Part #3 Of The Building Of Jim's Furnace
Part #3 Of The Building Of Jim's Furnace
Because I'm shipping this to Jim in Canada, he'll be installing the refractory, so I'll show you what it looked like when I did one of my reverberating furnaces.
I'll be using pictures from several builds as examples,
so they might look a little different in places.
Now that we've got the body/frame made, we have to think about making
the molds/forms to insert in there when we pack in the refractory.
Here are a couple of designs I've used. Make sure you make your pattern
at least an inch to two taller then the frame.
Each pattern must be sanded smooth and any holes or dents can be
filled in with body putty; if you want an even better finish you
can coat and sand a coating of plaster of paris to fill in any
(Making it a little on the thin side you can put on several
coats, sanding between each coat.)
Get a bunch of paint sticks as they are great to use for spacers
to hold your mold centered while ramming in the refactory.
This top mold is being held in place by the burner tube.
Mixing up the refractory can be labor intensive. The refractory
is NOT to be mixed like cement... it has to be thick and doughie like
cookie dough or a very soft clay texture. In this first picture you can
see that it's shiny/wet and in the second picture after adding in a little
more how it became more like a dough texture.
Now to start packing in your mud in this type of furnace you have
to fill the base with 2+" and then pack it down, (You can't have
any air pockets or your furnace might explode by super heating the
trapped air pocket.)
Once that is done now install your mold/pattern firmly on top of the
refractory and center it. (This is were the paint sticks come in handy.)
Using a large tablespoon or serving spoon, spoon in the refractory
all around then pack down. After about an inch is in 'raise' your spacers
about 2"and repack it down to fill it in under the spacers. now just repeat
it all the way up till the body is OVER-full.
IMPORTANT:Make sure you build up the refractory higher than
the body of that furnace section, (At least 3/8"), as you can see below,
also you might want to put some weight on the mold to keep it from
floating up as you pack in the refractory.
Take your time with this as you will be able to work with the
refractory for several hours if you have to, so do it right
the first time and you'll have a great furnace.
It's now about 14 hours later and I've removed the molds. The refractory
is still 'green'/soft so it can now be contoured. This time depends on the
size of your furnace and the thickness of the refractory wall.
With a wood rasp I shaved it so the two halves
meet flush and will make a good seal.
When it's getting close I might take a piece of sheetmetal
and sandwich it between a couple of sheet of 80/100 grit
sandpaper and then slide it back and forth between the two halves.
(You can get a good spray-on adhesive for sanding disks from
any auto parts store.)
Now it's a waiting game.... You have to let it dry/cure
for several days to as much as a week or more.
Once it's fully cured, it's time to bake it in.
This is just a guideline every build is a little different
- FIRST BURN: Turn your gas presure real low and run it for
about 15 minutes, (You only want about 250° at the start),
then shut it down and let it "TOTALLY" cool down.
(NOTE: If you were getting a lot of steam during this
heating repeat this step again or let it dry a few more days.)
- SECOND BURN: Use the same settings, but let it run for about 30 minutes.
(DO NOT let the temp get over 400°. Again let the furnace completely
cool down to room temperature and check it for cracks or popped air
- THIRD BURN: If you haven't had any problems to this point increase
your pressure and run it for another 30 minutes and then again let it cool down.
- FOURTH BURN: Everything 'OK'? Let's go for it. Turn your gas pressure
up to your normal settings and run it for 20 to 30 minutes, then check the
furnace for any problems, if it's all good... GO MELT SOME METAL!!!