WO2009013716A2

WO2009013716A2 - Placing of superhard material

Info

Publication number: WO2009013716A2
Application number: PCT/IB2008/052956
Authority: WO
Inventors: David Patrick Egan
Original assignee: Element Six Limited; Donald, Heather June
Priority date: 2007-07-23
Filing date: 2008-07-23
Publication date: 2009-01-29
Also published as: WO2009013716A3

Abstract

The present invention relates to a method of placing particles of superhard material on a surface in a random or predetermined pattern, the method including the step of rendering all of or a portion of the surface predisposed to receive particles of superhard material. The invention further relates to a tool including a surface having superhard particles placed in a random or predetermined pattern according to the method.

Description

PLACING OF SUPERHARD MATERIAL

INTRODUCTION

This invention relates to the placing of superhard material onto a surface. In particular, this application relates to the placement of superhard particles at predetermined positions on surfaces.

BACKGROUND TO THE INVENTION

GB1262724, (Nippon Toki, 1972) teaches a method of making grinding stones comprising mixing a particulate abrasive material with a synthetic resin binder and/or a synthetic or natural rubber binder in liquid form to produce a slurry-like mixture, squeezing the mixture on to a support by the screen-printing technique to form a print of the mixture on the support and curing and aging the print to obtain a grinding stone. The resin may be a phenolformaldehyde resin of the resol or novolak type, which may be employed as solutions, and unsaturated polyester resins and rubbers, liquefied by heating. Curing agents of which numerous examples are given may be present. The abrasive materials may be diamond, fused alumina, sintered alumina, silicon carbide, boron carbide, emery and garnet. Fillers, of which many are specified, may be present as well as other additives such as accelerators, tackifiers and stiffeners. The support may be of paper, glass fibre cloth, non-woven glass fibre cloth, or non-woven synthetic resin cloth. The thickness of the print can be controlled by keeping the screen a suitable distance away from the support, repeating the squeezing operation, or bonding two or more prints to each other.

EP1087899 (Addison, deBeers, 2001) teaches a particle retrieving apparatus provided for individually retrieving particles such as diamond particles using a reciprocating vacuum needle. A balance arm is provided having a hopper at its free end for receiving the diamond particles. The balance arm is adjusted so that it is in a position of equilibrium. As the needle tip contacts a particle, the balance arm is displaced downwardly, with such downward displacement being sensed by an opto-sensor which is thereby used to sense the contact position of the needle as it comes into contact with the diamond particle. The contact position is recorded at a micro-processor-based controller, which is then used to control the subsequent motion of the needle in the next retrieval cycle on the basis of the recorded contact position.

Single layer diamond tools, such as surface grinding discs can be made by brazing diamond to the surface of a disc. However, one difficulty encountered when manufacturing these tools is that it is not easy to place the diamond where it is wanted, i.e. to have a pattern of areas which have diamond brazed and other areas where there is no diamond. Also, when melting the braze, it tends to spread over the complete surface and can thus agglomerate abrasive particles. While diamond and other superhard material can be air brazed to a surface as a single layer tool, it is difficult to get an even/regular distribution of diamond and the required amount of braze material to bond each particle in a specified position on the surface.

A need therefore exists to be able to accurately place superhard particulate material on a surface such that tools utilizing such material can be efficiently manufactured.

SUMMARY OF THE INVENTION

According to a first aspect to the present invention there is provided a method of placing particles of superhard material on a surface in a predetermined pattern, the method including the step of rendering all of or a portion of the surface predisposed to receive particles of superhard material.

Preferably the surface is rendered predisposed to receive the particles such that the particles are maintained on the surface in a manner sufficient for the particles to be brazed to the surface at that position.

Figures 1-4 illustrate non-limiting examples of this aspect to the invention wherein:

Figure 1 shows a schematic perspective view of a plate (flat disc) including a spiral groove. The groove is filled with wet flux paste (flux powder and water) and clad/encapsulated diamond particles placed in the groove where they embed in the wet flux. Upon heating the diamonds are retained on the surface.

Figure 2 shows a schematic perspective view of a plate (flat disc) including circular grooves. The grooves are filled with wet flux paste (fiux powder and water) and clad/encapsulated diamond particles placed in the groove where they embed in the wet flux. Upon heating the diamonds are retained on the surface. Figure 3 shows a schematic perspective view of a cylinder including a spiral groove machined into the cylinder. Along a 25 um diameter brass wire, a spot of flux was placed every 3 mm and a single encapsulated particle was attached to the wire using the flux as an adhesive. The wire was then attached at one end of the cylinder, placed in the groove and wrapped around the cylinder. Once the wire reached the other end of the cylinder, it was cut and the end attached to the steel cylinder. The outside of the cylinder was then sprayed with flux. The arrangement was then transferred to a furnace where the diamond was brazed to steel cylinder by heat treating for 3 minutes at 835^°C.

Figure 4 shows a schematic perspective view of a masked steel disc. The surface of the steel disc was masked in order to produce an abrasive element with the configuration as shown. This is described further in example 1.

The superhard material may be selected from diamond, cubic boron nitride, wurtzitic boron nitride, a carbide, oxide or suicide, Si₃N₄, SiC, AI₂O₃, AIC, SiO₂ and/or clusters of any of the above. Most preferably the superhard material is diamond. The diamond may be natural or synthetic. Synthetic diamond may be synthesized by chemical vapour deposition or High Pressure High Temperature (HPHT) techniques.

The superhard particles are preferably at least about 0.01 um, preferably at least about 0.1 um, more preferably at least about 1 um in diameter. The superhard particle is preferably no greater than about 5mm, preferably no greater than about 4mm, more preferably no greater than about 3mm in diameter. Preferably the particle has a size of from about 1 um to about 1.5mm, measured across the greatest dimension of the particle. In this size range, the particles are known as micron, grit or monocrystal.

The grit, preferably diamond grit, may be encapsulated. In a preferred embodiment of the present invention, the grit is encapsulated in accordance with co-pending applications claiming priority from South African patent application Nos. ZA2007/06077, ZA2007/06074 and ZA2007/06075, the contents of which are included herein by reference.

Alternatively, or in combination with encapsulation, the grit may be coated. In a preferred embodiment of the present invention, the grit is coated in accordance with the co-pending applications set out above.

In one embodiment of the present invention the surface is rendered predisposed by indenting, drilling, turning, scoring, chemical etching or rolling the surface with indents sized to accommodate the particles. The indentations may also be produced during manufacture of the substrate i.e. using powder metallurgy.

The particle is preferably diamond and may be coated, encapsulated, clad or all of the aforementioned. Most preferably the particle is encapsulated with a braze alloy powder.

By encapsulating or cladding the diamond with the required amount of braze material and flux (if needed), the required amount for the desired brazing of each particle can be controlled.

Suitable braze pastes include:

Silver Brazing Alloys: Silver-flo Cadmium Free Range

(Registered Trade Mark (RTM))

Silver Brazing Alloys: Easy-flo Cadmium Bearing Range (RTM)

Copper Phosphorus Alloys: Copper-flo Range (RTM)

Silver Copper Phosphorus: Sil-fos Range (RTM)

Base Metal Brazing Alloys: Argentel and Bronze Brazing

Copper Based Brazing Alloys: Copper and Bronze Alloys

Palladium Brazing Alloys: Pailabraze Range (RTM)

Gold Brazing Alloys: Orobraze Range (RTM) Nickel Based Brazing Alloys: Johnson Matthey (JM) Nickel alloys Soft Solder Alloys: JM Solders

The encapsulated superhard particle may have a single or multiple layers. The layer(s) can include(s) a discrete or continuous gradient. Encapsulation may be achieved by any known method in the art, including by a fluidised bed, rotating pan, shovel rotor or any combination thereof. The shovel rotor is described in co- pending application claiming priority from South African patent application No. ZA2007/06077, the contents of which are incorporated herein by reference.

For the purposes of the present invention, a braze is a relatively low melting point metal/alloy which wets the target particle and substrate surface when molten bonding the particle to the surface upon cooling. A flux is typically a mixture of salts and has the following uses:

(1) cleans the surface to be brazed and removes oxides to improve wetting.

(2) provides protective barrier to minimise oxidation of the substrate surface and braze alloy.

By preparing the surface onto which the diamond is to be brazed with recesses, (indentations) positioning of the diamond particles on the surface can be controlled. The recesses can all be the same size or can have a varied diameter/depth. In the case of variable depth, a regenerating tool can be produced. The too! is described as regenerating in the sense that, once the particles in the shorter recesses are removed, particles in the deeper recesses will become the working particles of the tool through the wear of the tool body.

The surface may be indented using a comb or other template including tines or spikes adapted to impact the surface to thereby create the suitably sized dimples or indentations.

Preferably the surface is that of a single layer braze tool. It will be appreciated that the present invention allows the controlled production of single layer braze tools avoiding overcrowding of diamond (minimum distance between particles) and placing of the diamond in desired or pre-determined areas/positions.

The indentation/modification of the surface also provides a support for the abrasive particles which improves the holding of the particle to the surface allowing the tool to be used more aggressively by preventing premature loss of the diamond.

According to a second embodiment of the present invention, there is provided a method of placing particles of superhard material onto a surface in a predetermined pattern wherein the surface is rendered predisposed to receive the particles of superhard material by printing a layer on the surface. The layer may be attractive to the superhard particles or the layer may be repulsive to the particles. Alternatively the layer may be attractive or repulsive to a braze material including the particles.

By using a screen printing technique, as heretobefore used extensively in the electronics industry, it is possible to print areas on (mask) a tool surface with a non brazing layer where the molten braze will not wet and to print a paste consisting of braze material, flux if needed, diamond and binder/solvent on to the bare areas. Alternatively, the diamond may be added separately to the printed braze paste layer. When heated, the braze melts binding the diamond to the substrate but does not spread outside the printed area thereby preventing spreading over the entire surface. Using this method, areas such as waterways (contiguous braze areas) can be designed in the tool. In addition, it can be understood that the screen printing technique can be used in combination with an indented surface on the tool, where the area in the region of the indentations is specifically targeted with braze paste. Melting of the braze can be done in an oxygen reduced atmosphere or vacuum when using uncoated diamond and an active braze. Alternatively, a coated diamond can be used with standard brazes in an oxygen reduced atmosphere or vacuum. Alternatively, a specially coated diamond can be used and the brazing performed in air.

It will be appreciated that one of the preferred embodiments of the present invention, i.e. using a coating that can be brazed in air, leads to the better design of tools, not least because of easier/cheaper manufacturing methods without needing a vacuum furnace, hydrogen furnace or an inert gas atmosphere.

According to a third aspect to the present invention there is provided a tool including a surface having superhard particles placed in a random or predetermined pattern according to a method as hereinbefore described.

According to a fourth aspect of the present invention, there is provided a method for controlling the position of superhard particles bonded to a surface of a tool, the method including applying heat and/or pressure to predetermined areas of the surface preloaded with superhard particles. In this method, particles encapsulated and/or clad with a braze material are placed on the tool surface which may or may not contain recesses. The encapsulated/clad particles may be single or multilayered. In a preferred embodiment of the present invention, a computer controlled rastering laser which has been preprogrammed to scan over certain areas of the surface of the tool, then heats certain areas containing encapsulated and/or clad diamond which melts the braze thereby bonding the abrasive to the surface of the tool. The areas which have not been laser bonded can be easily removed, thereby providing a designed abrasive/grinding surface. Fig 4 shows a non-limiting illustration of a possible configuration of bonded grit to the surface of a tool. The design can be changed by changing the computer software which controls which areas are heated. In another preferred embodiment of the present invention, clad and/or encapsulated diamond can be attached to a wire/tape (which can be a polymer or metal) at predetermined distances along the wire. This diamond loaded wire can then be draped across or coiled around a tool surface. The tool can then be heated in order to melt the braze and bond the diamond to the surface of the tool. This aspect of the invention is particularly suited to forming abrasive layers on tools with complex geometries such as cylinders or curved surfaces. In a preferred embodiment, the surface of the tool may be predisposed to receiving the wire or tape by incorporating grooves, indentations or any form of recess on the surface of the tool. The distance between abrasive particles on the wire/tape can be manipulated in order to match a distance between indentations on the surface of the tool. In order to melt the braze, the following techniques can be used: hot furnace, blow torching, open gas flame, induction heating, laser heating, microwave heating, resistance heating of the wire/tape by passing a current.

For any of the above embodiments, placement of coated, encapsulated or clad grit can be carried out by hand or by automatic or semi-automatic pick and place processes. An example of such a process is that of using a syringe capable of applying negative pressure to pick up a particle and positive pressure to dispense or place the particle in the required position.

The invention will now be described with reference to the following non-limiting examples.

Example 1 : Disc of steel, mask areas and screen print. Single layer of TZ on JM braze paste (argobraze 56(RTM)). Heat in oven for 3 min at 750°C-800°C.

1 ,000 cts of diamond grit 20/25 US mesh size (0.81 mm) was coated with a primary coating consisting of 0.6 urn TiC layer applied by chemical vapour deposition (CVD), a secondary coating consisting of 0.4 um W layer applied by physical vapour deposition (PVD) and an outer coating consisting of a 0.5 um Ag applied by PVD. The surface of a steel disc was masked in order to produce an abrasive element with the configuration shown in Figure 4. Johnson Matthey's argobraze 49H (RTM) braze paste was screen printed on the surface of the disk to a thickness of 0.5mm. The mask was removed and a layer of the coated grit described above was placed on the surface of the braze paste by sprinkling the coated diamond on top of the braze paste and then pressed into the paste. Any excess or loose diamond was removed from the surface of the tool by lightly tapping the side of the disc at an angle. The above arrangement was then transferred to a furnace where the diamond was brazed to the disc by heat treating for 3 minutes at 720°C-740^°C.

Example 2: Disc of steel with 380 um wide groove. TZ coated 40/50 (380 um) diamond, clad with copper 50 um thick (particle 430 um) placed in groove. Set up sprayed with flux. Heat in oven for 3 min at 1100°C.

1 ,000 cts of diamond grit 40/50 US mesh size (380 um) was coated with a primary coating consisting of 0.6 um TiC layer applied by chemical vapour deposition (CVD), a secondary coating consisting of 0.4 um W layer applied by physical vapour deposition (PVD) and an outer coating consisting of a 0.5 um Ag applied by PVD. A copper / Zinc cladding with a thickness of 50 um was then applied by electroless and electrolytic deposition.

Grooves with a diameter of 380 um and a depth of 380 um were cut into the surface of a steel disk. The coated/clad diamond was then placed into the grooves and any excess material was removed from the remainder of the surface of the disc. A flux was then placed over this arrangement. The arrangement was then transferred to a furnace where the diamond was brazed to the disc by heat treating for 3 minutes at 900'C. Example 3: Disc of steel with round recesses with same diameter of diamond administered with centre punch and hammer. Individually place air brazeable coated/encapsulated with braze material (80/20 bronze). Spray with flux. Heat in oven for 3 min at 875-900°C.

1.000 cts of coated diamond was prepared as per Example 2. The coated diamond was then encapsulated using a fluidised bed with a layer of an 80/20 bronze braze alloy. The encapsulated particles were built up to a diameter of 500 urn. Recesses on the surface of a steel disc with a diameter approximately the same as that of the average diamond particle (i.e. 380 urn) were prepared using a centre punch. A single coated/encapsulated particle was then placed in each of the recesses and the arrangement was sprayed with flux. The arrangement was then transferred to a furnace where the diamond was brazed to the disc by heat treating for 3 minutes at 875-900°C.

Example 4: Disc covered with single layer of coated / encapsulated 49H in powder form (i.e. no solvents or binders), Spray specific areas with flux, Laser heat to melt specific areas.

1.000 cts of coated diamond was prepared as per Example 2. The coated diamond was then encapsulated using a fluidised bed and rotating pan system with a layer of Johnson Matthey's argobraze 56 (RTM) powder. The encapsulated particles were built up to a diameter of 500 urn. The surface of a steel disc was sprayed with flux and a layer of the coated/encapsulated particle was placed on top. A computer controlled rastering laser which had been preprogrammed to scan over certain areas of the surface of the tool then heated certain areas on the surface of the disc which melted the braze thereby bonding the abrasive to the surface of the tool in those particular areas. The areas which had not been laser bonded were removed, thereby providing a designed abrasive/grinding surface.

Example 5: As per Example 4 but with indents and particles clad with electroplated brass (60/40).

1.000 cts of coated diamond was prepared as per Example 2. A 60/40 brass cladding with a thickness of 60 urn was then applied by electrolytic deposition. Recesses on the surface of a steel disc with a diameter approximately the same as that of the average diamond particle (i.e. 380 urn) were prepared using a centre punch. A single coated/clad particle was then placed in each of the recesses and the arrangement was sprayed with flux. A gas flame torch was used to melt the braze thereby bonding the abrasive to the surface of the tool.

Example 6: 250 um air brazeable coated and encapsulated with JM argobraze 632 (RTM) to bring diameter to 350 um. Brass wire 25 um in diameter. Encapsulated particle attached every 3 mm by using flux as an adhesive.

1 ,000 cts of diamond grit 60/80 US mesh size (230 um) was coated with a primary coating consisting of 0.6 um TiC layer applied by chemical vapour deposition (CVD), a secondary coating consisting of 0.4 um W layer applied by physical vapour deposition (PVD) and an outer coating consisting of a 0.5 um Ag applied by PVD. The coated diamond was then encapsulated using a fluidised bed and rotating pan system with a layer of Johnson Matthey's argobraze 632 (RTM) powder. The encapsulated particles were built up to a diameter of 330 um. Along a 25 um diameter brass wire, a spot of flux was placed every 3 mm and a single encapsulated particle was attached to the wire using the flux as an adhesive. Example 7: Hollow Steel cylinder 40 mm long x 35 mm OD, 20mm ID with groove turned along outside edge using a lathe. V shaped groove with depth and width equal to the average diameter of the diamond. Wire wrapped around cylinder following the groove. Spot welded wire at start and at the end. Outside sprayed with flux. Heat in oven for 3 min at 835^°C.

On a steel cylinder 100 mm long and 75 mm, a V shaped groove approximately 230 urn wide and 230 urn deep was machined by a lathe along the length of the disc in a spiral design. The wire from Example 6 was then attached at one end of the cylinder, placed in the groove and wrapped around the cylinder. Once the wire reached the other end of the cylinder, it was cut and the end attached to the steel cylinder. The outside of the cylinder was then sprayed with flux. The arrangement was then transferred to a furnace where the diamond was brazed to steel cylinder by heat treating for 3 minutes at 835^°C.

Example 8: 400 um particle on wire encapsulated to bring up to 600 urn. Wire wrapped around cylinder with indents.

1 ,000 cts of diamond grit 40/45 US mesh size (400 um) was coated with a primary coating consisting of 0.6 um TiC layer applied by chemical vapour deposition (CVD), a secondary coating consisting of 0.4 um W layer applied by physical vapour deposition (PVD) and an outer coating consisting of a 0.5 um Ag applied by PVD. The coated diamond was then encapsulated using a fluidised bed with a layer of Johnson Matthey's argobraze 56 (RTM) powder. The encapsulated particles were built up to a diameter of 600 um. Along a 25 um diameter brass wire, a spot of flux was placed every 3 mm and a single encapsulated particle was attached to the wire using the flux as an adhesive. On a steel cylinder 100 mm long and 75 mm, recesses, 3 mm apart, along the length of the cylinder were prepared using a centre punch. The recesses were 400 urn in diameter. The wire was then attached at one end of the cylinder, placed in the groove and wrapped around the cylinder so that each encapsulated particle sat into a recess. Once the wire reached the other end of the cylinder, it was cut and the end attached to the steel cylinder. The outside of the cylinder was then sprayed with flux. The arrangement then transferred to a furnace where the diamond was brazed to steel cylinder by heat treating for 3 minutes at 750⁰C.

Claims

1. A method of placing particles of superhard material on a surface in a predetermined pattern, the method including the step of rendering all of or a portion of the surface predisposed to receive particles of superhard material.

2. A method according to claim 1 wherein the surface is rendered predisposed to receive the particles such that the particles are maintained on the surface in a manner sufficient for the particles to be brazed to the surface at that position.

3. A method according to claim 1 or 2 wherein the superhard material is selected from diamond, cubic boron nitride, wurtzitic boron nitride, a carbide, oxide or suicide, Si₃N₄, SiC, AI₂O₃, AIC₁ SiO₂ and/or clusters of any of the above.

4. A method according to any preceding claim wherein the superhard particles are at least about 0.01 urn and no greater than about 5mm in diameter measured across the greatest dimension of the particle.

5. A method according to any preceding claim wherein the superhard particles are encapsulated and/or coated.

6. A method according to any preceding claim wherein the surface is rendered predisposed by indenting, drilling, turning, scoring, chemical etching or rolling the surface with indents sized to accommodate the particles.

7. A method of placing particles of superhard material onto a surface in a predetermined pattern wherein the surface is rendered predisposed to receive the particles of superhard material by printing a layer on the surface.

8. A method according to claim 7 wherein the layer is attractive to the superhard particles and/or braze material or the layer is repulsive to the particles and/or braze material.

9. A tool including a surface having superhard particles placed in a predetermined pattern according to a method according to anyone of claims 1 to 8.

10. A method for controlling the position of superhard particles bonded to a surface of a tool, the method including the step of applying heat and/or pressure to predetermined areas of the surface preloaded with superhard particles.

11. A method according to claim 10 wherein a rastering laser heats certain areas containing encapsulated and/or clad diamond.

12. A method according to claim 1 including the steps of:

• attaching clad and/or encapsulated diamond to a wire/tape at predetermined distances,

• draping or coiling the wire/tape across or around a tool surface, and

• heating the tool in order to melt braze and bond the diamond to the surface of the tool.