Casting problems, looking for help

OdysseySlipways · Post by **OdysseySlipways** » Sun Feb 13, 2005 10:56 am

I have started using Polytek's resin (about 3 - months ago) Easy Flo 65 and like it. I'm about to finish my current 2 gallon kit and order more.

I thought since I am using their resin, I'll try some of their rubber mold material too (why not, just order all of my supplies from one place). I bought a 9-10 lb kit of their 70-11 rubber. I was using Alumilite's HSIII rubber (but with them no longer carrying my resin). The 70-11 seemed to match up perfectly so I thought I'd give it a try.

The softness of the rubber was the same, but got more volume for the money over the HSIII, so I wouldn't have to get use to the feel of the rubber.

I have been trying to cast up in it now for the last couple of days and have been having no luck with all of the large molds. The resin casting seem to come out with an uncured film on the outside of the casting. I thought at first it might have been an oily residue (like you find with using some release sprays) that just needed washing off, but that doesn't seem to be the case, it's like the outside of the resin casting rather than having a hardness to it as it should is more like a handling a damp piece of bubble gum, slightly tack and slimy.

Has anyone every used this rubber before and could tell me if they had any problems with it?

The molds appear to be perfectly fine and usable.

I know it's not the resin because some of the other castings in the tank come out perfect. It's just the larger 70-11 molds that are the problem.

I have tried wiping out the mold with 99% pure alcohol (not the watered down stuff you normally buy for 1st aid stuff) to clean it up, but that didn't work either.

any ideas?

I have contacte Polytek, but that was after lunch this past friday, so I haven't heard nothing back yet. If i don't hear from them before lunch on monday, i'm going to call them.

DasPhule · Post by **DasPhule** » Sun Feb 13, 2005 11:24 am

Some silicones need to be post cured to bake out the residual oils and alcohols left behind from the setting up process. It's probably these that are inhibiting the setting of your resin. Don't know about your particular brand of silicone, but SmoothOn products suggest baking the molds at 175 for 1 hour per inch or so of thickness to cook off the excess alcohols. Check with you rdistributor or the product instructions to see if this is covered.

I have the same problem if I don't post bake. You can either let the mold sit for a couple of weeks and let them set up, bake them, or use some fast resin that gets hot and just keep pouring until the problem goes away. It usually stops for me after about 10 pours.

The parts are salvagable, too. Just bake them or set them in the sun to finish curing the resin, then give them a really good wipe down with lacquer thinner.

Now if the parts are leeching a clear goo and won't stop no matter how much you wipe them, you probably need to just simply shake your resin before pouring. Resins do come out of solution if left to sit too long. Leeching parts are usually not salvagable.

Erin
<*>

OdysseySlipways · Post by **OdysseySlipways** » Sun Feb 13, 2005 11:33 am

Thanks for the info. I am trying to find the papers that came with the rubber (no matter where i put something [mainly to read] it always gets moved and theri answer is "I don't know where it was put, maybe if you just put it away", hell, the reason i left it out was to read it!), if not, i'll just see if thy can send me a copy via email.

Come to think of it, I think there was something i took note to in the papers about cooking after molding............... now if i can just find them papers.........need more file cabenets.........(lets see, I have 3 4-draw steel cabenets, 1 7-draw plans cabenet, 2 2-draw cabenets, 1 12-draw index card sized [and that has them split draws, so tht would be 14 draws I guess] i stock some of my "cast only when needed molds in) ......... yes yes, more file cabenets........

OdysseySlipways · Post by **OdysseySlipways** » Sun Feb 13, 2005 11:48 am

i thought of a few other questions since that post.......

when i bake, do i need to worry about scrubbing out the oven afterwards or is it safe to cook in afterwards? I'd be baking with the oven blower on.

also, since I have used these molds already and have used spray release on them, i'd clean them up with that acohol first to clean off as much (if any) residue of the spray and resin.

now do you just sitt your molds on a flat cookie sheet? can they be wrapped up in foil (sealing the the mold in) to prevent any resin or spray burn off from getting into the oven and getting on the oven's surface (requiring cleaning the oven).

I sent off an email to Polytek asking for the information on the baking of the molds. I'm also going to take a look at their site too (to see if it's posted in there)

DasPhule · Post by **DasPhule** » Sun Feb 13, 2005 12:44 pm

Again, not sure of the brand you're using, but silicone is silicone so I guess it's all the same.

No, no cleaning is required after baking. All you're doing is getting out the excess alcohol that's inhibiting the cure of your resin. Set the oven to 125-175, place the mold on a cookie sheet, put it in for about 2 hours then come back and you should notice that the surface of the mold is, um, different. It'll be less shiny and feel less slimy. You'll also smell the alcohol when you open the oven. Just let it air our and it'll be fine. The fumes are almost non existant, really not a big deal at all. The molds won't pop or squirt or anything, so don't worry about having to clean the oven. About the biggest danger is if you grab the mold and it feels warm, it is! Hurry up and put it down, cuz it'll get REALLY hot the longer you hold it! After baking, set the molds on a flat surface and let them cool.

As for releaser and resin on the mold, it doesn't make any difference. I've baked molds that were caked with resin and it still worked just fine. In fact, the baking allows you to get that uncured resin off the mold because the heat forces it to set up. And dude, stop wiping the molds with alcohol! That is what is inhibiting the curing of the resin to begin with. Only release agents should touch the mold, ever.

Erin
<*>

OdysseySlipways · Post by **OdysseySlipways** » Sun Feb 13, 2005 3:37 pm

DasPhule

And dude, stop wiping the molds with alcohol! That is what is inhibiting the curing of the resin to begin with. Only release agents should touch the mold, ever.

sorry, i'll have to read what I posted earlier to make sure it's readying the way I was thinking, but........

What i was saying about the Acohol is that I was trying to remove any residue from the molds surface, after that I sprayed it with the release spray.

I never clean my molds (wiping them down with anything) other than when i take out the casting and somethng is left behind in either the fill or venting holes. About the only thing I do extra is coat the fill and vent lines so the resin pulls out freely.

I'm currently using Mann Ease release spray, yuck, goiong to have to go back to using Stoner, it releases my brass pins an stuff with no problem from the castings.

Stephen Sekulic · Post by **Stephen Sekulic** » Mon Feb 14, 2005 3:12 am

Substuff , reading your post I suspect your mold release is the culprit , Mann ease?. Does Polytech recomend there own brand of mold release? If so , stick with the product line , Smooth on is the same way . The chemistry is VERY finiky with other brands.
Stoner mold release is awsome , it seems to be the most stable with all the slicones I have currently used , including the Smooth on brands. Stick with it if you can.
You could always just try a casting with out it to see if there is any difference, or use a non scented baby powder as a release , that helps with alot of resins I have found and it's a cheap release agent.
Most silicones are designed to be used with out a release agent . The silicone gives off it's own type of release and most times that is what causes problems with resins that are not thier own . Come to think of it some resins are desinged to give off there own release as well, chemistry what a pain!!!
Despite what you may have heard , keeping molds clean and properly stored will give them longer life. This is fact not fiction , I have molds that are more than five years old and they are every bit as good as the stuff I have poured recently. Hope it helps , take care.

IFcdn

P.S. Silicones I have used that are VERY user friendly, they could be a back up for you at a later date: Mold All, Gi-1000, Gi-650, Synair Si-12 Si-25, Smooth On Mold Max 10, 20, 30 , Viasil .

chiangkaishecky · Post by **chiangkaishecky** » Mon Feb 14, 2005 9:53 am

IFactorycdn wrote:P.S. Silicones I have used that are VERY user friendly, they could be a back up for you at a later date: Mold All, Gi-1000, Gi-650, Synair Si-12 Si-25, Smooth On Mold Max 10, 20, 30 , Viasil .

Sweet ....

OdysseySlipways · Post by **OdysseySlipways** » Mon Feb 14, 2005 11:18 am

Well I dug and dug and dug and finaly found the papers that come with the mold material. it states to either leave the molds sit ina warm room for a couple of days of heat the in the oven for 4 hours at 212 degrees.

I have them sitting ona cookie tray (covered it with foil) and have the molds sitting open faced in the oven right now. I'll be taking them out at 1pm. I din't take notice to any acohol smell, but i can sure smell the rubber being warm! I'm glad my mother sin't here right now or i'd be up $h!ts creek right now.

All I have to do is keep the fan on for another hour after I take the molds out and hope the smeel is gone by the time my mother gets in from work.

OdysseySlipways · Post by **OdysseySlipways** » Tue Feb 15, 2005 6:15 pm

Well i got the second batch of molds heated up this morning. I casted with the ones I did yesterday, so in a little while, i'll be finding out if all has been corrected or not.

OdysseySlipways · Post by **OdysseySlipways** » Fri Feb 18, 2005 1:46 pm

Well the Baking did the trick, everything is working out just fine. I found the papers on the rubber (they were in the dambest place) and it called for 4 hours at 212 degrees. the only problem now is, the oven smeels of the rubber! I have heated it up 3 times now and the smell is just about gone..................... now i just have to figure out how to bake these last few molds, my mother's not working for the next week or so and i need them badly!

Migmaker · Post by **Migmaker** » Fri Feb 18, 2005 5:48 pm

just a little side note Chris, HSII and HSIII are actually manufactured by Dow corning...it's one of the best silicones out there, got molds over 15 years old still...I guess Alumilite took and offered it with their resins