GB951353A - Improvements in or relating to grinding machines - Google Patents

Abstract

951,353. Grinding. E. W. BLISS CO. Feb. 26, 1962 [March 22, 1961], No. 7480/62. Heading B3D. [Also in Division G3] A grinding machine for grinding steel goblets B comprises a table 28, Figs. 1 and 2, a grinding wheel mount 230 having limited vertical yielding movement relative to a support 188 to which the mount is connected and about which connection the mount is movable, reversible power means operable to effect vertical reciprocation of the support for moving the grinding wheel into and out of engagement with a workpiece on the table, and control means operable in conjunction with the reversible power means to automatically maintain a substantially uniform preselected pressure between the grinding wheel and the workpiece. The grinding wheel 232 is belt-driven from an electric motor 233 and its mounts 230 are supported on arms 220 secured to a plate 221. The arms and plate are connected by pivots 228 to further arms 223 secured to a second plate 192 welded to a sleeve 185 joined to a pair of collars 188 slidable on uprights 160. A spring 241 acts between the plates 192, 221 to provide a yielding movement when the grinding wheel engages the workpiece. Vertical movement of the support for the grinding wheel is effected by a rack-and-pinion mechanism 192, 200 driven through a reduction gear 202 by an electric motor 203, the weight of the support and drive for the grinding wheel being counterbalanced by a weight 180 connected by a cable 181 to the sleeve 185. The vertical supports 160 are secured to the top plate 165 of a carriage 161 having wheels 168 engaging rails 170 on a base 171. An hydraulic piston-and-cylinder device is provided to move the carriage micromentally at the end of each stroke of the table 28 carrying the billet. The table is supported by rollers 31 on rails 20 secured to base members 24 and is driven by a reversible electric motor 45 connected to the table by a rack-and-pinion mechanism 41, the motor being reversed at the end of its stroke by the engagement of shoes 142 with limit switches 143. The billet is held on the table by being clamped between end plates and jaws engaging its sides. The end plates 117, Fig. 8, have wear-resistant pads 124 and are urged into contact with the ends of the billet by piston-and-cylinder devices 118, 120. A slide 112 carrying a jaw and its device 120 is movable by a screw-and-nut mechanism 130, 132 driven by an electric motor 135 to accommodate variations in length of the billets. The side jaws 85, 93, Fig. 10, are operated by piston- and-cylinder devices 102. In their operative position, the jaws clamp the workpiece which rests on a bar 70. When the jaws are retracted they also move downwardly and a portion 84 is lowered by a further piston-and-cylinder 77 to the level of a surface 72. The billet thus rocks about the bar 70 and drops on to the surface 72 so that when the portion 84 is again raised and reclamped by the jaws 85, 93 it has been indexed through 90 degrees to present a different surface to the grinding wheel. The preselected pressure between the grinding wheel and workpiece is effected by controlling the motor 203 for moving the grinding support vertically on the columns from the motor 233 for rotating the grinding wheel. The load on the motor 233 varies the current in a transformer connected to a rectifier, and the D.C. output from the rectifier is supplied to a potential divider. The algebraic sum of the voltage across the divider and that from a reference voltage across a second potential divider is fed to a coil in a generator for the motor 203. The polarity of the voltage in the coil determines the direction of rotation of the motor and the second potentiometer is adjusted to vary the reference voltage which, in turn, varies the pressure with which the grinding wheel engages the billet. Such an arrangement ensures that the grinding pressure is constant irrespective of any curvatures on the surface of the billet. When the grinding wheel is positioned for grinding either the front or rear edge of the billet, a shunt circuit is used to increase the voltage across the second potential divider to control the motor 203 so that the wheel engages the billet with less pressure. The voltage supplied to the feed motor 203 is also reduced as it is lowered from an upper position to reduce the pressure with which the grinding wheel first engages the work. In operation, the machine cycle starts with the grinding wheel in an upper position. The cycle is prevented from starting until a billet is clamped between the end jaws 117 and switches associated therewith are closed to permit the motor 203 to lower the support so that the grinding wheel engages, under light pressure, the billet which is reciprocated by the motor 45. At each reciprocation, the hydraulic piston- and-cylinder device controlling the transverse movement of the support receives a predetermined amount of fluid to move the grinding wheel micromentally, the voltage supplied to the feed motor while the grinding wheel is grinding the front and rear edges of the billet being controlled so that the wheel engages the billet with less pressure than when engaging the areas away from the edges. When the grinding wheel is in its rearmost position, limit switches are actuated to control the motor 203 so as to raise the grinding wheel as the carriage carrying the support is returned to its forward position by its piston-and-cylinder device. During these movements, the piston-and-cylinder devices 77, 102, 120 are actuated to release the billet and index it through 90 degrees to enable the grinding wheel to grind the second surface. When all four sides of the billet have been ground, the finished billet is fed on to a conveyer, such as described in U.S.A. Specification 2,819,563, and a new billet fed to the clamping jaws. The limit switches controlling the forward and rearward movement of the carriages are mounted on plates having nuts engaging oppositely-handed portions of a screw which can be driven by a motor to carry the positions of the switches so as to compensate for wear of the grinding wheel; the plates also carry the switches which control the motor 203 so that the wheel engages the edges of the billet with a light pressure.