It's hard to answer this question without knowing more about your oven. There was a time when a V/D
for 1 mm wire was as low as 10-15. It looks like right now for 0.75 you have a V/d of about 52. What did the manufacturer tell you it should be for that size wire.

Using the V/D calculation, The 1.5mm should have a speed of approximately 35 m/min at the same temperatures as the .75mm .

Please keep in mind the using a V/D formula only gets you close to an operational speed and is not a given. Cure verification is always needed to determine optimal operating speeds and temperatures.

Tech 1: You are right about the V/D curves that come with most enameling ovens. Several years ago my experiences showed that when you went to Europe and looked at a piece of equipment they always performed better on Euro-enamels than on USA enamels. Not sure why. There was always a significant difference. When we could get the USA manufacture to try and match the Euro-enamels the speeds got better.

Typically the charts are for a single build, single enamel such as polyurethane or the modified polyesters. They seldom included 200 degree materials with various overcoats.

They are best when used as a guide and not as law.

Dear spectre07,
We got information from manufacturer and gave us V/D. We are now trying several diameters and will tell you if will success or not.

Dear tech1,
How you can we check the tangent delta. Should we have an instrument ? If yes, How does it work and do you know a supplier of it. The second test you have suggested with alcohol, the coat of wire didn't crack.
Thank you

Wire,
I think this is one of the first times that someone that has asked for help actually posted the results of the tests. Hopefully your 1.5mm wire is now performing similar to the .75mm wire. There are a few machines out there that can check for cure using ( Tg ). The one that Iam familiar with the called a "Dansks" . iam not sure if they sell a unit that is capable of the sizes that you are using but, you may wnt to check it out anyway. A simple search on the net should get you there. And Thanks for posting your results of the tests you performed.