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Heat Treating and Metallurgy Discussion of heat treatment and metallurgy in knife making.

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  #1  
Old 03-03-2009, 10:57 AM
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Heat treat oven exterior temps? (homemade and/or factory made?)

Hey guys,

Yet another question about HT ovens:

As I've stated in previous threads, I'm working on designing my own HT oven, and I'm trying to decide how many layers thick I need to lay the brick, and/or what kind of insulation, if any, to use.

I'm hoping that there is a way to keep the exterior relatively cool (maybe even to the touch?) when the oven is at high temperature.

For those of you who have made your own ovens or use brand name ovens, how hot does the exterior shell get when running at high temps? (Like 1800? F)

Do any of them really stay very cool? Are you able to touch them? If so, how thick are the refractory bricks? Is there any type of insulation?

I plan using refractory mortar to seal the bricks together, and hopefully that will keep more of the heat in as well.
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Old 03-03-2009, 01:19 PM
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I only used one layer of the soft bricks inthe one that I made and it regularly gets to 1900. I have never had an issue with the outside heating up. I can easily put my hand on the outside. It is warm but that is it. I used a single layer of brick then sheathed it in sheet steel.
Steve


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Old 03-03-2009, 01:59 PM
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Did you mortar your bricks together?
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Old 03-03-2009, 02:06 PM
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Yes I did. I spent a fair bit of time talking to Pottery Supply House here in Canada. I believe they have a US branch as well. They were very helpful and also supplied the brick and the mortar and the element and controller. The chamber on mile is only 4" high by 6" wide but is 18 " deep. It can reach 1900 in about 45 minutes.
Steve


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Old 03-03-2009, 03:42 PM
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Got any pics SV?

I've been talking with a guy that owns a local refractory with a few high temp furnaces, and he seems to think I'll need to stack my bricks a couple layers deep at LEAST to keep the outer shell cool enough to hold my hand against for any amount of time

He has also recommended that I not use Kaowool.

While the guy has been doing this kind of stuff for 30 years or so, I'm a little skeptical of needing two layers of brick, after seeing the average small HT oven.

I'm gonna experiment with a couple things I think...


And how about the rest of you guys out there? What are your experiences with outer shell temperatures?
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Old 03-03-2009, 06:25 PM
Burke Burke is offline
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my 14 inch paragon can have a hand put and held on it with comfort. my 45 inch deep paragon can be touched but gets a uncomfortable holding your hand on it but it isn't hot enough to burn you. the two evenheats and the sugar creek that I have had the oportunity to use would all give 1st to second degree burns if touched.


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Old 03-04-2009, 10:36 AM
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I think there are two different types of brick that we are talking about. I am pretty sure refractory brick and kiln brick are two different things. I have never used refractory brick but the kiln brick is very very soft and relatively light. It tends to absorb the heat and hold it internally. You may want to check to see if we are all talking the same material.
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Old 03-04-2009, 01:44 PM
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Quote:
Originally Posted by SVanderkolff
I think there are two different types of brick that we are talking about. I am pretty sure refractory brick and kiln brick are two different things. I have never used refractory brick but the kiln brick is very very soft and relatively light. It tends to absorb the heat and hold it internally. You may want to check to see if we are all talking the same material.
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STeve
Refractory brick is also known as soft fire brick, or insulating fire brick.

I think it's the same thing as your "kiln" brick. It's very easy to cut, comes in a few different grades (2300?, 2600?,3000? I believe), and it too is supposed to be light. It's usually a white/light colored brick.

I may try to go pick some up today at a local refractory. I'm still waiting for a price quote though. Typicially they're about 4 to 5 dollars a brick? Hopefully I can get a better deal though, because the guy i've been talking too just ordered a few hundred bricks, and while they don't normally distribute to the public, he's willing to sell me a few for what they end up paying for them.

You don't happen to have any pics of your HT oven do you?
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Old 03-04-2009, 02:37 PM
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Not sure if I have any pics. I will try and get some tonight
Steve


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Old 03-05-2009, 12:39 PM
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My home made oven uses the 2 1/2 inch thick refractory brick. Iusually run it at 1550 degrees and you can touch the outside. After a time the outside will get to hot to touch.
I think I would go with the 3 inch brick instead of 2 1/2.
I built the oven in British Blades. Works great
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Old 03-05-2009, 12:55 PM
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I'm using 2.5" brick because that's what I can get locally. However, I might insulate it further with some ceramic blanket on the top, back, and sides on the outside if I can figure out the shell design to immobilize the bricks and allow for that addition..


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Old 03-05-2009, 02:40 PM
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Quote:
Originally Posted by pipecrafter
I'm using 2.5" brick because that's what I can get locally. However, I might insulate it further with some ceramic blanket on the top, back, and sides on the outside if I can figure out the shell design to immobilize the bricks and allow for that addition..
I'm gonna try to get some 3" brick at a local refractory next week, if I can get a hold of the guy I've been talking to. Missed him the last couple days.

I'm gonna seal them together with some refactory mortar and then wrap the top, bottom, back, and sides with some 1" ceramic fiber blanket before I put the shell on. I figure the mortar will help keep the bricks in place as well as sealing the heat in that much more.

I'd prefer to use fiber board, or even paper I think, if the darned stuff wasnt so much more expensive.
Ideally, I would at least put some underneath the bricks since the bricks would crush the blanket on the bottom side, but I might just make a bracket to hold the bricks up.... I'm not sure yet. I'm still turning quite a few idea's around for my oven's design.
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