WO2014171959A1

WO2014171959A1 - Abrasivejet cutting head with improved abrasive conduit interface

Info

Publication number: WO2014171959A1
Application number: PCT/US2013/057157
Authority: WO
Inventors: Gary N. Bury; Steven E. May
Original assignee: International Waterjet Parts, Inc.
Priority date: 2013-04-19
Filing date: 2013-08-28
Publication date: 2014-10-23

Abstract

Substantially symmetrical frictional contact is generated between the abrasive-carrying conduit and the wall of the cutting head's abrasive inlet channel as the conduit is inserted therein, thereby minimizing or eliminating the differences in friction resulting from sliding contact that can create misalignment. A portion of the cutting head's abrasive inlet channel is configured to form a contact area that provides generally symmetrical frictional contact with the abrasive-carrying conduit, while the remaining portion of channel is sized to provide a clearance fit with the conduit.

Description

Title: Abrasivejet Cutting Head With Improved Abrasive Conduit Interface 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. Background 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 "abrasivejet". The abrasivejet 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 abrasivejet. The resulting abrasive-laden waterjet is then discharged against a workpiece through an abrasivejet nozzle that is supported closely adjacent the workpiece. 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. 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 abrasivejet nozzle securely held at or within its downstream end. The cartridge can provide an integral unit comprising the mixing region and the jet-forming orifice. As will be apparent to those of ordinary skill in the art, the invention herein is not limited to an abrasivejet system wherein the mixing region is located within such a cartridge, or wherein a cartridge is used at all. As described above, abrasive is drawn into the abrasivejet cutting head from a hopper via a conduit that communicates with the interior of the hopper. As best illustrated in Figure 2, conduit tubing 3 that conveys the abrasive media into the mixing chamber 4 of the cutting head has conventionally had asymmetric contact with the cutting head, whereby one side 3b of the tubing touched the body over a short distance, while the other side 3a touched the body over a longer distance. Because the conduit is typically secured within the cutting head via a slight interference fit, this dissimilar contact area, and the consequential difference in friction resulting from the sliding contact, can create a misalignment between the tubing and the conduit-receiving channel. The misalignment has the potential of causing a binding that is sensed by a person inserting the conduit as a sign that the conduit is correctly seated within the cutting head adjacent the mixing region. If the conduit is not correctly seated, the interior of the cutting head is exposed to destructive incoming abrasive media. This defeats the purpose of the overall design of the cutting head. The long contact path with a constant bore diameter increases the damping ratio of the dynamic motion between the body and tubing, leading to a difficult "feel" of the tubing. Accordingly, the "feel" of the tubing as it is inserted is important. The ideal "feel" is defined as a constant force being required to push the tubing all the way to its landing. The damping ratio of the dynamic motion between the tubing and body is constant. However, the dissimilar contact area described above has made "by feel" control of the tubing as it is inserted very difficult. Moreover, owing to manufacturing tolerances of the conduit and conduit-receiving channels, some cutting head bodies have had had too small a channel, where the tubing would not go through. In other cutting head bodies, the channel has been too big, rendering the part useless since the tubing could not be retained, nor could the channel be appropriately resized. Tighter tolerances could be cost-prohibitive to the market. Summary In accordance with the invention, a structure is provided that enhances control of the interface between the conduit and the body of the cutting head, while using commonly available materials for the abrasive conduit, and without requiring special materials. An abrasivejet cutting head body disposed about a longitudinal axis between upstream and downstream ends, and an internal generally longitudinally-extending passageway in fluid communication with both said ends, is provided with a generally obliquely-extending abrasive-inlet channel for accepting the insertion of an abrasive-carrying conduit in such a way that abrasive material from a source external to the cutting head body is conveyed to said longitudinal passageway. A portion of the abrasive inlet channel is sized as a contact region that provides a generally symmetrical interference fit for the abrasive-carrying. The remaining portion of the conduit-receiving channel is sized to have a clearance fit with said conduit. Consequently, substantially symmetrical frictional contact is generated between the conduit and cutting head body as the conduit is inserted therein towards the longitudinally- extending passageway, minimizing or eliminating the differences in friction resulting from sliding contact that can create misalignment between the abrasive-carrying conduit and the conduit-receiving channel. Further details are provided in the Detailed Description of the Currently Preferred Embodiment of Invention below, of which the Drawing is a part. Description of the Drawing In the Drawing: Figure 1 is a perspective view of three preferred main cutting head components; Figure 2 is a longitudinal sectional view in schematic of the preferred abrasive conduit tubing within a preferred abrasivejet cutting head in accordance with the invention; Figure 3 is a magnified view in schematic of a portion of the preferred conduit- receiving channel within a preferred cutting head body in the vicinity of a contact area constructed in accordance with the invention; and Figure 4 is a magnified view in schematic of a portion of the conduit-receiving channel of Figure 2 in the vicinity of a contact area constructed in accordance with the invention. Detailed Description Of The Currently Preferred Embodiment of Invention Figure 1 illustrates three preferred main cutting head components: a cutting head body 2, a cartridge 1 that integrates a jet- forming orifice member with a mixing region in a single replaceable structure, and abrasive-carrying conduit tubing 3. The cartridge 1 and body 2 are preferably formed from heat-treated 17-4 precipitation hardened stainless steel. The tubing 3 is made preferably formed from a polyurethane -based plastic that has been proven in the waterjet industry to withstand the constant friction of abrasive media. These components provide the means for introducing abrasive media into a stream of ultra-high pressure water at typical pressures between 10,000 psi (689.48 bar) and 100,000 psi (6894.76 bar), although pressures outside this range can be used as well for abrasivejet cutting. The body 2 receives the cartridge 1 while the tubing 3 provides the means to convey the abrasive media to the cartridge. The tubing material is extremely abrasion resistant, suitable to withstand the constant friction of the abrasive media over many hundreds of hours of operation. Together, these components for the abrasive interface are shown in Figure 2. In accordance with the invention, the tubing 3 is retained by the body 2 by a short contact area 5 of axial length "x", where the internal diameter of the conduit-receiving channel is smaller than the outer diameter of the tubing 3. As will be appreciated from Figure 2, the contact area, and consequential symmetrical sliding friction, between the tubing and body over a constant distance "x" on all sides of the tubing prevents the body 2 from "pushing" the tubing 3 off of its inclined axis. The relatively short distance "x" compared to the channel length, reduces the amount of friction to a level providing the correct feel to a user trying to properly seat the conduit within the cutting head, and the location of the contact area adjacent the mixing region provides that feel as the conduit approaches its proper seating position while, as described below, the remaining portion of the channel has little or no contact with the moving conduit to thereby avoid binding. The contact area is preferably placed as close to the mixing region as possible.

In the illustrated embodiment, wherein a replaceable cartridge preferably integrates the jet- forming orifice member with the mixing region in a single structure, the contact area is preferably configured to lie outside the cartridge. This is currently preferred to eliminate a tactile difference in feel that could arise as the abrasive tubing enters the cartridge and mislead the user into believing that the tubing is securely seated. Moreover, the preferred clearance for the tubing in the cartridge is, as a practical matter, greater than the clearance for the tubing in the body 2 due to stacked tolerances. It is therefore better to avoid reliance on contact between the tubing and cartridge during insertion so that the only contact to be felt is when the tubing is fully and securely seated. Lastly, it is believed that the cartridge would need to be larger to accommodate a contact area, and that the increase in size would be a negative in the marketplace. The internal diameters of the conduit-receiving channel upstream and downstream of the contact area 5 have dimensions and tolerances so as to be larger than the outer cross- section or diameter of the conduit 3, preventing the body 2 from influencing the path of the tubing 3 as it is inserted by the user. Those skilled it the art will also appreciate that if the tubing 3 is pushed too far off of its intended path, the edge of the tubing could get hung up on the cartridge 1, preventing the tubing from seating against the mixing chamber within the cartridge, and exposing the body 2 to incoming abrasive media. Further examination of the contact area is shown in Figure 3. The preferred conduit- receiving channel is a bore of varying diameters. Figure 4 shows a closer view of the tube contact area 5. The geometry of a conduit-receiving channel constructed in accordance with the invention allows a preferred manufacturing method whereby the body 2 is machined in one piece, without requiring additional parts to interface with the tubing 3, and the tolerance of the diameter of the contact area 5 is comparatively easy to control. Because of the enhanced feel to conduit insertion into the cutting head, the user has a lower probability that the tubing will be inserted incorrectly, thereby maximizing the effectiveness of the cutting head design, the life of the internal components and the efficiency of abrasive usage because the conduit is seated correctly adjacent the mixing region. In practice, it has been found that a clearance fit of approximately 0.01 inches (0.25 mm), and preferably 0.010 inches (0.254 mm) between the conduit and channel wall outside the contact area 5, together with an interference fit of approximately 0.02 inches (0.51mm), and preferably 0.020 inches (0.0508 mm), between the conduit and wall within the contact area, provides the desired feel that accomplishes the desired result. A contact area having an axial length "x" of approximately 0.09 - 0.11 inches (2.29 - 2.79 mm) provides the desired result while sized to lie within the body 1 without extending into the cartridge 1. Other channel and conduit dimensions, tolerances and geometries can be utilized as well to provide the generally symmetrical sliding friction between the channel walls and the conduit, but the preferred geometry, dimensions and tolerances described herein are believed at the present time to provide the best results with the most cost-effective method of manufacture. Manufacturing the conduit-receiving channel out of one solid piece is advantageous due its cost-effectiveness. In practice, a channel having approximately the internal diameter of the contact area 5 is first formed in the cutting head body along the entire axial length of tubing insertion. Additional wall material is then removed from the interior of the channel downstream (i.e., inwardly) of the contact area to increase its diameter, using a milling technique known as circular interpolation, and additional wall material is removed from the portion of the channel upstream from the contact area by milling or in any desired manner.

Although a currently preferred embodiment of the present invention and its advantages have been described in detail above, it should be understood that various details, changes, substitutions and alterations will be apparent to those of ordinary skill in the art having the benefit of the foregoing specification. It is intended that all such variations be within the scope and spirit of the invention, and that the invention be solely defined by appended claims that shall be given the broadest allowable interpretation consistent with the Doctrine of Equivalents.

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Claims

What is claimed is: 1. An abrasivejet cutting head body disposed about a longitudinal axis between upstream and downstream ends, and having

a generally longitudinally-extending passageway in fluid communication with both said ends, and

a generally obliquely-extending abrasive-inlet channel formed in said body for accepting the insertion of an abrasive-carrying conduit in such a way that abrasive material from a source external to the cutting head body is conveyed to said internal passageway, a portion of said abrasive inlet channel being sized as a contact area that provides an interference fit for said abrasive-carrying conduit that creates generally symmetrical frictional contact with the abrasive-carrying conduit,

the remaining portion of said abrasive inlet channel being sized to have a clearance fit with said conduit.

2. The abrasivejet cutting head of Claim 1 wherein the contact area is sized to have an interference fit with said conduit of approximately 0.02 inches (0.51 mm).

3. The abrasivejet cutting head of Claim 2 wherein said remaining portion of the abrasive inlet channel is sized to have a clearance with said conduit of approximately 0.01 inches (0.025 mm).

4. The abrasivejet cutting head of Claim 3 wherein the length of the contact area is approximately 0.09 inches (2.29 mm) to approximately 0.11 inches (2.79 mm).

5. The abrasivejet cutting head of Claim 2 wherein the length of the contact area is approximately 0.09 inches (2.29 mm) to approximately 0.11 inches (2.79 mm).

6. The abrasivejet cutting head of Claim 1 wherein the length of the contact area is approximately 0.09 (2.29 mm) inches to approximately 0.11 inches (2.79 mm).

7. The abrasivejet cutting head of Claim 1 wherein said remaining portion of the channel is sized to have a clearance with said conduit of approximately 0.01 inches (0.025 mm).

8. The abrasivejet cutting head of Claim 1 wherein the length of the channel contacting substantially any side of the conduit within the contact area is substantially the same as the length of the channel contacting the conduit on the opposite side.

9. A method for manufacturing an abrasivejet cutting head of the type having a generally longitudinally-extending passageway in fluid communication with both said ends, and

a obliquely extending abrasive-inlet channel formed in said body from the exterior of the cutting head to said passageway for accepting the insertion of an abrasive-carrying conduit in such a way that abrasive material from a source external to the cutting head body is conveyed to said passageway,

the method comprising the steps of:

forming the channel with cross-sectional dimensions between opposing interior walls that provide an interference fit with the conduit;

defining a contact area for releasably securing the conduit within the cutting head through frictional contact by (a) removing enough additional wall material from the portion of the channel between the contact area and the passageway to form a clearance fit with the conduit, and (b) removing enough wall material from the portion of the channel between the contact area and the exterior of the cutting head body to form a clearance fit with the conduit.

10. The method of Claim 9 wherein step (a) is performed by circular interpolation.

11. The method of Claim 9 wherein the cross sectional dimensions provide an interference fit of substantially 0.02 inches (0.51 mm).

12. The method of Claim 9 wherein the wall material is removed from

substantially the entire portion between the contact area and the passageway.

13. The method of Claim 9 wherein the wall material is removed from

substantially the entire portion between the contact area and the exterior of the cutting head.

14. The method of Claim 9 wherein wall material is not removed from approximately 0.09 inches (2.79 mm) to approximately 0.11 inches (2.29 mm) of the channel to thereby substantially define the contact region.