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The Annealing Process of Fused Cast AZS Block

The thermal annealing of fused cast AZS block involves a solidification process. The cracks in the fused cast AZS are almost all caused by the casting stress. In order to eliminate the casting stress and reduce the possibility of cracking, the annealing method should be reasonable. 
Fused Cast AZS Block
The annealing process can be divided into four stages:
Stage 1: the shell of the castings begins to harden but the central part is still liquid and can flow freely. in this step, even if there are cracks caused by the external force, the cracks can be filled immediately by the melt.
 
Stage 2: most of the casting is in solid state. The solid phase has formed a complete skeleton and has concern strength. However, the glass phase in solid phase is fragile and is easy to be destroyed stress. The isolated viscous glass liquid can not fill and fix it and then cracks are formed. 
 
Stage 3: all of the casting is solidified and in plastic state. Small stress can be absorbed by the plastic deformation of the glass phase, but if the stress is too big, cracks will be formed. 
 
Stage 4: the state of the casting will be changed from the plastic state to the elastic state. The change is not sudden and happens during a temperature range. 
 
The annealing begins from the end of the casting process at 1800℃ and the real annealing begins at 1150-1200℃. The annealing method can be divided into thermal annealing and tunnel kiln annealing. 
 
Thermal box annealing involves the use of a mental box which has a large fire clay brick at the bottom and is filled with clinker sand or quartz sand. The clinker sand or quartz sand have great insulation effect and reduce the radiating rate. The fire clay brick can absorb heat and forms a temperature gradient toward the casting nozzle. It is energy saving and economic.
 
Tunnel kiln annealing refers to annealing on the tunnel kiln car. The tunnel kiln consists of insulation zone and cooling zone. The casting must be put into the insulation zone after the casting process is completed in order to ensure the casting solidified and cooled under the most suitable cross section temperature differential. It generally takes only two days. The quality of products is stable, but it is costly. 

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