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The "2 bucks" furnace


The adventure begins

I wanted a small propane fired furnace for efficient aluminum and bronze melts. I figured that the coffee can furnace mentioned elsewhere on the internet was too small, but metal 12 quart buckets seemed just right for my 4" diameter crucible. -- Jan./15/2002


CAUTION! Metalworking can be dangerous, especially when proper safety precautions are not taken. Because of the variations in materials, workmanship and other variables there are no guarantees on the information in/on this web site. This information is simply what I have been successful with in my own experiments. I am not and will not be responsible nor will I assume responsibility for any injury, loss, or damage no matter how serious or minor that may result from following the instructions, diagrams, advice, plans and/or general information on this web site. There are always dangers in metalworking and related activities and they have been pointed out whenever possible but it is neither the purpose nor responsibility of me nor this web site to mention all known or unknown dangers.

Here you can see the "plinth" (crucible holder) in the bottom of the furnace. Notice the trench forms extending from below the plinth. The refractory has been curing for about 4 1/2 days at this point and is very hard (but not rock hard).

I let the concrete in it cure for a day uncovered, then I covered it with a plastic bag for the remaining 3 1/2 days while spritzing water on it with a spray bottle every once in awhile.

Here is the bottom half of the furnace with crucible set in. Take a gander at how I rebuilt this crucible. The cardboard ring will prevent the lid's refractory from fusing to the base's refractory. I'm not really sure if it was necessary though.

The crucible is in there because I looked at it this way... Since the furnace has to get up to melting temperature to harden the lining I might as well slap a crucible in there and get a melt or two!

Here's what the furnace looks like with both halves together. Isn't it a beaut! I attached a temporary bucket handle (from the bucket as a matter of fact) until I build the lifting mechanism.

The Adventure begins

At first I was using the Oliver-upwind burner with a flare. The furnace was blazing nicely (except for a slight amount of sputtering) for about a minute when suddenly there was just a PSSSSSS... Good grief! The flame went out. I switched the propane off, removed the furnace lid and blew through the burner support pipe to clear out propane. I ignited it again and about a minute later it went out again! At this point I'm worrying that there is a flaw in the furnace design and burner cutoffs will be a constant problem! Without clearing the air in the furnace (bad idea) I reignited the burner and was greeted by a FFFFFFWWWWWOOOOOPP BLOOOOF! Complete with jet of fire ripping out the vent hole. It sounded very much like a cannon, or more specifically a "spud gun" (a.k.a. spudzooka, a.k.a. potato cannon) if you know what those are. Lesson #1: ALWAYS ventilate the furnace if the burner flame extinguishes.

I decided to remove the flare and try the burner without it. To my surprise it burned perfectly without even sputtering. Hey! Those guys are right, you don't always need a flare inside a furnace. I've been having trouble with that particular flare anyways since I've rolled and re-rolled it so many times its no longer concentric. I began thinking that the crucible and scrap metal would absorb to much heat and prevent the refractory from totally curing. So I took it out and the burner started sputtering. I began adjusting the regulator and sliding the burner in and out to adjust it but the sputtering just got worse. In fact jets of flame began shooting out the burner support pipe toward my hand each time it sputtered. Needless to say, that's when I stopped adjusting it! The burner went out and I quickly shut off the propane and figured that removing the crucible must make the chamber to wide open for the burner to keep burning without a flare. So I put the crucible back in.

I reignited the furnace and the freak'n burner went out again! Now I'm worrying again. I readjusted the regulator and slid the burner in and out a bit and suddenly there was a beautiful, smooth, FFFFFFRRRRRRRR and the burner continued to burn that perfectly for the rest of the melt! Whew.

In this pic the cardboard ring and the cardboard vent and drainage hole forms are burning out. Within 15 minutes I had some nice molten aluminum. As it was melting away I hurried off to finish welding a large ingot mold from heavy angle iron. Suddenly I hear; FFFFFFWWWWWOOOOOPP THIDUUUUD (a dull thud) and the furnace is rocked! I race over to check the burner thinking the furnace backfired again only to notice the burner was fine but...

A chunk of refractory had blown out the lining! Here is a picture of it after the furnace run. I must have left a void in the refractory and steam blew a chunk out. Lesson #2: Ram your refractory thoroughly! I kept the furnace going because I wanted to melt a garbage can full of lawn chair aluminum tubing that's been taking up space in the basement.

Oh well, at least I still have my crucible I worked so hard to rebuild...

OH NO! The crucible burned thru and metal is spilling out the drainage hole! If I actually expected to NEED the drainage hole on the FIRST run with this furnace I'd have put a container of sand under it!

At least I know the trenches and drainage hole works... Note to self; Buy driveway patch on next trip to Home Depot...

Here is the crucible with a solidified pool of metal still sticking to it as if to mock me. It all came thru a hole in the weld area thatís been plaguing this crucible. I've tried to weld it shut several times. In fact I tried to weld it shut only minutes before this furnace run!

After cleaning the furnace out I noticed that the damage isn't that bad. I can easily mix up some more refractory to patch the spot and the furnace will be good as new. I'm not sure if the void was in the top or the bottom but it blew a corresponding chunk out the opposite half!

The rest of the refractory is rock hard with only minor cracking! Notice the drainage trenches. The flame was so hot it vaporized the forms. I didn't even find carbon residue from them.

The flame was so hot that the sand in the side of the plinth that was in contact with the flame turned to green glass! And feels similar to ceramic glazing! Some of it even dripped and fused to the furnace base.

Here are extra plinths I made from the remaining refractory. The used one is in the front on the left.

Part 1: Building the furnace - Part 2: Firing this bad boy... - Part 3: Back in business


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