Blade for a gas turbine

1. A blade, for a gas turbine, comprising a blade airfoil, having a shroud segment arranged on its upper end, the shroud segment together with shroud segments of other blades of a blade row forming an annular shroud which delimits hot gas passage of the gas turbine, and said shroud segment, on sides on which it adjoins adjacent shroud segments of the annular shroud, is provided with upwardly projecting side rails which extend along a side edge, to improve sealing to the hot gas passage, wherein the side rails comprise rail-parallel or essentially rail-parallel, upwardly open slots through which cooling air, which is introduced via the shroud segment from an interior of the blade airfoil, discharges into the space above the shroud segment.

2. The blade as claimed in claim 1 , wherein an arrangement is made on an upper side of the shroud segment for a plurality of cooling tubes, extending transversely to the side rails, the cooling tubes extend from a center piece arranged between the side rails and from there are impinged upon with cooling air, and which terminate in the side rails and are in communication with the slots in said side rails.

3. The blade as claimed in claim 2 , wherein the center piece is arranged in a middle between the side rails.

4. The blade as claimed in claim 3 , wherein the cooling tubes extend parallel or essentially parallel to each other, and the center piece extends essentially parallel or virtually parallel to the side rails.

5. The blade as claimed in claim 4 , wherein the cooling tubes extend in a circumferential direction of the shroud.

6. The blade as claimed in claim 4 , wherein the cooling tubes extend obliquely to a circumferential direction of the shroud.

7. The blade as claimed in claim 2 , wherein the center piece is arranged in an offset manner to a middle between the side rails.

8. The blade as claimed in claim 7 , wherein the cooling tubes extend parallel or essentially parallel to each other, and the center piece extends essentially parallel or virtually parallel to the side rails.

9. The blade as claimed in claim 8 , wherein the cooling tubes extend in a circumferential direction of the shroud.

10. The blade as claimed in claim 8 , wherein the cooling tubes extend obliquely to a circumferential direction of the shroud.

11. The blade as claimed in claim 2 , wherein the cooling tubes each have a cooling hole configured to convectively cool the shroud segment.

12. The blade as claimed in claim 2 , wherein the cooling tubes are formed on the shroud segment.

13. The blade as claimed in claim 2 , wherein cooling tubes of blades of adjoining shroud segments are arranged in a staggered manner.

14. The blade as claimed in claim 1 , wherein the shroud segment is delimited in the axial direction by circumferentially extending wall segments, and the cooling air which discharges from the slots is fed via cooling holes in a region of the wall segments and of the side rails.

15. The blade as claimed in claim 1 , wherein the shroud segment is delimited in an axial or essentially axial direction by circumferentially extending wall segments, and comprises an intermediate wall segment which is arranged in a middle between the wall segments, parallel or virtually parallel to said wall segments, and wherein the side rails, between the intermediate wall segment and the wall segments each comprise a slot.

16. The blade as claimed in claim 15 , wherein the slots of a side rail are interconnected by a cooling hole which extends in the side rail.

17. The blade as claimed in claim 1 , wherein film cooling holes project from the cooling holes which supply the slots and on the underside of the shroud segment open into the hot gas passage.