Flexibility

HI,

Issue
Process : magnet round copper wire
Problem : fault in flexibility test (mandrel or 1D test), cracking of coating after bending.

Information
wire size: 1.20 mm
enamel type : polyester imide (2L)
oven type : horizontal
oven temperature: 580 C
anneal temperature : 550 C
speed : 85 m/min
number of passes : 22 - 23 passes
tangent delta : good
elongation :good

Thanks a lot for any advice to resolve this issue.

Nima

Sounds like over cured insulation to me. What are your cut through values?
Also you say the tan delta is good but where is in the range of what is good?

Thank you for your reply
According your request ;

1- For cut through standard value is 300 c at 2 min. And our cut. was 320
2- For tangent delta standard range for this size is 195 to 210 and our actual values in different oven regulations (different temperatures and speeds) was 197.4, 200.7, 211.4, 214.6, 200.8 and all of them not OK in flexibility.

Thanks.

Isn't the standard test a 3X mandrel? Assuming the cracks in the insulation are not being caused by problems with the bare wire (do a 1X test of the bare wire and check surface quality) I still think that you have an over cured insulation. You can check this by increasing the speed slightly (easier than chaning curing temperatures and air flow) while maintaining dimensions. Test the wire after doing this and see if it cracks

Dear Nima

I also believe that its an over cured wire . For giving solution to this problem i would like to know few things.

1) You are checking tangent delta with cooling to heating method or heating to cooling method ?
2) What does your enamel manufacturers technical datasheet says with regards to the tangent delta value ?
3) What is the peel value and springiness value of enamel wire against standard requirement ?

One more additional thing you have to check is surface condition of bare wire before entering application area. It should be bright and clean.

All of the above you can check homogeneity of enamel insulation if you have that testing facility.

Best Luck

I had the same problem in two vertical Sicme Ovens.
The problem was in one of them I passed the mandrel test, in the other one no.
The only thing different was the adjustements of the oven, I mean Temperature and Flow air.

Regards

Nicola