Alternator blades stiffness

[reinoud]

Dear folks,

in an attempt to fabricate a axial flux alternator i've glued two times 18 `toy' magnets (NbFeBo 20x20x3 mm M45) on 1 mm steel discs. The magnets love it On second thought i could have placed the magnets a bit further to the edge increasing the spacing between them.

When i tried out assembling with the magnets on it -- before coating it with polyester epoxy -- the forces were that unexpectedly big since they boost each other a lot that it buckled the two steel discs to each other until they touched Only the spacer area was still flat :-|

Breaking them apart was hard but with some effort i managed. The magnets were still fine though one had had such a big pull on it that it separated from its nickel coating and detached! The others are fine.

I wonder what to do... flattening them again was no problem but Will coating the discs with a 3-4 mm polyester resin all the way including the center (no hole in the middle) provide enough stiffness? Shall i use the glass fiber mat covering the magnets method Hugh advises? or should i (also) try something else? I wouldn't like to see the polyester crack up and the plates ruined again, maybe for good this time.

I hope waxing the three m6 bolts will keep them out of the resin since i wanted to double them as lid fixings.

Any advice and help would be much appreciated!

Thanks in advance,

Reinoud

[SparWeb]

Your disks are too thin.  The structural failure will recur unless you use a plate about 4 times thicker.

Another problem with a disk that is too thin is that some of the magnetic field can "leak out" the back.  Try sprinkling some iron filings on the back of your disk.  If some sticks, you have "leakage".  Thicker disks are demanded for that reason, too.

I'm using thin disks, but that's because I scavenged up some 4130 stock.  There is a barely detectable leakage out the back.

[Slingshot]

Can you bond another disk to the back side of each of your rotors?

[reinoud]

i feared so

I've managed to get hold of a piece of 2 mm steel plate (phew!) and will cut out extra supporting discs. I've tested the effect on the flux and even with a single 1 mm plate at the back the flux is gone; this is propably due to the lamination effect. Attaching the 2 mm plate will thus be fine

I'm planning to glue the 2 mm plate to the back of the 1 mm as much as possible and to use a series of (non rvs) m3 bolts on the outer edge of the disc to bolt the two plates together for extra support. It would have been more eastatical to have single plates but oh well.... i've learned a thing and this way i dont have to throw away my 36 magnets. (95 eurocent a piece)

For your information, i've used a very strong two-component glue that at the conditions i use it in ought to give me around 1200 N per cm2 (can get to 3000 N per cm2 under heat). Getting the two plates flat enough to give a nice bond might be a problem though...

wish me luck!

Reinoud