Fused Cast AZS Block Vs. Bonded AZS Block

In glass industry, the most widely used refractories in contact with the melten glass are AZS (alumina-zirconia-silica) refractories. AZS refractories of both fused and bonded types are good refractory materials for the glass industry because they can withstand the aggressive conditions during liquid processing of glass. Both have their pros and cons when applied to glass furnaces.

Fused cast AZS blocks are manufactured by melting mixtures of raw materials in an electric furnace and casting the melt into moulds where it solidifies. High density, small or large shapes are obtained. When appropriate, a finish is made by grinding with diamond tools.

 

Compared to bonded AZS blocks, fused cast  blocks have higher bulk density and lower apparent porosity, so they have better corrosion resistance. They have higher strength under normal and high temperature and also have lower blisterign potential in most applications. 

 

The superior corrosion resistance of fused cast AZS blocks is attributed primarily to the microstructural features. They are not homogenous in their chemistry and microstructure within one block. The major phases are ZrO2, alpha alumina and glass phase. The glass phase can be considered the bonding structure holding the block together. 

Bonded AZS blocks are also known as sintered AZS blocks. Thet are made by sintering raw materials under 1700-1750℃. Bonded blocks can be made by different methods, such as traditional dry pressing, iso-pressing and vibro-casting. The chemical composition of bonded blocks is similiar to fused cast  blocks but bonded blocks do not contain carbon. 

 

The major phase of bonded AZS are ZrO2, alpha alumina and mullite. They contain little or no glass phase. Mullite forms the bond in the bonded refractories. Compared to fused cast block, Bonded blocks is relatively homogeous in their chemistry and microstructure. The bonded blocks have lower thermal conductivity and lower thermal expansion, so they have lower heat loss and better thermal shock resistance. 

 

The reliability of a refractory for glass furnaces is determined for his corrosion resistance to the molten glass, as well as its mechanic strength and thermal shock resistance. AZS blocks are the preferred choice as they have better corrosion resistance to melten glass compared to bonded blocks. 

 

Fused cast AZS blocks have better performance and longer service life. However, the bonded AZS blocks has lower prices, so they are an economic alternative to fused cast block in many applications.