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  #41  
Old 02-20-2013, 07:04 PM
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As a completely "unknowledgeable person" on the topic of brick. Here is my opinion why soldier course might be used.

Standing them on edge, with the thin face pointed inwards makes it very easy to make a rounded shape.

If splits are 1/2 thickness brick; then they would produce even a smoother arch.

Cast the normal soldier course area from refractory castable--then wait for it to break wherever it pleases, then blame it on shrinkage!
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  #42  
Old 02-20-2013, 07:22 PM
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Originally Posted by david s View Post
I have never really understood why a soldier course is recommended.
I re-read your post and it occurred to me that I answered with a Neapolitan dome in mind, not a Pompeii. I'm with you now, and there really is no advantage to starting with a soldier course that I can see.
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  #43  
Old 02-20-2013, 10:11 PM
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Default Re: Share your crack stories

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Originally Posted by mikku View Post
As a completely "unknowledgeable person" on the topic of brick. Here is my opinion why soldier course might be used.

Standing them on edge, with the thin face pointed inwards makes it very easy to make a rounded shape.

If splits are 1/2 thickness brick; then they would produce even a smoother arch.

Cast the normal soldier course area from refractory castable--then wait for it to break wherever it pleases, then blame it on shrinkage!
Good point. Better still design about 3 or four joins in it where you want, making sure you span a brick over the top of each join.
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  #44  
Old 02-21-2013, 02:10 AM
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How similar are the coefficients for expansion of stainless steel and castable refractory? I am thinking they are very similar!

When we did linings of kilns, some areas that were difficult to build or that required special attention for abrasion were either gunned or rammed in place. We used stainless forks (forget the proper name) that were welded to the kiln steel shell. Then the area was built up to proper thickless.

Other areas, like in the pre-heat and cooler areas had same type of forks but then pourable refractory was used.

Ceiling areas had stainless anchors welded to an overhead steel structure that would retain a modified brick that resembled a cone, but square shaped cone if you can imagine that. Then we would form from below up to these bricks and fill from above with another type of castable.

In none of these applications did the castable and stainless anchors interact causing damage to the build.

With those "facts" in mind, do you think that you could use an inner reinforcement net of "stainless steel" similar to concrete mesh to prevent these cracks from ever occurring. Or prevent the cracks from opening that would cause a problem?
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  #45  
Old 02-21-2013, 02:52 AM
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How similar are the coefficients for expansion of stainless steel and refractory
I don't know the answer, but it is rather complicated because they vary at different temperatures. Normal steel has almost the same expansion as structural concrete, but then it is not subject to the extreme temperature we use and not at such a high rate of temp rise.The recommended reinforcement for this application is stainless steel needles. I think this is largely because larger sizes will attract more heat because stainless steel is more conductive than the refractory and therefore attracts more heat to itself causing more expansion and resulting stress. With the needles, they are surrounded by more refractory and their heat is more easily dissipated into it resulting in similar temperatures with similar expansion. By the way normal steel is about 3 times more conductive than stainless so is therefore presumably not suitable for that reason, also corrodes more easily especially in the presence of heat. Stainless is about 10 times more conductive than brick (presumably castable refractory too)

Last edited by david s; 02-21-2013 at 02:56 AM.
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  #46  
Old 02-21-2013, 04:09 AM
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That is a first--from what I have read on this forum.
Good that I can find a question that right off your head no answer pops out.
Let me know-- the details I described are for huge kilns, refractory maker was AP Green - I think the company has merged with another company but its products are still readily available throughout US .
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  #47  
Old 02-21-2013, 06:20 AM
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Speaking in terms of oven construction and the materials used, even how they may react during heating cycles and peak temperatures is interesting, but not important to the fact that your oven will crack. Scores of engineers have built ovens here on fornobravo, they stick to the plans almost without exception. Fits of creative thought are normal in the design phase for all of us. This too will pass, and hopefully you will decide to stick to the plans!

It would take government backed research, experiments, and demonstration and validation projects to construct an oven without cracks. Then, it would probably crack anyway after some use.

The beauty of the pompeii design is that it works as designed! Thousands of us have recorded cracks on this forum, yet the ovens all still work (with two exceptions that I recall where the ovens actually crumbled when they got wet, which were defect in the builder's mortar).

Design the oven as you wish. It will crack. You have about a 99% chance that it will be usable after it cracks.....If you stick to the plans.
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  #48  
Old 02-21-2013, 06:37 PM
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Government backed research, experiments, demonstration and validation projects would only result in regulations, EPA studies, FDA restrictions, special permits, fees and quite possibly the ban of wood fired ovens. That crack is now a signature of my hand built oven.
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  #49  
Old 02-21-2013, 06:58 PM
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I'm with you now, and there really is no advantage to starting with a soldier course that I can see.
I believe the thinking of going that route was more room. If you build a small dome it may make sense and help. I built a 42 so the little bit it buys you is squat...
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  #50  
Old 02-22-2013, 07:31 AM
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I built a 42 so the little bit it buys you is squat...
Yeah, too little to say it makes a difference.
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