HOME FAQs BOOKS JOBS: Help Wanted Suggestions      you are here: Hotline/Forum => Letter 15043

---

Annealing of copper wire blackens it

++

Dear Sir,

We are manufacturing copper uninsulated wire used for electric cable and also super enamel insulated wire. The size of the wire varies from SWG 1 to 32. We are facing a problem of having the wire oxidized/blackened soon after bringing it out from annealing Chamber. The annealing Chamber is of vacuum type having Induction coil to heat the copper wire. The Vacuum that can be applied to the Chamber is 500 mm Hg while the temperature approx.800+ centigrade. Please note the Chamber does not have any temp.meter. This is the process we are following to anneal the Copper wire. So, may I request to let me know how we can get rid of the problem of getting the wire oxidized/blackened in course of annealing.

Hope to hear soon.

Thanking you,

M.SADEK
- Dhaka, Bangladesh.

---

++

Try letting the copper cool in an inert atmosphere before exposing it to air.

Trevor Crichton R&D practical scientist The Pheasantries - Chesham, U.K.

---

++

Alternatively let it cool in the vacuum environment used for the annealing.

Bill Reynolds    consultant metallurgist Ballarat, Victoria, Australia It is this website's profoundly sad duty to relate the news that Bill passed away on Jan. 29, 2010.

---

+++++

We are facing the same exact problem and I thought it has something to do with annealing current / voltage ...we uses stainless steel cylinders for annealing.
(not nickel coated as usual ..)

any idea ?

Amir Sharon
- Israel

---

++++++

You have not mentioned the quantity of your batch for annealing and also the kilowatt rating of induction heating. You have to also mention the cycle time of heating, soaking and quenching. What is the sealing mechanism used during annealing to prevent outside air entering. Without temperature indicator, how did you measure the temperature of your batch during annealing continuously?

Balasubramanian Venkatraman
- Navi-Mumbai, Maharashtra, India

---

+++++++

WE ARE MANUFACTURING COPPER TUBE, TO BE USED FOR ELECTRICAL TERMINATIONS. WE CONTINUOUSLY CAST THE TUBE , THEN DRAW THEM DOWN ON LONG HYDRAULIC BENCHES.

AFTER SEVERAL DRAWS, THE TUBES BECOME TOO HARD AND SNAP. WE LOAD THE TUBES (ON AVERAGE 2 TO 3 MTR LENGTHS) ON TO A RACK.
ROLL THE RACK INTO A ELECTRIC ELEMENT FURNACE (3.4 MTRS LONG)
WHEN THE TEMPERATURE REACHES 550 DEG C THEN THE RACK IS REMOVED,

THE TUBES ARE LIFTED OUT OF THE RACK USING CHAINS AND A HOIST AND THEN LOWERED INTO A WATER BATH TO QUENCH

WE ARE LOOKING FOR A MORE ACCURATE WAY OF ANNEALING TO IMPROVE OUR QUALITY AND PREVENT CRYSTAL REGROWTH.

ARNE HERZ
ENGINEERING - JOHANNESBURG SOUTH AFRICA

---

December 30, 2008

We manufacture Hot dipped tin plated copper wire. After drawing the wire the elongation is about 12 to 15%.

We use vacuum annealing furnace. The heating is carried out using diesel burner & it is controlled by electrical circuitry to control the temperature.

The temperature raised & is maintained @ 250 C & the duration is about 2 Hrs. Burners are switched off automatically at this time.

The furnace is kept under vacuum containing copper wire, until the temp. drops down to ambient.

The elongation of copper wire after the process is about 25% to 28 %.

Can any one guide us to achieve more elongation Say about 35 % max. ?

Sudheer Shedbalkar
mfg. hot dip tin plating - Pune, Maharashtra, India

---

January 8, 2009

Try faster cooling .

Cair Shishani
aircraft maintenance - Abu Dhabi, United Arab Emirates

---

March 29, 2009

we r a cable manufacturing company n want to know how copper can be annealed and to what temperature ? is there any cooling curves to follow or is there any need for a vacuum furnace to put in so to avoid oxygen contamination ? please give us useful sites for this respect ..thanks a lot

Eng.Amjad Qade
employee - Kuwait

---

January 14, 2011

I am doing copper wire annealing in vacuum, my problem is copper looses its reddish color after annealing.
Vacuum: 760mm of Hg
Chamber temperature: 500 degree celsius

I also tried annealing using nitrogen instead of vacuum. But the result is same. Although annealing improves.

Can anyone suggest me how to maintain copper color during and after annealing?

How should I use nitrogen for annealing? At what temperature should I use nitrogen? And up to which temperature should I heat the copper wire.

Anuj Jain
- Delhi