Custom molds?

[colu41]

Now that I finally have heat hot enough to completely liquify my silver and gold, I can't use my wooden molds anymore. Too hot of a melt, just burns the shape of the mold away too fast.

Now, without spending $20, $30, even $50 some on a custom graphite mold, how could I make one myself?

Any suggestions?

I was thinking of making one from steel but I dont know if that would work. Just looking for a simple 5 oz mold. I wanted it larger than most 5 oz bars and thinner.

Thanks for any info.

 

[Geo]

keep your melted PM's away from other metals. you can make some crude molds from plaster or clay, just make sure the clay does not contain iron or other metals. they wont last very long, maybe one shot. be sure they are completely dry or it could bust or even explode from steam build up.

 

[colu41]

Hm. Never thought of clay. Would that have to be baked? Or can it just be set out to dry?

 

[element47.5]

The following occurred to me. To make a steel mold for somewhat larger sized bars, why could not one take a short piece of I-beam, as pictured below, (or channel, but I-beam would be stronger and furnish better welding seam) then sand the heck out the inside, trim the ends at a slight angle, then weld some steel squares onto the ends, creating an internal cavity that is a trapezoid viewed from either axis. The internal cavity of the I-beam is already beveled, with a nice round fillet at the base.

 

[colu41]

Thats actually an awesome idea! But like you said thats for bigger bars. I was hoping for something smaller. Hmm

 

[element47.5]

Well, you can get channel down to...pretty small, I have definitely seen 2" (distance across the external widest dimension...the surface that would naturally be oriented down when pouring) and there's no reason to believe you couldn't find something smaller (that isn't showing up in the catalogs I am looking at) wandering around a metals scrapyard. Two feet of the stuff and you'd have enough to make a few prototypes and a final version or two. IMO a 2" "web" would, by the time you reduce that by about 1/2" net (taking into consideration the wall thickness and the fillet curvature on the inside, the cavity) would produce about a 1.5"-1.7" bar width. That seems about the size of the 10 oz bars I have. I think I would prefer the I-beam, because of the stiffness, has a built-in base, slightly easier weld, and better heatsinking for bar cooling. Find this as a piece of scrap at an ironworks and your cost would be miniscule.

I'd be wary of clay. There is a YouTube of a guy who casts silver in clay, but any moisture and the thing will explode. The guy in the video seems like he has been doing it for quite a number of years (hint, hint) Plus you have to remake your clay mold periodically, maybe for each pour, and for that, you need something of another mold if you want your bars to be uniform. I also believe you'd be in for more cleaning of the finished bars and be more subject to inclusions but I don't know that for a fact.

And by the way, there are a zillion types of "clay" and without a knowledgeable analysis, you have almost no way of knowing what's inside any particular sample of clay. IMO you would have to buy some product sold as and known as "molding clay", and you'd possibly have to buy a 50# bag. You would have to carefully dry out your mold, not just set it out in the sunshine. Talking some number of hours in an oven and maybe even hotter. The bad news is, if it blows up, it will blow up....when? When you are there with your ladle of hot metal, standing over it, yes, with your safety gear on but your charge gets splattered all over the place. I am absolutely sure there are reliable techniques to create clay molds, but personally, I just wouldn't go in that direction for the reasons I cited. I like steel. It is stupid cheap, essentially indestructible. Weld it with the same torch you already have. Done, finished.

 

[publius]

Clay can be used for molds and has been for centuries as has plaster. Heat your clay/plaster molds to about 450 (f) until there is no longer a change in their weight. This indicates that all the moisture has been removed. Soot them up and keep them hot and they will last at least one pour... Reinforcing them with fiberglass fibers will not hurt either.

My $0.02

(Curing fat finger syndrome symptoms)

 

[Smack]

Channel would be cheaper than I beam.

 

[etack]

I'm saving up to get torch that will melt enough to fill a corn bread mold so it will look like buttered corn. :lol:

You could also use new lead molds cast iron wont hurt you metal pour just if you melt in it.

Eric

 

[samuel-a]

element47.5

This is an exelent idea.
About two months ego i had the same idea sparked in my mind and i produced several molds from an i-beam for a client to pour copper anodes.

It is a wonderfully cheap substitute for cast iron molds that are always over priced.

 

[colu41]

So after making a mold from steel, is there any prepping for it? Any possibility of explosion? Or should I always "soot" up the mold?

 

[element47.5]

I think there are a few considerations as to how you'd complete the mold, long before you pour metal into it. You're going to have to make the weld of the "ends" of the channel with some intelligence. First, you're going to have to really, really clean up any rust and scale from the throat of the channel. That's pretty easy. The question I have is, what's the best way to weld the ends on? If you weld on the outside, you're going to produce teeny seams that silver could flow into, and if the silver flashes into a hairline seam, and I believe it would, you could have big problems ejecting the ingot from the mold. You'd have to finish the ends of the channel very, very nicely. So, it'd be better to weld on the inside, which makes the fitup much less critical. But then you have an issue getting the welds nice and smooth. A die grinder would be the ideal tool for that. As usual, it's a question of having the right tool.

I'd love to see a pix or two of Sams' molds he made this way. I' m very confident making molds this way could work.

The soot is your release agent, as I understand it. It also helps prevent any soldering action between the metal and the mold.

 

[Smack]

Weld the ends on the inside and outside, then use a die grinder to mill the inside welds down smooth, just don't under cut anywhere because the bar may stick on the way out. A very minimal amount may be ok because the bar will shrink some after it solidifies. And you should always carbonize your mold (aka soot). The carbon from sooting is an insulator, not a release agent, if you don't soot metal molds you run a greater risk of contaminating your pour.

 

[Geo]

years ago, we used channel iron for aluminum molds. we had our company initials welded to the bottom inside of the mold. when the ingot came, it had the initials in the ingot. you just have to weld the letters backwards or they will come out reversed. :lol:

 

[etack]

Intead of welding on the ends what if you used a clamp and made the ends removable?

Just a thought.

Eric

 

[element47.5]

I thought about just clamping the ends on. I have not done this myself so I speak only from indirect YouTube watching experience. Molten silver apparently has a way of finding its way into very small cracks in a mold. So even if you finished the ends of the channels and the "caps" pretty damn well, you might still get some flashing into the seams if they were not sealed by being welded. Now I guess this wouldn't be the biggest of big deals because the mold would come apart, meaning, the ingot would not be locked into the mold, unejectable. But you'd have some finishing work to do. And maybe a healthy dose of soot would prevent the issue altogether. Ideally, for repetitive use I think one would like to have a mold with the fillet on the sides and a similar fillet on the ends. If the ends were (only) clamped you'd have the nice rounded edge the long way and a sharp break the short way. Like most endeavors, it's probably a "pay me now or pay me later" type of thing. Meaning, if you spend the time & effort to make the mold exactly the way "it oughta be" then you don't have the flashing, you don't have to clamp-unclamp, you don't have to grind off the flash, and your ingots come out looking better and obviously more uniform in weight.

 

[philddreamer]

If the inside seams of the steel mold were welded with Heli-arc, the weld would be much smoother, thus, the ingot would look much better.

Just a tought.
Phil

 

[sena]

i been using the crucible cylindrical one , 1 kg capacity ,,

 

[samuel-a]

Sorry element, no picture. We did it in the client shop and he is not too happey about taking pictures.
We welded the inside as well as the outside.

Pretty bars did not came out of it, that's for sure.
I planed on making some for myslef, and after reading here, i'm pretty sure i will not weld the steel plates in my molds, just clamp them tightly as you suggested.
Less work, same outcome. So thank you for the idea.