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Grain Size
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Nonferrous topics such as copper and aluminum, annealing, etc. go here.
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TOPIC: Grain Size

Grain Size 2 years, 3 months ago #1610

I have two queries :

01. Does grain size of copper in magnet wire
affect its windability or softness ?

02. If yes , then what should be ideal grain size
of copper conductor in 1.00 mm and 0.800
mm magnet wire?

Re: Grain Size 2 years, 3 months ago #1611

Hi there,

The answer to your first question is yes, grain size is a factor affecting the flexibility of copper wire. Unfortunately it is only one of many variables and I have never personally come across a technical paper relating grain size to the mechanical properties of a particular diameter of copper wire. Perhaps others will give us more information.

There was a paper in the October 1991 (Page 91) edition of The Wire Journal International titled "The Effects of Deformation and Annealing Conditions on the Flexibility of Copper Wire" by Y.T. Kim, J.Y. Jang, C.H. Kang, and K.H. Hahn, all of GoldStar Cable in Korea. It focused on bare copper wire destined to become magnet wire.

The header for the paper states "The amount of deformation before annealing should not exceed a critical value, because severely deformed copper wire is hard to recrystalize."

I recommend you purchase a reprint of this paper and carefully read it. You can order a copy of it by sending an E-mail with the full title of the paper including year, month and page number to This email address is being protected from spambots. You need JavaScript enabled to view it.

Kindest regards,
Peter J. Stewart-Hay
Stewart-Hay Associates

Re: Grain Size 2 years, 3 months ago #1612

It would be nice if Horace Pops or Wright or someone like them would sign in.

I think that the grain size is less important than the organization of the grain. There were some papers explaining inline wire drawing enamelling and it explained why it works and the importance of grain organization. When it is right you get better tensile strength and better ductility.

Re: Grain Size 2 years, 3 months ago #1613

The following response to the discussion thus far comes from WAI Past President Horace Pops:

My comments are based upon the assumption that the use of the word “organization” should actually be “orientation”, which is a term usually associated with annealing textures that form within conductors.

Both grain size and orientation affect the mechanical properties of annealed specimens. In the case of copper, which is very anisotropic, lower tensile elongation and LSE, coupled with higher springback occur when the final reduction in area exceeds about 90%. This practice is harmful to the performance and windability of finish magnet wire. The aforementioned properties are directly dependent upon the specific annealing texture, which is affected by the amount of cold work prior to annealing. Poorest properties also occur for aluminum at similar high reductions. In contrast to copper, however, the decrease in elongation, windability and LSE with increasing prior reduction is attributed to the resulting finer grain size.

Marc Murray
Proj. Mgr., Technical Dept.
The Wire Associational International, Inc.

Re: Grain Size 2 years, 3 months ago #1614


I was posting late in evening and I did mean orientation. There was a paper written about 1967-69 by a BICC engineer discussing inline wire drawing as it relates to magnet wire. If I remember right you supposedly used a supply wire which you could reduce between 35% and 85%. If you reduced less or more then you should have a different size supply. the nice part about inline wire drawing was that you could have an enameling system that could coat 18 to 28 AWG and would only need perhaps 3 different sizes of input wire. Without inline you would have needed an input size for each finished size. You also have bigger payoff packages and slower payoff speeds.

Also when done right, the finished enameled wire had a higher tensile strength and better ductility or a lower spring back value.

The explanation was that the orientation of the grain and the size was uniform??

Re: Grain Size 2 years, 3 months ago #1615

"The Metallurgy of Copper Wire", a paper by Dr. Horace Pops in December 1997 can be found here:
It discusses the 90% reduction in area without intermediate annealing as well as some of the factors influencing grain size.

Kindest regards,
Peter J. Stewart-Hay
Stewart-Hay Associates
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