Patent Application
20110081834
This application claims priority under 35 U.S.C. §119 to German application number No. 10 2009 043 697.9, filed 1 Oct. 2009, the entirety of which is incorporated by reference herein.
1. Field of Endeavor
The present invention relates to the field of working on workpieces with water jets. It concerns a method for working on, in particular cleaning, a workpiece with a water jet that contains abrasive and emerges from a nozzle under high pressure, and to a water jet installation useful for executing the method. Moreover, the invention relates to a method for application of the water jet method.
2. Brief Description of the Related Art
Components of power plant installations are subject to high mechanical and thermal load during their operation. This applies particularly to gas turbine components exposed to the flow of hot gas, whose surfaces, in addition to being exposed to the extreme mechanical and thermal loads, are additionally exposed to unwanted thermal and chemical reactions with the formation of non-metallic layers, such as scale or corrosion coverings, with negative effects on the operating behavior. This necessitates regular service intervals for checking the state of these components and removing and/or cleaning, repairing or, if necessary, replacing them.
Methods for cleaning gas turbine components such as, for example, blades, are known in a multiplicity of realizations. The methods that are known and have been introduced in this field include that of sand blasting. Air that is compressed to a plurality of bars and to which an abrasive material is added, is directed on to the surface to be treated. The particles of the abrasive material impacting with high energy on the surface produce a cleaning effect. Disadvantages of this method, however, are an imprecise scattering and a relatively coarse removal of material, with disadvantageous alterations of the surface quality of the workpiece.
Another type of cleaning method is based on the high-pressure water jet technique, wherein pure water jets or water jets mixed with an abrasive are applied to the surface to be cleaned. The high-pressure water jet technique uses water pressures of up to 600 MPa, in order to produce a high-power water jet. Such a high-power water jet can be used as a tool for cutting or cleaning applications that acts in all directions.
Depending on the respective application, water jets operating according to three differing principles are used, namely:
(1) pure water jets (see
(2) water jets containing abrasive that are generated through injection of an abrasive into a previously produced pure water jet (abrasive injection water jets, AIWJ; see
(3) water jets containing abrasive in which the jet is produced through a pressurized suspension of the abrasive emerging from a nozzle (abrasive suspension water jets, ASWJ; see
In the case of the first principle, represented in simplified form in
For cleaning applications, it is mainly systems operating with a pure water jet that are used. Typical parameters for cleaning with a pure water jet are working pressures of up to 300 MPa and volumetric flow rates of approximately 30 liters/min, which result in a high energy consumption (up to 150 kW). Corresponding high-pressure pumps are likewise very expensive.
In the case of the second principle, represented in
all metals (steel, aluminum, copper, titanium, etc)
glass
synthetic materials
composite materials, and
concrete.
The ASWJ jets (abrasive suspension water jets) produced according to the third principle are generally used for mobile and special applications. The advantages of the ASWJ jets, as compared with the AIWJ jets produced according to the second principle, are a higher efficiency (higher by a factor of up to 4-5) and the possibility of being able to use these jets in all positions and environments.
In the case of the third principle, represented in
The main disadvantages of the currently known systems operating, according to the third principle, with pressures of between 50 MPa and 200 MPa are:
the imprecise control of the proportion of abrasive in the suspension;
the lack of possibility of continuous operation, since after a certain period of time it is necessary to interrupt operation and refill the pressure tank with abrasive; and
the high working pressures require correspondingly dimensioned components of the water jet installation, with the consequence of more difficult handling and a limited scope of application in respect of confined spatial conditions.
One of numerous aspects of the present invention includes a method, in particular suitable for cleaning applications, for treating workpieces with a water jet that contains abrasive and emerges under high pressure from a nozzle, which method can be operated continuously and avoids the disadvantages of known methods described above, and a water jet installation for executing the method. Another aspect includes providing such a method and such an installation that meet the requirements of use for power plant installations, for example turbines. This domain of application requires effective use in confined spatial conditions, such as in narrow gaps, and moreover is highly demanding with respect to the surface quality following the working operation.
Another aspect of the present invention includes, in a first step, an abrasive suspension containing abrasive and water is provided at normal pressure, in a second step the provided abrasive suspension is brought to a working pressure that is above normal pressure, and in a third step a water jet containing abrasive is produced, with a nozzle, from the abrasive suspension that is at the working pressure.
Owing to the preparation of the suspension being effected at normal pressure, suspension can be provided continuously, without the need to interrupt the production and application of the jet. In a manner known per se, in this case the abrasive contained in the water very greatly augments the cleaning effect of the jet.
According to one exemplary embodiment of the invention, a mixture of water and the abrasive is produced in an open mixing vessel, for the purpose of providing the abrasive suspension that is at normal pressure. It is thereby ensured that the suspension in the mixing vessel can be replenished without difficulty at any time.
Preferably, the mixture in the mixing vessel is kept continuously in motion, in particular by an agitator.
Another exemplary embodiment of the method is distinguished in that a working pressure of a plurality of MPa, in particular of approximately 15 MPa to 25 MPa, is used. The comparatively low working pressure makes it possible to use less expensive components (e.g., pumps) and reduces the energy consumption. In addition, another advantage of the invention includes that the low working pressure allows the use of small-dimension and flexible components of the water jet installation, such as pressure lines and cleaning heads, as a result of which even those surfaces that are difficult to access can be treated effectively. As a result, in certain cases, it is possible to dispense with the resource-intensive removal of the workpieces to be cleaned. In the power plant industry, above all, this constitutes an advantage not to be underestimated, resulting in considerable cost savings for the power plant operator.
According to a further preferred embodiment, an abrasive having a hardness of at least 7 according to the Mohs scale is added to the water. The particles of the abrasive have a diameter in the range from 0.1 mm to 0.3 mm.
Preferably, the abrasive suspension is brought to the working pressure by a pump, and the abrasive suspension brought to working pressure is routed from the output of the pump directly to the nozzle, via a pressure line, a diaphragm pump, in particular, being used as a pump.
An embodiment of the water jet installation according to principles of the present invention is characterized in that the pump is a diaphragm pump, the diaphragm pump has a pump chamber that is delimited by a diaphragm and connected to the intake line via an inlet valve and connected to the pressure line via an outlet valve, and the valves each have a valve sleeve, which constitutes a central valve passage and which is closed, at the downstream end, by a closing element that rests on a valve seat and that is spring-biased contrary to the direction of flow. In comparison with other pump types, such as piston pumps, the use of a diaphragm pump has the advantage of low wear.
A preferred further development is characterized in that the valve sleeve and the closing element of the valves are produced from a hard metal, in particular tungsten carbide, and the valve seats are ground-in.
In particular, the closing element is ball-shaped in the region corresponding to the valve seat, and is biased in the closing direction by a pressure spring.
Another embodiment of the installation according to principles of the present invention is characterized in that a pressure relief valve is arranged in the pressure line.
Preferably, the mixing vessel has an agitator equipped with a motor, and is realized as an open vessel.
Methods embodying principles of the present invention can be used, advantageously, for cutting and/or cleaning tasks in the case of power plant components, in particular boilers, heat exchangers and turbines.
Through application of features defined more fully herein, it has become possible, for the first time, to combine in an advantageous manner the advantages of various known methods of the water jet technique and thereby to open up new application possibilities for this technique.
The invention is to be explained more fully in the following with reference to exemplary embodiments in conjunction with the drawing, wherein
The simplified diagram of a water jet installation operating with abrasive suspension, according to an exemplary embodiment of the invention, is reproduced in
An abrasive suspension 34 is mixed and held ready under normal pressure in the mixing vessel 31. An agitator 33, which is driven by a motor 32, is provided to mix and maintain the abrasive suspension. The mixing vessel 31 can be open at the top, such that the components of the abrasive suspension can be replenished if required and without interruption of operation. The operation under normal pressure facilitates considerably the controlled addition of water and abrasive to the mixing vessel 31 for the purpose of maintaining a constant mix ratio. Variants of an automated loading of the mixing vessel 31 are preferred in this case, and can be realized with comparatively simple technical systems. Continuous operation of the water jet installation is therefore ensured with a small amount of equipment.
The diaphragm pump 36, which has a pump chamber 38 delimited by a diaphragm 37, draws in suspension from the mixing vessel 31, via an inlet valve 41, during an intake stroke (movement to the left in
Owing to the abrasive component in the water jet, the pressure in the pressure line 39 can be reduced, as compared with the technique operating with pure water (
Owing to the abrasive component in the pumped suspension, a diaphragm pump 36, the structure and function of which are described, for example, in the printed publication U.S. Pat. No. 6,899,530, can be used instead of a conventional piston pump. These pumps are normally used for pumping corrosive and abrasive media, but at comparatively low pressures. In the present application, the drawn-in suspension is brought to pressures of approximately 15 MPa to 25 MPa by such a pump. Operation at these pressures is achieved in that the inlet and outlet valves 41, 42, which are subject to particular wear, have been modified according to
Diaphragm pumps are pumps that operate volumetrically, which produce pressure through the mechanical displacement of synthetic diaphragms. In order to achieve a constant pressure and flow, each pump chamber (38 in
The standard design of the valves of the pump chamber of a diaphragm pump of the type described is reproduced in
In the case of the valve 42′, a main problem consists in that, if the valve does not close properly, or no longer closes properly, high local flow velocities occur at the site of the leakage, and erode the closing element 48′ and the valve sleeve 46 to a very great extent. Even tungsten carbide valves become thus eroded in less than half an hour. The reason for the lack of tightness in the case of such standard valves is the lack of centering of the disk-shaped closing element 48′ in the valve sleeve 46: the closing element 48′ does not have sufficient guidance and, owing to the (flat) shape of the standard closing element 48′ (ground-in radius of the valve seat 47′), there are some regions in which there is no surface contact between the closing element 48′ and the valve seat 47′ if the closing element 48′ is not perfectly centered.
In order to remedy this, the valve geometry has been altered, according to
With an installation according to
In the case of steam boilers, the tubes of the tube bundle can be cleaned.
In the case of turbines, the blading or other components can be cleaned, it being possible, frequently, to dispense with removal of the same since, according to principles of the present invention, even spaces between the blades can be cleaned in an effective manner when in the mounted state. This allows considerable cost savings as compared with conventional methods of cleaning.
Furthermore, advantageously, according to principles of the present invention, surfaces in power plants can be worked on:
Water jet honing: the central bores of steam turbine rotors are worked on. This enables the machine times to be reduced considerably, as compared with conventional methods.
Blade reconditioning: the blade surfaces of gas turbines are worked on, in order to remove surface cracks.
As compared with the systems based on pure water jets, the following advantages can be achieved in this case:
Lesser energy consumption;
Improved cleaning performance;
Settable surface characteristics in the case of the surfaces to be worked on;
Superior surface quality;
Settable material removal rates;
Improved handling capability, owing to the reduced pressure;
Smaller dimensions of feed lines (for example, having a flexible tube diameter of less than 12 mm) and nozzles;
Smaller radius of bend of the feed line, of less than 50 mm, allows use in confined spatial conditions, even in narrow gaps; and
Lower costs of the installation.
While the invention has been described in detail with reference to exemplary embodiments thereof, it will be apparent to one skilled in the art that various changes can be made, and equivalents employed, without departing from the scope of the invention. The foregoing description of the preferred embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The embodiments were chosen and described in order to explain the principles of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents. The entirety of each of the aforementioned documents is incorporated by reference herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2009 043 697.9 | Oct 2009 | DE | national |
