Hi Richard,

In the world of plastics; thermoplastics do not cross-link and thermosets do. This means that thermoplastic materials deform when reheated but cured (cross-linked) thermosert plastics do not. Indeed, one type of thermosetting plastic cures in the ambient air, in a steam bath or immersed in hot water and this is generally called a moisture cure thermoset.. The chemistry to do this is a bit complicated but it works very well, mostly for low voltage applications. Ambient air moisture cure thermosetting plastics can continue to cure over an extended period of time.

As far as magnet wire is concerned, and because I have no strong expertise in this area, I take my direction from what you say..

I just assumed that the magnet wire enamels used the same thermoplastic/ thermoset definitions in the same fashion as the plastics do. That however does not mean a drop in the dielectric strength as time goes by. Your fracturing and cracking theory certainly seems plausible but I find it quite troubling..A loss of dielectric strength by an increased degree of cross-linking seems quite alien to me and my first reaction would be that there was something very wrong with the batch of enamel that was used.

Peter

Hi every one

I think it's better to have a summation. Please look at the attachment and if possible answer briefly for each of states.

Thanks a lot

General informations:
copper wire : size 2.65 mm
enamels type : (base coat : polyesterimide) and (top coat : polyesteramidimide).
test parameter : BDV

Hello again,

First, I'm not sure I completely understand your "pdf" presentation graphic.

1. I presume green designates a pass in the breakdown voltage test. Does orange indicate a failure?
2. What does the heading "status" on the left hand side refer to? The whole situation?
3. Do the numbers "1 through 8" refer to individual spools of magnet wire?
4. How did you determine that samples 5 through 8 had no moisture in the liquid enamel?
5. On the BDV test time columns where are the BDV test results "After two weeks or more storage" for those that passed BDV "immediately after production"? (Items 1, 3, 5,7)
6. All orange color coding should be changed to white to the left of the columns under "BDV test time"
7. Similarly all green color left of the columns under "BDV test time" should be changed to white
8. Place "Status" above the metric and place something else in that title area like "Sample Number" or "Spool Number" Likewise, underneath the metric, please describe what the color coding all means.

Other Questions

• a) Is your top coat description "polyesteramidimide" also known as "polyester-amide - imide", "polyester amide -imide" and/ or perhaps "polyesteramide - imide"?
• b) Likewise is your base coat described as "polyesterimide" also known as "polyester-imide"?
• c) Are both these enamels "Bondable"? See www.mwswire.com/inschar.htm
• d) Are you using aluminum conductor and if so how do you make sure it is absolutely clean before the enameling process?
• e) Have you talked with the chemical people at your enamel manufacturer. What are they saying?

Thank you.

Hello again,

First excuse me for Weaknesses in writing because I'm learning the language. I'm sorry that I was not able to fully pass my purpose. I hope the issue can be clarified with fallowing descriptions:

The theory: based on the above there are three key variables affecting on voltage drop

• 1 - The liquid enamel (with hygroscopic phenomenon or without hygroscopic phenomenon).
• 2 - The humidity of storage area.]
• 3 - The storage time before testing BDV]

Regarding your questions:

• 1 - The green and orange colors in the table ]have no meaning
• 2 - The heading "status" on the left hand side refer to different states that may occur.
• 3 - The numbers "1 through 8" don't refer to individual spools of magnet wire. Each row must be considered as a separate state that may happen during production.
• 4 - The lack of moisture in the liquid enamel (rows 5 -8 ) is only a hypothesis and this situation may exist in the enameling process.
• 5 - Please interpret each row as below
• a - Row "1 " must be read : What will be the result of BDV test immediately after production on spools with enamel contain of moisture (hygroscopic phenomenon) and stored in a location with relative humidity at 70-80%.
• b -Row "2" : What will be the result of BDV test after storage two or more weeks later on spools with moisture( hygroscopic phenomenon) and stores in a location with a relative humidity at 70-80% .
• 6 - Base coat enamel description is : (Elantas, Polyesterimide Deatherm E 642/40P) www.elantas.com/elantas-italia/products/.../polyesterimide.html and top coat description is (Elantas, Polyamideimide Deatherm I 720/34S). www.elantas.com/elantas-italia/products/.../polyamideimide.html
• 7- Both these enamels are not bondable..
• 8- We are not using aluminum conductor..
• 9- We talk to the chemical people at our enamel manufacturer and they suggest we change our enamel to improve the tangent delta !! .

Please note that this all shows us that the moisture is the reason of our problem but we don't understand why when we store the spools (with good BDV after production) in a place with humidity of 70-80% we face BDV problems a few weeks later.

We control the relative humidity during the enameling process and in the enamel tanks but we have these questions and/or concerns:

• a - We don't know if we can store the finished magnet wire spools in a location where the relative humidity is over 70%.
• b - On the other hand, if we produce very good magnet wire spools (good BDV) and store them in any location for a few weeks, will be still have good BDV?
• c -Why is this phenomenon occurring? Is it related to thermoplastic or thermoset characteristics?
• d - Why when we re-pass the magnet wire spools with bad BDV results through our oven again, we don't have a bad BDV?! and,
• e - Why when we take same spools that have been re-passed through our oven and store them in a place with over 70% relative humidity for a few weeks, they will have a bad.BDV?

Thanks a lot

Hello Again,

I'm at a point where I am not sure what to tell you anymore. However I do want to repeat a couple of points that Mr. Burke made. He is of course a magnet wire specialist.

"Whenever you have a problem with a purchased product you should call your supplier, tell them your problem and ask why? I assume that they still keep samples of each batch of enamel and should be able to pull a sample and evaluate it. Magnet wire can be damaged by physical stressors, electrical stressors, and environmental stressors. An environmental stressor would include storing it in a warehouse that has an "open air" environment."

"I think what might happen is that there is incomplete cross-linking (curing) but at the time the wire was pulled from the machine it looked good and met all properties. If then it continues to cure while sitting on the shelf and since the wire tested good when it was not properly cured, now when you start making coils you may have cracks and fractures in the insulating film." There seems however to be a contradiction with this second point because the breakdown voltage improved once the bad magnet wire was run through the oven again. Later it again failed when stored in a high humidity environment as you advised.

I did as well note the following on magnet wire manufacturers web sites. " The enamel on the magnet wire surface is very stable in ambient environments. Storage in any dry, room temperature environment will ensure the best shelf life. Bare copper and silver items react to oxygen and other trace elements in the air. To slow surface oxidation on bare or plated items they are packaged in anti-tarnish wrappers and plastic bags."

"The enamel on the magnet wire surface is very stable in ambient environments. Storage in any dry, room temperature environment will ensure the best shelf life. Bare copper and silver items react to oxygen and other trace elements in the air. To slow surface oxidation on bare or plated items they are packaged in anti-tarnish wrappers and plastic bags." You may wish to consider storing the finished magnet wire spools inside very low relative humidity, sealed plastic bags along with a small dessicant filled pouch to keep the relative humidity down inside the bag...

We also noticed:the following statement.

"Magnet wire shelf life is not established in commercial specifications. As long as the wire has been carefully stored it may be usable for years to come. Bondable wire should not be stored at temperatures exceeding 100°F"

Your problem is indeed a puzzlement for us and it may very well be a true chemical issue that we do not have the training or experience to resolve. Elantas however is a very good company and it is worldwide. Your best bet in resolving this problem is to work with Elantas. It may mean that you have to change enamels, modify your method of storing magnet wire or both. I think you are at the point that you need a well experienced Elantas chemist at your plant ASAP.

I feel that we have failed you and I apologize for that but it seems that your issue is a very specialized, possibly chemical problem with your selected magnet wire enamels when the finished product is stored in a high relative humidity environment. Please let us know how you resolved the problem because it is certainly one for the books.

Thank you.

Peter if you go to the ollowing webesite or the references you can ge a good expnation of how some materials can be in either form.

www.polymertechnology.com

Chemical Economics Handbook, SRI International, Modern
Plastics Encyclopedia, Whittington’s Dictionary of Plastics, The Condensed
Chemical Dictionary, The SPI Plastics Engineering Handbook, The Story of
the Plastics Industry (SPI).