Spring Wire Draw

[sbozy25]

Soemone please help prove me right.

Say you are using annealed chrome silicon spring wire and you were pulling it through a draw die. The wire stayed in constant tension from the main spool to the die, and then wrapped around another spool. There is potential for the wire to not be in tention once it is around the second spool. Is it possible for the wire to try to return to it's original diameter since it is not in tension? For an example, say I pull .630" wire through a .521" draw die, is it possible for the wire to end up .524" after it is let to sit? I believe this is so, but everyone else is arguing with me that it isn't possible and once you reduce it, it is set..... any thoughts?

 

[sreid]

Clearly a wire under tension will have a smaller "Diameter" than when the tension is relieved. 0.003 inch seem a bit much but there could be some additional growth due to stress relief.

 

[NickE]

Unless there is some sort of phase transition I have to agree with everyone else here.

When in tension there will be some amound of diametrial shrinkage, direct result of Poisson's law. However that amount is relativley small in comparison to the diameters you are talking about.

IF it comes out of the draw die at .521, I'd expect it to be at .521 after re-coiling.

nick




Nick
I love materials science!

 

[sbozy25]

For those still interested... I have spoken with a wire expert and he told me the following about this phenomena...

You can expect a few thousandths of growth in material due to the nature that it is spring steel. However, the softer the steel, the less growth you will see.

If the wire does not hit the die at exactly 90°, we will cause an ovate condition which will more than likely cause the wire to grow in one direction more than the other.

If our die angle is to shallow, we will cause more lube to go through the die and force more stresses into the wire over a longer period of time. As a result, the wire will have a tendency to spring back more than if it were a sharper die angle. However, if the angle is to sharp, it will cause a shearing effect, and possible pull the material apart.

Japanese material suppliers anneal their wire before they send it, and as a result it is smoother, and softer than what we would get from American sources.