Hello amirkhi,

We note that you are a process or perhaps chemical engineering consultant to the actual magnet wire manufacturer.

It is impossible for us to understand exactly how you are running your tests in the plant and your latest eleven word answer is surely not helping.

You did not confirm Spectre's comment:

"I assume by not getting the proper results you mean that the wire coil when you remove it from the test oven is cracked."

Spectre also asked:

"How are your cut through values, DF values, etc. If they are very good (high) that would support the thought that you may be slightly overcuring the wire."

You did not answer that!

Likewise you did not tell us anything about your recent experiments other than the fact that the insulation failed again somehow. We received no specific data from you at all in regards to what experimentation you did at the plant and we cannot read your mind! We don't even know if your insulation thickness is uniform! You have also not told us anything else such as the type of enamel, type of machine(s), if the problem is universal to a number of ovens or only one (Was that checked?), etc. etc.

How are we supposed to help you when you don't tell us anything except that you have a problem? We don't even know what standard you are referring to.

Because you have given us only the broadest general information, we can, in return, only give you very generalized technical advice:

(1) What you are going to have to do is set up a series of proper and tightly controlled experiments to prove or disprove the possibility that overcuring of the insulation is indeed occurring. We assume by this statement that you have good experience and training in the design of experiments.

(2) Once (1) is complete and if the problem is still not resolved, talk over the problem (with full and specific details) with the enamel manufacturer just in case you have a bad or very old lot of material.

Good luck with your experiments.

Kindest regards,
Peter J. Stewart-Hay (WAI Forums Moderator)
Principal
Stewart-Hay Associates
www.Stewart-Hay.com

Cracking of the insulation from a mandrel wrap on copper wires can be caused by under cured or over cured coatings.Some or most polymers react differently in these circumstances. Sometimes, (and this may be you're case) that the coating is fine and the copper may be the problem. Some alloys tend to get surface cracks when bent in tight radius's causing the coating to appear to be cracking. The best way to verify coating cure is by Dissipation factor vs temperature. The Dansk system www.dse.dk is a popular piece of equipment for measuring this.

Hello Tech1; haven't heard from you in a long time.

You are of course right about cracking from over cure/under cure. Typically unless the wire is dramatically under cured, the heat shock test procedure will further cure the wire plus wire that cracks from under cure looks different than wire that cracks from over cure. Sometimes under cured wire will crack when winding the coil - the solids in the enamel are not (cannot think of the correct word) unified. If the enamel is colored it may be either darker or in some cases the color will be faded.

DF is a good test and the enamel manufactures will provide you a range in which good wire will fall within. To utilize DF you need to profile and develop curves for each oven because even identical ovens operating with the same temperature and wire speed may not have the same DF.

Also the wire may be within the recommended DF range and it could still fail the heat shock test.

A pull mandrel test is also a good test of the quality of the insulation. Wire that passes pull mandrel test, should pass heat shock.

Tech1 has worked with a variety of alloys, but for copper wire, the situation he mentions should not matter--unless the copper is not very good. You can wrap the bare wire around a mandrel it's the same diameter of the wire and then look at it under a 5-10X scope of loop to see if there is cracking.

Peter thanks for asking for more info.

just wondering if situation has improved or if there are any answers to Peter's questions.

Hi Amirkhi

I've experienece with this before when produce a sample to a famous motor producer. The wire sample failed few times in heat shock test and ultimately I found that the varnish / enamel is the main factor to give excellent heat shock properties. Believe or not, you can request your enamel supplier give you some "imide" modify enamel sample to try (excellent resistance to heat shock).
Regarding the undercure or overcured, I agreed that this is one of the factors. However I have done testing previously with various speed in order to produce some samples of overcure or undercure wires but the result is all fail with NEMA Heat Shock test. On contrary, I use another type of enamel with excellent resistance to heat shock (thermal), I produce few samples with undercure and overbake, they all PASS. BTW, I have to agree that in the first scenario that the overbake insulation crack "more" if compare with "under bake" wires.

Hope help

Have a nice day everybody

JIT

there are several different types of insulating varnish or enamel. they are also some that are used as overcoats or in between coats. Depending upon the varnish used, the thermal rating of the wire will vary. Without knowing what material you are using, it is somewhat difficult to know what standard you are testing to.