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TOPIC: Magnet Wire Failing In PinHole Test
Re: Magnet Wire Failing In PinHole Test 2 years, 2 months ago #273
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,
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.
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.
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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