Thread: 101 now called 102 ?

In my younger days I designed mine haulages and winders for a living. I knew a bit about wire ropes for those purposes.

Though I never had to design a capstan winch, the design handbooks give the following wire rope requirements for capstan winches:

• Ordinary lay - the most common lay, where the wires of the strands are laid in one direction and the strands are laid into the rope in the opposite direction (this helps prevent the rope twisting as it stretches).
• Should be flexible - flexibility increase as more, smaller diameter wires are used to make the strands.
• Should provide a good gripping surface on the face of the capstan drum.
• Should be reasonably resistant to wear. Small diameter wires don't wear as well as larger wires.

Recommended construction for capstan winches is 6x24(15/9/F)/F. This construction has 6 stands with 24 wires in each strand - each strand has 15 outer wires over 9 inner wires laid over a fibre rope core, the strands are laid over a fibre rope core.

In 9mm diameter, the outer wires would be approximately 0.48 mm diameter. The weight would be approximately 25.8 kg/100 m. The minimum breaking strength is 35.6 kN (3629 kg, or 8000 lbs force) for 1570 MPa wire.

This is obviously not the construction that you have because yours has a wire rope core.

The closest rope construction to that but with wire rope core that I can find listed in 9 mm diameter is 6x36(14/7+7/7/1)/IWRC. In 9 mm diameter, the outer wires would be approximately 0.50 mm diameter. The weight would be approximately 33.9 kg/100 m. The minimum breaking strength is 51.1 kN (5209 kg, or 11,484 lbs force) for 1770 MPa wire.

When a wire rope is bent over a drum or sheave, the stress increases in the outer wires of the rope - this is possibly (but could have been previous damage at that point) why your rope broke at the capstan drum (where the wire stress is highest).

The ratio of the drum (or sheave) diameter to rope diameter and the ratio of the drum (or sheave) diameter to outer wire diameter is an important factor to reduce the stress rise in the wire to an acceptable limit. As drum (or sheave) diameter is increased, the rope and outer wire diameter can be increased.

The rope diameter (9 mm in your case) is nominal. The diameter of a new rope will be larger by as much as 7% for a 9 mm rope (approximately 9.63 mm).

The swaged terminal on your rope is similar to those used for yacht rigging. A good wire rope merchant should have these and the tools to swage them, or else try some of the places that do yacht rigging. Perhaps you can find a Ronstan catalogue on line.

Edit: BTW, 6x36 IWRC is commonly used hoist rope for cranes.

Edit 2: My very old Ronstan catalogue has a swage eye for 3/8" wire that might do. It lists 8 and 10 mm but not 9 mm, but newer catalogues might have 9mm. 3/8" is 9.52 mm. The part number for 3/8" swage eye is RF1500-12, if they had a 9 mm swage eye it would look like RF1501-9.

Originally Posted by 101 Ron

...
I did have a check of the construction in I know it is 7 strand with 6 strands around the central one.
Each strand has 19 wires with 10 being a larger size around 9 smaller ones.
The cable is very flexiable for its size.
...

6x19/IWRC is a common wire rope construction and is recommended for marine and general purpose.

But the strand construction 10/9 is not listed in either of my wire rope catalogues - one for wire ropes made in Australia and one for Haggie Rand (Haggie Rand are from South Africa - BTW South Africa is a world leader in wire ropes - they have the deepest mines and very demanding of wire rope winders for hauling ore from underground). Thinking about some more, 10/9 strand construction would be hard to make.

The 2 usual constructions used for strands with 19 wires are:

• 12/6/1 - 12 outer wires over 6 wires and a single wire at the centre. The wire diameters are all close to the same - probably indistinguishable by eye.
• 9/9/1 - 9 outer wires over 9 smaller wires and a single wire at the centre. The centre wire is close to the same diameter as the outer wires, the 9 inner wires are noticeably smaller than the outer wires.

9 mm rope using common 6x19(9/9/1)/IWRC construction is available in 2 strengths using 1570 Mpa or 1770 MPa wire.

For 1570 MPa wire the weight is approximately 30.8 kg/100m and minimum breaking strength is 42.2 kN (4302 kg, or 9484 lbs force).

For 1770 MPa wire the weight is approximately 33 kg/100m and minimum breaking strength is 51.1 kN (5209 kg, or 11,484 lbs force).

Outer wire diameter is approximately 0.72 mm.

Because of the larger diameter of the outer wires, 6x19 wire rope is not as flexible as the 6x24 or 6x36 constructions mentioned in my earlier post.

The drum and sheave diameters need to be larger to avoid over stressing the outer wires. From memory, 6x19 construction is not permitted (it is certainly not recommended) for use in cranes.

However for our vehicle winching purposes; usage is infrequent (compared to a crane), and the larger wires stand up to abrasive wear better than smaller wires.

BTW, I see a lot of galvanised wire ropes used on vehicle winches. Galvanised wires are susceptible to martensitic cracking when pulled under load over sliding surfaces, such as fairlead rollers that don't turn. In these cases black ropes are better (as long as rusting is not a problem).