versatility to a rope in terms of fray prevention and connectivity to anchors, equipment and other ropes.

While fittings and assemblies are important, there are three basic elements of which wire ropes are composed: wire filaments, strands and cores. The first components, filaments, are cold drawn rods of metal materials of varying, but relatively small diameter. Though steel is perhaps most common, several different metal wires are available including aluminum, nickel alloy, bronze, copper and titanium. A strand is formed when the individual wires are twisted or braided together. A single strand can consist of as few as two or as many as several dozen filaments and different gauges depending upon the strength, flexibility and wear resistance requirements. The core is an extremely versatile element of wire cables. This is the central element around which strands are wrapped and it may be composed of metal, fiber or impregnated fiber materials depending on the intended application. Cores may also be another strand of wire called an independent wire rope core (IWRC); wire rope cores maintain a considerable amount of flexibility while increasing strength by at least 7.5% over the strength of fiber core wire ropes. As important as each individual element is the manner in which they are combined. The helical winding of the strands around the core is known as the lay. Ropes may be right hand lay, twisting strands clockwise, or they may be left hand lay, twisting strands counter-clockwise. In and ordinary lay the individual strands are twisted in the opposite direction of the lay of the entire rope of strands to increase tension and to prevent the rope from coming unwound. Though this is most common Lang's lay has both the strands and the rope twisted in the same direction while alternate lays, as the name suggests alternate between ordinary and Lang style lays.

While alternative rope designs are available, the helical core design is often favored as it allows a wire cable to hold a lot of weight while remaining ductile. Even the heaviest industrial loads may be lifted with a well made wire rope because the weight is distributed evenly among constituent strands. The lay is crucial to this characteristic of wire ropes. As the cables play an integral role in the safety of many operations and structures, careful analysis of a wire rope and all of its capabilities and features is vital. Important qualities and physical specifications include diameter, breaking strength, resistance to corrosion, difficulty of flattening or crushing, ability to be bent, and average lifespan. Each of the aforementioned considerations should be compatible with the specific application for which the rope is intended as well as the environment in which such operations are undertaken. Temperature and corrosive environments often require specially coated wire ropes with increased durability. When dealing with industrial wire rope it is important to remember that rated load, breaking strength and other specifications are the measured capabilities under normal circumstances. Rust, kinks, fraying and even carefully performed splicing will all have an impact on the performance of wire ropes which should be inspected regularly and cleaned or lubricated as needed. Properly maintained wire ropes often boast a long working life and are therefore favored in many applications.

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Image Provided by Bergen Cable Technology, LLC

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Wire Rope Types

• Aircraft cables are strands, cords and wire ropes composed of special strength wire. Aircraft cables are mainly for aircraft controls and various aircraft industry uses.
• Cable assemblies are fittings which are attached to the end of bundled wires.
• Cable railing is used in the barriers that run along the edge of stairs and landings, especially in industrial or outdoor locations.
• Control cables are specialized wire ropes designed for the positive and precise transmission of mechanical motion. Incorporated into equipment and machinery, these cables are responsible for connecting moving parts and controlling the interaction of those parts.
• Galvanized cables are wire ropes that have undergone a metallurgical process known as galvanizing to increase corrosion resistance, durability and temperature resistance. Galvanizing involves dipping wire components in a bath of molten zinc which causes a chemical reaction and creates a permanent bond.
• Plastic coated cable is usually coated with a vinyl or nylon-type polymer for ease of handling and extra corrosion resistance in a range of outdoor and indoor applications involving repetitive use or submerged cable use.
  
• Push pull cable offer multi-directional control and are often used as remote-access latch release cables and safety break cables.
• Stainless steel cable is specialized wire rope composed of two or more chrome-nickel steel wires braided or twisted together to form a larger strand the is resistant to corrosion.
  
• Steel cables are strong metal ropes used for various applications. Steel cables are composed of several individual filaments which are twisted into strands before being helically wrapped around a core to form a wire rope.
• Steel wire rope is composed of non-galvanized carbon steel (bright), stainless steel wire, or galvanized carbon steel. The scope of diameters and compositions of steel wire rope include 1/16 inch to five inches or greater. But, whichever the kind of steel, diameter, or the specific composition, all stainless steel wire has the same physical construction of multiple strands of wire wound helically about a central core.
  
• Stranded wire consists of a cable that is made up of strands of wires and is identified by the number of strands and the amount of wires per strand; a 7 x 18 cable would have seven strands with 18 wires in each strand.
  
• Wire rope assemblies are wires ropes that have their ends changed through a splice or fittings add-on. Their uses include running controls, incorporation into machinery and equipment or as slings or hoists.
  Wire rope fittings are hardware components found predominantly at the points of termination on wire ropes to improve connectivity, versatility and to prevent fraying.
  
• Wire rope hoists are hoists that use wire ropes as the means for lifting and consist of a rope storage drum, motors, gearbox and braking system. A trolley suspends the hoist from a bridge beam or monorail, although a stationary mounting is also possible.
  
• Wire rope slings  re short lengths of wire rope made especially to accommodate lifting attachments. Slings use Independent Wire Rope Cores (IWRC) and may consist of Improved Plow Steel, Extra Improved Steel, or Extra, Extra Improved Plow Steel.

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Wire Rope Terms

Breaking Strength - A calculation of the load necessary to break a wire rope that is in tension.

Core - Element of a wire rope around which the strands are helically laid. The core could be made of fiber (cloth), independent wire rope or wire strand.

Drum - A round and flanged barrel, which is tapered or uniform in diameter for storage or operation, around which rope is wound.

Extra Improved Plow Steel - Steel that is designed for applications, which require greater safety features with no increase in diameter size and the highest resistance to abrasive wear. This steel is fifteen percent stronger than Improved Plow Steel, and the tensile strength of this grade ranges from 280,000 to 340,000 psi.

Galvanize - To coat with zinc for the protection of the wire, strand or rope from corrosion.

Grade - A classification according to breaking strength.

Guy Line - Steel wire or strand, typically galvanized, that braces or supports a structure.

Improved Plow Steel (IPS) - A high-carbon steel having a tensile strength of approximately 260,000 psi that is roughly fifteen percent stronger than Plow Steel. Most commercial wires are made from IPS.

Independent Wire Rope Core (IWRC) - Wire rope that serves as the core for a greater rope.

Iron - A low carbon steel wire of approximately 10,000 psi, which is pliable and capable of repeated stresses from bending around small sheaves. This grade is effective for tillers, guys and sash ropes.

Lay/Laid - The manner in which the wires are helically wound to form rope. Lay refers specifically to the direction of the helical path of the strands in a wire rope; for example, if the helix of the strands are like the threads of a right-hand screw, the lay is known as a right lay, or right-hand, but if the strands go to the left, it is a left lay, or left-hand.

Rope Grades - A classification of wire rope according to its breaking strength. The rank of grades according to increasing breaking strengths is as follows: Iron, Traction, Mild Plow Steel, Plow Steel, Improved Steel, Extra Improved Steel.

Sheave - A pulley wheel with a channel, mounted in a frame, that guides or alters the direction of the cable or rope.

Strand - An assembly of wires that are helically wound around an axis, fiber or wire center (core) to create a symmetrical portion.

Strand Grades - Classification of strands according to breaking strength. The ranking of increasing breaking strengths is as follows: Common, Siemens Martin, High Strength and Extra-High Strength; a utility's grade strand is available for certain requirements.

Swage - The act of fastening a termination to a wire rope through physical deformation of the termination about the rope via a hydraulic press or hammering. The strength is one hundred percent of the wire rope rating.

Swaged Fittings - Fittings into which wire rope can be inserted and fastened through a cold flow method.

Traction Steel - A grade of rope material that has a tensile strength range of 180,000 to 190,000 psi. Traction steel has great resistance to bending fatigue with a minimum of abrasive force on sheaves and drums, which contributes to its long use in elevators, from which the steel gets its name.

Wire - A continual span of metal that has been cold drawn from a rod.

Wire Rope Fittings - essential parts of cable assemblies, wire rope assemblies and wire rope slings that assist spliced or swagged rope ends in connecting to other cables and keeping cables and rope from unraveling.

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