Burnout furnace info

ArtMetal
Bramblebush


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Posted by Rob Frink on March 19, 19100 at 18:04:12:

Based on info posted by BPF, I made this one� from a 55 gallon

drum and is lined with 2" ceramic insulation. It is natural gas fired with

a burner from a barbecue grill. Locally,� a gas grill shop sold me

a round replacement burner for a 22" weber grill.�� The natural

gas is feed to the burner from below where I welded some stand-off brackets

to a piece of pipe and bolted it to the bottom of the drum. The salesman

sold me a three position valve fitted with a 40,000 BTU orifice.�

In retrospect.....instead of the valve, copper tubing could have been used

with a small hole (about 1/16") drilled in it for the orifice and 40,000

BTU is overkill. .� Anyway here is a photo underneath to see what

I did. I used a ball valve at the hose connection and found that it works

better to control the gas flow.

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Combustion air is provided by 4 tuyeres welded through the side of

the drum. I just guessed on what was needed and didn't use any rocket science

here. In this photo, you are looking at the round burner and the four tuyeres.

I found that the tuyeres were originally too close to the burner such that

the natural convection draft actually blew out the flame on the burner

by the tuyeres.� I found this out after the lining was installed and

everything was welded together so I just reached in with a cutting torch

and whacked them off a bit. Looks ugly but works much better now.

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The insulation was purchased locally from a refractory supplier. It

is 2" ceramic insulation that is supposed to be good up to 2400F. It came

in a roll 24" X 25' and ran about $240.

The exhaust chimney is a piece of muffler pipe welded into the top.�

I extended it well down into the furnace to try to maintain some BTUs before

blowing them out the stack by forcing a down draft before existing.�

I played with the idea of bringing my combustion air pipe in through the

exhaust stack so the the combustion air could be preheated and make everything

more efficient.� Ahhh...way too complicated and as it turned out...not

needed.

Here is a shot of the exhaust stack.

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That's about it! A drum, a burner, some insulation and a day of labor.�

Does it work?� YES, YES! I fired it up and poked my lance pyrometer

in through the top. The temp quickly rose up to 800,900,1000 then slowed

down and maxed at about 1275F.� With the pyro reading 1200F and the

inside softly glowing, the outer shell was only warm to the touch! This

insulation stuff is incredible.� I found that I had� too much

combustion air and put some duct tape over the tuyeres to close them up

a bit. Also the chimney is probably too big at 2 1/2 inches as I found

that I got more temp by blocking it with a plate. The flame required is

suprisingly small and soft. The burner flame has quiet little candle like

plums around the circumference without roaring or turbulance.� Not

what I expected.

Since investment casting is new to me, I'm not sure if I'll do ceramic

shell or plaster.� Now that I have a furnace, I learn more in the

next few weeks.

Oh yeah, I forgot to mention the shelves or racks. I just plan rigging

something up on a "as needed" basis to fit what I'll be doing at the time.

The goal with this posting is to provide some insight to help out the

beginner.� Everything that you saw here was done to fit my needs or

simply because I didn't know any better.� Maybe some of the more experienced

casters can add to this as well as critique it to make this posting a great

resource for anyone as lost as I was.� Feel free to make recommendations

based on what your using or have seen.

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Be safe and have fun,

Rob Frink


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