Choices regarding Smooth-On products (Smoothcast)

[chadcham]

I am in the process of trying to mold and cast several prop pieces generated from 3d models that have been prepared / sanded to a nice finish. Ideally, I would like to cold cast the items using the aluminum metal powder. I am familiar with the molding and casting process, however I am a little confused as to what works with what when it comes to the rubber, casting material, and release agents. I would like to have the pieces be very strong (and not very flexible) which has guided my initial selections below.

Here are my questions:

1) Would Smooth-cast 380 or 385 be appropriate for this purpose? Which one is more appropriate for mixing with metal powder? I also considered Smooth-cast 325 but from reading it seems like 380/385 would create a ‘stronger’ or ‘harder’ cast.

2) For the mold, would OOMOO 30 be sufficient or is there a better option? I’ll be using boxes I built and oil based (non-sulfur) clay during initial molding.

3) Lastly, would Ease Release 200 be appropriate as a releasing agent assuming the mold & casting choices above? From what I read it will work with silicone & urethane resins.

Thank you for any pointers!
Chad

 

[robn1]

Smooth-cast 325 is translucent and would require tint to avoid making a clear part. If you want an aluminum or metal look I would say use black tint with the aluminum powder.

380/385 are filled resins, they are very hard but also brittle, they could break in thin sections. If you're casting a large part they should be fine, but avoid using it in thin or small parts.

For most parts where I want a hard but not too brittle part I would use Task 2 or 3, very good resins with low shrink. They're white so would need some tint along with the powder.

Ease Release 200 is fine, but lately I've been using dry lubricants and I prefer it. I'm using Liquid Wrench dry lube with "Cerflon", which is PTFE or "Teflon". It sprays on wet but the carrier dries leaving a dry film of Teflon, works great.

Oomoo is fine for simple parts that you only need a few copies of, but it's not very strong. The low viscosity is good for releasing bubbles so it's fine as long as long life isn't a factor.

 

[Duncanator]

Listen to robn1, he knows what he's talking about! Good advice.

If you are wanting the finished piece to have an aluminum look; I've had good luck with dusting the inside of the silicone mold with aluminum powder and then casting with a clear resin filled with aluminum powder. It looks pretty good, though it's hard to get it to truly look like machined metal.

If you are only making a couple of castings, you probably don't even need mold release for urethane in a silicone mold. But if you want your molds to last longer, they are a good idea.

 

[chadcham]

robn1 -

Great - thank you for the feedback! I am going to give Task a try and I'll order some 325 as well to compare how they work with the metal powder.

Is there a better option over OOMOO that you would recommend that is also low viscosity?

Also, I assume this is the Liquid Wrench dry lubricant you were referring to: http://www.amazon.com/Liquid-Wrench-L512-Lubricant-CERFLON/dp/B000CPJLE4

Duncanator - Thanks. I saw another article that also talked about dusting prior to casting for a greater metal effect. I will give that a try.

 

[robn1]

Yes that's the lube I use, I get mine at my local ACE hardware.

I can't think of an alternative to Oomoo that would be any better. Generally the low viscosity goes hand in hand with lower tear strength. You could add silicone thinner to another silicone to reduce viscosity but it will make the cured rubber weaker. I've never used Oomoo but I hear good things about it, just don't expect to get a hundred pulls from it.

 

[smick6]

Hey robn1,
What type of mold materials have you used that Liquid wrench on? I usually use mold max 20 and was thinking of trying that stuff on there.

 

[robn1]

I've used it on Mold Max XLSII, making fiberglass parts with Epoxacoat brushed in as a gel coat. The epoxy was really eating up my molds, and Ease Release and other "wet" releases make it too hard to brush in the gel coat. But the Liquid Wrench works great, my molds are holding up longer and I have no difficulty with the gel coat.

 

[Keevanski]

I've had good luck with dusting the inside of the silicone mold with aluminum powder and then casting with a clear resin filled with aluminum powder. It looks pretty good, though it's hard to get it to truly look like machined metal.

And you don't need to add any extra pigment to the clear resin? Just mixing the powder with the resin and that's it? Because it's the idea that I want to do.

From the shop where I will buy the materials they recommend me to buy SmoothCast 325 and add a pigment, but if this works without pigment, it would be nice.

I saw this video from a guy aparently doing that just with powder, but I don't know if he used clear or colored resin.

https://www.youtube.com/watch?v=x_V4vX2TuYQ

Thank you in advance!

 

[Duncanator]

325 is a good resin for that. A pigment will alter the color of the aluminum powder, which can be good sometimes and bad in others. I usually use the aluminum powder with no pigment.

 

[Keevanski]

Oh thank you so much for your quick answer!

Yeah, I think I will try first without the pigment. I just find another video doing exactly the same and the result is so good:
https://www.youtube.com/watch?v=Z04YmPQssAg


I have another noob question. In the shop they have iron powder and only this imitation of silver powder (they haven't aluminum powder): http://www.formx.es/images/zilverpoeder250gram.jpg

Any of you know the results with the fake powders? I'm thinking this option because I think the iron powder will be a little dark for my prop...

I want to achieve a color something like this: http://fc00.deviantart.net/fs71/f/2013/212/0/8/witcher_medallion_04_by_gekk3-d6g3m34.jpg

In any case, if you have any advice to add light (like a polish or something) to the finished piece of iron, please let me know!

Thank you so much for your attention! (And sorry if I made mistakes with my bad english, it isn't my first language).

 

[Kevin Gossett]

The silver powder you linked to will be very bright (and it gets everywhere!) The iron powder will be dark. Check with the shop to see if the can order the aluminum. I've had best results using black resin with aluminum powder to give a more realistic metal finish.

 

[Keevanski]

Ok, so definitely I will go with the aluminium, if I can't buy it in this shop I'll try another.

Thank you sooooo much!!! n_n