Patent GB-775860-A (GB)
Title: Improvements in or relating to machines for use in performing surfacing operations on work-pieces
Inventor: SHARMAN JOHN CHARLES
IPC: B24B17/00
Filed: 1954-06-15
Abstract: 775,860. Grinding. GARRINGTONS, Ltd. Sept. 1, 1955 [June 15, 1954], No. 17501/54. Class 60 A machine for surfacing workpieces such as gas turbine blades or forging dies used in the production of such blades comprises a main slide .22, Figs. 3 and 6, supporting a carriage 23 which carries both a workpiece 31 and master form 30 and is arranged to be reciprocated in a direction at right angles to the direction of movement of the main slide, a head 34 carrying a power - driven abrasive band 49 for acting upon the workpiece and a tracer 48 for engaging the form, and means operated by the carriage in its reciprocating motion for automatically controlling the feeding movement of the slide. The head 34, Fig. 3 is carried by arms 37, 38 from two horizontal shafts 35, 36 so that the abrasive band 49 and tracer 48 can move up and down in relation to the workpiece and form on the carriage as the latter is reciprocated in a direction transverse to the longitudinal axis of the workpiece on te slide 22 which is fed forward longitudinally of the workpiece between the reciprocations. Rearward extensions 40 of the arms 37 are connected to vertical stems 41 carrying a weight 42 which partially counterbalances the weight of the head; upward movement of the head is effected by admitting fluid to a pneumatic or hydraulic cylinder 45, the piston rod 44 of which passes freely through a crossbar 43 secured to the stems and has spaced abutments 46 for engaging the cross-bar. The abrasive band 49, Fig. 6, is driven by an electric motor and passes around a barrel-shaped roller 51 where it engages the workpiece; the tracer 48 is a barrel-shaped roller carried by a support 47. The inclination of the axes of the rollers 48, 51 is continuously tilted during the operation by mounting the upper arms 38 so that they can slide axially through transverse holes in the shaft 36 under the action of a double-acting pneumatic or hydraulic cylinder 86 associated with a speed-controlling dash pot 87; the cylinder 86 is so controlled by valves 86a, 86b, Fig. 11 actuated by abutments 86c, 86d on the carriage that the rollers are tilted through one complete reciprocation of the carriage. The workpiece 31 and form 30 are carried by blocks 29, Fig. 2 which are secured by clamps 19 against the sides of a F- shaped locating member 25 on the carriage 23. The carriage is reciprocated on the main slide 22 by a double-acting pneumatic or hydraulic cylinder 52, Figs. 6 and 11, controlled by two valves 52a, 52b which are actuated to reverse the drive at each end of the stroke by abutments 53a, 53b on the carriage; the rate of movement of the carriage is controlled by a dash pot 88 which is disposed at the side of the latter remote from the cylinder 52. The feed movements of the carriage are effected by a longitudinal lead screw 54, Fig. 3, engaging a nut 55 on the main slide 22 and carrying a ratchet wheel 56, Figs. 3 and 11, controlled by pawl mechanism 57, 58 actuated by a pneumatic or hydraulic cylinder 62 so arranged in the control circuit as to rotate the screw for feed movement when the carriage is stationary at one end of its reciprooatory stroke. When the main slide has been fully traversed in the longitudinal direction it actuates a valve 45a, Fig. 11, controlling the cylinder 45 so that the head 34 is raised to its inoperative position where it is retained by a latch 80 engaging the cross-bar 43; release of the latch to permit lowering of the head under gravity is caused by a pneumatic or hydraulic cylinder 81 controlled by a hand-operated valve 81a. The head may also be lowered slowly when desired by operating a hand valve arranged to release pressure gradually from the cylinder 45. The slide 22 may be returned rapidly to its initial position by an electric motor 66, Fig. 3, carried by a pivoted L-shaped structure 71 which, when raised by a hand wheel acting through a cord or chain, closes a switch 77 in the motor circuit and brings a friction driving wheel 69 on the motor shaft into engagement with a disc 70 fixed on the lead screw; an abutment 78 on the slide 22 forces this structure 71 downwardly into inoperative position when the slide reaches its initial position. The various pneumatic or hydraulic cylinders and valves are included in a control circuit as shown in Fig. 11, together with a start valve 92 and relay valves 91, 94 controlling, respectively, the cylinders 62, 86. The carriage is given a complete to-and-fro reciprocation between adiacent feed movements, the latter being effected when the carriage is at one end of its stroke bv the action of the corresponding valve (52a and 52b) upon the relay valve 91 and thence the cylinder 62; when the carriage is at the other end of its stroke the cylinder is actuated to return the pawl mechanism 57, 58 idly to initial position. The return of the slide 22 at the end of its full feed traverse may be effected automatically, and a dash pot may be provided for controlling the downward movement of the head 34. 'Lubricant is supplied to the surface of the abrasive band from a motordriven pump in the machine base, and when the lubricant is readily volatile the workpiece is surrounded by a shroud provided with means for extracting the vapour generated. The Provisional Specification describes also the feed of the slide at the end of each uni-directional stroke of the carriage and the actuation of the valve 45a to raise the head 34 by means of an abtument on the L-shaped structure 71 when the latter is raised; it also contains a reference to Specification 775,856.