EP2308646B1 - Method for working on workpieces by means of a water jet that contains abrasive and emerges under high pressure from a nozzle, water jet installation for executing the method, and application of the method - Google Patents

Description

TECHNICAL AREA

The present invention relates to the field of machining work pieces by means of water jets. It relates to a method for processing, in particular cleaning, of a workpiece by means of a high-pressure emerging from a nozzle, abrasive-containing water jet according to the preamble of claim 1, and a water jet system for implementation of the procedure. Moreover, the invention relates to a method for using the inventive water jet method.

STATE OF THE ART

Components of power plants are subject during their operation of a high mechanical and thermal stress. This is particularly true for the hot gas flow exposed components of gas turbines whose surfaces in addition to the extreme mechanical and thermal stresses also unwanted thermal and chemical reactions to form non-metallic layers, such as scale or corrosion coatings, are exposed with negative effects on performance. This requires regular maintenance intervals to check the condition of these components and their removal and / or cleaning, repair or replacement if necessary.

Methods for cleaning gas turbine components, such as blades, are known in a variety of forms. Sandblasting is one of the known and established methods in the field. Air compressed to a pressure of several bars, to which an abrasive is added, is directed to the surface to be treated. The particles of the abrasive which impinge on the surface with high energy cause a cleaning effect. Disadvantages of these methods, however, are inaccurate control and in a relatively coarse material removal with adverse changes in the surface quality of the workpiece.

Another type of cleaning method is based on the high-pressure water jet technique, with pure or added with an abrasive water jets are applied to the surface to be cleaned. The high pressure water jet technique uses water pressures of up to 600 MPa to produce a high velocity water jet. Such a high velocity water jet can be used as an omnidirectional tool for cutting or cleaning applications.

1. (1) reine Wasserstrahlen (siehe Fig. 1),
2. (2) schleifmittelhaltige Wasserstrahlen, die durch Eintrag eines Schleifmittels in einen vorher erzeugten reinen Wasserstrahl generiert werden (Abrasive Injection Water Jets AIWJ; siehe Fig. 2), und
3. (3) schleifmittelhaltige Wasserstrahlen, bei denen der Strahl durch den Austritt einer unter Druck stehenden Suspension des Schleifmittels aus einer Düse erzeugt wird (Abrasive Suspension Water Jets ASWJ; siehe Fig. 3).

Depending on the particular application, water jets working according to three different principles are used, namely:

1. (1) pure water jets (see Fig. 1 )
2. (2) Abrasive water jets generated by the introduction of an abrasive into a previously generated clean stream of water (Abrasive Injection Water Jets AIWJ; Fig. 2 ), and
3. (3) Abrasive water jets in which the jet is generated by the exit of a pressurized suspension of the abrasive from a nozzle (Abrasive Suspension Water Jets ASWJ; Fig. 3 ).

At the in Fig. 1 Simplified illustrated first principle 10 water is supplied via a water supply line 11 of a pressure pump 12 in a water jet system and pumped at high pressure into a pressure line 13, which leads to a suitable nozzle 14. The high pressure water in the pressure line 13 then exits the nozzle 14 as necessary to form a high energy water jet. With such pure water jets soft materials such as fabrics, leather, solidified foams, food, etc. can be cut.

For cleaning applications mainly systems using pure water jet are used. Typical parameters for pure water jet cleaning are working pressures of up to 300 MPa and volume flow rates of about 30 liters / min, resulting in high energy consumption (up to 150 kW). Corresponding high pressure pumps are also very expensive.

• alle Metalle (Stahl, Aluminium, Kupfer, Titan etc.)
• Glas
• Synthetische Materialien
• Verbundwerkstoffe, und
• Beton.

At the in Fig. 2 In a water jet installation 20, water is again supplied via a water feed line 11 to a pressure pump 12 and pumped at high pressure into a pressure line 13, which leads to a suitable nozzle 14. The high pressure water in the pressure line 13 then exits the nozzle 14 as necessary to form a high energy water jet. In a subsequent mixing tube 16 is the pure water jet then admixed in an entry device 17, an abrasive which has been introduced via an abrasive supply 18. At the end of the mixing tube 16 then exits a high-energy abrasive containing water jet 19. Such a system is for example in the document WO-A1-2005 / 051598 described. Such AIWJ (abrasive injection water jet) jets are mainly used in stationary cutting applications. With them you can cut all technical materials like:

• all metals (steel, aluminum, copper, titanium etc.)
• Glass
• Synthetic materials
• Composites, and
• Concrete.

In the device according to GB 2073630 a partial flow is branched off from a pressurized water jet in order to produce an abrasive suspension in a reservoir (8, 9, 10). By forming the nozzle (2) as a jet pump, the suspension produced is sucked from a chamber (10) of the storage container (8) and conveyed into the nozzle (2), where it is accelerated and entrained by the water jet flowing at high speed.

The ASWJ (abrasive suspension water jets) produced according to the third principle are generally used for mobile and special applications. The advantages of the ASWJ beams compared to the AIWJ beams generated by the second principle are a higher efficiency (up to a factor of 4-5 higher) and the ability to use these beams in all layers and environments.

At the in Fig. 3 In a water jet installation 30, water is again supplied via a water feed line 11 to a pressure pump 12 and pumped at high pressure (up to 200 MPa) into a pressure line 13 which leads to a suitable nozzle 14. At a tee 21, the water flow is split. A part flows via a first throttle valve 27 and a mixing piece 28 directly to the nozzle 14. A second, smaller part flows in a bypass line 23 via a second throttle valve 22 in a filled with abrasive and after removal of a blind plug 25 refillable pressure tank 24 and from there via a shut-off valve 26 to the mixing section 28. While the water through the Pressure tank 24 flows, it rips the abrasive particles with. The resulting water / abrasive mixture is then placed in the mixing section 28 in the main water stream. With the throttle valves 22 and 27, the proportion of abrasive in the emerging from the nozzle 14 abrasive-containing water jet 29 can be controlled. Such a system is for example in the document DE-A1-199 09 377 described.

WO 97/31752 shows a method in which the treatment suspension between a collecting container (30), in which simultaneously the workpiece (10) is treated, and one of a high-pressure pump (72) acted upon chamber (64) is circulated. From the collecting container (30), the suspension is filled by means of a pump (80) in the high-pressure chamber (64). Once the intended level has been reached, the system is ready for operation. By operating a piston (74), the abrasive-containing suspension is blasted through the nozzle (20) onto the surface (12) of the workpiece (10) under an overpressure of up to 80 MPa. After emptying the high-pressure chamber (64), the surface treatment is discontinued until the completion of the refilling of the chamber (64).

The device according to US 4854090 is also characterized by a batch to be filled pressure vessel (201), which is emptied in the filled state by applying a carrier liquid under high pressure through the nozzle (222). By a convenient arrangement and circuit of pumps (209, 210) and valves (211, 212, 213, 221) is changed between loading and unloading cycle. During the filling process of the pressure vessel (201), the reservoir (205) is under pressure, outside the filling process, it can be pressure relieved.

• die ungenaue Steuerung des Schleifmittelanteils in der Suspension;
• die fehlende Möglichkeit eines kontinuierlichen Betriebs, da nach einer gewissen Zeit der Betrieb unterbrochen und der Drucktank mit Schleifmittel wieder aufgefüllt werden muss; und
• die hohen Arbeitsdrücke erfordern dementsprechend dimensionierte Komponenten der Wasserstrahlanlage mit der Folge einer erschwerten Handhabung und eines begrenzten Einsatzbereichs hinsichtlich enger Raumverhältnisse.

Major disadvantages of the currently known systems operating at pressures between 50 MPa and 200 MPa according to the third principle are:

• the inaccurate control of the abrasive content in the suspension;
• the lack of possibility of continuous operation, because after a certain time the operation has to be interrupted and the pressure tank has to be refilled with abrasive; and
• the high working pressures require accordingly sized components of the water jet system, resulting in a difficult handling and a limited range of application in terms of narrow space.

PRESENTATION OF THE INVENTION

It is an object of the invention to provide a suitable in particular for cleaning applications method for treating workpieces by means of a high pressure emerging from a nozzle abrasive containing water jet, which can be operated continuously and avoids the disadvantages of known methods described above, and a water jet system for carrying out the To create a procedure.
In particular, the invention has for its object to provide such a method and such a system, which are the requirements of an application for power plants, such as turbines, grown. This field of application requires effective use in confined spaces, such as in narrow gaps, and also places high demands on the surface finish after machining.

These objects are achieved by the totality of the features of the independent claims. It is essential for the invention that in a first step in a mixing vessel at normal pressure an abrasive and water-containing abrasive suspension is provided, that in a second step, the provided abrasive suspension by means of a pump from the mixing vessel aspirated to a working pressure above normal pressure of 15 MPa to 25 MPa is brought, and that in a third step from the standing under the working pressure abrasive suspension by means of a nozzle a abrasive-containing water jet is generated.
By the preparation of the suspension carried out under normal pressure, it is possible to continuously provide suspension without having to interrupt the jet generation and application. The abrasive contained in the water massively increases the cleaning effect of the jet in a conventional manner.

According to one embodiment of the invention, a mixture with water and the abrasive is prepared in an open mixing container to provide the abrasive suspension under normal pressure in an open mixing container. This ensures that the suspension in the mixing container can be added at any time without difficulty.

Preferably, the mixture is kept in motion in the mixing container continuously, in particular by means of an agitator.

The comparatively low working pressure of about 15 MPa to 25 MPa allows the use of less expensive components (eg pumps) and reduces energy consumption. An outstanding advantage of the invention is also that the low working pressure allows the use of small dimensioned and flexible components of the water jet system, such as pressure lines and cleaning heads, whereby it is now possible with the aid of the invention to effectively treat difficult to access surfaces. As a result, it is possible in certain cases to dispense with the elaborate removal of the workpieces to be cleaned. Especially in power plant construction, this represents an advantage that should not be underestimated, leading to considerable cost savings for the power plant operator.

According to another preferred embodiment, an abrasive having a hardness of at least 7 according to the Mohs scale is added to the water.
The abrasive particles have a diameter in the range of 0.1 mm to 0.3 mm.

Preferably, the abrasive suspension is brought to the working pressure by means of a pump and the abrasive suspension brought to working pressure is passed via a pressure line from the outlet of the pump directly to the nozzle, wherein a diaphragm pump is used as a pump.

An embodiment of the water jet system according to the invention is characterized in that the pump is a diaphragm pump, that the diaphragm pump has a pump chamber limited by a diaphragm, which communicates via an inlet valve with the suction line and an outlet valve with the pressure line, and that the valves respectively a valve sleeve forming a central valve passage, which is closed at the downstream end by a valve member seated, against the flow direction resiliently biased closing element. The use of a diaphragm pump has the advantage of low wear compared to other pump types, such as piston pumps.

A preferred development is characterized in that the valve bushing and the closing element of the valves are made of a hard metal, in particular tungsten carbide, and that the valve seats are ground.

In particular, the closing element in the area corresponding to the valve seat is spherical and biased by a compression spring in the closing direction.

Another embodiment of the system according to the invention is characterized in that a pressure relief valve is arranged in the pressure line. Preferably, the mixing container has an agitator equipped with a motor and is designed as an open container.

The method according to the invention is advantageously used for cutting and / or cleaning tasks in power plant components, in particular boilers, heat exchangers and turbines.

By applying the novel features defined in more detail in the claims, it is now possible for the first time to combine the advantages of various known methods of water jet technology in an advantageous manner and thus to open up new application possibilities for this technique.

BRIEF EXPLANATION OF THE FIGURES

Fig. 1

das vereinfachte Schema einer mit reinem Wasser arbeitenden Wasserstrahlanlage nach dem Stand der Technik;

Fig. 2

das vereinfachte Schema einer mit Schleifmittelzusatz nach dem Injektionsprinzip arbeitenden Wasserstrahlanlage nach dem Stand der Technik;

Fig. 3

das vereinfachte Schema einer mit Schleifmittelsuspension arbeitenden Wasserstrahlanlage nach dem Stand der Technik;

Fig. 4

das vereinfachte Schema einer mit Schleifmittelsuspension arbeitenden Wasserstrahlanlage gemäss einem Ausführungsbeispiel der Erfindung;

Fig. 5

den Längsschnitt durch ein herkömmliches Ein- bzw. Auslassventil einer für die Anlage nach Fig. 4 geeigneten Membranpumpe; und

Fig. 6

den Längsschnitt durch ein gegenüber Fig. 5 modifiziertes und für die Anlage nach Fig. 4 optimiertes Ein- bzw. Auslassventil.

The invention will be explained in more detail with reference to embodiments in conjunction with the drawings. Show it

Fig. 1

the simplified scheme of a prior art water jet water jet system;

Fig. 2

the simplified diagram of a prior art abrasive applicator using water jet apparatus;

Fig. 3

the simplified scheme of an abrasive suspension water jet plant according to the prior art;

Fig. 4

the simplified scheme of working with abrasive suspension water jet system according to an embodiment of the invention;

Fig. 5

the longitudinal section through a conventional inlet and outlet valve for a plant after Fig. 4 suitable diaphragm pump; and

Fig. 6

the longitudinal section through an opposite Fig. 5 modified and for the plant Fig. 4 optimized inlet and outlet valve.

WAYS FOR CARRYING OUT THE INVENTION

In Fig. 4 is the simplified scheme of working with abrasive suspension water jet system according to an embodiment of the invention reproduced. The water jet system 40 comprises a mixing vessel 31, a diaphragm pump 36 connected on the input side to the mixing vessel 31 via a suction line 35 and a nozzle 44 connected to the outlet of the membrane pump 36 via a pressure line 39.

In the mixing vessel 31, an abrasive suspension 34 is mixed under normal pressure and kept ready. For mixing and maintaining the abrasive suspension, an agitator 33 is provided which is driven by a motor 32. The mixing container 31 may be open at the top so that the components of the abrasive suspension can be replenished as needed and without interrupting the operation. Working under normal pressure greatly facilitates the controlled addition of water and abrasive into the mixing vessel 31 to maintain a constant mixing ratio. Variants of an automated charging of the mixing container 31 are preferred and can be implemented with comparatively simple technical means. Thus, a continuous operation of the water jet system is guaranteed with little equipment.

The diaphragm pump 36, which has a pump chamber 38 limited by a diaphragm 37, sucks in an intake stroke (movement to the left in FIG Fig. 4 ) via an inlet valve 41 from the mixing container 31 suspension and pushes them in a working stroke (movement to the right in Fig. 4 ) via an outlet valve 42 at high pressure in the pressure line 39. The suspension flows through the pressure line 39 (in which a pressure relief valve is arranged to prevent damage to the pump 36 by overpressure) directly to the carbide (tungsten carbide) existing nozzle 44. There is a schleifmittelhaltiger water jet 45 formed, which can be punctiform, spread or otherwise shaped depending on the requirement of the application.

Because of the proportion of abrasive in the water jet, the pressure in the pressure line 39 may be higher than that of pure water ( Fig. 1 ) from 200 MPa to 15 MPa to 25 MPa, preferably 20 MPa, without impairing the cleaning effect. This allows the use of small dimensioned pressure lines in the form of hoses with diameters below 12 mm. Such hoses have a high flexibility (bending radius less than 50 mm) and are therefore also suitable for use in tight space conditions, as prevail, for example, within the blading of turbines.

Because of the proportion of abrasive in the pumped suspension, a diaphragm pump 36 is used instead of a conventional piston pump whose structure and function, for example, in the document US B2-6,899,530 is described. These pumps are commonly used to pump corrosive and abrasive media, but at comparatively low pressures. In the present application, the sucked suspension is brought to pressures of about 15 MPa to 25 MPa with such a pump. An operation at these pressures is achieved in that the inlet and outlet valves 41, 42, which are subject to a special wear, according FIGS. 5 and 6 have been modified.

Diaphragm pumps are volumetric pumps that generate pressure by mechanical displacement of synthetic membranes. To achieve constant pressure and flow, each pump chamber (38 in Fig. 4 ) with two valves (41, 42 in Fig. 4 ) fitted. A pump usually contains three to five such pump chambers. Because of the high flow speed The abrasive suspension when opening the valves are mainly exposed to wear (the erosion is very much dependent on the speed of the eroding particles).

The standard design of the valves of the pump chamber of a diaphragm pump of the type described is in Fig. 5 reproduced: The valve 42 'of Fig. 5 includes an (annular) valve sleeve 46 defining a central valve passage 50. A disc-shaped closing element 48 'is pressed by means of a compression spring 49 against a valve seat 47' at the downstream end of the valve sleeve 46 and thus closes the valve passage 50 and thus the adjacent pump chamber. When pressure is generated in the pumping chamber 38 by the diaphragm 37, the closing element 48 'lifts against the pressure of the spring 49 from the valve seat 47' and a volumetric flow leaves the pumping chamber 38 through the associated valve passage.

A major problem with the valve 42 'is that if the valve does not close or does not close properly, high local flow velocities will occur at the location of the leakage and the closure member 48' and valve sleeve 46 will erode very severely. Even tungsten carbide valves are eroded in less than half an hour. The reason for the lack of tightness in such standard valves is the lack of centering of the disk-shaped closing element 48 'in the valve bush 46: The closing element 48' does not have sufficient guidance, and because of the (flat) shape of the standard closing element 48 '(ground radius of the valve seat 47th ') there are some areas where there is no surface contact between the closure member 48' and the valve seat 47 'when the closure member 48' is not perfectly centered.

To remedy this, the valve geometry is according to Fig. 6 been changed. The closing element 48 of the valve 42 now has the shape of a ball or a spherical section. This has the consequence that, even if the closing element 48 is not perfectly centered, 47 surface contact still prevails over the entire circumference of the valve seat and the tightness is ensured. At the same time is the Contact surface on the valve seat 47 has been significantly increased. In addition, all sealing surfaces are ground to achieve a good seal. As the material for the closing element 48 and the valve sleeve 46 tungsten carbide is used. It has been proven that the necessary maintenance intervals can be considerably extended by these measures. Intervals of 50 hours and more have proven to be sufficient.

• Bei Dampfkesseln können die Rohre der Rohrbündel gereinigt werden.
• Bei Turbinen können die Beschaufelung oder andere Komponenten gereinigt werden, wobei auf einen Ausbau derselben häufig verzichtet werden kann, da nach der Erfindung selbst Zwischenräume zwischen den Schaufeln im Einbauzustand wirksam gereinigt werden können. Dies erlaubt erhebliche Kosteneinsparungen gegenüber herkömmlichen Methoden der Reinigung.

With a system according to Fig. 4 can now be produced in continuous operation, a abrasive water jet with a pressure of about 15 MPa up to 25 MPa, which can be used with particular advantage in the field of power plant technology. In particular, the following cleaning tasks can be performed:

• In steam boilers, the tubes of the tube bundles can be cleaned.
• In turbines, the blading or other components can be cleaned, with an expansion of the same can often be dispensed with, since according to the invention even gaps between the blades in the installed state can be effectively cleaned. This allows significant cost savings over traditional methods of cleaning.

• Wasserstrahl-Honen: Es werden die zentralen Bohrungen von Dampfturbinen-Rotoren bearbeitet. Hierdurch lassen sich gegenüber herkömmlichen Methoden die Maschinenzeiten erheblich reduzieren.
• Schaufel-Aufarbeitung: Die Schaufeloberflächen von Gasturbinen werden bearbeitet, um Oberflächenrisse zu beseitigen.

Furthermore, can be processed according to the invention in the power plant area with advantage surfaces:

• Water jet honing: The central boreholes of steam turbine rotors are machined. As a result, the machine times can be significantly reduced compared to conventional methods.
• Shovel workup: The blade surfaces of gas turbines are machined to remove surface cracks.

• Weniger Energieverbrauch;
• Verbesserte Reinigungsleistung;
• Einstellbare Oberflächeneigenschaften bei den bearbeiteten Oberflächen;
• Überlegene Oberflächengüte;
• Einstellbare Materialabtragungsraten;
• Verbesserte Handhabbarkeit aufgrund des verringerten Druckes;
• Geringer dimensionierte Zuleitungen (beispielsweise mit einem Schlauchdurchmesser von weniger als 12 mm) und Düsen;
• Geringer Biegeradius der Zuleitung von weniger als 50 mm ermöglicht einen Einsatz unter engen Raumverhältnissen, selbst in engen Spalten;
• Geringere Anlagenkosten.

Compared to systems based on pure water jets, the following advantages result:

• Less energy consumption;
• Improved cleaning performance;
• Adjustable surface properties of the machined surfaces;
• Superior surface quality;
• Adjustable material removal rates;
• Improved handling due to reduced pressure;
• Less dimensioned supply lines (eg with a hose diameter of less than 12 mm) and nozzles;
• Low bending radius of the supply line of less than 50 mm allows use in confined spaces, even in narrow gaps;
• Lower plant costs.

LIST OF REFERENCE NUMBERS

10,20,30,40

WaterJet

11

water supply

12

pressure pump

13.39

pressure line

14.44

jet

15

waterjet

16

mixing tube

17

entry device

18

Abrasive feed

19,29,45

Water jet (containing abrasive)

21

Tee

22.27

throttle valve

23

bypass line

24

Pressure tank (with abrasive)

25

blind plug

26

shut-off valve

28

mixed piece

31

mixing tank

32

engine

33

agitator

34

Abrasive suspension

35

suction

36

diaphragm pump

37

membrane

38

pump chamber

41

intake valve

42.42 '

outlet valve

43

Pressure relief valve

46

valve sleeve

47.47 '

valve seat

48.48 '

closing element

49

compression spring

50

Valve passage

Claims (12)

1. Method for working on a workpiece by means of a water jet (45) that contains abrasive and emerges under high pressure from a nozzle (44), wherein in a first step an abrasive suspension (34) containing abrasive and water is provided at normal pressure, in a mixing vessel (31) is mixed and the mix ratio is kept constant, wherein in a second step the provided abrasive suspension (34) is sucked out of the mixing vessel (31) by means of a pump (36) and is brought to a working pressure of 15 MPa to 25 MPa that is above normal pressure, wherein in a third step the abrasive suspension (34) under the working pressure is fed to a nozzle (44), and in a fourth step a water jet containing abrasive emerges from the nozzle (44) for the purpose of acting on the workpiece surface.
2. Method according to Claim 1, characterized in that, for the purpose of providing the abrasive suspension (34) that is at normal pressure, the mixture in the mixing vessel (31) is kept continuously in motion, in particular by means of an agitator (32, 33).
3. Method according to either of Claims 1 and 2, characterized in that the abrasive has a hardness of at least 7 according to the Mohs scale.
4. Method according to any one of Claims 1 to 3, characterized in that the particles of the abrasive have a diameter in the range from 0.1 mm to 0.3 mm.
5. Method according to any one of Claims 1 to 4, characterized in that the abrasive suspension (34) is brought to the working pressure by means of a diaphragm pump (36), and the abrasive suspension (34) brought to working pressure is routed from the output of the pump (36) directly to the nozzle (44), via a pressure line (39).
6. Water jet installation (40) for executing the method according to any one of Claims 1 to 5, which water jet installation (40) comprises, for the purpose of realizing a water jet (45), a nozzle (44) that is connected, via a pressure line (39), to the output of a pump (36) that generates a pressure, characterized in that the pump (36) is a diaphragm pump which on its input side is connected, via an intake line (35), to a mixing vessel (31) that is at normal pressure and contains an abrasive suspension (34), for mixing and for maintaining a constant mix ratio of the abrasive suspension (34).
7. Water jet installation according to Claim 6, characterized in that the diaphragm pump (36) has a pump chamber (38) that is delimited by a diaphragm (37) and connected to the intake line (35) via an inlet valve (41) and connected to the pressure line (39) via an outlet valve (42), and the valves (41, 42) each comprise a valve sleeve (46), which constitutes a central valve passage (50) and which is closed, at the downstream end, by a closing element (48) that rests on a valve seat (47) and that is spring-biased contrary to the direction of flow.
8. Water jet installation according to Claim 7, characterized in that the valve sleeve (46) and the closing element (48) of the valves (41, 42) are produced from a hard metal, in particular tungsten carbide, and the valve seats (47) are ground-in.
9. Water jet installation according to Claim 7 or 8, characterized in that the closing element (48) is ball-shaped in the region corresponding to the valve seat (47), and is biased in the closing direction by a pressure spring (49).
10. Water jet installation according to any one of Claims 6 to 9, characterized in that a pressure relief valve (43) is arranged in the pressure line (39).
11. Water jet installation according to any one of Claims 6 to 10, characterized in that the mixing vessel (31) has an agitator (33) equipped with a motor (32), and the mixing vessel (31) is realized as an open vessel.
12. Application of the method according to any one of Claims 1 to 5 for cutting and/or cleaning tasks on power plant components, in particular boilers, heat exchangers or turbines.

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