Wire rope - why not aluminum? 1

[neomoses]

I'm in a DFM class at the moment and am actually trying to use all of the 'tools' they have taught us to this point to select a material and process for manufacturing all the parts in our design.

So.... we're stuck at the wire rope (cable). All of the material properties are pointing us in the direction of an aluminum wire rope, but when we look at what's available in production today, I see no off-the-shelf alumiminum wire rope. The only criteria we can find at the moment to discount aluminum would be if we chose to go with infinite life rather than a design life of 10^7 cycles.

Can someone give me some other good reasons why aluminum is not used as a wire rope material today?

Bryan

 

[ivymike]

do power transmission lines count as rope?

 

[TheTick]

Consider that flexing, coiling, and twisting all count toward fatigue cycling. As does each guitar-string like cycle when a tensioned wire rope gets a "twang". You can reach 10⁷ cycles mighty quick.

 

[IFRs]

I has poor abrasion characteristics and there is a lot of movement within stranded wire rope. It just won't last. And it stretchs a lot more than steel.

 

[arunmrao]

Al wire is soft,has a high % elongation,gets easily deformed while twisting and coiling. any nicks or cuts on the aluminium wire will be disatrous for a load bearing application.

An everyday example is of ACSR grade where a steel reinforcement is introduced to prevent it from sagging.

 

[Philrock]

While aluminum is a lot lighter than steel, steel is a lot stronger. On a strength-to-weight basis, wire rope steel is 10.6% stronger (ultimate tensile) than 7075 aluminum. This, combined with what's mentioned above, make steel the clear winner.

What led you to feel aluminum would be the way to go?

 

[neomoses]

The main thing that puts aluminum ahead of steels is the strength to weight ratio. I'm not sure what references you're using, Philrock, but mine are saying that most aluminum alloys have a higher strength to weight ratio than most stainless steels.

corrosion resistance was one criteria that forced us away from plain steels to stainless steels.

Also, it appears that most aluminums have a much lower % elongation than most steels. I'm guessing this is a big factor that makes steels more favorable because you can use smaller diameter pulleys without permanently setting the cable. The only aluminums that I found with high % elongations had very poor yield/fatigue strengths.

We've ended up choosing a stainless steel for the material, but are wanting to ensure that we have reasonable justifications to eliminate the aluminum alloys.

Bryan

 

[sreid]

How about using Spectra plastic rope? Very strong, light and available.

 

[TVP]

neomoses,

The steels used for wire rope applications will have extremely high strength-- tensile strength over 2000 MPa depending on the diameter. The latest generation of small diameter steel wires for cables/ropes and tire cord applications has tensile strength ~ 4000 MPa.

Corrosion resistance is improved by using zinc coatings (galvanizing).

arunmrao was referring to elastic deformation when he said % elongation, not the amount of plastic deformation (fracture strain) that occurs during tensile loading. Since Al is only 1/3 as stiff as steel, it will deflect elastically more than steel for a given load and size.

 

[JStephen]

You normally see aluminum compared to steel with wording that says "pound for pound, aluminum is stronger than steel". Of course, aluminum is bulkier, but in many applications, that's no problem, you just make the aluminum member bigger and thicker and there you are- it's as strong, but still lighter. But in the case of a cable, this works against you. To get the same tensile strength, you need a bigger cable, but that dramatically increases the bending stresses in the cable, and that in a cable that is susceptible to bending fatique.

Another aspect is that the aluminum-to-steel comparison is usually looking at fairly low-strength steels, such as structural steel. Steel cable is usually a good bit higher yield stress than structural steel, and would be at less disadvantage when compared pound-for-pound.

 

[rb1957]

if your objective is infinite life, and Al doesn't have an endurance limit, then Al isn't going to satisfy the requirements ... no matter how light it is !

good luck

 

[CoryPad]

Al does have an endurance limit, it just may be in the gigacycle (10⁹) regime:

http://www.ingentaconnect.com/content/maney/imr/1999/00000044/00000001/art00001

http://www.ingentaconnect.com/content/bsc/ffems/1999/00000022/00000007/art00205

http://www.ingentaconnect.com/content/els/01421123/2001/00000023/90000001/art00167

http://www.sciencedirect.com/scienc...serid=10&md5=a6745dea865ec694192e523e7e216723

http://www.sciencedirect.com/scienc...serid=10&md5=b06d97beb10d0955b184d066135ca468

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[FACS]

Maybe it's the size of rope you are looking for. I've found sources in the blue book for all kinds of wire rope.

Every utility pole I see has a wire rope made of aluminum.

Charlie

http://www.facsco.com

 

[Philrock]

FACS, If you're talking about utility pole guy wires, it's very unlikely they're aluminum. Guy wires are usually galvanized steel, which certainly can look like weathered aluminum.

 

[FACS]

Phil,
We just had a tornado rip apart our neighborhood last August. All the guy wires were replaced, and they were in my yard for a few weeks. They were all aluminum.

Charlie

http://www.facsco.com

 

[FACS]

Maybe they were just aluminum clad...... hmmm

Charlie

http://www.facsco.com

 

[ivymike]

an internet search says that both types exist (steel core aluminum and aluminum). Perhaps a sparky could tell us about application differences.

 

[JStephen]

Note that one difference in a guy wire is it doesn't have to flex much- unlike, say, a crane hoist line, which is continually wrapping and unwrapping around a drum.

 

[arunmrao]

All guy wires in India are made of steel.Steel is less prone to theft perhaps.

Else rolls of Al conductor,both bare type and insulated are often stolen.

 

[JStephen]

ivymike- do you mean guy wires or transmission lines?