Propane furnace optimization

[Smack]

I have an extra steel table I would give you if you were not so far away.

 

[MysticColby]

neat pour. REALLY hot. based on the glow, I'd estimate about 1200 C (2200 F) (orange yellow glow, visible in sunlight).
I probably pour colder than that (about 1000 C - dim orange glow), but that's probably why my bars don't look as pretty. I should work on that....

 

[MysticColby]

Where did you get those lift out tongs? I've been looking for some (for a larger #10 crucible), but they all seem to be about $300. I nearly decided to make my own.

 

[Noxx]

They are homemade

Fairly easy to make if you know how to weld. I had to reinforce from the original design because they flex too much when lifting a heavy crucible.

 

[MysticColby]

I DO know how to weld (just bought a MIG a couple weeks ago)
I'll make my own, then. I was planning on something like this:

and this:

From your video, I see it's possible to just have the first one, but I feel I'd get better control with the second.

 

[Noxx]

I'll post pictures of my design later today or tomorrow.

 

[goldsilverpro]

I know this is heresy, but I always used just charging tongs (designed to put metal bars into the crucible) to handle the crucible in and out of the furnace and to pour. The ones I had were either 36" or 42". I was told they were safe on #16 crucibles or less and that's what I used them on. I never had a mishap with them in 30 years.

 

[Westerngs]

I use about the same as your charging tongs except that mine are curved to grip the crucible better. Haven't had a problem in over 20 years. They work well for stuff up to 150 t.o.

Anything over that I use a larger furnace with a yoke for the crucible.

Noxx... Does your flame come in at an angle to the crucible? I could not tell from the video. Furnaces seem to heat better if the flame comes in at an angle say about 45 degrees and swirls around the crucible. It seems to heat more evenly.

 

[MysticColby]

So far, I've only gripped the edge of crucibles with tongs. But so far, I have only used small ~1 kg crucibles or large cast iron. I felt nervous about lifting a 10 pound crucible with 10 pounds of molten aluminum in it by it'd edge, which is why I wanted those vertical lift-out tongs for when I replace the cast iron crucible with a graphite one. Graphite is easier to break than cast iron...

My tongs are half-done so far bent them into a basic shape, twisted, and made them scissor-like. just need to bend the part that actually touches the crucible, then weld them on. I'll post pictures when it's all done and not looking like an amateur made them (they're the first steel-working things I've made)

 

[ericrm]

Noxx, do you know the propane consumption of your furnace?(combien de gaz sa boit a l'heure)

 

[greatgems]

would this design with acetoleen work better and get hotter i need a good 1600c to melt copper fast

 

[Harold_V]

would this design with acetoleen work better and get hotter i need a good 1600c to melt copper fast

You mean acetylene, I assume.
If you make that your choice, you'll spend more money on fuel than the copper is worth.

What you need is most likely not greater heat, but more btu's. It's not the same thing. Copper can be melted perfectly well with propane or natural gas. I did it time and again with natural gas, and it's done that way routinely by foundries that are still melting with gas fired furnaces.

Copper is not friendly to melt and pour. I expect you're going to discover that fact.

Harold

 

[Barren Realms 007]

would this design with acetoleen work better and get hotter i need a good 1600c to melt copper fast

The furnace I posted picture of in this tread should do what you want to do. The crucible pictured will melt about 700g of silver powder in roughy 8-10 minutes once the furnace is up to full temp. I generally melt one charge remove and add a 2nd charge and then melt that and then pour in the mold. When I am melting silver my regulator is only turned on about 60-75% so you could get more BTU's out of it if nescessary, if you need more BTU's you can look at safely injecting oxygen to bring the temps up. The furnace is desighned to hold a #6 crucible that will hold about 12 lbs of copper.

 

[MysticColby]

I had a request for plans for that mini forge pictured earlier, figured I'd share with everyone:

Total cost of everything consumed is about $4 for the fire brick. Initial cost includes about $30 for tools.
Things to get:
one insulating fire brick (9" x 4.5" x 2.5" or 9" x 4.5" x 3")
3 inch carbide hole saw (normal hole saw will work, but won't last as long. looks something like: http://ecx.images-amazon.com/images/I/21Nk%2BQugqxL._SL500_AA300_.jpg)
1 to 2 inch spade bit (looks something like: http://benrroberts.files.wordpress.com/2010/10/spade-bit.jpg)
5/8 inch spade bit
carbide hack saw (normal hack saw will work, but won't last as long)
Doing this on a drill press is best and easiest but a power drill should work alright

1) take out the center drill in the hole saw. Most can be removed by unscrewing, but may require to be cut off.
2) cut off pointy part of the 1 to 2 inch spade bit. Use a hack saw or dremel. Afterward, it should look close to have a square end.
3) cut fire brick exactly in half. use a tape measure and sharpie to mark a line, then use carbide hack saw to cut it. Doesn't have to be perfect, but as close as possible gives most insulation.
4) drill circle hole in both halves of the brick. put hole saw in drill press, set it to stop when it is 3/4 inch from the bench. Align hole saw in center of one of the faces of one of the brick halves, drill down so that it forms the outline of a hole that leaves 3/4 inch intact on bottom. Do the same to the 2nd brick half. (if bricks are 2.5 inches, the hole will be 1.75 inch deep and final chamber will be 3.5 inch tall. if bricks are 3 inches, the hole can be shallower to allow for thicker floor which increases insulation)
5) remove inner part of hole. put 1 to 2 inch spade bit in drill press, set it to stop when it is 3/4 inch from the bench. Drill out inside part of the holes you just drilled. works best if you drill out very center, move it half an inch, drill out that part, and so on. Careful not to drill outside of the hole. Do this for both halves.
6) drill hole for torch and exhaust. put 5/8 inch spade bit in drill press. align to center of one of the brick halves, drill a hole. The hole should be on the side for the second half, off center so the flame swirls around the crucible. It doesn't require perfect placement, but if that's what you want: 1-1/16 inch from bottom and 1-1/16 inch from side.
7) Place both halves together so 3 inch holes are facing each other. final dimensions should be 3 inch diameter cavity, 3.5 to 4.5 inch tall, 3/4 inch thick walls at thinnest. Best to place on top of another insulating fire brick (when in use) as most of the heat will be lost to the table (also to avoid catching table on fire).
8) The end.

I recommend editing the sizes of the drills to match what you have (my torch has a 5/8 inch diameter, so that's the size hole I wanted). If you have a smaller crucible, make it a smaller hole.
Drilling into brick results in a bit bigger hole than the size it should be.
It just occurred to me that you might be able to get a 3 inch spade bit and just use that (instead of the 3 inch hole saw).
I read somewhere that the size of the furnace should be 1.2 times the size of your crucible for maximum efficiency. (2.5 inch diameter, 2.75 inch tall crucible = 3 inch diameter, 3.3 inch tall furnace)
The neat thing about this furnace is that when it's opened, you can directly grab the crucible by the side with appropriate tongs. This means you can potentially melt more in the crucible as you won't have to reach tongs inside to grasp the crucible wall. Just be aware: larger volume = takes longer to melt = less efficient due to heat lost through walls.
Do not touch the outside with your bare hands while it's on (you can touch it, at least for a short time, if you're wearing welding gloves)
The largest crucible that will fit in this furnace is a size B0000 (3-1/16 tall, 2-5/8 diameter, 811 g silver max) or A1 (2-1/2 tall, 2-1/2 diameter, 1,234 g silver max) (http://www.budgetcastingsupply.com/Crucibles.php)