FR3137405A1 - Turbojet turbine housing equipped with mobile cooling tube fixing devices - Google Patents

Abstract

The invention relates to a turbomachine casing, comprising a wall of revolution equipped with circumferential tubes (11) for blowing air onto this wall in order to cool it, these tubes (11) being carried by bars (12) equipping the casing extending parallel to its wall of revolution, each tube (11) being secured to a bar (12) by a fixing device (13), in which at least one fixing device (13) comprises a collar (14 ) enclosing a tube (11) being terminated by two legs extending parallel to each other, each leg having a hole, in which a bolt (16) passes through the holes of the two legs and a hole in the bar (12), and in which the hole in the bar (12) is an oblong hole extending parallel to the tube (11). Figure for abstract: Figure 3

Description

Turbojet turbine housing equipped with mobile cooling tube fixing devices

The invention relates to the cooling of a turbojet turbine casing, which is ensured by tubes surrounding this casing and diffusing air towards the external face of this casing to maintain it at a desired temperature.

STATE OF PRIOR ART

A low-pressure turbojet turbine casing 1, part of which is shown on the comprises a wall of revolution 2, which surrounds a turbine comprising a non-visible rotor carrying blades movable relative to this casing 1.

The radial clearance existing between the ends of the moving blades and the internal face of the casing strongly conditions the efficiency of the engine, because the quantity of losses is all the more limited as this clearance is low, given that these losses correspond to fluid which is propelled into the engine without driving the blades.

In operation, the thermal fluctuations to which the engine components are subjected cause differential expansions of these components resulting, among other things, in a modification of the radial clearance existing between the ends of the movable blades and the turbine casing.

For this reason, the crankcase is cooled, so as to limit its radial expansion, in order to ensure that the radial clearance remains minimal at different engine operating conditions.

This cooling is ensured by tubes 3 fixed to the external face of the wall of revolution 2, these tubes being supplied with fresh air which they blow to the external face of the wall 2 to cool it, the fresh air supplying these tubes being taken from an engine compressor.

As seen more clearly on the , these tubes 3 are carried by bars 4 to which they are fixed by collars 6. These bars 4 extend longitudinally and are themselves fixed to circumferential ribs located at the ends of the wall of revolution 2.

Each collar 6 surrounds the tube 3 which it carries and is fixed to the bar 4 by a bolt 7. Additionally, each bar 4 is fixed to the ribs of the wall of revolution 2 by at least two bolts located at its ends.

Taking into account the differential expansions occurring in such an assembly subjected to cycles of temperature variations, it is necessary for the tubes 3 to slide in the collars 6 which carry them.

In practice, these slippages lead to wear on the external face of the tubes at the level of the collars which enclose them, and this wear can lead to rupture of the tubes. It is then necessary to replace the entire cooling arrangement, which corresponds to a significant maintenance cost.

One possibility to limit this phenomenon is to equip the collars with sheaths made of anti-friction material including PTFE (polytetrafluoroethylene) to reduce the frictional forces of the tube in relation to the collar in order to reduce wear.

However, given the high temperature, combined with significant efforts, these materials deteriorate too quickly, so that this solution does not prove satisfactory.

The aim of the invention is to provide a solution making it possible to increase the longevity of such an arrangement while limiting the maintenance operations necessary for its proper functioning.

For this purpose, the subject of the invention is a turbomachine casing, comprising a wall of revolution equipped with tubes for blowing air onto this wall in order to cool it, these tubes being carried by bars equipping the casing by extending parallel to its wall of revolution, each tube being secured to a bar by a fixing device, in which at least one fixing device comprises a collar secured to the bar by a bolt, the collar enclosing a tube being terminated by two tabs extending parallel to each other, each tab having a hole, the bolt passing through the holes of the two tabs and a hole in the bar, and in which the hole in the bar is an oblong hole extending parallel to the tube.

With this arrangement, the entire collar is able to slide relative to the bar thanks to the oblong hole, during movements of the tube relative to the bar which result from differential expansions, without the tube sliding in this collar.

The invention also relates to a casing thus defined, in which the bolt comprises a screw receiving a self-locking type nut.

The invention also relates to a casing thus defined, comprising a first washer surrounding a screw of the bolt by being interposed between a head of this screw and the bar, and a second washer surrounding the screw by being interposed between the bar and the tabs of the collar , and in which these washers carry an anti-friction coating.

The invention also relates to a casing thus defined, in which the bar has faces carrying an anti-friction coating around the oblong hole.

The invention also relates to a casing thus defined, the anti-friction coating of which is deposited with a physical vapor deposition process.

The invention also relates to a casing thus defined, comprising a ring interposed between the two washers, this ring having an external diameter corresponding to the diameter of the oblong hole, and having a thickness substantially greater than the thickness of the bar.

The invention also relates to a casing thus defined, in which the oblong hole has a length corresponding to the width of the tabs of the collar.

The invention also relates to a turbomachine comprising a casing thus defined.

There is a partial perspective view of a portion of the casing according to the state of the art;

There is a partial perspective view of a tube fixing system according to the state of the art;

There is a perspective view of a tube fixing arrangement according to the invention;

There is a perspective view showing the collar and the bar of the arrangement according to the invention;

There is a perspective view showing the bar equipped with a screw of the arrangement according to the invention;

There is a perspective view showing the collar fixed to the bar by bolting in the arrangement according to the invention.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

The idea underlying the invention is to ensure the fixing of a tube to a bar with a collar which encloses the tube without allowing it to slide, but which is secured to the bar with mobility in translation according to the direction longitudinal of the tube.

On the , a tube 11 is fixed to a bar 12 by a fixing device 13 comprising a collar 14 enclosing the tube 11, while being carried by a face 15 of the bar 12 to which it is secured by means of a bolt 16. The tube 11 is here substantially rectilinear at the level of the device 13, and extends in a circumferential direction denoted DC. This circumferential direction extends at a distance from the cylindrical external wall of the casing while being centered on the axis of this cylindrical wall.

This collar 14 is formed of a strip which may be metallic which is folded on itself to constitute a body 17 in the form of a portion of a cylinder which encloses the tube 11, and which has two ends constituting two legs 18 and 19 appearing more clearly on the .

These two legs which are folded against each other each have a hole 21, and the collar 14 is secured to the bar 12 by means of a bolt 16 passing through the holes in the legs and an oblong hole 22 formed in the bar 12. This oblong hole 22 which appears on the extends in the DC direction of the tube. It has a diameter corresponding to the diameter of the holes in the legs, and a length corresponding substantially to the width of the legs along the axis AX.

As visible in Figures 5 and 6, the securing of the collar 14 to the bar 12 is ensured with a bolt 16 comprising a screw 23 engaged in the oblong hole 22 and in the holes of the legs, this screw having its head 24 located at the face of the bar 12 which is opposite to the face carrying the collar 14.

The head 24 rests on the face of the bar 12 via a first washer 26 engaged around this screw 23, this washer 26 being interposed between the head and the face. A second washer 27 is engaged around the screw 23 to rest on the face 15 of the bar 12, so as to be interposed between this face 15 and the tab 19 of the collar 14.

The washers 26 and 27 are anti-friction type washers, that is to say having the lowest possible coefficient of friction with the material of the bar 12, so as to allow easy sliding of these washers on the faces of the bar 12 against which they are applied.

Advantageously, the faces of the bar 12 are themselves covered with an anti-friction coating to further reduce the friction forces when these washers slide on the faces of the bar 12. This anti-friction coating can be provided with a physical deposition process by vapor phase, generally referred to by the acronym PVD (“ Physical Vapor Deposition ”) which is a metallization process allowing thin layers of material to be deposited under vacuum using steam on a surface.

Mounting the collar 14 consists of engaging the screw 23 carrying the first washer 26 in the oblong hole 22, then engaging the second washer 27 around the screw 23 on the face 15, before engaging the tabs 18, 19 around the screw 23, through the holes 21 by placing the tab 19 on the second washer 27, after which a nut 28 can be screwed around the screw 23.

The collar 14 can be attached to the bar 12 already surrounding the tube 11, or the tube 11 can also be engaged in the collar once the collar has been installed on the bar 12.

When the assembly is in place, the nut 28 is tightened, so that the collar 14 encloses the tube 11 so that it cannot slide along the collar in the direction DC.

The tightening torque of the nut 28 is chosen to be not too high so that sliding of the washers on the bar remains possible so that the assembly formed by the collar with the washers and the bolt is movable in the oblong hole, while being high enough for the collar to grip sufficiently to prevent movement of the tube relative to the collar.

The nut 28 is advantageously of the self-locking type, also known as a self-locking nut or locking nut. It is also possible to use instead of nut 28 a nut associated with a lock nut tightened against each other to ensure they are locked on the screw.

Additionally, two Belleville washers can be provided to reduce the forces exerted by the washers 26 and 27 on the faces of the bar 12, so as to facilitate their sliding. These Belleville washers are then interposed respectively between the head 24 and the first washer 26, and between the second washer 27 and the nut 28.

Another possibility is to provide around the screw 23 a ring having a thickness slightly greater than that of the bar 12, interposed between the washers 26 and 27, this ring having an internal diameter corresponding to that of the screw 23 and an external diameter significantly lower than that of the oblong hole 22.

In this configuration, the tightening of the nut 28 makes it possible to firmly grip the collar 14 around the tube 11 without the washers 26 and 27 gripping the bar 12, which ensures that the assembly formed by the collar 14 and the bolt 16 is freely movable in the direction DC while remaining secured to the bar 12.

In operation, when the engine is put into service, the increase in its temperature, and in particular that of the crankcase, results in an increase in the diameter of the crankcase which is hot. As the tubes 11 pass through a flow of cooling air, they undergo a much less significant increase in temperature than the casing.

Given the significant expansion of the casing relative to the tubes, these tubes tend to slide relative to the casing in the circumferential direction. Thanks to the invention, it is each fixing device 13 which slides relative to the bar 12 in the direction DC along the oblong hole 22, while remaining rigidly attached to the tube which it carries.

Under these conditions, differential expansions do not damage the tubes since they do not slide relative to the collars which carry them, because it is only the collars which slide relative to the bars to which they are secured.

Claims (8)

Turbomachine casing, comprising a wall of revolution equipped with tubes (11) for blowing air onto this wall in order to cool it, these tubes (11) being carried by bars (12) equipping the casing while extending parallel to its wall of revolution, each tube (11) being secured to a bar (12) by a fixing device (13), in which at least one fixing device (13) comprises a collar (14) secured to the bar ( 12) by a bolt (16), the collar (14) enclosing a tube (11) being terminated by two legs (18, 19) extending parallel to each other, each leg (18, 19) comprising a hole (21), the bolt (16) passing through the holes of the two legs (18, 19) and a hole (22) of the bar (12), and in which the hole (22) of the bar (12) is an oblong hole extending parallel to the tube (11). Carter according to claim 1, in which the bolt (16) comprises a screw (23) receiving a nut (28) of the self-locking type. Carter according to claim 1 or 2, comprising a first washer (26) surrounding a screw (23) of the bolt (16) while being interposed between a head (24) of this screw (23) and the bar (12), and a second washer (27) surrounding the screw (23) while being interposed between the bar (12) and the tabs (18, 19) of the collar, and in which these washers (26, 27) carry an anti-friction coating. Carter according to one of the preceding claims, in which the bar (12) has faces (15) carrying an anti-friction coating around the oblong hole (22). Casing according to claim 3 or 4, in which the anti-friction coating is deposited with a physical vapor deposition process. Carter according to claim 3, comprising a ring interposed between the two washers (26, 27), this ring having an external diameter corresponding to the diameter of the oblong hole (22), and having a thickness substantially greater than the thickness of the bar ( 12). Carter according to claim 1, in which the oblong hole (22) has a length corresponding to the width of the tabs (18, 19) of the collar (14). Turbomachine comprising a casing according to one of the preceding claims.