Abrasive fluid jet system

Abstract: The invention is directed to an abrasive fluid jet system and a mixing tube for use in an abrasive fluid jet system. A mixing tube (54) and an abrasive fluid jet system that are more efficient and convenient to use can be provided by the provision of a mixing tube body (54) having a reference member (106) provided at a selected location on an outer surface (108) of the mixing tube body (54), such that when the mixing tube body (54) is placed into the bore of the cutting head (46), the reference member contacts a bottom surface (110) of the cutting head (46) and prevents the mixing tube body (54) from being inserted any further into the bore, thereby locating the mixing tube body (54) in a desired location.

Description: Technical Field This invention relates to an abrasive fluid jet cutting system and a mixing and ejecting tube for use in an abrasive fluid jet cutting system. Background of the Invention The cutting of numerous types of materials, for example, glass, metal, or ceramics, may be accomplished through use of a high-pressure abrasive fluid jet that is generated by mixing abrasive particles, for example, garnet, with a high-pressure fluid jet. Although different fluids may be used, high-pressure fluid jets are typically water, and are generated by high-pressure, positive displacement pumps that can pressurize water to 138-5170 bar (2,000-75,000 psi). Currently available systems for generating abrasive fluid jets are adequate, but have some disadvantages. For example, abrasive is fed to the system from a bulk hopper to a secondary hopper that has a metering device mounted in its base. Typically, the secondary hopper is filled by a feed tube in a self-regulating fashion, in which the abrasive will rise to some level in the hopper and then stop. The secondary hopper, although smaller than the bulk hopper, typically has a diameter on the order of 152-203 mm (6-8 inches) and a length of 381-508 mm (15-20 inches), which can be cumbersome, given that it is typically desirable to mount the secondary hopper on motion equipment. Furthermore, currently available systems do not always have a controlled or consistent feed rate of abrasive, which contributes significantly to the cost of operation. Also, manufacturing is somewhat cumbersome. Applicants therefore believe that an improved system for generating abrasive fluid jets is possible, and desirable, both from a manufacturing and performance viewpoint. An abrasive fluid cutting system in accordance with the preamble of claim 1 is known from document DE 3 631 512 A1. Summary of the Invention It is therefore an object of this invention to provide a mixing and ejecting tube and an abrasive fluid jet cutting system that are more efficient and convenient to use. This object is solved by the abrasive fluid jet cutting system of claim 1 and the mixing and ejecting tube of claim 3. Preferred embodiments are disclosed in the dependent claims. The high-pressure fluid jet can be generated by forcing a volume of high-pressure fluid, typically water, through a nozzle body and through a high-pressure orifice. The orifice is set into a tapered mount assembly, which in turn is seated in the cutting head. The high-pressure orifice is recessed in a top surface of the mount assembly to prevent the orifice from being damaged, for example, by being touched by an operator that will likely have abrasive on his or her hands. The sidewalls of the mount assembly are shallowly tapered, such that only the top surface of the mount assembly seals the high-pressure fluid, and the mount assembly does not swage itself into the cutting head. As a result, even after continued running at ultra-high pressures such as 3790 bar (55,000 psi), the mount drops out easily from the cutting head and does not require special tools to be removed, as is typically required with conventional taper mount systems. The high-pressure fluid jet emitted by the high-pressure orifice enters a mixing chamber wherein it entrains abrasive through an abrasive inlet port provided in the cutting head. The abrasive and high-pressure fluid jet are then mixed and ejected as an abrasive fluid jet through a mixing tube that is provided in the cutting head. The cutting head is provided with a simple bore into which the mixing tube is inserted. A reference member is provided at a selected location on an outer surface of the mixing tube, such that the reference member registers against a bottom surface of the cutting head, thereby positioning the mixing tube at a desired location. The mixing tube is then held in place by a retention device such as a nut Brief Description of the Drawings Figure 1 is a partial cross-sectional, elevational view of a preferred embodiment of the present invention. Figure 2 is an enlarged cross-sectional, elevational view of several elements of the preferred embodiment illustrated in Figure 1. Figures 3A and 3B are cross-sectional, elevational views of a portion of the preferred embodiment illustrated in Figure 1. Figure 4 is a partial cross-sectional, elevational view of an alternative embodiment of the present invention. Figure 5 is a partial cross-sectional, elevational view of an alternative embodiment of the present invention. Detailed Description of the Invention An improved abrasive fluid jet cutting system 10, provided in accordance with a preferred embodiment of the present invention, is illustrated in Figure 1. A volume of abrasive particles 18 is fed from abrasive bulk hopper 16 by compressed air at low velocities into air isolator 12 via inlet port 14. Although different types of abrasive may be used, a preferred embodiment uses garnet particles, on the order of 16-220 mesh. A baffle 22 is provided within the air isolator 12, the baffle having a hole 24 through which abrasive may fall. In a preferred embodiment, as illustrated in Figure 2, an angle α of the baffle, as measured between the baffle 22 and a horizontal plane 28 intersecting the lower-most edge 30 of the baffle, is 20°-60°, with preferred results being achieved when the baffle is 41°. It will be understood that the angle of the baffle may be changed to accommodate various vessel geometries. By providing an air isolator 12 having a baffle 22, air is vented from the abrasive as it passes through the baffle. The venting is further enhanced by providing vents 20 in a top region 36 of the air isolator 12. The venting of air from the abrasive ensures that the flow rate of abrasive through the system is independent of the pressure of the air pushing the abrasive from the bulk hopper. This improved consistency in abrasive feed rate is significant, in that it substantially reduces operating costs. Furthermore, by venting air from the abrasive in this manner, the air isolator 12 may be lightweight and 5-10 times smaller than its conventional counterpart, making the system more efficient and simple to use, particularly if it is necessary to mount the air isolator on equipment that moves during operation of the system. In a preferred embodiment, the air isolator has an outer diameter of 60.5 mm (2.38 inches), an inner diameter of 508 mm (2 inches)and a length of approximately 152 mm (6 inches). A discharge orifice or port 32 is provided in a bottom surface 34 of air isolator 12, the discharge orifice being selectively open or closed via operation of on/off device 58, as seen in Figure 2. In a preferred embodiment, the on/off device 58 comprises a rod 56 that passes through the hole 24 of baffle 22, the rod 56 being selectively raised to a first position 62 and lowered to a second position 64 via pneumatic cylinder 19. Rod 56 is coupled to a stopper 60 which covers the discharge orifice 32 when the rod is in a lowered position 64, thereby preventing the discharge of abrasive from air isolator 12. The rod and stopper are made of wear-resistant materials, and are only required to move short distances, thereby ensuring reliable performance and longevity. In a preferred embodiment, the on/off device 58 is controlled by the operator via conventional means, for example, a solenoid switch. By providing the on/off device 58 within air isolator 12, the system is simplified and made more compact, as compared to conventional systems where the on/off device is typically external to the hopper feed system. As best seen in Figure 2, a metering disk 40 having an orifice 42 is provided adjacent the bottom surface 34 of the air isolator 12, the orifice 42 of the metering disk being aligned with the discharge orifice 32. The size of the metering disk orifice controls the flow rate of abrasive through the system, and it may therefore be selected and changed, depending on the desired flow rate. In a preferred embodiment, a gap 38 between the metering disk 40 and bottom of the air isolator 12 is less than 1/16 of an inch (1.59mm), to ensure that abrasive backs up in the bottom of the air isolator. If the gap 38 is too large, the stream of abrasive may neck down, thereby pouring through the metering disk orifice in a stream that is smaller than the orifice, such that the metering disk fails to provide its desired function. Also, by providing a system in accordance with a preferred embodiment of the present invention, the abrasive flow may be stopped and started quickly and efficiently. As further illustrated in Figures 1 and 2, abrasive passing through the metering disk 40 enters a first port 68 of an adapter 66, which is further provided with a second port 70. In a preferred embodiment, the first port 68 and second port 70 are provided at an angle γ to each other of 30°-60°, with preferred results being obtained when γ is 45°, The second port 70 is provided with a vent 72 through which fluid and abrasive may be ejected from the system, for example, if a clog downstream 78 of the adapter 66 causes fluid and abrasive to flow in an upstream direction 74. As a result, water is prevented from backing up into the air isolator, such that the abrasive does not clump together, and continues to flow freely. Adapter 66 is further provided with one or more secondary vents 76 that allow air to enter the first port 68, thereby ensuring that the flow rate of abrasive through the metering disk and through the first port 68 is due to gravity, and is substantially independent of suction in the feedline 44. (It will be understood that the abrasive flow rate is typically measured in pounds/minute). To further shield the system from water spray, a protective shield 27 is provided around adapter 66. As illustrated in Figure 2, a bottom region 114 of air isolator 12 and a top region 116 of adapter 66 selectively and easily engage and disengage each other to facilitate cleaning. Although any conventional locking mechanism may be used, in a preferred embodiment, three pins 21 are engaged and locked into recesses 23 when the air isolator and adapter are turned a quarter turn relative to each other. It should also be noted that due to the small size of the air isolator 12, only 1-2 pounds of abrasive must be dumped when cleaning the system, as opposed to 5-300 pounds in conventional systems. After passing through adapter 66, abrasive 18 flows through feedline 44 that is coupled to a cutting head 46. More particularly, as best seen in Figure 3A, abrasive is gravity fed through the first port 68 as described above, and then is drawn through the second port 70, the feedline 44 and a first inlet 26 into mixing chamber 48, by a vacuum generated by a high-pressure fluid jet 50. The high-pressure fluid jet 50 thereby entrains the abrasive such that the fluid jet and abrasive are mixed and ejected through mixing tube 54 as an abrasive fluid jet 52. The high-pressure fluid jet 50 is generated by forcing a volume of high-pressure fluid 96, for example, water, from a high-pressure fluid source 11 through nozzle body 17 and a high-pressure orifice 94. The high pressure orifice 94 is set in a tapered mount 98, and is recessed in a top surface 100 of the tapered mount to reduce the likelihood that the orifice will be touched, for example, by an operator's hand which may have abrasive on it. The orifice is therefore less likely to be damaged. As best seen in Figure 3B, an angle β of the circumferentially tapered side surface 102 of the mount is preferably 55°-80° with preferred results being obtained when the included angle is 60°. By providing a shallow taper, the mount 98 does not swage itself into the cutting head. The mount may therefore be easily removed without the use of a tool, even after continuous running at ultra-high pressures, as is typically required in conventional systems. Also, top surface 100 is slightly tapered such that the high pressure fluid is sealed by top surface 100 only, not by side surface 102. The mixing tube 54 is provided with a reference member 106 on an outer surface 108 of the mixing tube. In a preferred embodiment, a metal ring is adhered to the outer surface of the mixing tube. The cutting head 46 is provided with a bottom surface 110 and a bore extending upward from the bottom surface, into which the mixing tube is inserted. By providing a reference member 106 at a desired location on the outer surface of the mixing tube, the reference member registers against the bottom surface 110 of the cutting head, thereby preventing the mixing tube from being inserted any further into the bore 112, thereby positioning the mixing tube in a desired location. The mixing tube 54 is further held in place via retention nut 15. By positioning the mixing tube 54 in accordance with the preferred embodiment of the present invention, manufacturing is simplified as compared to conventional systems wherein the means for registering the mixing tube are located internally in the cutting head. The length 92 of mixing chamber 48 is minimized and optimized, thereby reducing wear in the mixing chamber 48, such that the need for a protective, and typically expensive, carbide shield is eliminated. It is believed that by minimizing the length of the mixing chamber, the high-pressure fluid jet 50 remains more coherent as it flows through the mixing chamber to the mixing tube 54, and that this reduction in turbulence results in less wear in the mixing chamber. Although it will be understood that the length of the mixing chamber will be dependent on different variables, for example the size of the orifice, and the angle at which the inlets 26 and 80 are provided in the cutting head 46, in a preferred embodiment wherein the mount accommodates orifices ranging in size from 0.076-0,508 mm (0.003 - 0.02 inch), the length of the mixing chamber is 10.2-19.1 mm (0.4-0.75 inch). In a preferred embodiment, the cutting head 46 is provided with a second inlet 80, such that the feedline may be coupled to either the first inlet 26 or second inlet 80, as may be desirable given operating conditions. If, for purposes of illustration, the feedline is coupled to the first inlet 26, the second inlet 80 may simply be closed off or it may be coupled to any selected attachment, for example, an assembly for monitoring the performance of the system, a piercing attachment, or another abrasive feedline. For example, as illustrated in Figure 4, a piercing attachment comprising an air eductor 88 and a pinch valve 90, is coupled to the second inlet 80. When starting a cut in a material where the cutting head is not at an edge of the material, it is desirable to first pierce the material, to ensure that the material is not damaged. (Brittle materials, for example glass, ceramic or stone, may be damaged by conventional start up techniques where abrasive is not present in the high-pressure fluid stream when the stream initially contacts the material. Similarly, such conventional start up techniques may de-laminate some materials such as composites.) To achieve this desired result, it is necessary to ensure that abrasive is present in the fluid jet when it first contacts the material. This is accomplished, in a preferred embodiment of the present invention, by opening a valve 90 and activating air eductor 88, such that abrasive is drawn into the mixing chamber prior to generating the high-pressure fluid jet 50. By maintaining a length of feedline 44 at no more than 12 inches, and by ensuring that metering disk 40 is elevated above mixing chamber 48, the vacuum required to draw abrasive into the mixing chamber is minimized, thereby simplifying the system. In an alternative embodiment, as illustrated in Figure 5, a vacuum gauge 84 is coupled to the second inlet 80 of cutting head 46 for monitoring the performance of the system. An improved abrasive fluid jet system has been shown and described. From the foregoing, it will be appreciated that, although embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit of the invention. Thus, the present invention is not limited to the embodiments described herein, but rather is defined by the claims which follow.

Claims: An abrasive fluid jet cutting system comprising: a cutting head (46) having an abrasive inlet port (26,80) coupled to a source of abrasive and a mixing chamber (48) into which a volume of abrasive (18) and a high-pressure fluid jet (96) are introduced; a high-pressure orifice (94) contained within a mount assembly (98) that is seated in the cutting head (46), a volume of high-pressure fluid being forced through the high-pressure orifice (94) to form the high-pressure fluid jet (96); and a mixing tube (54) coupled to the mixing chamber (48), the abrasive (18) and the high-pressure fluid jet (96) being mixed and discharged through the mixing tube (54) as an abrasive fluid jet (52), characterized in that the mixing tube (54) is provided with a reference member (106) at a selected location on an outer surface (108) of the mixing tube (54) and the cutting head (46) is provided with a bottom surface (110) and with a simple bore (112) extending upwards from the bottom surface (110), the mixing tube (54) being inserted into the bore (112) of the cutting head (46), such that the reference member (106) contacts the bottom surface (110) and prevents the mixing tube (54) from being inserted any further into the bore (112), thereby locating the mixing tube (54) in a desired location. The abrasive fluid jet cutting system according to claim 1, wherein the reference member (106) is a ring coupled to the outer surface of the mixing tube (54). A mixing and ejecting tube for use in an abrasive fluid jet cutting system comprising: a mixing tube body (54) having a reference member (106) provided at a selected location on an outer surface (108) of the mixing tube body (54), such that when the mixing tube body (54) is placed into a simple bore (112) of a cutting head (46), the reference member (106) contacts a bottom surface (110) of the cutting head (46) and prevents the mixing tube body (54) from being inserted any further into the bore (112), thereby locating the mixing tube body (54) in a desired location. The mixing and ejecting tube according to claim 3, wherein the reference member (106) is a ring coupled to the outer surface of the mixing tube body (54).

Inventors: BURNHAM CHIP, ERICHSEN GLENN A, MANY ROBERT P, MASSENBURG JOHN C, O'CONNOR THOMAS HARRY, SMITH RHONDA R, ZARING KATHERINE, BURNHAM, CHIP, ERICHSEN, GLENN A., MANY, ROBERT P., MASSENBURG, JOHN C., O'CONNOR, THOMAS HARRY, SMITH, RHONDA R., ZARING, KATHERINE
Applicants: FLOW INT CORP, FLOW INTERNATIONAL CORPORATION
Application year: 1996
Main classification: B24C7
IPC codes: B24C1, B24C7