Casting Safety

[Dick Morris]

A couple of thoughts/notes on casting safety.

When I put the flask back in the electric foundry furnace yesterday after pouring out about half of its contents, this is what I found. There is a vertical crack in the upper rim. After pouring the rest of the contents I noticed that crack extended down the side. If you see this dispose of the crucible as soon as possible.

I've had a crucible fail when full of about 2KG of bronze in it. The only result was a mess to clean up, but it could have been a lot worse.

A couple of things I do to lessen the hazard. I use two pairs of tongs when lifting and pouring a crucible from the electric foundry furnace. One to lift it about half way, then the second to help left it the rest of the way and give support when tipping the crucible so all the stress isn't on the rim of the crucible.

I'm posting a couple of photos of my casting area. Note the plywood next to the table. In case a crucible fails the wood blocks the splash of hot metal from hitting your legs. (Mine could actually be a bit higher.)   

[A7er]

Are the crucibles graphite?

[Dick Morris]

Yes, graphite.

[Alyn Foundry]

Hi Dick.

From your photo it appears to me that the crucible is almost a “ dead fit “ in the furnace opening, is that the case? This could be the cause of the premature failure. We always allowed a good clearance between the furnace walls and the pot. The tongs could then be placed at roughly the middle point for lifting out.  Lifting from the top can put quite a heavy stress through the material.

Are you heating your tongs prior to the lift? Cold tongs can cause a seriously drastic change in temperature ( thermal shock ) which can also cause cracking.

I’m envious of the electric furnace, is it an Induction variety? We used gas and air for the higher temperature metals and the noise was incredible. Luckily we didn’t have any neighbours close by when we were casting.

   Graham.

[Dick Morris]

The crucible is a loose fit and is the one that fits this generic type of Chinese foundry. They are on Amazon as having a 3KG (of gold) capacity. It's low tech and uses a resistance coil. I keep a spare crucible on hand, but usually they just erode to the point where they need to be replaced. This was something new in about 100 melts. The initial lift from the furnace needs to be by the grooved flange at the top of the crucible. As the crucible can be fairly heavy when full of bronze, I use a second set of tongs to support it. It's possible that cooling by the tongs is a problem, but I don't think so. They are about 5/16 rod that fits around the crucible rim on an extended set of plyers.

This type of furnace is convenient and doesn't have the exhaust products that a gas furnace has. I'm in Alaska and can't use a foundry outside for five to six months of the year.  However, it's slow. An initial melt in bronze to 1090c takes about an hour. 

[ddmckee54]

Dick:

Last year I purchased a non-working version of this foundry at a very reduced price.  I figured that I could fix it and still be ahead in the game.  They had miss-wired the +5V and Common wires to the solid state relay.  Once that mistake was corrected I had a working foundry.

I got mine as a future project to cast parts for my WAY too many other hobbies.  I plan on casting mostly aluminum or one of zinc/aluminum alloys.  If I've done the math right, 3Kg of gold translates to about 0.42Kg of aluminum, or about 0.92Lbs for us non-metrified folk.

What's this translate to in usable casting size?  Got any pictures of the largest casting you've made with your 3Kg Chinese foundry?

You mentioned 100 melts, was that using this crucible or total melts for this foundry?

Don

[Dick Morris]

Don,

I have two of them. The first was 110 v and kept tripping the GFCI. Tuauto was were very responsive about making things right. First trying to trouble shoot via email and then sending me a new one and letting me keep the first one (at my request, the second was 220v.) I found that the common side of the AC touched the case. I fixed it and had two. The element in the 220v one failed after a couple of melts and they were again very responsive and sent me a new ceramic inner liner that had a new element. I also replaced the element in the spare liner with a new one using Kanthal wire so I now have a spare liner with element.

Mine both have mechanical relays.

I think the biggest items I have cast were the steamboat cylinders pictured in another post a couple of days ago. Two pounds for the casting and a couple of ounces more for the sprue button and there was still some left in the pot. They are about six inches long.

100 melts between the two furnaces may actually mischaracterize the number. I recharge the crucible three or four times while it is hot and have probably poured about 100 molds. I think I have only done one melt in aluminum in them. I think I average maybe 10 casting sessions a crucible gets thin to the point that it's time for a new one. I've only had two that cracked. This one and one about a year ago that dropped bronze all over my casting table, which is when I started using a fence to protect me from splashes.

[ddmckee54]

which is when I started using a fence to protect me from splashes.

Probably a good idea, it could keep you out of the running for a Darwin Award.