Abrasivejet Cutting Head With Enhanced Abrasion-Resistant Cartridge

Abstract

The cutting head of an abrasivejet cutting system preferably includes a replaceable generally tubular cartridge supporting a waterjet-forming orifice-defining member on one side of a mixing region, and an abrasivejet nozzle positioned on the opposite side of the mixing region in axial alignment with said orifice. The cartridge is formed from a material having tensile strength, yield strength and fatigue strength sufficient to withstand the operating pressure of the cutting system and sufficiently malleable and ductile to form a hard seal with a water-inlet tube to which it is coupled. The mixing region is defined within the cartridge by a layer of another material that is more abrasion-resistant than the cartridge material.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to abrasivejet cutting wherein the flow path of an incoming abrasive material intersects the flow of a high velocity fluid jet in such a way that the abrasive becomes entrained with the jet to form a material-cutting medium.

2. Description of the Related Art

The use of high velocity, abrasive-laden liquid jets to precisely cut a variety of materials is well known. Briefly, a high velocity fluid jet is first formed by compressing a liquid to an operating pressure of 3,500 to 150,000 psi (24.13-1,034.21 MPa), and forcing the compressed liquid through an orifice having a diameter approximating that of a human hair; namely, 0.003-0.040 inches (0.08-1.02 mm). The resulting highly coherent jet is discharged from the orifice at a velocity which approaches or exceeds the speed of sound. The material defining the jet-forming orifice is typically a hard jewel such sapphire, ruby or diamond.

The liquid most frequently used to from the jet is water, and the high velocity jet described hereinafter may accordingly be identified as a waterjet. Those skilled in the art will recognize, however, that numerous other liquids can be used without departing from the scope of the invention, and that the jet is more precisely a “fluid” jet shortly after its formation in that its actual cross-sectional composition includes air and liquid; since the most common liquid used is water, the terms “waterjet” and “water” will be used throughout the specification but are not to be interpreted as a limitation requiring the “waterjet” to consist of or comprise water.

To enhance the cutting power of the fluid jet, abrasive materials have been added to the jet stream to produce an abrasive-laden waterjet, typically called an “abrasive jet”. The abrasive jet is used to effectively cut a wide variety of materials from exceptionally hard materials (such as tool steel, aluminum, cast iron armor plate, certain ceramics and bullet-proof glass) to soft materials (such as lead). Typical abrasive materials include garnet, silica, and aluminum oxide having grit sizes of #36 through #200.

To produce the abrasive-laden waterjet, the waterjet passes through a “mixing region” wherein a quantity of abrasive is entrained into the jet by the low pressure region which surrounds the flowing liquid in accordance with the Venturi effect. The abrasive, which is under atmospheric pressure in an external hopper, is drawn into the mixing region by the lower pressure region via a conduit that communicates with the interior of the hopper. In operation, quantities of up to 6 lbs./min of abrasive material have been found to produce a suitable abrasive jet. Those skilled in the art recognize that the abrasive material represents the highest hourly operating cost associated with abrasivejet cutting.

The resulting abrasive-laden waterjet is then discharged against a workpiece through an abrasivejet nozzle that is supported closely adjacent the workpiece.

The waterjet, incoming abrasive and abrasivejet are so destructive that the jet-forming orifice, mixing region and abrasivejet nozzle become worn, and cutting efficiency decreases dramatically. The result is that the cutting process is dramatically slowed, and an excess of abrasive material is consumed in performing the cutting operation. In practice, the orifice member, mixing region and abrasivejet nozzle are securely supported by a “cutting head” into which the abrasive is conducted via an abrasive-carrying conduit from a hopper external to the cutting head. To maximize the life of the mixing region and abrasivejet nozzle, it is highly desirable to axially align them with the waterjet's axis. Because the fluid path through the cutting head body and abrasivejet nozzle is several inches long, very minute alignment errors (e.g., a few tenths of a thousandth inch (a few tenths of 0.03 mm) are enough to cause premature failure of the abrasive jet nozzle.

One known structure for minimizing the possibility of non-alignment is a generally tubular cartridge with upstream and downstream end regions that fits within the cutting head to securely hold the waterjet-forming orifice member within its upstream region in extremely close alignment with an abrasive jet nozzle securely held at or within its downstream end. An example of such a structure is illustrated and described in U.S. Pat. No. 6,601,783 wherein a generally cylindrical insert member is described and illustrated as supporting a waterjet-forming orifice member in axial alignment with an abrasivejet discharge nozzle located at the downstream end of the cutting head, and providing an integral unit comprising the mixing region and the jet-forming orifice.

Inserts of the type described and illustrated in the foregoing patent have typically been made from stainless steel. Stainless steel is the material of choice because it is resistant to corrosion in the presence of water, and its top surface can provide the requisite sealing contact necessary to withstand the fluid pressure (e.g., 3,500 to 150,000 psi (24.13-1,034.21 MPa)) upstream of the orifice member supported within the insert. The stainless steel interior encompassing the mixing region, however, has a limited life expectancy owing to the destructive action of the incoming abrasive.

When the jet-forming orifice is formed in ruby or sapphire, the orifice member wears to an undesired degree prior the mixing region. When, however, the jet-forming orifice is formed in diamond, the diamond orifice member will outlast conventional mixing regions, necessitating an unnecessary replacement of the supported orifice member at the time a new insert is required. Diamond orifice members are relatively expensive, and the premature replacement represents a wasteful cost of production to the user.

It is accordingly desirable to maximize the life of the insert to approximate that of the diamond orifice member.

BRIEF SUMMARY OF THE INVENTION

An abrasivejet cutting system includes a cutting head with a replaceable and generally tubular cartridge that supports a waterjet-forming orifice-defining member on one side of a mixing region, and is configured to direct the waterjet into an abrasivejet nozzle positioned on the opposite side of the mixing region in axial alignment with said orifice. The cartridge is formed from a material having tensile strength, yield strength and fatigue strength sufficient to withstand the operating pressure of the cutting system and sufficiently malleable and ductile to form a hard seal with a water-inlet tube to which it is coupled. The mixing region is defined within the cartridge by a layer of another material that is more abrasion-resistant than the cartridge material.

Additional details concerning the invention will be apparent to those of ordinary skill in the art from the following description of the preferred embodiment, of which the Drawing forms a part.

DESCRIPTION OF THE DRAWING

FIG. 1 is an exploded fragmentary perspective view, in schematic, showing a cartridge and insert constructed in accordance with the invention;

FIG. 2 is a magnified view of the insert of FIG. 1;

FIG. 3 is a sectional drawing in schematic of the insert of FIG. 2, taken along line 3-3 therein;

FIG. 4 is a fragmentary longitudinal sectional view in schematic of a cutting head assembly constructed in accordance with the invention; and

FIG. 5 is a fragmentary longitudinal sectional view in schematic of a cutting head assembly constructed in accordance with the invention illustrating its preferred mating with a water inlet tube.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring initially to FIG. 1, a cartridge 10 configured to accept an insert 20 is illustrated. As illustrated in FIGS. 1 and 4, the cartridge and insert are securely positioned within the body 30 of an abrasivejet cutting head.

As best illustrated in FIG. 4, a waterjet-forming orifice member 12 is securely held within the upper region (hereinafter, the “upstream region”) of the cartridge 10 and creates a waterjet via orifice 12a that is axially directed downstream about an axis 40. The cartridge 10 has a longitudinally extending through-passage that is axially aligned with waterjet axis 40. The illustrated through-passage includes a relatively upstream portion 16a, a relatively downstream portion 16b, and a gap therebetween into which the insert 20 is inserted via an insert-accommodating passage 17 which extends between the cartridge's exterior at one end and the gap 15 at the other end. The through-passage extends axially upstream of the orifice member 12, terminating at an inlet hole 16c in the upstream end of the cartridge. Those of ordinary skill in the art will recognize that high-pressure water (or other fluid) is introduced into the cartridge at the inlet hole from an external source via the internal passageway 64 of an inlet tube 60 (FIG. 5). The high pressure water enters the cartridge via the inlet hole 16c and is forced through the orifice 12a in the orifice member 12 to form the waterjet.

The cartridge is enclosed within the body 30 of the cutting head by a cap 50. The cap 50 includes an externally threaded region 52 that mates with an internally threaded upper region of the cutting head body 30. The cap further includes an internally threaded through passage 54 that mates with external threads 62 of the inlet tube so that the inlet tube can be tightened down against the top surface of the cartridge 10 with sufficient force to seal against it.

It will be appreciated that the inlet hole 16c in the cartridge is preferably formed in the center of the top surface as best illustrated in FIG. 1; however, an inlet can alternatively be formed elsewhere upstream of the orifice member without departing from the scope of the invention.

As illustrated in FIG. 4, the cartridge 10 has an enlarged upper end forming a shoulder 14 that seats precisely against a shoulder 32 formed within the interior of the body 30. The cartridge 10 is formed from a material having tensile strength, yield strength and fatigue strength sufficient to withstand typical waterjet pressures using reasonable design practices. Those of ordinary skill in the art are aware of commercially acceptable design standards; for example, it is not commercially acceptable use 3-inch (76 mm) thick material to withstand the pressure and achieve the desired design life. Moreover, the cartridge material should be corrosion resistant in an oxidizing environment; e.g., from the water or other fluids used in producing the abrasivejet. In addition, the cartridge material should be malleable and ductile enough to form a hard seal between the cartridge and inlet tube, as described below.

Currently, the preferred material of choice for the cartridge is a mildly heat-treated, precipitation-hardened stainless steel that can be directly sealed to the water-inlet tube, which is typically stainless steel as well. The steel-to-steel contact deforms slightly at 66 (FIG. 5) as the inlet tube is tightened down into the cutting head, creating a hard seal through which the incoming high pressure water cannot escape. Accordingly, there is no need for intermediate sealing components that could adversely affect or complicate the axial alignment of the cartridge with the waterjet. The deformation is slight and, in practice, the required sealing can be repeated with numerous replacement cartridges before the water-inlet tube must be replaced.

The relatively downstream portion 16b of the cartridge's through-passage is dimensioned to accept the proximal end region of an abrasivejet nozzle 60 in secure axial alignment with the axis 40 of the waterjet.

As described above, the insert 20 is inserted into the cartridge within the gap 15 between the relatively upstream and downstream portions 16a, 16b of the cartridge's through-passage. The insert is formed from a material has an abrasion resistance sufficient enough to withstand degradation from abrasive media moving across the intended surfaces for the desired design life. The material is more abrasive-resistant than that of the cartridge, but need not possess the malleability and ductility of the cartridge material. The currently preferred insert material is a carbide having greater wear resistance to the abrasive than the material from which the cartridge is made but, as will become apparent, not requiring the ability to directly seal a very high pressure region such as the typical 3,500 to 150,000 psi (24.13-1,034.21 MPa) to which the region upstream of the orifice member is subjected. While other grades and specifications of carbides may be suitable to use, the presently preferred carbide material used for the insert is a tungsten carbide (WC—Co) with 6% of the weight being cobalt binder. Its grain size is on the submicron scale, and this material has been proven to be ideal for its wear-resistance to abrasive media.

The preferred insert 20 is configured to provide a substantially carbide-enclosed interface between the cartridge 10 and an abrasive feed line 80 in order to prevent abrasive-induced wear to the cartridge body that could, for example, require premature replacement of the cartridge substantially prior to the end of its orifice-member's life. As illustrated in FIG. 4, the abrasive feed line 80 is preferably inserted up to position 82, the incoming abrasive thereby bypassing any contact with the cartridge material surrounding the abrasive inlet path through the cartridge. Preferably, the inner diameter of the abrasive feed line 80 is the same as the abrasive inlet channel 27 where the feed line 80 butts up against the insert interior at 82. The insert 20 further provides a substantially carbide-enclosed mixing region, shielding the cartridge's interior from contact with the abrasive that has entered the mixing region for entrainment by the waterjet.

As illustrated in FIGS. 1-4, the insert 20 has an orifice member-facing surface 22 having a waterjet inlet 23 leading into a waterjet passage 24 that is axially aligned with the waterjet axis 40 when the insert is properly inserted into the cartridge 10. The waterjet passage 24 terminates in a mixing region 25 substantially enclosed by the interior wall of the insert but for an outlet 26 that is also axially aligned with the waterjet axis 40 when the insert is properly inserted into the cartridge.

The insert 20 additionally includes an abrasive-inlet passage 27 sized to accommodate the abrasive feed line 80 in such a way that the inserted abrasive-discharging end of the abrasive feed line terminates within the carbide-enclosed mixing region of the preferred insert at an angle with respect to the axis 40 that maximizes the efficiency of abrasive entrainment into the waterjet.

The insert 20 is preferably inserted into the cartridge 10 from the side (as illustrated by way of example in FIG. 1). The inter-engaging surface shapes, dimensions and/or dimensional tolerances of the insert's exterior and the interior of the insert-accommodating passage 17 provide secure and precise alignment of the insert within the cartridge. In preferred form, the body of the insert is generally prismatic in shape.

The insert 20 is secured within the cartridge 10 with a set screw 18 (having a preferred cone-shaped leading end 18a) which mates with an internally threaded through-hole 19 in the side of the cartridge to tighten against a recess 28 in the side of the insert.

The abrasive nozzle 60 is preferably secured in the cartridge 10 up against the insert 20 as shown in FIG. 4. The abrasive feed 80 is inserted through the body 30 and into the carbide insert and securely held, for example, by an interference fit.

Accordingly, in the presently preferred embodiment, the abrasive feed is entirely contained within wear resistant carbide at a sufficiently high angle to provide uninterrupted abrasive flow. There is no contact between the abrasive flow and the body 30 or cartridge 10. This allows a diamond orifice member, for example, to perform at its full potential and thereby provides the maximum amount of cutting time to the end user. This high angle, coupled with a substantially uninterrupted abrasive flow (i.e., substantially no steps or obstructions) provides the maximum efficiency for abrasive use by taking advantage of gravity and the vacuum generated by the waterjet stream.

An additional advantage of the preferred embodiment is that the mixing region is encompasses in a material such as carbide, which is very resistant to abrasive-induced damage while the orifice member, which cannot currently be firmly seated against carbide, can be seated in a material such as stainless steel that can deform enough to form the requisite seal.

The preferred side-insertion of the insert 20 allows the incorporation of the entirely contained interface between abrasive feed and insert in one small piece, while the preferred prismatic shape of the insert allows precise positioning of the thru hole where the waterjet stream meets the abrasive. Those skilled in the art will recognize that an insert could be inserted from a direction other than the side of the cartridge. For example, one could increase the diameter of the body 30 and cartridge 10 from the preferred diameter illustrated herein in order to accept a large diameter, cylindrically shaped insert from the bottom of the cartridge. The diameter would have to be increased dramatically from the preferred diameter herein, however, to accommodate the singular interface between the abrasive feed and mixing chamber; in other words, to have the abrasive feed line completely enclosed in the more wear-resistant material (e.g., carbide), and still make the insert out of one piece, the diameter must encompass that feature as well as the thru hole for the waterjet stream. This is, accordingly, not a preferred variation.

One way to avoid the large diameter, bottom-assembled insert is to use a slightly smaller diameter, top-assembled insert. This would allow one to include all relevant features in a single carbide piece; however, one must introduce an additional metal sealing surface to the top of the cartridge because carbide cannot deform enough to seal a metal part at ultra-high waterjet pressures. This is also not a preferred variation because it defeats the ability to rely on the cartridge to provide precise alignment between the jet-forming orifice and the abrasivejet nozzle without additional sealing mechanisms that complicate and/or adversely affect the ability to hold to the tolerances demanded for proper axial alignment of the orifice member and abrasivejet nozzle.

Although the preferred embodiment and its advantages have been described in detail, it should be understood that this is an example of the invention only, and that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as will be defined by appended claims.

Claims

1. An abrasivejet cutting head comprising:

a cutting head body;

a waterjet-forming orifice member supported within said body and having a waterjet-forming orifice formed around a longitudinally-extending axis;

a generally tubular cartridge extending between relative upstream and downstream ends and positioned within said body to surround the waterjet formed by the orifice member as the waterjet flows towards the downstream end, the cartridge including an insert-accommodating passageway extending from the exterior of the cartridge to its interior; and

an insert sized to fit within the insert-accommodating passageway and having a jet-accommodating through-hole for permitting through-passage of the waterjet towards said downstream end, the insert including an abrasive inlet passage for directing incoming abrasive towards the waterjet for entrainment therewith as the waterjet passes through the insert, the insert being shaped to substantially shield the cartridge from contact with the incoming abrasive.

2. The cutting head of claim 1 wherein the waterjet-forming orifice member is supported in the region of the upstream end of the cartridge.

3. The cutting head of claim 1 wherein the insert-accommodating passageway extends generally radially from the exterior of the cartridge to its interior.

4. The cutting head of claim 3 wherein the insert-accommodating passageway is substantially perpendicular to the longitudinal axis.

5. The cutting head of claim 1 wherein the insert-accommodating passageway and the insert have complementary surface features to precisely position the insert within the cartridge in such a way that the jet-accommodating through-hole is substantially aligned with said longitudinal axis.

6. The cutting head of claim 5 wherein the insert and the insert-accommodating passageway are substantially prismatic in shape.

7. The cutting head of claim 1 wherein the orifice within said orifice member is in diamond.

8. The cutting head of claim 7 wherein the cartridge is formed at least in part from stainless steel.

9. The cutting head of claim 8 wherein the insert is formed from carbide.

10. An abrasivejet cutting head comprising:

a housing having a first longitudinally-extending passageway formed about a longitudinal axis between upstream and downstream ends, said body being adapted to be coupled to a source of high pressure liquid at said upstream end, and to receive an abrasivejet nozzle at said downstream end,

a removable cartridge within the first longitudinally-extending passageway, said cartridge having upstream and downstream faces, a second generally longitudinally-extending passageway in communication with said faces and in substantial axial alignment with the first longitudinally-extending passageway, and a generally radially-extending passage extending from the exterior of the cartridge into the second longitudinally-extending passageway at an interface region, the cartridge having a surface characteristic at the region of its downstream face for receiving the upstream end of a separable abrasivejet nozzle in substantial axial alignment with the second longitudinally-extending passageway;

an orifice member having a waterjet-forming orifice and supported within the cartridge upstream from the interface region with its orifice in substantial axial alignment with the second longitudinally-extending passageway;

an insert extending into the cartridge via the generally radially-extending passage, the insert having a third longitudinally-extending passageway in substantial axial-alignment with the second longitudinally-extending passageway to conduct the formed waterjet through the interface region towards the abrasivejet nozzle, and further having a through-passage oriented to conduct abrasive delivered from a region exterior to the cutting head into the interface region without its conducted abrasive contacting the cartridge.

11. For use in an abrasivejet cutting system of the type including a waterjet-forming orifice member, a generally tubular cartridge extending between upstream and downstream ends for conducting the waterjet from the orifice member to the downstream end, the cartridge including an insert-accommodating passageway extending from the exterior of the cartridge to its interior; and

an insert sized to fit within the insert-accommodating and having an abrasive inlet oriented to direct incoming abrasive into the conducted waterjet as it passes through the cartridge while the cartridge is shielded by the insert from contact by the incoming abrasive.

12. An abrasivejet cutting head including:

a body;

a waterjet-forming orifice member;

a tubular metal cartridge positioned within the body and having a downstream end region and an upstream end region supporting the waterjet-forming orifice member so that the waterjet is longitudinally directed towards the downstream end region within said cartridge;

a carbide insert extending generally radially into the cartridge and having a jet-accommodating through-hole permitting the waterjet to pass through the insert, the insert further including an abrasive passageway for permitting externally introduced abrasive to interface with the waterjet as the waterjet passes through the insert, the insert being shaped substantially enclose the interface region to shield the cartridge from incoming abrasive.

13. A replaceable cartridge for use in an abrasivejet cutting system for supporting a waterjet-forming orifice-defining member on one side of a mixing region, and for positioning an abrasivejet nozzle on the opposite side of the mixing region in axial alignment with said orifice,

the cartridge being formed from a material comprising stainless steel and configured to permit the ingress of abrasive into the mixing region for entrainment with the formed waterjet and to permit the abrasive-entrained waterjet to exit towards the abrasivejet nozzle,

the stainless steel being shielded from contact from the incoming abrasive by an internal layer of carbide material.

14. A replaceable and generally tubular cartridge for use in the cutting head of an abrasivejet cutting system for supporting a waterjet-forming orifice-defining member on one side of a mixing region, and for positioning an abrasivejet nozzle on the opposite side of the mixing region in axial alignment with said orifice,

the cartridge being formed from a first material having tensile strength, yield strength and fatigue strength sufficient to withstand the operating pressure of the cutting system and sufficiently malleable and ductile to form a hard seal with a water-inlet tube to which it is coupled, the cartridge being configured to permit the entering of abrasive into the mixing region for entrainment with the formed waterjet,

the mixing region being defined within the cartridge by a layer of a second material that is more abrasion-resistant than the first material and which shields the first material from abrasive entering the cartridge.