CHAPTER 5 WIRE ROPE

Wire rope is stronger, lasts longer, and is much more resistant to abrasion than fiber line. Because of these factors, wire rope is used for hoisting tasks that are too heavy for fiber line to handle. Also, many of the movable components on hoisting devices and attachments are moved by wire rope.

Wire rope is an intricate device made up of a number of precise moving parts. The moving parts of wire rope are designed and manufactured to maintain a definite relationship with one another. This relationship ensures that the wire rope has the flexibility and strength crucial to professional and safe hoisting operations.

WIRE ROPE

This chapter discusses the construction, the characteristics and specifications, and the criteria used for the selection of wire rope. The related attachments and the proper handling procedures for wire rope are also discussed.

NOTE: In the Navy, you may hear wire rope referred to as wire or rope but never as line.

WIRE ROPE CONSTRUCTION

Wire rope is composed of three parts: wires, strands, and core (fig. 5-1). 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 is then laid together symmetrically around the core to form the wire rope.

Wires

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,

Figure 5-1.-Fabrication of wire rope

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.

When they are not shaped before fabrication, the wire rope is termed nonpreformed wire rope.

The most common type of manufactured wire rope is preformed. When wire rope is cut, it tends not to unlay and is more flexible than nonpreformed wire rope. With nonpreformed wire rope, twisting produces a stress in the wires; therefore, when it is cut or broken, the stress causes the strands to unlay.

WARNING

When wire rope is cut or broken, the almost instantaneous unlaying of the wires and strands of nonpreformed wire rope can cause serious injury to someone that is careless or not familiar with this characteristic of the rope.

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