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Tony Coiro

What could go wrong?

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I'm back after an 8 or 9 month hiatus. Been doing that college thing for awhile and one of the classes Purdue offered was an intro to metalworking class, so I figured it would be ideal to help with my workshop withdrawals. Let's just say that blades, knives and swords haven't been mentioned, but brooches, tea infusers, rings and necklaces sure have. This might come as a shock to you guys, but I have every intention of "reclaiming" all of my copper, brass and silver for a more noble purpose now that the class is almost over. My plan is this, I've already welded together a 2x2x2 inch box of mild steel 1/4 inch thick. I would cut or saw the copper up and fit as much as I could in my homemade crucible and when it gets molten, cast it in a homemade sand mold and hopefully make somehing that looks like bar stock if you're drunk or squint your eyes. I could then file/cut/sand into fittings. I would then do the same with the brass and silver. Oh ya, I've never cast anything before and this crucible I made was the first thing I've ever welded. What are some of the things that could go wrong? You can make a list if you like.

Photo_120108_001.jpg

Crucible, arc-welding on a rebar handle at some point at one of the corners, that way the it would be poured from one of the other corners, if that makes sense. It's water-proof, but I am most concerned about air pockets in the welds at +2,000 degrees. Like I said, I've never done this before, but it would be a great skill to have and I have 3 weeks until winter break to plan it. Any comments/advice/expressions of outrage would be great. Thanks.

Tony

Edited by Tony C

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Should work good for melting. I would use a traingle file in the corner to make a better spout. The molten metal will be more apt to want to stick/follow the thich metal and not pour accurately.

Edited by B Finnigan

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I have cast a few things before and wouldn't worry if your cube holds water. My crucible is a pipe nipple with a plate welded on the bottom. Your welds should hold fine at temperature. One suggestion is to place the crucible in mabye a bread pan if you are worried about it leaking. You plan on making ingots sounds like a bunch of work. Why don't you make a few wooden patterns of the general shape you are after and cast them into that? Should work fine in even a open faced mold if your not worried about having to file afterwards anyway and should save you some sweat.

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Try what Ed said about making a pattern. Otherwise, you could probably just make a divot in a piece of fire brick and torch melt your scrap. It should form up into a ball that might be close enough to a block to work with. Don't forget to keep some flux if you want it to flow and float off impurities.

 

Practice on the copper, and save the silver scrap for a special application.

 

Good luck with the project, Craig

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(1) Your steel crucible will get fairly floppy at copper melting temps.

 

(2) Molten copper alloys will dissolve iron, such as the iron in your steel crucible. The zinc in your brass also becomes corrosive to iron at high temperatures. (This may also be true of silver. I don't know.) This will add impurities to your copper and brass (and maybe your silver), and it'll eventually eat your crucible away from the inside-out. Even if your welds are perfect, sooner or later you will spring a leak. Plan accordingly.

 

Judging from the photo, you don't seem to think that you need a very large crucible. That being the case, maybe you could afford to spring for a commercial clay-graphite crucible. Small ones aren't very expensive, and they don't suffer from the problems that steel crucibles do (though even ceramic crucibles will eventually fail).

 

http://www.lmine.com/Merchant2/merchant.mv...Product_Count=1

 

I like the idea of casting into a divot in a firebrick. It's even cheaper than a clay-graphite crucible, and it solves all the steel crucible problems.

 

If I understand Ed's suggestion correctly, he's recommending a wood ingot mold. That might work, but I wonder if it wouldn't produce some awfully gassy ingots?

 

Cast iron muffin tins are often used as makeshift ingot molds. Yes, copper/brass may eventually dissolve them, but it'll take a long time.

Edited by Matt Bower

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Copper is a royal pin in the rear to cast by it's self without having bubbles in it. As counter-intuative as it may seem, an oxidizing fire is better than a reducing one for melting copper. Phos-copper de-gasser is handy to have around as well.

 

My ingot mold is two pieces of channel iron, smooth edged so they match up thusly [] and about 4 inches long. Pouring an ingot well, without splashing and bubbles so that you can work it down to sheet takes a little practice.

 

Silicon bronze is far easier to cast than copper or brass. Silver is simple and forgiving, but expensive. Good luck ! :)

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Awesome, I am looking forward to experimenting with this. The problem I have found with actual crucibles are the size, which is the reason I made this. I am using my forge to reach casting temperatures, so the crucible must be less than 3 inches high. Also, Matt Bower, there is no danger of my welds being perfect, so I will certainly be keeping an eye on them.

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Added to Matts comments:

 

When melting copper, you get pretty close to the burning temperature of the steel as well. So using steel crucibles is definately not recommended for higher temperature metals (tin and pewter etc. fine).

 

Then there's the big safety problem of melting metals. I definately would not melt any brass without anything to remove the fumes, as they are dangerous. The same goes for the copper, if you don't know what's in it. At any rate, aviod melting anything that could potentially contain zinc, lead, beryllium, antimony, arsenic etc. as they will either kill you directly or eventually.

 

Also keep in mind that the hot metal contains enough energy to cause explosions if it is released instantly. So avoid moist in moulds at all costs. I've heard of exploding ingots cast in probably damp steel mould f.e.

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Hi Tony, I did something like this after my Metals class at Western Michigan after I graduated. I found a piece of scrap something that was like a steel shot glass with about a 1/4 inch wall thickness and I put all my scrap silver, and a few ugly projects as well, into the "shot glass" and sprinkled some borax on top and stuck it in the forge while I was working on something else. I kept an eye on it and after everything looked melted I took the "shot glass" out and let it air cool, then I cut up the "shot glass" and had a nice little puck of silver which I forged into a stick like shape. I keep loosing it and finding it, at random times over the years.

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I know the Whitechapel bell founders in London used to use willow rods to stir the bronze melt, it was later discovered that the salicylic acid in the willow bark acted to de oxygenate the melt the same may be true of copper so I guess you could chuck a couple of aspirin in

Edited by JJH

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