How To Improve the Porosity of Insulation Bricks

Insulation bricks are high porosity refractories with low thermal conductivity and high porosity (no less than 45%) used to reduce heat losses and thus to maximize heat conservation within the furnace.

The desirable feature of insulating bricks is the low thermal conductivity, which usually results from a high degree of porosity. Insulating material contains pores filled with air which has low thermal conductivity and can prevent the heat from being conducted. The thermal conductivity is lower if the volume of air space is larger. Importantly, the thermal conductivity of a brick does not so much depend on the size of pores as on the uniformity of size and even distribution of these pores. Hence, uniformly small sized pores distributed evenly in the whole body of the insulating brick are preferred.

 

Based on the operating temperature, insulation bricks can be divided into low temperature insulation bricks(600-900℃), middle temperature insulation bricks (900-1200℃) and high temperature insulation bricks (higher than 1200℃). Based on the bulk density, it can be divided into light weight brick and ultra-light weight brick. According to the raw material, it can be categorized into fireclay brick, high alumina brick, silica brick and magnesia brick. 

 

The high porosity of the brick is created during manufacturing by adding a fine organic material to the mix, such as sawdust. During firing, the organic addition burns out, creating internal pores. Ways to accomplish high porosity involves:

1)Add materials such as sawdust which can burn out or sublimate to the mixture. During the firing process, these materials are burnt out and leave pores. 

2)Add foaming agents to a whipping machine to produce small uniform bubbles and then add the bubbles to the mud. 

3)Add chemical substances which can produce gases through chemical reactions such as carbonate and acids, metal powders and acids and caustic alkali and aluminum powder. 

4)Add substances which by themselves have open texture e.g. insulating brick grog, vermiculite, ex-foliated mica, Expanded perlite, raw diatomite etc.

 

Because of their high porosity, insulating bricks inherently have lower thermal conductivity and lower heat capacity than other refractory materials