Cutlery – Pipe and rod cutters – Rotary
Reexamination Certificate
1999-09-27
2001-08-14
Watts, Douglas D. (Department: 3724)
Cutlery
Pipe and rod cutters
Rotary
C175S434000
Reexamination Certificate
active
06272753
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to polycrystalline diamond composite (“PDC”) cutters with multiple cutting surfaces used in drag bits for drilling bore holes in earth formations.
PDC cutters have a cemented carbide body and are typically cylindrical in shape. The primary cutting surface of the cutter is formed by sintering a PDC layer to a face of the cutter. Secondary cutting surfaces are formed on the cutter body by packing grooves formed on the cutter surface with diamond and then sintering the diamond to form polycrystalline diamond cutting surfaces.
The cutters are inserted on a drag bit outer body exposing at least a portion of the cutter body and the diamond cutting surface. Typically, the cutter makes contact with a formation at an angle, i.e., the diamond cutting layer is at an angle to the formation surface. As the bit rotates, the PDC cutting layer edge makes contact and “cuts” away at the formation. At the same time portions of the exposed cutter body also make contact with the formation surface. This contact erodes the cutter body surrounding the secondary cutting surfaces, revealing a secondary surface cutting edge or wear surface.
One preferable way to prolong the life of a cutter during drilling, is to increase the hardness of the substrate forming the cutter body. The increase in hardness tends to provide a stiffer or more rigid support for the PDC cutting surface. This will help reduce the magnitude of the tensile stresses in the PDC cutting surface induced by a bending moment during the cutting action, thereby reducing the frequency of cracks in the PDC layer which run perpendicular to the interface. However, a stiffer, harder substrate typically has a lower fracture toughness value and in some cases a lower transverse rupture strength. As a result, once a crack is initiated in the PDC, the substrate is unable to slow the propagation. If a crack is allowed to propagate, it can cause the cutter to fracture and fail catastrophically resulting in the eventual failure of the bit.
Accordingly, there is a need for a cutter having secondary cutting surfaces with an increased resistance to breakage. Moreover, there is a need for a cutter having a stiff, hard substrate supporting the cutter cutting layer for improved cutting but which prevents the propagation of crack growth through the cutter body.
SUMMARY OF THE INVENTION
The present invention is an improved polycrystalline diamond composite (“PDC”) cutter having multiple cutting surfaces and a body which is composed of at least two grades of carbide; and a method for making the same. In a preferred embodiment, a cutter body or substrate is formed from layers of carbides. For descriptive purposes, the substrate layers are also referred to as “wafers.” Each wafer has a top end, a bottom end and a body therebetween.
The cutter body is formed by bonding the wafers of cemented carbide together, one on top of the other. It is preferred that a stiffer grade cemented carbide is used to form the uppermost portion of the cutter which interfaces with the primary PDC cutting layer. A stiffer substrate provides better support for the cutting layer which results in enhanced cutting.
Secondary cutting surfaces are formed by compacting and sintering diamond in grooves formed on the body surface of the wafers. The grooves preferably span the length of the wafers. The grooves can be of any shape. Generally, the shape and orientation of the grooves is dictated by the formations to be cut. In addition, the orientation of the grooves, and hence, of the secondary cutting surfaces, may be varied by rotating the wafers in relation to each other. For example, the wafers may be oriented such that the grooves on their surfaces are aligned for forming grooves that are continuous between the wafers. Moreover, different grades of diamond may be compacted and sintered in different grooves.
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Christie Parker & Hale LLP
Smith International Inc.
Watts Douglas D.
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