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On the theme of thermal expansion, generally for the service temperatures we take our ovens to, the expansion is not much of a problem because it's only around 0.5-0.7% (or 5-7 mm for every metre). However, as this thermal cycling occurs every time the oven is fired it is constantly expanding and contracting. The analogy of an expanding chest during breathing is a good one. A tight belt around the chest simply restricts free and easy breathing.
Water elimination, expanding steam and steam spalling is a completely different issue.
A semi-circle arch is a relatively stable form two dimensionally and improved in three dimensions, but not completely self supporting. The only true self supporting arch is the catenary arch and it is unfortunately an unsuitable form for an oven because of the low angle at the base and the high crown. In its three dimensional form the catenary dome requires no assistance from either buttressing or bracing. See "Pizza oven becomes a kiln"
Because kilns experience more than double the service temperatures to that of an oven and the corresponding more than double thermal expansion experienced, methods of supporting the structure were developed. Ovens are not kilns, but the same principles apply. Heavy buttressing introduces energy sapping thermal mass, so lighter weight steel bracing is usually the preferred method. The greater the arch radius, the greater the outward thrust and the greater the need for support.
If an oven cracks, and many do, it is simply creating its own expansion joint where it needs to. The usual method for refractory engineers designing kilns and furnaces, is to observe where the cracking occurs and then engineer expansion joints at those positions.
I believe it is preferable to allow the inner oven to expand and contract freely within the outer shell, allowing the insulation layers to act as the expansion joint. But the firing of an uninsulated oven is asking for trouble because of the huge temperature difference between the outer and inner surfaces of the inner oven.
Water elimination, expanding steam and steam spalling is a completely different issue.
A semi-circle arch is a relatively stable form two dimensionally and improved in three dimensions, but not completely self supporting. The only true self supporting arch is the catenary arch and it is unfortunately an unsuitable form for an oven because of the low angle at the base and the high crown. In its three dimensional form the catenary dome requires no assistance from either buttressing or bracing. See "Pizza oven becomes a kiln"
Because kilns experience more than double the service temperatures to that of an oven and the corresponding more than double thermal expansion experienced, methods of supporting the structure were developed. Ovens are not kilns, but the same principles apply. Heavy buttressing introduces energy sapping thermal mass, so lighter weight steel bracing is usually the preferred method. The greater the arch radius, the greater the outward thrust and the greater the need for support.
If an oven cracks, and many do, it is simply creating its own expansion joint where it needs to. The usual method for refractory engineers designing kilns and furnaces, is to observe where the cracking occurs and then engineer expansion joints at those positions.
I believe it is preferable to allow the inner oven to expand and contract freely within the outer shell, allowing the insulation layers to act as the expansion joint. But the firing of an uninsulated oven is asking for trouble because of the huge temperature difference between the outer and inner surfaces of the inner oven.
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