General Guidance on Wire Rope Selection

When selecting a steel wire rope to suit a particular application the following characteristics should be taken into consideration.

• Strength
• Rotation resistance
• Fatigue resistance
• Resistance to wear and abrasion
• Resistance to crushing
• Resistance to corrosion
• Rope extension

Strength

The responsibility for determining the minimum strength of a wire rope for use in a given system rests with the manufacturer of the machine, appliance, or lifting equipment. As part of this process the manufacturer of the machine, appliance or lifting equipment will need to be aware of any local regulations, standards or codes of practice which might govern the design factor of the wire rope (often referred to nowadays as the coefficient of utilisation), and other factors which might influence the design of sheaves and drums, the shape of the groove profiles and corresponding radius, the drum pitch and the angle of fleet, all of which have an effect on rope performance.

Once the strength (referred to as minimum breaking force or minimum breaking load) of the wire rope has been determined it is then necessary to consider which type of wire rope will be suitable for the intended duty. It is important therefore for the designer to be fully aware of the properties, characteristics and limitations on use of the many different kinds of steel wire ropes which are available.

Important note for crane operators Certex recommends that once the machine, appliance or lifting equipment has been taken into service, any replacement rope should possess the required characteristics for the duty in question and should, as a minimum, at least comply with the minimum guaranteed breaking force stated by the original equipment manufacturer.

Every rope produced by Bridon is “Powerchecked” to confirm compliance with the minimum guaranteed breaking force or load stated in this catalogue.

Resistance to Rotation

It is important to determine whether there is a requirement to use a low rotation or rotation resistant rope. Such ropes are often referred to as multi - strand ropes.

Six or eight strand rope constructions are usually selected unless load rotation on a single part system or “cabling” on a multi - part reeving system are likely to cause operational problems. When loaded, steel wire ropes will generate:

- “Torque” if both ends are fixed.
- “Turn” if one end is unrestrained.

Torque When both ends of a rope are fixed, the applied force generates “torque” at the fixing points.	Turn When one end of a rope is free to rotate, the applied load causes the rope to turn.

The torque or turn generated will increase as the load applied increases. The degree to which a wire rope generates torque or turn will be influenced by the construction of the rope. Having recognised what can happen when a rope is loaded it is necessary to select the correct type of rope. It should be noted that all ropes will rotate to some degree when loaded.

The diagram serves to illustrate the differences in rotational properties between the four basic types of stranded rope.

The tendency for any rope to turn will increase as the height of lift increases. In a multi - part reeving system the tendency for the rope to cable will increase as the spacing between the parts of rope decreases. Selection of the correct rope will help to prevent “cabling” and rotation of the load.

“Endurance” low rotation and rotation resistant ropes ensure that problems associated with cabling and load rotation are minimised.

Certex is pleased to offer advice on any specific problems associated with rope rotation.

Bridon is able to verify the rotational characteristics of individual wire ropes through testing on its specially designed in house torque/turn machine. All Bridon products intended for lifting applications have been subject to this “Twistcheck” testing programme.

Wire Rope Fatigue Resistance

Steel wire ropes are likely to deteriorate due to bend fatigue when subjected to bending around a sheave or drum. The rate of deterioration will be influenced by the number of sheaves in the system, the diameter of the sheaves and drum, and the loading conditions.

When selecting a wire rope for an application where bending fatigue is a principal cause of deterioration it is important to select a rope containing small wires e.g.
6x36 WS (14/7 & 7/7/1) as opposed to a 6x19 S (9/9/1).

Bridon carries out extensive testing on their products, providing comparative fatigue data to allow customers to make an informed choice.

Additional resistance to fatigue leading to real cost savings can be achieved by selecting a “Dyform” wire rope.

The smooth surface of the “Dyform” product provides improved rope to sheave contact leading to reduced wear on both rope and sheave.

Increased cross-sectional steel area and improved inter - wire contact ensures that the rope will operate with lower internal stress levels resulting in longer bending fatigue life and lower costs.

This graph illustrates a “doubling” in life when moving from Blue Strand 6x36 to Endurance Dyform 6. This same relationship can be found when moving from any construction into an equivalent Dyform construction
e.g. 18x7 to Endurance Dyform 18 or 35x7 to Endurance Dyform 34LR.

Wire Rope Resistance to Abrasive Wear

Abrasive wear can take place between wire rope and sheave and between wire rope and drum but the greatest cause of abrasion is often through “interference” at the drum.

If abrasion is determined to be a major factor in rope deterioration then a wire rope with relatively large outer wires should be selected.

Comparison of outer wire sizes for single layer 22mm diameter rope.

6x7	6 outer wires	2.20mm
6x19S	9 outer wires	1.83mm
6x25F	12 outer wires	1.47mm
6x36WS	14 outer wires	1.29mm
6x41WS	16 outer wires	1.16mm

Wire rope on adjacent drum laps can cause point contact and accelerated wear . Non Dyform wire rope on adjacent drum laps can cause point contact and accelerated wear.

Selection of a Dyform product will reduce abrasion through improved contact conditions. The smooth surface of Dyform rope creates better contact and leads to longer life.

Wire Rope Crush Resistance

In multi-layer coiling applications where there is more than one layer of rope on the drum it is essential to install the wire rope with some back tension. Bridon recommends an installation tension of between 2% and 10% of the minimum breaking force of the wire rope. If this is not achieved, or in certain applications where high pressure on underlying rope layers is inevitable e.g. a boom hoist rope raising a boom from the horizontal position, severe crushing damage can be caused to underlying layers.

Selection of a steel core as opposed to a fibre core will help this situation. Additional resistance to crushing is offered by a Dyform rope resulting from its high steel fill-factor.

Dyform ropes are recommended for multi - layer coiling operations where crushing on lower layers is inevitable.

Wire Rope Corrosion resistance

If the wire rope is to be used in a corrosive environment then a galvanised coating is recommended. If corrosion is not a significant issue then a bright rope can be selected. Where moisture can penetrate the rope and attack the core, plastic impregnation (PI) can be considered.

In order to minimise the effects of corrosion it is important to select a wire rope with a suitable manufacturing lubricant. Further advantages can be gained by lubricating the rope regularly whilst it is in service.

Wire Rope Extension

If wire rope extension is critical refer to technical data in the Bridon Crane Rope Catalogue.

Ordering a Wire Rope

Communicate as much background information as possible when ordering or enquiring about wire rope. The following is necessary:

Application / intended use.
Rope length and tolerance where applicable.
Nominal Diameter.
Construction, class or brand name.
Core (FC; FFC; WSC; IWRC)
Rope Grade (1770; 1960; 2160)
Wire finish (Bright; Galvanised)
Lay type (Ordinary; Langs)
Lay direction (Left Hand; Right Hand)
Minimum breaking force.
Termination requirements.
Special packaging requirements.
Special identification requirements.
Third party authority (LR; DNV; ABS etc.)