DETAILED DESCRIPTION OF THE INVENTION

[0026] As illustrated in FIG. 1, an improved high-pressure abrasive waterjet assembly 10 is provided in accordance with a preferred embodiment of the present invention. (While the present invention is described herein in the context of an abrasive waterjet, it should be understood that the present invention is not limited to abrasive waterjets, but may be used to generate and manipulate any type of high-pressure fluid jet.) The assembly 10 includes a cutting head 22 that contains a jewel orifice 20 held by an orifice mount 11, and mixing tube 49. As is known in the art, high-pressure fluid is provided to the orifice 20 through nozzle body 37 to generate a high-pressure fluid jet, into which abrasives may be entrained via port 74. (The cutting head is provided with a second port to allow the introduction of a second fluid, for example air, or to allow the cutting head to be connected to a vacuum source or sensors.) The high-pressure fluid jet and entrained abrasives flow through mixing tube 49 and exit the mixing tube as an abrasive waterjet.

[0027] In accordance with the present invention, and as best seen in FIGS. 2 and 3, the orifice mount 11 has a frusto-conical outer surface 12 that seats against a corresponding frusto-conical wall 26 formed in a bore 23 of cutting head 22. As discussed above, it is desirable for the frusto-conical surface 12 of the orifice mount 11 to form an included angle 18 of 55-80°. This angle allows the orifice mount to be easily placed into and removed from the cutting head.

[0028] Applicants however, have further improved the performance of the orifice mount 11, by reducing the length 69 of the frusto-conical surface 12. As such, a radial distance 13 between a midpoint 15 of the frusto-conical surface 12 and the longitudinal axis or centerline 14 of the orifice mount 11 is reduced, as compared to conventional mounts. By minimizing the distance 13 between the longitudinal axis of the orifice mount and the center point 15 of the frusto-conical surface 12, deflection of the mount adjacent the jewel orifice 20 when under pressure is reduced. Furthermore, by reducing distance 13, the mount is more stable when subjected to pressure during operation of the system. To further improve the accuracy of the system, distance 16 between the midpoint 15 of the frusto-conical surface 12 and a top surface 17 of the orifice mount 11 is also maximized, thereby increasing the stability of the orifice mount under pressure. In a preferred embodiment, length 69 is 0.1-0.2 inch. In a preferred embodiment, distance 13 is 0.11-0.19, and preferably 0.15-0.185 inch. In a preferred embodiment, distance 16 is 0.15-0.3 inch.

[0029] As seen in FIG. 3, this preferred geometry for the orifice mount 11 is appropriate whether the jewel orifice 20 is recessed below the top surface 17 of mount 11, or is substantially flush with the top surface of the orifice mount. While the geometry provides improved stability and reduced deformation regardless of the type, location and method of securing the jewel orifice, applicants believe the increased stability achieved in accordance with the present invention is particularly beneficial when the jewel orifice 20 is mounted with a hard seal, for example, with a metallic seal.

[0030] In an alternative embodiment, as shown in FIG. 3, the orifice mount 11 is provided with an annular member 19 extending parallel to the longitudinal axis 14 of the orifice mount, below the frusto-conical surface 12. When assembled into a cutting head, the annular member 19 may be aligned with a vent 35, as shown in FIG. 4A, that is open to atmosphere. In a preferred embodiment, vent 35 extends laterally from an outer surface 36 of the cutting head 22 to the bore of the cutting head, to a point adjacent the annular member of the orifice mount, downstream of the frusto-conical wall 26 of the cutting head. The provision of a vent 35 relieves a vacuum that typically forms below the orifice mount during operation of the high-pressure fluid jet system. A vacuum in this area causes reverse flow of abrasives and results in mixing inefficiency. This problem is reduced in accordance with the present invention.

[0031] In a preferred embodiment, the orifice mount 11 is made from a material having a 2% yield strength of above 100,000 psi. Examples of preferred materials include stainless steel PH 15-5, PH 17-4, and 410/416.

[0032] As best seen in FIGS. 4A, 4B, and 10, the cutting head 22 is provided with a bore 23 extending therethrough along a longitudinal axis 24. A first region 25 of the bore 23 forms a frusto-conical wall 26 in the cutting head body. Similar to the structure of the orifice mount 11, a radial distance 27 between the longitudinal axis 24 of the cutting head and a midpoint 28 of the frusto-conical wall 26 is reduced as compared to conventional cutting heads. In a preferred embodiment, distance 27 is 0.11-0.19 inch, and preferably 0.15-0.185 inch. It will be appreciated from the drawings that when the orifice mount 11 is positioned in the cutting head 22, the longitudinal axes of the orifice mount and the cutting head are aligned. Also, in a preferred embodiment, the midpoint 28 of the frusto-conical wall 26 approximately aligns with the midpoint 15 of frusto-conical surface 12 within a distance of 0.05 inch. Given that the length 68 of the frusto-conical wall 26 must be sufficient to support the load created by the pressure acting on a diameter 70 of a bore 38 of nozzle body 37, a ratio of length 68 to diameter 70 is 0.2-0.47. Similarly, in a preferred embodiment, a ratio of the length 69 of the frusto-conical surface 12 to diameter 70 is 0.2-0.47.

[0033] As discussed previously, high-pressure fluid is provided to the cutting head via nozzle body 37. As best seen in FIGS. 1 and 5, nozzle body 37 has a bore 38 extending therethrough along longitudinal axis 39. A first region 40 of nozzle body 37 is provided with a plurality of threads 41 on an outer surface of the nozzle body. The nozzle body 37 is further provided with a first pilot wall 42 upstream of the threads 41 and a second pilot wall 43 downstream of threads 41. As best seen in FIG. 4A, a region 29 of the bore 23 extending through cutting head 22 is provided with a plurality of threads 30. This region of the cutting head bore is also provided with a first pilot wall 31 upstream of threads 30 and with a second pilot wall 32, downstream of the threads 30. When the nozzle body 37 is screwed into cutting head 22, the first and second pilot walls of the cutting head engage the first and second pilot walls of the nozzle body, respectively, thereby increasing the accuracy of the alignment of the nozzle body and cutting head. Applicants believe that providing two pilot diameters, longitudinally spaced from one another, provides improved results over conventional systems that use only a single pilot surface.

[0034] As further illustrated in FIG. 4A, the bore 23 of cutting head 22 further defines a mixing chamber 33 and a shoulder 34, downstream of mixing chamber 33. In a preferred embodiment, a mixing tube 49, having a bore 50 extending therethrough along a longitudinal axis 51 to define an inlet 63 and an outlet 64, is positioned in the cutting head 22. As illustrated in FIG. 6, the mixing tube 49 is provided with a collar 52 rigidly fixed to an outer surface 53 of the mixing tube, in an upper region 54 of the mixing tube. To rigidly affix the collar to the mixing tube, a variety of methods may be used, including press fitting, shrink fitting, or a suitable adhesive material. The collar can also be formed during the manufacturing process for making the mixing tube and machined to final dimensions by grinding. The collar may be made out of metal, plastic, or the same material as the mixing tube.

[0035] The collar 52 has a sufficiently small outer diameter to slide upward through the bore 23 of the cutting head, yet the outer diameter of the collar is sufficiently large that it seats against shoulder 34 and prevents the mixing tube from being inserted further into the cutting head 22. In a preferred embodiment, as shown in FIG. 6, a wall thickness 75 of collar 52 is 0.01-0.2 inch. Because the collar 52 is rigidly fixed to an outer surface of the mixing tube, it precisely locates the mixing tube axially, within the bore of the cutting head 22, without the need for pins, inserts or other structure currently used in the art to locate the mixing tube. An o-ring 73 may be positioned between the collar 52 and shoulder 34 to seal the mixing chamber 33 from back flow.

[0036] In a preferred embodiment, the collar 52 is cylindrical, and is used to position the mixing tube against the collet 71 and collet nut 72, that is selectively tightened and loosened against the assembly. As best seen in FIGS. 1 and 4A, the bore 23 of cutting head 22 is conical downstream of shoulder 34, to matingly engage the outer walls of collet 71. When the collet nut 72 is loosened, the collar 52 rests on the upper surface of the collet 71, preventing the mixing tube 49 from falling out of the cutting head 22, and from being pulled out of the cutting head. Alternatively, as shown in FIG. 7, the collar that is rigidly fixed to an outer surface of the mixing tube may be frusto-conical, such that when the mixing tube 49 is inserted into the distal end of the cutting head, the collar 58 locates the mixing tube both axially and radially.

[0037] Collar 52 may be rigidly fixed to an outer surface of the mixing tube 49 at any desired location, to precisely position the inlet 63 of the mixing tube at a specific location in the cutting head bore 23. While the exact location of collar 52 may be fine tuned depending on the operating parameters, in a preferred embodiment, a distance 57 between a top surface 55 of the mixing tube and a bottom surface 56 of collar 52 is 0.02-2.0 inch. In this manner, the tool tip accuracy of the system is improved.

[0038] In an alternative embodiment, as shown in FIG. 8, the mixing tube 49 is provided with a first cylindrical region 65 adjacent the inlet 63 to the mixing tube, the outer diameter 66 of the first cylindrical region 65 being less than the outer diameter 67 of the mixing tube 49 downstream of the first cylindrical region. In this manner, a step caused by the change in outer diameter of the mixing tube seats against the shoulder 34 in the cutting head 22, accurately locating the mixing tube in a selected axial position.

[0039] In an alternative embodiment, as illustrated in FIGS. 9A and 9B, a frusto-conical collar 59 is positioned on mixing tube 49, which in turn is held via an interference fit in a nut 60 that has threads 61 to engage a threaded inner surface 62 of a cutting head.

[0040] As seen in FIG. 1, the improved apparatus for generating a high-pressure fluid jet provided in accordance with the present invention, includes a shield 44 coupled to an end region 46 of the cutting head. The shield 44 is provided with a flange 45 that forms an interference fit with a groove in the collet nut 72. An annular skirt 47 extends downward from the flange 45 surrounding an end region of the mixing tube 49. In this manner, the shield substantially contains spray from the fluid jet. In a preferred embodiment, as shown in FIG. 1, a disk 48 of wear-resistant material, such as polyurethane, is positioned in an inner region of the shield 44.

[0041] From the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.