WO2005103324A1 - Process for coating the inside of a through-channel - Google Patents

Abstract

Existing inner coating processes produce an irregular and/or incomplete coating on a channel inside a component. The claimed process generates for example a pressure gradient in the through-channel (7, 192, 195) so that the pressure-dependent precipitation rate (r(p)) of the coating process makes it possible to locally adjust the precipitation rate (r) by means of the pressure gradient.

Description

 Process for the interior coating of a through-channel

The invention relates to a method for internally coating a through-channel according to claim 1.

Depending on the stage, turbine blades of steam or gas turbines have cooling air channels, which are through-channels through which air or steam flows during operation to cool the blade.

To protect against oxidation and corrosion, the channels are e.g. coated with aluminum and / or chrome using a CVD process. The coating oxidizes or corrodes during operation, the resulting oxide layer preventing further corrosive attack on the base material of the blade. In the case of an aluminum coating (internal alitation), the aluminum is largely converted into aluminum oxide. Since the cooling air ducts are sometimes of considerable length in relation to their diameter, the uniform coating of the inner surface of the cooling air ducts is a problem. Both the complete covering of the entire inner surface and the achievement of a uniform layer thickness from the inlet to the outlet of the Cooling air ducts can hardly be guaranteed by a CVD process. In the CVD process, aluminum and / or chromium-containing gaseous precursors are passed through the cooling air channels. The chemical reaction and the resulting coating are initiated by heating the blade (thermal CVD).

US 5,807,428 discloses a CVD method for internally coating turbine blades, in which the gas is introduced through an inlet at the base of the turbine blade. GB 1 549 845 discloses a method for internal coating using aluminum, in which the maximum pressure is 100 torr, that is to say that there is a negative pressure.

A method for gas diffusion coating of hollow workpieces is known from DE 40 35 789, that is to say the gas migrates into the hollow workpiece due to the diffusion gradient, so that no external pressure is applied.

It is therefore an object of the invention to demonstrate a method in which there is a complete and uniform coating of the inner surface of through-channels such as cooling air channels.

The object is achieved by a method according to claim 1.

The measures listed in the subclaims represent further advantageous measures, which can also be combined with one another in an advantageous manner.

Show it

1 shows a component with a through-channel, FIG. 2, 3 shows an exemplary pressure curve according to the invention,

FIG. 4 shows the dependence of the reaction equilibrium on the pressure.

5 shows the dependence of the deposition rate on the pressure and FIG. 6 shows a section of a turbine in which the method according to the invention is applied.

FIG. 1 shows a component 1 which, for example, a turbine component of a gas 100 (FIG. 6) or steam turbine, such as a guide 120 (FIG. 6) or rotor blade 130 (FIG. 6) or a combustion chamber 110 ( 6) is a gas turbine 100. The component 1 has an elongated cavity or a long, in particular meandering through channel 7, which is surrounded by an outer wall 4, an inner surface 8 in the through channel 7 and an outer surface 9.

The through-channel 7 has an inlet 10 and an outlet 13. ^"

The gases, for example gaseous metals, gaseous metal mixtures or gaseous precursors, are introduced in the region of the inlet 10 and are distributed in the through-channel 7.

The concentration c _{g of} the coating material, for example the metal or the metals in the gaseous precursor, decreases over the length x of the through channel 7 due to the process, since the metal or the metals deposit on the inner surfaces 8 of the through channel 7 from the beginning, so that there is less metal in the gas at the end of the channel. According to the prior art, there is a decrease in the concentration c _g over the length x of the through channel 7 over the length x (FIG. 1). This results in an uneven coating, a greater layer thickness being achieved in the area of the inlet 10 than in the area of the outlet 13.

The curve profile of the concentration c _g is then similar to a layer thickness of the coating 11 or concentration c _{g of} the coating material (metal), for example Al, Pt, Cr, combinations of Al, Pt, Cr or alloys, in the through channel 7 along the length x.

The graphical representation of the decrease in concentration c _g with respect to the metal (coating material) in FIG. 1 is only shown schematically and can have any other course of a decrease in the concentration c _g over the length x. When the gases or gaseous precursors flow through the passage channel 7, there is not necessarily a pressure gradient between the inlet 10 and the outlet 13 so that the gases can flow through the passage channel 7, but because of a difference in concentration there is also a movement due to the diffusion law (grad c) the material of the gas.

The chemical reactions and equilibria (not final) in the through channel 7 can be represented as follows:

B_g O B_s

B _g OB _s

For example, two gaseous precursors Pi and

P ₂ to a coating material B or possibly also to an escaping gas G or the coating material B changes from the gaseous state B _g to the solid state B _Ξ .

A precursor P _x can likewise convert into coating material B and escaping gas.

The reaction equilibrium g of these reactions can be shifted by the pressure p.

The method according to the invention provides a pressure gradient over the length x along the through-channel 7 (FIG. 2), the pressure p being greatest in the area of the inlet 10 (x = 0) and being smaller towards the outlet 13 (x = L) as used in the CVD process (Fig. 2).

The pressure gradient according to the prior art, which is necessary for a flow, for example, is shown in FIG. 2 with the dashed line 19. According to the invention, a larger gradient (curve 16, FIG. 2) is generated in the flowing gas, in which For example, the flow rate is increased, for example by using a pump.

Due to the increased pressure p in the area (for example at least 1.0 or 1.5 bar) of the inlet 10 (x = 0), the reaction equilibrium is shifted to the left side, so that the deposition rate r drops.

This pressure gradient is generated at least temporarily or always during the coating process.

For example, the pressure decreases continuously over the length x. The course 16 shown in FIG. 2 is only shown schematically. The curve p (x) can of course show a different course (e.g. linear).

According to the prior art, a certain pressure level (for example 1 bar) is present in the area of the inlet 10 (x = 0), which is indicated in FIG. 3 by the line 20. The pressure gradient increased according to the invention in particular runs such that the pressure p in the area of the outlet 13 (x = L) corresponds at least to this level 20 (FIG. 3). Therefore, the pressure p in the area of the outlet is somewhat higher than the ambient pressure, for example, and the pressure in the area of the inlet is, in particular, significantly increased.

The invention is based on the knowledge that the deposition rate r of the coating process, here for example from the gas phase, depends on the pressure p, as is shown, for example, in FIG. At a high pressure p there is a low deposition rate r, whereas at a low pressure p the deposition rate r increases. The curve r (p) can of course show a different course (eg linear). The gas flowing through the passage 7 can be a vaporized coating material such as aluminum, that is to say an aluminum vapor, but, for example, a carrier gas can also be used, which is added to the coating gas in order to adjust the pressure gradient. The carrier gas can be any gas which, at the temperatures in component 1 and at the corresponding temperatures, does not cause an undesirable reaction (corrosion, ...) with the material of component 1. Noble gases such as argon or helium or nitrogen or carbon dioxide, optionally also hydrogen, can preferably be used.

The pressure at the inlet 10 ^is' at least Ibar. In particular, the pressure p (x = 0) at the inlet 10 does not exceed the value of 6 bar.

A pressure of greater than 2 bar at inlet 10 is preferably used.

Special advantages for a pressure at the inlet 10 result for pressure values between lbar and 5bar or lbar and 4bar.

Pressure values between 2 and 5 bar and 3 bar and 6 bar can preferably also be used at inlet 10.

There are also advantages if pressure values at inlet 10 are used for values from 1 bar to 2 bar, 2 bar to 3 bar, 3 bar to 4 bar, 4 bar to 5 bar or 5 bar to 6 bar.

FIG. 4 shows the dependence of an equilibrium constant g of a chemical equilibrium on the pressure p.

The quotient g is formed, for example, by the concentration of the end product B divided by that of the starting materials Pi + P ₂ . A value> 1 for g means that the equilibrium is on the side of the end product B. At a value <1 for g, the equilibrium of the reaction lies with the starting materials P _x and P ₂ . By increasing the pressure p, less material B is deposited in the through-channel 7.

The curve g (p) is given for each reaction (e.g.: P _x + P ₂ <=> B). Since the pressure in the area of the outlet 13 (x = L) is, for example, almost the ambient pressure (for example, p «l bar), the coordinate point 23 in the diagram x (p) is specified for x = L, since L is known. The intersection point 29 is now determined, which then represents the value for the pressure p ₀ at x = 0 in the diagram x (p).

By the pressure pO (x = 0) and by a dashed line 26 running horizontally to the p-axis in the diagram g (p), which runs through the intersection at p ₀ with the g (p) curve, the value g _P becomes at a distance from the value g = 1 and in the diagram x (p) the point 0 is determined on the X axis and the resulting intersection 29 is determined with the line 26 at p = Po in the x (p) diagram. This point 29 determined in this way can be entered in the diagram x (p), so that the pressure gradient (p ₀ -l bar) in the channel 7 is determined by the measuring points 23, 29.

The value for the equilibrium constant g is increased, for example for the value p = 1 or «1, by the amount g _B over the value g = l. The ratio g _B to g _P can be set as desired by varying the pressure p ₀ .

There are, of course, other options for determining the pressure ratio at the inlet and outlet or the pressure gradient.

Thus, by generating the pressure gradient at

CVD deposition at the inlet 10 of the cooling air channels 7 with a high metal concentration in the gas (FIG. 1) tends to reduce the deposition due to the increased pressure p and at the outlet 13 with a lower metal concentration in the gas tends to increase the deposition rate r with the lower pressure p, so that despite uneven concentration c (over the length x of the through-channel 7) an equalization of the deposition rate r is achieved.

According to the prior art, there is a specific one in the area of the inlet (10) of the through-channel (7, 192, 195)

Concentration (cι ₀ ) and a certain concentration (c _i3 ) of the coating material in the gas (7) in the area of the outlet (13) of the through-channel (7, 192, 195). According to the ratio (c ₁₀ / c ₁₃ ), the pressure (p) in the area of the inlet (10) can be increased compared to the normal pressure.

With a very reactive material, e.g. Chromium, with the method according to the invention, a continuous coating of a long channel 7, 10, i.e. which has an aspect ratio (length by diameter) of greater than 10, 30 and even 100.

The invention can be applied to other coating methods such as e.g. Transfer PVD procedure.

The process can also be applied to long blind holes, since a pressure gradient can also be created there, even if no medium is flowing. However, the method can also be carried out, for example, in such a way that the blind hole is built up in such a way that a gas can flow out at the end of the blind hole and the blind hole is closed again at the end of the coating process. Another possibility is to insert a probe into the blind hole so that the gas flows out of the probe at the end of the blind hole.

The deposition rate r can of course also be alternatively or additionally controlled by other parameters, such as temperature T (x) or concentration c (x), which are locally different or have a gradient. It is important here that the coating parameter p, c, T is influenced in such a way, that is to say that it differs locally, that the deposition rate r along the through channel 7 is made uniform or, in particular, is the same everywhere.

FIG. 6 schematically shows an example of how turbine blades 120, 130 are cooled. In order to achieve a comparatively high efficiency, the gas turbine 100 is designed for a comparatively high outlet temperature of the working medium M emerging from the combustion chamber 110 of approximately 1200 ° C. to 1300 ° C. In order to make this possible, at least some of the moving blades 120 and the guide blades 130 are designed to be coolable by cooling air K as the cooling medium. It can be seen in FIG. 4 that the working medium M flowing out of the combustion chamber 110 first encounters a number of guide vanes 130, which form the so-called first row of guide vanes 115 and are suspended in the combustion chamber 110 via their respective platforms 180. Seen in the direction of flow of the working medium M, the blades 120 forming the first row of blades follow, the guide vanes 130 forming the second row of blades, and the blades 120 forming the second row of blades.

The blades 120 are designed for a particularly reliable supply of cooling air K essentially over the entire base cross section of their respective blade root 183. For this purpose, the blade root 183 is the respective one

Blade 120 each provided with a plurality of inflow openings 186 for cooling air K. The inflow openings 186 of each rotor blade 120 are arranged one behind the other, for example in the longitudinal direction of the turbine shaft 102. Each inflow opening 186 is guided through the airfoil 189 of the respective rotor blade 120. ter subchannel 192 or 195 assigned for cooling air K, which are to be coated according to the invention.

The subchannel 192 of the respective rotor blade 120, which is assigned to the front inflow opening 186 in the flow direction of the working medium M, is guided, starting from the associated inflow opening 186, in a meandering manner through the front part of the respective rotor blade 120, as is shown only schematically in the figure.

The sub-channel 192 opens on the outlet side into a number of outlet openings 198 for the cooling air K, which are arranged on the front edge 201 of the respective rotor blade 120, as seen in the direction of flow of the working medium M. In contrast to this, the rear inflow opening 186 of the respective rotor 120, as seen in the direction of flow of the working medium M, communicates with a sub-channel 195 which is likewise meandering in the rear part of the respective rotor 120. The sub-channel 195 opens on the outlet side in a number of at the rear edge 204 of the respective one Rotary blades 120 arranged outlet openings 207.

The subchannels 192, 195 of each rotor blade 120 are completely decoupled from one another on the cooling air side. In other exemplary embodiments of blades, the subchannels 192, 195 form a meandering channel with, for example, an inlet.

This enables each sub-channel 192, 195 to be supplied with cooling air K which is adapted to the respective requirements with regard to its coating parameters. In particular, it can be taken into account that the pressure level that the cooling air K must have or exceed in the area of the outlet openings 198 or 207 is dependent on the position of the respective rotor blade 120 along the. Turbine shaft 102 and whether the cooling air K exits counter to the flow direction of the working medium M or in the flow direction of the working medium M. Therefore must In particular, the cooling air K supplied to the outlet openings 198 have a higher operating pressure than the cooling air K supplied to the outlet openings 207.

Both the subchannels 192, 195 and the outlet openings 198 can be coated using the method according to the invention.

In order, for example, to enable the sub-channels 192, 195 to be supplied separately with cooling air K in order to comply with these different boundary conditions, the cooling air supply system of the gas turbine 100 is adapted accordingly. In particular, the cooling air supply system comprises a first supply chamber 210 integrated in the turbine shaft 102, which in the exemplary embodiment according to FIG. Is connected via a bore 213 guided in the turbine shaft 102 to the first inflow opening 186, seen in the longitudinal direction of the turbine shaft 102, of each of the rotor blades 120 forming the first row of rotor blades is.

Furthermore, the cooling air supply system comprises, for example, a second supply chamber 216 for cooling air K. This is arranged behind the first supply chamber 210, as seen in the longitudinal direction of the turbine shaft 102, and is likewise integrated into the turbine shaft 102. The second supply chamber 216 is connected on the cooling air side via a bore 219 to the rear inflow opening 186, as seen in the longitudinal direction of the turbine shaft 102, of each of the rotor blades 120 forming the first row of rotor blades. Furthermore, the second supply chamber 216 is connected via a bore 222 to the front inflow opening 186, as seen in the longitudinal direction of the turbine shaft 102, of each of the rotor blades 120 forming the second row of blades.

With regard to each individual rotor blade 120, this cooling air guide ensures that each inflow opening 186 of each rotor blade 120 is assigned a separate cooling air supply integrated into the turbine shaft. each Inflow opening 186 and with it also the respective downstream subchannel 192, 195 can thus be acted upon with cooling air K independently of the other subchannel 195 or 192. The partial flows of cooling air K thus formed can therefore be adapted to the individual conditions specified on the outlet side. In particular, the subchannel 192 can be charged with cooling air K which is at a higher pressure than the subchannel 195. For this purpose, the first supply chamber 210 is supplied with correspondingly high-quality cooling air K which is under comparatively high pressure. In contrast, the second supply chamber 216, from which the second sub-channel 192 of the blades 120 forming the first row of blades is supplied with cooling air K, is supplied with comparatively inferior cooling air K which is at a lower pressure. The total amount of high-quality cooling air K which is under particularly high pressure can thus be kept comparatively low and can be limited only to those areas of the respective rotor blade 120 for which the supply of such high-quality cooling air K is actually necessary.

According to FIG. 6, the inflow openings 186 of the rotor blades 120 are arranged in the base region of the respective blade root 183.

Claims

Patent claims 1. Method for the internal coating of a through-channel (7, 192, 195) of a component (1) by means of a coating process, in which the deposition rate (r) of the coating process for the internal coating depends on at least one coating parameter (p, c, T) depends, characterized in that within the through-channel (7, 192, 195), at least temporarily, at least one coating parameter (p, c, T) is locally influenced in such a way that the deposition rate (r) along the through-channel (7, 192, 195 ) is more uniform than without influencing this at least one coating parameter (p, c, T). 2. The method according to claim 1, characterized in that at least temporarily during the internal coating a local gradient of at least one coating parameter (P, c, T) is present in the through-channel (7, 192, 195). 3. The method according to claim 1 or 2, characterized in that the concentration (c (x)) is set as a function of the location (x) within the through-channel (7, 192, 195). Method according to claim 1, 2 or 3, characterized in that the temperature (T (x)) is set as a function of the location (x) within the through-channel (7, 192, 195). 5. The method according to claim 1, 2, 3 or 4, characterized in that, according to the prior art, a gas flows through the through-channel (7, 192, 195) due to a pressure gradient, and that the pressure gradient is increased compared to the prior art . 6. The method according to claim 5, characterized in that the pressure (p) at the inlet (10) of the through channel (7, 192, 195) is greater than or equal to one bar. 7. The method according to claim 5 or 6, characterized in that the pressure (p) at the inlet (10) of the through channel (7, 192, 195) is at most six bar. 8. The method according to claim 5 or 7, characterized in that the pressure (p) at the inlet (10) of the through channel (7, 192, 195) is at least two bar. 9. The method according to claim 1, 5, 6 or 8, characterized in that according to the prior art in the area of the inlet (10) of the through channel (7, 192, 195) a certain concentration (cι ₀ ) and in the area of the outlet (13) of the through channel (7, 192, 195) a certain concentration (Cι ₃ ) of the coating material is present in the gas (7), and that the pressure (p) in the area of the inlet corresponds to the ratio (cι ₀ / c _i3 ). (10) is increased in accordance with this ratio compared to the normal pressure. 10. The method according to one or more of the preceding claims, characterized in that the coating process is a PVD process 11. The method according to one or more of the preceding claims, characterized in that the coating process is a CVD process. 12. The method according to one or more of the preceding claims, characterized in that a gas flows through the through-channel (7, 192, 195), and that the gas contains a coating material, in particular in the form of precursor. 13. The method according to one or more of the preceding claims, characterized in that the through-channel (7, 192, 195) has an inlet (10), and that the pressure (p) at the inlet (10) is highest, in particular greater than 1 cash. 14. The method according to claim 5, 9 or 13, characterized in that the pressure (p (x)) runs continuously over the length (x) of the through-channel (7, 192, 195). 15. The method according to claim 1, 5, 13 or 14, characterized in that a carrier gas is also used. 16. The method according to claim 15, characterized in that the carrier gas is an inert gas, in particular a noble gas, in particular argon or helium or nitrogen. 7. The method according to claim 1, 13, 14, 15 or 16, characterized in that according to the prior art, i.e. without an increased pressure gradient at the inlet (10), a certain pressure level (20) prevails, and that according to the invention in the through-channel (7, 192, 195) in the area of the outlet (13) the pressure (p) corresponds to at least this pressure level (20), in particular close to ambient pressure. 18. The method according to claim 1, characterized in that a turbine component such as a guide (130) or rotor blade (120) of a gas (100) or steam turbine or an element of a combustion chamber (110) is treated as a component (1). 19. The method according to claim 1 or 18, characterized in that the through channel (192, 195) of the component (1) is designed to be meandering. 20. The method according to claim 1, 18 or 19, characterized in that the through channel (7, 192, 195) of the component (1) has an aspect ratio of greater than 10. 21. The method according to claim 1, 18 or 19, characterized in that the through channel (7, 192, 195) of the component (1) has an aspect ratio of greater than 30. 22. The method according to claim 1, 18 or 19, characterized in that the through channel (7, 192, 195) of the component (1) has an aspect ratio of greater than 100.