WO2009001301A1

WO2009001301A1 - Waterjet mixing tube comprising multiple components

Info

Publication number: WO2009001301A1
Application number: PCT/IB2008/052533
Authority: WO
Inventors: Gerrit Jan Pels; Herman Philip Godfried; Johannes Cornelis Lamers; Paulus Adrianus Cornelis Kriele; Rene Antonius Lambertus Maria Diks; Wilhelmus Gerarda Maria Nelissen
Original assignee: Element Six B.V.; Donald, Heather June
Priority date: 2007-06-25
Filing date: 2008-06-25
Publication date: 2008-12-31
Also published as: GB0712314D0

Abstract

A method is disclosed of manufacturing a mixing tube for an abrasive waterjet system. The method comprises providing a plurality of mixing tube components having opposed ends, and each comprising at least a layer of superhard material; and assembling the plurality of mixing tube components. The components are assembled with the layers of superhard material therein extending adjacent to one another about an axis to define a mixing tube with an axially extending bore. Preferably the assembled components define joins between them which extend longitudinally, parallel to the bore. In one version of the method, a groove is formed at the surface of the layer of superhard material of each mixing tube component, the groove extending between the opposed ends of the mixing tube component, and the plurality of mixing tube components are assembled with the grooves therein extending adjacent to one another about an axis to define the axially extending bore. Each mixing tube component may be an elongate body comprising a first layer of substrate material with a second layer of superhard material being located on one side of the body. Alternative versions of the method are disclosed.

Description

WATERJET MIXING TUBE COMPRISING MULTIPLE COMPONENTS

BACKGROUND OF THE INVENTION

THIS invention relates to a mixing tube for an abrasive waterjet system and to a method of manufacturing such a mixing tube.

In waterjet cutting of hard materials, a high velocity jet of water is produced by feeding water under high pressure through a waterjet nozzle having a suitably shaped orifice. A fine-grained abrasive is entrained in the waterjet, to enhance the cutting properties of the waterjet. This is done by mixing the abrasive downstream of the nozzle orifice in a mixing chamber and having the waterjet entrain and accelerate the abrasive particles further down in a mixing tube (also known as a focusing tube). The waterjet exiting the mixing tube has excellent cutting properties and can cut very hard materials.

The mixing tube has a longitudinal bore, with the accuracy of the bore profile having a significant impact on the precision of the cutting jet. The bore is subject to severe abrasion by the abrasive particles entrained in the waterjet, and consequently tends to have a limited service life. Consequently, mixing tubes are generally formed from, or lined with, hard materials such as WC (tungsten carbide), in most cases a special type of WC is used that does not contain a binder such as cobalt. Use of this special type of WC results in an improved service life with respect to mixing tubes made from other types of WC, but it is still a relatively short lifetime, in this respect it is important to note that in the past few years the increasing use of nozzle inserts manufactured out of diamond instead of traditional materials such as ruby and sapphire has resulted in a significant increase in the service life of these inserts, as a result of which the mixing tubes are now the components that determine the service interval for the waterjet cutting machines in which they are used. Therefore improvement of the service life of these components has become even more important to enhance overall productivity and lower the cost of ownership of these machines.

In US patent 6,452,805 a method is disclosed of improving the service life of a mixing tube by lining the bore of the mixing tube with a superhard material such as cubic boron nitride or diamond. The lining is shaped into a suitable form by electric discharge machining and therefore must be electrically conductive to allow electric discharge machining.

In another known type of mixing tube, a hole is formed in each of a number of pieces of superhard material and the pieces are stacked with their holes aligned to define the bore of a mixing tube. Alternatively, the bore can be formed through the stacked pieces in situ. In the first case, alignment of the multiple sections of the mixing tube can be problematic, while in the second case, it can be difficult to drill or machine the necessary bore through the length of the mixing tube as defined by the stacked sections.

It is an object of the invention to provide an alternative mixing tube and method of manufacture thereof, that addresses the problems of rapid wear of current mixing tubes. SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a method of manufacturing a mixing tube for an abrasive waterjet system, the method comprising:

providing a plurality of mixing tube components having opposed ends and comprising at least a layer of superhard material; and

assembling the plurality of mixing tube components with the layers of superhard material therein extending adjacent to one another about an axis to define a mixing tube with an axially extending bore.

Preferably, the components define joins between them which extend longitudinally, parallel to the bore.

The method may comprise forming a groove at the surface of the layer of superhard material of each mixing tube component extending between the opposed ends of the mixing tube component, and assembling the plurality of mixing tube components with the grooves therein extending adjacent to one another about an axis to define the axially extending bore.

The mixing tube components may be elongate bodies comprising a first layer of substrate material with a second layer of superhard material being located on one side of the body.

For example, such elongate bodies may be generally parallelepipedic or prismatic in shape, or may have a shape corresponding to a segment of a cylinder.

The groove in each mixing tube component may be formed in the layer of superhard material in a number of ways. -A-

For example, the groove may be formed by laser cutting, electric discharge machining or another cutting method.

Alternatively, the groove may be formed by forming a layer of superhard material on a substrate having a negative shape defining the required groove, and removing the substrate to expose a groove formed in a surface of the superhard material that had been in contact with the substrate, to form a mixing tube component comprising the layer of superhard material without the substrate. The term "negative" is used in the sense of "opposite", so that a ridge or bump may be the "negative" shape that forms the groove in the deposited layer.

In another embodiment the groove may be formed by depositing a layer of superhard material on a substrate having a positive shape defining the required groove so that the layer of superhard material assumes said positive shape at a surface thereof that is not in contact with the substrate, to form a mixing tube component comprising both the substrate and the superhard layer.

The plurality of mixing tube components may be clamped into position against one another, or may be cemented or brazed together, for example.

According to a second aspect of the invention there is provided a method of manufacturing a mixing tube for an abrasive waterjet system, the method comprising:

providing a plurality of strips of superhard material having opposed ends;

assembling the strips of superhard material concentrically about an axis to define a mixing tube with an axiaily extending bore defined between the opposed ends of the strips.

The strips may be discrete bodies of superhard material. Alternatively the strips may comprise layers of superhard material on a substrate.

The strips may be curved or shaped to define grooves, the grooves being aligned when the strips are assembled to define the bore so that the bore is generally circular in section.

Where more than two strips are used, the surfaces of the strips defining the wail of the bore may be flat, so that the bore is polygonal in section.

in some of the variations of the method defined above, the bore may be finished further after assembly of the mixing tube components or strips, to smooth or shape it.

Typically the bore will be smoothed and its cross sectional shape adjusted from an initial rough form towards uniform circularity.

For example, the bore of the assembled mixing tube may be finished by electric discharge machining, wire lapping, hot metal polishing or wire polishing, or a combination of these techniques.

According to a further aspect of the invention, there is provided a method of manufacturing a mixing tube for an abrasive waterjet system, the method comprising:

assembling a plurality of mixing tube components, at least some of the components comprising at least a layer of superhard material;

assembling the plurality of mixing tube components to define a mixing tube with an axially extending bore defined by said superhard material; and performing a finishing step comprising wire lapping and/or wire polishing to finish the surface of the bore to a required degree of smoothness.

Still further aspects of the invention are described below.

The invention extends to mixing tubes formed by the above defined methods.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a pictorial view of a composite disk of PCD diamond material with a WC backing used as a blank in one embodiment of a method according to the invention;

Figure 2 is a pictorial view of a component for a waterjet mixing tube comprising a single strip or slab cut from the blank of Figure 1 and formed with a groove in the PCD layer thereof;

Figure 3 is a pictorial view of two of the components of Figure 2 assembled face to face to define a waterjet mixing tube with a central bore;

Figure 4 is an end view of a waterjet mixing tube formed by an alternative embodiment of the method and comprising four components;

Figure 5 is an end view of a waterjet mixing tube formed by a further alternative embodiment of the method and comprising eight lamellae supported in a frame or holder;

Figure 6 is a sectional view of a blank formed by depositing diamond material by CVD on a "negatively" shaped substrate, for use in a further alternative embodiment of the method; and Figure 7 is a similar view to that of Figure 6 of a blank formed by depositing diamond material by CVD on a "positively" shaped substrate, for use in yet a further alternative embodiment of the method.

DESCRIPTION OF EMBODIMENTS

In a first embodiment of the invention, a mixing tube for a waterjet cutting system is made from two strips of poiycrystalline diamond (PCD) backed with tungsten carbide (WC).

Referring first to Figure 1, the first step in this embodiment of the method is to provide a sintered disk 10 comprising a layer 12 of poiycrystalline diamond with a WC backing 14. Such disks are typically about 50mm in diameter. The disk is polished on the diamond side so as to produce a smooth flat surface. A pair of elongate slabs or strips 16 and 18 are cut out from the central portion of the disk on either side of its diameter d. The strips are approximately 5 mm wide and 50 mm long (the length being substantially equal to the diameter of the disk). The overall thickness of the diamond and the WC backing is typically 10 mm, with the diamond layer having a thickness of 0.5 mm or greater.

Referring now to Figure 2, the next step is to form a longitudinally extending groove 20 in the surface of the diamond layer 12, in the middle of the slabs or strips 16 and 18 and typically extending the full length of each strip. This could for instance be done with a YAG- or UV-laser, or by electric discharge machining (EDM) or by some other processing method, known to those skilled in the art. In one embodiment, the groove 20 had a depth of approximately 0.35 mm and a width of approximately 0.7 mm. Since the diamond layer has a thickness of more than 0.5 mm the groove does not penetrate the diamond layer to expose the WC backing. It is preferred that the profile of the groove be generally part-circular. Once the grooves have been formed, the two slabs or strips 16 and 18 are assembled and clamped together as shown in Figure 3, with their diamond layers 12 adjacent and in contact with one another and with the respective grooves 20 aligned so as to define a bore 22 with a length equal to the lengths of the two strips. Alternatively the strips could be bonded together by applying a thin braze coating (e.g. CuAgTi) to the diamond surfaces, pressing them together, and applying heat to make the braze flow, or the strips could be glued together using a one- or two-component epoxy such as Epotek 353ND, or they could be pressed together by sintering them in a sintering material such as a sintered metal or ceramic.

Now the focusing or mixing tubes normally need a well defined bore, and this can be achieved by a further finishing step. A preferred technique to use is wire lapping and/or polishing of the inner surface of the bore. Wire polishing is a standard technique well known from wire dies in which the defining hole of the die is produced by wire polishing. In the present invention the application of this technique is not straightforward, since the length of the tube is much longer than the length of bores commonly prepared in wire dies and the initial shape of the assembled tubes had strong deviations from the final required shape of the bore due to imperfections in the shapes of the grooves and imperfect alignment of these grooves in the assembly.

To accommodate these large deviations a different mode of processing called wire lapping was used to obtain an approximate final shape, and only then could it be followed by wire polishing in a second step. Initially, when the surface had a shape which was still far from the required final cylindrical shape, a wire was chosen with a diameter which was between 50 and 100 μm below the final diameter of the bore. A slurry of diamond grit particles in a mixture of water and oil was introduced into the bore at one end of the tube (typically the upper end when processing in a setup where the bore axis is in a vertical direction) and the wire was pulled through the bore of the mixing tube in an oscillatory movement. The mixing tube was mounted on a rotary stage which was rotating at a speed of between 300 and 1 000 rpm. The siurry contained diamond grit with a particle size varying between 10 and 70 μm. The metal wire used could be made from a number of materials. Preferably copper, brass, or steel wires are used.

In the first part of the finishing process the diamond slurry particles are not embedded in the wire but are forced to move in the tiny space between the wire and the unfinished bore of the mixing tube. This mode of processing is called lapping. Rapidly, the bore acquired a cylindrical shape although the final roughness, Ra, at the surface was of the order of several microns, when using a relatively large size grit. Better (i.e. reduced roughness) could be obtained by successively going to a finer size grit. Typically the roughness, Ra, could be brought down to approximately 1 μm by using diamond grit with particle sizes of several microns.

As an alternative to the wire lapping method described above, electric discharge machining could be applied, in the case of electrically conductive material, as a first step to approximate the final required cylindrical shape of the bore, and when a sufficiently close approximate shape was obtained wire lapping could be applied to obtain the final required cylindrical shape. Wire lapping makes it possible to obtain a very accurate approximation of the final shape but it leaves a rough surface.

In most cases the mixing tube was left finished as per the above described processes. However, if a smoother surface was required, the focusing tube could be finished further by a process caϋed wire polishing in which a metal wire with a diameter which is substantially equal to the required final diameter of the bore is pulled through the mixing tube. This wire has diamond grit particles with a typical size of several micrometers embedded in the metal surface. Since the particles now cannot roll over the surface the processing mode is different from the wire lapping process described above and it is called wire polishing. Wire polishing is a lot slower than wire lapping in removing material from the surface of the mixing tube bore, but it is possible to obtain a very smooth surface eventually with a roughness, Ra, which is substantially below 1 μm.

For mixing tubes according to an example embodiment of the invention, with a bore diameter of 0.8 mm, the wires were first thinned down over a length exceeding the length of the mixing tube to enable pulling the wire through. A slurry of diamond particles was then added and the wire was pulled trough even further. Since the space between the wire and the bore of the mixing tube was very small in this stage of the processing, the diamond particles were forced into the surface of the wire. Preferably, a relatively soft material such as a soft steel, brass, copper or aluminum was used here for the wire. With the grit particles firmly embedded in the wire the surface of the bore could be polished to a very high finish. Typically, a surface roughness, Ra, of 50 nm or better could be achieved with this process, but for the specific mixing tubes in question this was not required and the polishing process was typically terminated once roughness and roundness of the bore in the tube were better than 1 μm.

If required, the WC material of the assembled tube can be shaped as needed, although this is non-essential. For example, it could be made rounded and concentric with the hole in the tube for easy alignment.

In a variation of the above described embodiment, the assembled tube comprises several segments instead of just two slabs or strips. For example, as shown in Figure 4, a focusing tube can be assembled from four segments 24, 26, 28 and 30, each produced by cutting a strip with a trapezoidal profile from a blank as shown in Figure 1. The diamond tip of each strip is provided with a quarter-circular groove in a similar process to that described for the first embodiment, and the four segments are assembled as shown, and clamped or brazed together. In the embodiment of Figure 4, the outer WC surface 32 of the assembled focusing tube has been machined round, concentrically with the central bore 34, which may be desirable in some applications. It will be appreciated that a three-segment tube, and also a tube having more than four segments, is also possible. However, it is thought that the use of more than four segments is probably not necessary and may be undesirable due to the increased complexity.

The advantage of a multi-segmented focusing tube is the fact that the PCD layer can be thicker than in the two-strip case of Figure 3: for a typical PCD layer thickness of 0.5 mm, a bore diameter of 0.8 mm would result in a focusing tube having a PCD layer which in the thinnest location is only 0.1 mm thick, while for a four-segment case it would be 0.47 mm thick.

In a variation of the above described methods, sintered polycrystaiiine cubic boron nitride (cBN) could be used to form the components of the mixing tube. cBN is a sintered material similar to the PCD described above, but the sintered particles consist of cBN. It is available both as solid disks of cBN or with a backing of WC. Disks of cBN, with or without a WC backing, are for instance produced by Element Six Ltd. of Shannon, Ireland.

Using this material, strips were produced that had half-cylindrical grooves in them that were applied by grinding, EDM or laser machining or a combination of these techniques. A mixing tube was then assembled from two or more strips of cBN material which were clamped, brazed, glued or sintered together, and the bore in the mixing tube was then further polished by wire lapping alone, or wire lapping in combination with wire polishing.

In a variation of the above described methods, Skeleton (trade mark) diamond material (sometimes also referred to as "silicon carbide cemented diamond" or "ScD") can be used to form the components of the mixing tube. Skeleton is a composite polycrystaiiine diamond product which is produced by Element Six Ltd. of Springs, South Africa. The characteristics of Skeleton material are described in the following patent publications, inter alia: WO99/12866 and WO00/018702. For the production of Skeleton diamond material, diamond powder is mixed with SiC powder, subjected to a thermal process to graphitize the surface of the diamond in a controlled manner and then infiltrated with molten silicon. SiC is then formed on the interface between the diamond grains and the liquid Si. This material can be shaped in the "green state" to form complex shapes prior to infiltration by many conventional ceramic forming techniques (e.g. pressing, molding etc.).

Using this material, strips were produced that had half-cylindrical grooves in them that were either formed during synthesis of the Skeleton material in a shaped mould, or applied afterwards by grinding or laser machining or a combination of these techniques. A mixing tube was then assembled from two or more strips of Skeleton material which were clamped, brazed, glued or sintered together, and the bore in the mixing tube was then further polished by wire lapping alone, or wire lapping in combination with wire polishing.

It is not essential that the bore of the mixing tube be perfectly circular with a precisely accurate radius, but it should be regular and uniform in shape. Essentially, the finishing step ensures a smoother curvature of the layers defining the bore and prevents or reduces discontinuities between the components. Thus the described method allows mixing tube components to be formed in which grooves are formed in superhard material which approximately define the shape of the bore when assembled, and which are then further finished to the required degree of smoothness and uniformity.

A number of alternative methods can be used to produce waterjet mixing tubes according to the invention.

In one such alternative method, a powder containing diamond grit mixed with a binder grit (e.g. cobalt powder) is sintered to the final form of the mixing tube about a former or mandrel.

Normally PCD is formed by compressing an alternating stack of WC pucks and layers of diamond grit, with binder grit (usually cobalt powder) interspersed in the diamond grit. After sintering, pucks of WC with a PCD coating or layer on them are made by cutting the stack transversely, midway through each layer of WC and PCD parallel to the planes of the WC disks. In this embodiment a round "axle" or cylinder of WC is introduced prior to sintering midway in the layer of diamond grit mixed with binder parallel to the planes of the WC disks. After sintering the stack is cut halfway through the WC disks only. The centra! WC rods which are now bound to the PCD are dissolved chemically or removed with a laser or EDM and the resulting tube is ready for use. Note that with this technique it is also possible to make a conical entry section. This is achieved by tapering one end of the WC rod.

In another alternative method, a lamellar tube is assembled from a plurality of flat lamellae. With reference to Figure 5, a mixing tube was made from eight flat-edged lamellae 36 that are inserted into a frame or holder 38. Each lamella is a strip of composite material comprising a relatively thick layer 40 of WC and a relatively thin layer 42 of PCD. The figure is a top view of an eight-segment lamellar tube. It will be appreciated that the number of lamellae can vary, and need not be an even number. The maximum number of lamellae is mainly limited by the complexity of the resulting structure. The central bore 44 (again with a diameter of approx. 0.8 mm) of the prototype has an octagonal shape instead of a circular section but this is dose enough for the cutting purpose of the tube. In this case a finishing step such as wire polishing is not necessarily required although it is still possible to do so. However the extra effort needed and the associated cost of the processing make this an option which is economically not attractive.

The lamellae fit into slots 46 in the frame 38 with the PCD layers oriented inwardly to form the inner wall of the focusing or mixing tube. Wear in the PCD material is accommodated by fitting the frame with springs 48, which press the lamellae inwards. They also ensure that the tube is closed, that is, that the inner wall of the tube is continuous. Alternatively the lamellae could be fixed in place in the slots in the frame using an epoxy or other suitable adhesive. In an alternative embodiment the lameϋae can be made out of strips of polycrystalline solid cBN or cBN on WC, of which the side facing the bore of the mixing tube has been lapped, or lapped and polished.

In another alternative embodiment the lamellae can be made out of strips of polycrystalline CVD diamond, of which the side facing the bore of the mixing tube has been lapped, or lapped and polished.

Other embodiments of the method utilise polycrystalline CVD diamond formed into appropriate shapes.

In one such embodiment, the mixing tube is made from two CVD diamond strips. Similar to the first embodiment described above, the focusing or mixing tube consists of two strips of polycrystalline CVD diamond, in each of which a groove with a half-circular cross section was made. This was done with a Nd:YAG laser (in a case where the diamond is electrically conductive due to doping with boron, the cutting or shaping can be done by EDM).

Alternatively the grooves could be made by hot metal polishing in which the CVD diamond and a low carbon steel wire are heated to approx. 900⁰C and brought into contact. By diffusion of carbon into the steel the groove is polished to its final dimension. Alternatively the grooves could be made by a combination of these techniques.

When the grooved strips are brought into abutment with the grooves aligned, a bore is defined by the grooves. Similar to the case in the first embodiment, the bore could be finished by wire polishing or also by hot metal polishing in which the assembly is heated to approx. 900⁰C and a wire made of a low carbon steel is passed through the bore. If the thickness of the CVD diamond is not enough (typically it can have a thickness up to 2.5 mm, although greater thickness is possible) the CVD diamond can be backed up by brazing a metal backing of, for example, WC or Molybdenum to it. Alternatively, the CVD diamond could be backed up by gluing some other material backing such as (stainless) steel, aiuminum alloy or brass to it. In another alternative the CVD could be grown on a materia! such as WC or Si to which it adheres after cool-down and removal from the reactor. Thus the CVD diamond would be backed by the WC or Si on which it was grown.

In a further embodiment, an axle or mandrel made of W, WC or Si (with or without a conical entry section) was coated with CVD diamond. The surface of the CVD that is in contact with the diamond obtains a roughness equal to the roughness of the axle surface. Therefore if this surface is well prepared no further shaping of the bore of the tube is necessary. If so desired the outer surface of the CVD layer can be polished by techniques known to those skilled in the art on a resin bond wheel containing diamond grit bonded in a resin to form a round outer surface or to give it some other shape that is convenient. If so desired a holder may be attached to the outer surface to support the CVD layer. Finally the inner axle is removed by EDM or by chemically dissolving the W, WC or Si. By using W for the mandrel material it is also possible that the diamond will release from the mandrel without any further need for chemical or EDM treatment.

Other embodiments involve growth of CVD diamond material on a "negative" or "positive" pre-shaped substrate comprising materials suitable for growth of CVD diamond such as W, WC, or Si or other similar materials, known to those skilled in the art.

In the case of a "negatively" shaped substrate, a layer 50 of CVD diamond is grown on a substrate 52 (typically W, WC, Si) that is pre-shaped with convex half-cylindrical "bumps" 54, as shown in the sectional view of Figure 6. Typically, the thickness of the CVD diamond layer is 0.5 mm or more. Preferably its thickness is 0.8 mm or more. The CVD diamond layer 50 (and the substrate if still adhering to the CVD diamond layer) is cut in a direction parallel to the "bumps" 54 with a laser or by EDM, for example. It is also possible to cut the substrate using an abrasive waterjet. The substrate is removed, if it still adheres to the CVD diamond layer, by chemically dissolving it. Two of the CVD diamond components are then aligned and brought into contact by clamping them together or by brazing, gluing or sintering, simiiarly to the method of the first embodiment.

The substrate is referred to as "negatively" shaped as the bumps or ridges are shaped oppositely to the eventual grooves formed in the CVD diamond iayer.

The use of a "positively" pre-shaped substrate is shown in Figure 7. This embodiment is simiiar to the embodiment of Figure 6 but now the substrate 56 has concave half-cylindrical grooves 58, which are filled with a fairly thin layer 60 of CVD diamond. Typically the thickness of the CVD diamond iayer is several tens of microns, e.g. 50-70 μm.

The substrate should in this case stay attached to the CVD diamond layer. Therefore materials such as WC or Si are preferred for the substrate. First the upper surface of the CVD diamond layer is polished to get a flat upper surface. After cutting the substrate and CVD diamond layer along the lines indicated, similarly to the preceding embodiment, two of the resulting strips are oriented with their grooves aligned and brought into contact. The strips are then either brazed, clamped, glued or sintered together as described previously.

In this embodiment, the eventual grooves have the same shape as the grooves in the substrate surface, rather than being oppositely shaped.

In both the negative and positive substrate versions of this embodiment, the bore of the assembled mixing tube is polished by, for instance, wire polishing. In the case where an electrically conductive CVD diamond layer has been applied, EDM shaping can be used to polish the bore. Alternatively, the cylindrical grooves can be polished by hot metal polishing before the strips are assembled to form the tube. Alternatively, hot metai polishing can be applied to the bore after the strips are assembled.

Note that in all cases the CVD diamond is polycrystalline and can have different heat conductivity. A high heat conductivity in this application is desirable because the abrasive particles that impact on the inner wall of the mixing tube have a high speed and thus carry a lot of energy which must be dissipated in the wall of the tube. Therefore CVD diamond with a heat conductivity above 600 W/m-K and preferably above 1000 W/m-K and even more preferably above 1500 W/m-K and most preferably above 1800 W/m-K is used.

In another embodiment, a shaped mold was used to form mixing tubes according to a further aspect of the invention. Using such a shaped mold, mixing tubes were made from Skeleton material that were finished in one step. Alternatively the material could be ground on the outside to obtain a final desired shape, or the hole or bore of the tube can be shaped by wire polishing.

In yet another embodiment, according to a still further aspect of the invention, stacked mixing tubes were produced, using single crystal or other types of diamond.

Such mixing tubes, made from natural or synthetic single crystal diamond, or from polycrystalline PCD or CVD diamond, or from Skeleton or cBN, could be made by drilling holes in plates made from these materials or combinations thereof, the plates having a typical thickness of 1 to 3 mm, and stacking the plates with their holes in line. The plates are bonded by brazing using, for example, Ti CuAg, or using a one- or two-component epoxy such as Epotek 353ND or could otherwise be clamped or sintered in place. Subsequent to the stacking and bonding of the plates, a further finishing step comprising EDM and/or wire lapping and/or polishing as described above is carried out.

Claims

1. A method of manufacturing a mixing tube for an abrasive waterjet system, the method comprising:

2. A method according to claim 1 wherein the assembled components define joins between them which extend longitudinally, parallel to the bore.

3. A method according to claim 1 or claim 2 comprising forming a groove at the surface of the layer of superhard material of each mixing tube component, the groove extending between the opposed ends of the mixing tube component, and assembling the plurality of mixing tube components with the grooves therein extending adjacent to one another about an axis to define the axially extending bore.

4. A method according to any one of claims 1 to 3 wherein each mixing tube component is an elongate body comprising a first layer of substrate material with a second layer of superhard material being located on one side of the body.

5. A method according to claim 4 wherein the elongate body is generally parallelepipedic or prismatic in shape.

6. A method according to claim 4 wherein the elongate body has a shape corresponding to a segment of a cylinder.

7. A method according to claim 3 wherein the groove in each mixing tube component is formed in the layer of superhard material by laser cutting, electric discharge machining or another cutting method.

8. A method according to claim 3 wherein the groove in each mixing tube component is formed by forming a layer of superhard material on a substrate having a negative shape defining the required groove, and removing the substrate to expose a groove formed in a surface of the superhard material that had been in contact with the substrate, to form a mixing tube component comprising the layer of superhard material without the substrate.

9. A method according to claim 3 wherein the groove in each mixing tube component is formed by depositing a layer of superhard material on a substrate having a positive shape defining the required groove so that the layer of superhard material assumes said positive shape at a surface thereof that is not in contact with the substrate, to form a mixing tube component comprising both the substrate and the superhard layer.

10. A method according to any one of claims 1 to 9 wherein the plurality of mixing tube components are clamped into position against one another.

11. A method according to any one of claims 1 to 9 wherein the plurality of mixing tube components are cemented or brazed together.

12. A method of manufacturing a mixing tube for an abrasive waterjet system, the method comprising: providing a plurality of strips of superhard material having opposed ends;

assembling the strips of superhard material concentrically about an axis to define a mixing tube with an axially extending bore defined between the opposed ends of the strips.

13. A method according to claim 12 wherein the strips are discrete bodies of superhard material.

14. A method according to claim 12 wherein the strips comprise layers of superhard materia! on a substrate.

15. A method according to any one of claims 12 to 14 wherein the strips are curved or shaped to define grooves, the grooves being aligned when the strips are assembled to define the bore so that the bore is generally circular in section.

16. A method according to any one of claims 12 to 14 wherein more than two strips are used, the surfaces of the strips defining the wall of the bore being substantially flat, so that the bore is generally polygonal in section.

17. A method according to any one of claims 1 to 16 wherein the bore is finished further after assembly of the mixing tube components or strips, respectively, to smooth or shape the bore.

18. A method according to claim 17 wherein the bore is smoothed and its cross sectional shape adjusted from an initial rough form towards uniform circularity.

19. A method according to claim 17 or claim 18 wherein the bore of the assembled mixing tube is finished by electric discharge machining, wire lapping, hot metal polishing or wire polishing, or a combination of these techniques.

20. A method of manufacturing a mixing tube for an abrasive waterjet system, the method comprising:

assembling the plurality of mixing tube components to define a mixing tube with an axially extending bore defined by said superhard material; and

performing a finishing step comprising wire lapping and/or wire polishing to finish the surface of the bore to a required degree of smoothness.