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.
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.
The three primary grades of wire rope are mild plow steel, plow steel, and improved plow steel.
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.
Plow steel wire rope is unusually tough and strong. This steel has a tensile strength of 220,000 to 240,000 psi. Plow steel wire rope is suitable for hauling, hoisting, and logging.
Improved plow steel wire rope is one of the best grades of rope available and is the most common rope used in the Naval Construction Force (NCF). Improved plow steel is stronger, tougher, and more resistant to wear than either mild plow steel or plow steel. Each square inch of improved plow steel can stand a strain of 240,000 to 260,000 pounds; therefore, this wire rope is especially useful for heavy-duty service, such as cranes with excavating and weight-handling attachments.
The term lay refers to the direction of the twist of the wires in a strand and the direction that the strands are laid in the rope. In some instances, both the wires in the strand and the strands in the rope are laid in the same direction; and in other instances, the wires are laid in one direction and the strands are laid in the opposite direction, depending on the intended use of the rope. Most manufacturers specify the types and lays of wire rope to be used on their piece of equipment. Be sure and consult the operator's manual for proper application.
The five types of lays used in wire rope are as follows:
Right Regular Lay: In right regular lay rope, the wires in the strands are laid to the left, while the strands are laid to the right to form the wire rope.
Left Regular Lay: In left regular lay rope, the wires in the strands are laid to the right, while the strands are laid to the left to form the wire rope. In this lay, each step of fabrication is exactly opposite from the right regular lay.
Right Lang Lay: In right lang lay rope, the wires in the strands and the strands in the rope are laid in the same direction; in this instance, the lay is to the right.
Left Lang Lay: In left lang lay rope, the wires in the strands and the strands in the rope are also laid in the same direction; in this instance, the lay is to the left (rather than to the right as in the right lang lay).
Reverse Lay: In reverse lay rope, the wires in one strand are laid to the right, the wires in the nearby strand are laid to the left, the wires in the next strand are laid to the right, and so forth, with alternate directions from one strand to the other. Then all strands are laid to the right.
The five different lays of wire rope are shown in figure 5-4.
The length of a wire rope lay is the distance measured parallel to the center line of a wire rope in that a strand makes one complete spiral or turn around the rope. The length of a strand lay is the distance measured parallel to the centerline of the strand in that one wire makes one complete spiral or turnaround theContinue Reading