초록 ▼

High purity alumina filters suitable for relatively high temperature molten metal filtering applications are prepared by providing a composition comprising fine grain reactive alumina and a burn out material in amounts sufficient to increase the porosity of the resulting filter structure, the compos

High purity alumina filters suitable for relatively high temperature molten metal filtering applications are prepared by providing a composition comprising fine grain reactive alumina and a burn out material in amounts sufficient to increase the porosity of the resulting filter structure, the composition being free of grain growth inhibitors in amounts sufficient to inhibit growth of the alumina grains during firing; forming the composition into a honeycomb structure by suitable means; and firing the structure beyond the temperature providing maximum densification of the reactive alumina employed whereby grain growth is fostered. The honeycomb structure is fired sufficiently long for significant growth of the particles (from sizes less than about 5 microns to sizes between 10 and 20 microns) and for the creation of wide grain boundaries between the resulting grains which further act as crack arrestors. A preferred composition includes 19 parts by weight reactive alumina, at least 99.5% pure Al2O3, and 1 part artificial graphite.

대표청구항 ▼

An apparatus comprising: a molten metal filter of honeycomb structure with a multiplicity of thin walls defining a multiplicity of open ended, substantially uniform, hollow cells extending between a pair of honeycombed outer surfaces of the filter, said thin walls being formed by a sintered aggregat

An apparatus comprising: a molten metal filter of honeycomb structure with a multiplicity of thin walls defining a multiplicity of open ended, substantially uniform, hollow cells extending between a pair of honeycombed outer surfaces of the filter, said thin walls being formed by a sintered aggregation of alumina grains, essentially all of said grains having a crystalline form with sharp crystalline corners and wide boundaries between the grains characteristic of alumina having undergone exaggerated grain growth, the aggregation further being at least 98% or more by weight Al2O3 and free of alumina grain growth inhibitors in amounts effective to having inhibited alumina grain growth; means for conveying molten metal to be filtered to one of said honeycombed surfaces of the filter; and means for conveying the molten metal from the remaining honeycombed surface of the filter after passage through said cells. A method of filtering molten metal comprising the steps of: providing a molten metal filter of honeycomb structure formed by a multiplicity of thin walls defining a multiplicity of open ended, substantially uniform, hollow cells extending between a pair of honeycombed outer surfaces of the filter, said thin walls being formed by a sintered aggregation of alumina grains, essentially all of said grains having a crystalline form with sharp crystalline corners and wide boundaries between the grains characteristic of alumina having undergone exaggerated grain growth, the aggregation further being at least 98% or more by weight Al2O3 and free of grain growth inhibitors in amounts effective to have inhibited alumina grain growth; conveying molten metal to be filtered to one of said honeycombed surfaces of the filter; passing the molten metal through said one honeycombed surface, the hollow cells of the structure and said remaining honeycombed surface; and conveying the filtered molten metal away from said remaining honeycombed surface of the filter.