Boring or penetrating the earth – Bit or bit element – Specific or diverse material
Reexamination Certificate
2000-12-07
2003-04-22
Tsay, Frank (Department: 3672)
Boring or penetrating the earth
Bit or bit element
Specific or diverse material
C175S431000, C175S434000
Reexamination Certificate
active
06550556
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to cutting elements used in drag bit for drilling earth formations. Specifically this invention relates to cutting elements having an ultra hard material layer having a shaped upper surface having a depression for contacting earth formations.
BACKGROUND OF THE INVENTION
A typical cutting element is shown in FIG.
1
. The cutting element typically has cylindrical cemented carbide substrate body
2
having an end face or upper surface referred to herein as the “interface surface”
3
. An ultra hard material layer
4
, such as polycrystalline diamond or polycrystalline cubic boron nitride layer, having a first surface
9
bonded on to the interface surface and a second exposed surface
5
opposite the bonded surface, forms a cutting layer. The cutting layer can have a flat or a curved exposed surface
5
.
Most commercially available cutting elements are made according to the teachings of U.S. Pat. No. 3,745,623, for example, whereby a relatively small volume of ultra hard particles such diamond or cubic boron nitride is sintered as a thin layer onto a cemented tungsten carbide substrate.
Generally speaking the process for making a cutting element employs a body of cemented tungsten carbide where the tungsten carbide particles are cemented together with cobalt. The carbide body is placed adjacent to a layer of ultra hard material particles such as diamond or cubic boron nitride particles and the combination is subjected to high temperature at a pressure where the ultra hard material particles are thermodynamically stable. This results in recrystallization and formation of a polycrystalline ultra hard material layer such as a polycrystalline diamond or polycrystalline cubic boron nitride layer on the interface surface
3
of the cemented tungsten carbide.
The problem with many cutting elements is the development of cracking, spalling, chipping and partial fracturing of the ultra hard material cutting layer at the layer's region subjected to the highest impact loads during drilling. This region is referred to herein as the “critical region”. The critical region encompasses the portion of the cutting layer that makes contact with the earth formations during drilling. The problems at the critical region are caused by the generation of peak (high magnitude) stresses imposed on the ultra hard material layer at the critical region during drilling. Because the cutting elements are typically inserted into a drag bit at a rake angle, the critical region includes a portion of the ultra hard material layer near to and including a portion of the layer's circumferential edge
6
which makes contact with the earth formations during drilling. The peak stresses at the critical region result in the initiation and growth of cracks
7
across the cutting element. Consequently, cracks are formed of sufficient length for causing the separation of a sufficiently large piece of ultra hard material, rendering the cutting element ineffective or resulting in the failure of the cutting element. When this happens, drilling operations may have to be ceased to allow for recovery of the drag bit and replacement of the ineffective or failed cutting element.
Thus, cutting elements are desired that can better withstand high impact loading at the critical region imposed during drilling so as to have an enhanced operating life.
SUMMARY OF THE INVENTION
Cutting elements are provided having a substrate over which is coupled an ultra hard material cutting layer. A radially extending depression is formed up on the exposed surface of the ultra hard material layer, thus defining a “shaped” ultra hard material layer. The radially extending depression extends preferably from the location near the center of the ultra hard material layer to the periphery of the layer. In an alternate embodiment, more than one radially extending depression may be formed on the exposed surface of the ultra hard material cutting layer. In yet a further embodiment, one or more radially extended depressions may be formed on the substrate end surface coupled to the ultra hard material layer. In such case, each radially extending depression formed on the ultra hard material exposed surface is aligned over a radially extending depression formed on the substrate end surface. The ultra hard material layer may be draped over the end surface of the substrate and within the radially extending depression(s) formed on the substrate so as to define corresponding radially extending depression(s) on the exposed surface of the ultra hard material cutting layer.
In yet a further embodiment, a plurality of abutting depressions preferably having a depth shallower than the maximum depth of the radially extending depression may be formed abutting the radially extending depression. Corresponding shallow depressions may be formed on the substrate end surface which is coupled to the ultra hard material layer. Furthermore, one or multiple transition layers may be incorporated between the substrate and the ultra hard material layer. The transition layers have properties between the substrate and the ultra hard material layer. The transition layer may also have a radially extending depression(s) and/or secondary budding depressions formed on its surface furthest from the substrate. If the substrate end surface has depressions, the transition layer may also be draped over the substrate end surface so as to define corresponding depressions.
When mounted on a drag bit, a radially extending depression formed on the exposed surface of the ultra hard material layer is aligned to be within the critical region of the cutting element so that the peripheral edge of the cutting layer intersected by the radially extending depression makes contact with the earth formations during drilling.
With any embodiment, a circumferential groove may be formed on the outer surface of the body of the cutting element that spans an arc that is approximately the same as the arc spanned by the critical region of the cutting element. The groove is preferably symmetric about a diameter of the cutting element dissecting the central region. An ultra hard material is packed into the groove forming a secondary cutting surface for improving the cutting efficiency of the cutting element as well as delaying the erosion of the cutting element during drilling.
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Eyre Ronald K.
Middlemiss Stewart
Smith International, Inc
Tsay Frank
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