Patent GB-808557-A (GB)
Title: Improved machine for polishing, or lightly grinding, elongated workpieces
Inventor: DAVIS BERNARD VICTOR
IPC: B24B17/02
Filed: 1955-05-31
Abstract: 808,557. Polishing. ARMSTRONG SIDDELEY MOTORS Ltd. May 28, 1956 [May 31, 1955], No. 15538/55. Class 60. [Also in Group XVIII] A machine for polishing, or lightly grinding, an elongated workpiece having a curved surface (e.g. a turbine blade or a compressor blade for a gas turbine engine) comprises a base supporting a vertically slidable member carrying a follower and a rotatably driven polishing head, a workpiece-carrying table beneath the polishing head and a former-carrying table beneath the follower, the two tables being automatically reciprocable in unison longitudinally of the base relatively to the head and follower, the workpiece and former each being rotatably supported at their ends clear of the surfaces of the respective tables and being rotatable in steps by means of, a positive drive applied synchronously to each end of both the workpiece and the former, whereby the whole of the curved surface of the workpiece is polished or ground in accordance with the contour of the former. A machine for polishing a twisted turbine blade comprises a rectangular base 11 having a rectangular slot 12 adjacent its mid-part above which is a vertical member 13 with a rectangular channel in which is carried a vertically slidable member 14 which at its upper end carries two arms ; one arm 15 supports at its outer end a pulley 16 comprising the rotatably driven polishing head which is open at one side to enable the head to polish close to an end platform of the blade 21 ; the other arm 17 supports at its outer end a rotatable spherical follower 18. The arm 15 is detachably mounted on the member 14 by screws 19 having alternative clamping positions in the member 14 to enable the position of the arm to be changed by moving it bodily laterally, so that the pulley 16 can be mounted on the opposite side of the arm in alignment with the follower 18 for polishing double-shrouded blades. The arm 17 is supported by dove-tail grooves 22 in the member 14 and is vertically adjustable by a manually operated screw 23. The spherical follower 18 is rotatably supported in a cup bearing 24. The former 25 is solid and generated as an envelope of predetermined thickness about the profile of the finished blade form. A polishing band 28 having an abrasive surface of emery passes over the pulley 16 (which has bonded on its outer surface a layer of hard rubber of part spherical contour), over pulleys 26, 27, 35 carried by the member 14 and over driving pulley 29 driven by the shaft 30 of an electric motor ; the motor is mounted on a platform 31 pivoted at 32 to the machine frame and carrying at its other end a weight 34 so as to keep the polishing band lightly in tension. The major part of the weight of the member 14 and parts carried thereby is counterbalanced by a weight 36 on a cable 37 passing over a pulley 38. The rod 103 of a piston in a cylinder 102 serves to raise and control the lowering of the member 14. Beneath the follower 18 is a formercarrying table 40 longitudinally slidable by means of a V-rail 41 engaged in a V-groove in the machine base ; beneath the pulley 16 is a workpiece-carrying table 42 longitudinally slidable relatively to the machine base by flat slide surfaces 42a. The slide surfaces 42a of the base 11 have inset felt lubricating pads ; the V-groove is provided at intervals with lubricating rollers. The two tables are integrally connected at their ends 43, 44 and are reciprocated by pneumatichydraulic pressure, roller-operated change over valves 45, 46 for reversing table movement co-operating with adjustable stops 47, 48. The tables may be operated by a handwheel 164, pinion and rack. The workpiece-carrying table 42 includes an oil bath 49 arranged so that when the bath is full the workpiece is immersed in oil ; the bath is provided with an adjustable tap 50 having an aperture 51 which acts as an overflow to prevent the bath being over-filled and which can be turned so that any one of a series of apertures 52 selectively coacting with ports in the top body at a lower level allows a predetermined quantity of oil to leave the bath through an outlet pipe 50a when a workpiece has been polished. On the workpiece-carrying table 42 are brackets 53, 54 in which are journalled sleeves 55, 56 ; wormwheels 57, 58 are fast with the sleeves. Keyed within each sleeve is a spindle, one spindle 59 being axially fast with its sleeve, the other spindle 62 being splined at 62a so as to be axially free in its sleeve. Work-holder plates 63, 64 are keyed and locked to the inner ends of the spindles 59, 62. The work-holder plates carry work-holders 65, 66, whose angular positions on the plates can be adjusted, and between which the blade 21 is supported. The former 25 is similarly supported between work-holders 68, 69 by spindles 70, 71 supported similarly from the former-carrying table. A cam 72 having an outer surface corresponding to a mid-section of the former 25 is fast with the spindle 71, the cam surface is contacted by an adjustable stop 74 carried by the piston of a pneumatic cylinder 73 mounted on the table connector 43. The wormwheels 57, 57a, are driven by worms 75, 76 fast on a shaft 79, and wormwheels 58, 58a are driven by worms 77, 78 fast on a shaft 80. The shafts 79, 80 carry at one end ratchet wheels 81, 82 each arranged to be angularly moved in steps by a pair of pawls 83, 83a arranged in tandem; each pair of pawls is carried by a slidable plate 84, the two plates being interconnected by the rod 85. The piston of device 73 operates a slidable plate 86 having a 45 degree end coacting with a 45 degree end on one of the plates 84, engagement being maintained by a spring 87. When the two tables, during their longitudinal movement, pass their central positions, a valve 90 is operated, by a cam 90a centrally fast with the base 11, to supply pneumatic pressure to the cylinder of device 73 and the piston acts through plate 86 to move plates 84 so that the pawls move in synchronism to turn the ratchetwheels 81, 82 synchronously, resulting in rotation of the blade 21 and former 25 through a small angle depending on the position reached by the cam 72. The hydro-pneumatic circuit is shown in Fig. 11. The table reciprocation is controlled by distributing valve 148 air-operated under control of valves 45, 46, a start valve 143 is provided. The cylinder 102 for raising and controlling the lowering of member 14 is controlled by valve 144. The indexing cylinder 73 is controlled by valve 90, a start valve 158 being provided.