Cu wire oxidation (discoloration)

Dear colleagues,

We produce copper wire (bare wire) and supply for cable manufacturers and also (tin) can welding applications.
Currently we get information from customer about wire oxidation. ( We call it discoloration.)
Discoloration is not complete and not continuous but spotty only.
We suspect (the discoloration is) due to remain(g) emulsion ( water + oil use(d) in the annealing system) on (the) wire surface and (that) causes (an) increase(d) oxidation rate and results in discoloration.

We have system to wipe off remain emulsion on wire surface but we suspect this system not always effective (and) that is why sometimes there is discoloration.
We have procedure to check wire surface dryness by contacting a very thin paper on (the dried) wire surface during process. ( This is done several times in every box/bobbin/basket). If there is trace of emulsion on paper surface, we decided wire was wet but further work is needed to determine if discoloration results.

We think this method not (adequate) because there are discoloration complaints from our customer.

My colleagues, perhaps you have had same experiences and already determined effective counter-measures. Please share your experiences with us.

My thought would be to apply such a instrument to measure/sense (continuously) emulsion on the wire surface and also to be able to measure wire temperature. We also suspect that wire temperature has role on oxidation rate. Higher wire temperatures will increase oxidation rate.
Perhaps you can share information about this thought.

Comments and advise are welcome. And thank you in advance.

Best regards,

Ganda Sirait (Mr.)

Dear Mr. Sirait,

Discoloration of the wire surface is usually by contamination of the wire surface during the compressed air wiping of the wire after annealing. There are six points here:

1) The annealer air wipe air pressure is turned up so high that moisture on the wire is spraying about and recontaminating the just cleaned and dried wire surface.

2) The annealer air wipe is just ineffective by design or that it is just worn out and needs to be replaced.

3) The drawing solution is somehow in contact with the just drawn wire and is spraying about. Revise the mounting of the exit drawing die and it's air wipe.

4) You have a poor air supply for the air wipe at the annealer. Make sure you have an adequate clean, continuous and controllable dry air supply.

5) Control your drawing solution so that the holding tank remains at a temperature lower than 55C or 130F. Talk with your drawing solution supplier about this so your system is in full compliance with their current recommendations. Have them visit and view your system. Make sure there are no copper soaps being formed.

6) Inspect your copper rod supply to ensure the rod surface is properly cleaned.

Thank you very much for replying and sharing information about discoloration.
I need more explanation for some points:

1. Actually wire flow vs spray air flow is counter-current to minimize wipe off moisture (liquid) contact again with dried wire surface --> we will check whether this condition running properly.

If you don't mind please inform me range of air wiping pressure. In our case we use 2 till 3 bar.
And may be you can share vendor name for air wiping technology so I can discuss further more with them and if possible to purchase their technology/system.

2. We have plan to reduce diameter of cooling dies ( system of dies + air wiping) to improve wiping. We think that lower gap between wire and inner diameter of cooling dies will increase air wiping effectiveness --> any comment about this thought?

3. We will check

4. Currently compressed air passed through air dryer and we control dew point, and along piping heading to air wiping system in annealler we install water trap and conducted water drain intermittently (controlled by timer).

5. Currently we controlled drawing solution temperature about 30 till 55 oC, and average about 40oC.
About copper soap, please let me know whether there is analysis method to control. Frankly speaking I do not know what is copper soap looks like. Please do not mind to share.

6. Actually we controlled quality of Cu rod supply in term of: roughness, flaws (with ECD), residual oxide surface (ROS) and also discoloration. In this case there is no abnormality on those items.

Thank you very much for your attention and consideration. Please do not mind to reply.

Bets regards,

Ganda Sirait (Mr.)