Stacking Factor versus compression force 2

[BigMotorGuy]

It is my understanding that the resultant stacking factor for an induction motor core is due to the lamination insulation layer but also the amount of compression on the core prior to welding/fastening. What is the best way to determine the compression force needed to obtain the maximum SF with a given lam thickness (.020" in this case)?

 

[electricpete]

Some quotes from “Electrical Steels For Rotating Machines” by Beckley may or may not help.

10.26.7.16 Stacking factor (space factor)
A stack of Epstein strips may be squeezed at 1.0N/mm2 pressure and the stack
thickness noted from a dial gauge. From this figure and the sample mass (and number
of strips) the percentage effective space occupancy by metal can be calculated. The
result is expressed as a percentage figure.

13.1…
In passing, mention may be made of the stacking factor or space occupancy. This
is the percentage of space occupied by metal in a given stack of laminations. A pile of
24 Epstein strips can have its notional thickness (24×individual) calculated, then be
placed in a squeezing jig which exerts a compression on the stack of an intensity typical
of machine use. The physical height of the stack (usually assessed by a micrometer
dial gauge) is compared with the notional value derived from weighing, etc:
(Notional value / Dial gauge reading) * 100 = stacking factor
Figures in the high 90s are usual. The figure for the stacking factor found will be
influenced by the presence of coatings (not much) and by the surface roughness of
steel. This latter may have been purposely raised to help avoid sticking

Some possible takeaways:
1 – you can measure stacking factor based on change in dimensions when compressed.
2 – High 90’s is mentioned as typical
3 – 1 N / mm^2 has sounds like it might be some standard … but whether for testing or typical of machines I’m not sure.


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(2B)+(2B)' ?

 

[Clyde38]

This paper may be of interest to you. .



[link

http://www.linkedin.com/in/clydehancock

]

[/url]

 

[BigMotorGuy]

Thanks electricpete.....I kind of figured that measuring the compressed height verses adding up the individual thicknesses of a given # of lams might be the best way. not sure if there is some kind of nonlineararity involved for long stacks versus short though.

Clyde38....I didn't even think about the stress levels affecting the actual magnetic properties, rather only thought about removing air pockets/voids between the lams. Great info though for review!