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Post by psitty46 on Oct 26, 2021 8:14:02 GMT -5
Hello,
I’ve been using the plat series silicone with Clear Slow resin for several years with no issue. I recently switched to the tin High Strength 3 since my part has a decent undercut and the flexibility is nice.
My question is (HS3): the de mold time being ~24 hours, how long after that time is the mold ready to be used for casting? I’ve made several molds, waited about 72 hours and the resin is not fully curing in it like it used to for me in the plat (Clear Slow, poured yesterday and it’s still tacky/flexible today). I used to be able to pour clear slow into the plat, and after the demo of time of 4 hours pull the casting out and it would have a smooth, hard surface. I’d then post-cure it.
The only thing that has changed in my process is the HS3 from Plat so I’m trying to figure that out.
Secondary question; silicon oil on Alumilites website suggests adding it to the mold when mixing to increase releasing ease. I added about 1 gram to a 250 gram mold, well under the max recommended amount, but could that also be causing it?
Thank you!
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Post by notoes on Oct 27, 2021 7:06:35 GMT -5
After curing the HS-3 should be fine to cast in at 72 hours. And slower curing resins usually take longer to hit full cure in both HS-3 and Plat, sometimes there are little differences in curing times between the two silicones. Now that being said, let's go over the process to nail down the problem.
1) Before pouring the resin in, are you "warming" the mold? A minute on high zap in the microwave is what I give mine when I need to warm them. You could also leave the mold on a griddle (not used for food ever again) on the lowest setting and take it off when the curing time for the resin is up. This should help a little with the surface being tacky and too soft.
2) Yes the oil can be doing that. You can always use the oil after the mold is cured, just wipe in a very small amount before casting as a release agent or whenever the mold feels "dry" - like it has lost a bit of flexibility.
Additionally, is the resin smooth after post-curing? If so, then it just needs a little extra curing to get where it should be. The major difference between the HS-3 and the Plat is one is a "tin" cure and the other a "platinum" cure, they're going to be a little different in how they handle things and cure a little differently but once you know how to work the differences, both are very good to use. Let us know how things go.
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Post by psitty46 on Oct 27, 2021 14:28:02 GMT -5
Thanks for the response!
Yes, I do warm the molds in my shop toaster oven. 150 degrees while I prep the rest of the materials.
I’ll try making some molds without the silicone oil embedded…simple solution if that works.
As far as smooth; the masters are like glass. So I expected the same. On the castings, there are portions that are smooth, and portions that came out with a texture. I just tried polishing the castings I did Sunday night and they are still too soft.
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Post by notoes on Oct 28, 2021 8:39:38 GMT -5
Yes try the molds without oil and let us know how it works.
Polishing should add heat so I'm not sure why they're not hardening up like they should. Try hitting them with some heat from either a heat gun (not too hot) or a hair dryer. Heat hurries along the cure but too much heat for too long while soften the resin back up until it cools back down.
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Post by psitty46 on Nov 1, 2021 21:01:37 GMT -5
The molds without the silicone oil resulted in cured resin. So that’s a win.
However, when the castings come out they seem to have an oily residue on them, and also a surface texture. The masters are high polished, almost glasslike, so I am not sure where the texture came from?
The molds were preheated at 150 degrees for about 10 minutes in the toaster. Resin thoroughly mixed. Alumilite clear slow. I have never had this issue and I’ve made almost 1000 castings just like this before with Plat 40. New masters. Only thing that changed is I went to High strength 3.
If there was a way to post a photo here I would, but I don’t see the option.
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Post by notoes on Nov 2, 2021 6:47:43 GMT -5
At least you have a couple wins there, the oily residue is just the silicon oil and you just wipe it off or rinse it off. But that texture is definitely a loss and I'm not quite sure why it's coming up.
When you made the mold, did you first brush on the HS-3 before pouring the rest of it? Can you open up the mold cavity and see if the texture is on the inside of the mold or if it's the polished surface it should be?
The way to attach a picture that I've found is to post a reply and then "Edit" it which gives you the full Editor window that has all the options on it, especially the Insert Image one that you need. Then you click Save Changes and the picture should show up.
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Post by psitty46 on Nov 2, 2021 8:33:44 GMT -5
 Yes, the inside of the mold looks just like the master; very smooth and even looks glossy. The master is the clear in the background. Hopefully the image quality allows you to see the texture in the purple ones surface. I appreciate your responses/help. |
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Post by psitty46 on Nov 3, 2021 8:04:21 GMT -5
Made a mold with Plat 25, and the casting came out as I expected; high gloss and fully cured.
Not sure what the issue with the HS3 is.
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Post by notoes on Nov 15, 2021 22:21:43 GMT -5
I see the texture on the purple one and if the inside of the mold is like it's supposed to be, so I'm thinking the Clear Slow resin is being "inhibited" inside the mold. Which is very likely the problem as it is recommended to "use platinum base silicone rubber molds when pouring Alumilite Clear and Water Clear". I had to look back over some of the technical data to be sure if what I was thinking the problem seemed be (that the cure was inhibited) was what it probably is.
So for now, I'd just the Plat 25 mold and if you still want to use the HS-3 mold be sure to get some Amazing Clear Cast (ACC and Alumilite Clear Slow are two different resins) to pour into that mold - you shouldn't have any problems with the Amazing Clear Cast getting inhibited in a HS-3 mold as I've used them together with no problems.
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