Question about casting materials

[Axaerukai]

Hello! I'm new to the forum, and I have a bit of a problem figuring out the best materials for a project I'm working on, so I figured I'd ask

So, the project is a shield (medieval kind, supposed to look like metal). I have made my mold (concave mold) out of flexible rubber, and made a shell out of fiberglass that the rubber sits in to hold its shape. The shield is pretty large, about 3ft across, and 5in deep at the center point.

What I'm trying to figure out is what materials/techniques I can use to produce not just one, but multiple shields (need more than one) in a timely, cost-effective manner. Also, I want to keep the weight down if possible.

I've come up with two ways to do it. One is to fill up the whole mold with some lightweight material (some kind of foam?). This would be a fast way to make reproductions.

The second is to make a shell inside the mold that will become a hollow shield. I have tried this method with gelcoat/fiberglass, and it's very time-consuming, rather expensive, and produces a pretty heavy shield.

Does anyone have suggestions of other ways to do it, or does anyone know of a material that would work well for this application?

Any help would be GREATLY appreciated!

Thanks,

~Axaerukai

[michael]

What purpose will these be used for? Do they need to be functional for SCA fighting?

I ask this because I have done some work with my brother on reinforcing his shields for SCA heavy combat using fiberglass and various polymer resins, but the shield cores are made of aircraft grade aluminum.

If they are only decorative you could use an expanding foam material available from Smoothon.com, but only if you have a completely enclosed mold. Is the mold 2 pieces? with a back that defines the thickness of the finished piece?

Good luck, I can try to help, but give me some details or photos

---MC

[Rojellio]

Smooth-on comes to mind. Polytek have pretty much the same things too with different names.

"Shell Shock" is a mayonnaise consistency urethane. Powder coat the mold with metal powder.. (Spray release agent, Then kind of like baking a cake where you flour the inside of the pan.. except do it with metal powder) Then mix in some metal powder into the "shell shock". Brush the Gel coat on. I haven't tried this with shell shock BTW.. So I dont know for sure if the cold casting thingie works with it. Although I can see no compelling reason it wouldn't, it is an isocyanate & polyol based resin with a slightly different forumlae than the average everyday resin used for cold casting. .

For the foam I would use Foam-It 8. An 8# density foam, (not too rigid and heavy, and not too light) white in color. As soon as the gel coat starts to set, you could pour the foam. Cover the top of the mold with a board, or 1/8th - 1/4" thick polypropylene plastic if you happen to have it. The cover should have a hole to allow excess to go out. Hold down on the board while the foam rises. This backpressure technique yields better foam casting, and keeps things tidy.. somewhat.

The Above would be fast. If fast is more a priority. You could probably pour and demold several in an afternoon.

Make sure you have Graduated cylinders to measure with, which makes it much easier. (plastic will do) From a lab supply place. "Doctor Gloves" are also required. Unfortunately the Foam it 8 is measured by weight.

Make sure you react / neutralize the little bit of urethane left in the empty containers. Drain empty A side, into B side. Stir it a bit. Then spray some ammonia and water into the A side container, also spray any drips etc from A side with Ammonia and water mix. I sometimes work for a mine construction outfit. I have plenty of experience with reacting, testing and handling isocyanate & polyol.

[anton]

hi and wellcome smooth-on has a flexfoam-it that you can color to what ever you whant it flexebell and light. cost ? that you have to get from smooth-on i got a sampel to play with and it exspand 10 time it volume . goto smooth-on at www.smooth-on.com and look at there how todo page as a start, thy make movie props out of it so ????
hope it helps
anton

[Rojellio]

Flex foam is pretty cool.. but I am guessing he does not want to make Nerf Shields.

[Axaerukai]

Thanks for the quick replies everyone

The shield is for looks only really, doesn't need to stand up to sword blows or anything.

I am in fact familiar with smooth-on, if not all of their products. I use mostly their silicone rubbers.

I had actually considered using the flex foam. however, it seems pretty expensive (even though it expands 10 times?). The shield is pretty darn big, and probably has a rather large volume to fill with such an expensive foam. I could be wrong though?

Is there a way I could spray gelcoat without having to invest too heavily in a specialized gelcoat sprayer? I'd like to avoid the gelcoat/fiberglass approach alltogether if possible, but it's still an option.

Thoughts?

Thanks

~Axaerukai

[Axaerukai]

Okay, so here's a diagram of my options as I see them.



I'm still looking for a good (and inexpensive) alternative to gel coat/fiberglass. Is there a way I can spray gelcoat without an expensive spray rig? I would work with that, possibly.

Anyone have ideas?

thanks

~Ax

[ahirschman]

Hi Ax, I have recently used quite a bit of Polytek 1512-x for making both castings and mother molds.

A 1/8 to 1/4" thickness area will yield an extremely strong mother mold. The stuff has a tensile strength of over 5000 PSI. You could make a thin coat of the 1512x mixed with another additive and then painted on with a brush (The additive should be dry (and of course, you should do a small test first))

Before the first coat hardens completely (or not much after that) paint more coats of the plain 1512x. You can thicken it to go quicker, or do more coats. The x stands for the accelerated cure, so it hardens fairly fast. Do that until you have your desired thickness. You may want to make the shield 1/8" thick, and then build up the edges to 1/3 or 1/2" with some thicker reinforcing ribs throughout. Depends on the final size.

Ari.

[Axaerukai]

Thanks What if I just took some regular polyester resin and added a filler like cab-o-sil? (little hollow glass spheres). I'm thinking this would make a thicker substance that could more easily be built up to thicker layers.

What do you guys think?

~Ax

[justme]

Hi,
Have you looked into Forton MG? It's a gypsum/resin composite. Terrifically easy to work with, not all that expensive, easy to reproduce, and great for picking up details.
I've cast quite a few pieces for people who couldn't afford bronze. It takes patina of any sort, sands and patches with no problem.
If you think you are interested, check out my website to see pieces cast in Forton... www.jsesti.com
Best of luck, j

[ahirschman]

Originally Posted by Axaerukai

Thanks What if I just took some regular polyester resin and added a filler like cab-o-sil? (little hollow glass spheres). I'm thinking this would make a thicker substance that could more easily be built up to thicker layers.

What do you guys think?

~Ax

The only time I have used polyester resin is as a binder in composits with reinforcing materials, such as fiberglass. Not sure how well it will work by itself.

I have never used Forton MG, but have literature and samples of the stuff. As Justme said, that would probably be a nice substance to use.

Ari.

[anton]

hi all have you consider use talk powder in resin same as mico ballon filler.
i use it in exposie resin to cast mixsing tool for paint ect. works well and is stong i have fond that the more filler you add to get a pasted like consistens that you can then paint , pore or smear on to the mould.
hope that help.

[Lucia]

Originally Posted by ahirschman

The only time I have used polyester resin is as a binder in composits with reinforcing materials, such as fiberglass. Not sure how well it will work by itself.

I have never used Forton MG, but have literature and samples of the stuff. As Justme said, that would probably be a nice substance to use.

Ari.

Hi. Have you consider the papier mache technique? It is simple to make, light weight and almost free.