Boring or penetrating the earth – Bit or bit element – Specific or diverse material
Reexamination Certificate
1999-07-06
2001-06-12
Neuder, William (Department: 3672)
Boring or penetrating the earth
Bit or bit element
Specific or diverse material
C175S434000
Reexamination Certificate
active
06244365
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 a nonplanar interface including a non-uniform portion between their substrate and their cutting layer.
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
3
. An ultra hard material layer
4
, such as polycrystalline diamond or polycrystalline cubic boron nitride, is bonded on to the upper surface forming a cutting layer. The cutting layer can have a flat or a curved upper surface
5
.
The problem with many cutting elements is the development of cracking, spoiling, 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”. These problems 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
.
Another problem facing cutting elements is the delamination and/or the exfoliation of the ultra hard material layer from the substrate of the cutting element resulting in the failure of the cutter. Delamination and/or exfoliation become more prominent as the thickness of the diamond layer increases.
SUMMARY OF THE INVENTION
The present invention provides for cutting elements or inserts which are mounted in a bit body and which have an increased thickness of the ultra hard material cutting layer at their critical region, i.e., the region of the cutting element subjected to the highest impact loads during drilling. This region is generally defined beginning at the edge of the cutting element which contacts the earth formations during drilling and can span up to 50% of the cross-sectional area of the cutting element. Preferably, the critical region extends to an area between 45° and 70° on either side of the point of contact of the cutting element with the earth formation and inward to an area near the central axis of the cutting element.
A main depression is formed on the body (i.e., the substrate) end face (i.e., the upper surface) of the cutting element. The main depression is defined by multiple secondary depressions defining a main depression surface having a depth which increases in a generally stepwise fashion in an outward radial direction along a critical diameter and which decreases arcuately on either side of the critical diameter. The critical diameter is the diameter that intersects the point of contact between the edge of the cutting element and the earth formation. An ultra hard material layer is bonded to the end surface of the substrate and has either a curved or flat upper surface such that an increased thickness of the ultra hard material layer is formed over the critical region with the maximum ultra hard material thickness occurring at or proximate the edge portion or edge point of the cutting element making contact with the earth formations during drilling.
Moreover, a circumferential groove is formed on the outer surface of the body of the cutting element and spans an arc that is approximately the same as the are spanned by the critical region of the cutting element. The groove is preferably symmetric about the critical diameter of the cutting element. 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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Christie Parker & Hale LLP
Neuder William
Smith International Inc.
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