GB1152796A - Method of Manufacturing Abrasive Articles - Google Patents

Abstract

1,152,796. Moulding grinding wheels. NORTON CO. 14 April, 1967, No. 17152/67. Heading B5A. [Also in Divisions C3 and C4] Resin bonded grinding wheels of improved performance are moulded from a mixture of abrasive particles and uncured phenol-aldehyde resin which is compacted and formed to the desired shape followed by curing, in which a relative humidity of 20% to 100% at atmospheric pressure is maintained around the wheel at at least 100‹ C. for at least 5 mins., and preferably 5 to 60 mins., for a conditioning period at the commencement of the curing process which is then completed at a lower relative humidity and a higher temperature e.g. 175‹ C. over an extended time e.g. 22 hrs. The process is thought to produce a more intimate blending of the particles and resin by increasing the plasticity of, and in addition promoting the cure of, the resin by preventing the escape of moisture thereform in the early stages of the curing process. The resin should contain at least 1% and preferably at least 5% by weight of water which may be added to the moulding mix or liberated by chemical reaction. Thus, with a phenol-formaldehyde two-stage resin, furfural may be added which may contain. 5% free water and releasing additional water during the curing process; inorganic hydrates or salts or other non-reactive compounds may be employed. A liquid one stage resin containing 2% water and releasing additional water e.g. 15-20%, may be mixed with a two-stage resin cured by hexamethylene tetramine. The conditioning may be achieved by covering or wrapping the wheel with a moisture impermeable film e.g. aluminium foil, applied in a manner whereby pressure build-up in the wheel above atmospheric is avoided. Alternatively the wheels may be suspended in the static saturated atmosphere of an oven containing water or saturated aqueous salt solution e.g. KF, KI or Pb(NO 3 ) 2 , in containers, and may either be introduced at 100‹ C. or brought up to 100‹ C. in the conditioning during which period the oven is preferably maintained at a lower relative humidity to avoid transfer of moisture on to or into the wheel. An air circulating oven may also be employed, preferably at humidities below 90% to avoid moisture transfer. Various compositions are specified employing as abrasive particles, aluminium oxide of 24, 46 or 60 grit, and 36 or 120 grit silicon carbide. The phenolic resin binder may comprise powdered two-stage resin, with hexamethylene tetramine as curing agent, and liquid phenol formaldehyde onestage resin to which may be added neutral anthracene oil. Alternative binders may comprise powdered hexamethylene tetramine twostage resin and neutral anthracene oil with powdered cryolite, powdered CaO and furfural; two-stage hexamethylene tetramine cured formaldehyde resin with one stage liquid formaldehyde resin and distilled water; paraformaldehyde or trioxane-novalak two stage resin; powdered two-stage formaldehyde resin with liquid one-stage formaldehyde resin, powdered iron pyrites and neutral anthracene oil; powdered two-stage formaldehyde with hexamethylene tetramine, rubber and sulphur and clay filler; liquid one-stage formaldehyde resin with shellac and castor oil.