Copper Wire Tarnished?

Hello again Eddy,

The formation of cuprous oxide is a function of both temperature and the concentration of oxygen in the atmosphere. The warmer the temperature, the faster the formation of cuprous oxide. At room temperature (20C) and at the standard concentration of oxygen (21% by volume), copper oxide will still form but it does take a longer period of time.

We never removed reels of copper wire from our bell annealers until the copper was back at room temperature, both in the center of the wind as well as at the surface. Saying this however, our schedulers would have been fired if they held any inventory of drawn and annealed copper for a total period longer than say 10 days, including holidays. (Just in time scheduling.)

Smaller wires like strands for bunched wire were always electrically annealed in-line, immediately after drawing.

We strongly recommend that you carefully reread the manual/ operating instructions that came with your vacuum annealer.

Kindest Regards
Peter J. Stewart-Hay
Principal
Stewart-Hay Associates
www.Stewart-Hay.com

Hello Peter,

Thank you your response. Please advise again with my doubts.

"Perhaps you haven't purged all the air from the vacuum annealer. (First obtain the vacuum and then let it sit for a period of time to see if the vacuum changes slightly"
As the temperature rises, the drum annealer pressure will drop slightly to 60cmHG and we have to re-vacuum the drum to the max of 75cmHG. We have to do it once every time throughout the annealing process and the pressure will maintained at 75cmHG after that.

Is there a specification to as how much pressure has to be reached for a certain amount of load or volume?

I have another question. Please correct me if I am wrong, copper starts to oxidize at around 200C, which is the reason why we need to isolate the wire from oxygen during annealing to prevent the formation of oxides, thus maintaining the shine of the copper. In this case why is it when we remove the wire from the drum annealer, the shine of the copper changes more rapidly if it is still warm? (Say around 50C - 60C)

Is there an ideal temperature that has to be maintained to prevent the formation of copper oxides?

Hello Eddy,

First of all, please read the following thread at the Forums so we are all speaking with the same terms:

www.wireassociation.com/forum/viewmessag...m?Forum=12&Topic=387

You seem to be having have a problem with cuprous oxide (brownish reddish color) for some reason and it does indeed have something to do with your manufacturing process because your supplier's wire does not exhibit the same problem.

Perhaps the core temperature of the annealed spools of copper wire is still too warm when removed from your vacuum annealer and oxidizes over a short period of time. Perhaps you haven't purged all the air from the vacuum annealer. (First obtain the vacuum and then let it sit for a period of time to see if the vacuum changes slightly

Regards
Peter J. Stewart-Hay
Principal
Stewart-Hay Associates
www.Stewart-Hay.com

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

Dear Mr. Sankhe,

Thank you very much for sharing the information.
I am very interesting about controlling wire temperature which is ideally below 100 C.
Please share about :
- Where temperature checked? at spooler (after full bobbin or we called it counter) or inline ( on wire during process, come out annealer and before spooler)
- What kind of instrument use (please share us brand and maker)

In our case we check wire temperature with touch type (probe). Probe touch into Cu wire surface after counter.

I hope you do not mind to share your experiences.

best regards,

Ganda Sirait (Mr)

Thank you for this information. I didn't know anything about this topic. I'll definitely like to read up more before I can take action