Cut-off wheels need to be thin to reduce the removed material in the cut-off operation and to reduce power consumption. Reinforcement is necessary, because the resin bond of cut-off wheels is too brittle and unsafe for side forces. Therefore, cut-off wheels are reinforced with glass fibers, nylon discs, carbon, cotton cloth, linen, wood, silk, materials on aramide basis, or other materials [COLL88, p. 908 f., FRAC10]. In particular, fiberglass reinforcements unleashed great potential of manual and automated cut-off grinding with their introduction in 1952 [TYRO03b].
Fibers can be woven into different weave or interlace types. For example, glass fibers with a thickness of about 5 ^ are combined into threads of rovings and then weaved like textile fabrics [TYRO03b]. The type of fiber yarn and of weave affect
Fig. 5.2 Example weave types for reinforcements after [COLL88, p. 909]
the extension behavior of the reinforcement body [TYRO03b]. The different interlace types have different performance profiles (Fig. 5.2) [COLL88, p. 908]. For example, the plain weave is isotropic and feasible for thin wheels; the matt weave is applied as inner layer of roughing tools and large cut-off wheels; the cross weave does not experience displacements and is applied for roughing wheels and the outer layer of cut-off wheels [COLL88, p. 908 f.].
Reinforcement material is impregnated with resins that have to be similarly adhesive and wetting for both the textile and the grinding layer mixture [COLL88, p. 909]. Then the reinforcement body is put into the mold with the mixture for the abrasive layer and pressed.
During grinding, glass fiber particles can be released and inhaled by the worker. Fiber glass can induce alterations of the cellular and enzymatic components of the deep lung [ABBA06]. Natural fiber cloth such as hemp is an alternative and does not release mineralic particles during wheel use [ESCH05]. Challenges, however, are the lower strength of the natural material, inhomogeneous composition, susceptibility to micro organisms and strong water assimilation. With cleaned and preprocessed hemp fibers, Eschner et al. [ESCH05] successfully produced cut-off wheels.
Joshi et al. [JOSH04] state that the production of natural fiber reinforced resins (NFR) is more environmentally friendly than the production of glass fiber reinforced resins (GFR). Furthermore, natural fibers can be incinerated and might even give energy credit (e. g. the incineration of china reed gives an energy credit of 14 MJ/kg) [JOSH04].