EP1612299B1 - Method and apparatus for surface treatment of a component - Google Patents

Abstract

Process for removing a coating containing a chromium and/or chromium oxide compound from a component comprises placing the coated component in a coating-removal bath to which is added an alkanol-amine compound as inhibitor and removing after a treatment time.

Description

The invention relates to a method for the surface treatment of a component according to the preamble of claim 1 and to an apparatus for carrying out a method for the surface treatment of a component.

Operationally stressed components, such as turbine blades of gas turbines are subjected to an electrolyte treatment, so that the component can then be worked up again.
In the case of gas turbine blades, the operationally stressed MCrAlX layers on the component are removed by immersing them in approximately 50 ° -80 ° C warm 20% hydrochloric acid. After a period of time derived from empirical values, the blades are removed from the acid bath, rinsed with water and then blasted abrasive. The process sequence electrolyte bath and blasting is repeated several times until the entire MCrAlX layer is dissolved or dissolved. The repetition of the individual process steps is usually necessary, since the electrolyte only dissolves near-surface aluminum-containing phases of the MCrAlX layer. Deeper areas of the MCrAlX layer can therefore not be resolved in one step. On the surface remains a porous layer matrix, which is subsequently removed mechanically by means of irradiation, for example.
The time that the blades remain in the electrolyte does not reflect the actual time required for the individual blade to stop the dissolution process, but is defaults to a certain time. The residence time in the electrolyte is determined based on general experience.

However, each component is subjected to different individual stresses, so that a fixed time specification leads to different or incomplete dissolution of the claimed surface of the component. In many cases, the components remain in the acid bath without any further progress of the stripping until the end of the predetermined period of time.

The EP 1 094 134 A1 as well as the US 2003/0062271 A1 disclose methods for electrochemically removing layers.

The US 4,539,087 discloses a method in which the current of an electrolytic process is measured, so that it can be decided on the basis of the current profile, when the process is to be discontinued.

It is therefore an object of the invention to provide a method that allows an individual specification of the minimum treatment time required per individual component (type, coating thickness, state after operating stress, etc.).

The object is achieved by a method for surface treatment of a component according to claim 1.

Another object of the invention is to provide a device that allows an individual determination of the minimum treatment time required per individual component.

The object is achieved by a device for surface treatment of a component according to claim 27.

In the dependent claims further advantageous measures are listed, which can be combined with each other in an advantageous manner.

Figur 1

eine Vorrichtung, um das erfindungsgemäße Verfahren durchzuführen,

Figur 2, 3, 4

einen zeitlichen Spannungsverlauf,

Figur 5, 6

zeitliche Verläufe von Spannungen und Strom, die sich bei der Durchführung des erfindungsgemäßen Verfahrens ergeben,

Figur 7

eine Turbinenschaufel,

Figur 8

eine Brennkammer und

Figur 9

eine Gasturbine.

Show it

FIG. 1

an apparatus for carrying out the method according to the invention,

FIGS. 2, 3, 4

a temporal voltage curve,

FIG. 5, 6

temporal courses of voltages and current, which result in the implementation of the method according to the invention,

FIG. 7

a turbine blade,

FIG. 8

a combustion chamber and

FIG. 9

a gas turbine.

FIG. 1 shows an exemplary device 1 according to the invention, with which the inventive method can be performed.

The device 1 consists of a container 3, for example metallic, ceramic or plastic (Teflon polymer, etc.), in which a treatment agent 6, for example an acid 6 or an electrolyte 6 (with coating material) is arranged, for surface treatment such as stripping or coating at least one component 9 is used.
During stripping, an acid or an acid mixture is preferably present in the container 3.
By contrast, during coating, the electrolyte 6 has the corresponding chemical elements for the coating.
In the treatment agent 6, for example, a single component 9 is arranged here, for example, whose surface area is to be dissolved. This happens, for example, due to the acid attack on the surface of the component 9 which is subject to operating conditions, for example.

If two or more components 9 are to be stripped, for example, both components 9 each form an electrode (ie anode and cathode), wherein as a treatment agent 6, a nitrogen-containing treatment agent 6 should be used.

According to the invention, there is at least one voltage / current source 18, which is electrically connected to the component 9 and another electrode 12 via electrical connection means 15. A first electric circuit can be closed by connecting the connecting means 15 to a further electrical pole, ie the electrode 12, which is arranged in the treatment agent 6 or to the container 3, so that a current I between the component 9 and the pole 3 12, which can also be measured. The current flows through the component 9 through the claimed surface of the component 9 and through the treatment agent 6 to the electrode 12 (or to the container 3).
A plurality of components 9 for stripping can also be arranged in a container 3, wherein a current curve I (t) can be determined individually for each component 9, so that the components 9 possibly remain in the treatment agent 6 for different lengths of time.

Another second circuit with lines 15 'and current / voltage source 18', for example for a measuring voltage 33 (FIG. Fig. 2 ) may also be present according to the invention, so that there also flows a current that can also be measured.
The lines 15 'are then also connected to the component 9 and the electrode 12.

The FIG. 2 shows an exemplary voltage profile according to the invention.

For the stripping of a large component 9, a pulsed treatment voltage 30 with a pulse duration t _{30 is} applied, which is, for example, correspondingly large Components 9 (38 cm in length) such as gas turbine blades 120, 130 ( Fig. 7 . 9 ) Generates currents up to 100 A.
The pulse duration t ₃₀ can always be the same or change with time t. Likewise, the amount of treatment voltage may change with time t.

However, these currents are too large for more accurate information (cooling times, for example, too long) to be obtained from the transition behavior of the current profile via the progress of the surface treatment.

Therefore, according to the invention, a smaller, for example, pulsed measuring voltage 33 (1 mV to 50 mV) is superimposed on the larger treatment voltage 30 (for stripping) in the circuit 18, 15, 9, 6, 12) or the treatment voltage 30 becomes short (ie at least temporarily) by the height the measuring voltage 33 increases.

The pulse duration t _{33 of} the measurement voltage 33 may be smaller, equal to or greater than the pulse duration t _{30 of} the treatment voltage 30.

When the pulse duration t _{33 of} the measurement voltage 33 is smaller than the pulse duration t _{30 of} the treatment voltage 30, the measurement voltage 33 may be applied at the beginning, middle or end of the pulsed treatment voltage 33.

The smaller measuring voltage 33 produces much smaller currents that are easier to measure.

The separation of the signals of treatment voltage 30 and measurement voltage 33 is effected, for example, by an analysis of the current curve by means of mathematical signal separation methods, such as e.g. the Fourier analysis.

According to the treatment voltage 30 for stripping and the measuring voltage 33, for example, three electrodes (another electrode 12 'for a second circuit ( Fig. 1 ) with lines 15 'and current / voltage source 18' for a measuring voltage 33 may also be present according to the invention; the leads 15 'are then also used with the component 9 and, for example, with the electrode 12' (indicated by dashed lines) and not connected to the electrode 12), the stresses being superimposed on the large surface. The metrological separation of the current signals, for example, by two partially decoupled circuits (15 + 18 + 9 + 6 + 12, 15 '+ 18' + 9 + 6 + 12 or +12 ').

The contribution of the smaller measuring voltage 33 to the electrolytic stripping is low or negligible.

Likewise, with pulsed treatment voltage 30, a DC measurement voltage 33 "(indicated by dashed lines) can be used.

FIG. 3 shows a further exemplary inventive voltage profile of the method according to the invention.

Here, too, a high pulsed treatment voltage 30 is used for stripping, which generates very high currents.

The measuring voltage 33 is also pulsed here, for example, and is applied during the pulse pauses 36 (t ₃₆ ) of the treatment voltage pulses 30 (t ₃₆ > t ₃₃ ). This is done by the synchronization of the voltage pulses 30, 33.

FIG. 4 shows further exemplary voltage curves.

Here is a constant high treatment voltage 30 (DC voltage) to the component 9 for electrolytic Stripping applied, the measuring voltage 33 is pulsed again and the treatment voltage 30 is superimposed.

In this case, the treatment voltage 30 (corresponding to a pulse-like increase) can be increased by the height of the measuring voltage 33, wherein only one circuit is necessary, or the measuring voltage 33 '(indicated by dashed lines) is superimposed on the treatment voltage, for example by a second circuit.

Likewise, a smaller DC measurement voltage 33 "can be used, in particular in a second circuit 18 ', 15', 9, 6, 12 or 12 '.
The pulse durations t ₃₃ , t ₃₀ may be the same or different (t ₃₀ = t ₃₃ , t ₃₃ <t ₃₀ , t ₃₃ > t ₃₀ , t ₃₀ = t ₃₃ and t ₃₆ > t ₃₀ , etc.).

A time characteristic of the current I (t) caused by the measuring voltage during electrolysis for stripping is FIG. 5 shown.
The current I (t) increases at the beginning with the time t and is initially substantially constant after a certain time. The stripping has not yet been completed, ie the stripping rate is still high.
After a certain time t, the current I decreases. The decrease (range or point 27 in the curve I (t)) of the current I indicates that only a small amount of layer material is dissolved. The dissolution process can therefore be stopped if, for example, a predetermined comparison value for the current intensity is reached or the current intensity decreases by a certain value (see difference measuring points 27, 22) or a trend line results in a decreasing profile for the current intensity.
This applies analogously to the coating processes when the electrolyte 6 is consumed or the coating thickness is determined from the area under the curve I (t).

The method can also be carried out in substeps. Here, in each case an intermediate process step, an abrasive stripping is carried out, which removes residues of acid products and / or accelerates stripping, since after a certain period of residence of the component 9 in the treatment agent 6, for example, a brittle layer has formed which is better abrasive can be removed.

Likewise, a washing (rinsing) of the component 9 can be carried out in a process intermediate step.
Thereafter, the component 9 is again placed in the treatment agent 6.
The process steps treatment of the component 9 in the treatment agent 6, abrasive irradiation can be repeated as desired.
The delamination of the component or components 9 also runs without the presence of a treatment voltage, ie there is then no electrolytic stripping process.

The FIG. 6 shows an experimentally mediated course of the measured or used currents and voltages.

To a turbine blade (length ≈ 18 cm, surface ≈ 150 cm ² ) is applied a constant treatment voltage 30 of 1.2V, being used as the electrolyte, for example, 5% HCl (hydrochloric acid) with 2% triethanolamine. The treatment voltage 30 is represented by the rhombus and generates a current I of 10 to 11 A (not shown).

The pulsed measuring voltage 33 for determining the end point here is for example 50 mV and is applied by pulses with a pulse length of, for example, 0.5 s. The ratio measuring voltage 33 to the treatment voltage 30 is therefore 1:24 and is, for example, 1:10 (or 1:20, 1:30 or more than 1:50, 1: 100).

The measuring voltage 33 is indicated by squares in the FIG. 6 shown. The current I, which is measured on the basis of the measuring voltage 33, is indicated by the triangles in FIG FIG. 6 shown. A dividing line (indicated by dashed lines) shows the intrapolated and expected time course of the current. This curve corresponds to the one in FIG. 2 ,

The time course 24 of the current I (t) can also be determined from individual measuring points 21, which are determined at regular or irregular intervals.

The components of the following description of figures which have been stripped off in this way can be coated again as explained in the following description of the figures.

FIG. 7 shows a perspective view of a blade 120, 130 which extends along a longitudinal axis 121.

The blade as an example of the component 9 may be a blade 120 or guide blade 130 of a turbomachine. The turbomachine may be a gas turbine of an aircraft or a power plant for power generation, a steam turbine or a compressor.

The blade 120, 130 has along the longitudinal axis 121 consecutively a fastening region 400, a blade platform 403 adjoining thereto and an airfoil 406.
As a guide blade 130, the blade at its blade tip 415 may have another platform (not shown).

In the mounting region 400, a blade root 183 is formed, which serves for attachment of the blades 120, 130 to a shaft or a disc (not shown).
The blade root 183 is designed, for example, as a hammer head. Other designs as Christmas tree or Schwalbenschwanzfuß are possible.
The blade 120, 130 has a leading edge 409 and a trailing edge 412 for a medium flowing past the airfoil 406.

In conventional blades 120, 130, massive metallic materials are used in all regions 400, 403, 406 of the blade 120, 130, for example.
The blade 120, 130 can be made by a casting process, also by directional solidification, by a forging process, by a milling process or combinations thereof.

Workpieces with a monocrystalline structure or structures are used as components for machines which are exposed to high mechanical, thermal and / or chemical stresses during operation.
The production of such monocrystalline workpieces, for example, by directed solidification from the melt. These are casting methods in which the liquid metallic alloy solidifies into a monocrystalline structure, ie a single-crystal workpiece, or directionally.
Here, dendritic crystals are aligned along the heat flow and form either a columnar grain structure (columnar, ie grains that run the entire length of the workpiece and here, in common parlance, referred to as directionally solidified) or a monocrystalline structure, ie the whole Workpiece consists of a single crystal. In these processes, one must avoid the transition to globulitic (polycrystalline) solidification, since non-directional growth necessarily produces transverse and longitudinal grain boundaries, which negate the good properties of the directionally solidified or monocrystalline component.

The term generally refers to directionally solidified microstructures, which means both single crystals that have no grain boundaries or at most small angle grain boundaries, and stem crystal structures that have probably longitudinal grain boundaries but no transverse grain boundaries. These second-mentioned crystalline structures are also known as directionally solidified structures.

Such methods are known from U.S. Patent 6,024,792 and the EP 0 892 090 A1 known.

Refurbishment means that, after use, components 120, 130 may have to be freed from protective layers by the method according to the invention (for example by sandblasting). This is followed by removal of the corrosion and / or oxidation layers or products. Optionally, even cracks in the component 120, 130 are repaired. Thereafter, a re-coating of the component 120, 130 takes place, for example, by the method according to the invention and a renewed use of the component 120, 130.

The blade 120, 130 may be hollow or solid. When the blade 120, 130 is to be cooled, it is hollow and may still have film cooling holes (not shown). As protection against corrosion, the blade 120, 130, for example, corresponding mostly metallic coatings and as protection against heat usually still a ceramic coating.

The FIG. 8 shows a combustion chamber 110 of a gas turbine.
The combustion chamber 110 is configured, for example, as a so-called annular combustion chamber, in which a plurality of burners 102 arranged around the turbine shaft 103 in the circumferential direction open into a common combustion chamber space. For this purpose, the combustion chamber 110 is configured in its entirety as an annular structure, which is positioned around the turbine shaft 103 around.

To achieve a comparatively high efficiency, the combustion chamber 110 is designed for a comparatively high temperature of the working medium M of about 1000 ° C to 1600 ° C. In order to enable a comparatively long service life for these operating parameters, which are unfavorable for the materials, the combustion chamber wall 153 is provided on its side facing the working medium M with an inner lining formed of heat shield elements 155 (further example for component 9). Each heat shield element 155 is equipped on the working medium side with a particularly heat-resistant protective layer or made of high-temperature-resistant material. Due to the high temperatures in the interior of the combustion chamber 110, a cooling system is additionally provided for the heat shield elements 155 or for their holding elements.

The materials of the combustion chamber wall and its coatings may be similar to the turbine blades.

The FIG. 9 shows by way of example a gas turbine 100 in a longitudinal partial section.
The gas turbine 100 has inside a rotatably mounted about a rotation axis 102 rotor 103, which is also referred to as a turbine runner.
Along the rotor 103 follow one another an intake housing 104, a compressor 105, for example, a toroidal combustion chamber 110, in particular annular combustion chamber 106, with a plurality of coaxially arranged burners 107, a turbine 108, and the exhaust case 109.
The annular combustion chamber 106 communicates with an annular annular hot gas channel 111, for example. There, for example, four turbine stages 112 connected in series form the turbine 108.
Each turbine stage 112 is formed, for example, from two blade rings. As seen in the direction of flow of a working medium 113, in the hot gas channel 111 of a row of guide vanes 115, a series 125 formed of rotor blades 120 follows.

The guide vanes 130 are fastened to an inner housing 138 of a stator 143, whereas the moving blades 120 of a row 125 are attached to the rotor 103 by means of a turbine disk 133, for example.
Coupled to the rotor 103 is a generator or work machine (not shown).

During operation of the gas turbine 100, air 105 is sucked in and compressed by the compressor 105 through the intake housing 104. The compressed air provided at the turbine-side end of the compressor 105 is supplied to the burners 107 where it is mixed with a fuel. The mixture is then burned to form the working fluid 113 in the combustion chamber 110. From there, the working medium 113 flows along the hot gas channel 111 past the guide vanes 130 and the rotor blades 120. On the rotor blades 120, the working medium 113 expands in a pulse-transmitting manner so that the rotor blades 120 drive the rotor 103 and drive the machine coupled to it.

The components exposed to the hot working medium 113 are subject to thermal loads during operation of the gas turbine 100. The guide vanes 130 and blades 120 of the first turbine stage 112 seen in the flow direction of the working medium 113 are in addition to the Ring combustion chamber 106 lining heat shield bricks most thermally stressed.
To withstand the prevailing temperatures, they can be cooled by means of a coolant.
Likewise, substrates of the components can have a directional structure, ie they are monocrystalline (SX structure) or have only longitudinal grains (DS structure).
As the material for the components, in particular for the turbine blade 120, 130 and components of the combustion chamber 110, for example, iron-, nickel- or cobalt-based superalloys are used.
Such superalloys are, for example, from the EP 1204776 . EP 1306454 . EP 1319729 . WO 99/67435 or WO 00/44949 known.

Likewise, blades 120, 130 may be anti-corrosion coatings (MCrA1X; M is at least one element of the group iron (Fe), cobalt (Co), nickel (Ni), X is an active element and is yttrium (Y) and / or silicon and / or at least one element of the rare earths) and heat through a thermal barrier coating.
The thermal barrier coating consists for example of ZrO ₂ , Y ₂ O ₄ -ZrO ₂ , ie it is not, partially or completely stabilized by yttrium oxide and / or calcium oxide and / or magnesium oxide.
By means of suitable coating processes, such as electron beam evaporation (EB-PVD), stalk-shaped grains are produced in the thermal barrier coating.

The vane 130 has a guide vane foot (not shown here) facing the inner housing 138 of the turbine 108 and a vane head opposite the vane foot. The vane head faces the rotor 103 and fixed to a mounting ring 140 of the stator 143.

Claims (28)

1. Process for the surface treatment of at least one component (9),
   in which the at least one component (9) is arranged in a treatment agent (6),
   a treatment voltage (30) for surface treatment being applied to the at least one component (9) and one further pole (3, 12), and in which
   a measurement voltage (33) that is lower than the treatment voltage (30), is applied to the at least one component (9) and the at least one further pole (12, 12'),
   so that as a result of the applied measurement voltage (33) a time-dependent current (I(t)) flows,
   the time profile of which current represents the state of the surface treatment and is used to reach a decision on when to terminate or interrupt the surface treatment.
2. Process according to claim 1,
   characterized in that
   the treatment voltage (30) used is a DC voltage.
3. Process according to claim 1,
   characterized in that
   the treatment voltage (30) is pulsed.
4. Process according to claim 1, 2 or 3,
   characterized in that
   the measurement voltage (33) used is a DC voltage.
5. Process according to claim 1, 2 or 3,
   characterized in that
   the measurement voltage (33) is pulsed.
6. Process according to claim 5,
   characterized in that
   the pulsed measurement voltage (33) at least at times is applied together with the pulsed treatment voltage (30).
7. Process according to claim 5,
   characterized in that
   the pulsed measurement voltage (33) is applied during an interpulse period (36) of the pulsed treatment voltage (30).
8. Process according to claim 5, 6 or 7,
   characterized in that
   a pulse duration (t₃₃) of the measurement voltage (33) is shorter than the pulse duration (t₃₀) of the treatment voltage (30).
9. Process according to claim 5, 6 or 7,
   characterized in that
   a pulse duration (t₃₃) of the measurement voltage (33) is equal to the pulse duration (t₃₀) of the treatment voltage (30).
10. Process according to claim 1,
    characterized in that
    the measurement voltage (33) has a ratio of at least 1:10 with respect to the treatment voltage (30).
11. Process according to claim 1,
    characterized in that
    the measurement voltage (33) has a ratio of 1:10 with respect to the treatment voltage (30).
12. Process according to claim 1,
    characterized in that
    the measurement voltage (33) has a ratio of 1:20 with respect to the treatment voltage (30).
13. Process according to claim 1,
    characterized in that
    the measurement voltage (33) has a ratio of 1:30 with respect to the treatment voltage (30).
14. Process according to claim 1,
    characterized in that
    the measurement voltage (33) has a ratio of 1:40 or more with respect to the treatment voltage (30).
15. Process according to claim 1,
    characterized
    in that the component (9) has a coating to be removed, and
    in that the surface treatment is used to remove the coating from the at least one component (9).
16. Process according to claim 1,
    characterized in that
    the surface treatment is used to coat the at least one component (9).
17. Process according to claim 1,
    characterized in that
    an electrode (12, 12'), in particular a further component (9), is used as a further pole in the treatment agent (6).
18. Process according to claim 1 or 15,
    characterized in that
    the treatment agent (6) used is an acid.
19. Process according to claim 1, 15 or 18,
    characterized in that
    the current (I(t)) initially rises with time (t) and then remains relatively constant.
20. Process according to claim 1, 15, 18 or 19,
    characterized in that
    a drop in the current (I(t)) over the course of time, in particular to a predetermined comparison value, marks an end point of the removal of the coating.
21. Process according to claim 1,
    characterized in that
    the surface treatment is carried out in substeps,
    with abrasive coating removal taking place in an intermediate step, and
    the at least one component (9) then once again being treated in the treatment agent (6).
22. Process according to claim 1 or 21,
    characterized in that
    the at least one component (9) is rinsed in at least one intermediate step.
23. Process according to claim 1, 19, 20, 21 or 22,
    characterized in that
    a single component (9) is treated.
24. Process according to claim 1, 19, 20 or 21,
    characterized in that
    at least two components (9) are treated,
    for each of which (9) an individual time profile (I(t)) is determined.
25. Process according to claim 1,
    characterized in that
    a common circuit (12, 18, 15, 9, 6) is used for the treatment voltage (30) and the measurement voltage (33).
26. Process according to claim 1,
    characterized in that
    a first circuit (12, 18, 15, 9, 6) is used for the treatment voltage (30) and a second circuit (12, 12', 18', 15', 9, 6) is used for the measurement voltage (33).
27. Apparatus (1) for the surface treatment of at least one component (9),
    which apparatus at least includes
    a component (9) to be treated, as an electrical pole,
    a further pole (3, 12)
    a treatment agent (6),
    in which the at least one component (9) and the further pole (3, 12) are arranged,
    electrical connection means (15),
    which connect the at least one component (9) and the further pole (3, 12) to an electric voltage source (18),
    characterized in that
    there are further electrical supply conductors (15'), which connect the at least one component (9) and the further pole (3, 12) to a further electric voltage source (18').
28. Apparatus according to claim 27,
    characterized in that
    a further pole (12') is used to form the second circuit.

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