Terminology & Properties
With precise, moving parts, designed and manufactured to bear definite relationship to one another, Wire Rope can be a complex mechanism. Wire rope is generally com-posed of wires, strands and the core (See Fig.). The wires are helically laid together in a precise geometric pattern to form the strand. The strands helically laid about the core to form the wire rope. The process of positioning the strands about the core is called “closing”. The process of positioning the wires within the strand is called “stranding”.
Wire rope varies:
- By Diameter
- The grade of steel utilized
- The direction of stranding and closing
- The finish on the wire (Bright, Galvanized, etc.)
- The core material
Each variation changes the performance characteristics of the wire rope.
The first differentiation of wire rope is by diameter. The diameter is measured at the diameter of the circle formed by the extreme outer dimensions of the strands. New wire rope is manufactured to an oversized diameter of approximately 2-1/2%. This allows for the normal reduction of diameter experienced when a new rope is placed under load because of constructional stretch.
CAUTION: At NO time should the measured diameter be less than the nominal diameter of
the wire rope.
The grade of steel (or other material) utilized in the construction of the wire rope has a major influence upon the ultimate break strength. Generally most steel wire rope today is at Improved Plow Steel Grade or IPS. In recent years Extra Improved Plow Steel (EIPS) wire rope has gained in popularity and is approximately 10% stronger than IPS. Manufacturers have begun producing limited construc-tions of Extra Improved Plow Steel (EEIPS), which is 10% higher than EIPS grade. Some special constructions exceed EEIPS grade.The “Lay” of the wire rope (the direction of stranding and closing) directly affects the operating properties. In Regular Lay wire rope, the direction of the wires are twisted in an opposite direction than the direction of the strands. Regular Lay may be Right Regular Lay or Left Regular Lay depending upon the direction of the strands. (See Fig.).In Lang Lay wire ropes the direction of the wires are twisted in the same direction as the strands. Lang Lay may be Right Lang Lay or Left Lang Lay depending upon the direction of the strands. The wires of a regular wire rope seem to travel parallel and along the length of the rope while those of a Lang lay rope appear to travel around the rope.In addition, the Lay Length, the length of the rope neces-sary for one strand to travel completely around the rope may be varied slightly by manufacturer.
Most wire rope has a Bright, self-colored finish and a coating of lubricant. However, many wire ropes are galva-nized, stainless steel, or plastic/vinyl/urethane coated.
Most wire ropes are supplied with either a fiber or steel core. The core’s primary function is to support the wire strands of the rope, maintaining the corrective relative posi-tions during the operating life. Fiber Cores are composed of natural Vegetable Fiber Core (VFC – sisal, etc.) or Syn-thetic Fiber Core (PFC- polypropylene, etc.) which have been formed into yarns and twisted into strands. Steel cores may be Independent Wire Rope Core (IWRC) or Wire Strand Core (WSC). These steel cores provide more sup-port than fiber cores to the outer strands during the rope’s operating life. Steel cores resist crushing, are more resistance to heat, reduce the amount of stretch, and increase the strength of the rope. Unreeling & Uncoiling The Right Way to Unreel. To unreel wire rope from a heavy reel, place a shaft through the center and jack up the reel far enough to clear the floor and revolve easily. One person holds the end of the rope and walks a straight line away from the reel, taking the wire rope off the top of the reel. A second person regulates the speed of the turning reel by holding a wood block against the flange as a brake, taking care to keep slack from developing on the reel, as this can easily cause a kink in the rope. Lightweight reels can be properly unreeled using a vertical shaft; the same care should be taken to keep the rope taut.
The Wrong Way to Unreel. If a reel of wire rope is laid on its flange with it’s axis vertical to the floor and the ropeunreeled by throwing off the turns, spirals will occur and kinks are likely to form in the rope. Wire rope always should be handled in a way that neither twists nor unlays it. If handled in a careless manner, reverse bends and kinks can easily occur.
The Right Way to Uncoil.There is only one way to uncoil wire rope. One person must hold the end of the rope while a second person rolls the coil along the floor, backing away. The rope is allowed to uncoil naturally with the lay, without spiraling or twisting. Always uncoil wire rope as shown.
The Wrong Way to Uncoil. If a coil of wire rope is laid flat on the floor and uncoiled by pulling it straight off, spirals will occur and kinking is likely. Torsions are put into the rope by every loop that is pulled off, and the rope becomes twisted and unmanageable. Also, wire rope cannot be uncoiled like hemp rope. Pulling one end through the mid-dle of the coil will only result in kinking.
Great stress has been placed on the care that should be taken to avoid kinks in wire rope. Kinks are places where the rope has been unintentionally bent to a permanent set.
This happens where loops are pulled through by tension on the rope until the diameter of the loop is only a few inches. They are also caused by bending a rope around a sheave hav-ing too severe a radius. Wires in the strands at the kink are permanently damaged and will not give normal service, even after apparent “restraightening.”
Drum Winding. When wire rope is wound onto a sheave or drum, it should bend in the manner in which it was origi-nally wound. This will avoid causing a reverse bend in the rope. Always wind wire rope from the top of the one reel onto the top of the other. Also acceptable, but less so, is re-reeling from the bottom of one reel to the bottom of another. Re-reeling may also be done with reels having their shafts vertical, but extreme care must be taken to ensure that the rope always remains taut. It should never be allowed to drop below the lower flange on the reel. A reel resting on the floor with its axis horizontal may also be rolled along the floor to unreel the rope.
Wire rope should be attached at the correct location on a flat or smooth-faced drum, so that the rope will spool evenly, with the turns lying snugly against each other in even layers. If wire rope is wound on a smooth-face drum in the wrong direction, the turns in the first layer of rope will tend to spread apart on the drum. This results in the second layer of rope wedging between the open coils, crushing and flatten-ing the rope as successive layers are spooled.
A simple method of determining how a wire rope should be started on a drum is shown in the above diagram. The observer stands behind the drum, with the rope coming towards him. Using the right hand for right-lay wire rope, and the left hand for left lay wire rope, the clenched fist denotes the drum, the extended index finger the oncoming rope.