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Old 06-24-2011, 12:25 AM
gmchm's Avatar
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Default Fire Brick Ouestion

I have a chance to buy new fire brick on Craig's List for a $1 a piece in Portland Or. They have stamped on the side maxfp20. Does anyone know what this means as far as the class of brick it is?
Also I was wondering if it were a higher firing brick, would you actually use less wood in the long run or does it take longer to heat up, for example? I find it difficult to believe that you could get the oven excessively hot with a wood fire, or at least it should be fairly easy to control. I'm saying this with about 25 years experience using wood as my primary heat source. The low duty fire brick advailable locally is $1.41 and I was told it has an alumina content 18%. Thanks, gmchm

Last edited by gmchm; 06-24-2011 at 12:36 AM.
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Old 06-24-2011, 12:53 AM
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Default Re: Fire Brick Ouestion

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Originally Posted by gmchm View Post
Also I was wondering if it were a higher firing brick, would you actually use less wood in the long run or does it take longer to heat up, for example?
The duty is the resistance to abrasion, or breaking down in the oven and has nothing to do with how they reatain/hold heat or use fuel.
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Old 06-24-2011, 01:39 AM
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Default Re: Fire Brick Ouestion

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Originally Posted by brickie in oz View Post
The duty is the resistance to abrasion, or breaking down in the oven and has nothing to do with how they reatain/hold heat or use fuel.
The duty usually refers to the pyrometric cone the brick is fired to ie the high duty fired to a higher temp.This is actually fairly irrelevant because a WFO never gets anywhere near the max. temp that the brick is capable of. The content of the brick and its ability to withstand spalling are more important factors and you may not be able to find out this info. In general the higher duty brick is likely to be more suitable but not always so. The high duty bricks are also always more expensive and probably don't warrant the extra cost. The density of firebricks, which is is an important factor, vary enormously, eg insulating hotface firebrick while being extremely refractory is unsuitable for the inner oven because you want density.
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Old 06-24-2011, 02:12 AM
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Default Re: Fire Brick Ouestion

Not sure what maxfp20 is, but my guess would be maximum firing pyrometric cone 20 which is around 1530 C. The reason high duty firebricks are so expensive is that they take way more energy/money to get to the higher temp. The greater the temp. the higher the heat loss. The time taken to heat up or hold heat relates to the bricks density.
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Old 06-24-2011, 09:15 AM
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Default Re: Fire Brick Ouestion

Thank you for the replys. I appreciate the clear technical explanations. Would weighting the brick measure it's relative density? I have an old fire brick that weights about 9 lbs.

Last edited by gmchm; 06-24-2011 at 09:16 AM. Reason: typo
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Old 06-24-2011, 12:48 PM
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Default Re: Fire Brick Ouestion

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Would weighting the brick measure it's relative density?
No. Alumina and Silica are similar in weight. This test just eliminates insulating (porous) firebricks, which are much lighter.
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Old 06-24-2011, 09:14 PM
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Default Re: Fire Brick Ouestion

Density= mass/Volume (D=M/V)
Measure and weigh the brick.
My dense refractory bricks are 230x310x80 mm and weigh 9 Kg
You can do the calculations and conversion to Imperial.
This should give you an idea.
Generally you would expect that the higher duty firebricks would be denser because of the increased vitrification and greater shrinkage, but not always so.

Last edited by david s; 06-24-2011 at 09:17 PM.
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