The resin bond consists of a synthetic resin or synthetic resin combination with or without fillers. For particular grinding wheel types, applications or different fabrication methods, there are many resins available. In the case of the dry mix method, phenol resol is used for the grit wetting as well as a phenol resin powder based on novolak hexamethylenetetramine [COLL88]. Despite the variety of synthetic resins available today, phenol resins or phenol plasters are still the most common bond components for grinding wheels bonded with synthetic resin.
In order to give the bond certain properties, it is customary to modify the phenol resin powder. Besides variations in the proportion of hexamethylenetetramine, bond hardness and brittleness can be manipulated by the addition of elastomeric bonds. In this way, wheel speed can be increased and the danger of crack formation due to large changes in temperature and pressure loads can be significantly decreased. In this context, particularly polyvinylbutyral, certain types of rubber and epoxy resins have proved useful. In the case of grinding wheels reinforced with glass fibre, adhesion to the fibreglass can be improved by means of epoxy resin modification [COLL88].
Of lesser importance among abrasive products bonded with synthetic resin are bond systems based on polyurethane, polyester and epoxy resin. In order to achieve particular grinding effects, like especially soft, smooth grinding or polishing effects, epoxy or polyester resins are utilised. An extremely high elasticity in the abrasive can be gained by using polyurethane resin.
When in contact with alkaline cooling lubricants, resin-bonded abrasives show a decrease in bond strength and hardness, which is attributable to the penetration of water molecules and particularly OH ions into the interface between the grit surface and the resin bond. To reduce this influence, grits are pre-treated with special adhesive agents and the wetting and wear properties of the resin are specifically influenced by a suitable choice of resin system [COLL88]. When using resin bonded grinding wheels, cooling lubricants mixed with water should not exceed a pH value of 9 [FRAN88].
Grinding wheels manufactured with synthetic resin bonds
• are insensitive to impact or shock as well as lateral pressure,
• allow for high rotational speeds and chipping volumes for abrasive cutters and rough grinders,
• permit high surface qualities by means of a high elasticity in the case of polishing and smoothing discs [COLL88].
Consequently, the primary areas of use for grinding wheels bonded with synthetic resin are abrasive cutting and rough grinding.