Chapter 13 Rigging

Figure 13-2.—Common strand construction. constructions are Ordinary, Seale, Warrington, and Filler (fig. 13-2). . Ordinary construction wires are all the same size. . Seale is where larger diameter wires are used on the outside of the strand to resist abrasion and smaller wires are inside to provide flexibility. l Warrington is where alternate wires are large and small to combine great flexibility with resistance to abrasion. l Filler is where very small wires fill in the valleys between the outer and inner rows of wires to provide good abrasion and fatigue resistance. Core The wire rope core supports the strands laid around it. The three types of wire rope cores arc fiber, wire strand, and independent wire rope (fig. 13-3). Figure 13-3.—Core construction. . A fiber core may be a hard fiber, such as manila, hemp, plastic, paper, or sisal. The fiber core offers the advantage of increased flexibility. It also serves as a cushion to reduce the effects of sudden strain and acts as an oil reservoir to lubricate the wire and strands (to reduce friction). Wire rope with a fiber core is used when flexibility of (he rope is important. . A wire strand core resists more heat than a fiber core and also adds about 15 percent to the strength of the rope; however, the wire strand core makes the wire rope less flexible than a fiber core. . An independent wire rope core is a separate wire rope over which the main strands of the rope are laid. This core strengthens the rope, provides support against crushing, and supplies maximum resistance to heat. GRADES OF WIRE ROPE The three primary grades of wire rope are mild plow steel, plow steel, and improved plow steel. Mild Plow Steel Wire Rope Mild plow steel wire rope is tough and pliable. It can stand repeated strain and stress and has a tensile strength (resistance to lengthwise stress) of from 200,000 to 220,000 pounds per square inch (psi). These characteristics make it desirable for cable tool drilling and other purposes where abrasion is encountered. 13-2