Temporary 5 brick & Kaowool propane mini-furnace

[rcushing1234]

I wanted a small furnace to concentrate and hold heat from a Bernzomatic TS8000 torch in order to melt silver powder in a 3" melting dish using propane and not MAPP gas. I looked on this forum and other sources. I didn't find exactly what I wanted with step-by-step instructions, dimensions and materials so I stole some ideas and made up others to create this mini-furnace that works very well.

Materials: (5) 4.5 x 9 x 1" firebricks; small amount of 1" thick Kaowool, about 6 sq inches; and about 2 feet of wire

BACK: cut one brick to 7" x 4.5" (I used hammar and chisel)
SIDES: cut two bricks each to 5.5" x 4.5" ( I used hammar and chisel)
TOP: one whole brick (cut two triangular pieces from scrap brick corners to support TOP at an angle)
BOTTOM: one whole brick
INTERIOR: line interior sides, bottom and back with Kaowool insulation
"DOOR": scrap 4.5 x 3.5 brick piece, no cutting necessary




Here's how I put it together. It's all temporary. Butt the sides and bottom against the back of the furnace. Use the wire to
bind the bricks together - see photo. Twist the wire ends together at the back with pliers to increase tension. Line the interior back, bottom and sides
of furnace with 1" Kaowool insulation. Set on the top and support it at an angle as seen in photo with scrap brick corners that you
split off -- they are approx 1 " x 1.5 x 1.8" triangle shape. The angle is arbitrary but too little angle results in torch "blow back" that interfers with your incoming torch flame. Push the "door" in place and that's it.

I first tried this arrangment without Kaowool and it was much slower to heat since a lot of heat was being transferred to the bricks instead of my dish. With Kaowool insulation the furnace runs much cooler on the outside and hotter on the inside.

Results are gratifying. My propane torch heats the dish to redness in 3 minutes or so, then throw in some silver powder and in 5 minutes it's melted. No need for MAPP gas just straight propane.

 

[jmdlcar]

Hi,

That it something like I want to build. Can you tell me how hot the outside gets and can you touch it with you hand?

Thanks
Jack

 

[rcushing1234]

Hi Jack,

There are two parts that get really hot: the top brick and the "'door" because neither of those are protected by insulation. I may insulate them too. I'm soaking my left hand in ice water right now...I grabed the front door thingie to move it out of the way to get better access to the dish with my tongs. It was shockingly hot on the inside surface! By the way, if you throw the hot brick to the concrete floor, it doesn't break. The bottom, back and side bricks get warm but not too hot to touch.

 

[jmdlcar]

Hi,

You might to a handle on the front door so you you could move it easy. I need to fine out where I can get some firebricks. How much did they cost?

Do you have a picture of your mini-furnace in use with TS8000 torch?

Thanks
Jack

 

[Woodworker1997]

I bought some of those bricks from Snyder Brick and Block for less than $1.50 a piece.

Derek

 

[philddreamer]

I used 6 bricks to make my little furnace. 2 at the bottom, side by side. One a sawed into 4 pieces, carved some grooves in 2 of them and used them to set the dish on them. the other 2 sawed pieces I palced at each others end. This creats a cavity when I place the top full brick with a 5/8th hole in the middle for the exhaust. And the other 2 brick placed as shown in the pic. The one birck has a rat hole where a place my first propane torch that pre-heats. I'll lift the top brick and finish melting with a second torch.
Phil