Boring or penetrating the earth – Bit or bit element – Specific or diverse material
Reexamination Certificate
1999-08-24
2001-08-07
Dang, Hoang (Department: 3672)
Boring or penetrating the earth
Bit or bit element
Specific or diverse material
Reexamination Certificate
active
06269894
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to cutting elements for rotary drill bits and particularly to cutting elements for drag-type drill bits comprising a bit body having a leading surface to which the cutting elements are fixedly mounted.
2. Description of the Prior Art
As is well known, one common form of cutting element for a rotary drag-type drill bit is a two-layer or multi-layer cutting element where a facing table of polycrystalline diamond is integrally bonded to a substrate of less hard material, such as tungsten carbide. The cutting element is usually in the form of a tablet, usually circular or part-circular. The substrate of the cutting element may be brazed to a carrier, usually also of cemented tungsten carbide, which is received in a socket in the bit body, or the substrate itself may be of sufficient axial length to be mounted directly in a socket in the bit body.
As is well known, polycrystalline diamond is formed by compressing diamond powder with a suitable binder-catalyst in a high pressure, high temperature press. In one common process for manufacturing two-layer cutting elements, diamond powder is applied to the surface of a preformed tungsten carbide substrate incorporating cobalt. The assembly is then subjected to very high temperature and pressure in a press. During this process cobalt migrates from the substrate into the diamond layer and acts as a binder-catalyst causing the diamond particles to bond to one another with diamond-to-diamond bonding, and also causing the diamond layer to bond to the substrate.
Although cobalt is commonly used as the binder-catalyst, any iron group element, such as cobalt, nickel or iron, or alloys thereof, may be employed. Polycrystalline diamond using iron group elements, or alloys thereof, as a binder-catalyst will be referred to herein as “conventional” polycrystalline diamond. Other forms of polycrystalline diamond are sometimes used as cutters in rotary drag-type drill bits, for example silicon may be used as the binder-catalyst or a conventional binder catalyst such as cobalt may be leached out of the diamond after formation. Such forms of polycrystalline diamond are not usually formed on a substrate and are generally more thermally stable than conventional polycrystalline diamond. However, problems may arise in the use of such materials as cutting elements.
When two-layer cutting elements using conventional polycrystalline diamond were first manufactured the polycrystalline diamond facing table was very thin in relation to the thickness of the substrate. More recently, however, the thickness of the diamond facing table has often been increased relative to the thickness of the substrate, particularly around the periphery of the cutting element. Such arrangements are shown, for example, in WO 97/30264. Also GB 2323110 suggests extending part of the diamond facing table through the thickness of the substrate, and up to the rear surface thereof, so that part of the diamond facing table engages the surface on which the cutting element is mounted so as to provide high modulus support (the modulus of elasticity of the diamond being greater than that of the substrate itself).
According to the present invention, the advantages provided by such arrangements are enhanced by use of cutting elements which consist entirely of conventional polycrystalline diamond material and do not incorporate an integral substrate.
SUMMARY OF THE INVENTION
According to the invention, there is provided a cutting element for a rotary drag-type drill bit comprising a body of polycrystalline diamond incorporating a binder-catalyst selected from iron group elements or alloys thereof, said body of diamond being unsupported by an integral substrate.
The term “iron group elements”, as used herein, includes iron and those other elements, such as cobalt and nickel, which are in the same group as iron in the Periodic Table of the elements.
The invention also provides a cutting element for a rotary drag-type drill bit comprising a body of polycrystalline diamond incorporating a binder-catalyst selected from iron group elements or alloys thereof, said body being brazed to a substrate by use of a brazing alloy.
In this case, the substrate may comprise a body of diamond/tungsten carbide/binder-catalyst composite material, or a body of cemented tungsten carbide, or two bodies of said materials respectively, brazed together by use of a brazing alloy.
The invention also provides a cutting element for a rotary drag-type drill bit comprising a body of polycrystalline diamond incorporating a binder-catalyst selected from iron group elements or alloys thereof which has been integrally bonded, in a high pressure, high temperature press, to a body of diamond/tungsten carbide/binder-catalyst composite material. Preferably a portion of the body of polycrystalline diamond which is nearer to the body of composite material includes a greater proportion of binder-catalyst than a portion thereof which is further from the composite material.
In any of the cutting elements according to the invention, the cutting element may have an outer surface which is coated with a material to allow the cutting element to be brazed to another material. Alternatively or additionally, the outer surface of the cutting element may be formed with a plurality of projections and recesses, which in use, interlock with a material within which the cutting element is embedded.
In any of the above arrangements the cutting element may be in the form of a tablet having generally parallel front and rear surfaces and a peripheral surface which may be circular, part circular, or of any other suitable shape.
The invention also provides a method of manufacturing a cutting element for a rotary drill bit, comprising the steps of forming a preform element by bonding a body of diamond particles to a surface of a substrate incorporating tungsten carbide and a binder-catalyst selected from iron group elements or alloys thereof, in a high pressure, high temperature press, so that binder-catalyst from the substrate migrates into the diamond layer, then subsequently removing the preform element from the press and removing the substrate so as to leave only a body of polycrystalline diamond incorporating the binder-catalyst, unsupported by a substrate.
The invention also provides a method of manufacturing a cutting element for a rotary drill bit comprising the steps of manufacturing a preform element by forming a mixture of diamond particles and particles of a binder-catalyst selected from iron group elements or alloys thereof and subjecting the mixture to high pressure and temperature in a press, sufficient to bond the particles together with diamond-to-diamond bonding.
In this method a layer consisting of diamond particles alone may be applied to the mixture of diamond and binder-catalyst particles before it is subjected to high pressure and temperature in the press, so that, during pressing, some binder-catalyst from the mixture migrates into the diamond layer.
The invention also provides a method of manufacturing a cutting element for a rotary drill bit comprising forming a mixture of diamond particles, tungsten carbide particles and particles of a binder-catalyst selected from iron group elements or alloys thereof, applying to the mixture of particles a layer of particles consisting of diamond alone, and subjecting the mixture and layer to high pressure and temperature in a press so that the particles bond to one another and some binder-catalyst from the diamond/tungsten carbide/binder-catalyst mixture migrates into the layer of diamond particles.
In a modification of this method, there is disposed between the diamond layer and the diamond/tungsten carbide/binder-catalyst mixture an intermediate layer comprising a mixture of diamond and binder-catalyst particles so that it is binder-catalyst from the intermediate layer which migrates into the layer of diamond particles alone.
REFERENCES:
patent: 3938599 (1976-02-01), Horn
patent: 4604106 (1986-08-01), Hall et al.
patent: 4
Camco International (UK) Limited
Daly Jeffery E.
Dang Hoang
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