Thread: Home Foundry Advice

You're on old buddy, I'll call ya ass first. Tis time for the next general meeting.

Happy Muver's day.

Kennefff

Hi GQ,

I could post my furnace design, which is based on a converted davy water pressure tank, but it's probably more useful to give you the general design guidelines.

Most designs you will find on line are based on fire brick or cast pyrocrete type designs, a better design approach is to go for low thermal mass and concentrate on lowest thermal conductivity. That way it gets up to temperature quicker and it's easier to get to higher temperatures.

All you need is a sufficiently thick layer of cerachem or kaowool, it's available in various ratings, for cast iron, Cerachem 1425.

A cast pyrocrete plinth for the crucible to stand on and a cast pyrocrete burner inlet are probably the only pyrocrete parts.

I've been running a normally aspirated lpg gas burner which works fine for bronze, it can melt 1 kilo of bronze in 7 minutes. But not enough for cast iron, so I'm part way through upgrading the burner to forced air, which should be enough for cast iron. The problem is the flare on the end of the burner where it goes into the furnace proper, I've now got a few scraps of titanium (good for 1700C) sheet that will form the hot end of the burner.

However, getting the crucible of molten bronze or cast iron is the easy part.. you then need crucible tongs, plan of attack to carry out the pouring safely, proper protective gear, full face shield, foundrymans gloves, good leather foundry jacket. If cast iron, you also need welding type shielding. Don't forget to tie up the dog, and keep the kids inside.

You need to make up the pattern, design and make the cores (if any) and figure out sprue placements and make a cope and drag... and on it goes... I recommend the CW Ammen book on sand casting as a good starting point.

[ame="http://www.amazon.com/Complete-Handbook-Sand-Casting/dp/083061043X/ref=pd_sim_b_1"]Amazon.com: The Complete Handbook of Sand Casting (9780830610433): C. Ammen: Books[/ame]


However, unless you want to build a muller and do a lot of mucking around with green sand recipes, I recommend that you forget green sand and buy a bucket of petrobond, you get better surface finish and more consistent results, although the initial cost is higher it's worth every penny.

I think it was BT who said that there's something inherently fascinating about pouring molten metal, he's right. Plus it's good wholesome entertainment for the whole family...

A friend remarked, when I explained what the bronze casting stuff was about, and his comment was a dismissive, "Yep, the Greeks were doing all that, 2000 years ago..."

He's right, it's not rocket science, but it does take a bit of planning and a bit of care.

Regards
Ray

PS. Forgot to add, the Cerachem is coated with IR reflecting material, I used ITC-100 ceramic coating The final construction is fragile, but more than adequate for home casting. If you do get holes in the coating, it's easily repaired.

Here are few basic design constants.
1. The flame temperature for propane is 1990 Degrees C
2. Propane will generate 12.9 KWh per Kg
3. You need 12.3 cubic meters of air per Kg of propane
4. The thermal conductivity of Cerachem 1425 is 0.15 W/mk

Hi GQ,

Here's a few tools for handling the crucible, the lifting tongs on the right are only ever used to lift the crucible out of the furnace. The crucible holder with the radiation shield for pouring is ok for small crucibles, but bigger ones you might need a more complex arrangement to control the pour. Maybe even a two man setup for larger pours. The extended handles at the end can give you fine control on the pouring rate if you need it. The shield has a flat spot, so that it sits stably at the right height for the crucible. The tongs in the middle are charging tongs for adding additional material to the crucible prior to pouring. The smaller tools on the left are skimmers for removing slag and stuff floating on the surface.

Here's a video I found of a bronze pour, that Josh and I did a while ago. The surplus bronze is poured into ingot moulds, lately I've taken to pouring cylindrical ingots, which are very handy for turning small parts.

[ame="http://www.youtube.com/watch?v=omrqSI1xFNk"]YouTube - Bronze Pour[/ame]

Regards
Ray

That doesn't look very hot
And its what? about 600C short of iron?

Great video Ray

Stuart

Nice video Ray.
A mate of mine worked in scrap melting plant up here where he used to control the ladle. He gave me a brand new long coat that they are issued their, that are flame retardant etc, and told me they where good to keep warm fishing and at parties,LOL. I would expect them to be expensive new.

One day I will get a furnace to try it out.

Dave

Hi Dave,
Those full cover leather aprons are perfect for this sort of stuff, so keep it handy, those jackets we got are leather heat resistant something or other from Elliot, if I recall correctly, only we got about 3 sizes too big! .. The gloves I got from the local BOC dealer, they have them listed as foundrymans gloves.

Which brings up an important point, and that is the practice runs with the crucible handling should be done wearing gloves and the full safety gear, because it's much harder to handle the tongs with gloves than without. Don't forget to make sure the area is clear of trip and fall hazards.

Regards
Ray
PS... Stuart, cast iron would probably be another 300 degrees or so hotter, that bronze is around 1100C or so.

Hi Ray,
I just had a look at that coat and it's not leather it's more like a fibre type material and is green in colour and weighs 3-4 kg. It has buttons to do up around your neck and comes down about 8-10 inches off the floor. There are no tags on it to say what it's made out of and the packet is long gone. He said they where to stop the heat of the ladle when poring.

Dave

Hi Dave,

Good quality safety gear for foundry work is hard to come by, I can't guess what the material might be, but sounds like it's exactly what you need. No pockets, button up to the neck and full coverage on arms and legs.

Maybe it's one of these.. Weld Wool Furnace Coat - Protective Clothing - Furnace, Weld Wool - Elliotts Product Detail

Regards
Ray

That looks pretty much identical to the one I have. The mate said they where worth something like $300 each 15 years ago. Come to think of it, it's been in the cupboard for a long time. LOL

Dave

Hi Dave,

I want one of these...



Scare the neighbours, if nothing else...

Regards
Ray

I think they would work great, you don't know any astronauts do you? The may have an old suit laying around, LOL

What sort of cost are they? The mate also gave me a few clear face shields that they used and where made of thicker plastic than the type you normally see getting sold. The only trouble is they are scratched up now after years of use their not much good.
He worked at comsteel where they melt down the scrap to send overseas.
He said it was a good job and liked it because you sat and watched TV or played cards between each ladle load then just got dressed in you heat proof gear and went out to control the cranes to empty it. I would have loved to go and watch, but they where strict on who entered the plant. He did grad me some good 50mm round etc steel that came in as scrap because they sold it to the employees at a low rate.

Dave

Interesting posts Ray and great video. Casting aluminium is on my (long) list of things to do and your info will come in handy.