Stator casting - epoxy/polyester/versamid

[South Easter]

I have made a few stators using Versamid epoxy resin.  Its a 1:1 mix and seems to set not as brittle as RTU 1:4 mix.  But I am concerned about warping...

Does anyone have some comments which may save me experimenting?  What are the pros and cons of epoxy RTU vs Versamid vs polyester resin?

Thanks in anticipation,

South Easter

http://windpower.org.za

[luckeydog]

I have used polyester resin and when I

build my next stator I will not use it

again.

And most certainly don't use it for the

rotor disks. I tried that with bad results.

I put the rotor in the freezer and the

polyester resin cracked and even popped off

in places due to the different rates that steel

and polyester resin contract.

Dan says he has had good results with vinyl ester resin.

and A quality epoxy also works well.

Luckeydog

.

[wdyasq]

One should not think of 'casting with resin' but should think of the resin as part of a matrix of materials, a system. That material should include the coils, the resin and reinforcing materials. The properties and problems if each of these materials should be considered.

The coils are probably a set material, copper. That leaves two materials, resin and the reinforcing fiber. There is little use of going beyond glass fiber for stator reinforcement. It is reasonable in cost and quite strong when properly used. As the strength of the glass fiber is much greater than the resin, as much glass as can be fit in the mold should be used. Epoxy and Vinyl ester resin have less shrinkage than polyester resin and better adhesion. Vinyl ester resin has better high temperature performance than epoxy and epoxy has better adhesion than vinyl ester resin.

It is my opinion that vinyl ester resin and plenty of glass reinforcement should be used in the stator. The magnet rotors should have the magnets bonded on with a good adhesive and if 'potting' is desired, it should be with epoxy and plenty of reinforcing fiber. The epoxy should be chosen for its' adhesion properties.'

Ron

[Titantornado]

Just as Dan is now doing, for the stator, I used vinyl ester resin mixed with aluminum trihydrate powder (1:1 by volume) for higher heat dissipation.  I chose it simply because it has one of the highest stability ratings for high temperatures, at a fairly reasonable cost. Epoxy typically doesn't have as high a temperature stability point, and I don't want to risk the stator warping and rubbing the rotors, messing up the whole machine.

I only cast rotors with epoxy, and preferably, West System epoxy.  Polyester and vinyl ester are NOT adhesives, period.  In fact, neither were ever meant for large volume casting without a high fiberglass content. Resin is a binder, not a structural component. I don't know why people assume they are.

[South Easter]

Thanks guys for your comments.  I use epoxy RTU 1:4 mix for the rotors - lets leave that subject.

For the stators I have used epoxy Versamid 1:1 with... umm... you wont like this.... NO fiber.  Just plain epoxy.  And I am making the stators 8mm thick now. I did get some warping on an earlier model, and the latest one has some aluminium beading set in the epoxy around the outside, which I hope will stiffen it.

Does the ATH additive you mention stiffen the epoxy, or just improve heat dissapation?  And do you use glass fiber as well?

And if you use glass fiber, what form do you use?  Woven matting shoved down into the mould, or do you mix the epoxy with chopped strands and just pour it all in?

Thanks again for your response,

South Easter

http://windpower.org.za

[South Easter]

BTW, why did you put the rotors in the freezer???

-South Easter

[luckeydog]

I put the rotor in the freezer because I live in a cold climate

here in Colorado. one thing one must do is build their machine to

withstand all their climate conditions where they are installing

the wind turbine.

Luckeydog

.