Abrasivejet Cutting Head With Novel Entrainment Structure and Method

Abstract

An abrasivejet cutting head assembly comprises abrasive inlet means for permitting entry of abrasive material into the head's longitudinally-extending passageway about an inlet axis that is preferably non-intersecting with the passageway's longitudinal axis. The abrasive is then prevented from entrainment into the waterjet by means within the passageway that only permits entrainment downstream from the region of abrasive entry after the abrasive particles have attained a generally coherent downstream velocity. The foregoing can be accomplished within the cutting head, within a user-replaceable insert in the cutting head or within the abrasivejet nozzle.

Description

FIELD OF THE INVENTION

The use of high velocity, abrasive-laden liquid jets to precisely cut a variety of materials is well known. Briefly, a high velocity liquid jet is first formed by compressing the liquid to an operating pressure of 3,500 to 150,000 psi, and forcing the compressed liquid through an orifice having a diameter approximating that of a human hair; namely, 0.003-0.040 inches. The material defining the waterjet-forming orifice is typically a hard jewel such sapphire, ruby or diamond. The resulting highly coherent jet is discharged from the orifice at a velocity which approaches or exceeds the speed of sound. 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 the recitation of the jet as comprising water should not be interpreted as a limitation.

To enhance the cutting power of the liquid 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 coupled with mechanical entrainment. The abrasive, which is under atmospheric pressure in an external abrasive-supply hopper, is drawn into the mixing region by the lower pressure region via an abrasive-inlet conduit that communicates with the interior of the abrasive-supply hopper. The hopper may be a gravity feed hopper. In operation, quantities of up to 6 lbs./min of abrasive material have been found in prior art systems to produce a suitable abrasive jet in prior art cutting systems. 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.

Because the waterjet, abrasive and abrasivejet are so destructive, internal wear of the cutting head's components is of concern. As the components become worn, 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, making it necessary to regularly change the jet-forming orifice, the mixing chamber and the abrasivejet nozzle.

SUMMARY OF THE INVENTION

Briefly, the invention herein is an abrasivejet cutting head assembly for use in an abrasivejet cutting system of the type wherein the cutting head is coupled to a source of abrasive via an abrasive-carrying conduit, and to a source of high pressure water. The cutting head assembly has a novel chamber structure for improving cutting efficiency. It has also been found that this chamber structure decreases wear caused by incoming abrasive. As will be appreciated, the novel chamber design can be provided as part of the cutting head structure or, alternatively, as a replaceable insert that is mounted within a cutting head body.

The abrasivejet cutting head assembly comprises a body having means defining a longitudinally-extending through-passageway extending about a longitudinal axis between upstream and downstream end regions, a waterjet-forming orifice member within the passageway for producing a generally axially aligned waterjet when the passageway upstream of the orifice member is coupled to a source of high pressure liquid, and abrasive inlet means for permitting entry of abrasive material into the passageway about an inlet axis that is preferably non-intersecting with said longitudinal axis. The abrasive is prevented from entrainment into the waterjet by means within the passageway that permits entrainment downstream from the region of abrasive entry after the abrasive particles have attained a generally coherent downstream velocity.

Means are also included for releasably securing a generally longitudinally-extending abrasivejet nozzle in alignment with said longitudinal axis to receive the abrasive-containing waterjet for discharge against a workpiece.

By introducing the abrasive upstream of the mixing region along a path that is non-intersecting with the longitudinal axis, improved cutting efficiency is obtained.

These and other details will become apparent from the following description of the preferred embodiment, of which the drawing forms a part.

DESCRIPTION OF THE DRAWING

In the drawing:

FIG. 1 is a front schematic view in partial section of an abrasive jet cutting head constructed in accordance with the invention;

FIG. 2 is a side view of the portion of the mixing chamber adjacent the abrasive inlet; and

FIGS. 3-5 are longitudinal section views illustrating alternative mixing region structures, with (a) illustrating the isolating conduit member, (b) illustrating the mixing region chamber and (c) illustrating the resulting mixing region configuration.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 schematically illustrates a front view in partial section of an abrasivejet cutting head constructed in accordance with the invention. As is known in the art, abrasivejet cutting heads comprise a body 10 having first internal longitudinally-extending through-passageway 12 extending about a longitudinal axis 18 between upstream and downstream end regions 10a, 10b. A waterjet-forming orifice member, schematically illustrated at 20, is positioned within the passageway for producing a generally axially aligned waterjet via its orifice 22 when the longitudinal passageway upstream of the orifice member is coupled to a source of high pressure water. There are numerous methods and structures known for mounting the orifice member within the abrasivejet cutting head, and this invention is not dependant on any particular method or structure, as will be appreciated from the following description. In addition, it will be understood that liquids other than water can be utilized within the scope of this invention, although water is the typical liquid and therefore referred to herein.

The abrasivejet cutting head also includes an abrasive inlet passage 44 which communicates between the exterior of its body 10 and its longitudinal passageway 12 to permit abrasive material, such as garnet, to enter the longitudinal passageway and be entrained in the flowing waterjet within the low pressure region surrounding the flowing waterjet to form an abrasivejet that will ultimately be discharged against a workpiece via an abrasivejet nozzle 50 that is releasably secured to the body 10 in axial alignment with the waterjet-forming orifice by any of a number of known means. The nozzle is a generally tubular body extending from an upstream end to a downstream end about a longitudinal axis and having an internal diameter in the range of approximately 0.015 inches to approximately 0.080 inches throughout at least the substantial portion of its length. One such arrangement for releasably securing the nozzle is illustrated in FIG. 1 is the use of an internally threaded nut 62 that mates with an externally threaded neck 64 of the body 10 to compress a captured collet 66 within the nut to thereby secure the nozzle 50 therein. Other arrangements are known in the art, as are arrangements whereby the nozzle is only released as an integral assembly further comprising the water-jet-forming orifice member. Any and all such arrangements can be used without departing from the scope of the invention.

An abrasive-conducting conduit 70 is coupled to the abrasive inlet passageway 44 via a sleeve 73 that is typically threaded into the body 10 via mating internal and external threads. The abrasive conduit can also be threaded directly into the body 10. The conduit is coupled to a hopper (not shown) or other abrasive source at its upstream end so as to conduct abrasive particles from the hopper directly into the body 10 or through the longitudinal passageway via passage 72 into the mixing region 42.

In accordance with the invention, the abrasive inlet passageway 44 permits entry of abrasive particles into the longitudinally-extending passageway of the cutting head about an inlet axis 74 that is non-intersecting with said longitudinal axis 18. This is best illustrated in FIG. 2, wherein the abrasive-inlet axis 74 is illustrated as being offset from the longitudinal axis by a distance d₅.

While the embodiment illustrated in FIG. 1 shows the sleeve 73 and abrasive conduit 70 coaxially aligned with the abrasive-inlet axis 74 where it enters the longitudinal passageway, it should be recognized that this is not necessarily the case. The sleeve 73 and conduit 70 can be mounted to the body 10 in any of a number of locations, positions and orientations, including along an axis that intersects the longitudinal axis 18, so long as the abrasive particles enter the longitudinal passageway 12 about a generally central inlet axis 74 that is non-intersecting with the longitudinal axis 18. Thus, while FIGS. 1 and 2 schematically illustrate the position of one possible non-intersecting inlet passage, the abrasive passage through the cutting head body may be curved, oblique or of other configuration to provide the desired position and orientation for abrasive entry.

In accordance with the invention, the abrasive particles are not permitted to contact the jet immediately upon entering the longitudinal passageway 12. The fact that one could permit a relatively small quantity of the abrasive particles to contact the jet upon entry into the passageway in an effort to circumvent this patent is foreseen and not excluded from the scope of the invention. The waterjet emerging from the orifice-defining member 20 is guided past the abrasive-entry location by an isolating conduit member 30 having an isolating conduit 31 in substantial axial alignment with the longitudinal axis 18. Entrainment of the abrasive particles is thereby prevented until the waterjet emerges from the discharge end 31a of the isolating conduit member 30 downstream from the region of abrasive entry. This enables the abrasive particles to gain a generally coherent downstream velocity prior to entrainment.

The isolating conduit member 30 preferably has a generally cylindrical tapered nose 32 that extends downstream about the isolating conduit 31 and generally concentrically with the longitudinal axis 18. When the waterjet is discharged from the downstream end of the nose 32, the abrasive particles entering the inlet 44 are drawn downstream by the low pressure region surrounding the waterjet,. The particles entering the passageway 12 from the abrasive-inlet passageway 44 tend to swirl around the nose as they travel downstream, having been introduced into the passageway at a position radially offset from the longitudinal axis 18.

As illustrated in FIG. 1, the substantial portion of the longitudinal passageway downstream of the waterjet-forming orifice is preferably a generally conically-shaped chamber within which the nose 32 extends downstream. The chamber is substantially co-axially disposed about longitudinal axis 18 between the outlet of the orifice-defining member and the abrasivejet nozzle 50, and has walls that preferably converge at approximately 20° in the downstream direction. The nose 32 of the isolating conduit member 30 thereby cooperates with the conical chamber to define a chamber of generally annular cross-section in which the abrasive particles travel. The nose preferably has a cone shape of smaller angle than the conical passageway; preferably 8° or so. It should be noted, however, that neither the chamber walls nor the nose need be tapered and can function in accordance with the invention, although it has not been found to provide aas great an increase in cutting efficiency. Further, chamber wall convergences of 10°-70° have been found operational, but that 20° appears to provide the best results for the dimensions utilized.

The movement of the abrasive particles is less chaotic when ultimately entrained in the described device. This is believed to result in greater efficiency of entrainment due, in part, to less disturbance of the coherent waterjet stream, thus maintaining a greater velocity after entrainment of the abrasive.. In the preferred embodiment, the off-center introduction of abrasive together with the controlled entrainment appears to result in less impact of abrasive against the walls of the mixing region and, consequently, less wasted kinetic energy from particle collision with other particles and passageway walls. The above-stated actions, in turn, result in greater cutting efficiency with less wall wear in the mixing region, increased entrained-abrasive velocity (and, thus, energy), and smoother wear of the abrasive nozzle's inside diameter than found in conventional abrasivejet cutting heads. Thus, there is a reduction in the quantity of abrasive used for a given cutting process, with attendant cost savings, and/or faster cutting speeds with attendant productivity gain. With less wear, the mixing region needs replacement less often, as well, resulting in less “down time” and component expense. It has been found that the smoother wear of the abrasivejet nozzle reduces the kerf produced throughout the useful life of the nozzle to only 0.003 to 0.005 inches compared with conventional kerf production of 0.010 to 0.015 inches over a substantially equivalent life. The reduced random abrasive motion and the long passageway 31 within the conduit 30 protect the orifice from collisions with abrasive particles that are found in prior art cutting heads, thus yielding increased service life of the waterjet-forming orifice.

The chamber thus described can be an integral part of the cutting head body, or may be provided as a replaceable insert to be utilized within a cutting head. FIGS. 3-5 are longitudinal section views illustrating alternative mixing region structures, with (a) illustrating the isolating conduit member, (b) illustrating the mixing region chamber and (c) illustrating the resulting mixing region configuration. If the chamber is provided as an insert, these Figures also illustrate alternative insert structures constructed in accordance with the invention. Components illustrated in alternative form in FIGS. 1 and 3-5 have been denoted with similar identifying numerals for visual clarity.

FIG. 3 illustrates the chamber 40 and isolating conduit member 30 illustrated in FIG. 1. The member 30 has a generally T-shaped longitudinal section. The side of the member's head 33 is tapered to preferably provide a line-to-line fit with the tapered interior wall of the chamber 40. The member 30 can accordingly be seated into the chamber (as shown in FIG. 3(c)) and is held firmly but releasably. When part of the abrasive cutting head assembly, it essentially cannot move.

FIG. 4 illustrates a configuration wherein the upstream portion of the chamber 40′ is counterbored at 41. The side of the member's head 33′ is not tapered (although it could be). The head 33′ seats with the counterbored portion of the cavity as illustrated in FIG. 4(c) with a few tenths of an inch of clearance. The tolerance is chosen to permit a slip fit without permitting the member 30′ to lose its substantial axial alignment with the jet-forming orifice when assembled into the abrasivejet cutting head.

FIG. 5 illustrates the currently preferred configuration. The head 33″ of the member 30″ has a non-tapered side of sufficient diameter to overly the chamber's upstream opening (as illustrated in FIG. 5(c). Moreover, the abrasive inlet passageway is formed in the side of the cavity as a U-shaped slot that cooperates with the bottom surface of the head 33″ to form the passageway. By forming the abrasive inlet passageway in this manner, formation of the passageway is easier and more cost effective. As illustrated, the nozzle body has the abrasive-inlet opening downstream from its upstream end for permitting entry of abrasive material into the interior of the nozzle from an external source along an inlet axis that is not coaxially aligned with said longitudinal axis. Further, the inlet axis is not parallel to the longitudinal axis and is preferably non-intersecting with the longitudinal axis.

In addition to the foregoing configurations, it is possible to configure the abrasivejet cutting head to form the mixing region within the upstream end region of the abrasivejet nozzle. In the preferred embodiment, the member 30, 30′, 30″ of FIGS. 3-5 can conveniently be mechanically linked or attached to the waterjet-forming orifice member, while the abrasive-inlet passageway 44 is formed in the abrasivejet nozzle, as illustrated by way of example at 44″ in FIGS. 5(b) and (c). In these configurations, the nose of the isolating passageway member 30, 30′, 30″ protrudes down into the upstream end region of the abrasivejet nozzle to a region longitudinally downstream from the abrasive inlet passageway. FIG. 5 represents the currently preferred embodiment of such a configuration.

By way of example, a chamber having the following dimensions has been successfully utilized in an abrasivejet cutting head with garnet as the abrasive:

Conical chamber: d₃=0.0.306 inches

• • d₄=0.160 inches
  • d₅=0.098 inches
  • taper: 20° taper
  • length: 0.570 inches

Isolating conduit member: L₁=0.155 inches

• • L₂=0.321 inches
  • d₁=0.434 inches
  • d₂=0.062 inches
  • nose taper: 8°

Abrasive inlet: 0.08 inch diameter

Those skilled in the art will recognize that many variations may be made in the disclosed embodiment without departing from the spirit of the invention. For example, the isolating conduit member can be formed within the passageway in any convenient manner.

Claims

1. An abrasivejet cutting head comprising:

a body having a first internal longitudinally-extending through-passageway extending between upstream and downstream end regions about a longitudinal axis,

a waterjet-forming orifice member within the passageway for producing a generally axially aligned waterjet when the passageway upstream of the orifice member is coupled to a source of high pressure water,

abrasive inlet means for permitting entry of abrasive material into the passageway about an inlet axis, said abrasive material becoming entrained with the waterjet within a mixing region within the passageway downstream from the entry of abrasive material;

means for substantially preventing entrainment with the waterjet until said abrasive material has acquired a generally longitudinal velocity; and

means for releasably securing a generally axially-extending abrasivejet nozzle in alignment with said longitudinal axis to receive the abrasive-containing waterjet for discharge against a workpiece.

2. The abrasivejet cutting head of claim 1 including means for imparting a generally swirling movement of the abrasive material about the passageway prior to entrainment as the abrasive material moves towards the mixing region.

3. The abrasivejet cutting head of claim 1 wherein the said inlet axis is non-intersecting with said longitudinal axis

4. The abrasivejet cutting head of claim 1 or 3 including

a generally tapered passageway between the waterjet-forming orifice member and the mixing region.

5. The abrasivejet cutting head of claim 1 or 3 wherein the walls of the passageway define a generally spiral path in the longitudinal direction.

6. The abrasivejet cutting head of claim 1 or 3 wherein the generally tapered passageway forms a cone.

7. The abrasivejet cutting head of claim 6 wherein the walls of the passageway converge at an angle in the range of between and including approximately 10° and approximately 70°.

8. The abrasivejet cutting head of claim 7 wherein the walls of the passageway converge at approximately a 20° angle.

9. The abrasivejet cutting head of claim 1 or 3 including means defining a second waterjet-accommodating passageway extending generally co-axially within said first passageway to carry the waterjet emerging from the waterjet-defining orifice past the entering abrasive to the mixing region.

10. The abrasivejet cutting head of claim 9 wherein said second passageway-defining means comprises a generally annular cone-shaped structure.

11. The abrasivejet cutting head of claim 10 wherein said generally cone-shaped structure has tapered exterior walls converging at approximately an 8° angle.

12. An abrasivejet cutting head comprising:

a body having a first internal longitudinally-extending through-passageway extending between upstream and downstream end regions about a longitudinal axis,

a waterjet-forming orifice member within the passageway for producing a generally axially aligned waterjet when the passageway upstream of the orifice member is coupled to a source of high pressure water,

abrasive inlet means for permitting entry of abrasive material into the passageway about an inlet axis, said abrasive material becoming entrained with the waterjet within a mixing region within the passageway downstream from the entry of abrasive material;

means for substantially preventing entrainment with the waterjet until said abrasive material has acquired a generally longitudinal velocity;

an generally axially-extending abrasivejet nozzle; and

means for releasably securing the generally axially-extending abrasivejet nozzle in alignment with said longitudinal axis to receive the abrasive-containing waterjet for discharge against a workpiece.

13. The abrasivejet cutting head of claim 12 including means for imparting a generally swirling movement of the abrasive material about the passageway prior to entrainment as the abrasive material moves towards the mixing region.

14. The abrasivejet cutting head of claim 12 wherein said inlet axis is non-intersecting with said longitudinal axis.

15. The abrasivejet cutting head of claim 12 or 14 including

a generally tapered passageway between the waterjet-forming orifice member and the mixing region.

16. The abrasivejet cutting head of claim 15 wherein the mixing region is within the abrasivejet nozzle.

17. The abrasivejet cutting head of claim 16 second means defining a second waterjet-accommodating passageway extending generally co-axially within at least a portion of the abrasivejet nozzle to carry the waterjet emerging from the waterjet-defining orifice past the entering abrasive to the mixing region.

18. The abrasivejet cutting head of claim 17 wherein said second passageway-defining means comprises a generally annular cone-shaped structure.

19. The abrasivejet cutting head of claim 18 wherein said generally cone-shaped structure has tapered exterior walls converging at approximately an 8° angle.

20. A user-replaceable insert for use in an abrasivejet cutting head of the type including:

a body having a first internal longitudinally-extending through-passageway extending between upstream and downstream end regions about a longitudinal axis,

a waterjet-forming orifice member within the first passageway for producing a generally axially aligned waterjet when the first passageway upstream of the orifice member is coupled to a source of high pressure water,

first abrasive inlet means for permitting entry of abrasive material into the first passageway about a first inlet axis, and

means for releasably securing the generally axially-extending abrasivejet nozzle in alignment with said longitudinal axis to receive the abrasive-containing waterjet for discharge against a workpiece,

the insert comprising:

an insert body having a second internal longitudinally-extending through-passageway extending between upstream and downstream end regions about a second longitudinal axis, the waterjet-forming orifice member being mounted within the second passageway for producing the generally axially aligned waterjet when the first passageway upstream of the orifice member is coupled to a source of high pressure water;

second abrasive inlet means for permitting entry of abrasive material into the second longitudinal passageway about a second inlet axis; and

means for substantially preventing contact between the waterjet and abrasive material within the second longitudinal passageway until the waterjet is downstream from said entry,

said insert being adapted to be mounted within the cutting head with the first and second longitudinal axes in substantial alignment and with the first and second inlet axes in substantial alignment where the abrasive enters the second longitudinal passageway.

21. The insert of claim 20 wherein the second inlet axis is non-intersecting with said second longitudinal axis.

22. The insert of claim 20 or 21 including wherein at least a longitudinally extending portion of the interior walls of the insert define a generally tapered passageway between the waterjet-forming orifice member and the mixing region.

23. The insert of claim 20 or 21 including a waterjet-isolation member having a third waterjet-accommodating passageway extending generally co-axially with the second longitudinal axis within at least a portion of the insert to carry the waterjet emerging from the waterjet-defining orifice past the entering abrasive to a mixing region.

24. The insert of claim 23 wherein the waterjet-isolation member has a generally annular cone-shaped outer structure circumscribing the third passageway.

25. The insert of claim 24 wherein said generally cone-shaped structure has tapered exterior walls converging at approximately an 8° angle.

26. An abrasivejet cutting head comprising:

a body having a first internal longitudinally-extending through-passageway extending between upstream and downstream end regions about a longitudinal axis,

a waterjet-forming orifice member within the passageway for producing a generally axially aligned waterjet when the passageway upstream of the orifice member is coupled to a source of high pressure water,

means for securing a generally axially-extending abrasivejet nozzle in alignment with said longitudinal axis to discharge an abrasive-containing waterjet against a workpiece;

a generally annular, longitudinally extending abrasivejet nozzle secured by said securing means to discharge from its distal end an abrasive-containing waterjet against a workpiece, and having an abrasive-accommodating abrasive inlet passage communicating between its interior and exterior for permitting entry of abrasive material into abrasive nozzle about an inlet axis, and

a prevention member for substantially preventing entrainment of the abrasive material with the waterjet until the waterjet reaches a position downstream for the abrasive inlet.

27. The abrasivejet cutting head of claim 26 wherein the said inlet axis is non-intersecting with said longitudinal axis.

28. The abrasivejet cutting head of claim 27 or 28 including a generally tapered passageway between the waterjet-forming orifice member and said downstream position of entrainment.

29. The abrasivejet cutting head of claim 28 wherein the walls of the passageway converge at an angle in the range of between and including approximately 10° and approximately 70°.

30. The abrasivejet cutting head of claim 29 wherein the walls of the passageway converge at approximately a 20° angle.

31. The abrasivejet cutting head of claim 26 wherein the prevention member is attached to the waterjet-forming orifice member.

32. The abrasivejet cutting head of claim 26 wherein the prevention member is mechanically linked to the waterjet-forming orifice member.

31. For use in an abrasivejet cutting head, an abrasivejet nozzle comprising:

a generally tubular, body extending from an upstream end to a downstream end about a longitudinal axis and having an internal diameter in the range of approximately 0.015 inches to approximately 0.080 inches throughout at least the substantial portion of its length, said body having an abrasive-inlet opening downstream from its upstream end for permitting entry of abrasive material into the interior of the nozzle from an external source along an inlet axis that is not coaxially aligned with said longitudinal axis.

32. The abrasivejet nozzle of claim 31 wherein the inlet axis is not parallel to the longitudinal axis.

33. The abrasivejet nozzle of claim 31 wherein the inlet axis is non-intersecting with the longitudinal axis.