Casting Problems

[windy]

 I recently poured my rotor and the vinyl ester didn't set up on top of the coils. Here is what I did. After wiring up all of the coils, I put small patches of fiberglass on top of the coils and used vinyl ester to hold the coils together. The vinyl ester set up, but it wasn't strong enough to support the coils when I tried to lift it out of the mold. So I used some 2 part epoxy, and after that set up, I could lift the coils out without any problems. I poured the stator and after a few days, I opened up the cover only to find that the vinyl ester didn't set up wherever the epoxy was. The rest of the stator set up fine. So I mixed up some more vinyl ester and poured over the fiberglass patches and closed the mold up again. Well, after 3 more days in a 80 degree room, I opened the mold only to find that it still didn't set up. I cut the outer fiberglass ring that was above the coils, only to find that the 2 part epoxy was dissolved and the fiberglass patches could easily be lifted off. When I got the stator out of the mold, the bottom of the stator did the same thing, only not as bad. It seems that the vinyl ester will break down the 2 part epoxy. So, now I am not sure what to do. I dug out as much of the epoxy from around the coils as I can. Do I take a chance and fill up the voids with vinyl ester which may again react to the epoxy or do I just fill it with 2 part epoxy and cover it with fiberglass? The coils look fine after I removed the patches and the wires are all solid. I am sure if I can get it waterproofed, it will be fine. Any comments?

Here are a couple of pictures.

[electronbaby]

What are you using for a mold release agent? Possibly, what ever it is, is retarding the cure of the resin. The reason I say this, is that the coils tend to have the most pressure against the mold when closed, and this may be causing your mold release agent to get into the fiberglass. I have seen this happen with certain types of synthetic greases. Make sure you wipe out as much release agent as you can and still leave the surface slippery as to not have the casting stick.

[windy]

electronbaby,

 Thanks for the reply. I used a mold release wax. The wax was dry when I poured the mold and I did wipe it off so everything was smooth, so it should not have gotten into the fiberglass.

windy

[Flux]

I am not sure if you got the catalyst amount right for the vinyl but you imply it set on the fibreglass, even so it may not have done so when you had problems with strength.

I am fairly convinced that it is a bad move to start mixing vinyl ester and epoxy. Not being a chemist I can't say exactly what will happen but I believe that vinyl ester is basically one part of the epoxy formula but catalysed in a similar way to polyester. Epoxy is a true chemical mix and component ratios are critical. If the epoxy was correctly mixed and completely set it may be ok with vinyl but before things are finally cured I suspect you have a recipe for disaster.

As Roy said you may also have some trouble from the mould release.

I doubt that you can salvage it now but try adding a little drop of vinyl catalyst in each soft area and stirring it best you can and then warm it. If it is basically sound and strong in parts and you can dry the sticky bits it may be ok.

Flux

[DanB]

That's a tough deal there...

I cannot say about vinyl ester on epoxy, but it sounds similar to what happens with polyester over epoxy.  I tried putting polyester over epoxy once...  the polyester never setup and it softened the epoxy.  So  -  you cannot put polyester over epoxy and I expect vinyl ester has the same problem.  You can go the other way round, epoxy will setup over hardened polyester or vinyl ester with no problems.

[fabricator]

Here is an interesting page I found out in the ether, there is some interesting stuff about water in there.

http://www.azom.com/details.asp?ArticleID=997

[defed]

i saw on a guy on a tv program pouring a stator in a mold w/ just a bottom, no lid.  i presume he leveled the bottom mold, then poured in the liquid and just let it self level to the top.

this seems to alleviate several problems i had w/ my mold using a lid....air bubbles, lugs for connecting wire to each phase, etc...

has anyone tried a mold w/ no lid?

[fabricator]

The top pushes the coils into the right thickness, without a top it seems like the stator would be slightly thicker.

[DanB]

Yes I think the lid is critical to mash the stator into the right thickness.  I'm sure there are ways without a lid that could work out but it'd take a good bit of convincing  to make me try it!

I have very few problems with air bubbles.  We take a lot of time during each step to work bubbles out.. first out of the first layer of fiberglass (on the bottom of the mold) - air gets trapped under that sometimes.  Then we put the coils in, and completely submerge them in resin, and press on them over and over again... to work resin into the coils and work the air out.  Then finally we'll put the top layer of fiberglass cloth on... and work as much air out as possible.  Then... a bit more resin, work that in and we put the lid on.  We spill a little resin every time but in the end we usually get very few air bubbles and most of them are very small (sometimes we get none).

All that said - the air bubbles are really a cosmetic defect only and you can fix them after the fact with epoxy, bondo... or more resin.  I do think it maybe important however to work lots of resin into the coils so the windings can't vibrate inside the stator.  In the process of doing that...  you remove a lot of air that would otherwise bubble up against the lid while you're casting.

[fabricator]

My next stator is going to be vacuum bagged, that will ensure there is no air anywhere in the stator.

[windy]

 From reading the information on this web site, it seems that epoxy would be a better choice over vinyl ester. Then again, vinyl ester is lot cheaper then epoxy.

windy