Copper Wire

Hardness can be related to brittleness. A hard metal will resist bending and denting, but will be more likely to break after being bent or deformed. The harder the metal the more brittle. A good example is cast iron, you just about cannot bend the stuff, but drop it on the floor and it can shatter.

A soft metal will bend repeatedly without breaking, same with denting. Metal-smiths make dishes in metal they usually use silver or copper because it is a good balance between hard and soft. They can work it for awhile before it becomes work-hardened. Work hardening occurs when metal is bent or deformed, it creates stresses within the metal. This is why you can break a copper or steel wire by repeatedly bending it at a specific point. Work hardening can be released by annealing with heat (you would have to check annealing tables for temps and times).

Your problem might occur through using too hard a wire in windings. If the wire were to crack in a sharp bend, the winding might pass inspections but break during use leading to upset consumers and loss of product confidence.

Hope this helps.

Drew

In almost every winding situation, you will not experience any difficulty with winding (I've seen a few quadrapole windings where this mattered, but that was unusual geometery) or in breakage. The primary difficulty you need to worry about is conductivity - the softer the copper, the better the conductivity. Thus, if you work-harden the wire during winding, or if you start with hard wire, you might find an actual resistance of 4.56Ω when you have calculated that it should be 3.87Ω.

You might also find (hopefully, this is an extremely rare event) that hardness indicates a poor quality alloy.

So hardening affects conductivity? Can you explain why? (not that I doubt you...I just want to know )

Also, how much would that extra resistance affect the performance of a motor? Extra heat and more power consumption?

I would guess it has something to do with the stresses within the material creating shear planes that inhibit electron flow, but that is just a guess.

Drew

Yes. In straightforward terms, the work hardening causes dislocations in the copper. This is the primary problem with high purity copper. Lower purity copper (as in what some vendors sell and call electrical grade) can have precipitation hardness from the impurities. Either case raises the resistivity. I don't have numbers handy anymore, but you should be able to get those if you want.

Yes, extra heat, reduced power result from this.

If it is hard is it near pure copper which should be soft or an alloy?