Aggregates for Non-ferrous Applications
Volume 3, Issue 2, Pages 73 - 78
In a refractory castable structure coarse grains or aggregates are typically bonded only by physical forces if the application temperaturedoesn’t exceed 1100 °C. In many non-ferrous production processes the castables don’t reach sintering temperatures that could support the bonding forces. Due to the thermal expansion mismatch between the aggregates and the matrix, microcrack formation is often the consequence. This weakens the bond between aggregate and matrix. This study demonstrates that calcium aluminate aggregates (CAA) are able to overcome that weakness. They build a strong physical and chemical linkage with much higher bonding forces between CAA and calcium aluminate cement (CAC). This effect is demonstrated here through two examples with two different CAA, a fused pore-free aggregate (R50) and a porous sintered CAA (R60). With R50 mechanical abrasion resistance and as well aluminium penetration resistance have been found superior to bauxite, with less castable required per 1 m3. R60 enables slightly lower castable density than fireclay and employs at the same time 50 % more open porosity. De spite this difference the flexural strength remains unchanged. This demonstrates that the bonding between CAA and CAC is much stronger than between aggregates from the alumina-silica system and CAC. Both, R50 and R60 are calcium aluminate aggregates which suit applications up to 1350 to 1400 °C for example in power plants, secondary aluminium industry, re-heating furnaces and back-up linings in many industrial furnaces.
Göller Verlag GmbH