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  #11  
Old 07-21-2012, 07:17 PM
david s's Avatar
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Default Re: Cheap fire bricks for sale!

Ok, but smashing a brick with a hammer will not tell you what it is made of or it's suitability. All it will do is give you an idea of its strength and therefore, probably it's degree of vitrification, neither of which will tell you if the brick is actually suitable.
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Old 07-22-2012, 05:33 PM
Journeyman
 
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Default Re: Cheap fire bricks for sale!

Quote:
Originally Posted by david s View Post
"Hit your planned bricks hard with a sledge hammer and check out the bits that it breaks into. If it crumbles into small pieces and sand/dust, forget them, but if they break into hard but larger pieces, then i would use them."

Neill,
This is not a particularly good test for the refractory suitability of a brick. For example an insulating fire brick which is highly refractory crumbles easily and a standard firebrick is usually more crumbly than a solid red, although it way out performs it. Also the temperature the brick has been fired to is also not a suitable indicator of its refractory ability. It is the content of the materials in the brick that is the most important factor, things like high levels of silica, fluxes, and oxides are not good and they are extremely difficult for the layman to test.
David s, this is not quite right. One of our former leading firebrick manufacturers in Victoria, for over 100 years, had a firebrick of 75% Silica which would have been their largest selling firebrick for wood ovens over the last 20 years. it had just 21% Alumina, and just 4% oxides, and with a bulk density of 2000kg/m3 was absolutely perfect for this situation.This would be regarded as a low duty refractory brick. Yes firing temperature has a small effect on suitability, as normal house brick are fired at 1050c vs 1350c of refractory bricks. It really does not make a big difference though as you point out.
In most cases, a sold red brick is pressed during its manufacturing process, the same as ALL refractory bricks, this gives the density. Normal house bricks, yes the ones with holes in them, are wire-cut, they come out of an extruder similiar to say Toothpaste coming out its container, and then just cut into required sizes, with no pressing. This is part of the many factors that influance the suitability of refractory products.
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Last edited by Johnny the oven man; 07-23-2012 at 05:02 PM.
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  #13  
Old 07-23-2012, 02:32 PM
david s's Avatar
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Default Re: Cheap fire bricks for sale!

OK, high proportions of silica in firebricks is undesirable for high temperature applications because it has a tendency to melt, in the presence of high levels of fluxes. As an example of this I once built a small experimental kiln out of mud bricks. At around 1100 C the inside of the kiln melted off in sheets. This is not a factor for a WFO application because it doesn't get hot enough. It was certainly not my intention to mislead anyone. I have removed the silica reference in my post.

Last edited by david s; 07-23-2012 at 03:20 PM.
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