US2726491A

US2726491A - Surface finishing with abrasive strips

Info

Publication number: US2726491A
Application number: US428351A
Authority: US
Inventors: Smedley John
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 1953-05-14
Filing date: 1954-05-07
Publication date: 1955-12-13
Anticipated expiration: 1972-12-13

Description

Dec. 13, 1955 J. SMEDLEY 2,725,491

SURFACE FINISHING WITH ABRASIVE STRIPS Filed May 7, 1954 6 Sheets-Sheet '1 Dec. 13, 1955 J. SMEDLEY 2,726,491

SURFACE FINISHING WITH ABRASIVE STRIPS Filed May 7, 1954 6 Sheets-Sheet 2 Dec. 13, 1955 J. SMEDLEY SURFACE FINISHING WITH ABRASIVE STRIPS 6 Sheets-Sheet 5 Filed May 7, 1954 //v VEN Jomv 611450 3. 1955 J. SMEDLEY SURFACE FINISHING WITH ABRASIVE STRIPS 6 Sheets-Sheet 4 Filed May 7, 1954 MUN" I MW m WM m n m m5 N M 5/ 4 wfl y m M e c- 1955 J- SMEDLEY 2,726,491

SURFACE FINISHING WITH ABRASIVE STRIPS Filed May 7, 1954 6 Sheets-Sheet 5 IN yf/Y T02 Joy/v JMEDLE Y Dec. 13, 1955 SMEDLEY 2,726,491

SURFACE FINISHING WITH ABRASIVE STRIPS Filed May 7, 1954 6 Sheets-Sheet 6 Ja v JM'DLEY United States Patent 2,726,491 SURFACE FINISHING WITH ABRASIVE STRIPS John Smedley, Chellaston, England, as'signor to Rolls- Royce Limited, Derby, England, a British company Application May 7, 1954, Serial No. 428,351

Claims priority, application Great Britain May 14, 1953 22 Claims. (Cl. 5162) This invention relates to methods of and apparatus for surface finishing of the kind in which a flexible abrasive carrier is moved in a predetermined path relative to the surface to be finished. I

The present invention has for an object to provide improved methods of and apparatus for surface finishing in which wear on the apparatus is reduced.

According to this invention, a method of finishing of the kind referred to for finishing curved surfaces on parts such as turbine compressor or like blades includes presenting the curved surface of a part to be finished into contact with the flexible abrasive carrier and effecting relative movement of the flexible carrier and the surface to be finished whilst feeding a liquid or gas under pressure to the back surface of the flexible carrier.

It has been found that the pressure liquid or pressure gas supplied in this manner not only functions as a cool ant for apparatus and the part being treated, but also reduces the tendency for particles of the abrasive material to permeate from the operative surface of the flexible carrier to its back surface. It is thought that it is for this reason that wear on the apparatus is reduced.

The invention also includes apparatus for carrying out the improved method and which apparatus comprises a pressure-fluid-supply member having delivery channels or apertures in a part thereof having a general contour shaped in determined relation to the desired form of the surface to be finished which member assists to determine the path of the flexible carrier. The member is also formed with one or more internal passageways communieating with the delivery channels or apertures for conveying a liquid or gas under pressure thereto and thus in operation to the back surface of the flexible carrier. In one arrangement, the pressure-fluid-supply member is a block having a surface of desired contour formed by a plurality of webs with correspondingly shaped edges and narrowly spaced apart longitudinally of the contour to provide a corresponding plurality of slot-like outlets from pressure fluid chambers in the block.

The block may be formed from a rigid material such as metal or may be made of rubber or other suitable elastomeric substance. In another arrangement the member is a trough-like block and with the edges of its ends contoured in relation to the desired contour of the surface and having spaced strip members extending from one end to the other with edges of the strips joining the contoured edges of the ends, thereby to define a series of outlets from within the trough to the path of the flexible strip over the member. The trough may be divided into a number of spaces by internal walls, each space having separate outlets. In yet another arrangement, the pressure-fluid-supply member is a block having a contoured surface formed with grooves extending over an area of the surface whereby the gas or liquid is supplied in a uniform manner over the surface.

In accordance with a feature of the invention the apparatus for finishing curved surfaces may include a memher as just set forth with a plurality of separate pressure fluid supply passageways communicating with differing areas of the grooved or apertured contour of the member and means to supply a liquid or gas under pressure selectively to said passageways depending upon the position of the flexible abrasive carrier relative to said contour. The adoption of this feature may be desirable where it is not possible to carry out the surface finishing of the whole of the part in one operation, the fluid supply member and the part being adjusted relative to the flexible carrier during finishing of the whole surface. For example in the case of a turbine blade having a root platform and possibly also a tip platform, either platform or both of said platforms may lie in a plane which is not at right angles of the spanwise axis of the blade; thus the blade may be finished at one. end with the abrasive carrier travelling along a path substantially parallel to the corresponding root platform, and finishing of the blade at the other end may be effected by relative adjustment of the fluid-supply member and blade with respect to the abrasive carrier to a position such that the abrasive carrier travels along a path parallel to the tip platform.

Preferably compressed air is supplied to the member, the quantity being appropriate to maintain cool the curved surface of the part being finished and the finishing apparatus guiding the flexible carrier and to inhibit the permeation of particles of abrasive through the flexible carrier.

The flexible carrier may be in the form of a continuous band; preferably, however, a length of strip abrasive carrier is reciprocated between the fluid supply member and the curved surface of the part under treatment. Preferably the method of operating apparatus in accordance with the invention involves (a) the application of the part to be finished to the flexible carrier wtih a preselected pressure, for example by feeding compressed air to a loading cylinder for urging the fluid supply meme ber and part towards one another, (b) the use of a new length of abrasive strip for each part to be finished, and (c) the use of a preselected pressure for pressure air or liquid supply to the fluid-supply member. With these preselected conditions the finish, which may necessitate the removal of metal from the curved surface of the part to an accurate dimension, may be determined by carrying out the finishing operation for a defined time, the speed of reciprocation of the strip of abrasive being predetermined by the design of the machine. The invention thus enables considerable uniformity of surface finish to be obtained; this is an important factor in the production of turbine and compressor blades.

One form of apparatus carrying the invention into effect and a number of modifications of parts thereof will now be described with reference to the accompanying drawings in which Figure 1 is a front view of the apparatus,

Figure 2 is a view in the direction of arrow 2 on Figure 1, parts of the apparatus being broken away to show details thereof,

Figure 3 is a rear view ofthe apparatus,

Figure 4 is a view of part of the apparatus to a larger scale than in Figures 1-3, parts being broken away to show details of construction,

Figure 5 is a view to the same scale as Figure 4 showing details of other parts of the apparatus,

Figure 6 is an electrical wiring diagram,

Figure 7 is a perspective view of one form of pressure fluid supply member suitable for use when surface finishing the concave surface of say a turbine blade,

Figure 8 is a section through the pressure fluid supply member of Figure 7,

Figure 9 is a perspective view of a pressure fluid supply member suitable for use when surface finishing the convex surface of say a turbine blade,

Figure is a corresponding view of an alternative construction,

Figure 11 is a section showing the internal construction of the pressure fluid 'supply-memberlof Figure '10, and

Figure 12 illustrates diagrammatically one form of blade which may be surface finished by the method and apparatus of this invention.

Referring first to Figures 1-5, the apparatus illustrated is one in which a flexible abrasive carrying strip 41 is drawn backwards and forwards over the surface of a blade. The strip may "be cloth say with emery particles adhering thereto. The apparatus comprises a machine bed upon which is mounted a base plate 21 supporting an upstanding standard 22. The standard 22 is generally of U-section being open at the rear and has a front web and side flanges 23 which partially enclose the driving mechanism for the machine.

Adjacent its upper end, the standard 22 has secured on it a pair of horizontally-extending

brackets

24, 25 respectively, one of which is disposed vertically above the other and as will best be seen from Figure 4 the brackets carry aligned thrust and plane bearings 26 wherein are journalled stub spindles 27 which project upwardly and downwardly from a triangulated cross beam 28. The

cross beam extends horizontally between the brackets 24,

25 and is supported by its spindles 27 to swing about a vertical axis.

The swinging beam 28 carries a chain mechanism to which the abrasive strip is attached to be drawn backwards and forwards over the blade being finished. The

swinging beam 28 has journalled in it a driving sprocket 29 for the chain 30, the sprocket 29 having its axis at right angles to and intersecting the common axis of the spindles 27. The swinging beam carries at its extreme ends a pair of sprockets 31 which are adjustable in slots 32 towards and away from thedriving sprocket 29. The swinging beam also carries a depending bracket 33 at the lower end of which there is a further jockey sprocket 34.

The swinging beam 28 alsohas mounted on it a pair of pneumatic rams 35 whereof the ram pistons carry at their ends sprockets 36. The driving sprocket 29 is dis posed slightly below the level of the sprockets 31 and the driving chain is arranged to pass beneath the driving sprocket 29 and over the sprockets 31 so that the chain 30 extends upwardly and outwardly from the driving sprocket 29 on eachside of 'it. The'rams ;are arranged one on each side of the driving sprocket 29 with their lines of action to be at right angles to the stretches of the chain running from the sprocket29, and the sprockets 36 carried by the ram engage the underside of the chain. Pressure fluid supply connections 37, 38 are made to the upper ends and lower ends respectively of the'rams 35. The rams in the finishing operation are employed to'exert a tension in the chain 30, and air being admitted to the lower ends of each of the rams and'accordingto the direction of travel of the chain one ram "yields against the tension in the chain 30 whilst the other extends to take up the correspondingslack; this arrangementavoidstearing of the strip 41. The ends of the chain 3% are connected by links 39 to clamps 40 wherein the abrasive strip 41 is gripped during operationof the machine. In fitting the strip 41 to the clamps 40 air is supplied to the upper ends of the rams 35. Subsequent application of pressure to the lower ends results in'tensioning of the strip.

The abrasive strip 41 is wound ontworeels 42, '43'and after each blade has been finishe'd the clamps '40 are released and a short length of fresh strip unwound from reel 42 and a corresponding length of used-strip is wound up on the reel 43 so that eachblade is treated in asirnilar way.

Mounted on the front of the standard 22, there is a mounting bracket 44 with dovetail guides 45 wherein during operation there is supported either a workpiece holder 46 as shown in Figu'resl and*2,"'or a'pr'essure fluid supply member 63, such asis shown in Figures 7 and 8,

or as is shown in Figures 10 and 11. The pressure fluid supply member 63 is adapted so that a pressure fluid, pressure air in this case, can be fed to the back of the abrasive strip 41, that is the surface of the strip not having the abrasive material on it, and it is found that by so supply pressure fluid to the back of the abrasive strip from a suitably contoured surface of the pressure supply member 63, the abrasive strip can be constrained to follow a desired path around the surface of the blade being finished, whilst at the same time wear on the parts of the machine is substantially avoided due, it is thought, to the pressure fluid preventing the abrasive particles penetrating through the band to the back thereof and holding the band out of contact from the pressure fluid supply member 63.

The workpiece holder 46 is supported in the guides 45 when finishing a convex blade surface, and the pressure fluid supply member 63 is mounted in the guides 45 when finishing a concave surface of -a blade.

The mounting bracket 44 also carries laterally-extending brackets 47 in which are rotatably mounted spool members 48 which form guides for the abrasive strip 41. The abrasive strip 41 runs on the spindles of the spools and the end flanges of the spools are provided to prevent damage to parts of the blade not required to be touched during the finishing operation.

Below the mounting bracket 44 there is provided a mounting member 65 which is vertically slidable within the base plate 21, and in operation the vertically slidable member 65 carries a holder 64 wherein is mounted either a workpiece holder 46 or a pressure fluid supply member 63. When a convex blade surface is being surface finished, the pressure fluid supply member is supported in the holder 64 and when a concave surface is being finished the workpiece holder 46 ,is mounted in the holder 64.

In each case the flexible strip 41 travels between the blade mounted in the workpiece holder 46 and the pressure fluid supply member'63 with the abrasive carrying face ofthe strip directed towards the blade.

The vertically slidable member 65"has connected to it a vertically-extending rod 66, the lower end of which is engaged by a roller 67 carried at one end of a pivoted lever 68, -the opposite end of which carries a counterweight 69. The mass and disposition of the counterweight on the pivoted lever 68 is selected in dependence upon the pressure fluidload on the flexible strip and it will be seen that whether or not the work-holder is supported in the mounting bracket 46 or in the holder 64, the pressure with which the abrasive band is pressed on the blade surface will be the same and so the same counterweight 69 can be employed for both blade surfaces.

Referring again to Figure 4, the driving sprocket 29 is connected through a universal coupling 50 to a further sprocket 51 journalled in a bracket 52 which is secured to the rear surface of the front wall 'of the standard 22 between the side flanges 23. The sprocket 51 is driven by a chain 53 which is in turn driven by a sprocket wheel 54 (see Figure 5) adjacent the bottom of the standard 22. The drive to the sprocket 54 is as follows. Mounted on the base plate 21 behind the standard 22 there is an electric motor 55 arranged to drive a crank wheel 56 which is connected by a connecting rod -57 to a further wheel 58 journalled in a gear-casing 59 mounted on the base 22a of the standard 22. Thepositions-of-the pivot pins for-the connecting rod 57 on the

wheels

56 and 58 are so chosenthat although the wheel 56 rotates continuously the wheel 58 is turned first in one direction and then the other. The spindle 60 0f the wheel58 has keyed to it a large gear wheel 61 which meshes with a pinion 62 carried on'the spindle of':the1sprocket-54. Inthis way although the motor 55 rotateszc'ontinuously in one direction, the sprocket 54 turns first in one direction and thenin the other and thechain '53 is reciprocated and so 'a feciprocating -'drive is-transmitted through the sprocket51 and universal coupling 50 to the driving sprocket 29 for the chain 30.

The operation of the machine as so far described is as follows.

A blade is set up in the work-holder 46 and the workholder either mounted in the mounting bracket 44 or in the holder 64 and the appropriate pressure fluid supply member mounted in the machine on the opposite side of the abrasive strip 41. The abrasive strip is gripped in the clamps 40 and pressure fluid is supplied to the rams 35 to tension the chain 30 and thus to tension the abrasive strip 41. The motor 55 is then started so reciprocating the abrasive strip and at the same time pressure air is supplied to the pressure fluid supply member 63 so in effect to hold the strip out of contact with the pressure fluid supply member 63 but at the same time constraining the band to follow a desired path when in contact with the blade, the path being determined by the contour of the pressure fluid supply member.

When the blade to be surface finished has no end platforms or has only one end platform, the cross beam 28 may be held in one position throughout the surface finishing operation, but when the blade is as illustrated in Figure 12 and comprises a vane portion 70, the surfaces of which are to be surface finished and end platforms 71 and 72 the surfaces of which are inclined to one another, the abrasive strip 41 may be constrained to travel over the surface to be finished first with its centre line parallel to one of the platforms 71, 72 and then with its centre line parallel to the other of the platforms 71, 72. For instance as indicated in Figure 12, the edges of the flexible strip 41 may travel along lines 73 during part of the surface finishing operation, and then the relative positions of the blade and strip 41 may be adjusted so that the edges of the strip travel along lines 74.

Conveniently for this purpose the cross beam is caused to swing about its spindles 27 and the following mechanism may be employed for this purpose. Referring to Figures 1, 2 and 3, the mechanism comprises an electric motor 75 arranged to drive a pulley 76 and through a flexible belt 77 to drive a further pulley 78. The pulley 78 forms the input member of a gear box 79, the output member of which is a chain sprocket 80 connected by a chain 81 to drive a further chain sprocket 82 which is journalled in a bracket 83 on the side of the standard 22. The sprocket 82 is arranged to drive through bevel gearing 84 a crank wheel 85 connected by a link 86 to a peg 87 upstanding from the cross beam 28. The link 86 is pivoted to the crank wheel 85 through a peg 85a which is adjustable radially of crank wheel 85 to preselect the throw of the crank according to the desired angular movement of the cross beam. It will be appreciated that when the motor 75 is operating the crank wheel 85 will be rotated so swinging the cross beam about its spindles 27.

The swinging operation may be controlled automatically, for instance the motor 55 may be arranged to drive a pulley 88 which drives a further pulley 89 by means of a belt 90. The pulley 89 is arranged to drive a worm 91 accommodated in a casing 92 and the worm-wheel 93 which meshes with the worm 91 is arranged to rotate a pair of

cams

94, 95. The

cams

94, 95 actuate a pair of micro-switches 96, 97 which are arranged to control starting-up of the motor 75. Limit switches 98, 99 are also provided to cut off the supply of current to the motor 75 when the cross beam 28 reaches the appropriate position. The

switches

96, 97,98 and 99 are shown as being connected through armoured cable to a junction box 100 from which suitable connections may be taken to the motor and the power supply.

The switches'96, 97, 98 and 99 may be arranged substantially as shown in Figure 6 between the power supply connections 101 and the motor 75. In this arrangement the limit switches 98 and 99 are normally closed and are opened when the cross beam 28 moves to a 6 position to engage and open them. The micro-switches 96, 97 are normally spring-loaded open and are closed when the cams 94, contact them and maintain them closed during swinging of the cross beam.

In operation, surface finishing is commenced with the cross beam 28 in one of its limiting positions and withthe controlling cam of the two

cams

94, 95 just clear of its switch 96 or 97. The current supply to the motor 75 is therefore cut off until the leading cam contacts its switch 96 or 97 so closing these contacts, for instance if the cam 9 is the leading cam the cam 94 first contacts its switch 96 so connecting the supply 101 to the motor 75 and causing the cross beam 28 to swing until the cross beam contacts the switch 99 and breaks the supply. Thereafter cam 94 disengages switch 96 allowing it to open. After continued operation the cam 95 contacts its switch 97 so completing the connections between the supply 101 and the motor 75. When the cross beam againreaches its original position the switch 98 is opened by the cross beam and so the current supply to the motor 75 is cut off. Thereafter cam 95 disengages switch 97 allowing it to open.

If desired, instead of adjusting the position of the abrasive strip 41 relative to the blade, the blade and pressure fluid supply member may be adjusted in position relative to the strip 41, for instance by mounting them in rotatable supports while retaining the strip in fixed structure.

Referring now to Figures 7 and 8, there is illustrated one form of pressure fluid supply member suitable for use when surface finishing the concave surface of a blade such as is shown in Figure 12.

The pressure fluid supply member comprises a block 105 having a surface 106 thereof contoured to correspond to the desired shape of the surface to be finished. The contoured surface has a plurality of apertures 107 opening to it and these apertures are conveniently formed by narrow slots or sawcuts extending into the block and are separated by webs 108 extending transversely to the longitudinal axis of the contoured surface. The apertures 107 lead to the contoured surface 106 from three

chambers

109, 110 and 111 formed within the'block 105 to which pressure air can be supplied through

ducts

112, 113 and 114 respectively. The chambers are separated from one another by means of brass strips 115 and 116 let into the block. In use pressure air is supplied to the central chamber 110 throughout the surface finishing operation and is supplied to that one of the

end chambers

109 and 111 which is covered for the time being by the abrasive strip 41.

This arrangement avoids excessive loss of air from those apertures 107 which are not covered by the abrasive strip.

Referring now to Figure 9, there is illustrated the associated form of pressure fluid supply member such as will be used when surface finishing the convex surface of a blade such as is shown in Figure 12. In this case it will be appreciated that the apertures formed by the slots or sawcuts extend to the lateral surfaces of the block 105 and to prevent excessive leakage of pressure air from the pressure fluid supply member longitudinal brass strips 117 are let into the block to extend along each side thereof.

Referring now to Figures 10 and 11, there is illustrated an alternative form of pressure fluid supply member for use in finishing a concave blade surface. In this construction the block 105 is formed with a trough-like contoured edges of the walls 124-. The strips 125 are spaced apart and so form a plurality of outlet apertures from the

spaces

120, 121 and 122 for the supply of pressure air to the back of the flexible abrasive strip 41 during the surface finishing operation.

In the use of the pressure-fluid-supply members just described, a changeover valve is provided by which a pressure air or pressure liquid supply is fed selectively to one passageway or the other when the carrier for the member and blade is adjusted relative to the abrasive strip. Such an arrangement avoids major loss of ressure fluid when the adjustment is made.

The adjustment may be effected automatically in accordance with a time cycle, for example by means of a pneumatic jack fed with pressure air through a timecontrolled solenoid-operated valve. The changeover valve in the pressure fluid' supply to the passageways may be automatically effected at the time.

When the pressure-fluid-supply member is a block having its contoured surface formed with grooves communicating with two air supply passageways, the grooves at one end of the block are connected to one passageway and those at the other end being connected to the second passageway. In one arrangement, the block is made of nickel plated cast iron with a rubber surface moulded to a desired form bonded to the nickel-plated surface. In use a silicone grease may be employed as lubricant on the rubber and on the back of the flexible band.

In another form of apparatus for finishing turbine or compressor blades having the root and tip platforms which are not parallel to one another, an abrasive strip is used which has a width less than the minimum spanwise length of the blade, and the fluid supply member and work holder are mounted on carriers which are rotatable about an axis at right-angles to the longitudinal axis of the blade. The pressure-fluid-supply member and the blade are set up so that the longitudinal axis of the strip is parallel to one blade platform, and so that one edge of the strip travels close to this platform. A portion of the blade profile surface extending spanwise from the blending fillet between the surface and the platform is then subjected to the finishing operation. Thereafter the carrier for the pressure-fluid-supply member and blade is rotated until the other edge of the abrasive strip is parallel to the second platform, and the position of the strip and blade adjusted to bring this edge close to the second platform by relative transverse movement of the strip and the member and blade carrier. The remainder of the blade profile surface is then finished.

Iclaim:

1. In apparatus for surface finishing a curved surface comprising a work holder adapted to receive the part to be surface finished, and a flexible abrasive carrier, said work holder and flexible carrier being mounted for relative finishing movement with the said part carried in the work holder in contact with the flexible carrier; means to supply a pressure fluid to the opposite surface of the abrasive carrier to that in contact with the said part comprising a member positioned adjacent said opposite surface so that the carrier is between the work hclder and said member, said member having internal passageways and a portion of its external contour shaped in predetermined relation to the desired form of the surface to be finished, means to deliver pressure fluid to said internal passageways of the member, and a plurality of outlets rom said internal ducts opening through said contour portion of the member, said outlets being disposed in said contour portion of the member in a manner uniformly to distribute the pressure fluid to said opposite surface where the abrasive carrier contacts the part to be finished.

2. Apparatus as claimed in claim 1, wherein the pressure-fluid-supply member and the work holder are mounted on fixed structure and there is provided means to support the flexible abrasive carrier and to draw it in said finishing movement between the pressure-fluid supplymember and the part mounted in thework-holder, said meansto support the flexible abrasive carrier being adjustably mounted on the fixed structure to permit adjustment of the line of travel of the flexible abrasive carrier over the'part.

3. Apparatus as claimed in claim 2, wherein the means to support the flexible abrasive carrier comprises a beam mounted on said fixed structure to swing about an axis aligned with the work holder'- and pressure-fluid-supply member and means to effect controlled swinging of the beam.

4. Apparatus as claimed in claim 3, wherein the means to draw the flexible abrasive carrier between the work holder and the pressure-fluid-supply member in said finishing movement comprises a number of chain sprockets mounted on the beam, a chain running over the sprockets and having at its ends clamps for gripping a length of the flexible abrasive carrier, oneof said sprockets being a driving sprocket, and means to rotate said driving sprocket alternately in opposite directions thereby to reciprocate the flexible abrasive carrier over a workpiece in the work holder.

5. Apparatus as claimed in claim 4, wherein the driving sprocket has its axis at right angles to and intersecting the swinging axis of the beam, and the driving means for the driving sprocket is supported by the fixed structure, there being a universal coupling between said driving means and the driving sprocket for the chain.

6. Apparatus as claimed in claim 5, wherein the driving means for the driving sprocket comprises a continuously rotating motor and means to convert the continuous rotation of the motor into a rotation of the driving sprocket first in one direction and then the other.

7. Apparatus as claimed in claim 6, wherein said motor is also adapted to control swinging of the beam to vary the line of travel of the flexible abrasive carrier over the workpiece.

8. Apparatus as claimed in claim 7, wherein said motor drives control cams controlling the supply of electric current .to an electric motor which is connected to cause swinging of said beam relative to the fixed structure, and wherein limit switches are provided to be operated by the beam to cut off the supply of current to the motor when the beam reaches a selected position.

9. Apparatus as claimed in claim 4, wherein means is provided to tension the driving chain for the flexible abrasive carrier.

10. Apparatus as claimed in claim 9, wherein the tensioning means comprises tensioning sprockets engaging the driving chain on each side of the driving sprocket and ram means to displace the tensioning sprockets in a sense to tension the chain.

11. Apparatus as claimed in claim 1, comprising also means to control the load with which the flexible abrasive carrier is applied to the surface to be finished.

12. Apparatus as claimed in claim 11, comprising a mounting member adapted to support the work holder or pressure-fluid-supply member and arranged for movement in the fixed structure of the apparatus towards and away from the flexible abrasive carrier and means to urge said mounting member towards the flexible carrier with a pre determined load.

13. Apparatus as claimed in claim 12, wherein the means to load said mounting member comprises a pivoted lever adapted to engage said mounting member with one end and a counter-weight of predetermined mass at the opposite end.

14. Apparatus accordingto claim 1, wherein said outlets are afforded by parallel apertures communicating through the member with the passageways, and open to said contour portion of the member.

15. In apparatus for surface finishing a curved surface comprising a work holder adapted to receive the part to be surface finished, and a flexible abrasive carrier, said work holder and flexible carrier being mounted for relative finishing movement with the said part carried in the work holder in contact with the flexible carrier; means to supply a pressure fluid to the opposite surface of the abrasive carrier to that in contact with the said part comprising a member positioned adjacent said opposite surface so that the abrasive carrier is between the Work holder and said member, said member being a trough-like block having ends With edges contoured in predetermined relation to the desired form of the surface to be finished, and having a plurality of spaced strips or webs extending from one end to the other with the edges of the strips or webs joining the contoured edges, thereby to define a series of outlets from the trough to the said opposite surface of the abrasive carrier, and means to supply pressure fluid to within the trough, whereby the pressure fluid is distributed in a uniform manner to said opposite surface where the abrasive carrier contacts the part to be finished.

16. Apparatus according to claim 15, wherein said trough-like block comprises internal wall means to divide the trough into a number of spaces with separate outlets from each space, and means to supply the pressure fluid selectively to said spaces.

17. Apparatus according to claim 15, comprising also means supporting said abrasive carrier, said work holder and said member for relative displacement to vary during said relative finishing movement the line of travel of the abrasive strip across the contoured surface and part to be finished, thereby to vary the portions of said contoured surface and part covered by the abrasive carrier, said selective supply means being actuated on said change of line of travel to supply pressure fluid only to those outlets covered by the abrasive carrier.

18. Apparatus according to claim 17, comprising carriers for said work holder and said member mounted to be rotatable about an axis normal to the surface of the abrasive carrier to vary the line of travel of the abrasive carrier.

19. In apparatus for surface finishing a curved surface comprising a work holder adapted to receive the part to be surface finished, and a flexible abrasive carrier, said work holder and flexible carrier being mounted for relative finishing movement with the said part carried in the work holder in contact with the flexible carrier; means to supply a pressure fluid to the opposite surface of the abrasive carrier to that in contact with the said part comprising a member positioned adjacent said opposite surface so that 10 the abrasive carrier is between the work holder and said member, said member being a block having internal passageways and a portion of its surface facing the abrasive carrier shaped in contour in predetermined relation to the desired form of the surface to be finished, said contoured surface being afforded by correspondingly shaped edges of a plurality of webs narrowly spaced apart longitudinally of the contour to provide a corresponding plurality of slotlike outlets opening internally of the block to the passageways and externally of the block to said contoured surface, and means to deliver pressure fluid to said passageways, whereby the pressure fluid is distributed in a uniform manner to said opposite surface where the abrasive carrier contacts the part to be finished.

20. Apparatus according to claim 19, comprising a plurality of separate passageways each connected to different areas of said contoured surface, and means to supply pressure fluid selectively to said passageways. 1

21. Apparatus according to claim 20, comprising also means supporting said abrasive carrier, said work holder and said member for relative displacement to vary during said relative finishing movement the line of travel of the abrasive strip across the contoured surface and part to be finished, thereby to vary the area of said contoured surface covered by the abrasive carrier, said means to supply pressure fluid selectively to the passageways being actuated on said change of line of travel to permit supply of pressure fluid only to the outlets in the area of the contoured surface covered by the abrasive carrier.

22. Apparatus according to claim 21, comprising carriers for said work holder and said member mounted to be rotatable about an axis normal to the surface of the abrasive carrier to vary the line of travel of the abrasive carrier.

References Cited in the file of this patent UNITED STATES PATENTS 2,170,792 Brooke Aug. 29, 1939 r 2,295,695 Stacey Sept. 15, 1942 2,296,990 Fowler Sept. 29, 1942 2,453,972 Clave et a1 Nov. 16, 1948 2,587,603 Czarnecki Mar. 4, 1952 FOREIGN PATENTS 708,219 Germany Mar. 31, 1939 835,191 France Dec. 14, 1938