Wire rope may be manufactured by either of two methods. If 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. If they are not shaped before fabrication, the wire rope is termed NON-PREFORMED WIRE ROPE. The most common type of manufactured wire rope is preformed. When cut, the wire rope tends not to unlay and is more flexible than non-preformed wire rope. With non-preformed wire rope, twisting produces a stress in the wires; therefore, when it is cut or broken, the stress causes the strands to unlay.

Figure 6-33.- Composition of wire rope.

CAUTION
When the wire is cut or broken, the almost instantaneous unlaying of the wire or strands of the non-preformed wire rope can cause serious injury. This situation is apt to occur especially to someone who is careless or not familiar with this characteristic of the rope.

Composition of Wire Rope
Wire rope is composed of three parts- wires, strands, and core (fig. 6-33). A predetermined number of wires of the same or different size are fabricated in a uniform arrangement of definite lay to form a strand. The required number of strands are then laid together symmetrically around the core to form the wire rope.

WIRE.- The basic component of the wire rope is the wire. The wire may be made of steel, iron, or other metal in various sizes. The number of wires to a strand varies, depending on the purpose for which the wire rope is intended. The number of strands per rope and the number of wire per strand designate wire rope. Thus a 1/ 2-inch 6 x 19 rope has six strands with nineteen wires per strand. It has the same outside diameter as a 1/ 2-inch 6 x 37 rope that has six strands with thirty-seven wires (of a smaller size) per strand.

STRAND.- 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, Seale, Warrington, and Filler (fig. 6-34) as follows:

ORDINARY construction wires are all the same size.

Figure 6-34.- Common strand construction.

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

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

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 are fiber, wire strand, and independent wire rope (fig. 6-35).

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 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 make the wire 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.