Wire Rope Basics
Wire rope is widely used in crane operations. It consists of three components.
Wire ropes are formed with a core in the centre. This is the foundation that holds the wire rope together. There are three types of cores:
- Fibre: synthetic or sisal (plant-based)
- Wire Strand Core (WSC): two or more wires laid around a single centre wire.
- Independent wire rope core (IWRC): a full wire rope that can be made of either the same or different materials as the outer-layer strands
Wires are the smallest part of wire rope. Most wire is made of high-carbon steel, but other types of materials may be used. Wires are twisted to form a strand.
Strands are then spiraled around a core to make the wire rope.
Metal Fatigue and Fatigue Resistance
Wire rope is subject to metal fatigue from bending stress while in operation. For this reason, the rope's strength gradually decreases the more it is used.
Fatigue resistance involves ways to fight metal fatigue. Wire ropes are designed and built to bend repeatedly under stress to overcome the effects of metal fatigue.
In general, a rope made of many smaller wires will have greater fatigue resistance than a rope of the same size made of fewer, larger wires. That’s because smaller wires have a greater ability to bend.
Pre-Use Inspections
Before using a wire rope, you should check to ensure that the wire rope has tags to identify the manufacturers information, working load limit (WLL) and the angle that the WLL is based on.
When inspecting wire rope, look for these defects:
- Broken wires •Severe abrasion or scraping
- Kinking, crushing or birdcaging such as unravelling
- Any damage from distortion of the rope structure
- Heat damage or electrical arcing
- Cracked end attachments
- Corrosion
If you find any of these defects, you must take the wire rope out of service and follow regulated rejection requirements.
Safe Work Practices
- Never bend ropes over sheaves or drums with diameters so small that wires can be kinked or bent excessively. Follow proper bending requirements.
- Apply safety factors when selecting wire rope. Choose a rope with a higher capacity than the lifting tasks requires to counter surface wear and metal fatigue.
- Reduce tension on the wire rope by not using a sling eye over a hook or pin with a body diameter larger than the natural width of the eye.
- Wrap sharp edges of the load to reduce the risk of damage to the rope.
References
Occupational Health and Safety Regulation Part 15, Sections 15.7, 15.25, 15.30, and 15.42–15.45
