Lifting Equipment LTD News

SPECIAL APPLICATIONS FOR THE USE OF CHAIN SLINGS

SPECIAL APPLICATIONS FOR THE USE OF CHAIN SLINGS.

OUT OF BALANCE LOADS:

Some loads are asymmetrical and therefore, don't balance about their centre point and require more careful handling. It is essential for the slinger to acquire the skill of estimating the position of the centre of gravity and then place the crane hook immediately above this estimated point.

If the shape of the load permits it, the sling should be positioned equidistant about the centre of gravity ensuring a safe horizontal lift.

If an out of balance load is fitted with a sling attached in such a way that the crane hook is not immediately above the centre of gravity, the load will tilt until the centre of gravity is directly beneath the crane hook. In this case, the sling leg nearer the heavy end will be withstanding a greater force than the leg at the lighter end. This situation could become progressively more extreme until one leg is supporting virtually all the load whilst the second leg is acting merely as a steadying leg.

It is impossible to give precise guidance since loads come in a variety of shapes and sizes but the slinger should be aware that when handling an out of balance tilted load the leg at the heavier end could be supporting anything up to 100% of the weight and in extreme cases a sling should be selected which is capable of safely supporting the whole load on one of its legs.

CLAMPING FORCE:

Multi-leg slings impact a clamping force or a compressive force on the load which increases as the included angle is increased. This force is also much increased in the type of sling where the hooks are threaded on a loop chain.

The slinger should be aware of this force so he can use it to his advantage and avoid the dangers which it may cause. E.g. with this shape of load, the clamping force is used to good effect in ensuring that the hooks are clamped tightly against the load.

Cases have occurred where the load has not been rigid enough to withstand the clamping pressure. Slingers should be aware of this danger and take steps to reduce the clamping force in the case of crushable loads, e.g lightweight frames.

COMBINATION SLINGS:

Concrete beams, steel joists etc. can be lifted with a two-leg sling in a choke hitch but if the work is repetitive, it is better to use two short reevable collar slings in conjunction with a two-leg sling as shown.

The reevable collar slings are more convenient to maneuver under the load and are cheaper to replace when worn.

When using combination slings the reevable collar slings must have the same size of chain as the multi-leg sling used in combination with them. In the case illustrated, therefore, the complete combination should be rated as a two leg sling in choke hitch.

Large packing cases, bundles of steel sheets and similarly shaped loads can be handled by a double basket sling but a more convenient alternative is a four-leg sling used in combination with 2 reevable collar slings as shown. For rating purposes this combination can be regarded as a double basket sling provided, as always, all slings in the combination are of the same chain size.

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