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If you have a question regarding coaxial, telephone, and building wire, power cable, insulation, extrusion, bunching, stranding, braiding, etc. post it here.

TOPIC: Magnet Wire Failing In PinHole Test

Re: Magnet Wire Failing In PinHole Test 5 years 10 months ago #261

Dear Ranjan,

As I am sure you already know that I am no expert when it comes to the manufacture of magnet wire even though the corporations I worked for had very large magnet wire plants.

My specialties are power cable, telephone cable, optical fiber cable, data cable and many other kinds of plastic and paper insulated cable.

Spectre07 is our true specialist in the manufacture of magnet wire and I certainly defer to his opinions. In fact, I wish I could recruit him to be a moderator at the WAI Forums but presently he has too many other work and personal responsibilities.

From what I have read, I suspect your issue could have been water trapping, solvent trapping or a combination of both. It needs however to be proven over the longer term. I really look forward to reading what Spectre07 has to say in response to your questions highlighted above.

Please note the following from Wikipedia "Properties of water"

"The low electrical conductivity of water increases significantly upon solvation of a small amount of ionic material, such as hydrogen chloride or any salt.

Any electrical conductivity observable in water is the result of ions of mineral salts and carbon dioxide dissolved in it. Carbon dioxide forms carbonate ions in water. Water self-ionizes in which two water molecules form one hydroxide anion and one hydronium cation, but not enough to carry enough electric current to do any work or harm for most operations. In pure water, sensitive equipment can detect a very slight electrical conductivity of 0.055 µS/cm at 25 °C."

Higher electrical conductivity is a measure of typically the quantity of salts in the annealer cooling water. If the annealer is electric, then the upper limit of 50 microsiemens/cm (µS/cm) is there to maintain good electrical resistance in the water. If the annealer is not electric then the upper limit is there to prevent quantities of salts drying on and thus contaminating the surface of the wire before enameling.

It would be my opinion therefore to carefully control the electrical conductivity and keep it as low as possible, below the upper limit of 50 microsiemens/cm. However I cannot see a requirement for deionizing equipment for the cooling water with the information you have provided so far. Finally, you have indicated that the cooling water electrical conductance increases with temperature. If the electrical conductance then reverts to its original value when cooled, I imagine this is the self-ionizing phenomenon at work. This is very easy for you to get a handle on and decide if it is of any importance.

Regarding the pH, I would try to hold it as close to neutral (7 is pure water) as possible but do not add salts. I guess the question I have is as follows:

If the water is slightly acidic going in (pH=6), where is the base coming from to make the cooling water as basic as seawater? (Maximum pH=8.5) It would appear that the flow of cooling water should be increased each time the pH climbs above say 7.25 and control between 7 and 7.5.


I was quite pleased to see that you already have an ISO 9001 program. (I spent six months of the last say nineteen months near Mumbai at a new cable complex and I am very much a proponent of the emerging new India.)

At my former company, we formally appended all of our process recipes and instructions to our 9001 program to ensure audited conformity on a regular basis. It is a nice way to formally hold manufacturing control as well as pleasing our customers greatly.

Regular but random cpk measurements are great for manufacturing process conformance by individual machine.

Best regards
Peter J. Stewart-Hay
Stewart-Hay Associates
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Re: Magnet Wire Failing In PinHole Test 5 years 10 months ago #262

A) Get the oven cleaned up as Spectre07 suggested you do.- Done
From what you told us you have a non-circulating oven and therefore air movement is critical. The oven can evaporate the solvents, but if the air flow is low, you have to keep an eye on condensate build up.

B) Make sure the wire is properly centered in the oven and make sure the wire does not touch any part of the oven. – Done
In addition to centering the wire in the “wire chamber” you have to consider your heaters. Are they on both sides of the wire lines or only on one side. If they are only on one side you might want to favor the side without the heaters. If they are just calrod or tubular heaters that run from side to side of the wire chamber, you might look into the chamber and see if you see any hot spots. Same for heated plates – they can also get hot spots.

C) Make sure that the surface of the wire is of very high quality. – Surface is of good quality. Not excellent. Meaning thereby at 60 x magnification we can see some marks on the surface probably due to slippage in drawing machine. But the same is not visible at normal 10 x magnification levels and the wire also feels absolutely smooth when touched.
If your surface quality is so good that it takes a 60x scope to see imperfection, then – don’t laugh, maybe your wire is too slick!

D) Get the oven ventilation back into a standard configuration. – Done. The first zones temperature of 350 deg C was not achieved so we are in the process of adding more heaters. We intend to run the machine at 350/400/450 configuration for the three zones. Hopefully with first zone at 350 should be high enough for the evaporation of the solvents.
I am a firm believer that the best temperatures are those that give you the best wire and best productivity. Without knowing how long each zone is, it is hard to comment on the temperatures that you are mentioning. In our vertical recirculation ovens the air flowed with the wire in the evaporation zone, against the wire in the cure zone. In the interchange the two air flows met. We had two different temperature zones in the evaporation section and only one in the cure zone. We could adjust air flow in each of the evaporation zones and the cure zone. We measured the temperature of the air not the temperature of the wall surfaces. For your type oven and the speed your run, it seems to me that the temperatures are pretty high. Again without knowing the length of the oven or zones and where you are measuring the temperatures, I might be wrong. You also say that your enamels are designed for slow speeds and if that makes it seem even more possible that your temperatures are high for the speeds.

E) Get the annealer quench tank water temperature up to 190F and keep it there. Currently it is at 75 degrees. We are trying to get it up to 190F /85C. One question though the conductivity of the water changes with temperature. We have been advised to keep the conductivity below 50 microsiemens. We are trying to keep it below 30. However this level is checked after allowing the water to cool down to around 40C and not at 80C. Also the pH in the quenching bath is being maintained at 7-8.5 pH and for this the inlet water to the quenching bath is maintained at 6 pH. Is this OK?
You appear to have a pretty good control of the quality of the water. We used a deionizer because our water came from multiple sources and they varied – the deionizer took care of that problem. I think that controlling the temperature of the annealer quench tank is very important. We built the quench tanks so that they filled when the level dropped but at the same time we used an automobile thermostat to maintain the temperature. If it got to hot the thermostat opened water drained off and fresh water was added. If the water temperature is right, the water rapidly evaporates from the wire. If the water is too cool it stays on the wire and slowly dries or makes it to the applicator. If you touch the wire between the annealer quench tank and the applicator and it is cold or cool is it also wet? You want the wire to be dry and warm but not so warm that it oxidizes. Also the wire being warm helps the evaporation process.

F) Make sure all other components of your oven are working properly. – Done. Checked by using the ampere rating and reading of all heaters.

G) Wipe the wire before the annealer to eliminate loose copper fines. Done. Double wipes before and after annealer.
Wiping is good.

H) Hold very tight control over all of your process and let us know in about a year how you made out managing this intermittent problem. – Will Do.

Peter, We are already an ISO 9001 approved organization and have started cpk measurement for some CTQ parameters as a part of Six Sigma drive. However, we are not able to pin-point the cause of this problem despite our best efforts.
Maybe you are spending too much time looking at your process. I cannot think of any way that I could make good wire today, that passes all of the tests, and then (it) fails, but then in about 6 months is good again. I have no idea how you can make a product (like that). It tells me that you need to make certain that both you and your customers are using the same test equipment and following the same test process. Again if the wire was good today, it should be good tomorrow or next week or next month.

So on the point raised by Richard regarding high speed of enamels. Here in India the problem is reverse. Since most of the machines are having vxd around 15 the enamels are suited for these machines. For very high vxd machines (above 100 ) there have been reports that the enamels available locally are not able of matching up.
Ask your enamel suppliers to give you some temperature profiles that are optimal for your type of equipment. They should be able to do this.

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Re: Magnet Wire Failing In PinHole Test 5 years 10 months ago #263

Ranjan, RM, Coolblue, what is the status of your problem?

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Re: Magnet Wire Failing In PinHole Test 5 years 10 months ago #264

Dear Richard & Peter,

Thank you for your response. I have been travelling for the past 10 days and have just arrived back today.

Will get back on the status update shortly.

Thanks and regards,

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Re: Magnet Wire Failing In PinHole Test 5 years 10 months ago #265


The problem seem to have been resolved by changing the ovens exhaust configuration as specified in my earlier mail.

However it is still very early to conclude. I will get back after a couple of weeks with a more definitive response.

Thanks a lot for all your valuable inputs,

With warm regards,

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Re: Magnet Wire Failing In PinHole Test 5 years 10 months ago #266


Since your machine does not have a catalyst that burns the fumes and allows you to recirculate the air, when you have too little exhaust, the solvents will build up in the wire chamber creating a saturated air condition. Increasing the exhaust opening allows more fume laden air to leave the wire chamber. It doesn't matter if you are boiling water or evaporating enamel solvents, if the air is full of the vapor, it is difficult to evaporate more solvent into the air because it is saturated.

Increasing the exhaust will increase the energy cost but the offset might or should give more production (productivity) and better quality which is the name of the game.

The IFPA or International Fire Protection Association says that enameling ovens should be designed so that the LEL (Lower Explosion Limit) is 25%. This means that if the combined air and solvents level to cause an explosion was equal to exhausting 250 CFM (Cubic Feet per Minute) then at 25% of LEL you should be exhausting 1000 CFM.

Recirculating ovens are able to have really low CFM exhausted because they burn of typically 90-98% of the solvents and reuse the air directly or to preheat incoming air or a combination of the two depending upon the design.

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