Method of roll grinding

#The invention relates to a method of roll grinding and to abrasives tools used in roll grinding.

#Roll grinding is a cylindrical grinding process wherein a bonded abrasive wheel grinds and smoothes the surface of a mill roll. A mill roll is a large (e.g., 7 feet in length, 2 feet in diameter) metal roller, typically made of forged steel, designed for use in the surface finishing of metal sheets. In grinding the surface of the mill roll, the grinding wheel must impart a uniform, smooth surface finish to the roll. Any imperfection, such as grinding patterns, feed lines, random marks, indentations, and the like, created on the roll surface during the grinding process will be transferred onto the metal sheets being processed by the roll.

#With unstable grinding systems, the grinding conditions cause the vibration amplitude between the grinding wheel and the workpiece to increase over time. This results in a series of undulations that develop and build along the surfaces of both the grinding wheel and workpiece. This process is referred to as regenerative or self-excited chatter and has been associated with certain imperfections in the surface of mill rolls following grinding (“chatter marks”). Roll grinding operators want “chatter-resistant” grinding wheels, having the capacity to stay in a round shape and maintain a resilient character as grinding progresses and the wheel is worn. Grinding vibration models have been developed (Inasaki I., Grinding Chatter—Origin and Suppression, CIRP Proceedings, 2001) to explain the relationship between wheel properties (such as decreased contact stiffness, increased damping) and the suppression of self-excited chatter.

#Abrasive Grain/Vitrified Binder Agglomerates

#Vitrified binding materials (see Table 1-1, footnotes b and c) were used to make agglomerated abrasive grain samples AV2 and AV3. The agglomerates were prepared according to the rotary calcination method described in U.S. Ser. No. 10/120,969, Example 1 using the materials described below. The AV2 agglomerates were made with 3 wt. % Binder A. The calciner temperature was set at 1250° C., the tube angle was 2.5 degrees and the rotation speed was 5 rpm. The AV3 agglomerates were made with 6 wt. % Binder E, at a calciner temperature of 1200° C., with a tube angle of 2.5-4° and a rotation speed of 5 rpm. The abrasive grain was a fused alumina 38A abrasive grain, 80 grit size, obtained from Saint-Gobain Ceramics & Plastics, Inc., Worcester, Mass., USA.

#The vitrified grain agglomerates were tested for loose packing density, relative density and size. Test results are listed in Table 1-1 below. Agglomerates consisted of a plurality of individual abrasive grits (e.g., 2 to 40 grits) bonded together by vitrified binding material at grit to grit contact points, together with visible void areas. The majority of the agglomerates were sufficiently resistant to compaction to retain a three dimensional character after being subjected to abrasive wheel mixing and molding operations. 1 TABLE 1-1 Abrasive Grain/Vitrified Binder Agglomerates Sample No. LPD Mix: g/cc Average grain, Weight Wt % Binding Volume % −20/ size Average % binding lbs (kg) Abrasive material binding +45 mesh microns relative material of mix Grain Wt % materiala fraction (mesh) density AV2 84.94 94.18 2.99 4.81 1.036 500μ 26.67 80 grit (38.53) −20/+45 38A, Binder Ab AV3 338.54 88.62 6.36 9.44 1.055 500μ 27.75 80 grit (153.56) −20/+45 38A Binder Ec aThe percentages are on a total solids basis, only include the vitrified binder material and abrasive grain, and exclude any porosity within the agglomerates. Temporary organic binder materials were used to adhere the vitrified bond to the abrasive grain (for AV2, 2.83 wt % AR30 liquid protein binder was used, and for AV3, 3.77 wt % AR30 liquid protein binder was # used). The temporary organic binder materials were burned out during the sintering of the agglomerates in the rotary calciner and the final wt % binding material does not include them. bBinder A (described in U.S. Ser. No. 10/120,969, Example 1) is a mixture of raw materials (e.g., clay and minerals) commonly used to make vitrified bonds for abrasive grinding wheels. Following agglomeration, the sintered glass composition of Binder A includes the following oxides (wt %): 69% glass formers (SiO2 + B2O3); 15% Al2O3; 5-6% alkaline earth oxides RO # (CaO, MgO); 9-10% Alkali R2O (Na2O, K2O, Li2O), and has specific gravity of 2.40 g/cc and an estimated viscosity at 1180° C. of 25,590 Poise. cBinder E (described in U.S. Ser. No. 10/120,969, Example 1) is a mixture of raw materials (e.g., clay and minerals) commonly used to make vitrified bonds for abrasive grinding wheels. Following agglomeration, the sintered glass composition of Binder E includes the following oxides (wt %): 64% glass formers (SiO2 + B2O3); 18% Al2O3; 6-7% alkaline earth oxides RO # (CaO, MgO); 11% Alkali R2O (Na2O, K2O, Li2O), and has specific gravity of 2.40 g/cc and an estimated viscosity at 1180° C. of 55,300 Poise.