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Home Made Refractory

Home Made Element

Refractory Recipes

Element Info & calculations

 

Home Made Refractory

I looked at many forms of refractory before I decided what to use.   I decided the Furnace Cement / Perlite version was what I wanted

The Perlite 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 lining.

I only 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 dry time. 

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.

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Home Made Element

If we 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.

10/29/02   After completing the furnace I have done several melts.  The element has held up well even when shorted out during my first melt.  It does take a long time (1+ hours) for the furnace to heat up enough for the first melt.  I do believe the element has some to do with this issue.  I also believe the construction plays a part as well see the Electric Furnace page for more details about this.   I would recommend making an element if you have the material available.  If you must purchase the wire I don’t believe it is economical or the best use of your time.

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