This application claims priority from GB Provisional Patent Application file No. 0901984.5 filed on Feb. 9, 2009, which is incorporated by reference herein for all it contains.
1. Field of the Invention
This invention relates to a cutting element and in particular a cutting element suitable for use on a drill bit for use in the formation of boreholes.
2. Description of the Related Art
One form of cutting element for use on a drill bit comprises a table of superhard material, for example polycrystalline diamond, which is bonded to a substrate of a less hard material, for example tungsten carbide. Cutting elements of this type are well known and are available in a range of shapes and sizes for use in a range of applications.
This type of cutting element is manufactured using a high temperature, high pressure process in which a tungsten carbide substrate element, diamond powder and a binder catalyst, for example in the form of cobalt, are exposed to high temperature, high pressure conditions, resulting in the formation of chemical bonds between the diamond crystals of the diamond powder to form a polycrystalline diamond layer which is also bonded to the substrate element.
The polycrystalline diamond layer defines a matrix of interstitial volumes containing the binder catalyst material. It has been found to be advantageous to remove the binder catalyst material from at least the interstitial volumes located adjacent a working surface of the cutting element, as described in, for example, WO 02/24603 and WO 02/24601, as such treatment results in the working surface being of improved abrasion and impact resistance.
In use, the exposed, untreated part of the diamond layer tends to wear more quickly than the treated part with the result that an unsupported, protruding lip forms, and this effect is particularly apparent where the treated layer, i.e. that from which the binder catalyst is removed, forms only a relatively small proportion of the overall depth of the diamond layer. In such arrangements, there is a risk of the unsupported lip fracturing. It is an object of the invention to provide a cutting element in which this disadvantage is of reduced effect.
According to the present invention there is provided a cutting element comprising a multilayered polycrystalline diamond element including at least a first layer and a second layer, the diamond element being bonded to a substrate of a less hard material, the diamond element defining a matrix of interstitial volumes, the interstitial volumes of a first region of the diamond element adjacent a working surface thereof being substantially free of a catalysing material, the interstitial volumes of a second region of the diamond element remote from the working surface containing catalysing material.
The first and second layers may include diamond particles of different sizes. For example, the first layer may comprise fine particles, coarser particles being included in the second layer.
The first layer may comprise a first multimode diamond layer and the second layer may comprise a second multimode diamond layer. A third layer, for example of monomodal form, may also be provided.
The first layer may be of a first thickness and a second layer may be of a second, different thickness. The first thickness is preferably smaller than the second thickness. For example, the first thickness may be approximately 0.08 mm and the second thickness may be approximately 0.10 mm. A third layer may be provided, the third layer being of a third thickness, preferably greater than the first and second thicknesses. For example, the third thickness may be of approximately 0.12 mm.
The diamond element may be of thickness up to approximately 2 mm.
The first layer preferably has a first volume diamond density, the second layer having a second, different volume diamond density. The first volume diamond density is preferably greater than the second volume diamond density. For example, the first volume diamond density may be approximately 98% whilst the second volume diamond density may be in the range of 94% to 98%. A third layer may be provided which preferably has a third, lower volume diamond density, preferably less than 94%.
The layers may be arranged parallel to the working surface. Alternatively, the layers may be arranged concentrically or arrange to extend across the element.
The first region may extend through at least part of both the first layer and the second layer. Alternatively, it may extend through just part of the first layer, or may extend to the depth of the second layer.
The working surface may comprise an end working surface region and a side working surface region. The first region may be located adjacent just the end working surface region or, alternatively, may be located adjacent at least part of both the end working surface and the side working surface, or just adjacent at least part of the side working surface.
The invention will further be described, by way of example, with reference to the accompanying drawings, in which:
Referring firstly to
As shown in
The element 24 of polycrystalline diamond has an end working surface 26, and is made up of diamond crystals 28 between which is formed a matrix of interstitial volumes or voids 30 (see
The first region 48 of the element 42 is itself of multi-layered form, comprising a first layer 58 adjacent the working surface 46, a second, intermediate layer 60, and a third layer 62 remote from the working surface 46. The first and second layers 58, 60 are both of multi-mode form, the diamond material of the third layer 62 being of monomode form. The first layer 58 is of a different thickness, preferably less than, the second layer 60. For example the first layer 58 may be of a first thickness of approximately 0.08 mm whilst the second layer is of a second thickness of approximately 0.10 mm. The third layer 62 may be of a thickness of approximately 0.12 mm and, overall, the diamond element 42 may have a total thickness of around 2 mm.
The first layer 58 preferably has a different, preferably higher, volume diamond density to the second layer 60. For example the first layer 58 may have a volume diamond density of around 98% whilst that of the second layer 60 may be in the range of 94% to 98%. The third layer 62 may have a lower volume diamond density, for example less than 94%. The first layer 58 may be of a finer particle size than the second layer 60, which may in turn be of finer particle size than the third layer 62.
Such an arrangement is advantageous in that, in use, as the cutting element 40 wears, the element 42 will tend to form a series of steps of different sizes, providing support for the part of the element 42 forming the working surface 46, as shown in
The first, second and third layers 58, 60, 62 are conveniently formed by appropriate layering of the diamond powder material used in the formation of the cutting element. For example, layers of different diamond powder materials may be introduced into a container, together with an insert forming the substrate and the binder catalyst material, before exposing the container and its contents to high temperature, high pressure conditions as outlined hereinbefore to fabricate the cutting element.
Although the cutting element 40 described hereinbefore makes use of the effects of different volume diamond densities, layer thicknesses, particle sizes and diamond structure, it will be appreciated that some of the benefits of the invention can be achieved by utilising only one or two of these effects.
In the arrangement illustrated in
A number of modifications and alterations may be made to the arrangements described hereinbefore without departing from the scope of the invention.
Number | Date | Country | Kind |
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0901984.5 | Feb 2009 | GB | national |