GB426480A - Improvements in or relating to the manufacture of ceramically bonded abrasive articles - Google Patents

Abstract

In the manufacture of abrading wheels &c. containing alumina, abrasive grains of alumina are purified by chemical treatment to remove detrimental impurities, and then toughened by heat treatment above 900 DEG C., and finally bonded with a ceramic bond. In an example, crushed and magnetically treated commercial fused alumina grain, containing about 97 per cent alumina, is boiled in an aqueous solution of hydrofluoric and sulphuric acids, for about 24 hours to remove iron and titanium compounds. It is then washed, milled and screened, and roasted for about 24--36 hours at a temperature of about 1300 DEG C. It is then cooled, screened and moulded with ceramic bonding material and fired at 1050--1080 DEG C.; after which it is gradually cooled. A suitable bonding material consists of a mixture of silica, boron trioxide, and alumina with a base or mixture of bases such as potassium or sodium oxide or lime.ALSO:A method of manufacturing ceramically bonded abrasive articles-e.g. grinding wheels-comprises the steps of purifying alumina abrasive grain by chemical-e.g. acid-treatment to remove detrimental impurities-e.g. titanium and iron compounds-toughening the purified grain by heat treatment above 900 DEG C., and bonding the grain with a ceramic bond. It is stated that the toughness of the grain approaches a maximum value at 1400 DEG C. In an example, crushed and magnetically treated commercial fused alumina grain, containing about 97 per cent alumina, is boiled in an aqueous solution of hydrofluoric and sulphuric acids in the proportions of 5 per cent hydrofluoric and 10 per cent sulphuric reckoned on the dry weight of the grain, for about 24 hours. It is then washed, mulled and screened, and roasted for about 24-36 hours at a temperature of about 1300 DEG C. It is then cooled, screened, moulded at a pressure of 1000 lbs. square inch with raw ceramic bonding material in the proportion of 92 1/2 per cent grain to 7 1/2 bond, fired at 1050-1080 DEG C., and gradually cooled. As an example of a fired bond composition is given 65 per cent silica, 15 per cent boron trioxide, 10 per cent alumina, and bases.