Patent GB-790788-A (GB)
Title: Improvements in or relating to grinding
Inventor: BALSIGER HAROLD EDWARD
IPC: B24B17/02
Filed: 1954-05-26
Abstract: 790,788. Grinding turbine blades &c. LANDIS TOOL CO. May 26, 1954, No. 15483/54. Class 60. A machine for grinding a turbine blade 56, Fig. 3, having convex and concave faces comprises means for rotating the blade about its longitudinal axis, means for effecting a to and fro movement between the blade and a grinding wheel 42, and means controlling such to and fro movement so as to hold the grinding wheel out of the concavity of the blade. The blade is supported between centres 54, 57 mounted on a spring-loaded cradle 11 to which the to and fro movement is imparted by a cam 50 and a follower 60 having a diameter equal to the mean diameter of the grinding wheel. The master cam is ground on the same machine by displacing the bearings 51, 52 between which it is supported to a position opposite the grinding wheel 42 and mounting a model (not shown) between the centre 54 and a footstock (not shown) to cooperate with an adjustable follower shoe having an operative surface with a radius equal to the mean radius of the grinding wheel. The model differs from the product blade in that the portion corresponding angularly to the concave portion of the blade is convex in contour so that the master cam produced will prevent contact between the work piece 56 and the grinding wheel during the time when the concavity in the blade is adjacent the wheel surface. When grinding the master cam, the cradle 11 is loaded by a counter-balancing arm. The drive to the work piece includes a motor 21, a fly wheel 22 and a pulley 27 which has a heavy rim so that it functions as a fly wheel. The grinding wheel is driven by a belt from a motor 43 and mounted on a base 40 which is slidably mounted on a carriage 41 for transverse and longitudinal movement on the bed 10 of the machine. A radius 93, Fig. 5, adapts the wheel to any longitudinal curvature in the blade 56 while a radius 92 grinds the fillet between the blade and its rest 91. The machine is preferably operated by first feeding the grinding wheel into the work to the full depth of cut and thereafter initiating a relatively slow traverse movement to effect a shear cut. At the end of one traverse movement the wheel and work are separated and the traverse movement is reversed. This cycle of operations is carried out automatically by the arrangement shown in Fig. 6 in which a switch 100 is closed to connect the supply L1, L2 to a wheel start button 102 and to allow current to flow through a wheel stop button 105 to a relay OP for starting the oil pump motor 107 which makes pressure fluid available throughout the hydraulic system. Button 102 is now depressed to close the circuit to a relay W for starting the grinding wheel motor. Energization of the motor 107 closes the circuit to the coil 111 of a coolant pump motor. To initiate the shear cut cycle, a lever 200, Fig. 3, is shifted to the left to operate a valve 203 which permits fluid to move a reversing valve 206 to the left and hence allow fluid to pass through a check valve 209 to one end of a cylinder 213 where it drives a piston 214 and a feed screw 215 downwardly to rotate a shaft 227 and cause a rapid feed of the grinding wheel towards the work piece, this movement being retarded by a dash pot 219 to grind the fillet of the blade. Simultaneously with this operation, fluid shifts a piston 222 to actuate a switch 120 which through relays HR, HF, CR4 and CR1 and a solenoid 130 starts the work drive motor and, through a jog switch 190, the coolant motor. As the piston 214 reaches the end of its movement, the feed screw 215 throttles the escape of fluid from a line 216 and thus produces a rise in pressure to shift a valve 230 and close a rapid feed switch 234 in readiness for a series of operations to reverse the carriage 41 at the end of the grinding traverse. The grinding feed is produced by a piston 260 which throttles a line 263 at the end of its movement to shift a valve 264 and hence direct fluid to a slow feed switch 267 which, through a traverse selector switch 171 and a contact TR1, energizes a relay CR2 and a solenoid 177 to shift a valve 270 to the left and a valve 277 to the right to cause piston 281 and hence carriage 41 to move to the right. Towards the end of this movement, a cam 45 on the carriage 41 closes a limit switch 44 to energize a solenoid 193 and shift a valve 285 to allow fluid to move a piston 289 which restores the valve 203 to the position shown where it causes fluid to move the valve 206 to the right to allow fluid to pass through check valve 295 and return the piston 214 to its starting position, a line 298 being uncovered during this movement to move slow feed piston 269 to the right to reset the feed mechanism and return switch 120 to the position shown. This switch closes a circuit to a brake 25, Fig. 3, in which a switch 320 is opened by reversal of the motor 21 to de-energize the solenoid 130 and release a contact 134 which opens when a cam 310 on the headstock spindle reaches a predetermined position to break the power supply to the motor 21. When pistons 214 and 260 return to starting position pressure is removed from switches 234 and 267 to open the circuit to traverse solenoid 177 and permit traverse valve 270 to be moved by a spring to the right where it allows fluid to flow through section 1 of traverse valve 274 to shift valve 277 to the left so that fluid may return piston 281 and carriage 41 to starting position. If the work is to be ground in a number of traverses, a reversing valve 224 may be actuated manually by a lever 225, Fig. 3, or by dogs on the carriage 41. A throttle valve 226 provides an adjustable tarry on reversal. The work may be plunge ground.