at many forms of refractory before I decided what to use. I
decided the Furnace Cement / Perlite version was
what I wanted
comes from the garden supply section of your local hardware / garden store.
It is used as a "soil conditioner". The price for a two gallon
bag of Perlite was about $2.75 at my local home
improvement store. (Lowes)
The Furnace Cement comes
from the furnace or fireplace section of your local hardware store. Look for
Furnace Cement that says something like "Withstands temperatures to 3000¡F"
and "Contains Silicates". It generally comes in
"11-ounce" tubes (like caulk) and 1 quart or half gallon plastic tubs.
I paid $5 for the first quart and $9.99 per half gallon for the rest.
You will need 1 part (by
volume) of Furnace Cement for each 4 parts (by volume) of Perlite.
For a two gallon bag of Perlite you will need
a half gallon of Furnace Cement. If you use much less
than four parts of Perlite for each part of Furnace
Cement all of the passages between Perlite beads
will be sealed and it will take a long time for the cement to set (it needs
contact with air). If you use much more than five parts of Perlite
for each part of Furnace Cement the resulting material will be quite weak. You
will also want to have some Furnace Cement to use as a sealing coat on your
found 1 quart of the recommended brand of cement and it has about the
consistency of roofing tar, quite sticky. It is a lot easier to work with if you
add about 1 cup of water per ½ gallon of cement. (so
I was told) This makes it more like a thin plaster.
I got my first quart at the local hardware and mixed it up. WooHoo
it works or it looked good anyway. I couldn’t
find more of the recommended brand of cement so I used what was available. It
came out very thick so I had to add about 3 times the water to get it to mix.
Well this also made the mix too sloppy. Since this
mixture sets by removing water and exposing the cement to air I wasn’t too
concerned. So far the only problem I have seen is a longer
You can mix a large
quantity and keep it in a sealed container for a long time. A 5-gallon bucket is
ideal for mixing a two-gallon bag of Perlite with
1/2 gallon of Furnace Cement. I had my mixture stored for 2
weeks before I used it. I found it easiest to mix the Cement
and water first. Then slowly add the Perlite
while mixing. This seemed to get the most even mix.
are building an electric furnace it stands to reason we need an element.
Before we get started a word about safety. You do need
to be familiar with electric formulas and the equipment used for measurements.
DO NOT just wing it here at best you will burn up your element at worst
you could kill yourself. I am providing enough info here for
some one with enough knowledge to fill in the blanks. If you
can’t fill in the blanks DON’T try this or find someone who can!
Elements are pretty easy to get from any ceramics supplier or Budget Casting Supply. The prices range from $30 to $40. So why make one? In my case this is a NO budget project so $30 could be used elsewhere and I happened to have some wire that “should” work.
I say should because most elements are made from some form of NiCrome wire and I used Stainless Steel. NiCrome wire can cost as much or more than the element its self. So I don’t consider this a viable trade off, buy an element. I happened to have a few (2,300) feet of 17 gauge stainless wire I use for safety wire, gardening. I know it was manufactured for an electrical purpose of some sort and figured I would give it a try. You need to know a few things before you wind up some wire and call it an element, specifically resistance of the wire. I also found out that figuring out all the variables can be a huge job so I simplified things. I cut 10 feet of wire wound it around a ¼” threaded rod and measured its resistance. This showed I would need about 73 feet of wire for a 3600 watt element.
I found that winding wire around a ¼ 20 threaded rod made a nice element measuring 3/8 OD. This is pretty close to commercial elements and will shrink just enough, when stretched to fit in a 3/8 groove. After winding you must stretch the element so the rings are separated, otherwise it will short out. You will also need to stretch it to fit in your furnace. So far things are working. I will add more about how well it works as I find thing out. The next section contains some info you will need to figure out what your element needs are.
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