Steel cable or rod?

kojikun · Post by **kojikun** » 2003-05-13 09:22pm

Whats the difference between steel cable and steel rod, assuming the same crosssectional area and material. And why would rigid cable ever be chosen for a task when rods would be easier to make?

aerius · Post by **aerius** » 2003-05-13 11:37pm

Steel cable would be a lot stronger in tension. Cables are made of small individual wires that are wound together into the cable. To make the wires, steel is drawn through dies and an effect of this process is that the wire is work hardened and has it's grain structure aligned in a more optimal manner. This strengthens the wire, and when it's wound into the cable the end product will be stronger than a rod of the same cross-sectional area.

Post by **Beowulf** » 2003-05-14 01:39am

And the difference is that you can bend the cable easily back and forth, but can't do the same with the rod.

kojikun · Post by **kojikun** » 2003-05-14 01:43am

easilly being relative to the thickness of the cable, ofcourse..

aerius, assuming the cable and rod have equal strength (for whatever reason, just assume), is the flex of the cable the only reason it would be chosen to be used?

phongn · Post by **phongn** » 2003-05-14 10:56am

Price might also be an issue, along with diameter.

kojikun · Post by **kojikun** » 2003-05-14 03:16pm

i think machining cable is more expensive then rod, however.

aerius · Post by **aerius** » 2003-05-14 08:02pm

kojikun wrote:aerius, assuming the cable and rod have equal strength (for whatever reason, just assume), is the flex of the cable the only reason it would be chosen to be used?

Strength being equal, it comes down to cost, aesthetics, and ease of use, and I have no idea which one costs less. For some applications a rod might look better than a cable, and the opposite is true in other cases, same thing with ease of use. A rod will need some kind of threads, clamps, or fittings to attach it to whatever it's supporting, same thing with a cable but it'll use different attachment fittings. It'll then depend on which kind of fittings go better with the chosen application as well as the price and looks.

BTW, cables aren't machined. They take huge rolls of wire from the steel mill which are then rolled and drawn through a series of dies to form the final diameter wire, which then gets wound/spun together into a cable. Rods are extruded through a die or they roll them from bar stock depending on the shape of the rod.

kojikun · Post by **kojikun** » 2003-05-14 08:09pm

I guess cables are safer too, no? Because one strand can break before the entire thing does, while a rod would just snap.

And is this big complicated system of making wire done in a machine?

Granted, its not a machine tool machine, but its still a machine. u.u

victorhadin · Post by **victorhadin** » 2003-05-15 10:10am

As mentioned, the process by which strands in the cable are worked, the grain structure tends to be aligned in more-or-less (but not absolutely, by any means) the same direction, given exceptional tensile strength in one direction and more extensive plasticity in another.

My materials science knowledge is by no means perfect, however, so forgive me if I am mistaken or inaccurate.

Zoink · Post by **Zoink** » 2003-05-15 01:41pm

kojikun wrote:I guess cables are safer too, no? Because one strand can break before the entire thing does, while a rod would just snap.

Yes. Cracks would not propagate through the entire cable. A cable structure would be designed not to fail even with only a percentage of intact cable strands,... maybe like 66% (I don't know what safety factors civil engineers use, it probably depends on the application, for aircraft its 1.5)

For a solid material, a small crack under tension will propagate through the structure until it fails. The rate of crack growth is known and an inspection interval is needed so that a crack will be found before it reaches a critical length. Depending on the material/application this might involve a simple visual check, or a detailed analysis to find microscopic cracks. If this is not possible, replacing the part at a given interval might be needed.