EP1393857A1 - Holder for a workpiece with a porous coating on its surface, and a method to polish this workpiece - Google Patents

Abstract

The guide device has two guide elements (6) spaced from each other by at least one spacer element (5), and a holder (7) for positioning the workpiece (2) between the two guide elements so that the workpiece can be guided contactlessly in the polishing container (4). Independent claim describes method for polishing especially rotationally asymmetrical workpieces which are guided contactlessly in the polishing container whereby polishing is carried out in a vibration polishing process using polishing elements.

Description

The invention relates to a guide device for guiding a workpiece with a porous surface coating in a polishing container Process for polishing a porous surface layer, as well as the Use of the method for polishing a porous thermal barrier coating one turbine blade and one polished by the process Turbine blade, according to the preamble of the independent claim respective category.

A whole range of different methods are known for polishing surface layers of workpieces, depending on the requirements, material and structure of the surface layer. The purpose of polishing, in addition to simply removing material from the surface, is often to reduce the roughness of the surface. This may be desirable, for example, for purely aesthetic reasons, e.g. to produce glossy surfaces, or may be required due to technical requirements, e.g. to reduce friction coefficients, to minimize the adhesion or inclusion of foreign particles, so that the required porosity of the surface is maintained or To prevent contamination of the surface. In technology, the roughness of the surface of a solid is usually characterized by different roughness measurements, which can be found in the relevant specialist literature. One of these roughness measurements is the so-called "mean roughness value R _a ", which is a measure of the roughness of a surface as a mean deviation of the absolute values of the roughness profile from a mean line within a predeterminable measuring section and, depending on the degree of roughness, is given, for example, in micrometers (µm) becomes.

As already mentioned, different methods are used to reduce the roughness of a surface, depending on the application. For example, turbine blades for aircraft turbines or for land-based gas turbines for generating electrical energy are provided with layers of metallic alloys, in particular with MCrAIY layers, where M stands for a metal such as nickel (Ni), cobalt (Co) or iron (Fe) and CrAlY (chrome, aluminum yttrium), a superalloy known for this and other purposes. These layers can, for example, be applied in a vacuum chamber with a thickness between 50 μm and 250 μm, a surface roughness R _a of approximately 6 μm-12 μm typically being achieved. In addition, it is often necessary to provide the above-mentioned MCrAIY layers with a thermal barrier coating, which the person skilled in the art also frequently refers to as a thermal barrier coating (TBC). Such TBC coatings can be produced, for example, on a zirconium oxide (ZrO ₂ ) basis, in a typical example the thermal insulation layer can be approximately 100 µm to 500 µm, in special cases over 1 mm thick and essentially 92% ZrO ₂ and 8% Contains yttrium oxide Y ₂ O ₃ for stabilization. The grain sizes of the grains that make up the layer can be, for example, between 45 μm and 125 μm, a porosity of the thermal insulation layer typically being between 5% and 20%. Typical values for the roughness of TBC coatings can be found in the range from 9 µm to 16 µm. At this point it should be pointed out that the parameters of the layers mentioned above, as well as their chemical composition in the specific case can of course also differ significantly from the examples cited above.

The surface roughness that the layers after application to the Have workpiece, but are often not acceptable and must can be reduced, for example, by polishing.

In the example of turbine blades of land-based turbines, which is important in practice _, values for the surface roughness R _a of max. 6 µm, but preferably values smaller than 4 µm are required, in particular to prevent increased pollution and to improve the flow dynamics.

With MCrAIY layers or more generally with metallic or metal alloys Surfaces can have the necessary surface roughness with different Procedure can be achieved. They are common, analogous to the classic Sandblasting, abrasive blasting techniques, e.g. with fine corundum, Shot peening or cut-wire peening with hard steel bodies, with stainless Steel bodies or with ceramic blasting bodies. To achieve the highest Surface qualities, i.e. minimal roughness and / or uniform roughness There are various methods of vibropolishing of material surfaces, often referred to as "vibropolishing" in combination with abrasive acting polishing elements are available.

However, only the last ones come to polish most TBC layers Vibropolishing mentioned in question, since this when Treat the surfaces with sufficient care so that in the porous TBC layers damage in the form of micro cracks, flaking of surface areas or similar damage can be avoided.

Two are widely used for vibropolishing Variants of polishing devices for use, namely so-called circular vibrators and trough vibrators. A trough vibrator is one Device essentially comprising a polishing container, the corresponding Contains polishing elements, includes and by suitable facilities in Vibration can be offset. The workpieces to be treated are in the simplest case placed in the polishing container so that the workpieces from the Polishing elements that are tough as a whole under vibration Behave liquid, be polished. Here, slide gate valves be provided that prevent adjacent workpieces in the Touch the polishing container and injure one another, or there may be one external fastening of the workpieces may be provided. Another protection For example, a masking of certain surface areas of the Offer workpiece with covers, especially plastic, so that only partial smoothing of the workpiece is permitted and / or For example, vulnerable edges are protected.

These have devices known from the prior art Disadvantages, especially when polishing rotationally asymmetrical Workpieces and / or workpieces with porous surfaces, such as for example turbine blades with TBC coatings lead to unsatisfactory results.

This allows workpieces clamped externally to be held in a trough vibrator treated, acting on unacceptably high mechanical loads, in the worst case, damage to the workpiece and / or to treating surfaces, especially porous / and or brittle Surfaces. Are the workpieces to be polished in accordance with the state of the art directly in the polishing container of the trough vibrator, that is without external attachment, there is a risk that the workpiece with the walls of the trough vibrator or with any existing ones Slide valves and / or in direct contact with neighboring workpieces can occur, causing damage to the workpiece or sensitive Areas of the surface of the workpiece, especially at edges, not are to be excluded. In particular, there is a risk that for example between the workpiece surface and an adjacent one Boundary wall a distance of less than two polishing elements sets so that between the workpiece surface and an adjacent one Boundary wall of a polishing element is jammed, which is enormous Point loads can lead to the surface of the workpiece.

Damage of the type described above can be caused by suitable Masking of vulnerable surface areas can be reduced. However of course this is only possible for those surface areas that do not need to be polished. On the other hand, this procedure is in practice quite complex, since often more than one surface area of the workpiece must be protected separately with a suitable mask, what with a complex assembly or disassembly of the corresponding parts connected and is therefore not very efficient from an economic point of view. On Another major disadvantage is that in particular rotationally asymmetrical workpieces, such as turbine blades for long-supported applications, the known methods to inadequate Surface roughness and / or in particular to unevenly polished, i.e. to unevenly rough areas on the surface of the workpiece to lead. Because of the asymmetrical mass distribution, for example one Turbine blade, the turbine blade will be in the polishing container between only rotate the polishing elements unevenly and the different oriented surfaces of the turbine blade are used for polishing different polishing pressure applied by the polishing elements, what ultimately causes different areas of the surface to be different Have surface roughness, and on certain surfaces of the Turbine blade a sufficiently high roughness is not attainable at all. The above also applies to the polishing process, in which the workpiece is attached externally. The disadvantages described above occur of course not only when polishing turbine blades on to whom the problem is exemplarily explained, but kick in general, especially with rotationally asymmetrical workpieces Vibropolishing on.

The object of the invention is therefore a different device and a another method for polishing a surface of a workpiece, in particular a porous surface of a rotationally asymmetrical To propose the workpiece.

The objects of the invention solving these objects are through the Features of the independent claim of each category characterized.

The respective dependent claims relate to particular advantageous embodiments of the invention.

The guide device according to the invention for guiding a workpiece with a porous surface coating in a polishing container, in particular of a rotationally asymmetrical workpiece, has two at least one spacer spaced guide elements, and a bracket for positioning the workpiece between the two Guide elements on so that the workpiece in relation to the Polishing container can be guided in the polishing container without contact.

The device according to the invention thus allows a workpiece in particular a workpiece with a porous surface coating, for example in a trough vibrator during a polishing process, without external fasteners for guiding the workpiece can be. Among other things, it can cause mechanical loads in the worst case, damage to the workpiece can be avoided and / or the porous surfaces to be treated. By the guide device according to the invention is avoided that the polishing workpiece with any separating slides and / or can come into direct contact with neighboring workpieces Damage to the workpiece or sensitive areas of the Surface of the workpiece, especially on edges, largely be excluded. In addition, in particular rotationally asymmetrical workpieces such as turbine blades Uniform use of the guide device according to the invention be polished. This is achieved in that even with asymmetrical Mass distribution of the workpiece, such as one Turbine blade, a through the design of the guide device uniform rotation of the workpiece can be achieved during polishing, so the workpiece with a substantially uniform Polishing pressure is applied by the polishing elements, which ultimately leads to this causes different areas of the surface to be approximately the same Have surface roughness and on all surfaces to be polished Turbine blade a sufficiently small roughness can be achieved.

For this purpose, the guide device comprises at least two guide elements, which are spaced apart by at least one spacer element. Furthermore the guide device has a holder for positioning the Workpiece between the guide elements. Here are the Guide elements arranged and designed such that the workpiece with respect to the boundary walls of a polishing container in which the Workpiece, preferably by vibropolishing, is polished without contact in the Polishing container is feasible.

The bracket used to position the workpiece in the Guide device is suitable, in a preferred embodiment include a cover member that allows an area of the surface of the workpiece that is not to be polished. The The cover element is preferably made of a suitable plastic constructed, but can also be made of other materials, depending on the requirements for example made of a metal or a ceramic. It is entirely possible to cover different areas of the workpiece several cover elements are provided, which are not part of the Bracket must be. Expediently, the holder / or the Cover element can be made in two or more parts, so that the workpiece easily mounted in the holder and / or in the cover element can be. The bracket / and or the cover elements preferably by fasteners on one or more Guide elements and / or one or more spacer elements attached. The fasteners can, for example, by elastic Plastic straps, through metal straps, with the help of suitable facilities can be clamped to fix the workpiece, or also for example by screws or any other suitable Fasteners can be realized. The cover element and / or the bracket can of course also be designed in one piece.

In particular, it is the in a special embodiment Guide device according to the invention also possible that several Brackets for positioning the workpiece are provided. So can the workpiece, for example, simultaneously by several brackets, from which one or more each on a guide element and / or are fixed to a spacer between the spacers be positioned appropriately.

The guide elements are preferably ring-shaped or in the form of a Circular disc designed, the guide elements through the Spacer elements arranged and configured in parallel to one another in this way are that the guide device is freely rotatable about a longitudinal axis and the workpiece in the polishing container can be guided so that the workpiece does not come into contact with the boundary walls of the polishing container. The Guide device is preferably arranged in the polishing container in such a way that the longitudinal axis of the guide device around which the guide device is free is rotatable, substantially perpendicular to the direction of the acting Gravity stands, i.e. becomes the longitudinal axis of the guide device preferably arranged in the horizontal direction in the polishing container. Of course, it is also possible to have the guide device in each position any other orientation in the polishing container.

In the inventive method for polishing porous Surface coatings of a workpiece, especially one rotationally asymmetrical workpiece, the workpiece is by means of a Guide device guided in a polishing container, the Guide device two, by at least one spacer spaced guide elements, as well as a bracket for positioning of the workpiece between the two guide elements. The The workpiece is touch-free in relation to the polishing container Polishing container guided.

The polishing of a workpiece is preferred in one Vibration polishing processes, for example by vibropolishing, with the help of Polishing elements performed.

The polishing container, which is known per se in a manner known per se Includes polishing elements by also known devices in Vibration offset, so that that is fixed in a guide device Workpiece, which guide device is suitable in the polishing container is positioned by the disordered movement of the polishing elements behave as a whole viscous liquid, is polished. As Polishing elements can be pyramidal or tetrahedral polishing elements, for example made of steel, corundum or other suitable materials typical dimensions in the range of a few millimeters come. Of course, other sizes or polishing elements can also be used from other materials can be used advantageously.

Through the design of the guide device according to the invention the guide device during the polishing process in a polishing container, also with rotationally asymmetrical workpieces such as turbine blades, preferred Rotational movements around a longitudinal axis, so that an even Roughness of the polished surfaces, especially the polished porous ones Thermal insulation layers (TBC layers) is achieved.

The guide device according to the invention is preferably used for polishing turbine blades with yttrium-stabilized thermal insulation layers based on ZrO ₂ . Such ceramic thermal insulation layers typically comprise 92% ZrO2, 8% Y ₂ O ₃ , the grain sizes in the thermal insulation layer being typically between 45 μm and 125 μm with a porosity of 5% to 20%.

In a preferred embodiment of the invention A method for polishing porous surface layers becomes one rotationally asymmetrical turbine blade in a holder that simultaneously acts as a cover element, fixed. The cover element is preferred executed in two parts, so that the turbine blade in a simple manner Bracket or the cover element can be assembled or disassembled.

The guide device according to the invention and the one according to the invention Methods are used in particular for polishing a porous Thermal insulation layer (TBC layer) of a turbine blade, the turbine blade polished according to the method according to the invention with porous thermal barrier coating a surface roughness of less than 15 µm, especially less than 8 µm, especially less than 4 µm having.

Fig. 1

schematisch eine Führungsvorrichtung mit Halterung und Abdeckelement im Schnitt;

Fig. 2

ein weiteres Ausführungsbeispiel gemäss Fig. 1;

Fig. 3

ein Ausführungsbeispiel einer Führungsvorrichtung gemäss Fig. 1 mit Polierbehälter;

Fig. 4

Turbinenschaufel mit poröser Wärmedämmschicht;

Fig. 5

zerlegbares Abdeckelement mit Turbinenschaufel.

The invention is explained in more detail below with reference to the drawing. Show it:

Fig. 1

schematically a guide device with holder and cover element in section;

Fig. 2

a further embodiment according to FIG. 1;

Fig. 3

an embodiment of a guide device according to Figure 1 with polishing container.

Fig. 4

Turbine blade with porous thermal barrier coating;

Fig. 5

demountable cover element with turbine blade.

Fig. 1 shows a schematic sectional view Guide device according to the invention, which is collectively referred to below is designated by reference numeral 1. The guide device 1 comprises two guide elements 6, which are spaced apart by two spacer element 5 are. Furthermore, the guide device 1 has a holder 7 Positioning a workpiece 2 between the guide elements 6. The guide elements 6 are arranged and designed such that the workpiece 2 in relation to a polishing container 4 not shown in FIG. 1 can be guided in the polishing container 4 without contact. In the illustrated in Fig. 1 In the exemplary embodiment, the holder 7 comprises a cover element 8 allows a portion of the surface 9 of the workpiece 2 to be covered should not be polished. The cover element 8 is preferably made of one suitable plastic, but can also, depending on the requirements be made of other materials. It is quite possible that several cover elements 8 are provided to cover different areas of the Cover workpiece 2 that should not be polished. Like through the line 81 indicated, the cover element 8 is made in two parts and that Workpiece 2 is fixed in the holder 7 by fastening means 82. The Fasteners 82 can, as shown in that shown here Embodiment to be realized by elastic plastic tapes 82. It can of course also other fasteners 82, such as metal strips 82, the clamped with the help of suitable devices for fixing the workpiece 2 can be, or for example screws 82 or any other suitable fasteners 82 are advantageously used. It can the cover element 8 and / or the holder 7 of course also be designed in three parts that can be dismantled or comprise more than three parts. In particular, the cover element 8 and / or the holder 7 can of course also be designed in one piece.

2 shows a further exemplary embodiment according to FIG. 1, at which the bracket 7 for positioning the workpiece 2, the here is exemplified as a turbine blade T between the Guide elements 6 is fixed to a spacer 5. The Cover element 8 is made in one piece in this embodiment and serves here to cover the contact edge of the turbine blade T, wherein in another embodiment, further cover elements 8 can be provided. The bracket 7 is made in several parts and that Workpiece 2, or the turbine blade T, is screwed 82 in the Bracket 7 fixed, of course, other fasteners 82 may be suitable.

In particular, it is possible for several holders 7 to be positioned of the workpiece 2 are provided. For example, the workpiece 2 simultaneously by several brackets 7, each of which one or several on a guide element 6 and / or on one Spacer 5 are fixed between the spacers 5 be positioned.

3 shows a preferred exemplary embodiment of a guide device 1 shown that a rotationally asymmetrical workpiece 2 in one Polishing container 4 leads. The two guide elements 6 are each ring-shaped or in the form of a circular disc, the bracket 7 with the Workpiece 2 is arranged on the guide element 6, which is in the form of a Circular disc is designed. Of course, both can also Guide elements 6 can be designed as circular disks or annular and it is also possible for more than two guide elements 6 are provided. The guide elements 6 are by two spacer elements 5 spaced, possibly in a special embodiment the guide device 1 according to the invention also only one Spacer 5 is provided for spacing the guide elements 6 can be. In particular, for example with heavy workpieces, more than two spacer elements 5 may also be provided. In the case of FIG. 3 illustrated preferred embodiment of an inventive Guide device 1, the two guide elements 6 are parallel arranged to each other and configured that the guide device 1 um a longitudinal axis L, which is perpendicular to the guide elements 6, free is rotatable and the workpiece 2 in the polishing container 4 can be guided so that the Workpiece 2 with boundary walls 41 of the polishing container 4 not in Contact is coming. The guide device 1 is preferably such Polishing container 4 arranged that the longitudinal axis L essentially is perpendicular to the direction of gravity, i.e. the Longitudinal axis L of the guide device 1 is shown in the essentially in the horizontal direction. Of course it is also possible the guide device 1 in any other orientation Position polishing container 4. In the present embodiment 3, the polishing container 4, which contains the polishing elements 10 from Devices not shown vibrated so that the workpiece 2 by the disordered movement of the polishing elements 10, which is a whole behave like a viscous liquid, is polished. Through the The guiding device 1 can be configured in the guiding device 1 Carry out rotary movements around the longitudinal axis L so that a uniform roughness of the polished surfaces, especially the porous ones Surface coating 3 of the workpiece 2 is accessible.

The guide device 1 according to the invention is preferably used in the polishing of a workpiece 2 in the form of a turbine blade T, which turbine blade T can in particular comprise a porous surface coating 3 in the form of a thermal insulation layer 3. 4, a turbine blade T is shown schematically. The turbine blade T comprises a base profile F with base plate P and a blade B, the blade B and base plate P being provided with a porous surface coating 3, in particular with a ceramic thermal insulation layer 3 based on ZrO _{2, the} base profile F not being polished should.

The turbine blade T is used for polishing, as exemplified in FIG. 5 shown, in a holder 7, which also acts as a cover element 8, fixed. The cover member 8 is that shown in FIG. 5 Embodiment executed in two parts, only that half in Fig. 5 of the cover element 8 is shown, which on the guide element 6 by fastener shown 82 is attached. The polishing in FIG. 5 half of the cover element 8 shown by a second half such adds that the foot profile F is covered by the cover element 8 and thus the foot profile F is not polished in the polishing process in the polishing container 4 becomes.

According to the invention, an apparatus and a method for Polishing a porous surface coating more rotationally asymmetrical Workpieces provided, the workpiece being polished in a polishing container without external fasteners. This effectively leads to unacceptably high mechanical loads the workpiece avoided, which in the worst case can damage the Can lead workpiece and / or the surfaces to be treated. In addition, the guide device according to the invention prevents the workpieces to be polished with the boundary walls of the Polishing container, for example a trough vibrator, possibly with existing slide valves. and / or with neighboring workpieces in Make direct contact, causing damage to the workpiece or sensitive areas of the surface of the workpiece, in particular Edges that can be practically excluded. Damage to the previous one described type can additionally in the form of suitable masking minimized by cover elements.

Another essential advantage of the inventive Guide device and the inventive method for polishing of porous surface layers is that in particular at Rotationally asymmetrical workpieces such as turbine blades are sufficient low surface roughness and / or to a large extent even polished surfaces can be produced. Because the Guide device with the workpiece in the polishing container between the Polishing elements can rotate evenly around an axis and thereby the differently oriented surfaces of the turbine blade when polishing with uniform polishing pressure is applied by the polishing elements, the previously highlighted high quality of the polished surfaces is achieved.

Claims (10)

Guide device for guiding a workpiece (2) with a porous surface coating (3) in a polishing container (4), in particular a rotationally asymmetrical workpiece (2), characterized in that the guide device has two guide elements (6) spaced apart by at least one spacer element (5). , as well as a holder (7) for positioning the workpiece (2) between the two guide elements (6), so that the workpiece (2) can be guided in the polishing container (4) without contact with respect to the polishing container (4). Guide device according to claim 1, wherein the guide elements (6) annular and / or in the form of a circular disc and parallel are arranged to each other. Guide device according to claim 1 or 2, wherein a cover member (8) for covering a surface area (9) of the workpiece (2) is provided. Guide device according to claim 3, wherein the holder (7) and / or the cover element (8) is designed to be dismantled in several parts. Method for polishing porous surface layers (3) of a workpiece (2), in particular a rotationally asymmetrical workpiece (2), in which method the workpiece (2) is guided in a polishing container (4) by means of a guide device, the guide device having two, by at least a spacer element (5) spaced guide elements (6), and a holder (7) for positioning the workpiece (2) between the two guide elements (6), characterized in that the workpiece (2) in relation to the polishing container (4) is guided in the polishing container (4) without contact. The method of claim 5, wherein the polishing in one Vibration polishing process carried out with the help of polishing elements (10) becomes. A method according to claim 5 or 6, wherein the porous surface layer (3) is a porous thermal insulation layer (3), in particular a ceramic thermal insulation layer (3) based on ZrO ₂ . Use of a guide device according to one of claims 1 to 4 or a method according to any one of claims 5 to 7 for Polishing a porous thermal barrier coating (3) of a turbine blade (T). Turbine blade (T) with a porous thermal barrier coating (3), polished according to a method according to one of claims 5 to 7. The turbine blade (T) according to claim 9, which turbine blade (T) is one Surface roughness of less than 15 µm, especially less than 8 µm, especially less than 4 µm.

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