GB2296678A

GB2296678A - Wire drawing dies

Info

Publication number: GB2296678A
Application number: GB9525714A
Authority: GB
Inventors: Ricardo Simon Sussman; George Richard Shafto
Original assignee: De Beers Industrial Diamond Division Pty Ltd
Current assignee: De Beers Industrial Diamond Division Pty Ltd
Priority date: 1994-12-21
Filing date: 1995-12-15
Publication date: 1996-07-10
Anticipated expiration: 2015-12-15
Also published as: ZA9510549B; FR2728487B1; FR2728487A1; JPH08229612A; ES2136484A1; GB2296678B; ES2136484B1; GB9426047D0; DE19547571A1; GB9525714D0; KR960023270A

Description

WIRE DRAWING D1IES BACKGRO OF THE UfVENTION This invention relates wire

drawing dies.

2296678 Wire drawing dies comprise a core of a hard material mounted in a relatively massive support and having a hole formed axially therethrough. The wire is drawn through the hole causing that wire to reduce in diameter. Examples of hard materials which have been used for the central core of wire drawing dies are cemented carbides, diamond compacts and CVD diamond, i.e. diamond made by chemical vapour deposition.

Diamond is the hardest substance known to man and may be found in nature or produced synthetically. One method of producing diamond synthetically is by chemical vapour deposition(CVD). Diamond produced by C7D is known as CVD diamond. CVD diamond may be produced by providing a gaseous carbon compound such as a hydrocarbon, subjecting the gaseous carbon compound to energy such as microwave energy to dissociate the compound into carboncontaining ions, atoms or radicals, in the presence of an activating gas such as hydrogen, and allowing the carbon-containing ions, atoms or radicals to deposit on a suitable substrate and form a diamond layer. Such methods are well documented in the literature, including the patent literature.

United States Patent No. 5,361,621 describes a CVD diamond wire drawing die which has smaller diamond grains adjacent an initial diamond growth surface with larger diamond grains adjacent an opposing surface with an opening having a wire bearing portion of substantially circular crosssection determinative of the diameter of the wire positioned more closely adjacent to the initial growth surface in a region of smaller grains than to the final large grained opposing surface. A preferred orientation of the diamond crystals is one in which the diamond crystals have a < 110 > orientation parallel, or essentially parallel, to the opening or hole through the die. A similar such CVD diamond wire drawing die is described in United States Patent 5,363,687.

United States Patent 5,377,522 describes another CVD diamond wire drawing die which comprises a body having a top surface and a bottom surface and an opening or hole which extends through the body from the top surface to the bottom surface. A preferred orientation of the diamond crystals is one in which the diamond crystals have a < 110 > orientation perpendicular to the axial direction of the opening. The wire drawing die is produced from a polycrystalline diamond film. The wire drawing die produced from such a film will have a diamond crystal orientation shown diagrammatically by Figure 3 of the attached drawing, i.e. a few of the diamond crystals will have an orientation radial relative to the opening, but the majority of the diamond crystals will have an orientation which is not radial, but is parallel, or essentially parallel, to a diameter of the die.

-3 SUNMARY OF THE INVENTION According to the present invention, a wire-drawing die blank comprises a body of CVD diamond having a hole of substantially circular cross-section extending therethrough, the predominant diamond crystal orientation in the body being radial relative to the hole. A wire drawing die may be produced from this blank by surrounding the blank with a relatively massive support to which it is secured. Such a wire drawing die also forms an aspect of the invention.

According to yet a further aspect of the invention, a method of making a wire drawing die blank as described above comprises producing a layer of diamond by CVD on a metallic wire or non-metallic filament and removing the wire or filament to produce a CVD diamond sleeve.

BRIEF DESMOPTION OF THE DRAWINGS Figure 1 Figure 2 Figure 3 Figure 4 is a longitudinal cross-section of an embodiment of a CVD diamond wire drawing die blank of the invention, is an end view of the blank of Figure 1, is an end view uf a wire drawing die blank produced by the method described in United States Patent 5,377,522, is a perspective view of a metallic wire having a layer of CVD diamond grown thereon, Figure 5 is a cross-section of a base having a plurality of wires extending therefrom and on which a CVD diamond layer has been deposited, and is a plan view of Figure 5.

Figure 6 DESCRIPTION OF EMBODEVIENTS

In the wire drawing die of the invention, the dominant diamond crystal orientation in the body is radial relative to the hole which extends therethrough and hence perpendicular to the direction of wire pulling. Preferably, the diamond orientation in the radial direction is either < 110 > or < 111 > or a combination thereof to provide the diamond core with optimum hardness and wear-resistance at the surface where it is most important, i.e. that which is contacted with the wire. Such as predominant diamond crystal orientation is not to be found in any CVD diamond wire drawing die blank of the prior art and provides the wire drawing die of the invention with better hardness and wear-resistance and lower grain (particle) pull-out than such prior art dies.

Preferably at least 50 percent, more preferably at least 75 percent, and better still at least 90 percent, of the diamond crystal orientation in the body is radial relative to the hole.

The wire drawing die blank will generally have a cylindrical shape which, in plan, may be circular, triangular, hexagonal, or rectangular.

The wire drawing die blank of the invention may be surrounded by relatively massive support and secured to that support to produce a wire drawing die. The blank may be secured to the support by brazing, mechanically or a combination thereof. Such securing methods are known in the art. The relatively massive support will typically be made of cemented carbide, steel or the like.

The wire drawing die blank of the invention is produced by depositing or producing a layer of diamond by CVD on a metallic wire or a non-metallic filament and then removing the wire or filament to produce a CVD diamond sleeve. The deposited layer will obviously extend completely around the wire or filament.

Ille CVD diamond sleeve, particularly if the wire or filament on which the CV1) diamond layer is deposited is relatively long, may be severed, e. g. cut, at one or more points along its length to produce two or more smaller sleeves or rings, each of which will constitute a wire drawing die blank.

The metal wire will typically be selected from transition metal wires. An example of a particularly suitable metal is tungsten.

The non-metallic filament will be one which is capable of allowing CVD diamond growth to take place thereon. An example of a suitable such filament is a silicon carbide filament.

A plurality of CVD diamond sleeves may be produced by providing a plurality of spaced wires or filaments extending beyond a surface of a base, depositing a layer of CVD diamond on each wire or filam--nt to provide a CVD diamond coating thereon, removing the coated wires or filaments from the base and removing the wires or filaments to produce a plurality of CVD diamond sleeves. The wires or filaments may be made of the same material as the base or of a different material such as that described above.

The wires or filaments may be removed from the CVD layers deposited thereon by methods known in the art such as acid etching.

Embodiments of the invention will now be described with reference to the accompanying drawings. Referring first to Figures 1 and 2, there is shown, respectively, a longitudinal cross-section of a CVD diamond wire drawing blank of the invention and an end view thereof. The blank comprises a right circular cylindrical body 10 having an outer circular peripheral surface 12 and a centrally located hole 14 extending therethrough from one flat surface 16 to an opposite flat surface 18.

The body 10 consists of CVD diamond having the diamond crystal orientation 20 (illustrated diagrammatically) predominantly radial relative to the circular hole 14. The diamond crystal orientation 20 will preferably be the < 110 > or < 111 > orientation or a combination thereof. It will thus be seen that the predominant diamond crystal orientation is perpendicular to the direction of wire drawing which provides the blank with excellent hardness and abrasion and wear-resistance and lower grain pull-out.

The diamond crystal orientation of the wire drawing die blank of the invention is to be contrasted with that produced following the teachings of United States Patent 5;377,522, described above. The wire drawing die blank of this United States patent is produced from a polycrystalline diamond film illustrated by Figure 2 of the patent. Such a wire drawing die blank will have a diamond crystal orientation shown diagrammatically by Figure 3 of the attached drawing. This wire drawing die blank 22 is also right-circular cylindrical in shape and has an outer surface 24 and a centrally located circular hole 26 extending therethrough. The diamond crystal orientation 28 is shown diagrammatically. It will be noted that some of the diamond crystal orientation 28 will be radial relative to the hole 26, but the predominant orientation is parallel, or essentially parallel, to a diameter of the blank.

A wire drawing die may be produced from the blank described above and illustrated by Figures 1 and 2 by securing, e.g. by brazing, mechanically or a combination thereof, the outer surface 12 to a relatively massive support.

The wire drawing die blank of the invention may be produced by the method which will now be described with reference to Figure 4. Referring to this figure, a wire 30, such as a tungsten wire, is provided and a layer 32 of CVD diamond is grown thereon by methods known in the art. The CVD diamond layer will extend completely around the wire. The layer 32 grows symmetrically on the wire providing it with a uniform thickness. The wire may then be removed, for example, by acid etching, leaving a CVD diamond sleeve having a hole extending therethrough. This sleeve may constitute the wire drawing die blank. Alternatively, if blanks having a lesser depth, i.e. a lesser distance between surfaces 16 and 18, are desired, then the sleeve may be severed, e.g. by cutting or chemical etching, along its length at one or more points to produce a plurality of smaller sleeves or rings, each of which constitutes a wire drawing die blank.

A possible advantage of the method of the invention is that the hole in the wire drawing blank is produced at source and does not have to be formed by the end user.

A plurality of CVD diamond sleeves may be produced by a method which will now be described with reference to Figures 5 and 6. Referring to these figures, a base 40, made of a material such as molybdenum, is provided and presents a lower surface 42 and an upper surface 44. Located in the base 40 and extending from the surface 44 are a plurality of spaced tungsten wires 46. A layer 48 of CVI) diamond is deposited on the surface 44 and over each individual wire to provide each wire with a CVI) diamond coating, as illustrated. Thereafter, the coated wires are removed, e.g. by cutting or chemical etching along the dotted line 52, and cut or chemically etched again along the dotted line 54 to produce a plurality of CVI) diamond coated wires as illustrated by Figure 4. The wires may be removed to produce CVI) diamond sleeves and the sleeves optionally cut further, as described above.

In an alternative to the embodiment of Figures 5 and 6, the wires 46 may be made of the same material as the base 40. They can be formed, for example, by eroding a base by means of spark erosion to provide one surface of the base with a spiked profile. The spikes will be integral with the base and act as substitutes for the wires 46.

Claims

1.

A wire drawing die blank comprises a body of CVD diamond having a hole of substantially circular cross-section extending therethrough, the predominant diamond crystal orientation in the body being radial relative to the hole.

2.

A wire drawing die blank according to claim 1 wherein at least 50 percent of the diamond crystal orientation is radial relative to the hole.

3.

A wire drawing die blank according to claim 1 wherein at least 75 percent of the diamond crystal orientation is radial relative to the hole.

4.

A wire drawing die blank of claim 1 wherein at least 90 percent of the diamond crystal orientation is radial relative to the hole.

5.

A wire drawing die blank according to any one of the preceding claims wherein the diamond crystal orientation is the <110> or <lIl> orientation or a combination thereof.

6.

A wire drawing die blank according to any one of the preceding claims wherein the body is cylindrical in shape.

7.

A wire drawing die blank according to claim 6 wherein the shape of the body, in plan, is circular, triangular, hexagonal, square or rectangular.

8.

A wire drawing die comprising a blank according to any one of the preceding claims surrounded by a relatively massive support to which it is secured.

9.

A wire drawing die according to claim 7 wherein the relatively massive support is made of cemented carbide, steel or the like.

10.

A wire drawing die according to claim 7 or claim 8 wherein the blank is secured to the support by brazing, mechanically or a combination thereof.

A method of making a wire drawing die blank according to any one of claims 1 to 7 comprises producing a layer of diamond by CVD on a metallic wire or non-metallic filament. and removing the wire jr filament to produce a CVD diamond sleeve.

12.

A method according to claim 11 wherein the sleeve is severed at one or more points along its length to produce two or more smaller sleeves.

13.

A method according to claim 11 or claim 12 wherein the layer of CVD diamond is produced on a metal wire selected from transition metal wires.

14. A method according to claim 13 wherein the metal is tungsten.

15.

A method according to any one of claims 11 to 14 wherein a plurality of spaced wires or filaments are provided to extend beyond a surface of a base, a layer of CVD diamond is deposited on each wire or filament to provide a CVD diamond coating thereon, the coated wires or filaments are removed from the base and the wires or filaments removed to produce a plurality of CVD diamond sleeves.

16.

A method according to claim 15 wherein coated wire or filaments are removed from the base by cutting.

17.

A wire drawing die blank according to claim 1 and substanti?dly as herein described with reference to any one of Figures 1 to 3.

18.

A method according to claim 11 and substantially as herein described with reference to any one of Figures 1 to 3, 5 and 6.