A few examples: 3000 mm drum / 76 mm wire = app. 40 d 3000 mm drum / 86 mm wire = app. 35 d

1500 mm drum / 86 mm wire = app. 17 d 900 mm drum / 76 mm wire = app. 12 d

The same is also valid, when the steel wire makes a big change in the rundirection.

E.g. when the steel wire is forced round a guide pin, the proportion will only be app 4 d (300 mm guide pin / 76 mm wire = 4 d).

For steel wires 6x36 and 6x41 a minimum of 20 d is recommended. The bigger – that better. Some suppliers of steel wires recommend a minimum of 40 d.

E.g. a 44-mm steel wire “demands” a sheave with a minimum diameter at 880 mm

A more essential fact is the stress, which will occur when a steel wire runs round a drum, roller and sheaves or change run of direction due to a guide pin or a spooling device. This stress will give a shorter life of the steel wire and the steel wire will be worn down before time as well.

When a steel wire is fed over e.g. a winch drum, stern roller, guide pin or a sheaf, certain complex tensions (a combination of bending, tensile and compression stress) are generated in the steel wire.

The greatest tension occurs in the wire threads furthest away from the steel wire’s bending centre. After repeated bends, stress failure will occur in these wire threads.

These stress failures occur due to many factors. E.g. the steel wire rope construction, tension applied, the ratio (d), use of a swivel, wear and tear of guide pins, spooling devices and stern roller together with martensite formation.

Martensite: Martensite formation.

Martensite is a structural change in the wire material causes by a very sudden cooling of the steel wire after a strong local heating generated by friction. E.g. bad spooling of the steel wire on the winch drum may cause the friction.

This structure change gives a hard and brittle surface and may cause fractures during normal operation or when spliced, even though the steel wire doesn’t show any visible signs of external wear

If a steel wire carries a current or the steel wire is wound on a drum in several layers, there will often be sparks. The surface temperature where the sparks appear will be over 800° C, making it quite probable that martensite will be formed. If there are many sparks, fracture on wire threads will happen and the wire may break.

Precautions against martensite:

•The blocks, guide pins, stern roller and spooling devices must not be worn down and should turn easily. Must be kept in good condition.

If equipment is repaired by welding, care should be taken to ensure that hardness of the welding material is maximum 300 Brinel.

•When a steel wire is wound on a drum, it should be in tight wraps without the layers crossing each other in order to prevent the top layer from cutting into the underlying layers.

•The steel wire should be lubricated at regular intervals in order to minimise the friction between wires and strands. The best would be to make a sort of continuously lubricating.

•The steel wire should be checked at regular intervals for crushing, minor cracks and mechanical damages, all of which might indicate martensite spots.

•Use of wires with less contents of carbon in the wire. (Are used in the fishing industry for trawl wires).

Re-socketing of steel wire:

•The old steel wire is cut of at the socket base.

•The steel wire piece is pressed out by use of a mandrel / jack.

When heated:

•Only slowly and equably.

•Only up to maximum degrees – depending on the product.

Do “bend / break – test” on the wire from the piece of steel wire, which is leading into the socket. If the wire threads break, they have been exposed to martensite. The steel wire will break in the area around the socket base because the steel wire works heavily in this area.

After Re-socketing remember to:

•The socket base to be filled with grease or oil. To be re-filled, when the steel wire isn’t in use over a long period, as the steel wire will dry out.

•The re-greasing is very important, when the socket in hanging down.

Recommendations:

•You must aim at a working load of maximum 1/3 of the Breaking load. In this way the steel wire can be loaded with peaks up to 50% of the original breaking load. You will also have room for using the swivel without complications.

•Guide pins, blocks, spooling devices and stern roller must be kept in a good condition. If equipment is repaired by welding, care should be taken to ensure that hardness of the welding material is maximum 300 Brinel.

•Avoid that the steel wire is slipping across the connections between the two stern rollers.

•The ratio of “d” to “D” must be as big as possible – and always at least

20, when we are dealing with a steel wire under load.

•The steel wire must be lubricated in order to minimise the martensite formations.

•Martensite formations must generally be avoided – if possible.

Jan 2002