Will This Furnace Work For Heat Treating?

[David Kirtley]

If you are worried about the longevity of the elements, they last quite a while. The embedded elements will last longer than exposed because the insulation will keep contaminants and oxygen away. As Ray mentioned, the thing that will kill it faster than anything else is contaminants on the metal. Especially salt and fluxes. They will combine with the insulation and form a glaze and will erode the insulation.

Any ceramics supply will have kiln furniture (the props and shelves and such) that will make it easier to put material in and not mechanically wear the insulation. The dust from the insulation is not something you want to breathe. It makes little needle like pieces that go in but don't like to come out. They will pretty much be a permanent addition to your lungs. Not like the clouds of stuff that people breathe in to get the really bad problems that cause black lung and asbestosis but it is something to avoid when you can.

Grit and dust will melt and form glass in the kiln. Not necessarily a problem but be aware of it. It can stick on the parts and is about the consistency of honey at that temp so you can have things come out as an unexpected surprise when you pull out the workpiece. You paint the furniture with what is called kiln wash that is a high temperature coating that keeps things non-stick. After a few applications, it will start to flake off. Just hit it with a wire brush to take off the loose stuff and paint it again.

 

[frostheave]

If you are worried about the longevity of the elements, they last quite a while. The embedded elements will last longer than exposed because the insulation will keep contaminants and oxygen away. As Ray mentioned, the thing that will kill it faster than anything else is contaminants on the metal. Especially salt and fluxes. They will combine with the insulation and form a glaze and will erode the insulation.

Any ceramics supply will have kiln furniture (the props and shelves and such) that will make it easier to put material in and not mechanically wear the insulation. The dust from the insulation is not something you want to breathe. It makes little needle like pieces that go in but don't like to come out. They will pretty much be a permanent addition to your lungs. Not like the clouds of stuff that people breathe in to get the really bad problems that cause black lung and asbestosis but it is something to avoid when you can.

Grit and dust will melt and form glass in the kiln. Not necessarily a problem but be aware of it. It can stick on the parts and is about the consistency of honey at that temp so you can have things come out as an unexpected surprise when you pull out the workpiece. You paint the furniture with what is called kiln wash that is a high temperature coating that keeps things non-stick. After a few applications, it will start to flake off. Just hit it with a wire brush to take off the loose stuff and paint it again.

Thanks David. I do like the fact that the elements are covered. Here is a furniture question. Say I wanted to heat treat a 1-2-3 block I just finished milling. Would I set it directly on a shelf in the furnace or should it be elevated above the shelf with something? The block has no holes in it. Thanks.

Bob

 

[David Kirtley]

Thanks David. I do like the fact that the elements are covered. Here is a furniture question. Say I wanted to heat treat a 1-2-3 block I just finished milling. Would I set it directly on a shelf in the furnace or should it be elevated above the shelf with something? The block has no holes in it. Thanks.

Bob

Personally I would elevate it. It makes it a lot easier to pick up when you can reach under the part. Not many things worse than having a red hot piece of metal that you don't have a firm grip on. Too exciting for me. I prefer operations like that to be boring.

 

[frostheave]

Personally I would elevate it. It makes it a lot easier to pick up when you can reach under the part. Not many things worse than having a red hot piece of metal that you don't have a firm grip on. Too exciting for me. I prefer operations like that to be boring.

Roger that! What would you use to elevate the part?

 

[12bolts]

Is there the facility to hang it from the roof? Otherwise up on a small piece of insulating fire brick, preferably aluminium oxide.

Cheers Phil

 

[KMoffett]

Roger that! What would you use to elevate the part?

Not sure what Paragon charges for shelves, but you can get shelves and feet (posts) relatively cheap from kiln accessory suppliers. Just make sure you select ones that will handle your temperature range.

Ken

 

[Ray C]

Lots of good info. Thanks Ray. I did some searching. That's a pretty impressive furnace you built! How well is it holding up? Would you use the wool again?

Below are two links that will be very informative and helpful.

Ray C Heat Treat Furnace Build: http://www.hobby-machinist.com/showthread.php?t=9929&highlight=heat

Reading Resources for Heat Treating: http://www.hobby-machinist.com/showthread.php?t=9653&highlight=heat

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Hi oldgoaly. Forgive my ignorance, but what is a Muffle Furnace? How is it different from the Kiln I bought? Thanks.

Bob

My old oven is doing just fine and it gets used about every three weeks. I had to change the wire once but that's no big deal and is to be expected. Wire is pretty cheap if you wind it yourself -and only takes a few minutes.

Yes. I'd use the wool again for sure. When the inside temps are 1600, the outside is only 100. That stuff is incredible!

As for elevating the part, I made a rack of 3/8" diameter stainless steel rods that are spaced about 1" apart. That allows heat to circulate and the actual contact with the part is very minimal. I took my time to make it as flat as possible and it's well supported in the center to prevent sagging when treating heavier parts. It's still going strong.

Heat treating happens to be one of my favorite shop tasks and it's a remarkably useful skill. Take your time and practice. In previous posts, I mentioned some very good reading resources and I highly recommend you read-up on the topic.


Ray

 

[David Kirtley]

They make a wide variety of different kinds of stilts for ceramic kilns that would hold the pieces well. Some are all ceramic, some have wire tacks sticking up through them so there is only a few points to file off when glazing. Racks, ring holders, cradles.

If you do a google image search for kiln furniture and kiln stilts, you can get an idea of the variety. Most is really cheap.

As to the temperature range they will withstand, the temperatures for heat treating are small beans in the ceramic world. Most steels will burn off in high fire ceramics kilns.

 

[frostheave]

My old oven is doing just fine and it gets used about every three weeks. I had to change the wire once but that's no big deal and is to be expected. Wire is pretty cheap if you wind it yourself -and only takes a few minutes.

Yes. I'd use the wool again for sure. When the inside temps are 1600, the outside is only 100. That stuff is incredible!

As for elevating the part, I made a rack of 3/8" diameter stainless steel rods that are spaced about 1" apart. That allows heat to circulate and the actual contact with the part is very minimal. I took my time to make it as flat as possible and it's well supported in the center to prevent sagging when treating heavier parts. It's still going strong.

Heat treating happens to be one of my favorite shop tasks and it's a remarkably useful skill. Take your time and practice. In previous posts, I mentioned some very good reading resources and I highly recommend you read-up on the topic.


Ray

Very good Ray. When my little furnace gets too small I'll be coming back to your build for inspiration. One off topic but related question. What would you recommend for a beginner needing a surface grinder? I haven't seen one for sale yet here in Alaska but I keep looking. Thanks again.

Bob

 

[lngknife29]

While you're testing this furnace, just be careful to NOT exceed the listed max temperature. That personal experience mistake cost me about $500.00 for new heating elements!

My furnace is about the same size as your's and has served me well.

Murray