Background to the In : ention It is well known to orovide apparatus for grinding the blade tips of turbine or compressor rotors, for example jet engine turbine rotors.

The process can be used at low speed, when the rotor blades are fixed in position, or at high speed when the blades are mounted loosely and project radially outwards from the rotor axis, under centrifugal force, as the rotor is rotated by the grinding apparatus. One example of the latter form of appara tus is described and claimed in Europe. n Patent 040 467.

The grinding apparatus typically uses a cylindrical grinding wheel to remove metal from the rotor blade tips and the removal of metal thereby invariably produces burrs on both the leading and trailing edges of the blade : ips. These burrs must then be removed in a separate de-burring, operation.

It is an object of 1his invention to provide a method of and/or apparatus for de-burring the ground tips of turbine rotors which is more efficient than those used heretofore, or which will at least provide a useful choice.

Srrunary of Ae Inve : ltion Accordingly, in a fir ; ; t aspect, the invention provides a method of de- burring the blade lips of a turbine or compressor rotor after the grinding thereof by grinding means, said method including contacting said blade tips by d-burring means and being characterised in that said rotor is contacted substantially simultaneously by said grinding means and by said d e-burring means.

Preferably said method further includes displacing the contact between said de-burring means and said blade tips, between the leading and trailing (dges of said blade tips.

Preferably said metlod still further includes changing the relative contact surface spee is between said de-bt meAns and said blade tips, during the de-burring operation, according to whether said de- burring means is substantially in contact with the leading or trailing edges of said blade tips. Said de-burring apparatus is preferably controlled so that, w : ien in contact with the leading edges of the blade tips, the contact sur. ace speed of the de-burring means is slower than the surface speed cf the blade tips, and when in contact with the trailing edges of the blade tips, the contact surface speed of the de- burring means is fas : er than the surface speed of the blade tips.

Preferably the relative changes in surface contact speeds are effected by maintaining said rotor at a substantially constant speed of rotation, and adjusting the speed of said de-burring means.

In a second aspect the invention provides blade tip grinding apparatus including : support means to support a turbine or compressor rotor for rotation about its axis ; grinding means arranged to contact the blade tips of said rotor when said rotor is mounted in said support means ; de-burring means arranged to contact the blade tips of c ; aid rotor when said rotor is m runted in said support means, said apparatus bein characterised in that said grinding means and said de-burring r leans are arranged to contact said rotor simultaneously but said de-burring means is positioned 1. : 0 engage said rotor after said rotor has been subjected to grinding by said grinding means.

Preferably said de-burring means and said grinding means are positioned substantially at the opposite ends of a diametral line through said rotor w zen said rotor is mounted in said support means.

Preferably said grin (ins means comprises a grinding wheel and said de-burring means co mprises a rotating de-burrmg brush.

Preferably said de-b erring brush is mounted for translatiom along a line parallel to the sxis of said rotor when mounted in said support means.

Preferably said de-burring brush is mounted for movement toward and away from the, is of said rotor when mounted in said support means whereby the contact force between said brush and said rotor may be varied.

Preferably said apparatus is configured to operate according to the method set forth abo ize.

In a third aspect the invention provides a method of controlling de- burring means for use in de-burring the blade tips of a turbine or compressor rotor fo lowing grinding thereof, said method including changing the relative contact surface speeds of said de-burrizg means and said blade tips whilst displacing the contact of said dz-burring means between the leading and trailing edges of said blade tips.

Preferably said method involves maintaining the rotational speed of said rotor substantially constant and adjusting the speed ol said dc- burring means.

Preferably the speec. of said de-burring means is adjusted between that when in conta' : t with the trailing edges of said blade : tips the surface speed of sa. d de-burring means is faster than thE surface speed of said blade tips, to that when in contact with the leading edges of said blade t. ps the surface speed of said de-burring means is slower than the surface speed of said blade tips.

Preferably the surface speed of said de-burring means is substantially 2000 feet per minute slower than the surface speed of the blade tips whilst de-burring the leading edges of said blade tips, and substantially 2000 1 eet per minute faster than the surface speed of said blade tips while de-burring the trailing edges of said blade tips.

Preferably said de-burring means is subjected to substantially constant acceleratioi : between the lower and higher speeds thereof.

In a fourth aspect the invention proxides de-burrind mear ! s for use with a blade tip grir der when controlled according to the method set forth above.

Many variations in the way the present invention can be performed will present themselves to those skilled in the art. The description which follows is intended as an illustration only of one mea ; of performing the invention and the lack of description of variants should not be regarded as limiting. Wherever possible, a description of a specific element should be deemed to include equivalent ; thereof whether in existence now or in the future. The scope of the invention should be limited by the appended claims alone.

Brief'Description of J ie Drat. vings The invention wil :. now be described with reference to the accompanying drawings in which : Figure 1 : shows a diagramatic general arrangement of blade tip grinding apparatus incorporating the various aspects of the inve lotion ; and Figure 2 : Shows a velocity/time plot for de-burring means inluded in the al paratus shown in Figure 1.

Detalled Description of Working Embodiment Referring to the drax Tings, the invention provides a blade tip grinding apparatus 5 for grincing the blade tips 6 of a turbine or compressor rotor 7. In accordance with conventional practice, the rotor is rotatably supported between pedestals 8 and the blade tips 6 are contacted by grinding means, preferably in the form of a grinding wheel 9. Following grinding, the blade tips are contacted by de- burring means, preferably in the form of de-burring wheel 1l) so as to remove the burrs or the leading and trailing edges of the blade tips, following grinding. The characterising feature is that both the grinding wheel 9 ard the de-burring wheel 10 are mounted on the apparatus 5 so as tu contact the rotor 7 simultaneously, though the de-burring wheel is obviously positioned so as to act on the blade tips after they have been ground by the grinding wheel 9.

The nature and operation of the rotor mounting, and the grinding wheel construction End operation, does not form part of the invention and may, for example, be substantially as described in European Patent 040 467.

The de-burring wheel 10 may be of any known or future type and may, for example, be of a nylon/carborudum composition he wheel 10 is preferably motmted on arm 11 which, in turn, is mounted on carriage 12 via cross slide 13. The carriage 12 is mounted for movement toward a 1d away from axis 15 about which, in use, the rotor 7 rotates between pedestals 8, as indicated by arrow 16. The cross slide 13 is mounted so as to be displaceable on carriage 12 along axis 14, parallt l to the rotor axis 15.

The cross slide may also incorporate a swivel 17 whereby the peripheral surface o : the de-burring wheel 10 may be adjusted to the desired angle with re 3pect to the blade tips 6.

A number of motors are provided to control the operation of the de- burring wheel 10. Motor 18 controls the cross feed or the displacement of the carriage along axis 14. This allows the dus-burring wheel to be selective y positioned in contact with the leading edges 19 or trailing edges 20"f the blade tips. Motor 21 rotates the de-burring brush 10, preferably through a varying speed range as will be described in greater detail below. Motor 22 pivots the cross slide 13 about axis 17 as is indicated by arrow 23.

In the embodiment depicted herein the de-burring wheel 10 is shown located diametrically opposite to the grinding wheel 9. It will be appreciated, however, that the de-burring wheel could be located at any convenient position around the rotor, the only obvious requirement being that the wheel 10 contact the rotor aftei grinding by the wheel 9.

In accordance with a further aspect of the invention, the invention provides a method oS controlling the relative speeds of the blade tips and the be-burring wheel to achieve efficient removal of burrs from both the lead and trailing edges of the blade tips. Whilst, conceivably, it would be possible to vary the rotor speed, we have found it most efficient to maintain the rotor speed substantially constant and vary the speed of the de-burring wheel 10 as, in turn, it contacts the leading or trailing ed ses of the blade tips 6.

In order to remove the burrs from the leading edges 19 of he blade tips, the surface or tangential speed of the de-burring brush 10 is set to run slower than the tangential or surface speed of the blade tips.

This forces each bur-in the opposite direction to that in which it was produced by the grinding wheel wheel and, and, as result, the burr i : ; lifted off the blade. In order to remove the burrs from the trailing edges of the blades, the surface o tangential speed of the be-burring brush is set quicker than the targential speed of the blade tips and so the trailing edges are de-burred.

Typically the tanger tial speed of the blade tips in apparatus of this type is about 2000 surface feet per minute (s. f/m). According to the invention the speec of the de-burring brush will be controlled by motor 21 so that the tangential speed of the brush 10 varies between about zero and 400C surface feet per minute ; or 2000 surface feet per minute either side,) f the blade tip speed. It is envisaged that the speed be varied sub ! tantially constantly between 0, 4000 and back to 0 surface feet per minute over a cycle of about 20 seconds, as shown in Figure 2. This sped variation is effected whilst the brush is being translated between t : ontact with the leading and trailing edges of the blade tips. Such s cycle will cover all possible speeds and thus achieve maximum dc-burring performance.

An important aspect of de-burring is to control the stresses applied to the blade tips by the de-burring process. To this end it is proposed to control the in-feed of the brush 10 against the blade tips (in the direction of arrow li')) by monitoring the torque of the motor 21 and using this as a feedback to the controller (not shown) controlling in feed in the direction of arrow 16. arronv same feature provides automatic compensa : ion for wear of the brush 10.

Although, in the embodiment described herein, only one de-burring brush is depicted, :. t will be appreciated that particular forms of apparatus might havs more than one brush