depending on what purpose the wire rope is intended. Wire rope is designated by the number of strands per rope and the number of wires per strand. Thus a 1/2-inch 6 by 19 wire rope has six strands with 19 wires per strand. It has the same outside diameter as a 1/2-inch 6 by 37 wire rope that has six strands with 37 wires (of smaller size) per strand.

Strands

The design arrangement of a strand is called the construction. The wires in the strand may be all the same size or a mixture of sizes. The most common strand constructions are Ordinary, Scale, Warrington, and Filler (fig. 5-2).

Ordinary construction wires are all the same size.

Scale is where larger diameter wires are used on the outside of the strand to resist abrasion and smaller wires are inside to provide flexibility.

Warrington is where alternate wires are large and small to combine great flexibility with resistance to abrasion.

Filler is where 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 are fiber, wire strand, and independent wire rope (fig. 5-3).

A fiber core maybe 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

Figure 5-3. - Core construction.

cushion to reduce the effects of sudden strain and act as an oil reservoir to lubricate the wire and strands (to reduce friction). Wire rope with a fiber core is used when flexibility of the 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.

When an inspection discloses any unsatisfactory conditions in a line, ensure the line is destroyed or cut into small pieces as soon as possible. This precaution prevents the defective line from being used for hoisting.

Wire rope may be manufactured by either of two methods. When the strands or wires are shaped to conform to the curvature of the finished rope before laying up, the rope is termed preformed wire rope.

Figure 5-2. - Common strand construction.