Hardening Sintra?

[IronFan3000]

Hi all,

I'm currently working on a 1940's MCU captain america shield. The one he goes on tour with before he gets the vibranium one. I have made it out of 1cm thick Sintra, but what I found was that the edges and corners really easily kind of broke and chipped off since the material was so soft. I want to be able to take it to conventions, and if people want to hold it, I don't want to have a heart attack over the possibility of pieces coming off if it is dropped.
I am based in Australia and am not sure if it's just the particular product from my area, as I have read about many people using it for stormtrooper amour and don't seem to have the same problem?
Can anyone tell me if this is just normal for the product or if I should be looking for a different company who sells it to see if I get better results. And if it is normal, does anyone have any suggestions on how to harden it or put a protective coating over it to make it indestructible?
Thanks in advance,
Em

 

[TazMan2000]

Indestructible? Not a chance. But you could coat it with a varnish or coating. Other than that, it would have to be re-created in a harder material, perhaps like stainless steel, aluminum or perhaps fiberglass. Perhaps you could overcoat the whole thing with fiberglass. It wouldn't make it indestructible, but it would lessen the chipping, if done correctly.

TazMan2000

 

[JPH]

Try an automotive clear coat on the visible side, fiberglass or slush cast resin on the inside.

The issue is your shield is weak to begin with. If sintra is left in the sun it gets brittle. It should be wobbly, not chipping easily, though. Id make a mold of the original then cast new ones when the old ones get broke.

Also, consider just making one out of 0.06 aluminum. The aluminum would be much more durable. Go up to 2mm thickness if you want some good weight.

 

[Riceball]

Another suggestion, if you can get your hands on something like ABS plastic, you could remake your shield using that, ABS should be much stronger than Sintra.

 

[TazMan2000]

Sintra is basically PVC foam. Lightweight, strong, and perfect for signs. But it still is foam.

TazMan2000

 

[JPH]

But R2D2 builders use 2 layers of 0.04 (1mm) sintra to skin their droids, it shpuld be so delicate as described.

But, y'know, once you make it, *THEN* you find out the flaws in the design, I know I'd do whatever I could to keep it usable.

 

[Valor]

But R2D2 builders use 2 layers of 0.04 (1mm) sintra to skin their droids, it shpuld be so delicate as described.

But, y'know, once you make it, *THEN* you find out the flaws in the design, I know I'd do whatever I could to keep it usable.

Sorry, but that's incorrect. You're confusing Styrene (which is a material) and Sintra (which is a brand name for a very different product). Sintra is expanded PVC. Meaning it's lightweight because of the sponge-like composition of the material. Styrene by contrast is solid throughout. R2 Builders use Styrene to skin their droids.

 

[IronFan3000]

Try an automotive clear coat on the visible side, fiberglass or slush cast resin on the inside.

The issue is your shield is weak to begin with. If sintra is left in the sun it gets brittle. It should be wobbly, not chipping easily, though. Id make a mold of the original then cast new ones when the old ones get broke.

Also, consider just making one out of 0.06 aluminum. The aluminum would be much more durable. Go up to 2mm thickness if you want some good weight.

I would absolutely love to make it out of real metal but the real shield from the movie is actually around 1cm thick not just a few millimetres, and I want that thickness in my shield. Unfortunately I'm on a pretty tight budget and that size and thickness of aluminium is very expensive where I'm from. Plus I would have no idea how I could shape it and put a curve in it with the very limited tools I have at home.

If I coat it in polyurethane resin on the front and back, would that be strong enough to be drop proof? Or as a last resort I could mould and cast the whole thing with resin, but I'm not sure how heavy it will be then. And also I have never cast something before.

 

[IronFan3000]

Another suggestion, if you can get your hands on something like ABS plastic, you could remake your shield using that, ABS should be much stronger than Sintra.

ABS actually sounds like the perfect material, but from my research it doesn't come thick enough. I'll keep looking though.

 

[JPH]

I know the round shield is 1/8th inch thick. Around 3mm. A 1 cm shield would be heavy. I dont think it is 1 cm thick. For instance, iron man's armor plates look to be about 1/4 inch thick or 6mm. No matter what you make the shield out of, it wont be completely drop proof. Aluminum will ding, resin may crack. Stuff like that always falls at the Murphy's Law angle. I thought the heater shield was only bowed left to right. That is easy for aluminum. If complex, then English wheel would be easiest, since it isnt a deep curve.

Smooth on 325 is great clear resin for slush casting. Just put a border around the edge of your shield and mix the resin, stir, pour it in and slowly dance it around until it hardens. It will be as heavy as you make it. Great tutorials for it.

If you are really worried about drops, Id mold it. Use a brush on silicone like Rebound 25 for soft mold, Free Form Air or plaster of Paris for rigid outer mold and slush cast with Smoothon 325. Smooth on is clear, so if you got fancy, you could actually.mold section in different colors.

 

[JPH]

Also, since worried about drops, just make it out of foam. A great paint job and no one will know it is foam

 

[IronFan3000]

I know the round shield is 1/8th inch thick. Around 3mm. A 1 cm shield would be heavy. I dont think it is 1 cm thick. For instance, iron man's armor plates look to be about 1/4 inch thick or 6mm. No matter what you make the shield out of, it wont be completely drop proof. Aluminum will ding, resin may crack. Stuff like that always falls at the Murphy's Law angle. I thought the heater shield was only bowed left to right. That is easy for aluminum. If complex, then English wheel would be easiest, since it isnt a deep curve.

Smooth on 325 is great clear resin for slush casting. Just put a border around the edge of your shield and mix the resin, stir, pour it in and slowly dance it around until it hardens. It will be as heavy as you make it. Great tutorials for it.

If you are really worried about drops, Id mold it. Use a brush on silicone like Rebound 25 for soft mold, Free Form Air or plaster of Paris for rigid outer mold and slush cast with Smoothon 325. Smooth on is clear, so if you got fancy, you could actually.mold section in different colors.

If you look closely at the movie the shield is actually really thick. Based on my scale calculations from several references it is 1cm. Here's some references I used. The first is the actual costume and prop from the movie at auction. And the second is a screenshot from the movie.
I have the Australian alternative to smooth on so if I run out of ideas I will try moulding it and see what happens. Quite a lot of silicone though.
Also with the foam idea, I did consider it but I think I want something more rigid.

 

[JPH]

Wow! You're right. Thanks for the home work.

 

[armamentfactory]

You can coat the edges with CA glue (the watery, industrial kind). Once the CA penetrates the pores, the area turns rigid.
I use the method for stiffening/reinforcing Sintra, also very useful if you're making very thin parts.

 

[TazMan2000]

I hope you're not thinking of casting the whole thing in resin without reinforcement. Resin is pretty strong in a block but even when it is 1cm thick over a wide area you have to be careful. Think of it like a ceramic dish. If you drill holes for the handle you are weakening the structure overall.

TazMan2000

 

[BrundelFly]

To harden edges....soak in Superglue.

 

[Darth Lars]

If I coat it in polyurethane resin on the front and back, would that be strong enough to be drop proof?

Probably not. More rigid often means less flexible and thus more brittle.
While there are different types of polyurethane, the regular varieties are not very adhesive, and quite rigid and brittle. Polyester resin is not better. CA glue adheres well but it is not good as a resin: it is also rigid and brittle and you could end up with the edges crumbling.
Laminating-epoxy might work best.

 

[IronFan3000]

You can coat the edges with CA glue (the watery, industrial kind). Once the CA penetrates the pores, the area turns rigid.
I use the method for stiffening/reinforcing Sintra, also very useful if you're making very thin parts.

Wow thanks! I'll definitely have to try that. Do you have a particular brand of glue you like to use?

 

[IronFan3000]

Laminating-epoxy might work best.

Just had to google it since I've never heard of laminating epoxy, excuse my inexperience. Considering it is used for surfboards which are just foam on the inside, and surfboards are super hardy, it's probably a safe bet that my shield will be ok with it. Surfboards are however glassed with a mix of this and fibreglass so do I have to fibreglass as well or can it be used on it's own? Where does the strength come from, the epoxy or the fibreglass? Any suggestions on how to get a smooth even coating over a curved surface? How do I stop the stuff from just running off?

 

[armamentfactory]

Wow thanks! I'll definitely have to try that. Do you have a particular brand of glue you like to use?

No problem!
I'm not sure which brand is available on your end, I have a local equivalent to industrial Cyanocarylate. It's called CYNO 2 on this side of the world.

EDIT:
You'll want the kind that doesn't have an exothermic reaction - you'll be coating edges with a lot of CA, if it's the kind that heats up, it'll tend to warp the Sintra.