Brushing – scrubbing – and general cleaning – Submerged cleaners with ambient flow guides
Reexamination Certificate
2003-05-28
2004-11-16
McNeil, Jennifer (Department: 1775)
Brushing, scrubbing, and general cleaning
Submerged cleaners with ambient flow guides
C015S003150, C451S066000, C451S106000
Reexamination Certificate
active
06817051
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a guide apparatus for the guiding of a workpiece having a porous surface coating in a polishing container, to a method for the polishing of a porous surface layer as well as to the use of the method for the polishing of a porous heat insulating layer of a turbine vane and to a turbine vane polished in accordance with the method of the invention.
A whole series of different processes are known for the polishing of surface layers of workpieces, depending on the application, material and structure of the surface layer. The purpose of the polishing frequently consists of reducing the roughness of the surface in addition to a pure removal of material at the surfaces. This can be desired, for example, for purely aesthetic reasons, for instance to produce glossy surfaces, or it can be required due to technical demands, for example to reduce coefficients of friction, to minimize the adhesion or inclusion of foreign particles such that a required porosity of the surface is maintained, or to prevent soiling of the surface. In the art, as a rule, the roughness of the surface of a solid is characterized by different roughness measuring parameters which can be found in the corresponding technical literature. One of these roughness measuring parameters is the so-called “average roughness value R
a
” which, as the mean deviation of the absolute amounts of the roughness profile from a central line within a pre-settable measuring path, is a measure for the roughness of a surface and which is given, in dependence on the degree of the roughness, in micrometers (&mgr;m) for example.
As already mentioned, different methods are used, depending on the application, for the reduction of the roughness of a surface. For instance, turbine vanes for airplane turbines or for land-based gas turbines for the generation of electrical energy are provided, for example, with layers of metallic alloys, in particular with MCrAlY layers, with M standing for a metal such as nickel (Ni), cobalt (Co) or iron (Fe) and CrAlY (chromium, aluminum, yttrium) designating a super alloy very familiar for this and other purposes. These layers can, for example, be applied in a vacuum chamber in a thickness between 50 &mgr;m and 250 &mgr;m, with a surface roughness R
a
typically being achieved of approximately 6 &mgr;m-12 &mgr;m. Furthermore, it is frequently necessary to provide the aforesaid MCrAlY layers with a heat insulating layer which the person skilled in the art also frequently calls a TBC coating (thermal barrier coating). Such TBC coatings can be manufactured, for example, on a zirconia (ZrO
2
) basis, with—in a typical example—the heat insulating layer being able to be approximately 100 &mgr;m up to 500 &mgr;m thick, in special cases more than 1 mm and substantially including 92% ZrO
2
and 8% yttrium oxide Y
2
O
3
for stabilization. The grain sizes of the grains making up the layer can lie, for example, between 45 &mgr;m and 125 &mgr;m, with a porosity of the heat insulating layer being typically reached at between 5% and 20%. Typical values for the roughness of TBC coatings are found in the range from 9 &mgr;m up to 16 &mgr;m. It should be pointed out at this point that the aforesaid parameters of the layers, as well as their chemical composition, can differ considerably from the previously cited examples in a specific case.
The surface roughnesses which the layers show after the application to the workpiece are, however, frequently not acceptable and must be reduced, for example, by polishing.
In the example important for practice of turbine vanes for land-based turbines, values are required for the surface roughness R
a
of max. 6 &mgr;m, preferably, however, less than 4 &mgr;m, in particular in order to prevent increased soiling and to improve flow dynamics.
With MCrAlY layers, or generally with metallic or metal alloy surfaces, the required surface roughness can be achieved using different methods, with—analogous to classical sandblasting—abrasive blasting techniques, for example with fine corundum, shot peening or cut-wire peening with hard steel bodies, with rust-free steel bodies or with ceramic blasting bodies, being customary. To achieve the highest possible surface qualities, i.e. minimum roughness and/or uniform roughness of material surfaces, various methods are available for vibropolishing in combination with polishing elements with an abrasive action.
However, only the last mentioned methods of vibropolishing are used for the polishing of most TBC layers, since they treat the surfaces sufficiently gently in the polishing process such that damage in the form of micro-tears, peeling of surface regions or similar damage in the porous TBC coatings can be avoided.
Two variants of polishing apparatuses are widely used for the carrying out of the vibropolishing, namely so-called round vibrators and tray vibrators. A tray vibrator is an apparatus which substantially includes a polishing container, which includes corresponding polishing elements and which can be set into vibration by suitable devices. The workpieces to be treated are, in the simplest case, placed into the polishing container such that the workpieces are polished by the polishing elements which behave overall under vibration in an analogous manner to a viscid liquid. Partitioning slides can be provided which prevent adjacent workpieces from touching or damaging one another in the polishing container and an external attaching of the workpieces can also be provided. A masking of specific surface regions of the workpiece with covers, in particular made of plastic, can also provide a further protection such that only a partial smoothing of the workpiece is allowed and/or, for example, endangered edges are protected.
These apparatuses known from the prior art have disadvantages which result in unsatisfactory results in particular in the polishing of rotationally asymmetrical workpieces and/or of workpieces having porous surfaces such as turbine vanes with TBC coatings.
For instance, unacceptably high mechanical strains can act on externally clamped workpieces treated in a tray vibrator which, in the worst case, can result in damage to the workpiece and/or to the surfaces to be treated, in particular to porous and/or brittle surfaces. If the workpieces to be polished are placed directly into the polishing container of the tray vibrator in accordance with the prior art, that is, without an external fastening, the risk exists that the workpiece can come into direct contact with the walls of the tray vibrator or with any possibly present partitioning slides and/or with adjacent workpieces, whereby damage to the workpiece or to sensitive regions of the surface of the workpiece, in particular at edges, cannot be precluded. The risk in particular exists that, for example, a distance of less than two polishing elements is adopted between the workpiece surface and an adjacent bounding wall such that a polishing element is jammed between the workpiece surface and an adjacent bounding wall, which can result in enormous point strains on the surface of the workpiece.
Damage of the previously described kind can admittedly be reduced by suitable masking of endangered surface regions. However, this is only possible for those surface regions which do not have to be polished. In addition, this method is very complex in practice since frequently more than one surface region has to be protected separately in each case by a suitable masking, which is associated with a complex installation or removal of the corresponding parts and is thus less efficient from an economic viewpoint. A further substantial disadvantage is the fact that, in particular with rotationally asymmetrical workpieces such as turbine vanes for land-based applications, the known methods result in insufficient surface roughnesses and/or in particular in non-uniformly polished regions, i.e. regions with non-uniform roughness on the surface of the workpiece. Due to the asymmetrical mass distribution, for example of a turbine vane, the turbine vane wil
McNeil Jennifer
Sulzer Metco AG
Townsend and Townsend / and Crew LLP
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