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Nonferrous topics such as copper and aluminum, annealing, etc. go here.

TOPIC: Storage of copper wire

Re: Storage of copper wire 5 years 11 months ago #1646

Hi everyone,

Thanks for enlightening me about this.

Currently we only use CCR copper. I don't have any OFC that I could try the experiment on. However, it certainly explains the phenomena that I experience. Maybe someone could try this out?

Yes, Peter, our rod supplier uses hydrogen as the gas for protection against oxidation during annealing of the rod. (If this is what you meant by reducing atmosphere.) I think this is common for all CCR copper rod.

Thanks again to all!
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Re: Storage of copper wire 5 years 11 months ago #1647

Hello again gan,

I always thought that there was no requirement for rod annealing because casting, rolling, pickling and coiling are all in-line and the residual heat in the rod during rolling provides the annealing function.

In my opinion, there should be no hydrogen around or near the just cast and rolled rod!

I think you have stumbled on a serious metallurgical problem with your copper rod and I suggest you have a very serious discussion with your rod supplier ASAP.

You must not have hydrogen embrittlement in your conductors.

Peter J. Stewart-Hay
Stewart-Hay Associates
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Re: Storage of copper wire 5 years 11 months ago #1648

Peter, Tonytang,

I don't know what kind of equipment that they are using to enamel the wire but a couple of comments:

Normal process is to run the wire through a pre-annealer. Why? Besides pre-annealing the wire cleans the wire. Preannealers have either steam or nitrogen pumped into the annealing chamber or tube. If you don't pump nitrogen or steam into your annealer then it is usually designed with a water seal at the wire exit and annealer tube is below the surface of the water. The hot wire hits the water causing steam. The temperature of the water is controlled so that the wire when it leaves the seal is cool enough that it will not discolor or oxidize and at the same time warm enough that the wire will be dry when it enters the applicator.

Another reason why the wire cannot be oxidized is because oxidized wire cannot be enamelled successfully. The wire will not meet adherence standards and therefore is "bad wire". In order for the wire to be considered good it has to adhear to the wire!


when you check the last couple hundred of feet or 100 meters of wire on a spool you are assuming if it passes all of the tests that all of the wire on the spool is good. For example depending upon the size you are running there may be thousands of feet or meters of wire on the spool. When you check the end of one spool you are saying that all of the wire is good or bad. You are also saying that the start of the next spool is also good. Several thousand meters later you again check the end of the spool and again you are assuming that all of the wire between the end of the first spool and the end of the second spool is good.

If you have good process controls you are probably right about the quality, however your samples are anything but random so it is difficult to make a statistical decision on thousands of meters of wire based upon a non random assessment that is maybe 100 meters long.

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Re: Storage of copper wire 5 years 11 months ago #1649

We reiterate, nobody in the wire and cable industry should be using hydrogen as a reducing atmosphere in an annealer unless they are exclusively using oxygen free copper.

Peter J. Stewart-Hay
Stewart-Hay Associates
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Re: Storage of copper wire 5 years 11 months ago #1650

Hello everyone,

I think that I have made a mistake in saying that Hydrogen is used as the reducing atmosphere. I was thinking about Nitrogen but have somehow written hydrogen.


You are right, we should not have any hydrogen embrittlement. What I wanted to say is that our rod supplier uses Nitrogen as the protective gas during rod breaking drawing process.

So if that is not the real problem that we are facing, then we are back to the same question again of how the storage of bare copper wire after some time could affect the elongation of the enamel copper wire?
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Re: Storage of copper wire 5 years 11 months ago #1651


I am not a metallurgist but this I do know: let us assume that you have good copper rod which you draw into a finished size that you will feed into an enameling system (pre-annealer, applicator, oven and is then spooled) and the finished wire is tested and meets all magnet wires mechanical specifications including elongation (tensile and springback?). Or you have good copper wire that you will draw to a feeder size which will then go into an enameling system (including inline drawing machine, pre-annealer, applicator, oven, and spooler) and the finished wire meets all mechanical specifications such as elongation, springback, and tensile.

That being said; When you draw wire you get a certain grain structure. When it goes through an enameling system the wire goes through a pre-annealing and the annealing process is finished in the oven. Depending upon oven temperatures and wire speeds, the finished enameled wire (with a little process control) will when tested for elongation, springback, and tensile fall within the specifications for that size wire.

The wire that passes through an inline drawing machine before pre-annealing and then enameling will also, with a little process control, fall within the specifications for that size wire.

There is however a difference in the conductor: The wire that is drawn to size, if examined metallurgically will display a random alignment of grain structure and the nomenclature for that grain structure will include 3 different sizes.

The wire that was drawn to a feeder size (depending upon the size may be only a size or three from an annealing cycle) is then drawn to size before entering the pre-annealer. The finished wire is uniquely different than the wire that was not inline drawn; it has better elongation, greater tensile strength, and lower springback. Metallurgically the grain structure is nearly 100% the same plus it is homogeneously aligned instead of randomly aligned.

This is the part that I may be going out on a limb and say that under normal storage conditions there is nothing that will alter the elongation (tensile or springback) of a piece of magnet wire that is just sitting on a spool in a warehouse somewhere unless there is a change in the metallurgically structure of the wire and that usually requires physically working the wire.

Most people that make hermetic wire save samples for years. perhaps someone can pull out some old samples and retest them and compare current data with the original data.
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