Annealing of copper wire blackens it
A discussion started in 2002 but continuing through 20182002
Q. 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.
- Dhaka, Bangladesh.
A. Try letting the copper cool in an inert atmosphere before exposing it to air.
R&D practical scientist
Chesham, Bucks, UK
A. Alternatively let it cool in the vacuum environment used for the annealing.
Ballarat, Victoria, Australia
We sadly relate the news that Bill passed away on Jan. 29, 2010.
Q. We are facing the same exact problem and I thought it has something to do with annealing current / voltage ... we use stainless steel cylinders for annealing (not nickel coated as usual).
A. 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
Q. 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) ONTO 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.
ENGINEERING - JOHANNESBURG SOUTH AFRICA
December 30, 2008
Q. 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 and is maintained at 250 °C and 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. ?
mfg. hot dip tin plating - Pune, Maharashtra, India
January 8, 2009
A. Try faster cooling .
- Al Ain, UAE
March 29, 2009
Q. We are a cable manufacturing company and 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 lotEng.Amjad Qade
employee - Kuwait
January 14, 2011
Q. I am doing copper wire annealing in vacuum, my problem is copper loses its reddish color after annealing.
Vacuum: 760 mm of Hg
Chamber temperature: 500 °C
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.
March 1, 2012
A. Annealing should be done at a temperature just below melting point. I would anneal copper to glowing red hot (about 1000 ° C). The hotter the better because you're charging the metal with energy to free the particles and remove any spring tension.
After annealing run the copper through an acid bath to clean it. I use sodium bisulfate, but sulfuric should do the job. That will remove the oxide.
student - New Zealand
October 27, 2012
Q. My problem is of annealing 0.254 mm copper wire bundles of about 5 to 6 kgs. I am annealing at 250 degree, duly monitored. This annealed copper wire is further drawn to 40 SWG and then silver plated. Silver plated copper wire is further drawn to 52 SWG, at this stage it felt that copper wire is not annealed properly or you need better annealing. Please help me by providing best possible temp of annealing copper of 0.254 mm dia. so as to get acceptable result at all level when it is further drawn to 52 or 55 SWG. Regards.jayantilal Jain
prathamesh copper - Pune, Maharashtra, India
Copper wire remains hard after annealingJuly 30, 2017
Q. I annealed copper wire in a pot of weight 400 kg, quantity of wire of all sizes is 600 kg. temperature given is 290 °C for 5.5 hours but wire elongation is not satisfactory. Please guide me.mayank bansal
Annealing of copper discolors itJanuary 17, 2018
annealed copper wire, 2.60 mm in diameter. This was annealed to 240 degrees in 4.5 hrs. Elongation is 34 to 37%
I work in a copper wire manufacturing firm. Though we also have the continuous resistance annealer coupled with our wire drawing machines, the need to use the older pot annealer is still in demand for big sizes above 2.0 mm dia. My problem is copper wire become reddish to brown color and also, portions of full bright perfectly annealed copper in section of the reel.
Our pot annealer is vacuum above 50 cmhg and can be set to reach 1000 °C. Any experienced and ideas shared from you guys will be highly appreciated. Thanks.Edgar Tabelin
Cpic - Metro Manila, Philippines
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