Cooling channel inside a wall

CA 02553860 2014-01-30 1 Cooling channel formed in a wall The object of the invention is a method for providing a cooling channel in a wall, an electrode used for the implementation of this method, a wall element in a wall. which is provided with a cooling channel and a hollow turbine engine blade comprising a wall element of this type.

More precisely, the invention relates to a wall element of the type comprising an interior surface and an exterior surface, this exterior surface being capable of being cooled by fresh air circulating in said cooling channel.

In addition, the cooling channel is of the type comprising a bore and a diffusion part, the bore opening on one side on the inner surface of the wall and, on the other side, substantially at the bottom of the diffusion part in forming an orifice, and the diffusion part widening out from this orifice and opening onto the outer surface of the wall.

Document US Pat. No. 6,183,199 Bi shows an example of a hollow blade wall element for a turbojet turbine, through which a cooling channel of the aforementioned type passes.

In this example, the piercing of the channel and the diffusion part are carried out by electroerosion in a single step, using a single electrode, the end of which has a front part of shape corresponding to that of the bore and a rear part of shape corresponding to that of the diffusion part of the channel.

An electrode of this type is described and represented in document US Pat. No. 4,197,443 to which reference is made in document US Pat. No. 6,183,199 Bi.

As can be seen, the shape of this electrode is particularly complex.

In addition, in general, providing a channel by spark erosion according to known methods remains a long and expensive operation.

The object of the invention is therefore to provide an alternative to the known methods, offering the possibility of providing a cooling channel of the aforementioned type, more quickly and at lower cost.

To achieve this aim, the invention relates to a method characterized in that said wall is drilled to produce said hole and in that an imprint is formed in said wall to produce said diffusion part, according to two distinct steps.

CA 02553860 2006-07-25 2 According to the method of the invention, it is therefore possible to use different techniques and materials to carry out the drilling and the diffusion part.

To carry out the drilling, the wall can be drilled by electroerosion or using a laser.

Advantageously, known laser drilling techniques are used, these techniques being much faster and more economical than electroerosion techniques.

Thus, to laser drill a hollow turbine blade wall, only a few tenths of a second are generally necessary.

If it is nevertheless desired to carry out the drilling and the diffusion part by spark erosion, two different electrodes are used for each of these parts.

These electrodes have a simpler shape than the electrodes used heretofore, so they are easier and more economical to manufacture.

For example, to carry out the drilling, one can use a cylindrical electrode.

According to another aspect of the invention, to produce the diffusion part, an electrode is used, characterized in that the end of this electrode has the shape of a cone, the end of which is rounded and the lateral conical surface of which has a flat, the axis of the cone not crossing said flat.

The aforementioned shape of electrode makes it possible, on the one hand, not to create a sharp angle at the bottom of the diffusion part, the sharp angles generally constituting the starting areas of cracks (cracks).

On the other hand, this electrode shape and its dimensions with respect to the bore make it possible to provide a diffusion part of sufficiently wide and flared geometry so that, taking into account the tolerances for making the bore and the diffusion part, whatever or the relative position of the bore with respect to the diffusion part, the latter ensures good diffusion (ie good guidance and good widening) of the air flow leaving the bore.

Another subject of the invention is a wall element in which a new type of cooling channel is provided.

Such a channel can be obtained using the method and the electrode according to the invention.

This channel is characterized in that it comprises a diffusion part with a substantially flat front bottom, inclined in the thickness of the wall, CA 02553860 2006-07-25 3 extending in front of the orifice in the direction of flow of the fresh air, and a border extending to the rear, to the sides and to the front of the orifice, this border joining the sides of the front bottom.

Advantageously, the angle formed between the edge and the front bottom in a plane perpendicular to the front bottom is not "sharp" in the sense that it is strictly greater than 900.

This avoids creating creeks starting areas.

Finally, the subject of the invention is a hollow blade for a gas turbine comprising a wall element of the aforementioned type.

The invention and its advantages will be better understood on reading the following detailed description.

This description refers to the appended figures, in which:

- Figure 1 is a section of an example of a wall element according to the invention comprising a cooling channel;

FIG. 2 is a perspective view of the end of the electrode used to produce the diffusion part of the channel of FIG. 1;

- Figure 3 is a top view of the channel of Figure 1, in direction III orthogonal to the outer surface of the wall;

- Figure 4 is a view of the channel of Figure 1 along direction IV, that is to say along the axis of the bore of the channel;

- Figure 5 is a section along the plane VV of Figure 3.

With reference to FIGS. 1, 3, 4 and 5, we will describe an example of a wall element according to the invention.

Said wall element has an inner surface 3 and an outer surface 5.

This element belongs to a wall 1 of a hollow gas turbine blade, such as a high pressure type turbine blade for a turbojet.

This type of hollow blade comprises an internal cooling passage 4, delimited in part by the internal surface 3, this passage being supplied with fresh air.

The outer surface 5 of the wall IL is, for its part, subjected to the hot gases passing through the turbine and must therefore be cooled.

For this purpose, cooling channels are provided in the wall 1.

At least part of these channels is of the type of channel 6 shown in Figure 1.

This channel 6 is crossed by the fresh air coming from the internal cooling passage 4 of the blade, and delivers this fresh air at the level of the external surface 5 CA 02553860 2006-07-25 4 in order to cool it.

The channel 6 is in two parts: an adjustment part formed by a bore 7 and a diffusion part 9 formed by an indentation made in the wall 1 at the level of the outer surface 5.

This is referred to as an adjustment part, because the minimum section of the hole 7 makes it possible to adjust the air flow through channel 6.

Advantageously, the bore 7 is simple in shape.

In the example shown, the bore 7 fits into a cylinder of revolution.

In addition, the axis B of the bore 7 is inclined at an angle G, relative to the outer surface 5 (or if this surface 5 is not plane, the tangent thereto at the level of the axis B ). The angle G is less than 900 and, preferably, between 15 and 80, in order to fold the air flow F towards the outer surface 5 so that it remains as close as possible to the latter.

In other words, the aim is to make the speed vectors of the air flow F at the outlet of the channel 6 as parallel as possible to the plane of the outer surface 5.

To further reduce the air flow F towards the outer surface 5 and widen this air flow F in the plane of the outer surface 5, the channel 6 has a diffusion part 9 surmounting the bore 7.

This diffusion part 9 flares around the orifice 11, through which the fresh air leaves the bore 7.

This orifice 11 is preferably located substantially at the bottom of the diffusion part 9, relative to the outer surface 5.

The diffusion part 9 comprises, at the front of the orifice, in the direction of flow of the flow F, a substantially planar front base 13, inclined in the thickness of the wall at an angle g with respect to the outer surface 5.

Preferably, the angle g is between 2 and 45 and, in any event, it is less than the angle G so that the air flow F, guided by the front cover 13, is folded towards the outer surface 5.

The front base 13 promotes the approximation of the flow of fresh air F leaving the bore 7, the outer surface 5.

Thus, this air flow remains in contact with the outer surface 5, which makes it possible, on the one hand, to cool the surface 5 by heat exchange and, on the other hand, to create a protective air film on this surface. 5 which keeps the hot gases at a distance from the medium in which the wall 1 is located.

Advantageously, the outline of the front base 13 has the general shape of a triangle, one of the vertices of which is turned towards said orifice 11 (see FIGS. 3 and 4), which makes it possible to widen the flow of air F leaving the hole 7 and therefore CA 02553860 2006-07-25 to cool and protect a larger part of the outer surface 5.

Of course, the base opposite said top is wider than the orifice 11, so as to widen the air flow F.

Behind, on the sides and in front of the hole 11 is a border 5 15.

The border 15 partially encircles the orifice 11 and joins, towards the front, the sides of the front base 13.

In the example of FIG. 5, the junction zones between the edge 15 and the front base 13 have edges 17. The angle P formed at these edges between the edge 15 and the front base 13 itself, in a plane perpendicular to the front base 13, is strictly greater than 900 so as not to weaken the wall element 1. The angle P is measured between the tangent T to the edge 15, at the level of the edge 17, and the front cover 13, as shown in figure 5.

It is also possible to provide a rounding in each junction zone in order to avoid the presence of edges.

In this case the angle P is measured between the general direction of the edge 15 and the front base 13.

In the example of FIG. 1, the rear part of the border 15 widens towards the rear at the level of the orifice 11 then has a lip 12 towards the front at the level of the outer surface 5.

This lip 12 helps guide the flow of cool air forward.

The front base 13 and the edge 15 are part of a cone 23, the end 24 of which is rounded and the conical surface 25 of which has a flat 26.

The front base 13 corresponds with this flat 26, while the edge 15, as shown in Figures 1 and 4, corresponds essentially, in its rear part, with the rounded end 24 of the cone 23 and, in its side and front parts , with the conical surface portions 25 bordering the flat 26.

Advantageously, the axis E of the cone 23 and the axis B of the bore 7 are parallel, the axis B preferably being offset towards the outer surface 5, as shown in FIG. 1.

The shape of the cooling channel 6 of the wall element 1 being well understood, we will now describe an example of a method according to the invention, making it possible to provide a channel of this type.

According to a first step of the process, the wall 1 is pierced with a laser.

Laser drilling techniques are known to those skilled in the art and CA 02553860 2006-07-25 6 ​​have the advantage of being rapid and less expensive than electroerosion techniques.

Then, in a second step, is formed by electroerosion in the wall 1, at the level of the outer surface 5, the imprint corresponding to the diffusion part 9.

Of course, this second step could be undertaken before the first step.

For this second step, an electrode 20 of the type of that shown in FIG. 2 is used.

The body of the electrode 21 is cylindrical while the end 22 of the electrode has the shape of a cone 23 with the rounded end 24 and the lateral conical surface 25 of which has a flat 26.

This flat 26 extends on one side of the cone 23, from the vicinity of the end 24 to the most flared part of the cone 23 and beyond.

The flat 26 is not crossed by the axis E of the cone 23: it therefore does not intersect the apex of the end 24 of the cone 23.

The cone 23 is symmetrical with respect to a plane of symmetry S perpendicular to the flat 26 and containing the axis E of the cone 23.

The half-angles of flare Y defined between the lateral edges 27 of the flat and the plane S are between 10 and 30 and, preferably, are close to 15.

As shown in Figure 1, the imprint corresponding to the diffusion part 9 is formed by spark erosion, by pushing the end 22 of the electrode 20 into the wall 1 on the side of the outer surface 5, the flat 26 being positioned opposite to this outer surface 5.

Advantageously, during this operation, the axis E of the cone 23 is oriented so that it is parallel to the axis B of the bore 7, these axes preferably being offset so that the axis B is the most close to the wall 1.

It will be noted that the presence and the size of the lip 12 of the edge 15 (ie its forward projection) depend on the radius of curvature retained for the end 24 and on the depth to which the electrode 20 is driven.

In general, when forming the impression, one chooses: the shape of the electrode 21, more particularly, the shape of the cone 23, the radius of curvature of the rounded end 24 and the position of the flat 26 (half - flaring angles Y); the positioning of the electrode, more particularly, the orientation of the axis E of the cone 23 relative to the axis B of the bore 7; and the depth of penetration of the electrode 20 into the wall 1, so as to form the front base 13 at the front of the orifice 11 and, at the rear and on the sides CA 02553860 2006-07-25 7 of the orifice 11, a flared edge 15 which joins the sides of the front base 13, forming two ridges 17.

These edges are not sharp enough not to create areas of weakness (see Figure 5).

The presence of the rear edge 15 makes it possible to produce the diffusion part 9 with a certain tolerance vis-à-vis the bore 7.

This is illustrated in FIG. 4, in which various relative positions of the orifice 11 with respect to the diffusion part 9 have been shown in dotted lines.

As can be seen, in all the cases shown, the orifice 11 opens entirely into the diffusion part 9, at a location such that the flow of fresh air is guided by the diffusion part 9, which guarantees cooling. correct outer surface 5.

Of course, the best diffusion is obtained when the orifice 11 opens out substantially at the bottom of the diffusion part 9, as shown in solid lines.