Boring or penetrating the earth – Bit or bit element – Specific or diverse material
Reexamination Certificate
1999-12-17
2002-10-08
Bagnell, David (Department: 3673)
Boring or penetrating the earth
Bit or bit element
Specific or diverse material
C175S426000
Reexamination Certificate
active
06460636
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to cutting elements for use in earth-boring drill bits and, more specifically, to a means for increasing the life of cutting elements that comprise a layer of superhard material, such as diamond, affixed to a substrate. Still more particularly, the present invention relates to a polycrystalline diamond enhanced insert comprising a supporting substrate and a diamond layer supported thereon.
BACKGROUND OF THE INVENTION
In a typical drilling operation, a drill bit is rotated while being advanced into a soil or rock formation. The formation is cut by cutting elements on the drill bit, and the cuttings are flushed from the borehole by the circulation of drilling fluid that is pumped down through the drill string and flows back toward the top of the borehole in the annulus between the drill string and the borehole wall. The drilling fluid is delivered to the drill bit through a passage in the drill stem and is ejected outwardly through nozzles in the cutting face of the drill bit. The ejected drilling fluid is directed outwardly through the nozzles at high speed to aid in cutting, flush the cuttings and cool the cutter elements.
The present invention is described in terms of cutter elements for roller cone drill bits, although its benefits can be realized in percussion bits as well as other fixed cutter bits. In a typical roller cone drill bit, the bit body supports three roller cones that are rotatably mounted on cantilevered shafts, as is well known in the art. Each roller cone in turn supports a plurality of cutter elements, which cut and/or crush the wall or floor of the borehole and thus advance the bit.
Conventional cutting inserts typically have a body consisting of a cylindrical grip portion from which extends a convex protrusion. In order to improve their operational life, these inserts are preferably coated with a superhard, sometimes also known as ultrahard, material. The coated cutting layer typically comprises a superhard substance, such as a layer of polycrystalline diamond, thermally stable diamond or any other ultrahard material. The substrate, which supports the coated cutting layer is normally formed of a hard material such as tungsten carbide (WC). The substrate typically has a body consisting of a cylindrical grip from which extends a convex protrusion. The grip is embedded in and affixed to the roller cone and the protrusion extends outwardly from the surface of the roller cone. The protrusion, for example, may be hemispherical, which is commonly referred to as a semi-round top (SRT), or may be conical, or chisel-shaped or may form a crest that is inclined relative to the plane of intersection between the grip and the protrusion. The latter embodiment, along with other non-axisymmetric shapes, is becoming more common, as the cutter elements are designed to provide optimal cutting for various formation types and drill bit designs.
The basic techniques for constructing polycrystalline diamond enhanced cutting elements are generally well known and will not be described in detail. They can be summarized as follows: a carbide substrate is formed having a desired surface configuration; the substrate is placed in a mold with a superhard material, such as diamond powder and/or a mixture of diamond with other material that forms transition layers, and subjected to high temperature and pressure, resulting in the formation of a diamond layer bonded to the substrate surface.
Although cutting elements having this configuration have significantly expanded the scope of formations for which drilling with diamond bits is economically viable, the interface between the substrate and the diamond layer continues to limit usage of these cutter elements, as it is prone to failure. Specifically, it is not uncommon for diamond coated inserts to fail during cutting. Failure typically takes one of three common forms, namely spalling/chipping, delamination, and wear. External loads due to contact tend to cause failures such as fracture, spalling, and chipping of the diamond layer. The impact mechanism involves the sudden propagation of a surface crack or internal flaw initiated on the PCD layer, into the material below the PCD layer until the crack length is sufficient for spalling, chipping, or catastrophic failure of the enhanced insert. On the other hand, internal stresses for example, thermal residual stresses resulting from manufacturing process, tend to cause delamination of the diamond layer, either by cracks initiating along the interface and propagating outward, or by cracks initiating in the diamond layer surface and propagating catastrophically along the interface. Excessively high contact stress and high temperature, along with a very hostile downhole operation environment, are known to cause severe wear to the diamond layer of cutting elements in percussion bits. The wear mechanism occurs due to the relative sliding of the PCD relative to the earth formation, and its presence as a failure mode is related to the basic bit type, abrasiveness of the formation, as well as other factors such as formation hardness or strength, and the amount of relative sliding involved during contact with the formation. Wear is not a typical failure mode in roller cone drill bits that utilize conventional diamond coated cutting elements. Instead, fatigue and impact of the diamond coating are the typical failure modes found.
One explanation for failure resulting from internal stresses is that the interface between the diamond and the substrate or a transition layer is subject to high residual stresses resulting from the manufacturing processes of the cutting element. Specifically, because manufacturing occurs at elevated temperatures, the differing coefficients of thermal expansion of the diamond and substrate material result in thermally-induced stresses as the materials cool down from the manufacturing temperature. These residual stresses tend to be larger when the diamond/substrate interface has a smaller radius of curvature. At the same time, as the radius of curvature of the interface increases, the application of cutting forces due to contact on the cutter element produces larger debonding and other detrimental stresses at the interface, which can result in delamination. In addition, finite element analysis (FEA) has demonstrated that during loading, high stresses are localized in both the outer diamond layer and at the diamond transition-layer/tungsten carbide interface. Finally, localized loading on the surface of the inserts causes rings or zones of tensile stress, which the PCD layer is not capable of handling.
In drilling applications, the cutting elements are subjected to extremes of temperature and heavy loads when the drill bit is in use. It has been found that during drilling, shock waves may rebound from the internal planar interface between the two layers and interact destructively.
All of these phenomena are deleterious to the life of the cutting element during drilling operations. More specifically, the residual stresses, when augmented by the repetitive stresses attributable to the cyclical loading of the cutting element by contact with the formation, may cause spalling, fracture and even delamination of the diamond layer from the substrate. In addition to the foregoing, state of the art cutting elements can lack sufficient diamond volume to cut highly abrasive formations, as the thickness of the diamond layer tends to be limited by the resulting high residual stresses and the difficulty of bonding a relatively thick diamond layer to a curved substrate surface. For example, even within the diamond layer, residual stresses arise as a result of temperature changes. Because these stresses typically increase as the thickness of the layer increases, this factor tends to be viewed as limiting on thickness.
Hence, it is desired to provide cutting elements that provide increased fatigue life, and/or impact resistance and/or wear resistance without increasing the risk of spalling or delamination.
SUMMARY OF THE INVE
Anderson Nathan R.
Belnap J. Daniel
Cawthorne Chris E.
Eyre Ronald K.
Huang Suprant J.
Bagnell David
Conley & Rose & Tayon P.C.
Kreck John
Smith International Inc.
LandOfFree
Drill bit inserts with variations in thickness of diamond... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Drill bit inserts with variations in thickness of diamond..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Drill bit inserts with variations in thickness of diamond... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2998580