I-beams for Ventilation Lamination? 2

[ManuSuissa]

Hello,

I am currently working on a project based on manufacturing a wind turbine motor.
My client is requiring me to include ventilation laminations within the lamination stacks, for both the rotor and stator.
For those of you who don't know what these are, these laminations consist of regular laminations with bars welded along each slot to create some small distance between two laminations.

I have had to manufacture vent laminations in the past, but the bars that were welded were typical rectangular flat bars.
This client is specifically asking for I-beam to be welded instead of flat bars. Does anyone know why someone would rather have an I-beam instead of a flat bar?

My reasoning was:
Structurally speaking, of course the I-beam would have lower deflection etc, but in this case the mechanical properties are not the key factors, even though the lamination stack is being pressed...?
Or, do flat bars bend more during the spot welding process?

BTW we're talking about an I-beam that is 8mm high (web height) and 4 mm wide.
Here's a pic of a Stator ventilation lamination showing the bar detail between each slot.

http://postimg.org/image/qshzwa12z/

What do you guys think?

 

[MikeHalloran]

The I-beam would weigh less than a flatbar of equal size.
One problem: Nobody rolls I-beams of that size in steel.
That 5/16" size should be available in brass, from a hobby shop.
If you prefer steel, it's possible to have the beams milled from flatbar, but it will be a little costly because the workpiece is delicate, so the feedrate has to be limited.
Alternatively, your I-beam could be made of a pair of channels spotwelded web to web, where the channels are formed from sheet or strip by a sheet metal shop.
As for what bends more than what, etc., you need to have a mechanical engineer look at what forces are applied during manufacture and installation, and select the dimensions appropriately.


Mike Halloran
Pembroke Pines, FL, USA

 

[ManuSuissa]

Exactly.
I have been having trouble finding a north american supplier that can manufacture these I-beams. These dimensions are more common in European specs, but either way having them done here or shipped from overseas both come out too costly.
I'll have to double check, like you said, the assembly process and the forces applied when motor is assembled and running.
On the other hand, I'm not sure if the TOTAL difference in weight between the I-beams and flat bars will have a significant effect on the total weight of the motor...

 

[MikeHalloran]

If they're going to be secured by welding, it might be appropriate to make Z-bars with 4mm flanges and 8mm height, from say 0.5mm to 1mm steel. Most any sheet metal shop could do that for way less than milling I-beams and considerably less than making two channels and welding them back to back.

The weight savings are probably too small to bother with, so I'm guessing maybe the client wants maximum airflow area, especially at the inner end.

I don't think that the silicon steel normally used for laminations will form very well, so you may be stuck with mild steel. ... and that may give you more eddy currents and more, uh, remanence(?) than you want. At least, whoever is doing detailed calculations to support performance estimates should be made aware of what's going on.





Mike Halloran
Pembroke Pines, FL, USA

 

[waross]

I would check what construction the competition is using.
Often a restrictive clause is inserted to steer the contract to a favoured vendor or manufacturer.
If no other vender supplies I-beam spacers you may consider saying NO, we do not recommend or warranty i-beam spacers.
I-beam spacers may be supplied at the customers expense and risk.
By the way, what force is applied to the stator lamination stack during assembly? Will an i-beam spacer withstand this force with an adequate safety margin?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ManuSuissa]

I've done a quick calculation and yes, the i-beams would withstand the applied force. The stator itself has 16 ventilation laminations and each of them have 90 i-beams at each slot. Distributing the load accordingly is well within tolerances.
As Mike mentioned, the Z-beams could be a good alternative to I-beams considering their availability...