Heat Shock test For Magnet Wire

Seems like Spectre asked for more details.

So what is the status of your heat shock problems.

Can you provide more info and stimulate a discussion? thanks.

Again with too much free time I have been revisiting some previous discussions. Regarding the problem of heat shock failures, regardless of the enamel used or the oven set up:

a) You might want to check your testing procedure and the standards that you are using. As previously mentioned, typically a sample of wire is elongated a specific amount, shaped into a coil, inserted into an oven that is at least 20 degrees centigrade higher than the factory thermal rating of the enamel. It stays in the oven a specific number of minutes, removed and quickly cooled. it is then looked at with 3x magnification for cracking, etc.
You can get more info at the following:

ASIEC60851 Methods of Test for Winding Wire;
TM D1676 - 03 Standard Test Methods for Film-Insulated Magnet Wire;
NEMA MW 1000 - Magnet Wire

b) It is inconceivable that every enamel that you are using is failing heat shock. Suggestion - get curing temperature recommendations from your enamel suppliers and then try to duplicate in your oven. Generally there is no single oven temperature profile that will work with every enamel!

c) I would have my lab oven tested to see that it meets the requirements of the test. BlueM and I am sure others make ovens that meet this standard. Most of these are recirculating ovens. If your placement of the sample in the lab oven exposes it to uneven or intense heat as opposed to average chamber heat, you are probably creating the failure. We used to leave our lab ovens on all of the time and would adjust the temperature as needed per test.

Most companies want heat shock values that are considerably higher then the minimum required. See example from Ess*x.

HEAT SHOCK RESISTANCE
Ess*x/GP/MR-EXTRA® magnet wire passes all UL heat shock resistance testing at 20°C above rated temperature.
TYPICAL PERFORMANCE: 300°C
REQUIRED PERFORMANCE: 240°C

This means that their wire while required to have a heat shock value of 240 will typically pass 300 degrees C.

d) Lastly as said many times, go back to ground zero, clean oven, etc. and start over at the oven and enamel mfg. suggested temperatures.

Richard