US2589782A - Machine for polishing blades - Google Patents

Description

MACHINE FOR POLISHING BLADES Filed Dec. 20, 1950 4 Sheets-Sheet l a: i a g) i g /5 [\k I dihl lfllllllnfii INVENTOR JOCREEK. PR

March 18, 1952 J. o. CREEK MACHINE FOR POLISHING BLADES Filed Dec. 20 1950 4 Sheets-Sheet 2 fiTTORNEY March 1952 J. o. CREEK 2,589,782

MACHINE FOR POLISHING BLADES Filed Dec. 20, 1950 4 Sheets-Sheet 5 I-I-l-IZ-I-I 1 555;: I j L 56 58 57 0 56 I "7/ B 1 5 l 65 v P i :52 J -3- H i :i B l l 24 I 5 ll B I 4/ 4 1 38X 34 A H 45 L 37 1 -4- 56 H e 36 ii I 8 3:: ii 2 l4 4 1 5 I i i B 6 i 23 .5 y w I4, 23 3 ,5 i 22 //vv/vTOR JQCREEH PA'R ATTORNEY March 8, 1952 J. o. CREEK 2,589,782

MACHINE FOR POLISHING BLADES Filed Dec. 20, 1950 4 Sheets-Sheet 4 Patented Mar. 18, 1952 UNITED STATES ATE T. OFFICE.

MACHINE FGR POLISHING- BLADES John Oliver- Creek, Brampton, Ontario, Canada,

assignor-to A. V. Roe Canada Limited, Malton, Ontario, Canada, a corporation.

Application December 26, 195i), SerialI Io..201,7 i31 19 Oiaims;

This invention relates to amachine for polishing blades and moreparticularly. to. a. machine for giving a fine precision polish'to. blades for gas turbine engines.

Various methods andapparatuses have been proposed from time to time for polishing articles, consisting basically in mounting: thearticles on a carrier and rotating the carrier tomove. the articles through an abrasive or polishing material in a liquid or granular suspension. Whilst such a process can be used for polishing; many articles, it cannot be applied: directly to. the polishing of blades for gas turbine engines. These bladeshave tobe made to.-a. high order-of accuracy and require a very high: degree of surface finish which must be applied after the completion of all forming operations. If: a blade of this kind were passed in the usual manner .through an abrasive or polishing medium sufiiwhich a circular motion is imparted to the polishing medium, setting up centrifugal forces which tend to compact the medium.

Hitherto, the blades of gas turbine engines have been finished by. hand-bufiing processes, which are slow and expensive and which also entail some risk of damage to the blades,par.ticularly at the trailing edges.

The main object of the present invention is, therefore, to provide a machine in which a plurality of blades may be polished simultaneously to a high surface finish without materially changing their profile, therebysaving-time; and avoiding the risks attendant upon hand bufiing processes.

Another objectof the; invention is toprovide a polishing machine having structural features whereby a more uniform density is obtained throughout the depth of the polishing medium, thereby ensuring amore even polishingaction on the blades.

The invention will be more-readily'understood by reference to the following description andthe accompanying drawings in whichv like reference characters designate corresponding parts throughout the several views, and'in'which:

Fig. 1 is a broken-away fragmentary elevation of apolishing machine constructed in accordance-with the invention;

Fig. 2 is a broken-away plan of the machine;

Fig. 3 is a broken-away elevation to an enlargedscale ofthe upper half of. the machine;

Fig. i isabroken-away perspective-of a. por- (Chil -.191)

tion of the machine viewed in the general direction of the arrow A in Fig. 3;

Fig. 5; is a schematic view of the mechanism which imparts an oscillatory rotation tothe workspindles, and the controls therefor.

A machine constructed in accordance with this invention comprises a hollow base I supporting a hollow column 2 to the upper end of which, is clamped a two-armed bracket 3-. At the end of a fork of the arm 3a is journalleda rotatableworkspindle carrier 3 (Fig. 3).

On the carrier are mounted several workspindles 5 each of which supports a holder, 6 in which is held a blade B which is to be polished; the workspindles are mounted for rotation about their-longitudinal axes; means being provided to impart to the workspindles a limited amount of rotation. Rotatably mounted on the lowerpart of the column 2- is a spider 1 comprising four radial arms which each support in a horizontal position, an annular trough 8 for thepolishing medium; the troughs are-adapted to be selectively brought into registration with the carrier 4 and'then raised upwardly into operative position so that the blades supported by the workspindles dip into the polishing medium. To hold each trough 8 in position when brought into registration with thecarrierll, leaf springs 9 are mounted on the underside of the respective arms of, the spider 7; these springs are adapted to snap into a recess in'a block It provided on the base of the machine.

At the outer end of each arm of the spider 1 are provided a pair of bushed bores H in which a trough support tube i2' is slidably mounted; the upper end of each support tube fits intothe hub l3 of a trough support plate l4. Located within the hollow base ofthemachine at apositionimmediately underneath the axis of the carrier 4 is an airjack' E5, the piston rod l6. of which extends through a suitable aperture provided in the topplate of the base and is adapted toengage the lower end of the support tube 12 ofwhatever trough isin registration withthe carrier 4; when the airjackis actuated, its piston elevatesthe trough into cooperative position with'the carrier.

Each-trough 8 is intended to contain a diiferent grade of.' granular polishing medium. such as wheat, flax seed, rice, sawdust or granulated cork, to which maybe added as is well known'in the. art a polishing or abrasive compound such assilicon carbide or jewellers rouge; waxmay also be added as abonding. agent.

At thelower end of each support tube I2; is provideda female airline connector. I? and' at the upper end of the pistonrod lfiis a maleaireline connector I8 adapted to register with the female connector I7, the male connector being connected by a flexible airline l9 to a source of compressed air. The compressed air passes through the two connectors and flows through the support tube l2 of the trough 8 in use, and is distributed by six equally spaced radial pipes 28 (Fig. 3) connecting the interior of the support tube to a manifold 2| provided at the bottom of the trough. From the manifold 2| the compressed air is introduced into the polishing medium through a series of apertures 22 in the bottom of the trough to elevate the particles of the polishing medium thus counteracting the increasing pressure or head towards the bottom of the trough and providing for a more uniform density throughout the mass of the polishing medium. a I V When the airjack |5 ;is actuated to lower a trough 8 which has'previously been brought into cooperative registration with the carrier 4, the said trough descends until the hub of its support plate I4 rests on the upper bushed bore H, in which position the trougliis clear of the blades B. In thisposition, the polished blades can be replaced by others which are to be processed. The piston-rod l6 of the airjack I5 is of course Wered to a position such that the male connector i8 is clear of the female connector thereby permitting thespider to be rotated to bring into registration with the carrier 4 another trough 8. i I

Baffies 23, which are inclined upwardly in the sense of rotation of the carrier 4, are arranged at spaced; intervals around the walls of each trough 8. g The polishing material displaced by the passage of the blades B through the trough is directed upwardly by the bafiies, thus relieving the loads on the tips of the blades which would otherwise occur due to the density gradient or increasing pressure of the polishing medium towards the bottom of the trough. These baffies not only cause a more uniform density throughout the mass of polishing medium but also tend to direct the polishing medium upwardly upon the roots B (Fig. 4) of the blades.

So as to facilitate replacing worn baffles 23 andalso in order to protect the inner sidewalls of the trough 8 from the wearing effect of the polishing medium, the said walls are lined with annular strips of metal, to which the baffles are secured. Also, the lower ends of the holders 6 are'fac'ed with rubber to protect them from abrasion.

As previously mentioned, clamped around the upper end of the column 2 is the bracket 3. At the outer end of the lower fork of the arm 3a is a hub 24 which provides a bearing in which is rotatably mounted the carrier 4. For this purpose a pulley sleeve 25 is journalled within the hub 24 by means of radial and thrust ball bearings. To the upper end of the pulley sleeve 25.is keyed a pulley 26 which is coupled by V-belts to a pulley 21 keyed at the upper end of a drive shaft 28 journalled within the column 2 and having at its lower end a worm wheel 29 driven through a worm, pulley, and V-belt assembly 39 by a change speed unit 3| incorporating an electric driving motor. At the lower end of the pulley sleeve 25 is a flange to which is secured to the workspindle carrier 4. Thus, when the motor is energized it will cause r0- tation of the workspindle carrier. Above the carrier 4 and around itssides is a fixed hood 32, secured to the lower end. of the hub 24.

Around the bottom periphery of the hood is a rubber sealing ring 33 which engages a similar ealing ring provided on the upper outer periphery of the trough 8 brought into registration therewith.

The workspindles 5 which are operatively arranged in pairs are journaled in ballbearings mounted in suitable bores formed in upper and lower internal flanges 34 and 35 of the carrier 4 (see Figs. 3 and 4). Secured to the lower flange 35 intermediate the workspindles of each pair is a pedestal 36, and on each pedestal is journalled a horizontally disposed stub shaft 3'! to which is centrally keyed a driving pinion 38 and at each end of which are keyed bevel gears 39. The bevel gears 39 mesh respectively with bevel gears 40 which are mounted on the workspindles 5 of the pair. As will be apparent particularly from Fig. 4, if pinion 38 is rotated, the two workspindles of the pair willrotate in opposite directions relative to each other.

A shaft 4| is slidably mounted in the bore of the pulley sleeve 25, and at the upper end of the shaft is secured a flanged sleeve 42, the flange of which lies between a pair of thrust bearings of a coupling 43 from the top of which extends a screw-threaded shank. At the lower end of the shaft 4| is keyed a rack Wheel 44, on the periphery of which are racks 45 which mesh with corresponding pinions 38. It will be apparent that if the shaft 4| is reciprccated, the racks 45 will rotate the corresponding pinions 38 to and fro thereby causing oscillation of the blades supported by the workspindles.

At the end of the upper fork of the arm 3a is provided a fixture 46 to the upper face of which is secured an air-operated power cylinder 4! and to the lower face of which is secured a hydraulic cylinder 48, which exercises a control on the operation of the power cylinder; the two cylinders are co-axial with the shaft 4|. In the power cylinder and in the hydraulic cylinder are provided pistons, the piston rod of which are coupled to each other; also, the piston rod of the hydraulic cylinder is connected to the screw threaded shank of the coupling 43.

- Secured to the coupling 43 is a horizontall extending yoke member 49, the outer end of which is forked to embrace a vertically disposed slideway 5|] extending from the arm 3a; the yoke member 49 permits the coupling to be moved vertically by the action of the piston in the power cylinder 41 but prevents rotation of thecoupling 43. It should be noted that the coupling 43 enables the shaft 4| to rotate without transmitting its rotation to the two piston rods.

The workspindles 5 are oscillated by the reciprocation of the shaft 4| as hereinafter described with particular reference to Fig. 5. Ports at opposite ends of the power cylinder 47 are connected by suitable air lines to'ports 5| of a distribution valve 52 secured to the arm 3a.

Air is supplied to the distribution valve by an airline 53 which passes through the column 2 into the hollow base and is conne'cted'to a suitable source of compressed air (not shown).

The distribution valve 52 is of the type containing a selectively displaceable spool, which, depending on its position, distributes compressed air supplied from the airline 53 to one of the ports 5| and connects the other port 5| to atmosphere through one of the outlets 54. I Both ends of the spool are under pressure due to the provision of narrow passages 53a in the body of the valve, and movement of the spool is caused by bleeding air from either of the ports 55 at opposite ends of the valve; the ports 55 are connected by airlines to bleed valves 58 and 56a mounted at opposite ends of the slideway of a control fixture '58. The control fixture is secured to the fixed hub 24 (see Fig. 3) and on its slideway 57 is slidably mounted a carriage 59. On the carriage is a cam member 60 having-adjustable boltstl whichprovide abutment surfaces adapted to contact the plungers of the bleed valves '56 and 56a to cause reversal of the air supply to the power cylinder The cam member also includes a cam surface b2 with which cooperates a follower wheel 53 mounted on the end of the spring-pressed spool spindle 64 of a flow control valve 65 for the hydraulic cylinder id. The flow control valve is secured to an extension of the control fixture 58.

Ports at either end of the hydraulic cylinder 58 are connected to the ports of the flow control valve 65 and thus a closed circuit is provided for the oil with which the system is filled. When the spring-pressed spindle 6 3 of the valve 65 is displaced by the cam surface 62 to the position shown in Fig. 5, the spool 66 on the spindle 64 clears the port 6? and thus the oil in the system of the hydraulic cylinder can flow freely, permitting the power cylinder ll to impart a rapid motion to the shaft ii which imparts a correspondingly rapid motion to each workspindle 5 about its own axis, as previously described. When, however, the follower wheel 63 is not displaced by the cam surface 62, the spool 65 closes the port 61 and the oil is constrained to flow through a metering orifice 8 regulated by an adjustable needle valve 69, and thus the speed of displacement of the shaft '3! by the power cylinder l! can be controlled, thereby limiting the angular velocity of the rotary motion imparted to the workspindles 5.

The carriage 59 of the control fixture 58 is connected by a push-pull cable is to the yoke member 49, the casing H of the cable being secured to the arm 3a; thus the carriage 59 moves in correspondence with the movements of the shaft 41. The stroke of the piston of the power cylinder 4?, and hence the range of angular displacement of the workspindles 5, is dependent on the design of the cam member 60 and more particularly on the adjustment of the bolts 6! which by actuating the bleed valves 56 and 56a control the stroke of the piston of the power cylinder 41. Furthermore, the angular velocity of the workspindles 5 is normally determined by the adjustment of the needle valve 69, except over the range of angular displacement coincident with the engagement of the cam surface 52 with the follower wheel 63-; the angular velocity over this range and the period when it occurs in the cycle of operation of the machine is of course deter mined by the configuration of the cam surface 62. It should be mentioned that for the practical operation of the machine, suitable quick release holders 6 in which the blades are held should be used, but such chucks will not be described as they do not per se form part of the invention. The holders are conveniently inserted and held in the workspindles 5 by bayonet-type couplings, which also permit their easy withdrawal therefrom.

7 Operation It is first necessary to construct a cam member placement about its longitudinal axis so as to 6 produce the desired polishingaction for the parsimilar shape of blade being treated. The cam member 60 is mounted on the carriage 59 and the blades to be polished are mounted in "the holders 6 which in turn are inserted in the workspindles 5.

Referring to Fig. 5, the various components or the control system are preferably set in such a manner that at the commencement of the operation the cam member 69 is at the right-hand side of its stroke and has actuated the bleed valve 58a to cause the spool of the distributio'n'valve 52 to move to the position opposite'to that shown in Fig. 5,-at whichposition the upper end of the power cylinder 4? is connected to the compressed air supply and the piston of this cylinder is about 'to-start its downstrolze. The rack wheel 44 is, therefore, in its upper position and the blades to'be polished have a predetermined angle of in cidence; for instance, as shown in Fig. 2, alternate blades have an angle of incidence of approximately and the other blades'ha'v'e an angle of incidence of approximately 30.

A trough 8 containing a coarse grade of polishing medium is then brought into registration with the carrier l and raised into operative position by actuation of the air-jack 55. Next, the drive f the change speed unit is started, to cause rotation of the carrier i and thus pass the blades in a continuous path through the polishing medium; the compressed air supply to the manifold 2% is turned on, thereby elevating the particles of polishing medium, and the compressed air supply to the distribution valve 52 is also turned on to cause a progressive change of angular displacement of the-blades B about their longitudinal axes during their travel through the polishing medium. The rate of change of this angular displacement is determined by the setting of the needle valve 69 since at this'stage the cam surface 62 is not in contact with the follower wheel 33 of the flow control valve t5; this change of angular displacement is continued until each blade reaches a limiting angle of incidence, for example, 30 in the case of blades which were initially at an angle of incidence of +30.

The essence of this invention is that each blade is moved in a continuous path through a polishing medium of substantially uniform density while the blade is given an angular rotation about its longitudinal axis between two angles of incidence appropriate to the aerofoil shape of the blade. The limiting angles of incidence may also vary according to the polishing medium used and the material of which the blade is made, though these considerations have perhaps a greater influence upon the choice of speed with which the blade is passed through the medium or with which the angle of incidence is changed, or both. Furthermore the limiting angular displacements need not be symmetrically disposed about the path of the blade as in the example described, in which the angle of incidence varies between +30 and 3 the range might lie between +5 and or between 0 and +30".

As stated, the choice of these limits depends primarily upon the aerofoil characteristics of the blade to be polished; for example the limits are determined largely by the stalling properties of the aerofoil, i. e., the shape of the aerofoil and the consequential angle at which a medium through which the aerofoil is passing tends to depart from the contour of the aerofoil; I have found by experiments that the limiting angles of incidence of the blade usually should not exceed the stalling angles, but occasionally they may be exceeded slightly to favour one or other of the blade surfaces. In all cases the initial and limiting angles of incidence are within 55 of angl of incidence, and the difference between the said initial and limiting angles is less than 70.

The speed of rotation of the blade about its longitudinal axis is relatively slow. The polishing action is achieved by the passage of the blade through the polishing medium in such a way that the relative movement between the blade and the medium is similar to the relative movement between the blade and the working fluid of the gas turbine engine in which the blade will eventually be installed. In other words the flow of the polishing medium past the blade is analogous to aerodynamic flow, wherein the relative movement between each surface of the aerofoil and the surrounding medium is in the same direction on both sides of the blade, that is from the leading edge to the trailin edge. The relatively slow rotation of the blade about its longitudinal axis produces no more than a change Of incidence or attitude, as hereinbefore described, and does not contribute directly to the polishing action of the medium upon the blade. It will be understood therefore that the polishing effect of the machine is ideally suited to aerofoil shapes or to any blade-like articles having a pronounced finesse ratio.

The polishing processmay be accelerated by passing the blades through the polishing medium firstly in one direction and secondly in the reverse direction and it is of advantage if this reversal can be effected automatically. In the machine described, therefore, after a blade has undergone a rotation about its longitudinal axis from an angle of incidence of +30 to an angle of incidence of 30, at a uniform speed, whilst the carrier 4 has made several complete revolutions, the cam surface 62 of the cam member 60 comes into contact with the follower wheel 63 and causes .displacement of the spool spindle 64 to open the port 57. The hydraulic cylinder 48 which was theretofore providing a damping action on the movement of the piston in the power cylinder 41 therefore virtually becomes inefiective, and consequently the power cylinder will suddenly force the piston rods and the rack wheel 44 downwardly at an increased velocity with a consequent increase in the angular velocity of each blade about its longitudinal axis. This rapid transition occurs over an angle of, for example, 120, that is until each blade is displaced approximately 180 from its initial position, whereupon the follower wheel 63 will leave the cam surface 52 of the cam member 60 which is moving towards the left-hand side in unison with the rack wheel shaft 4|. If desired, the speed of rotation of the carrier 4 may be reduced or its rotation may be arrested during this operation, to avoid damage to the blades as they pass through high angles of incidence to the polishing medium. The opposite edge of each blade is now meeting the polishing medium and since the follower wheel 63 is no longer in contact with the cam surface 62, the angular dis- 'further angle of 60, whereupon the left-hand side adjustment bolt 6! of the cam member 60 actuate's the bleed valve 56 and initiates the return stroke of the piston of the power cylinder 41 and hence initiates an angular movement of the blades in the reverse direction. The above described cycle can be repeated as often as required. It will be understood that, in this example, the total angular travel of the workspindles 5 is 240", comprising the first range (60) of the polishing operation, the transition range and the second range (60) of the polishing operation; the cycle does not involve a complete 360 rotation of the blades.

Since the speed of rotation of the carrier 4' tation imparted to the blades, and since this oscillatory rotation can be of many different characteristics dependent on the design of the cam member 69, a wide range of polishing actions is available to suit the requirements of diverse forms of blade constructions.

It will be appreciated that by rotating alternate blades about their longitudinal axes in opposite directions in accordance with this invention, the alternate blades displace the polishing medium during their passage therethrough in opposite directions so that the polishing medium is not compacted on one side of the trough as would occur if all the blades had the same angle of incidence. Moreover, since the trough 4 remains stationary throughout the polishing operation, the polishing medium is not compacted against the outer wall of the trough by centrifugal forces as occurs in polishing machine construction in which the container of polishing medium is rotated.

It is thought that the construction and use of the invention will be apparent from the above description of the various parts and their purpose. It is to be understood that the form of the invention herewith shown and described is to be taken as a preferred example of the same and that various changes in the shape, size and arrangement of parts may be resorted to, without departing from the spirit of the invention or the scope of the subjoined claims.

What I claim as my invention is:

1. A machine for polishing blades, comprising a carrier, a container for a polishing medium disposed adjacent the carrier, the carrier-and container being mounted for movement relative to each other, means mounted on the carrier for holding the blades in the polishing medium, means for translating the carrier and container relative to each other to pass the blades in a continuous path through the polishing medium, means to render the density gradient of the polishing medium immediately prior to contact with each blade no greater than the density gradient of the polishing medium when at rest and means for changing, during the translation of th carrier relative to the container, the angles of the holding means relative to the direction of said translation to vary the angles of incidence of the blades between initial angles and limiting angles.

2. A machine for polishing blades, comprising a carrier, a container for a polishing medium disposed adjacent the carrier, the carrier and container being mounted for movement relative to each other, means mounted on the carrier for holding the blades in the polishing medium, means for translating the carrier and container relative to each other to pass the blades in a continuous path through the polishing medium, means to render the density gradient of the polishing medium immediately prior to contact with each blade no greater than the .density gradient of the polishing medium when at rest and means for changing, during the translation ofth'ecarrier Telativeto the container, the angles of the holding means relative to the direction of said translation, to vary the angles of incidence of the blades between initial angles and limiting angles, the initial and limiting angles of incidence being within 55? of angle of incidence and the difference between the said initial and liinitingangles being less than 70.

h 3. A machine for polishing blades of 'aerofoil shape, comprising a carrier, 'a container for a polishing medium disposed underneath the carrier, the carrier'and container being mounted for movement relative to each other, a pair of spindles rotatably mounted on the carrier "for suspending the blades in the polishing medium,

means for translating the carrier and container relative to each other to pass the blades in a continuous path through the polishing medium,

and means for progressively rotating the two spindles in mutually opposite senses during the translation of the carrier relative to the container tovary the angle of incidence of each blade.

4. A machine for polishing blades comprising a stationary frame, a carrier mounted on the frame for rotation about a substantially vertical axis, a plurality of containers for polishingmediums selectively "positionable in registration with the carrier, means for raising a registering container into -co-op'erative position with the carrier, spindles rotatably mounted on the carrier for suspending the blades in the polishing medium contained in the container co-operatively positioned with the carrier, means for rotating the carrier to pass the blades in a continuous path through the said polishing medium and means for progressively rotating the spindles during the rotation of the carrier to vary the angle of incidence of each blade between an initial angle and a limiting angle.

5. A machine for polishing blades of aerofoil shape, comprising a stationary frame, a carrier mounted on the frame for rotation about a sub stantially vertical axis, a container for a polishing medium disposed underneath the carrier, spindles rotatably mounted on the carrier for suspending the blades in the polishing medium, means for rotating the carrier to pass the blades in a continuous path through the polishing medium, means for progressively rotating the spindles during the rotation of the carrier to vary the angle of incidence of each blade between an initial angle and a limiting angle, and means in the container to elevate the particles of the polishing medium as the blades pass therethrough.

6. A machine for polishing blades of a'erofoil shape, comprising a stationary frame, a carrier mount-ed on the frame forrotation about a substantially vertical axis, a container for a polishing medium disposed underneath the carrier, spindles ro'tatably mounted on the carrier for suspending the blades in the polishing medium, means for rotating the carrier to pass the blades in a continuous path through the polishing medium, means for progressively rotating the spindlesduring -the rotation of the carrier to vary the angle of incidence of each blade between an initial angle and a limiting angle, and air jets extending upv fardly from the bottom of the container to elevate the particles of the polishing medium and provide a more uniform density threughout the mass of the said medium.

7;. machine for polishing blades of aerofoil 'shhpe, comprising a stationary frame, a carrier mounted on the frame for rotation about a substantially vertical axis, an annular trough for a polishing medium disposed underneath the car rier co-axially therewith, a perforated air inanifold at the bottom of the trough, a source of compressed air connected to the manifold for .tween an initial angle and a limiting angle.

8. A machine for polishing blades, comprising a stationary frame, a carrier mounted on the frame for rotation about a substantially vertical axis, a multi-arrned spider mounted on the frame for rotation about anothersubstantially vertical axis, a sleeve at the end of each spider arm, a hollow shaft slidably mounted in each sleeve, containers for polishing mediums supported at the upper ends of the respective shafts, a perforated manifold at the bottom of each container and connected to the passage in the hollow shaft, the containers being selectively positionable in registration with the carrier, means engaging with the lower end of a hollow shaft supporting a container positioned in registration with the carrier for raising the said container into co-operative position with the carrier, a coupling at the upper end of the container raising means connected to a source of compressed air and connecting to the source of compressed air the hollow shaft in engagement with the container raising means, the compressed air being thus conveyed to the manifold and ejected through the apertures therein into the polishing medium to elevate the particles 'of the medium and provide a more uniform density throughout the mass of the said medium, spindles rotatably mounted on the carrier for suspending the blades in the container co-operatively positioned with the carrier, means for rotating the carrier to pass the blades in a continuous path through the said polishing medium, and means for progressively rotating the spindles during the "rotation of the carrier to vary th angle of incidence of each blade between an initial angle and a limiting angle.

9. A machine for polishing blades of aerofoil design comprising a stationary frame, a carrier mounted on the frame for rotation about a substantially vertical axis, an annular trough for a polishing medium disposed underneath the carrier co-axially therewith, spindles rotatably mounted on the carrier for suspending the blades in the polishing medium, means for rotating the carrier to pass the blades in a continuous path through the polishing medium, baffles on the sidewalls of the trough, the said bailies being inclined upwardly in the sense of rotation of the carrier, and means for progressively rotating the spindles during the rotation of the carrier to vary the angle of incidence of each blade between an initial angle and a limiting angle, the bafiles elevating the particles of the polishing medium which are projected thereagainst by the blades as they pass through the polishing medium.

19. A machine for polishing blades of aerofoil design comprising "a stationary frame, a carrier mounted on the frame for rotation about a sub- 11 stantially vertical axis, a stationary container for a polishing medium disposed underneath the carrier, spindles rotatably mounted on the carrier for suspending the blades in the polishing medium, means for rotating the carrier to pass the blades in a continuous path through the polishing medium, and means for progressively rotating the spindles during the rotation of the carrier to vary the angle of incidence of each blade in three stages, namely from an initial angle to a first limiting angle at a low rate of change, then from the said limiting angle to another limiting angle at a high rate of change, and finally from the said other limiting angle to a final angle at a low rate of change.

11. A machine for polishing blades of aerofoil design comprising a stationary frame, a carrier mounted on the frame for rotation about a substantially vertical axis, a stationary container for a polishing medium disposed underneath the carrier, spindles rotatably mounted on the carrier for suspending the blades in the polishing medium, means for rotating the carrier to pass the blades in a continuous path through the polishing medium, and means for progressively rotating the spindles during the rotation of the carrier, and a control to control the velocity of the power means in three stages, namely a first stage at .which the blades are rotated from an initial angle to a first limiting angle at a low rate of change, then from the said limiting angle to another limiting angle at a high rate of change, and finally from the said other limiting angle to a final angle at a low rate of change.

12. A machine for polishing blades of aerofoil design comprising a stationary frame, a carrier mounted on the frame for rotation about a substantially'vertical axis, a container for a polishing medium'disposed underneath the carrier coaxially therewith, spindles rotatably mounted on the carrier for suspending the blades in the polishing medium, rack means adjacent the carrier and mounted for rotation therewith, the said rack means being reciprocatable in a direction parallel to the axis of rotation of the rotation of the carrier, means coupling the rack means to the spindles whereby reciprocation of the rack means causes to and fro rotation of the spindles; and a power and control mechanism for the rack means for progressively rotating the spindles during the rotation of the carrier to vary the angles of incidence of the blades between an initial angle and a limiting angle.

13. A machine for polishing blades of aerofoil design comprising a stationary frame, a carrier mounted on the frame for rotation about a substantially vertical axis, a container for a polishing medium disposed underneath the carrier coaxially therewith, spindles rotatably mounted on the carrier for suspending the blades in the polishing medium, the said spindles being rotatable in pairs, a bevel gear on each spindle, pillars mounted on the carrier between the spindles of each pair, a horizontally disposed rotatable shaft supported by each pillar and having at opposite ends bevelgears which engage respectively with the bevel gears of the spindles of the pair, a pinion on each of the saidshafts, a rack member'adjacent the carrier and mounted on the frame for rotation with the carrier, the said rack member being reciprocatable in a direction parallel to the axis of rotation of the carrier, racks on the rack member engaging with the respective pinions, and a power and control mechanism for controllably translating the rack 12 member to rotate progressively the spindles during the rotation of the carrier to vary the angles of incidence of the blades between an initial angle and a limiting angle.

14. A machine for polishing blades of aerofoil design comprising a stationary frame having a vertically disposed bearing, a sleeve journalled in the bearing, power means coupled to the upper end of the sleeve to rotate it, a disc providing a workspindle carrier secured to the lower end of the sleeve, an annular trough for a polishing medium disposed below the lower face of the disc co-axially therewith, a plurality of pillars mounted on the top face of the carrier and positioned above the trough, workspindles mounted for rotation on the carrier at opposite sides of each pillar, the workspindles passing through the carrier and being adapted to support at their lower endsblades which extend into the polishing medium, a bevel gear at the other end of each workspindle, a horizontally disposed shaft journalled in each pillar and having at opposite ends bevel gears which engage respectively with the gears of the workspindles at opposite sides of the pillar, a pinion on each shaft, a power shaft translatably mounted in the sleeve and extending therethrough, a rack member secured to the lower end of the power shaft and disposed above the top face of the carrier, racks on the rack member engaging with the respective pinions, and a power and control mechanism coupled to the upper end of the power shaft for controllably translating the power shaft to progressively rotate the spindles during the rotation of the carrier, thereby varying the angles of incidence of the blades.

15. In a machine tool having a rotatable workspindle carrier, workspindles rotatably mounted on the carrier, and reciprocating means coupled to the workspindles to cause to and fro rotation of the workspindles, a power and control system for the reciprocating means, comprising a power jack including a piston reciprocably mounted within a cylinder, a second jack including a piston reciprocatably mounted within a cylinder, the pistons of the two jacks being serially connected to the reciprocating means, a source of fluid pressure, a valve having an inlet connected to the source and outlets connected to the cylinder of the power jack at opposite sides of the piston therein, a two position selector in the valve to selectively connect the inlet to the outlets thereby enabling the fluid pressure to urge the piston of the power jack in one sense or in the opposite sense, means actuated by the pistons when they reach the end of their stroke in one sense to move the selector from one position to the other position to enable the fluid under pressure to urge the piston of the power jack in the opposite sense, a closed fluid circuit connected to the cylinder of the second jack at opposite sides of the piston therein, a restricted passage in the circuit to impede the flow of fluid in the circuit thereby retarding the movement of the pistons, a valve in parallel with the restricted passage selectively adjustable to open and closed positions, the last mentioned valve when adjusted to open position allowing the fluid to flow freely in the circuit thereby enabling the pistons to move at a high velocity under the urging of the fiuid flow system.

16. In a machine tool having a rotatable workspindle carrier, workspindles rotatably mounted on the carrier, and reciprocating means coupled to the workspindles to cause to and fro rotation of the workspindles, a power and control circuit for the reciprocating means, comprising a power jack including a piston reciprocatably mounted within a cylinder, a second jack including a piston reciprocatablymounted within a cylinder, the pistons of the two jacks being serially connected to the reciprocating means, a source of fluid pressure, a valve having an inlet connected to the source and outlets connected to the cylinder of the power jack at opposite sides of the piston therein, a two position selector in the valve to selectively connect the inlet to the outlets thereby enabling the fluid pressure to urge the piston of the power jack in one sense or in the opposite sense, means actuated by the pistons when they reach the end of their stroke in one sense to move the selector from one position to the other position to enable the fluid under pressure to urge the piston of the power jack in the opposite sense, a closed fluid circuit connected to the cylinder of the second jack at opposite sides of the piston therein, a restricted passage in the circuit to impede the flow of fluid in the circuit thereby retarding the movement of the pistons, a valve in parallel with the restricted passage, an element in the said valve positionable to valve opening and valve closing position, the said valve allowing the fluid to flow freely in the circuit thereby enabling the pistons to move at a high velocity under the urging of the fluid flow system when the element is adjusted to valve opening position, a cam for selectively positioning the valve element, and means linking the pistons and the cam to position the cam in correspondence with the position of the pistons.

17. A machine for polishing blades, comprising a carrier, a container for a polishing medium disposed adjacent the carrier, the carrier and container being mounted for movement relative to each other, means mounted on the carrier for holding the blades in the polishing medium, means for translating the carrier and container relative to each other to pass the blades in a continuous path through the polishing medium, means to render the density gradient of the polishing medium immediately prior to contact with each blade no greater than the density gradient of the polishing medium when at rest, and means for changing, during the translation of the carrier relative to the container, the angles of the holding means relative to the direction of said translation to vary the angles of incidence of the blades between initial angles and limiting angles at such a speed relative to the speed of passage of the blades through the polishing medium that the relative movement between the medium and one surface of the blade is always in the same direction as the relative movement between the medium and the opposite surface of the blade.

18. A machine for polishing blades, comprising a carrier, a container for a polishing medium disposed adjacent the carrier, the carrier and container being mounted for movement relative to each other, means mounted onthe carrier for holding the blades in the polishing medium, means for translating the carrier and container relative to each other to pass the blades in a continuous path through the polishing medium, means to render the density gradient of the polishing medium immediately prior to contact with each blade no greater than the density gradient of the polishing medium when at rest, and means for changing, during the translation of the carrier relative to the container, the angles of the holding means relative to the direction of said translation to vary the angles of incidence of the blades between initial angles and limiting angles at such a speed relative to the speed of passage of the blades through the polishing me- .dium that the relative movement between the medium and one surface of the blade is always in the same direction as the relative movement between the medium and the opposite surface of the blade, the initial and limiting angles of incidence being within 55 of 0 angle of incidence and the difference between the said initial and limiting angles being less than 19. A machine for polishing blades of aerofoil shape, comprising a carrier, a container for a polishing medium disposed adjacent the carrier, the carrier and container being mounted for movement relative to each other, means mounted on the carrier for holding the blades in the polishing medium, means for translating the carrier and container relative to each other to pass the blades in a continuous path through the polishing medium, means for changing, during the translation of the carrier relative to the container, the angles of the holding means relative to the direction of the said translation to vary the angles of incidence of the blades between initial angles and limiting angles, and means in the container to elevate the particles of the polishing medium as the blades pass therethrough.

JOHN OLIVER CREEK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 464,584 Patterson et al. Dec. 8, 1891 1,925,751 Diffenderffer Sept. 5, 1933 2,083,773 Burroughs June 15, 1937 2,218,353 Gruenberg Oct. 15, 1940 2,434,513 Palmer Jan. 13, 1948 FOREIGN PATENTS Number Country Date 119,823 Great Britain Oct. 17, 1918

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