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Nonferrous topics such as copper and aluminum, annealing, etc. go here.
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TOPIC: Copper Wire Tarnished?

Re: Copper Wire Tarnished? 2 years 8 months ago #1440

Hello again Eddy,

OK well you have just provided us with some new and quite interesting information in that your supplier's wire changes color in your plant as well, at least on the outer surface layer of their reel. (bright orange.) We believe that is cuprous oxide and your stored copper wire may also be showing this effect as well, but......

It is difficult to compare the effects on the two separately manufactured wires because of different drawing lubricants, the different age of the drawing lubricant solutions, different contaminants in the drawing lubricant solutions, different annealing equipment and perhaps if electric annealing, the application of a lubricant in the annealer cooling water. For those reasons, the effects witnessed on the two different supplies of wire may be confusing the issue and thus clouding the logic. We recommend that you focus on wire manufactured your facility and ignore the secondary supply of wire until your problem is cleared or at least well understood.

With regard to your question (a) above, we believed the oxidation on the inner layers to be the result of removing the reels from the vacuum annealer while they were still too hot although the outer layers were say at room temperature. We cannot see any other explanation at this time with the information we presently have. You are going to have to run a series of well controlled experiments to really understand what is going on. Assume all of your present data is bad.

With regard to your question (b), we are not prepared to say that you have a problem with your storage at this point time.

Let us know how you make out with your tightly controlled experiments.

Kindest Regards
Peter J. Stewart-Hay
Principal
Stewart-Hay Associates
www.Stewart-Hay.com
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Re: Copper Wire Tarnished? 2 years 8 months ago #1441

Very interesting post. If I understand correctly, when the wire is finished annealing and cooled the alloy is bright and shiny. Although, after a few months the wire becomes tarnished but other wires bought fom a supplier lasts much longer than yours manufactured.
This really sounds like an alloy and storage issue. For example, ETP Cu will not oxidize as easily as say grade 2 Cu. If it is storage issue before use, why not use copper paper to prevent oxidation ?
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Re: Copper Wire Tarnished? 2 years 8 months ago #1442

Wire101, Tech1,
My experience with tub or batch annealers, we ran the vacuum pump continuously. I would suspect that if you are intermittenly maintaining the vacuum, that is a potential problem even if it does not contribute to your problem.

When at General Cable we batch annealed the wire, depending upon the number os reels, wire size, etc. it generally took more than 2 days to adequately cool the wire. We could open a tub, and slowly the wire would oxidize and darken. Additionally some times we could send a spool to the redraw machine and it would be shiny on top but as we got into the spool it was discolored. Generally it meant that it was not totally cool. Warm copper will discolor faster than room temperature copper.

A good test, is the hand test. As your hand nears the wire do not put your hand on the wire if you can feel heat radiateing from the wire. If you do not feel heat, them place palm on wire. If you cannot leave it there, then the wire is probablly too warm.

I've seen wire look shiny for a period of time, but if you have high humidity, or if you have fumes from other processes in the air, the wire will discolor.

Maybe you need to visit your supplier to see how they are doing things.
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Re: Copper Wire Tarnished? 1 year 3 months ago #2588

Hi Friends

I am new to this forum but i think i can help you on this matter.

1) Do you have high speed machines for drawing fine wires ?

If yes, do following exercise

1) Produce one batch of fine wire at lower speed in drawing and measure temperature of wire before it gets wound on the drum. The ideal temperature is below 100 degrees depending on atmospheric condition with regards to humidity and temperature.

With my past experience and study for the same kind of problem i found its a phenomenon of inadequate heat dissipation. when you are drawing fine wire at high speed and the temperature of wire is very high. Heat inside the copper wire is not dissipated as it gets wound on the take up drum . Wire wound over a still hot previous wire in a very short period of time is where the tarnishing takes place.

This tarnishing does not happen to the top layer as it stays exposed to atmosphere and heat dissipation is normal. Top layer may become tarnished but after batch annealing it will be bright.

Try this and I think your problem will be resolved. Then, to main machine productivity, repeat this exercise 2-3 times and standardize the temperature of your wire during production. You may have to change the lubricant to get the temperature down. Likewise, check drawing reduction/pass, If possible increase the distance between drawing machine and take off unit with the help of diversion pulleys.

Best Luck

Prashant
Last Edit: 1 year 3 months ago by Peter J Stewart-Hay.
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