Replicate sea shell in brass: incomplete

You are probably right. No contact with any of the admins connected with his site.
Do you have any bronze sculptures in the pipe line Richard?

 

Ceramic shell is probably the way to go for such a casting. It doesnt need huge expense in equipment and materials. I buy small amounts as I need them and I use simple everyday items for shell production. A burn out kiln for ceramic shell is not needed just a cheap weed burner or similar, and you can suround with fire bricks for a bit of insulation. But I have seen it done with just the weed burner.
These video of mine shows my method for shell application and burnout

 

Use plaster of paris and make a mold of the thing. You can even make a silicone mold of the thing with a tube of hardware store silicone.

 

Probably you mean for making a wax casting to be burnt out. It is indeed locally available here as a tube for a caulking gun. It is well worth the try. How long does the silicone take to set ?

 

Couple days. There is something you mix in it. Run a YouTube search, you'll find someone making a mold with some caulking.

 

I have made some with tube silicone. I add corn starch and thin it with naphtha. It has limits. It shrinks a lot, unlike real silicone rubber, but for small items, it works.

R

 

Posted: Wed Jan 07, 2015 11:11 am Post subject: low cost alternative for some RTV silicone applications
Found this on Alloy Avenue... Funny how little gems of information just pop up.... I'm off to buy a tube of silicone sealant... I've got several small things I need a mold of....


Ok there is a bit of a story here first...
A few years back I worked at the local museum here. They were building some dioramas of the local aboriginal people as they lived centuries ago. The one diorama was a fish camp. In this camp they needed a pile of caught fish and a pile of fish being cleaned including the internal organs of the fish. They had live fish which they speared and stacked, then froze them. Same with the cleaned fish and fish guts, also frozen. They were not casting these in metal but in polymer resins and such, but the molds interested me.
They did not use RTV silicone, which here is kind of pricey. The stuff they used cost less then 1/4 of the cost of RTV. Plus the frozen fish were molded and placed back in the freezer for the mold to set. This product will set at room temperature or even in a freezer. All the details of the fish were captured in the mold. The product is simply washed silicone sealant/caulking.

Not that this will replace every application of RTV silicone, it does make a robust silicone mold, on the cheap.

Here is how you wash it. This process is very smelly, like very strong vinegar. Good ventilation is highly recommended.

Get 100% silicone caulk in the application tube. What we will be doing is washing out the chemical inhibitor they add to the silicone to stop it setting in the tube. Cut the end off and push the entire contents into a 5 gallon pail with 3-4 gallons warm water and a couple drops of dish soap. Gently knead the blob, under water the whole time, stretch and squish it to effectively wash out the inhibitor. You will feel it start to get stiffer and lots less gooey. Try not to fold the blob and trap water pockets in it, as this is not desired.
Now remove from the water and apply to the piece you are molding. If your form is solid just press the silicone into place and let it set up. I do use a silicone release spray on my model, and that should be mentioned.

For plastercine models, I freeze them and they are then solid and I can mold them without damaging them.

I cut my piece out of the silicone mold, but I do make a 2 part plaster casing, first, that will hold my mold closed when filling. So if I cut out the silicone mold, say, North-South, then my casing will split, East-West. I cut my silicone in a sort of zig zag pattern cut on several angles, with a hook blade razor knife. This helps the mold want to fit back together with minimal slip or distortion later.

I thought I would share this info as there may be a time when you want to make a wax of something, like an Ice Sculpture, and this would be the way to do it. Did I mention it sets in a freezer?
_________________
If someone has a gun and is trying to kill you,
it would be reasonable to shoot back with your own gun...The Dalai Lama..Seattle 2001
Fredo
The preceding post reminded me of the above info I copied off AA and posted on TK560.com. That's the site that helped me when I designed and built my 2 vacuum formers.. The site was started and maintained for people who wanted to make their own plastic, Storm Trooper armor.. It was the only site that had any DIY help on building a vacuum former on the cheap.. Also plans for more expensive kit-built VFs..

 

Good idea, I didn't know that. But the biggest challenge is applying the de-inibitorized caulk to the (ceramic) shell model. The outside is rather rough, so I am afraid that the mold cannot be removed without damaging it. Is there a way to prevent sticking of the caulk to the shell ?
I tried thin plastic foil between and then evacuating it in a vacuum chamber hoping that air pockets under the plastic move out. But that did not work, probably because the outside (i..e. outside the plastic foil, but inside the vacuum chamber) absolute pressure is still the same as under the foil, which are both well below ambient pressure.

 

Normally people are not too bothered about damaging the original once the mould is made because you can then cast as many wax copies as you want and as many metal copies from them

 

UMR universal mold release, 15-22$ on amazon.. I found a silicone only spray at Home Depot.. It works the same as a umr, I have both.. Don't get the one with a petroleum additive. The cans look alike and are both labeled silicone. I did, it smelled like WD-40.
I have used silicone spray since 1970, on vulcanized rubber I'd use a number 11 scalpel to cut the mold..
I have a half gal, hand pump wax pot I use to inject ring molds.. Also fill straws with wax for gates and vents. My pot was made before air injection was popular and has its advantages. Two screws and the pump lifts out, and I can dip out wax for larger pours.. Amazing, the fact that it still works and maintains temps. after more than 50 years. It's not perfect, the little light that turns off/on as the element heats, that doesn't work..
Thankfully I'm not stupid enough to take it apart.

 

Now I wrapped the shell into silicone caulk and after one day it appears to dry, but I'll wait for a few more days.

In the meantime I found two other shells (yes very sililar to the logo of a large oil and gas multinational) which I sandmolded and the smaller one (2" across) filled entirely, but the larger (3" across) did not. I thing that adding phosphorus also helped. I put 2g mixture of NaPO3 + Al powder + silica sand in a small copper tube and added it to the already molten metal. These ingredients react above 700 C to isolate phosphorus which dissolves in the metal.
So still, thin casting appears to work, but yet I'll try with investment as well when the caulk has set on the first model.

Left the casting (with sprues still attached), right the snell models.





The casting viewed sideways with two sprues.

 

I came across this today.

 

Great idea using the removeable wood parts from the mold frames, and the vents to the surface to help the air escape. So simple, Outside the mold box thinking.
Fredo

 

Watching that video for the first time I found his flask construction a little unusual when I realized it was going to be cast vertically, it made sense. Reading through the comments to that video and of particular interest to us here, he says,

 

Good idea, he uses vents. It is the same vertical cast as I tried earlier, but without vents. The latter might do the trick. But it also maybe that his shell pattern is thicker.

 

How did your silicone mold come out?

 

Metallab, suggestion: use one sprue right at the center, and add another inch or two of height to the sprue to exert more static pressure, should be able to get it

 

Here I tried a 2" sized shell of which I made two molds.
The left one is cast in a 30 degree tilted flask (as shown in the picture): both risers filled (and overflowed a bit), the right one is just a default horizontal cast: one riser did not fill (rightmost), but the other did.
So using risers is probably the solution.

 

Today I finally cast the 'original' shell with which I started a week ago.
Making an investment was not a success. I put silicone on it in the hope it would make a better finish, but the silicone remained sticking to the model, so I had to clean up the model shell extensively, so I could use it as a model again.
But now I used the red 'Delft casting method' sand, a petrobond sand with a smoother finish.
And now I cast the bronze into it with the same tilted mold as the 'flat' shell yesterday (previous post) and it filled entirely. Sprue is left, riser is right, the other riser did not fill, but the mold did.