Vitrified bonded silicon carbide abrasive articles

Claim 1

A FIRED GRINDING WHEEL OR OTHER ABRASIVE ARTICLE COMPRISING ABRASIVE GRAINS AT LEAST 75% BY VOLUME OF WHICH ARE SILICON CARBIDE ABRASIVE GRAINS, AT LEAST TWOTHIRDS BY VOLUME OF SAID SILICON CARBIDE GRAINS BEING AT LEAST AS COARSE AS NO. 30 GRIT SIZE, AND GLASSY BOND OF COMPOSITION FROM 50% TO 90% BY WEIGHT SILICA, FROM 4% TO 25% BY WEIGHT ALUMINA, FROM 2% TO 15% BY WEIGHT ALKALI OXIDE FLUX WITH AT LEAST 1% K20, AND FROM 1% TO 15% BY WEIGHT OF OTHER FLUX, SAID GLASSY BOND CONTAINING AN INSUFFICIENT AMOUNT OF CRYSTALINE PARTICLES TO RESTRICT THE FREE FLOW OF THE BOND DURING FIRING, SAID ABRASIVE GRAINS BEING BOUND TOGETHER IN A MATRIX SAID GLASSY BOND WHICH FORMS A SMOOTH COATING ON SAID ABRASIVE GRAINS AS THE RESULT OF SAID FREE FLOW DURING FIRING, SAID ABRASIVE GRAINS CONSTITUTING FROM 60 VOLUME PERCENT TO 67 VOLUME PERCENT OF THE WHEEL AND SAID BOND CONSTITUTING FROM 2 VOLUME PERCENT TO 20 VOLUME PERCENT OF THE WHEEL, SAID WHEEL BEING A HARD GRADE SILICON CARBIDE WHEEL.