Wire rope is one of the many types of lifting equipment used in lifting operations. It is a sophisticated product, and selecting the right wire rope requires careful consideration of many different factors. There are numerous wire rope constructions, each designed for specific lifting applications. In this article, you'll discover what to look for when selecting the right wire rope.
The Construction of Wire Rope
The core forms the centre of the wire rope. Around this core are strands, and each strand consists of multiple individual wires.
The strands can be laid around the core in two different ways: regular lay (cross lay) or Lang lay. The most suitable lay type depends on the intended application of the wire rope.
A Wide Choice of Materials
Both the core and the wires of a wire rope are available in a variety of materials.
The core may be made from fibre, synthetic material, or steel, although fibre cores are becoming less common in modern lifting applications.
The wires themselves are available in several finishes, including bright steel, galvanised steel, and stainless steel. Wire ropes are also manufactured in different tensile grades, allowing the correct balance between strength, flexibility, and wear resistance to be selected for each application.
Each material offers its own advantages and limitations.
Breaking Load, Design Factor and Working Load Limit
The Minimum Breaking Load (MBL) is the maximum load a wire rope can withstand before it fails.
The Working Load Limit (WLL) is the maximum load the wire rope is permitted to lift safely during normal operation.
The relationship between the MBL and the WLL is known as the design factor (or safety factor).
For example, with a design factor of 5, the Working Load Limit is one-fifth of the Minimum Breaking Load. A wire rope with an MBL of 40 tonnes therefore has a Working Load Limit of 8 tonnes.
End Terminations
Wire rope end terminations can be divided into two categories:
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Permanent terminations, such as poured sockets and Talurit ferrules.
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Non-permanent terminations, such as wire rope grips, wire rope clamps, and U-bolt clips.
It is important to remember that almost all end terminations reduce the Working Load Limit of the wire rope. This reduction is known as the efficiency factor or termination efficiency.
Minimise Bending
Every time a wire rope passes over a sheave or drum, it is subjected to bending stresses.
Over time, repeated bending leads to fatigue and wear, reducing the service life of the rope.
For this reason, the number of bends should be kept to a minimum wherever possible. The routing of the wire rope also has a significant effect on its lifespan. Factors such as the bend direction and the distance between sheaves should always be considered during system design.
Corrosion
Corrosion can significantly reduce the service life of a wire rope.
Regularly inspect the rope for signs of corrosion. Surface rust or flash rust can often be controlled by applying a suitable wire rope lubricant.
However, pitting corrosion indicates serious deterioration of the steel and generally means the wire rope should be replaced. If in doubt, consult a wire rope specialist.
Inspection
Wire ropes should be formally inspected at least once a year by a competent person appointed by the employer.
In addition, operators should carry out a pre-use inspection every day before using the wire rope.
Pay particular attention to vulnerable areas such as end terminations and locations where the rope comes into contact with sheaves, drums, or other components that may cause wear or damage.
Maintenance
Proper lubrication can significantly extend the service life of a wire rope, depending on the operating environment.
In dusty environments, lubrication may attract dirt and abrasive particles, making lubrication less suitable.
For outdoor applications, it is generally recommended to apply a thin coat of an appropriate wire rope lubricant during the spring and autumn. Heavy grease should be avoided, as it can trap dirt and prevent proper penetration into the rope.
Knowledge file Safe Lifting
Use lifting equipment safely and correctly. Learn how to sling loads properly and how to inspect, examine, and certify lifting equipment to ensure safe and responsible lifting operations.
