Abrasive grains consisting of polycrystalline alumina

Abstract

The invention relates to an abrasive grain containing electro-fused alumina, formed of crystals of hexagonal structure less than 100 μm in size, preferably less than 30 μm, and further preferably less than 5 μm, having a density that is greater than 97%, preferably 98%, of the theoretical density of alumina and a Knoop hardness of more than 2000. A further purpose of the invention is a method for producing abrasive grains containing alumina, comprising melting of the alumina, its casting at a constant flow rate of less than 80 kg/min, and its cooling by dispersion of the molten alumina in fine droplets to give particles with a size of less than 1 mm. This dispersion is, preferably, conducted by ultrasound-assisted atomization using a frequency of between 15 and 50 MHz. The abrasive grains of the invention are used in particular to produce grindwheels.

1 . Abrasive grain containing electro-fused alumina, characterized in that it is formed of crystals of hexagonal structure less than 100 μm in size, having a density that is greater than 97% of the theoretical density of alumina and a Knoop hardness of more than 2000.  
     
     
         2 . Abrasive grain according to  claim 1 , characterized in that crystal size is less than 30 μm.  
     
     
         3 . Abrasive grain according to  claim 2 , characterized in that crystal size is less than 5 μm.  
     
     
         4 . Abrasive grain according to  claim 1 , characterized in that its density is less than 98% of the theoretical density of alumina.  
     
     
         5 . Abrasive grain according to any of  claims 1  to  4 , characterized in that its Knoop hardness is greater than 2050.  
     
     
         6 . Method for producing abrasive grains containing electro-fused alumina, comprising melting of the alumina, its casting at a constant flow rate of less than 80 Kg/min, and its cooling by dispersion of the molten alumina in fine droplets to give particles having a size of less than 1 mm.  
     
     
         7 . Method according to  claim 6 , characterized in that the casting flow rate is less than 50 kg/min.  
     
     
         8 . Method according to either of claims  6  or  7 , characterized in that casting is conducted through a nozzle heated by induction.  
     
     
         9 . Method according to any of  claims 6  to  8 , characterized in that the dispersion of the molten alumina is obtained by ultrasound assisted atomization.  
     
     
         10 . Method according to  claim 9 , characterized in that the ultrasound frequency lies between 15 and 50 kHz.