SAFETY SLING COMPANY
Serving Industry Since 1945

1.800.242.1540

sales@safetysling.com

Criteria for Selecting Wire Rope

Several factors must be considered when attempting to select the most suitable type of wire rope for a job. An accurate assessment of the following requirements will help attain optimum performance and extend the useful life of wire rope.

  • Strength–Resistance to breaking
  • Resistance to bending fatigue
  • Resistance to vibrational fatigue
  • Resistance to abrasion
  • Resistance to crushing

It is fundamentally impossible for a single wire rope to have attributes that will maximize performance against each selection criterion. In fact, a high rating in one area generally means a lower rating in another. Job requirements must be carefully analyzed so that a rope satisfying the most important criteria and sacrificing the least important advantages can be selected.




1. Strength-Resistance to breaking
It has been noted that wire rope is a machine-a fairly complex device that transmits and modifies force and motion. The very first consideration in choosing a "machine" is to determine the potential work load. Stated in terms of wire rope, this means establishing the actual load that is to be moved.

In addition to the known "dead" weight, loads caused by abrupt starts (acceleration), sudden stops, shock loads and high speeds must be considered when determining the true total load that will ultimately be handled.

For most operations, this total load is multiplied by a "design factor" of five to calculate the breaking strength of the wire rope required for that operation. Higher design factors of 8, 9 or even 10 may be desirable if there is danger to human life or the load is especially valuable. (See the chart "Generally Accepted Design Factors" below.)

With regard to the general purpose wire rope classifications, there is no difference in nominal strength between 6 x 19 and 6 x 37 wire rope with comparable cores. IWRC wire ropes are stronger than FC ropes and the nominal strength of the EEIPS grade exceeds that of EIPS, which exceeds that of IPS.

2. Resistance to bending
To describe this, a close analogy can be made with a paper clip. If it is repeatedly bent back and forth at one point, it will eventually break. The reason for this is a phenomenom called "metal fatigue". To some degree, the same thing happens when a wire rope is bent around shaeves, drums, and rollers. The sharper-or more accute-the bend, the quicker the fatigue factor does its work. Accelerating the rate of travel also speeds up fatigue; close-coupled reverse bending will speed it up at an even greater rate.

Fatigue can be greatly reduced if sheaves and drums have, at the very least, the suggested minimum diameter. As for the rope, there is one governing rule: the greater the number of wires in each strand, the greater the resistance of rope to bending fatigue.

3. Resistance to vibrational fatigue
Vibration, from whatever source, sends shock waves through the rope. These waves are a form of energy that must be absorbed at some point. This point may appear at various places-the end attachment, the tangent where the rope contacts the sheave, or at any other place where the waves are damped and the energy absorbed.
In the normal operation of a machine or hoist, wire ropes develop a wave action that can be observed either as a low frequency or as a sharp, high frequency cycle. Excessive vibration will eventually lead to broken wires and rope failure.
Another type of vibrational fatigue is found in operations where there is cyclic loading. Such loadings would be found, for example, in the boom suspension systems of draglines. Here, the energy is absorbed at the end fittings of the pendants or at the tangent point where the rope contacts the sheave. In this case, the "vibration" is torsional as well as transverse.

Wire Rope

4. Resistance to abrasion
Abrasion is one of the most common destructive conditions affecting wire rope. It usually occurs on drums and sheaves or whenever rope rubs against itself or other material. Abrasion also occurs internally whenever wire rope is loaded or bent and it weakens the rope simply by wearing away metal from inside and outside wires.
When excessive wear is encountered in an operation, the problem frequently stems from faulty sheave alignment, incorrect groove diameters, inappropriate fleet angles or improper drum winding. There may, however, be other causes. If none of these conditions exist, switching to a more suitable rope construction may be necessary. When doing so, it should be noted that larger outer wires and lang lay ropes are more abrasion resistant than regular lay ropes.

Wire Rope

5. Resistance to crushing
Crushing is the effect of external pressure on a rope, which damages it by distorting the cross-section shape of the rope, its strands or core-or all three.
Crushing resistance therefore, is the ability to withstand or resist external forces, and is a term generally used to express comparison between ropes.
When a rope is damaged by crushing, the wire, strands and core are prevented from moving and adjusting normally in operation.
It is helpful to remember that IWRC and regular lay ropes are more crush resistant than fiber core and lang lay ropes.


Generally Accepted Design Factors
Type of Service
Minimum Factor
Guy Ropes
3.5
Overhead and Gantry Cranes
3.5
Jib and Pillar Cranes
3.5
Derricks
3.5
Wire Rope Slings
5.0
Miscellaneous Hoisting Equipment
5.0
Ski Lift Ropes-slopes under 3,000 feet
Ski Lift Ropes-slopes over 3,000 feet
5.0
4.5
Haulage Ropes
5.0
Small Electric and Air Hoists
5.0
Rotation Resistant Ropes-Minimum
Rotation Resistant Rope            s-Recommended
5.0
7.0
Hot Ladle Cranes
8.0
Elevator Hoist and Counterweight Ropes (Passenger)
500 FPM
750 FPM
1000 FPM

10.25
11.15
11.55

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