Author Topic: Sawed off cupola (Read 127804 times)

vtsteam · « **on:** May 25, 2013, 03:28:14 PM »

I've been asked for pics of my new furnace in Rob Wilson's cupola thread, so I figured I better open a new thread for this one which has more of a Depression era aesthetic than his fine workmanship!

It's actually not new now -- I built it last fall from a discarded industrial vacuum cleaner barrel. The main body was stainless steel. The intent was to make a short single charge cupola, that might double as a small crucible furnace. It already has had a trial by fire melting a couple of aluminum pours (as a crucible furnace). But has yet to be used for iron.

The cupola's single tuyere is blocked up presently and the tap hole has been used for blast.

I haven't had a lot to spend on it, so I used materials I had on hand to line it -- hard firebrick and sand and fire clay (Hawthorn). The lining is 4" thick and the bore is 7".

I bent up a 4" wide ring for a lid -- but haven't lined that yet or made a lift mechanism for it. For the aluminum melts I used an older 2" thick lid I salvaged from my old popcorn tin melter. But for Iron, I want to have the bigger lid.

This is the furnace I want to try hardwood charcoal with -- there is no source for coke locally that I can find. Though just this weekend I did find a source for blacksmith coal -- don't know if that could be converted to coke or not for an occasional melt.

The capacity of the furnace I hope, will be about 10 lbs of iron, but that remains to be seen. I'll post pics of it here as I can.

First, the salvaged vacuum cleaner can. I took the wire basket and hose outlet off, after this pic.

vtsteam · « **Reply #1 on:** May 25, 2013, 03:30:18 PM »

First course of fire brick set in place. An aluminum tube was set in the bottom to act as a form for the tap hole area.

vtsteam · « **Reply #2 on:** May 25, 2013, 03:34:00 PM »

The lid form. Some steel reinforcing mesh was welded into it for support of the lining.

vtsteam · « **Reply #3 on:** May 25, 2013, 03:36:36 PM »

First course of firebrick completed. You can see a piece of steel pipe on the right, which would be the tuyere for the furnace as a cupola. The hole above that will be closed in -- it was where the vacuum hose fitting was removed.

vtsteam · « **Reply #4 on:** May 25, 2013, 03:40:23 PM »

Second course of brick in and the top screeded off. Some wood chips are in the bottom on top of sand, getting ready to fire the lining.

vtsteam · « **Reply #5 on:** May 25, 2013, 04:27:40 PM »

Ready to fire. It was getting cold, toward evening with snow threatening.

vtsteam · « **Reply #6 on:** May 25, 2013, 04:28:57 PM »

A wood fire was gradually built up.

vtsteam · « **Reply #7 on:** May 25, 2013, 04:39:07 PM »

After the wood had burned down, a layer of charcoal briquettes was poured in. When lit successive layers were added until the furnace was filled. It was left to heat soak for 30 minutes, and then blast air was applied to the tapping hole to bring the furnace up to temperature. Charcoal briquettes were added to keep it topped up over the next 3 hours of firing. It was dark and beginning to snow when I finally cut the air and bricked off the hole in the cover and the inlet.

vtsteam · « **Reply #8 on:** May 25, 2013, 04:44:22 PM »

The next morning the furnace was sitting in a melted area after the snow. I walked over to feel the exterior to see if the outer shell was still warm. Yeooowwch, I jerked my hand away!

It was really hot 11 hours after it had been shut down, in subfreezing temperatures.

vtsteam · « **Reply #9 on:** May 25, 2013, 04:49:05 PM »

It was cool enough to open by evening. Here's what the fired lining looked like. Not bad, only one real crack through the lining at the top of the furnace.

vtsteam · « **Reply #10 on:** May 25, 2013, 04:55:39 PM »

What I removed. This clinker shows how much junk there is in store bought charcoal briquettes. But I did take it as a positive sign for ultimately melting iron. In my older furnace, briquettes formed a lot of loose powder ash. But it was never fused like this was. So temps were clearly a lot higher in the new furnace even thought the fuel was a poor one.

Rob.Wilson · « **Reply #11 on:** May 26, 2013, 03:21:15 AM »

Hi Steve

Your lining has fired well

your allot closer to melting Iron than I

Rob

Mayhem · « **Reply #12 on:** May 27, 2013, 06:21:15 AM »

Thanks for posting this. I will be watching with interest.

vtsteam · « **Reply #13 on:** May 27, 2013, 06:15:39 PM »

Thanks Mayhem.

Some accessories for the cupola. Made the botting irons and tapping bars this week from reinforcing rod.

The blower was actually once a turbine, believe it or not. I originally built it to see if I could harness a valveless pulsejet's output by attaching a turbine. It worked.

Basically a pulsejet puts out low velocity, low pressure high volume exhaust. Some people online have suggested that a Tesla disk turbine might be run off of one, but I thought that was wrong. Having built and run a disk turbine, I knew that it was a high pressure device, completely mismatched to a pulsejet's output.

So instead I went in the opposite direction and decided that a turbine shaped like a flat bladed scroll fan, and calculated the same way you would a blower requirement, would match up much better. And possibly wouldn't interfere with the resonance of a valveless pulsejet -- another problem when people have tried to do this in the past. I had used a manometer to measure the exhaust velocity of a pulsejet, and built the fan/turbine to suit

After I sized the fan for the output , I built it with ABEC 7 roller skate bearings and aluminum vanes. The bearing housing was a pipe flange, and a section of water pipe. The disk on the end is half black and half reflective to check RPM with a laser tach. Of course the aluminum vanes melted during the first trial in about 45 seconds! I replaced them with steel. After the switch to steel blades it ran fine. I hit it right on the numbers for RPM, too.

Back to cupolas.... this becomes just a fan if you rotate it with a motor, so I think I'll try to use it for the cupola. Assuming the output is suitable. I will have to try step up or down pulleys with a motor and a manometer to check the output. I also built a manometer back when I was making this as a turbine. Hope this fan is the right size for the cupola.

Mayhem · « **Reply #14 on:** May 30, 2013, 09:00:04 AM »

OK - what are tapping irons and blotting bars used for?

Any pics of the build of the blower? I note that both you and Rob Wilson have built them and this would be a good project log...

vtsteam · « **Reply #15 on:** May 30, 2013, 01:31:16 PM »

Mayhem basically they are used for corking and uncorking your cupola!

The botting iron gets a plug of clay sand refractory mix ( a bot) and you push it into the tapping hole when melting iron. At a point when it is judged the iron is running and hot enough to be useful. Sealing it off allows it to begin collect behind the bot in the well.

The tapping bar has a chisel point on the end and is used to knock out the bot to let the iron out and down the spout into the waiting pre-heated pouring ladle. The spout is lined with refractory. The dam at the bottom of Rob's spout is there to hold the refractory in and something to pack it against. The actual channel for the metal would be above that.

I'll try to get some photos of the blower construction this evening. Can't now -- must work on legs for furnace. Rob is surging ahead......

vtsteam · « **Reply #16 on:** May 30, 2013, 07:31:57 PM »

Okay, fan first.

Taking off the cover. Lots of nuts. You can see one of the ABEC 7 skate bearings. There are two.

The arbor was a piece of 5/16" drill rod. The arbor casing is a 3/4" pipe nipple. The pipe nipple was cleaned up on the outside on the lathe, and then bored to take the ball bearing races. With the nipple still in the chuck, the pipe flange was screwed onto one end and it was faced in the lathe. This made everything true and square to the arbor, and the bearings aligned true.

The fan casing was made of thin plate. The flare at the end was made of stovepipe and is very thin. I flame welded a lot of this as I didn't have a good enough arc welder to work with thin metal -- just a Lincoln tombstone buzzbox stick welder.

vtsteam · « **Reply #17 on:** May 30, 2013, 07:39:37 PM »

The cover off. You can see the flare and a lotta ugly welds! didn't clean much up here, but didn't ever expect to show this and I was anxious to see the results of my experiment.

I'm no welder.

dsquire · « **Reply #18 on:** May 30, 2013, 08:07:34 PM »

VT

As long as you keep the air movin fast it won't have time to see if the welds are purty or not.

It looks good enough for me and if your satisfied with it then that is all that matters. I enjoy following along with your build and with Rob Wilson as well. I don't care who get finished first because I know that you will both be winners.

Cheers

Don

vtsteam · « **Reply #19 on:** May 30, 2013, 08:11:11 PM »

I stick welded pieces of threaded rod all around. To get them to align with the holes, I drilled the holes first, then threaded nuts onto the studs and placed thm in the holes. They were then welded in place.

vtsteam · « **Reply #20 on:** May 30, 2013, 08:13:39 PM »

Thank you kindly Dsquire!

vtsteam · « **Reply #21 on:** May 30, 2013, 08:23:53 PM »

The guts.

The original blades were made of aluminum, as I said. They melted almost instantly in the heat of the pulsejet. As did the ball retainers (plastic) in the cages of the cheaper ball bearings (skate) I had used.

I replaced with steel blades (made from stovepipe) and better bearings, and all was well. The blades are fastened in place with steel pop rivets. I used a hub from a discarded utility fan for the hub here and welded it in place.

vtsteam · « **Reply #22 on:** May 30, 2013, 08:41:26 PM »

It's funny, to size the turbine (fan) I built some of the equipment normally used to power a cupola furnace. I built a manometer (blast gage) and used it on the pulsejet to characterize exit pressure and velocity. That was what told me they were surprisingly low -- indicating to me that the volume was good and it might respond to a broad flat blade fairly well. Just like a spinnaker or square sail is a good running sail for high volume low velocity air by comparison with a Marconi rig. on a sailboat -- I was pretty familiar with those. Because velocity was low, blade area needed to be big, and RPM low. If I remember correctly I shot for about 3500 RPM in the design of the turbine, and hit it pretty close in reality,

Anyway, the funny thing is I have never used the manometer to characterize the fan. So I have no idea how it will perform when I add a motor. Normally you'd build a fan for the requirements of the cupola and then blast gauge to characterize the fan output. So it's all going to be new to me, though I've had this stuff for many years.

Here's the manometer (blast gauge) that I built. (Needs some water -- a lot has evaporated.) believe I used David Gingery's fan book to build both, Though Steve Chastain repeats a lot of that information in his cupola furnace book.

Mayhem · « **Reply #23 on:** May 30, 2013, 08:47:47 PM »

VT - thanks for the info. That is really useful stuff.

vtsteam · « **Reply #24 on:** May 30, 2013, 08:57:14 PM »

You're welcome Mayhem.

The end of the probe for the blast gauge is what is called a pitot tube. Pilots are familiar with those. They measure relative airspeed. They can also measure dynamic pressure.

This one was made from some copper tubing. The end is a turned brass plug and has a hole drilled in it. A very thin copper tube is soldered to the plug internally and runs inside the outer copper tube to the far end of the probe where it exits in a tee fitting. I believe I used the tubing from a heating furnaces pilot light probe. These are available as replacement parts.

You can also see a ring of small holes drilled further back in the outer tube. This outer tube also exits from a different leg of the tee fitting.

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Author Topic: Sawed off cupola (Read 127804 times)

Rob.Wilson