The Wire
The basic element of wire rope is, of course,the wire—usually round, but sometimes shaped.It is all“cold drawn” to the desired diameter and physical properties after special heat treating. Most wire is made to one of two
grades—Extra Improved Plow Steel (EIP), or Double Extra Improved Plow Steel (EEIP) which has about 15% greater tensile strength. Both grades are carbon steel that is tough and re-sists wear. When the wire has a natu-ral finish, it is called “Bright”.Otherwise it is plated, galvanized, or may have some other surface treatment for spe-cial applications.
The Strands
The greatest differences between wire ropes occur in the number of strands and in the number and pat-tern of wires per strand. There are two general types—round, strands, and strands that have been shaped or formed. Strand design is a pre-cise engineering science.
Preforming
In most ropes made today, the strands are “preformed” just before they are layed together to make the rope. Preforming is a mechanical op-eration by which the individual strands are formed into a continu-ous helical shape which causes them
to be at rest in the rope. Preforming serves two functions: It maintains the rope’s shape when it is cut, and it forms the strands in such a way that they
will slide and adjust together more smoothly within the rope when the rope works.
The Lay
The word “lay” is used to describe three physical characteristics of wire rope. It is both an engineering term
and a descriptive term. Lay describes:
- The DIRECTION strands
“lay” in the rope—RIGHT or LEFT. When you look along
a rope, strands of a Right Lay make the rope.
- The RELATIONSHIP between the direction strands lay in the rope and the direction wires lay in the strands. In a REGULAR Lay rope, wires lay OPPOSITE the direction of the strand. In a LANG Lay rope, wires lay in the SAME direction as strands.
- The LENGTH along the rope which one strand uses to make one complete spiral around the rope core.
The Core
Rope cores are usually one of three types: 1. Fiber rope core-either natu-ral sisal fiber, or man-made fiber such as polypropylene. 2. Wire rope core- literally an independent wire rope, which is called IWRC. 3. Strand core- which is a typical wire rope strand. The primary purpose of a rope core is to provide a foundation, or support, for the strands. Approximately 7-1/2% of the rated strength of a 6-strand IWRC rope is attributed to the core.
A comparison of typical wire rope lays:
- right regular lay
- left regular lay
- right lang lay
- left lang lay
- right alternate lay