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Magnet Wire Failing In PinHole Test

7 years 2 months ago #273 by Archived Forum Admin
Some comments and thoughts:

1. The problem is latent IE it is not evident at the time of manufacture. The problem is probably there, you just have not been able to identify it. If you are referring to the pin holes that appear 7-10 days later, there is no way that they can mysteriously appear 7-10 days later.

2. It is most probably not due to insulating enamel or the enameling process (some of the wires that fail have been processed on enameling machines have catalytic systems) I have a pretty good understanding of catalyst and I can tell you that as far as your problem as you have described it, there is no reason why a catalyst would or would not make a difference. I’ve said before, if have a good enamel and decent bare wire, and a reasonable work environment, a good magnet wire technician could make good wire using toasters! More importantly he would not have mysterious pin holes appear.

3. Apart from salt water continuity of covering defects, the problem does not manifest itself in any other low reading, IE the BDV (Breakdown Voltage) values, peel, adhesion, cut through heat shock etc are all found way above minimum required levels. This is how that test is conducted: When the magnet wire coils are placed into the salt water-phenolphthalein solution, the presence of pinholes will allow electrolysis to occur. The change in pH will result in the salt water turning pink at the pinholes, thus indicating the presence of pinholes. Are you seeing “pink” or air bubbles?

4. The drawn copper surface is very bright and shiny to the naked eye and under 10 x magnification is reasonably good and without any major indentations or marks Reasonably good is a suggestive evaluation and is not objective. At 10X magnification you should see most everything: how long a sample are you looking at?

5. There is visual evidence of higher than usual generation of copper dust. If there is evidence of a higher level than usual, then you should be checking what the conditions were when there was less dust. You’ve said the wire looks reasonably good – did it look great when there was less dust? I would take a serious look at my wire drawing operation. See other comments with Peter’s! Are you seeing this dust before or after it passes through the pre-annealer?

6. The problem is more acute during rainy season. Some enamels are hygroscopic – most are some more so than others. You can control this problem some by keeping enamel tanks covered, don’t put any in buckets and let sit waiting to be used, and minimize the amount of enamel in the tanks near the oven.
Awaiting your inputs,

Peter’s Comments:

1 If you are really sure that your issue is indeed a unquantified "higher than normal" amount of copper dust somehow attached to the surface of the copper wire, you had better go back to first principles of the drawing process itself because all of your mechanical surface cleaning devices at your ovens are not getting to the root cause of the problem. Further, blowing hot air on the surface of the wire is nothing more than a way to blow copper dust and other contaminants into the air and this could contaminate the outer surface of the just applied enamel before the wire enters the ovens. Peter is exactly right here. The purpose of the pre-annealer is to clean the wire and pre-anneal it. The annealing process is mostly provided during the multiple passes the wire makes through the enameling oven. You are not inline drawing so keep in mind that when you draw the wire the surface defects lie down in the direction of from the wire first put on the spool toward the end of the full spool. When you feed this wire into the enameling system it is reversed and what sometimes happens is the heat in the annealer causes the surface defects to pop up and when that wire goes through a wipe or even the die, the surface defect flips back or breaks off leaving a surface defect generally in the form of small irregularly shaped crater. Sometimes it will also hold micro-droplets of water from the annealer water bath if you have one or from the steam if you inject it into the annealer.

2) Regardless of whether you have installed a centrifuge for the filtration of wire drawing lubricant or not, the reality is that essentially all copper wire has to some degree or another a thin film of dried drawing lubricant on it and that there will be copper fines embedded in that film. Thus copper fines can always be found by using a wipe of hard white felt or some other form of clean wire wipe at the next downstream operation. (A weighted down, very hard white felt is commonly used to prevent felt fibers from being carried along with the wire.) I know lots of people have had great success with centrifuge type filters but I have not. I would take a serious look at my drawing machines – if they are too clean you probably are lacking lubricity and if too dirty then it makes the wire harder to clean. You cannot put a wipe on the wire and never change it. We used sanitary napkins – purchased by the thousands- and the machine operator moved it often during spool fill up and replaced it with every spool. Once the wipe gets really dirty it become a copper paste applicator!

3) The copper dust on the wipe is always mixed with the dried drawing lubricant film in the form of a copper paste and there can be more or less dust on the wire by virtue of the health of your drawing fluid itself. This is something that I have experienced first hand at a very large data cable plant that really should have known better. In that case, and even with a new lubricant charge, the emulsifier in the drawing fluid had begun to break down and that lead to much more copper dust on the surface of the wire. The solution was to dump the whole system and start again but this time properly. We discussed numerous times quick ways to check the lubricant: if it smells bad it probably is (I know that is a subjective test and no offense intended, works better in some countries than in other.) Another quick test is if your hands are dirty, if the lubricant has any emulsifiers left you should be able to wash your hands clean in the lubricant! I have found that wire drawing lubricant is the source of most problems in a drawing mill because it can change so fast. I never worried about % fat as long as I was drawing good wire. I almost always operated at a higher than suggested % plus every day we added some fresh lubricant to maintain the desired parameters. Sometimes we ran the compete lubricant tests a couple of times a day as we made adjustments. We’ve previously mentioned using a stainless rod to test your lubricant- if the lubricant opens up on the rod then it is not wetting properly if it rolls back similar to rolling a sock off your foot, and has minimal holes, then it is probably OK. pH is especially critical.

4) The whole game is therefore to minimize the amount of copper wire surface contamination to an acceptable level for your downstream process.

I have spent a fair amount of time in your country and my first suspicion is that your drawing fluids may not be as well managed as they should be. I am in full agreement with Peter on this – most companies underestimate how important lubricants are!

5) The water for your drawing fluid is often trucked to a plant from a well somewhere in the region if not on site, so the start is to exclusively use deionized water as a base for your drawing fluids. Moreover the tanks must be completely cleaned out from the previous lubricant charge before creating and using a new drawing fluid. I am in full agreement with using deionized water. We once received water from the city and they had 3 different sources: river water, well water, and cistern and our lubricants reacted differently with each source. A deionizer solved a lot of problems!

6) After mixing up the new lubricant, there must be proper and tight management of your drawing fluid which means pH control, temperature control, % fat concentration monitoring, detergency, tramp oil contamination monitoring and so on. Long term data and graphical information should be available on your computer local area network for all to see and be aware of. Tight control and frequent checking and monitoring is a must!. Once you have established what works best for you – maintain it. Temperature control is important because it can cause your lubricants to invert or split and that is not good.

7) At the electric annealer, use deionized water with no lubricant in it. Moreover the air going to the air wipe should be clean and dry meaning desiccant drying medium and then high quality filtration at the annealer. Air wipes are not often used on enameling machines however if you are using one, the air needs to be dry and also OIL free! Deionized water to the annealer quench tank or steam generator is also a must thing to do.

8) We cannot comment on the phenomenon of more problems during the rainy season because we do not know if you are referring to the perceived degree of copper dust on the surface of the conductor before enameling or the wire failure rate after enameling. In any event, don't use air wipes to blow copper dust off the surface of the wire. Again some insulating enamels are hygroscopic and if tanks, buckets, etc. are open to the air which they generally are in most plants, they will absorb moisture from the air.

9) Finally we recommend that you purchase WAI's "Nonferrous Wire Handbook, Vol. 3" from www.wirenet.org/waistore/productdetail.cfm?productid=14 just as soon as you are able and use this 704 page handbook as your company's definitive reference book for drawing and drawing lubricant problems and issues.

Additional Thoughts:
1. Are your insulating varnishes thermoset or thermoplastic?
2. Using your 10X magnification are you able to see copper flakes or dust in the insulation on the finished wire?
3. Have you taken failed samples of wire and examined the site of the pin hole failure and determine if it is something in the insulation or is it a surface defect on the conductor. I’m betting you haven’t.
4. I go back to my comment on processing aluminum wire.
a. I would isolate the first enamel pass, keep the enamel from the first pass separate from the second and additional passes.
b. I would scrap the enamel from the first pass – not let it return to supply, be filtered and reused!
c. I would get better enamel filters and make certain that the enamel was pumped through the filter before it was applied to the wire.
5. I would take a serious look at the finished wire that is failing the test. In theory, what happens is the test solution creates a chemical reaction to the bare copper causing either a pink color or an air bubble, I suspect that there is copper dust in the enamel coating and some of it reacts to the test solution and it looks like it is failing. Not sure how you are passing high voltage dielectric if it is this or real pin holes?

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7 years 2 months ago #250 by Archived Forum Admin
Couple of thoughts;

You have fairly old equipment that does not have heat recovery or pollution reduction. Do your ovens recirculate the air or is it just exhausted out one end of the oven? With a dv of 15 for about 1 mm wire that equates to about 50 feet per minute which is not particularly fast.

If your air only passes through the oven once then you are always drawing 100% fresh air into the oven. Recirculating ovens typically exhaust about 10% of the air which means they draw in about 10% of the air.

This is significant if you have high humidity. Some wire enamels or varnishes are hygroscopic meaning that they will adsorb moisture from the air. This moisture is in form of microscopic droplets of water. Since water does not mix with enamels that are not water based, these droplets are applied to the wire and since water evaporates at a higher temperature than most solvents used in enamel, they become trapped bubbles and, as the wire is heated, the bubbles burst leaving pin holes. Sometimes the next coat of enamel will cover the pin hole(s) and if you get lucky, the wire passes. You can also get pinholes if you get entrapped solvents in the enamel and same thing happens as mentioned with the moisture.

I am not certain how:

a) Pin holes can naturally occur 7 – 10 days after manufacture. I think that they are already there because of the moisture that gets in the enamel.

(b) At the same time I am not sure how months later the wire that failed earlier can now pass. Some enamels continue to cure while sitting on the shelf but that should not cause pin holes to close.

If you had a lot of pin holes that would lead to poor BDV test results.

Think of it like this, you are forcing a high voltage into the wire.

- If the insulation is good and defect free, you can continue to increase the voltage until it is very high and exceeds the ability of the enamel to insulate.

- If you have pin holes that means that there is less enamel insulating the conductor at that point. As you increase the voltage a failure occurs because you have exceed the ability of the defective coating to insulate. This usually occurs at a voltage that is well below the required level. Not an unusual event for wire with pin holes.

I think that in your case you might need to talk to the enamel suppliers. Enamels have evolved a lot and so have machine speeds. A dv of 40-70 and faster for 1 mm wire is not unusual. Enamel suppliers like to provide generic enamels, not enamels to meet every customer’s needs. I suspect that the operating characteristics of your enamels are out of sync with you ovens due to design, age, etc.


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7 years 2 months ago #251 by Archived Forum Admin

Some information for those of us not in the magnet wire segment of the wire and cable industry:

"dv" is also known as "vxd" is the product of the coating speed in meters per min and the magnet wire nominal diameter in millimeters. Thus the higher the value of "vxd", the more effective the enameling machine.

For example: If the coating speed was 120 meters per minute and the wire nominal diameter was 0.5 millimeters, the "vxd" would be 120 x 0.50 = 60. Now if you wished to know the coating speed on this very same machine for a wire nominal diameter of 0.30 mm the answer would be (vxd/d) = 60/ 0.30 = 200 meters per minute.

"BDV" is an acronym for the breakdown voltage.

Peter J. Stewart-Hay
Stewart-Hay Associates

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7 years 2 months ago #252 by Archived Forum Admin
Dear Richard,

Thanks for the fairly detailed response. Let me try and respond the the queries point wise :

One hypothesis that even I was having was that due to the presence of moisture in the atmosphere and due to the hygroscopic nature of enamels; microscopic water droplets could be trapped and escape later causing pin holes. Alternatively solvent trapping could also be one of the causes.

My response to this is that if there was water or solvent trapping the tan delta curve/value should show the same. We were not able to get any clue from the same. I have the graphs of the material and we can send the same to you on your email-id (if provided).

Secondly what is indeed perplexing that there is no deterioration in any of the other properties especially in BDV.

However, if for any reason this is the cause, what should be done – given the limitations of existing system.

My other hypothesis is that due to extremely fine copper dust (which somehow gets bonded on to the copper conductor due to static or some other phenomena!!!!) reacts with the enamel film later.

However, to argue against this would be the point that the wire passes through a pre-annealer in which it is heated up to 400-450 degrees and then goes into a quenching bath - the properties of water quality – I have already mentioned in my first post.

Lastly could poor conductor surface also play a role ? Normally pin hole defects due to poor conductor quality occur immediately after production.

Still perplexed…….
Thanks and regards,

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7 years 2 months ago #253 by Archived Forum Admin
Dear Ranjan,

Copper dust is stuck to the wire by residual drawing lubricant or some other contaminant on the surface of the wire. Make sure your annealer (quenching bath) water is absolutely clean and contains no lubricants of any kind. Likewise make sure your water is changed regularly so that there is no build up of contaminants in that water. This is a very common problem in the wire industry.

How do you manage to get a "bad" surface on your copper wire? Presumably you are using ETP continuous cast copper rod as the feedstock.

Peter J. Stewart-Hay
Stewart-Hay Associates

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7 years 2 months ago #254 by Archived Forum Admin
Hello, dv is indeed the diameter (d) in mm multiplied by the speed (v) in meters per minute. Easiest for me for reference is that 18 awg is approximately 1 mm in diameter. Therefore if running with a dv of 15 the speed is 15 meters/minute or about 50 fpm. What is unique about magnet wire is that the dv will vary with every wire size and the insulation. Lower thermal rated wire typically run at faster speeds then higher thermal rated wire - when they have about the same percentage of solids. urethanes run faster than modified polyesters which run faster than polyester whioh runs faster than ML. throw in an overcoat and you change things again. to be continued.

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