Patent GB-755116-A (GB)
Title: Alumina abrasive and grinding wheels made therefrom
IPC: C09K3/14
Filed: 1954-02-12
Abstract: Phenolic resin bonded grinding wheels containing an alumina abrasive (see Group III), may be made by mixing reactive phenol formaldehyde powdered resin with the abrasive, moulding the mixture and pressing while heating to resin curing temperature of about 175 DEG  C.  Such wheels may also contain fillers which are mixed with the resin and abrasive prior to moulding, e.g. cryolite, iron pyrites and potassium fluoborate or combinations thereof.  In an example a grinding wheel was formed from a mixture of 54 volume per cent of the abrasive and 46 volume per cent of bond and fillers, of which the phenol formaldehyde resin bond constituted 55 volume per cent, iron pyrites filler 21 volume per cent, potassium fluoborate filler 21 volume per cent, and lime, which was added as a dehydrating agent to eliminate water liberated during curing, 3 volume per cent.  The mixture was moulded at 2 1/2 tons per sq. inch at 160 DEG  C.  The moulded wheel was baked at temperatures rising from room temperature to 140 DEG  C. in 4 hours and then at 140 DEG  C. for 18 hours.ALSO:An abrasive in particulate form is produced by grinding calcined bauxite to a fine powder, treating the powder obtained with hydrochloric acid to bring the iron oxide content within the limits set forth below, washing the powder free from acid and drying to a water content of about 2 per cent, screening to break up the aggregate, pressing the screened powder to about 2,500 lbs. p.s.i. to form bricks, which are then dried and sintered at from 1550 to 1650 DEG C. for at least two hours, after which the sintered bricks are crushed to the desired particle size for the final abrasive.  The abrasive contains 65 to 97 per cent alumina and 4 to 35 per cent iron oxide, together with silica, titania, lime and magnesia impurities within specified ranges and has a hardness of about 9 on Mohs's scale, is finely crystalline and has a strength greater than that of fused alumina.  Phenolic resin bonded grinding wheels containing the abrasive may be made by thoroughly mixing reactive phenol formaldehyde powdered resin with the abrasive, moulding the mixture and pressing while heating to resin curing temperature of about 175 DEG C., for example, by a steamheated hot press.  Such wheels have a porosity of 2 per cent or less.  The grinding wheels may also contain fillers which are mixed with the resin and abrasive prior to moulding, such as cryolite, iron pyrites and potassium fluoborate or combinations thereof.  According to an example, a grinding wheel was formed from a mixture of 54 volume per cent of the abrasive and 46 volume per cent of bond and fillers of which the phenol formaldehyde resin bond constituted 55 volume per cent, iron pyrites filler 21 volume per cent, potassium fluoborate filler 21 volume per cent, and lime, which was added as a dehydrating agent to eliminate water liberated during curing, 3 volume per cent.  Such mixture was moulded into a wheel of 16 inches diameter by 2 1/2 inches thick with a 6 inch diameter central hole in a hot press at 2 1/2 tons per sq. inch at 160 DEG C.  After moulding and pressing the wheels were baked at temperatures rising from room temperature to 140 DEG C. in 4 fours and then at 140 DEG C. for 18 hours.