3.1.1 Chemistry and Types of Resin Bonds
A resin bonded grinding wheel consists of abrasive grits in a resin bond with or without fillers (Fig. 3.2). This wheel type has commonly a low porosity compared to vitrified bonded tools.
Resins are viscous liquids capable of hardening. They are polymers, i. e. large molecule chains composed of monomers. Monomers are substances with the elements C, H, O, N, Cl, S, or F, from which oligomers (“resins”) are synthesized [GARZ00, p. 109]. These are then transformed to crosslinked, insoluble polymers in a second step, called curing, which optionally involves heat, catalysts, fillers, or pressure [GARZ00, p. 109].
Resin bonds for abrasive tools consist of single resins or a resin combination with or without fillers (see Sect 3.1.3 “Fillers in Resin Bonds”). The resin itself is typically manufactured by esterification or soaping of organic compounds. Filler material has not only the task to reinforce the bonding in toughness, heat resistance, strength, and breakage safety, but also to support the grinding process as secondary abrasive [COLL88]. Silicates, dulfides, halogenides increase the bonding strength and wear resistance and hinder the oxidative degradation of the resin [KREB06]. In cut-off wheels, the resin bond is additionally enforced by body materials of glass fiber, linen cloth, etc. (see Sect. 4.2 “Coated Abrasive Tools”).
Resin bonds can be divided into three classes based on strength and temperature resistance [KLOC05a, p. 43, MARI07, p. 119, COLL88, p. 896 f., ROWE09, p. 41, MENA00]:
• Phenolic resin,
• Polyimide and polyamide resin, and
• Epoxy or urethane resin, often called plastic bonds.