The term ‘textile sling’ encompasses slings made from fibre rope and webbing and those of endless roundsling construction. Natural fibre rope is by far the oldest lifting medium and, although its popularity has declined, there is still a current standard for manila, sisal and hemp fibre rope slings. Natural fibres have largely been superseded by manmade fibres such as polyamide, polyester and polypropylene. The harmonised European standard for both natural and man-made fibre rope slings is EN 1492-4.

Size for size the strength varies according to the type of fibre. Hemp and sisal are of similar strength and are the weakest. In ascending order, the others are manila, polypropylene, polyester and polyamide (usually known as nylon). Nylon is approximately two and a half times as strong as grade 1 manila of the same diameter. Polypropylene rope has the advantage that it will float in water.

Natural fibres are susceptible to rot and mildew in damp conditions and are not suitable for most chemical environments. Manmade fibres are immune from rotting but have varying resistance to chemicals. Manmade fibre ropes have varying resistance to chemicals as follows:

  • Polyamide (nylon) is virtually immune to alkalis but it is attacked by moderate strength acids. It loses up to 15% of its strength when wet.
  • Polyester is resistant to moderate acids but is damaged by alkalis.
  • Polypropylene is affected little by acids and alkalis but damaged by solvents.

All fibre ropes are prone to deterioration at high temperatures. Manmade fibres rarely show a sharp melting point. They will either soften over a range of temperatures or they will char or decompose before melting. Generally textile slings should not be used above 80°C or below 0°C without consulting the supplier.

Fibre rope slings are soft compared to chain and wire rope and are therefore less likely to damage the surface of a load. However they can easily be cut if loaded over a sharp edge or corner without adequate packing and the length of a fibre rope sling cannot be adjusted.

Fibre rope slings are amongst the cheapest types of sling although other types of textile sling are very competitive and becoming more so. Some users regard them as disposable and replace them every six months rather than have them thoroughly examined.

Webbing slings are manufactured in a similar variety of materials as manmade fibre ropes although by far the most popular are those made from polyester. The harmonised European standard for webbing slings is EN 1492-1. They are light in weight and can be made in various widths, which is an advantage when lifting loads that are vulnerable to local damage from a narrow point of contact.

However it is essential that they are not loaded across a corner at an angle such as will occur if a pair of slings is used to cradle a load in basket hitch. This causes the load to be imposed on the outer edge of the webbing rather than uniformly across it. This can result in the edge of the webbing tearing and, once initiated, a tear is likely to continue across the webbing.

Unprotected webbing slings can easily be cut by a sharp edge but there are several ways to provide protection. Loose packing can be used but many manufacturers can supply captive edge protection or captive sleeves. Some manufacturers offer their own specialist slings which are coated, have protection bonded to the surface or are made from high performance yarn.

Webbing can be used to make multileg slings but the most popular and versatile are single leg slings. The eye terminations are made by turning the webbing back and stitching. Except for the narrow webbing, the width at the crown of the eye is reduced by folding the material in one of several patterns. The crown is also reinforced to protect it against wear. Reducing the width of the eye in this way facilitates connection to other components such as shackles or hooks. An alternative is the use of metal end fittings which are the full width of the webbing and usually provide the facility to reeve the sling in choke hitch.

Roundslings are endless manmade fibre slings formed by winding one or more yarns round a former and joining the ends to produce a single hank. The hank is inside a protective woven tubular sheath which is not load bearing. They can be made in a variety of materials but by far the most popular for general lifting purposes is polyester. The harmonised European standard for roundslings is EN 1492-2.

They are light in weight and can flatten and spread to the shape of the load giving some of the advantages of webbing slings whilst avoiding the edge loading risk associated with webbing slings. General purpose roundslings are susceptible to being cut by sharp edges although the outer sheath offers some protection to the load bearing core. They can also be fitted with protective sleeves or protected by conventional packing. They have a similar resistance to chemicals and temperatures as the manmade fibre ropes. However there are manufacturers that can supply roundslings made from special high performance yarns and covers which offer a superior performance, including high resistance to cuts and abrasions.

Roundslings can be made into permanent multi-leg assemblies with metal terminal fittings but the vast majority are supplied without captive fittings. The rigger is left to assemble them with other items into the configuration required for the particular application.

In general, textile slings, whether made from fibre rope, webbing or of the roundsling construction, offer a lightweight, easy to handle alternative to chain and wire rope. As with chain and wire rope, advances in technology have resulted in increased performance from manmade fibres. For some applications they offer by far the best solution.

Textile slings can also be used to great advantage in combination with chain or wire rope slings. For example, to lift a large machined component, textile slings can be wrapped around finely finished surfaces to provide lifting points without damage to the surfaces. A multi-leg chain sling can then connect to the textile slings providing any necessary adjustment to the final leg length.

Rating assumptions
The standard ratings for general purpose slings are based on certain assumptions about the way they are used. If the way they are used varies from those assumptions, the rigger must allow for the effect of the difference. Single leg slings are normally rated for use in a straight vertical pull. If two single leg slings are to be used in combination to form a two leg assembly, an allowance must be made for the angle each sling will make to the vertical.

Multi-leg general purpose slings are rated for the legs in straight pull at an angle of 0-45° to the vertical with an optional second rating for an angle of 45-60° However what is not always appreciated is that this assumes that all legs are at the same angle. Also, for three and four leg slings, it is assumed that, when viewed from above, the angles between adjacent legs are equal. If either of these conditions varies, an allowance must be made.

For any configuration, the load in each single leg sling or each leg of a multi-leg sling can be determined using trigonometry or by graphical methods but that is outside the scope of this article. What I want to convey is an understanding of the effect of different sling geometries and modes of use.

I’ll start with a two leg sling with both legs at the same angle. For a given load, as the angle increases, the tension in each leg increases. A range of angles is already accommodated within the rating so no further allowance is required. However if the legs are at different angles, the one nearest the vertical takes the greater share so an allowance is required. Ultimately if one leg is vertical it will take all the weight and the other will take none.

The same applies with three and four leg slings although there is a further matter to consider: the angles between the adjacent legs when viewed from above. Assuming the angles to the vertical are all the same, if the angles between the adjacent legs are the same then the legs will be equally loaded. However consider a three leg sling with two legs close together. The third leg will take the greater share so an allowance will be required. Again taken to the extreme, if two legs are touching they will only share half the weight between them with the third leg taking the other half.

With four leg slings there is a further assumption to take account of. Four leg slings are rated the same as three leg slings because of the likelihood that the four legs will not be evenly loaded even when the geometry is uniform. With a four legged chair, if the legs are not exactly equal and the floor flat, it will rock. The same is true of a four leg sling, particularly if the load is rigid. The standard rating makes some allowance but not all that may be required. With a very rigid load it is likely that a four leg sling will carry the load on only two diametrically opposite legs and an extra allowance is required.

The same applies when using single leg slings in combination to make a multi-leg assembly, except that there is no in-built allowance in their rating for the angle to the vertical.

In the standard ratings considered so far they all assume a straight pull. Quite often the sling leg is wrapped around the load and choked. This causes additional local stresses at the point of choke so again an allowance is required. There are other variations from straight pull, such as basket lift, which, unlike all the allowances mentioned so far can, in some circumstances, actually increase the sling’s lifting capacity. The capacity of webbing slings and roundslings is printed on a label attached to the sling and helpfully includes the rating for choke hitch and basket hitch. Unfortunately, for other types of sling, this is impractical and must be calculated.

As the allowances are cumulative it is often necessary to start with the weight of the load, the number and position of the lifting points and method of connection, then work back to the force in each sling leg and select the slings accordingly. This may seem rather onerous but it does illustrate the thought process which the rigger should follow when selecting lifting slings. A skilled rigger should be able to make a quick assessment and need only make precise calculations if the results seem marginal.