Coating processes – Restoring or repairing – Metal article
Reexamination Certificate
1999-12-17
2001-12-25
Beck, Shrive P. (Department: 1762)
Coating processes
Restoring or repairing
Metal article
C427S140000, C427S156000, C427S235000, C427S239000, C427S287000, C427S300000
Reexamination Certificate
active
06333069
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the field of technology of thermal machines, in particular gas turbines and/or burners, having walls of gas-cooled parts through which the cooling holes extend and which are covered on their outside with a protective coating.
BACKGROUND OF THE INVENTION
The coating of thermally stressed parts of gas turbines or burners equipped for the cooling of their walls with cooling holes for the air or gas cooling usually cannot be renewed easily by using overlay coating and/or thermal barrier coating, TBC, because the cooling holes are at least partially closed or constricted by the repeat coating, so that the cooling effect is changed and/or adversely affected. This is true, in particular, if the cooling holes have been provided in the wall after the original coating.
Several solutions have been described for preventing harm from constrictions formed when coating parts provided with cooling holes. In one type of solution, measures are taken to prevent the constrictions from even forming. To accomplish this, the cooling holes are closed or filled prior to the coating. The filling of the cooling holes prevents coating material from penetrating into the holes. After the coating process is complete, the filling is again removed from the cooling holes, and the cooling holes are available with their original through-cross-section. Such techniques are known, for example, from U.S. Pat. No. 4,743,462 and U.S. Pat. No. 5,800,695.
In another proposed solution, the cooling holes are left open, and the constrictions formed in the holes during coating are removed after the coating, by using a pluse UV laser beam as is known from U.S. Pat. No. 5,216,808. It would also be conceivable, however, to remove the constrictions by pressing a grinding fluid through the cooling holes (U.S. Pat. No. 5,702,288) that abrades the constrictions in this manner.
The disadvantage of this method is that the individual cooling holes must be carefully closed and then again exposed or freed from the constriction again carefully so that the originally intended cooling effect is fully preserved at all places on the cooled part, and no local overheating occurs as a result of insufficiently removed constrictions. In parts equipped with a large number of finely distributed cooling holes, this creates significant work during the processing.
SUMMARY OF THE INVENTION
It is therefore the objective of the invention to provide a method in which the through-cross-section of the individual cooling holes can, in a simple manner and without intensive filling or abrasion steps, practically be held constant during the repeat coating of the parts. This objective is accomplished by permitting constrictions of the cooling holes to be formed during the repeat coating. The constant through-cross-section of the cooling holes is achieved by using cooling holes with a larger through-cross-section than needed, and the desired through-cross-section is adjusted with an artificial constriction. If the cooling holes later are constricted during the re-coating due to a deposit of the coating material, the artificial constriction is removed. Since the artificial constriction is chosen so that it corresponds to the constriction forming during the re-coating, the through-cross-section of the cooling holes also is maintained after the re-coating.
A preferred embodiment of the method according to the invention is characterized in that the first means include first inserts that rest in a covering manner against the insides of the walls and are provided with first openings, each of which is associated with the individual cooling holes and which constrict these cooling holes. Such prefabricated inserts make it possible to simultaneously and evenly constrict all cooling holes in a simple manner.
In a preferred further development of this embodiment, the first inserts are taken away after the overhaul without any substitutions. This makes it especially simple to remove the artificial constrictions.
If, however, the inserts have a permanent function in the part, it is, according to another further development of the embodiment, advantageous to replace the first inserts after the overhaul with second inserts that have second openings that are larger than those of the first inserts.
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patent: 4743462 (1988-05-01), Radzavich et al.
patent: 5216808 (1993-06-01), Martus et al.
patent: 5441767 (1995-08-01), DeSaulniers
patent: 5702288 (1997-12-01), Liebke et al.
patent: 5800695 (1998-09-01), Kang et al.
patent: 5902647 (1999-05-01), Venkataramani et al.
patent: 6004620 (1999-12-01), Camm
patent: 6042879 (2000-03-01), Draghi et al.
patent: 0 807 744 (1997-11-01), None
Alstom (Switzerland Ltd
Beck Shrive P.
Burns Doane Swecker & Mathis L.L.P.
Kolb Jennifer
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