Advice from Nobles Engineering on the proper use of swivels

Friday, 8 March 2019

Lifting swivels are such a familiar item of rigging hardware, often people don’t give them much thought. Swivels perform a variety of important roles. These include:

 - Alignment

 - Allowing a suspended payload to rotate (pivot)

 - Avoiding having a suspended payload rotated (spun) by the equipment it hangs from

 - Suspending or pulling a device that rotates under load at speed.

 - Protecting a rope (or something else) from damage.

 - To complicate things, the swivels which are offered to perform these roles vary considerably.

Any swivel will have three basic elements, the interfacing parts at either end and the bit in the middle that does the actual swiveling:

The nature of the swiveling element is critical to determining the suitability of a swivel. The swiveling element can be equipped with:

 - a roller thrust bearing,

 - a plain bearing such as a PTFE or bronze thrust washer,

 - a basic metal washer acting as a thrust bearing, or

 - it can be a simple ‘plain swivel’ with nothing to ease rotation beyond the bare, dry steel on steel of the main components.

This may be confusing without a diagram:

Basic layout of a swivelling element

The swiveling element almost always consists of these basic elements. The ‘body’ of the swivel could be in several forms including: the bow of a swivel self-locking hook, the cross-head of a crane hook block, or the barrel of a sealed bearing swivel.

The nut must be secured.

One thing we notice about the diagram is the nut. This is usually threaded on to the shank, sometimes instead it is a more elaborate assembly of collars and rings BUT if the nut comes loose, we have a disaster!

Securing a swivel’s nut requires a mechanical device to prevent the thread from undoing. Often this is a dowel pin or cotter bolt driven through the nut and shank, or a keeper plate in a slot.

The nut must be secured with something which is strong enough for the application and type of swivel used, otherwise it can easily be broken because the forces, friction and leverage exerted by lifting gear in use can be very large.

It is vital that the security of the swivel is inspected, maintained and assured in accordance with the manufacturer’s instructions.  It is also vital that the right swivel is used in the right place. The rules are simple and they all hinge upon the nature of the bearing.

Bearing.

If the bearing does not have rollers or balls - > then the swivel is for alignment only

If the bearing looks like a washer, or a stack of washers, or there is nothing there at all - > then the swivel is for alignment only.

Typical swivel found on the end of a chain sling

Swivels made for alignment only must not be rotated under load, or failure may result.

 

Alignment problem - The lug seems aligned to the sling, but isn’t. if the chain is short or poorly rigged it may have a pronounced twist.

Swivels for alignment are nevertheless very useful. A natural alignment of lifting components is often elusive and can result in unacceptable twists in the rigging, or difficulty in connecting parts.

Only if a roller (or ball) thrust bearing is fitted can rotation under load be allowed.

Cutaway diagram of a Nobles TSF swivel model

Rotation under load is important to many lifting applications. Various standards, (for example AS3850 for tilt-up concrete construction) will require lifting tackle such as sheave blocks and hooks to be equipped with roller bearings where swiveling under load is required.

Not so fast!

Lifting swivels with a roller bearing are generally only designed for slow and limited movement. They are capable of pivoting a payload, and other limited rotations.

What they cannot do is cope with continuous rotation and high-speed rotation. Lifting swivels are devised with lifting cycles in mind. If they are fitted to rotating machinery or suffer continuous and high-speed rotation then the bearings, shanks and other components can rapidly expire and a regular lifting swivel may be entirely unsuitable.

Manufacturer advice should always be sought and purpose built equipment specified as soon as continuous or high speed rotation is a necessity.

Are there times when a swivel must NOT be used?

Unfortunately yes. If we fit swivels to the end of a rope, the rope must be of a type which will not unlay itself under load. If this happens, then both the breaking load and the fatigue life of the rope can be severely reduced.

Some ropes do not unlay themselves under load and are rotationally stable. These ropes need a swivel to avoid torsional damage from imposed torques. Modern, high performance ropes that are called ‘rotation resistant’ fit into this category.

For cranes and other winch driven machinery Nobles can provide the expert advice necessary to ensure the best rope selection for the machine design. Leading manufacturers such as Bridon and the standard ISO16625 provide guidance as to which ropes should have a swivel and which ropes cannot have one.

Does your rigging already have a swivel?

The answer (perhaps surprisingly) is almost always ‘yes’. The bottom hook or hook block of your crane will more than likely be designed with a roller bearing swivel built-in.

Care should be taken therefore when suspending something beneath a crane hook. Any rope which is hung beneath must fit the definition of an approved wire rope sling in accordance with AS1666 and the conventional rope selection and design factors must be in use – otherwise competent advice must be sought to avoid adverse effects due to the swivel that is present.

If you are lifting, you will be using swivels. Nobles are uniquely placed to help with the right products and advice for swivel applications including swivel chain fittings and swivel equipped lifting points of every type. We also offer our own roller bearing TSF series swivel hooks and SBS range of sealed bearing swivels built to Australian Standard AS2318. For specialised applications, bespoke devices and customer’s existing swivels Nobles offers comprehensive inspection, design and refurbishment services.

To speak to one our lifting & rigging specialists please call us on 1300 711 559 or send us an email at sales@nobles.com.au.

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