Tacky resin, yellowing clear resin.... (Alumilite RTV )

Locke_333 · Post by **Locke_333** » Mon Jul 10, 2006 8:13 pm

Hi, i've started casting some clear parts for various projects and have encourtered some problem.I Thought, why not ask some help from the GURU around here! i'm currently using 2 types of "resin" ( EasyCast epoxy and Envirotex )with the same result so far for both. When using brush on rubber mold, the casting come out clear, solid as one would expect but it take forever to make mold in those media.... I decided to try something different, i bought 1 pound of Alumilite RTV rubber and made a mold of the same piece to compare the result and here's my problem... :

After the mold was cured, i cleaned up what was over and it looked perfect. I left it on the shelf for 2 weeks because i didn't had the time to start the casting. When i got back to it, i found out the a yellowish substance was coming out of the mold( much like the catalyst used ). I cleaned the mold so there was no residu left and started castin in those new mold.

First thing i noticed when i took the newly pieces out of the mold( Alumilite : They are tacky. I laid them to rest because i read somewhere that sometime it solve the problem but after a week, they are still tacky. Anything i can do to get rid of the tackyness ?

Second, the pieces cured in the Alumilite rubber have a yellowish tint( Not again that catalyst !? ) and the piece cast in the brush on rubber is perfectly clear....

Any idea what i could have done wrong? Any help would be appreciated!

Martin

Sparky · Post by **Sparky** » Mon Jul 10, 2006 8:39 pm

Sorry I thought we had mentioned this in the resins and or rubber section. When I tried Envirotex lite with Tony Augstin's Alumilte molds it was a no goo, something in the mold draws out the catalyst in the resin leaving the areas where the part contacts the mold, uncured. I did not have this problem with oommoo 25/30. I have not tried it in moldmax. However I recently tried it in a very old oomoo mold and it ate the mold, it would not realease and tore the mold apart. It was this part:

http://www.kc6sye.com/images/images_11_ ... d_ribs.jpg

Some have suggested pre coating the mold, maybe with future (an acrylic layer) maybe with talc. But I'd say envirotex and alumilte are not compatable.

Post by **TER-OR** » Mon Jul 10, 2006 9:11 pm

I have used envirotex in a fresh oomoo mold without trouble.

I have also used a very thin coat of petroleum jelly as a mold release when working with envirotex, and that was much better - even in an old mold. Just give Envirotex two days to fullly cure.

Locke_333 · Post by **Locke_333** » Tue Jul 11, 2006 5:20 am

yah, i remeber that thread sometime back... Found it, thanks for remembering it to me! If anyone interested ...Envirotex Troubles

Well, so fard i haven't had trouble with releasing the Envirotex piece. In fact, without any release agent, i barely bend the mold and the piece just pops out of it on it's own... i'll try to post cure the mold as the other tread says

macfrank · Post by **macfrank** » Tue Jul 11, 2006 10:49 am

Locke_333 wrote:. i'll try to post cure the mold as the other tread says

That was my thread. The only thing I found that would help was to bake the mold as Shinnentai suggested. How are you mixing the RTV? By eye or by weight? I usually do it by eye, and for everything but clear resins it works great. I'm thinking of mixing it more accurately - maybe this will help reduce the excess silicone that's leaching out of the molds.

Baking is also the oly way I've found to get rid of or reduce the yellowing... which makes me think that better mixing would help.

Polyvinyl Siloxane (a two part, equal mix mold material used by dentist) works great with Envirotex and Alumilite, but it's just too expensive for large scale molds. It also cures within minutes.

Frank

Locke_333 · Post by **Locke_333** » Tue Jul 11, 2006 10:56 am

It's supposed to be by weigh but there is a mesuring cup that came with it that said 1 cup for xoz of rubber and that's what i used. How much time did you bake your? The original thread said 6 hours at 300F

macfrank · Post by **macfrank** » Tue Jul 11, 2006 1:33 pm

Locke_333 wrote:It's supposed to be by weigh but there is a mesuring cup that came with it that said 1 cup for xoz of rubber and that's what i used. How much time did you bake your? The original thread said 6 hours at 300F

I've tried between 4 - 8 hours at 200F - 300F. The higher temps tnd to yellow the molds, so I bake them at about 230F-250F for 4-6 hours every time I pour clear Alumilite. I haven't tried it in a while though.

Time will leach out some of the inhibitor, but you still have to bake the molds. The Alumilite clear also works best in warm molds.

Reading the original thread reminds me that I should try making a mold with Oommoo; it's a nice mold material, but it's so much thicker than the Alumilite RTV.

Frank

Locke_333 · Post by **Locke_333** » Tue Jul 11, 2006 2:36 pm

Every time ... !!! Oh well, meabe i'll try another king of mold then, i've got a dozen pieces to cast and i ain't going to cook them each time.

Thanks for you help!

macfrank · Post by **macfrank** » Tue Jul 11, 2006 3:00 pm

Locke_333 wrote:Every time ... !!! Oh well, meabe i'll try another king of mold then, i've got a dozen pieces to cast and i ain't going to cook them each time.

Thanks for you help!

Remember, the Alumilite clear resin likes a warm mold. According to the Alumilite page, about 150F for thin casts.

Sparky · Post by **Sparky** » Tue Jul 11, 2006 3:08 pm

I've tried using an old crockpot, I taped over the hole in the bottom and filled it with sand, setting in a ceramic cat water bowl. (Yes the girls have a water fetish and can no longer use a water bowl.) This lets me pre heat the part a and part b, then I set the mold in the bowl (after pouring the parts. This helps for small things, like a cockpit insert.

Locke_333 · Post by **Locke_333** » Tue Jul 11, 2006 3:34 pm

macfrank wrote:
Locke_333 wrote:Every time ... !!! Oh well, meabe i'll try another king of mold then, i've got a dozen pieces to cast and i ain't going to cook them each time.

Thanks for you help!
Remember, the Alumilite clear resin likes a warm mold. According to the Alumilite page, about 150F for thin casts.

The thing is, i'm not using Alumilite clear resin. I'm using envirotex and Easycast clear resin

but i know in general that warm mold tend to give better casting but for what i need them, that not really a concern...