Machinery's Handbook, 31st Edition
Wire Rope
2711
Strength and Properties of Wire Rope Wire Rope Construction.— Essentially, a wire rope is made up of a number of strands laid helically about a metallic or non-metallic core. Each strand consists of a number of wires also laid helically about a metallic or non-metallic center. Various types of wire rope have been developed to meet a wide range of uses and operating conditions. These types are distinguished by the kind of core; the number of strands; the number, sizes, and arrange- ment of the wires in each strand; and the way in which the wires and strands are wound or laid about each other. The following descriptive material is based largely on information supplied by the Bethlehem Steel Co. Rope Wire Materials: Materials used in the manufacture of rope wire are, in order of increasing strength: iron, phosphor bronze, traction steel, plow steel, improved plow steel, and bridge rope steel. Iron wire rope is largely used for low-strength applications such as elevator ropes not used for hoisting, and for stationary guy ropes. Phosphor bronze wire rope is used occasionally for elevator governor-cable rope and for certain marine applications as life lines, clearing lines, wheel ropes and rigging. Traction steel wire rope is used primarily as hoist rope for passenger and freight eleva- tors of the traction drive type, an application for which it was specifically designed. Ropes made of galvanized wire or wire coated with zinc by the electro-deposition pro cess are used in certain applications where additional protection against rusting is re- quired. As will be noted from the tables of wire-rope sizes and strengths, the breaking strength of galvanized wire rope is 10 percent less than that of ungalvanized (bright) wire rope. Bethanized (zinc-coated) wire rope can be furnished to bright wire rope strength when so specified. Galvanized carbon steel, tinned carbon steel, and stainless steel are used for small cords and strands ranging in diameter from 1 ⁄ 64 to 3 ⁄ 8 inch and larger. Marline clad wire rope has each strand wrapped with a layer of tarred marline. The clad ding provides hand protection for workers and wear protection for the rope. Rope Cores: Wire-rope cores are made of fiber, cotton, asbestos, polyvinyl plastic, a small wire rope (independent wire-rope core), a multiple-wire strand (wire-strand core) or a cold-drawn wire-wound spring. Fiber (manila or sisal) is the type of core most widely used when loads are not too great. It supports the strands in their relative positions and acts as a cushion to prevent nicking of the wires lying next to the core. Cotton is used for small ropes such as sash cord and aircraft cord. Asbestos cores can be furnished for certain special operations where the rope is used in oven operations. Polyvinyl plastics cores are offered for use where exposure to moisture, acids, or caus- tics is excessive. Wire-strand core often referred to as WSC, consists of a multiple-wire strand that may be the same as one of the strands of the rope. It is smoother and more solid than the independent wire rope core and provides a better support for the rope strands. The independent wire rope core , often referred to as IWRC, is a small 6 × 7 wire rope with a wire-strand core and is used to provide greater resistance to crushing and distortion of the wire rope. For certain applications it has the advantage over a wire-strand core in that it stretches at a rate closer to that of the rope itself. Wire ropes with wire-strand cores are, in general, less flexible than wire ropes with inde
pendent wire-rope or non-metallic cores. Ropes with metallic cores are rated 7 1 ⁄
2 percent stronger than those with non-metallic
cores.
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