Need help choosing silicone and resin

[Machinepriest]

Hello everyone.
I'm just getting started with a project in school and I need some help choosing the right silicone and resin for the job.

I am to sculpt a miniature in polymer clay which I will cast and hopefully sell if the demand is high enough.

I have my own vacuum and pressure set-up which I plan to use to eliminate any bubbles, my school will pay for the silicone and resin, but it's up to me to find the right type for this project (As you know, it's a jungle when it comes to casting materials).

So!
I was thinking that I need a silicone that doesn't shrink much and that has enough working time for me to be able to mix, degas, pour and place in the pressure pot (If that's really needed)
The silicone we have at school apparently shrinks 4-5% which seems a bit much when it comes to miniature casting.
Not sure what to go for when it comes to shore hardness either.

As for the resin, I'm not sure if I should degas it directly after mixing it or if I should do that when I've poured it into the mould, before I place it into the pressure pot.
Whatever I do I'm guessing I need a resin that has a long pot life.

Any help would be greatly appreciated!

[mangozac]

I wonder what sort of silicone it is that your school has that has such significant shrinkage? Hardness between ShoreA 20 and ShoreA 30 (around 25 is optimal).

Since we don't know what products are available in Sweden can you send a link to the catalogue of a local supplier? That will make making recommendations much easier!

[Machinepriest]

I was thinking 4% sounded a bit much as well, and looking at the specs for the silicone I'm pretty sure it's 0.4%. That silicone is called M4514.

It would be much appreciated if you could find the time and look at the catalogue, it is in Swedish however. But you might be able to make sense of it anyway since a lot of the words are quite similar in English. I think Chrome can translate sites as well

Addition silicones: http://www.abic.se/pdf/ElastosilAdditionshardande.pdf

Condensation silicones: http://www.abic.se/pdf/Tabell-Elastosil ... rdande.pdf

We were thinking of trying this one out, but it has a shoreA of 40, is this too much?
http://www.alchemie.com/2011/05/rtv-250/

These seems to be the resins that Abic chemistry carry.
http://www.synthene.com/en/polyurethane ... esins.html
What worries me about these resins is that the datasheets mention preheating and storing the moulds in an oven set to 70 degrees Celsius, something I've never heard of before.

[mangozac]

[Machinepriest]

Elastosil M4514 it is then!

Now I just need the right resin...
I'm still not sure which qualities I'm looking for here as I don't really know if I need to degas it or if pressure will be enough.

I was thinking:
Mix resin
Degas resin
Pour into mould
Degas mould
Pressurize mould

Do you think this is overkill?
The miniature I'll be casting isn't overly complex.

It seems hard to find a resin with enough pot life for all these stages.
I was looking at trusty old smooth-cast. 305 to be exact, but I doubt 7 minutes would be enough for two trips in the vacuum chamber and one in the pressure pot.

Maybe if I just degas it after mixing and then pour it into the mould and let the pressure do the rest?

http://www.benam.co.uk/products/plastic ... -cast-300/

I don't necessarily need to buy the resin from Sweden. Any suppliers based in the EU with quick, reliable service would suffice, as long as they don't charge an arm and a leg for shipping.
I'm going to ask them, but I don't think Bentley ships to Sweden.

I don't have much time left on this project so I really need to get my hands on the right resin ASAP.

Thanks for the help mangozac, you are a gentleman and a scholar!

[mangozac]

[Machinepriest]

Oh right! I thought the degassing was essential, but I guess pressure will take care of any bubbles.

I have two separate set-ups for degassing and pressure, so I'll have to switch during the process.

I can't say anything about the price of PR402 as I do not know, but I sent the company an E-mail and they instead recommended two other resins.

RenCast FC 52 which is apparently quite similar to Smooth-On's products, and a much slower setting resin called Renpim 5219.

Rencast FC 52:

Renpim 5219: http://www.mouldlife.net/renpim-5219-1276-p.asp

I'm pretty sure I can convince my school to order me some Smooth-Cast 305 or 310 from the uk as well.

So, what say you? Which would serve me best do you reckon?

[mangozac]

FC52 sounds like it would be worth a try. The datasheet does mention post curing - you should confirm with the supplier just how necessary that is.