Rotor pour driving me CRAZY!

[machinist]

Poured stator and it came out of the mold looking great. I've made 3 rotor pours and they all looked like a$$. I've read every post on here that has to do with casting fiberglass resin. The last pour looked great about 3/4 way around, but the last 1/4 was cracked like peanut brittle. I'm going to try one more time then I'm going to buy some of that smooth cast 300.

My question is, can I just put this stuff on in thin layers with the cloth in it? Will I still have the cracking problems?

Sorry, just blowing off steam.

machinist

[Airstream]

Cracking is usually from unnecessary fast cure rate where the resin & mold gets hot too fast from excess hardener added then shrinking unevenly as it hardens/cools. To make solid 'deep' castings takes withholding a part of the usual amount of hardener, the art in that is knowing how little to add. It also means being prepared for a two, three or five day cure time or even a finishing heat soak, the slower the cure the better the casting. Mixing the resin and hardener enthusiastically without injecting air bubbles is another art - by your description the hardener might not have been mixed in thoroughly.

You don't say which resin you are using - there may be bonding issues with multiple layers if the resin has wax added to aide sanding and finishing. Doing multiple layers adds to the chances there will be air pockets at/on/in the coils themselves which could mean wires chaffing on each other and ultimately shorting. As far as the glass cloth is concerned it wont mind getting new layers scabbed on as long as you are using build-up resin and not the waxed finish resin..

[machinist]

"ART" is a very good word for this process. I guess after the stator I thought it was a no brainer. Chemicals are not my strong suit. I'll do some more reading.

Thanks

machinist

[Flux]

I assume this is polyester resin? The hardener is a catalyst and if you have too much the thing runs away thermally and that is probably what you have happening. If you halve the normal small quantity catalyst it should be better behaved. The whole thing is temperature dependent and high temperatures make the thing worse. If you reduce the catalyst it may take some time to harden and in some cases you may have to warm it to kick the reaction off. Just use enough heat to get it started, too much heat may again set it exotherming. You will do far better with some filler in the resin such as talc or ATH even if you use glass cloth for strength. The filler moderates the reaction with large quantities of resin.

If you are using epoxy the the resin /hardener ratio is fixed and you must not change it, the only thing you can do to slow the reaction is work at lower temperatures.

Not sure about vinyl ester it is somewhere between the two systems, I am not sure if it is a catlaysed reaction like polyester or whether it is a 2 part system like epoxy.

There may be differences in the resin from different sources and some may need more hardener than others for polyester, it seems likely you are using too much for the volume of resin.

Flux

[tanner0441]

Hi

To repeat. You don't say what resin you are using, you say nothing about the conditions in your workshop.  Did you monitor the cure to see if it became hot while curing? Normally cracking is due to excessive heat generation while the resin cross links (cures) by exothermic reaction. Once it has gone past a certain point you can artificially slow the process down with cold water, but water before that point will prevent it from curing.

It can get hot enough to actually burst into flames, you said it was on the rotor with Neo magnets it can get hot enough to give them amnesia.

Did you add a filler of any kind, ie. Talk or erosill?  You could lay it up in layers but you have to pour the next layer before the previous layer totally cures.  It could still take off if the mix is wrong and it is hourendously time consuming.

Send more information and someone on here will be able to tell you where or if you are going wrong.

Brian

[vawtman]

 Hi Machinist

What did you use to adhere the mags to the rotor?With proper prepping and proper epoxies you could do away with the blanket.

 My opinion and any pics.

[electrondady1]

 it sounds as if you didn't stir it up enough

3/4 of the pour is ok but 1/4 of it has a lot of cracks?

so if you v the cracks for penetration and brush on more properly mixed resin

you should be ok.

.

 

[machinist]

I'm alot calmer today. Useing the Bondo polyester stuff. After alot of reading, I realize that I'm useing WAY too much hardener. I superglued the magnets to the plates. They aren't moveing, even after chipping that stuff off twice. How much of the talcum powder would you put in a quart of resin? I may try to fix the cracks like was suggested.

Thanks

machinist

[Flux]

You will probably find that you can add a similar quantity of talc to resin without it thickening much. Beyond a certain quantity it starts to thicken quite a lot but it takes a surprising amount.

Flux

[machinist]

Poured friday night. 1 qt. resin, 3/8 tube hardener, 9 oz. johnsons baby powder. Fiber mat all thru the thing. Didn't put the mold cover on, I'll just turn it on my lathe. Stirred it for 15 minutes. Getting hard but not real fast, 40 degrees in shop saturday.

Finished welding last night. I'll try to post some pictures today(Sunday).

Thanks for all the help

machinist

aka Kerry Bullard