Table 1-2.- Safe Working Load of Fiber Line

APPROXIMATE SAFE WORKING LOADS OF NEW FIBER LINES - POUNDS Three-Strand Line Safety Factor = 5 Nominal Line Manila Nylon Polypropylene Polyester Polyethylene Diameter (inches)

Nominal Line Diameter (inches) 1/ 4

Table 1-3.- Safe Working Load of Braided Synthetic Fiber Line

APPROXIMATE SAFE WORKING LOADS OF NEW BRAIDED SYNTHETIC FIBER LINES (LB) SAFETY FACTOR = 5 Nylon Cover Nylon Cover Polyester Cover Nylon Core Polypropylene Core Polypropylene Core

Construction

Wiie rope consists of three parts: wires, strands, and core (fig. 1-3). In the manufacture of wire rope, a number of WIRES are laid together to form the STRAND. Then a number of STRANDS are laid together around a CORE to form the wire ROPE.

Wire rope that is made up of a large number of small wires is flexible. The small wires are, however, easily broken, so the wire rope does not resist external abrasion. Wire rope that is made up of a smaller number

The basic unit of wire-rope construction is the individual wire, which may be made of steel, iron, or other metal in various sixes. The number of wires to a strand will vary, dependingonthepurpose for which the wire rope is intended. Wiie 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 will have six strands with 19 wires per strand; but it will have the same outside diameter as a 1/ 2-inch, 6 by 37 wire rope, which will have six strands with 37 wires of much smaller size per strand.

Figure 1-3.- Parts of a wire rope.

of larger wires is more resistant to external abrasion but is less flexible. The CORE, the element around which the strands are laid to form the wire rope, may be of hard fiber, such as manila, hemp, plastic, paper, or sisal. Also, a wire-strand core may be used. Each type of core serves the same basic purpose- to support the strands laid around it. A FIBER CORE offers the advantage of increased flexibility. Also, it serves as a cushion to reduce the effects of sudden strain and acts as a reservoir for the oil to lubricate the wires and strands to reduce friction between them. Wire rope with a fiber core is used in places where flexibility of the wire rope is important.

A WIRE-STRAND CORE not only resists heat better than a fiber core but it also adds about 15 percent to the strength of the wire rope. On the other hand, the wire strand makes the wire rope less flexible than a fiber core would. An INDEPENDENT WIRE-ROPE CORE is a separate wire rope over which the main strands of the wire rope are laid. It usually consists of six seven-wire strands laid around either a fiber core or a wire-strand core. This core strengthens the wire rope more, provides support against crushing, and supplies maximum resistance to heat.

Wire rope may be made by either of two methods. If the strands or wires are shaped to conform to the curvature of the finished wire rope before laying up, the wire rope is termed preformed. If they are not shaped before fabrication, the wire rope is termed nonpreformed. When cut, preformed wire rope tends not to unlay, and it is more flexible than nonpreformed wire rope. With nonpreformed wire rope, twisting produces a stress in the wires; and, when it is cut or broken, the stress causes the strands to unlay. In nonpreformed wire rope, unlaying is rapid and almost instantaneous, which could cause serious injury to someone not familiar with it.

The main types of wire rope used by the Navy have 6, 7, 12, 19, 24, or 37 wires in each strand. Usually, the wire rope has six strands laid around a fiber or steel center.

Two common types of wire rope, 6 by 19 and 6 by 37 wire rope, are shown in figure 1-4. The 6 by 19 type of wire rope, having six strands with 19 wires in each strand, is commonly used for rough hoisting and skidding work where abrasion is likely to occur. The 6 by 37 wire rope, having six strands with 37 wires in each strand, is the most flexible of the standard six-strand wire ropes. For that reason, it is particularly suitable when you are going to use small sheaves and drums, such as are used on cranes and similar machinery.