BRPI1004657A2 - Method for removing particles from a substrate and Method for removing sand particles from the surface of at least one backing device on an alloy substrate for super high temperatures - Google Patents

Abstract

METHOD FOR REMOVING SUBSTRATE PARTICLES AND METHOD FOR REMOVING SURFACE SAND PARTICLES AT LEAST ONE PROTECTIVE COATING DISPOSED IN A SUPERLEVENT TEMPERATURE ALLOY SUBSTRATE. It describes a method for removing sand particles from a substrate. The method includes the step of treating the substrate with an acid solution comprising H ~ x ~ AF ~ 6 ~, wherein A is selected from the group consisting of Si, Ge, Ti, Zr, AI, and Ga, and wherein H ~ X ~ AF ~ 6 ~ is present in a concentration between about 5 weight percent and about 40 weight percent.

Description

"METHOD FOR REMOVING SUBSTRATE PARTICLES AND METHOD FOR REMOVING SAND SURFACE PARTICLES FROM AT LEAST ONE PROTECTIVE COATING ON A ALLOY TEMPERATURE ALLOCATION"

The invention relates to the cleaning of substrate surfaces, more particularly the removal of sand particles from turbine surfaces such as airfoils.

Sand scale has recently emerged as the main factor that significantly degrades the performance of turbine components. For example, aircraft engines that fly domestic routes often experience significant sand deposits due to heavy sand ingress during flight idle, takeoff, and landing. It has been established that the main mechanism for fouling is the increased roughness of the compressor blades due to ingestion of sand. Specifically, this increased roughness results from the formation of microcavities due to the impact of the particles. Then sand particles smaller than 10 microns in size accumulate in these cavities to form the scale layers. High temperatures in the compressor outflow stages result in the sand particles baking, which increases airfoil sand adhesion. Therefore, water wash treatments often used to clean turbine components are often unsuccessful in removing accumulated sand particles.

As a consequence, the need for a

A method of removing sand particles and sand scale layers from turbine components, for example, which at the same time produces minimal effect, or no effect, below the surface of the airfoil on any protective coating on such surface.

Brief Description Of The Invention A main embodiment of this invention shows a method for removing sand particles from a substrate. The method includes the step of treating the substrate with an acidic solution comprising HxAF6, where A is selected from the group consisting of Si, Ge, Ti, Zr, Al, and Ga, with HxAF6 present at a concentration of approximately 5 weight percent and approximately 40 weight percent.

graphics

-10 These and other configurations, aspects and advantages of this

invention will be better understood by reading the following detailed description by reference to the accompanying drawings, in which equal characters represent equal parts in all drawings, where:

Figure 1 is a cross-sectional view of a part of a

turbine component; and

Figure 2 illustrates a method for removing sand particles from

a substrate.

Detailed Description Of The Invention

Embodiments of the present invention relate to a method for removing sand particles from a substrate. The method includes the step of treating the substrate with an HxAF6 acid solution that has a concentration of from about 5 weight percent to about 40 weight percent. As described in detail below, milder processing conditions such as lower concentrations of HxAF6 acid in the aqueous solution, lower temperatures, and shorter treatment times are typically preferred to remove sand particles from the substrate. without causing substantial damage to the underlying coating.

As used herein, "sand" can generally be defined as a naturally occurring granular material composed of finely divided stone particles and minerals. The most common component of sand is silica (silicon dioxide, or SiO2), typically in the form of quartz. However, the sand composition can vary widely. In some embodiments, the term "sand" is specifically intended to refer to "CMAS" materials, which are materials based on a mixture of calcium oxide, magnesium oxide, alumina and silica. Usually the measurement of sand particles is the submicron. In one embodiment, the average particle size of the sand particles is from about 0.5 microns to about 10 microns.

It was concluded that sand fouling often occurs in aircraft engines that fly in geographical locations with desert areas. The airfoils in the compressor sections of such aircraft engines show significant accumulations of fine sand. Turbine component surfaces, such as blades, may accumulate sand, resulting in reduced airflow and a significant increase in specific fuel consumption (SFC). Sand accumulation occurs both as particles and as vitrified layers.

Sand particles less than 10 microns accumulate on the compressor airfoils. High temperatures in the compressor outflow stages result in the sand particle firing, which increases airfoil sand adhesion. Consequently, water washing, often effective in cleaning turbine components, often fails to remove accumulated sand particles. The process includes treating the substrate with an aqueous solution.

HxAF6 acid at a selected temperature for a set period of time, then rinse the turbine component in an aqueous medium. As used herein, the term "mild aqueous solution of HxAF6 acid" refers to an aqueous solution of HxAF6 substantially free of strong acids, such as phosphoric acid. The process of this invention employs fluosilicic acid or derivatives thereof having the formula HxAF6. In this formula, A is selected from the group consisting of Si, Ge, Ti, Zr, Al, and Ga. Subscript "x" is a quantity from 1 to 6, more characteristically from 1 to 3. Materials of this type are commercially available, or can be prepared without much effort. The preferred acid is H2 SiF6. It is designated by various names, such as "hydrofluoro silicic acid", "flurosilicic acid", "fluosilicic acid", "hexafluoro silicic acid", and "HFS". Such materials are described in U.S. Patent No. 6,599,416 (to Kool et al.), Which is incorporated herein by

reference title.

As described herein, the use of the compound

HxAF6 provides considerable advantages to the sand removal process. In many cases such a process is quite suitable, for example when high removal rates are required. Surprisingly, it has been found that by employing the aqueous solution of fluosilic acid and / or the derivatives of fluosilic acid, the sand particles can be removed from the surface of the airfoils without damaging the surface of the underlying alloy or any coating. brought as described below.

It is also possible to use HxAF6 acid precursors. As used herein, a "precursor" refers to any compound or group of compounds that may be combined to form the acid or its dianion AF6-2, or which may be transformed into the acid or dianion under reactive conditions. for example the action of heat, agitation, catalysts, and so on, so one can, for example, form the acid in situ in a reactive vessel.As an example, the precursor may sometimes be a metal salt, an inorganic salt, or an organic salt, to which the diion is ionically bonded Nonlimiting examples include salts of Ag, Na, Ni, and K, as well as organic salts, such as the quaternary ammonium salt. Dissociation of salts in aqueous solution often produces acid In the case of H2SiF6, a suitable salt that can be employed is Na2SiF6.

Those skilled in the art are familiar with the use of compounds which cause HxAF6 formation within an aqueous composition. For example, H2SiF6 can be formed in situ by reacting a silicon-containing compound with a fluorine-containing compound. Si02 is an example of a silicon-containing compound, while hydrofluoric acid (ie aqueous hydrogen fluoride) is an example of a fluorine-containing compound.

Referring now to Figure 1, there is a cross-sectional view of a portion of an example turbine component generally designated by reference numeral 10. In this case, the turbine component is an airfoil. Component 10 includes a concave surface 12 and a convex surface 14. Sand particles may be removed from both surfaces, or from passages, recesses,

or several cavities in these surfaces.

The type of turbine component is not intended to be limited and may vary from a housing, turbine blade or blade, nozzle or vane, diaphragm component, seal component, valve stem, nozzle housing, nozzle plate, and so on. You can use the terms "blade" and "turbine blade" interchangeably. In general, a blade is a rotating airfoil of an aircraft turbine, and a turbine blade is a rotating airfoil of a terrestrial power generation turbine. In addition, the term "nozzle", which generally refers to a stationary fin on a gas or steam turbine, may be used interchangeably

with the term "flip".

The turbine component, for example substrate 12, may generally comprise a variety of metal alloys, for example steel or alloys thereof, or titanium alloys (e.g., Ti-6AI-4V). In some preferred embodiments, the alloy turbine component is formed for super high temperatures, which may be employed at high temperatures, often about 0.7 above the absolute melt temperature. Alloys for higher temperatures are based on nickel, cobalt, iron, or some of their combinations. Many are described

in the aforementioned Kool et al patent.

As those skilled in the art understand, turbine components with one or more protective coatings are very often provided. Accordingly, the present invention contemplates removing sand from the surfaces of such coatings as well as removing sand from an uncoated substrate. Typically, many different types of protective coatings are employed, for example diffusion and absorption surface coatings or layer coatings as described in the Kool patent. In addition, layer coatings such as "MCrAI (X)" materials (considered to be metallic coatings) may be covered by thermal barrier coatings (TBC's). Non-limiting examples of the latter include ceramic coatings, such as yttria stabilized zirconia. Some of the TBCs are described in U.S. Patent No. 6,921,586 (Zhao et al.), Which is incorporated herein by reference. The thickness of the protective coating (s) will depend on a number of factors, such as the type of part coated, the composition of the substrate, and the environmental conditions to which the part is exposed. Figure 2 is an illustrative flowchart for a nonlimiting exemplary method of removing sand from a substrate. In block 20, the substrate is treated with an HxAF6 acid solution that has a concentration of from about 5 weight percent to about 40 weight percent. For example, the substrate can be treated by at least partially immersing the substrate in a bath of the HxAF6 acid solution. The bath may be mechanically shaken during treatment.

The preferred level of HxAF6 acid to employ will depend on several factors. These include the type and amount of sand to be removed, the location of the sand on the substrate, the type of substrate, the thermal history of the substrate, and the sand material (eg, how strongly adherent to the substrate is the sand). time and temperature used for treatment, and the stability of the acid in the treatment solution.

As a general rule, HxAF6 acid is present in a treatment composition of from about 5 weight percent to about 40 weight percent. Usually, the level is between about 10 percent by weight and about 30 percent by weight. In the case of H2SiF6, a preferred concentration (herein in molar units) is approximately 0.2M to approximately 2.2M. Adjustment of the amount of HxAF6 acid and the other components described below can be readily made by considering stoichiometric parameters and observing the effect of specific compositions on

sand removal from the substrate.

Usually, the temperature of the HxAF6 acid solution can be maintained to approximately 100 ° C. In some specific embodiments, the temperature is maintained below 50 ° C. In some especially preferred embodiments, the temperature range is from about 50 ° C to about 80 ° C. Characteristically, environmental pressure is appropriate when treating the substrate with HxAF-

The time required to remove sand particles (i.e. the soaking time within the aqueous composition) can vary considerably. Factors influencing the selection of a suitable time include the specific composition of the sand-based material to be removed, as well as its density and thickness. The time may also vary with the temperature of the fluosilic acid solution. For example, for a higher temperature of the fluosilicic acid solution the treatment time may be shorter, and vice versa. Usually, the substrate is at least partially immersed in a wetting agent bath for a period of time from about 1 minute to about 36 hours, preferably from about 5 minutes to about 8 hours. In some cases, the especially preferred range of immersion time is from about 10 minutes to about 2 hours. The immersion time for the substrate in the bath usually depends on the temperature of the bath and the type of protective coating on the substrate. For example, longer dipping times for substrates having protective coatings such as MCrAIY and TBC are accepted due to the inert nature of such protective coatings relative to the HxAF6 acid solution. Consequently, in the case of such protective coatings, the underlying substrate remains largely undamaged - even after prolonged immersion of the substrate in the HxAF6 acid solution.

The aqueous composition employed for the present invention may include various other additives that serve a variety of functions. Inhibitors, dispersants, surfactants, chelating agents, wetting agents, deflocculants, stabilizers, anti-settling agents, and antifoam agents are non-limiting examples of such additives. Those skilled in the art are familiar with the specific types of such additives and the effective levels of their jobs. An example of an inhibitor for the composition is a relatively weak acid such as acetic acid, mentioned above. Such a material tends to reduce the activity of the basic acid in the composition. This is desirable in some cases, such as to reduce the possibility of any damage to the underlying coating (s) or substrate surface.

The aqueous HxAF6 acid solution of the present invention is not only effective in removing the deposit containing the sand particles on the substrate, but is also benign to the aerofoil underlying metal and any of the protective coatings. In other words, with proper monitoring of the treatment process, the underlying surfaces are not adversely affected.

Optionally, as shown in block 22, the substrate is treated with a wetting agent, such as a surfactant, prior to treatment with the HxAF6 acid solution. Treatment with the wetting agent may facilitate better interaction between the sand particles and HxAF6 acid to facilitate coating removal.

Non-limiting examples of suitable surfactants include detergents, stable acid surfactants, stable non-acid surfactants, or combinations thereof. An example of an acid stable surfactant may include polyethylene oxide, commercially available as Triton x-100 ™ (manufactured by Research Chemicals Limited [CAS Number 9002-93-1]). An example of a stable non-acid surfactant includes trisodium phosphate, commercially available as Alconox TSP ™.

Optionally, as exemplified in block 24, the substrate is rinsed with water prior to treatment with the wetting agent. Rinsing the substrate with water removes any dirt particles or loose sand particles from the substrate surface.

Optionally, in block 26, the substrate may be rinsed with water or other liquid after treatment with HxAFe acid solution to remove any unwanted debris or chemicals from the substrate surface. In one embodiment, rinsing may be done

applying a jet of water.

In addition to (or in place of) the rinse step 26, the treatment

The sand encrusted surface may also include at least one subsequent step to remove any or different sand residue. As described in the referenced Kool patent, a post-cleaning or "dusting" operation may be experienced. It can occur as an abrasion step that reduces damage to the substrate or protective coatings. As an example, a particulate jet may be directed by directing across the surface a pressurized air stream containing aluminum oxide particles. Air pressure is usually less than about 100 psi. Particulate jetting is performed for a period of time sufficient to remove any residual material. Instead of particle jetting, other known techniques can be used to grind the surface. Many of them are described in U.S. Patent No. 5,976,265, incorporated herein by reference. For example, the surface may be scrubbed manually with a fiber bushing, such as a polymeric, metal, or ceramic fiber bushing. Alternatively, the surface may be polished with a flexible disc or belt on which alumina or carbon silicon particles are embedded. Alternatively, liquid abrasive materials may be used on discs or belts. These alternative techniques must be controlled to maintain a contact force against the surface that is no greater than the force in the above-treated particle jet technique. Other techniques (or combinations of techniques) may be employed instead of abrasion to remove any residual material. Examples include tapping the part (for example, water tapping) or laser ablation of its surface. Alternatively, the waste material may be scraped off the surface. Alternatively, sound waves (eg ultrasonic) can be directed against the surface causing vibrations that can vibrate the degraded material. For each of these alternative techniques, those skilled in the art should be familiar with operating adjustments made to control the relevant force applied against the workpiece surface (as in the case of abrasion technique) to reduce substrate or coating damage. overlapping protectors. The part is occasionally rinsed after this step, for example using water or a combination of water and a wetting agent.

The bath may be mechanically shaken during this step of

waste removal. For example, the bath may be mechanically shaken (as described above) while treating the substrate in the HxAF6 acid solution. In one embodiment, the bath may be mechanically shaken while treating the substrate with a wetting agent. As previously mentioned, one can still employ the

present invention to effectively remove sand from any internal region or cavity in the workpiece, for example, recesses, hollow regions, passages, or holes. In the case of a turbine airfoil, the internal region is often in the form of radial cooling holes or coil passages. The process of the present technique has a synergistic effect and results in an extremely effective cleaning method for airfoils and other turbine parts containing tightly adhered sand particles. Although only certain embodiments of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is therefore to be understood that the appended claims are intended to cover all such modifications and changes when they fall within the scope of the invention.

Claims (10)

1. A method for removing particles from a substrate, comprising the step of treating the substrate with an HxAF6 acid solution, where A is selected from the group consisting of Si, Ge, Ti, Zr, Al, and Ga with HxAF6. present at a concentration between about 5 weight percent and about 40 weight percent. A method according to claim 1, wherein the acid HxAF6 is an aqueous solution. A method according to claim 1, wherein HxAF6 acid is between approximately 10 weight percent and approximately 30 weight percent. A method according to claim 2, wherein the HxAF6 acid is maintained at a temperature no greater than approximately 100 ° C during treatment. A method according to claim 1, wherein the substrate is treated with a wetting agent prior to treatment with the fluosilicic acid solution. The method of claim 5, wherein the wetting agent comprises a surfactant. The method of claim 5 further comprising rinsing the substrate with water prior to treatment with the wetting agent. A method according to claim 1 further comprising rinsing the substrate with water after treatment with the HxAF6 acid solution. A method according to claim 1, wherein at least one protective coating is arranged on the substrate, and the particles that are removed are those that adhere to a surface of the protective coating. 10. METHOD FOR REMOVING SURFACE SAND PARTICULARS FROM AT LEAST ONE PROTECTIVE COATING ARRANGED IN A SUPERLEVEL TEMPERATURE ALLOY SUBSTRATE, comprising the step of treating the substrate coated with an acid solution comprising HxAF6l from the group A It consists of Si1 Ge1 Ti, Zr, Al, and Ga, and in which HxAF6 is present in a concentration between approximately 5 weight percent and approximately 40 weight percent.