Magnet Wire Failing In PinHole Test

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.

Dear Peter,

The properties of the water in the quenching bath has already been mentioned in my post above and is continuing overflowing.

The poor surface was due to bad surface of the RBD Capstan which has since been rectified.

Regards,
Ranjan

Ranjan,

Conductor fines are not generally a problem with copper wire. It can be a problem with aluminum and that is why most of the time the first pass through the enamel applicator is isolated from the rest the passes. Due to being so soft if you do not isolate the first pass, aluminum fines will build up in the enamel making it a metal flake coating. The enamel in that isolated pass has its own filtration system, etc. Once the initial pass is cured, aluminum dust will not flake off. When you have metal flakes in the insulation you will fail more than pin hole. We always had a wipe before the annealer to remove the lose copper particles. If there are surface imperfections in the copper, when it passes through the annealer they pop up and unless you are doing inline drawing, they pop up in a way that when the wire goes through the drawing die it bends or folds them back over the length of the wire. That of course occurs if you have split dies which will spring open. If you have solid dies, you have to worry about the wire breaking or the die being pulled from the applicator.

I know this is probably not answering you question or solving your problem, however when there is an unusual problem, I usually clean up the entire system, try to put everything like it should be and try again. This is especially true when the problem occurs with different enamels. If the problem jumps from one material to the other, the problem is somewhere in your system.

Back to your annealer quench tank, we used to control the flow with an automobile thermostat to a temp of about 190f. We had a float control for refill. If the water is too cool or flows to fast, the water on the wire will not evaporate fast enough or dry quick enough. You can put some isopropyl alcohol in the water and that will help.

RB

Dear Richard,

Thanks for virtually eliminating the copper fines issue even though we have recently bought a centrifuge based lubricant filtration system. Though just a small question there – Is it safe to run Copper and Aluminum wire on the same enameling machine? I know for wire drawing different set up is required. But what about the Enameling Machines ??

As regards the quenching bath – we have a visual control with overflow happening because of continuous inflow from the water tank. We too keep the temperature at around 70 – 80 degrees Celsius which is around 160F. Will try to up it to the levels you suggested.

We have tried cleaning up the system many times but have not been able to isolate the problem which keeps on recurring from time to time without any correlation with the data at all.

Based on your suggestion of Solvent Entrapment I went through some old tech. literature in my e-library and have extracted a 1964 paper which has been attached to this mail. This paper talks about:

…...premature polymerization of the outer layer of the wet enamel film was trapping non-evaporated solvents beneath the surface:

And

Solvents near the film surface will be released more rapidly resulting in "surface sealing" Solvents trapped below the surface will subsequently be released by miniature explosions, puncturing the sealed surface, and resulting in surface distortions, known as blisters and craters.

Now I have enclosed the schematic drawing of the exhaust system in our machines which is slightly different from those found in other conventional machines like Roldro’s (Mumbai Machine Manufacturer). Using this design we use the cooling fan to create an air curtain to prevent excessive loss of heat. But this is leading to the solvent laden fumes being pushed back into the oven as low as the second zone and occasionally fire in the oven as well. Also another notable feature is that a lot of fumes are coming out from the top of the oven along with the wire. Shouldn’t they be normally exhausted out?

In the standard design the cooling is given slightly higher than the exhaust which reduces its downward pressures and allows the exhaust to be more effective even while consuming more electricity.

Could this also be the cause ???? The possible reason for this could the presence of the solvent laden fumes within the oven that would prevent the proper release of the solvents from the enamel film.

Also enclosed are Tan Delta Graphs of the same reel in which pin holes have been found after 10 days. One graph of TD at the time of production and the other for after detection of pin holes around 10 days later. The values have gone up from 165 to 173 during this period. Does this co-relate with our hypothesis?

Is this the end of the Tunnel?

Regards,
Ranjan

Dear Ranjan,

I suspect that you are actually at the end of the tunnel as follows:
A) Get the oven cleaned up as Spectre07 suggested you do.
Make sure the wire is properly centered in the oven and make sure the wire does not touch any part of the oven.
C) Make sure that the surface of the wire is of very high quality.
D) Get the oven ventilation back into a standard configuration.
E) Get the annealer quench tank water temperature up to 190F and keep it there.
F) Make sure all other components of your oven are working properly.
G) Wipe the wire before the annealer to eliminate loose copper fines.
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.
We all, including yourself, cannot resolve this problem academically from behind a desk or computer now*. You must go out and affect all these changes, properly and permanently. Then you must monitor the situation for a long period of time. If you do all these things, I, for one, believe you will have good success.

*Those of you who were formally trained in Kepner-Tregoe Analytic Trouble Shooting will understand exactly what I am referring to here. www.kepner-tregoe.com/

The next courses in Analytic Trouble Shooting in English near you Ranjan are here: www.kepner-tregoe.com/pdfs/PubWorkBro/2010SEA_ATS.pdf

Likewise Ranjan, if you haven't already done so, you should consider the implementation of ISO 9001 and Six Sigma at your plant but be warned these can be long and difficult roads.

Regards
Peter J. Stewart-Hay
Principal
Stewart-Hay Associates
www.Stewart-Hay.com
WAI Forums Moderator

Peter, Sorry that I have been side tracked.

With Regard to Ranjan's Oven

Once before I said a good technician could make magnet wire with a toaster and it is true. Some of the early machines in reality were little more than long toasters. The article by Art Windsor is a very good article and he gives a brief overview of oven history and then discusses the MOCO (Michigan Oven Company) recirculating oven.

The biggest difference I see between your oven and a recirculating oven is that your heated air flows in the direction of the wire and then at some point is drawn from the oven. You also inject cold air into the top of the oven and it goes out along with the heated air. Your oven wants to be a chimney.

The cold air that is injected in the top varies with the weather and barometric pressure. When the wet wire enters the heated oven, solvents are evaporated however in this oven the vapors move with the wire and build up in vapor concentration and when it reaches a certain level the combination of fumes, fresh air and heat = a fire.

On a recirculating oven, the air flows with the wire in the evaporation zone and against the wire in the curing zone. In between the two is the interchange zone where the fumes are removed from the oven. In the evaporation zone, the temperature is lower and the velocity of the air is lower and laminar to the wire. In the cure it is hotter, and counter to the direction of the wire. This helps strip more solvents from the wire. The wire cooler may seal the top of the oven or strip the fumes from the wire, but you are not forcing large volume of air into the oven like you are with your oven.

Most of today's enamels are made for newer type or style ovens. This means that the evaporation characteristics, etc. are different than the enamels used 50 years ago (note age of Art Windsor article).

rb