Hello everyone

There is a need of your help and your expertise to explain a strange situation which happened in our production. Would you please advise us what could cause the following problem:

A month ago we had a production of a round copper wire with the following specifications:

Wire size : 2.65 mm (0.1043 Inches)
Grade : 2L
Enamel type: PE:642/40P+ OC.720/34S (Elantas)
oven temp. : 430°C
Tangent Delta : 201.4

The first day of production all the tests passed with the best results. The breakdown voltage (VBD) was 5.5 kV up to 9 kV. After two weeks sitting in the warehouse we had a dramatic failure. The break down voltage dropped on majority of the spools. On some of the test results we had a breakdown voltage maximum 2.5 kV and even as low as 0.7 kV. We did not notice anything unusual in the production and we were not able to pin point to anything unusual. Your help is greatly appreciated and looking forward to hear from you. Our factory is Placed near sea. (Humidity is about 60% to 80%).



Kind regards,

Hello Ms Roshandel;

Take a look at this magnet wire thread.

www.wirenet.org/forum/5-electrical/751-i...enameled-copper-wire

Thank you

I assume you are saying that the wire once it has been processed it test good and then after it sits in the warehouse a couple of days it fails.

This is very large wire. I would guess that the operating speed is very low. My concern would be how often are you having to fill the enamel tank. If the tank is 90-120 liters or more it might take a day or so to empty the tank. With 60-80% humidity, I'm guessing that the enamel is adsorbing water from the air and this is affecting the wire. You can calculate how much enamel or varnish you are using per hour and only put what you need for 1-2 hours and replenish frequently. Try this and see if it helps.

Thanks for your information and help. I think that "as you said" we have hygroscopic problem in our enameling process. but one subject is not clear to me. Guide me please:

When we were trying to find the source of this problem, we produced same wire size (2.65 mm) with the same equipment and the same product parameters. Then we placed a full spool in warehouse with humidity around 70-80%. After a week we had a VBD (Voltage Breakdown) . another spool from same product was placed in room temperature with humidity of 40-50% and after a week we didn't have a VBD. can you analyze this phenomena?

thanks a lot

I will be happy if somebody answers my question.

Thanks

Hello Mr Rahati;

Mr. Burke advised you that he expected you would have breakdown voltage problems with high (relative) humidity in the air (60% to 80% RH) during the enameling process itself. The problem was presumed to be the absorption of moisture into the hygroscopic enamel while it was stored in the tank at the enameling machine.

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You have now stated that because of two different relative humidities in two separate rooms, one test spool stored at 70 to 80% RH failed VBD while another test spool stored at 40 to 50% RH passed VBD. Further, it was said that the two spools were from the same production run.

First, the absorption of moisture by the liquid enamel in the tank would take place over a period of time, thus the major questions would be:

1. How long was the hygroscopic liquid enamel exposed to the high relative humidity before it was applied to the wire for any particular spool of enameled wire?
2. Did the relative humidity in the air stay constant while the production run was performed?
3. Because you are drawing conclusions from a straightforward experiment with only two spools of enameled wire and unless you have the first two questions and any other variables under under tight measurement and / or control; we wonder:
   • (a) If you are using two consecutive spools of wire from the same production run?
   • (b) If other production variables were unchanged (Such a refilling the enamel tank on the enameling machine.) between the two production spools of wire?
   • (c) If you well understand and can perform Weibull analysis (Statistical conclusions from very limited amounts of data.)?

It may indeed be possible that your two spool data might not be particularly relevant.

We therefore suggest that you have your plant immediately organize to significantly reduce the time the hygroscopic liquid enamel is exposed to high relative humidity air. There are of course a number of ways to accomplish this. After a few of weeks of good production, you should end up with very tight control on enameling under high relative humidity conditions.

A written Process Specification appended to your ISO program would certainly be a great way to completely eliminate this particular production problem in the future.

After some longer period of time, we ask that you let us know how your plant made out with these recommendations. Good luck and thank you.