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Things to Consider in Selecting Wire Rope Slings
This blog post is part of a new feature on AWRF where our members provide valuable insight into the industry.
Mishandling of workplace materials is the single largest cause of accidents in the workplace. Fortunately, most of these accidents are avoidable. With wire rope slings playing an important role with cranes, derricks, and hoists, it’s important to understand how to make a proper selection.
A wire rope sling is made of wire rope. It is composed of single wires that have been twisted into strands. These strands are then twisted to form a wire rope.
Here are 4 important characteristics to keep in mind when selecting a wire rope sling
1. Strength
The strength of a wire rope sling is a function of size, grade, and construction. It needs to accommodate the applied maximum load. The more a sling is used, both the design and the sling’s strength are reduced. A sling loaded beyond it strength will fail. For older slings it’s important to inspect often.
2. Fatigue
Wire rope slings must be able to take repeated bending without wires failing due to fatigue, sometimes called bending without failure. The best way to preventing fatigue failure is to use blocking or padding to increase the radius of bend.
3. Abrasive Wear
The ability of wire rope to withstand abrasion. It’s determined by size, number of wires, and construction of the rope. Remember that smaller wires bend easier and offer greater flexibility, which also means they are more susceptible to abrasion.
4. Abuse
The misuse of a wire rope will cause the sling to be unsafe well before any other reason. Kinking or bird caging will reduce the strength of a wire rope. Bird caging is forcibly untwisting the wire rope strands and they become spread outward. Be sure to keep up proper use per the manufacturer specifications.
These are just four factors to consider when determining the best wire rope slings for your application. Keep in mind that weight, size, flexibility, and shape of the loads being handled will also affect the life of a wire rope sling.
Common Wire Rope Fittings You Need To Know
Wire Rope Fittings
Wire rope can be prone to fray easily at the ends making it difficult to connect to equipment. Wire rope fittings or wire rope terminations are used to secure the ends of wire rope and prevent fraying. There are many different types, sizes and finishes of wire rope fittings which are suitable for most types of rope. Some of the more common types of wire rope fittings are detailed below.
Wire Rope Thimbles
A wire rope thimble is used in wire rope assemblies to prevent the wire rope eye from being crushed and reducing wear on the rope itself. When a wire rope assembly is fitted with an eye at the end, a thimble is inserted to form the eye of the loop before the rope is secured in the ferrule or wire rope grip.
Wire Rope Grips
A wire rope grip is used to clamp the loose end of a wire rope after it has been looped back to form an eye. Wire rope assemblies generally require a minimum of three wire rope grips, depending on the wire and application to properly secure the ends.
Wire Rope Ferrules
Wire rope ferrules are used to terminate wire rope ends. Oval shaped sleeves are crushed around the wire rope to form eyes or to create a stopper on the end of a wire rope assembly. This can be done either by hand tools or via a hydraulic press. Hand pressing ferrules is only recommended on smaller diameters of wire ropes.
Turnbuckles/Rigging screws
These are wire rope fittings that are attached to wire rope assemblies and can be used to adjust the tension of wire rope. Turnbuckles typically consist of two eye bolts, one at each end of a metal frame. The tension of the wire rope can then be adjusted by rotating the frame.
Wire Rope Sockets
A wire rope socket is permanently attached using a hydraulic press to fit it to the end of the wire rope. These can be used instead of thimbles, wire rope grips or ferrules. Please don’t try this one at home, it takes specialised tools and knowledge to fit these to wire ropes.
Steel Wire Rope
Steel wire rope is several strands of metal wire twisted into a helix forming a composite “rope”, in a pattern known as “laid rope”. Larger diameter wire rope consists of multiple strands of such laid rope in a pattern known as “cable laid”.
In stricter senses the term “steel wire rope” refers to diameter larger than 3/8 inch (9.52 mm), with smaller gauges designated cable or cords. Initially wrought iron wires were used, but today steel is the main material used for wire ropes.
Wire Rope Inspections EN
Historically, steel wire rope evolved from wrought iron chains, which had a record of mechanical failure. While flaws in chain links or solid steel bars can lead to catastrophic failure, flaws in the wires making up a steel cable are less critical as the other wires easily take up the load. While friction between the individual wires and strands causes wear over the life of the rope, it also helps to compensate for minor failures in the short run.
Steel wire ropes were developed starting with mining hoist applications in the 1830s. Wire ropes are used dynamically for lifting and hoisting in cranes and elevators, and for transmission of mechanical power. Wire rope is also used to transmit force in mechanisms, such as a Bowden cable or the control surfaces of an airplane connected to levers and pedals in the cockpit. Only aircraft cables have WSC (wire strand core). Also, aircraft cables are available in smaller diameters than steel wire rope. For example, aircraft cables are available in 3/64 in. diameter while most wire ropes begin at a 1/4 in. diameter. Static wire ropes are used to support structures such as suspension bridges or as guy wires to support towers. An aerial tramway relies on wire rope to support and move cargo overhead.
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