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Wire Rope & Strand Characteristics Size Ropes are referred to by a diameter. The correct way to measure wire rope is shown below. Fibre Core (FC) A fibre core, generally sisal, provides a resilient foundation for the strands in the rope structure. Fibre cores are used for ropes that are not subjected to heavy loads and where fl exibility in handling is required. Fibre Cores are inadequate where wire rope is subjected to heavy loading, prolonged outdoor exposure and crushing on small drums and sheaves. Wire Rope Core (WRC) Construction The main components of wire rope are shown below. In the example above, each individual wire is arranged around a central wire to form a 7-wire strand. Six of these strands are formed around a central core to make a wire rope. The rope is specifi ed at 6 x 7 (6/1) i.e., six strands of seven wires. The actual range of wire rope Constructions is wide and varied but the number could be limited to approximately twenty-five. The size and number of wires in each strand, as well as the size and number of strands in the rope greatly affect the characteristics of the rope. In general, a large number of small-size wires and strands produce a fl exible rope with good resistance to bending fatigue. The rope Construction is also important for tensile load (static, live or shock) abrasive wear, crushing, corrosion and rotation. Cores A number of core types is available and each gives specified properties to the rope: 1. Wire Strand Core (WSC) - Strand usually of the same Construction as the outer strands. 2. Fibre Core (FC) - Sisal or polypropylene. 3. Wire Rope Core (WRC) - a wire rope usually of 6 x 7 (6/1)/1 x 7 (6/a) Construction. Wire Strand Core (WSC) Wire rope core is preferred for operating ropes in applications of high tensile stress, high compression loads on small drums and sheaves (such as on earthmoving equipment) and high operating temperatures (such as cranes handling large quantities of molten metal). A rope with WRC is approximately 11% heavier and 7.5% stronger than fibre cored rope of the same size. Lay This refers to the way the wires in the strands, and the strands in the rope are formed into the completed rope. The wire strands are essentially laid up in a planetary motion with controlled twist being imparted to produce a tightly formed rope. The term Lay is used in three ways: 1. To describe the direction in which the strands are laid in the rope right or left. In a Right Hand Lay strands are laid around the rope core in a clockwise direction - see illustration. In a Left Hand Lay, the strands are laid anti-clockwise - see illustrations. Steel Wire Ropes are conventionally produced Right Hand Lay unless special circumstances require Left Hand Lay. 2. To describe the direction in which the wires are stranded in relation to the direction of the strands in the completed rope, e.g. Ordinary Lay or Lang’s Lay. Ordinary Lay means the wires in a strand are laid in a direction opposite to the direction in which the strands are laid in the final rope. Lang’s Lay means the wires in a strand are laid in the same direction in which the strands are laid in the fi nal rope. Lang’s Lay ropes have superior properties in resistance to wear, abrasion, fatigue and scuffi ng. This is illustrated below, where it can be seen that wear on an outer wire is distributed over a far greater area than in Ordinary Lay. 3. ‘Lay’ is also a measure of the ‘pitch’ of a strand in a rope. 01 - WIRE ROPE & <strong>STRAND</strong> These cores are chiefly for standing ropes (guys or rigging), and offer high tensile strength and, owing to the larger wires in the core, greater resistance to corrosion. WWW.BULLIVANTS.COM 7
Characteristics of Lay RIGHT HAND ORDINARY LAY Wire ropes are usually supplied in the following tensile ranges: Black (bright, ungalvanised) wire Minimum Tensile Abbreviated Description 1770 MPa B1770 grade Galvanised wire 1570 MPa G1570 grade 01 - WIRE ROPE & <strong>STRAND</strong> 8 LEFT HAND ORDINARY LAY RIGHT HAND LANG’S LAY LEFT HAND LANG’S LAY ONE ROPE LAY The direction of rope Lay does not affect the breaking force of a rope. However, the combination of strand lay and rope lay will greatly affect the rope characteristics and this factor must be taken into consideration when choosing a rope. Although the lay length can slightly affect rope behaviour the dominant aspect that infl uences performance is the direction of lay and whether it is Lang’s Lay or Ordinary Lay. For example, the importance of rope lay is evident in a four-part high lift grab where rotation of the grab is prevented by the use of alternate right-hand and left-hand ropes. Lubrication When a rope is operated over a drum or sheave, the strands and wires move relative to one another. To reduce the resultant friction within the rope as well as the friction between the rope and drum or sheave, ropes are lubricated in manufacture. In addition this lubrication also retards corrosion and inhibits possible rotting of the fi bre core. In special applications a combination of lubricants may be required for example, the core and inner wires of the strands may be heavily lubricated while the lighter lubrication may be applied to outer wires and strands. Wire rope cores are normally heavily lubricated irrespective of the outer strand lubrication. Regular lubrication is more benefi cial than applying large amounts infrequently. Quality Control Standard Specifications All ropes are produced to comply with the requirements of the Australian Standards. These specifi cations require wire to be produced to AS1394. All ropes comply to AS3569 Steel Wire Ropes. The company’s testing facilities are constantly engaged on the testing of both works production and samples received for examination. For investigation and customer service purposes, a nondestructive testing unit, operated by Bullivants trained staff is available. Enquiries concerning use of this equipment or advice on non-destructive testing please contact your local Bullivants branch. A full report of all site examination is issued. Steel Quality - Tensile Strength Production methods, equipment and quality control in steelmaking and wire drawing ensure that wire rope conforms to Australian and International Standards. NOTE: G1770 (Galvanised 1770 Mpa) is the preferred grade for galvanised ropes other than standard multiple operation ropes of 6 x 7, 6 x 19, 6 x 24 and 6 x 36 Construction. However, other special tensile ranges can be supplied in both galvanised and black as follows: 1220 MPa, 1420 MPa, 1970 MPa, 2070 MPa and 2250 MPa. With the increasing use of heavy-duty and more compact equipment (e.g. power winches on mobile cranes and mine winding) there is a gradual upward trend in the required rope wire tensile range. However, as factors other than strength influence the life of wire rope, the specifi cation application must be kept in mind when the tensile strength of the wire is selected. Care and Maintenance Breaking In A wire rope may be looked upon as a machine composed of a large number of moving parts. As such it should be broken in as soon as it is installed, by loading it very lightly for a few cycles and then gradually stepping up the load, to enable both wires and strands to ‘bed down’ into the working positions, with the load distributed as uniformly as possible. The use of ‘spinners’ or swivels should be avoided whenever possible. All ropes should be reeled onto winch drums as tightly and uniformly as possible during the initial installation. Lubrication Lubrication impregnated into the rope during manufacture is not sufficient to last the life of the rope. Additional lubrication should be done during the service. The frequency of lubrication in the field is determined by the operating conditions of the rope e.g., high-speed heavy duty operation calls for more frequent lubrication, as do wet and/or corrosive conditions. For general purpose applications medium viscosity black oil is considered suitable. For corrosive conditions a high penetrating, water repellent rush-inhibiting oil should be used. Inspection Wire rope is tough and durable, but nonetheless expendable and eventually reaches the end of its safe service life. Rope deterioration becomes noticeable through the presence of broken wires, surface wear, corrosion, wire or strand distortion due to mechanical abuse, or drastic reduction in diameter and lengthening of the lay. Also deterioration can be detected by the use of non-destructive testing techniques. Wire ropes should periodically be inspected for signs of deterioration. Wire Rope Terms Minimum Breaking Force (MBF) MBF is the minimum load or force, guaranteed by the manufacturer after which the rope will break. It is based on the use of wires of nominal size and the minimum tensile strength. This is the figure which should be used for design of rope equipment. Diameter The measurement across the centre line of the circle circumscribing the outer wires of a strand or the outer strands of a rope. Design Factor Term applied to the required ratios of rope breaking force to total rope force due to load. Normally set by Statutory bodies, e.g. Mines Departments, Navigation Departments, Lifts and Scaffolding Departments. 1300 722 999
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STRAND

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