Abstract:
A mobile collecting device ( 22 ) for the high-pressure water jet ( 26 ) of a water-jet tool ( 18 ), especially for working in confined places with difficult access in turbines or the like, in which a more flexible and safer operation is achieved by a closed collecting chamber ( 24 ), which extends over a large area and includes an outlet ( 30 ), and in which a rigid first collecting bed ( 34 ) formed of a first high-pressure-resistant material is arranged.

Description:
This application claims priority under 35 U.S.C. §119 to Swiss application no. 00036/08, filed 10 Jan. 2008, the entirety of which is incorporated by reference herein. 
     BACKGROUND 
     1. Field of Endeavor 
     The present invention refers to the field of machining of workpieces by material stripping. It relates to a mobile collecting device for the high-pressure water jet of a water jet tool and also to a method for its operation. 
     2. Brief Description of the Related Art 
     It has been known for a long time to use a water jet, which issues under very high pressure from a nozzle, for the machining, especially the cutting, of workpieces. In the case of so-called “abrasive water-jet cutting” (AWJ), water pressures of more than 300 MPa are used in order to produce a water jet, which is laden with abrasive substances, with a jet diameter of typically 1 mm. Such a water jet can be used as a cutting tool which acts in all directions and with which a wide range of metallic and non-metallic materials, with thicknesses of up to 200 mm, can be cut through. In this case, it is important not to only collect and drain off the water of the high-pressure water jet, but especially to render the kinetic energy of the water jet harmless by conversion into thermal energy if this water jet has worked its way through the workpiece and discharged rearwards (downwards) from the workpiece. 
     In the case of stationary systems, in which the nozzle head of the water-jet tool is movable in a plane in X and Y directions, the mostly plate-form workpiece is fixed on a largely jet-penetrable support base. Beneath the support base, special devices are then arranged over a large area for collecting and rendering harmless the high-pressure water jet which passes through the workpiece (see for example U.S. Pat. Nos. 4,112,797 and 5,295,425). 
     Compact collecting devices have already been proposed, however, which can be moved together with the water-jet tool and can also be used in the case of confined space conditions at the application site (see for example EP-A2-0 244 966 and EP-A2-0 252 657). In this case, however, it is disadvantageous that the entry areas which are provided for the water jet are very small so that the collecting devices have to be adjusted very accurately to the water-jet tool. 
     In a prior application of the assignee of this application, it was proposed to use a water-jet tool with turbine rotors and other components of power plants. With the turbine rotors fitted with rotor blades, according to  FIGS. 1 and 2 , it is a matter of separating the blades  12 , which are detachably fastened on the turbine wheels  11  of the rotor  10 , from the rotor  10  by cutting up the bolts  17 , which are interference-fitted in corresponding holes  16  and connect the blade roots  14 , which are beneath the blade platform  13  and recessed in annular grooves  15 , to the turbine wheel  11 , by a water-jet tool  18  in the longitudinal direction, and then forcing out the bolt sections from the holes  16 . The water-jet tool  18 , which includes a tool body  19  and an angled nozzle head  20  and is supplied with water via a water feed line  21 , is introduced into the interspace between adjacent turbine wheels  11  and  11 ′ ( FIG. 2 ) for this purpose. If the bolt  17  is cut through in the longitudinal direction, the high-pressure water jet discharges on the other side of the turbine disk  11  into the interspace which exists there and can cause damage if it is not collected and rendered harmless. 
     SUMMARY 
     One of numerous aspects of the present invention includes a collecting device for the high-pressure water jet of a water-jet tool which, even in inaccessible places and in the case of confined space conditions, can be used in different spatial positions in order to safely collect the water jet which passes through the workpiece during workpiece machining, and also a method for its operation. 
     According to another aspect, a closed collecting chamber, which extends over a large area and is provided with an outlet, and in which a rigid first collecting bed having a first high-pressure-resistant material is arranged, is advantageously provided for the device. 
     One exemplary development includes that the first collecting bed includes a plurality of layers, having the first high-pressure-resistant material, which are arranged one above the other, each of the layers is constructed from bars, formed of the first high-pressure-resistant material, which lie parallel in one plane next to each other, and the bars of consecutive layers are oriented orthogonally to each other. 
     Another exemplary development includes that a hard material is used as the first high-pressure-resistant material, wherein tungsten carbide (WC) is preferably used as the hard material. 
     A further exemplary development includes that the first collecting bed fills out the lower part of the collecting chamber, the upper part of the collecting chamber is filled with a filling material, and waste or fragmented material of the first high-pressure-resistant material is used as the filling material. 
     Another exemplary development includes that the collecting chamber is accommodated in a cubic housing and on the upper side which faces the high-pressure water jet is closed off by a cover of the housing. 
     According to a preferred exemplary development, a safety chamber is arranged after the collecting chamber in the direction of the high-pressure water jet, wherein in the safety chamber, a rigid second collecting bed formed of a second high-pressure-resistant material is arranged, the second collecting bed includes a plurality of layers, formed of the second high-pressure-resistant material, which are arranged one above the other, each of the layers is constructed from bars, formed of the second high-pressure-resistant material, which lie parallel in one plane next to each other, the bars of consecutive layers are oriented orthogonally to each other, and wherein the second high-pressure-resistant material is identical to the first high-pressure-resistant material. 
     Another exemplary development includes that the collecting chamber and the safety chamber are separated from each other by a partition, the safety chamber has openings, and a moisture sensor is associated with the openings and detects water which discharges from the opening of the safety chamber. 
     Furthermore, it is advantageous if an acceleration sensor is arranged on the collecting device for detecting penetration of the high-pressure water jet through a workpiece which is to be machined and located upstream of the collecting device. 
     In particular, the sensors are connected to a signal processing device which, at a signal output, generates a signal for controlling the water-jet tool. 
     Exemplary methods according to principles of the present invention include that the first impact of the high-pressure water jet upon the collecting device is detected in each case, and a corresponding signal is used for controlling the use of the water-jet tool, or a malfunction of the collecting device is detected and a corresponding signal is used for terminating the use of the water-jet tool. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is to be explained in more detail in the following based on exemplary embodiments in conjunction with the drawing. In the drawing 
         FIG. 1  shows in a perspective view a detail of a rotor with blades which are fastened on the rotor by means of bolts; 
         FIG. 2  shows, in a view which is comparable to  FIG. 1 , a method for removing the fastening bolts of the rotor blades by a high-pressure water jet; 
         FIG. 3  shows a mobile collecting device for a high-pressure water jet according to  FIG. 2  according to an exemplary embodiment of the invention; and 
         FIG. 4  shows the internal construction of the collecting device from  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     In  FIG. 3 , a mobile collecting device for a high-pressure water jet according to an exemplary embodiment of the invention is reproduced. This collecting device  22  is particularly suitable for applications when machining turbine rotors ( FIG. 2 ) and components of power plants, in which the space which is made available is limited. The external dimensions of the exemplary collecting device  22  are approximately 200 mm×80 mm×80 mm so that it can be used in the narrow interspaces between adjacent turbine wheels ( 11 ,  11 ′ in  FIG. 2 ) or rotor disks. 
     The collecting device  22  of  FIG. 3  has a cubic housing  23  which is closed off at the top by a cover  27 . The interior space of the housing  23  or of the collecting device  22  is divided by a partition  28 , which lies parallel to the cover  27 , into two chambers, specifically the (upper) collecting chamber  24 , in which the residual kinetic energy of the abrasive high-pressure water jet  26  is absorbed and converted into thermal energy, and the (lower) safety chamber  25 , by which it can be established when the device fails in its normal service so that the machining process can be aborted in sufficient time. The internal structure of the collecting device  22  is reproduced in  FIG. 4  in side view. 
     The collecting chamber  24  is filled at the bottom, i.e., directly above the partition  28 , with a first collecting bed  34  formed of at least four layers  34   a - d  of bars  36 , advantageously made of tungsten carbide (WC), which lie one above the other. The bars  36  of the same layer in this case are oriented parallel to each other, but perpendicularly to the bars of the adjacent layers so that a crosswise alternating lamination results. Above the layers  34   a - d , the collecting chamber  24  is filled with loose filling material  33  which includes or consists of WC waste or fragmented material (for example, used WC reversible tips). The filling material  33  serves for breaking down the coherence of the high-pressure water jet which enters the chamber. At the bottom of the collecting chamber  24 , an outlet  30  is attached, by which the material (water and solid particles) which enters the collecting chamber can be sucked out by a suction device in order to keep the application area clean. 
     The safety chamber  25 , which lies beneath the partition  28 , at the bottom is filled with a second collecting bed  35  formed of at least two layers  35   a, b  of bars  36  made of tungsten carbide, which are again arranged in a crosswise manner. A plurality of openings of small diameter, which serve as outlets and to which a moisture sensor  29  (drawn in with a dashed line in  FIG. 3 ) is allocated, are provided on one side of the safety chamber  25 . The moisture sensor  29  is activated if the high-pressure water jet  26  breaks through the collecting chamber  24  into the safety chamber  25  which lies beneath it so that the machining process can be stopped in sufficient time. The two layers  35   a, b  contain the jet in the process until the moisture sensor  29  has been safely activated. 
     An acceleration sensor  38  can be advantageously attached on the outer side of the collecting device  22  and is activated if the high-pressure water jet  26  passes for the first time through the workpiece, which is to be machined, onto the collecting device  22 . 
     Both the acceleration sensor  38  and the moisture sensor  29  can be used for controlling or checking the machining process. For this purpose, the sensors are connected to a signal processing device  31  which at a signal output  37  delivers corresponding control signals to the control unit (not shown in the figures) of the machining processes. The collecting device thus becomes part of the control system of the water-jet tool. If the moisture sensor  29  is activated, the machining process is aborted. If the acceleration sensor  28  is activated, for example the next machining step is initiated. 
     The collecting device  22  is simply and inexpensively constructed and represents an easily exchangeable wear-resistant component. It can be installed in an exchangeable manner in an application-specific holder. 
     LIST OF DESIGNATIONS 
     
         
         
           
               10  Rotor (turbine) 
               11 ,  11 ′ Turbine wheel 
               12  Blade 
               13  Blade platform 
               14  Blade root 
               15  Annular groove (turbine wheel) 
               16  Hole 
               17  Bolt 
               18  Water-jet tool 
               19  Tool body 
               20  Nozzle head 
               21  Water feed line 
               22  Collecting device 
               23  Housing 
               24  Collecting chamber 
               25  Safety chamber 
               26  High-pressure water jet 
               27  Cover 
               28  Partition 
               29  Moisture sensor 
               30  Outlet (collecting chamber) 
               31  Signal processing device 
               32  Opening (safety chamber) 
               33  Filling material (for example WC waste) 
               34  Collecting bed 
               34   a - d  Layer (for example WC bars) 
               35  Collecting bed 
               35   a, b  Layer (for example WC bars) 
               36  Bar 
               37  Signal output 
               38  Acceleration sensor 
           
         
       
    
     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.