Wells – Means for perforating – weakening – bending or separating pipe... – Cutter rotates circumferentially of pipe
Utility Patent
1998-01-29
2001-01-02
Lillis, Eileen D. (Department: 3673)
Wells
Means for perforating, weakening, bending or separating pipe...
Cutter rotates circumferentially of pipe
C175S426000, C407S113000, C407S115000, C407S116000, C407S114000
Utility Patent
active
06167958
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
Not Applicable
FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
BACKGROUND OF THE INVENTION
This invention relates generally to a new method for applying a plurality of cutting edges to a tool for cutting or milling downhole metal items, such as fixed casing strings in a well bore, and to a new type of cutting element used in this method.
Heretofore, cutting tools for cutting metal items downhole, such as well casing or casing strings, have been provided with one of two types of cutting elements mounted on the cutting surfaces of the cutting tool. Generally, the two types of cutting elements which have been used are an aggregate of crushed tungsten carbide particles, or a pattern of whole cutting inserts. The cutting surfaces on which the aggregate or whole inserts are mounted have been fixed blades, swinging blades, or the tool body itself, depending upon the intended function of the tool.
Generally, the whole insert type of cutting element has been made of cutting grade tungsten carbide, in the shape of discs, triangles, rectangles, parallelograms, or other shapes. These inserts have been bonded to the cutting tool, sometimes in a uniform pattern, and sometimes in a random pattern. The random pattern is easier and more economical to apply, but the uniform pattern has been more effective. Most of these whole inserts have had generally flat front faces, and generally flat rear faces, with the rear face being bonded to the cutting tool, and the front face being presented to the workpiece as a cutting face. Most of these inserts also have substantially parallel front and rear faces. One other known insert is a pyramid shape having four flat triangular sides.
It is important to cut relatively short, thick, metal chips from the workpiece, to allow efficient removal of the chips from the well, via the flow of drilling fluid. If this is not done, long, thin, stringy metal chips can be formed. These long, thin chips can adhere together, in a “bird nesting” effect, which can clog the drilling fluid flow passages.
In order to promote the cutting of relatively short metal chips from the workpiece with the whole cutting inserts, at least two types of features sometimes have been employed. One such feature has been the provision of a surface irregularity on the front face of each cutting insert, to curl each metal chip back toward the workpiece until it breaks off at a relatively short length.
The second such chip breaking feature has been to tilt the front face of each insert at a non-orthogonal attack angle relative to the surface of the workpiece. In this context, the term “rake angle” has been used to refer to the condition where one portion of the front face of the insert is advanced ahead of another portion, in the direction of rotation of the cutting tool. The degree of advancement is usually small, with approximately 20° being the upper limit, resulting in an angle between the front face of the cutting insert and the surface of the workpiece of 70° to 90°. The rake angle can be “positive” or “negative”, depending upon which portion of the front face of the cutting insert is advanced. If the leading portion of the front face contacts the workpiece surface, a “positive” rake angle is said to exist. If the trailing portion of the front face contacts the workpiece surface, a “negative” rake angle is said to exist. The use of a rake angle can cause the front face of the insert to “drag” across the workpiece, or to “gouge” the workpiece, depending upon the particular type of rake angle employed, and depending upon the contour of the cutting portion of the insert. A negative rake angle is generally considered to achieve the best chip breaking effect.
The front face of the insert can have a “radial” rake angle, where the front face lies in a plane which is parallel to the rotational axis of the cutting tool, but which extends non-radially from the cutting tool. Or, the front face of the insert can have an “axial” rake angle, where the front face lies in a plane which intersects, but does not contain, the rotational axis of the cutting tool. Or, the front face of the insert can have a “compound” rake angle having both radial and axial components.
A rake angle on the front face of the cutting insert can be the result of an angle on the cutting tool surface on which the cutting insert is mounted, or an angle between the front face of the cutting insert and the rear face, or both.
When tungsten carbide aggregate has been used as the cutting elements instead of whole cutting inserts, it has not been possible to employ either of the two chip breaking features discussed above. The tungsten carbide particles used as cutting elements in the aggregate are not uniform either in material or in conformation. They are typically made by crushing whole inserts or worn out tungsten carbide machine components, such as extrusion dies, rollers, or hammers. This produces a wide assortment of shapes and sizes of particles, or chunks, of varying formulations of tungsten carbide material. Some of these particles or chunks are not even “cutting grade” tungsten carbide, and some of the faces or edge profiles of these particles or chunks are not suitable for use on cutting elements. Even where surface irregularities are present on the crushed carbide particles, they are not uniformly distributed or optimally arranged on the front face of each cutting element, so their effect is greatly reduced or eliminated.
The crushed aggregate is typically applied to the cutting tool in a more or less random pattern, and each particle is randomly oriented on the surface of the cutting tool. In one method, the crushed aggregate is formed into a solid bar by randomly suspending the particles in a matrix of brazing material, such as a nickel/brass matrix. The bar is then bonded to the cutting tool as a unit. In another method, the crushed aggregate is randomly suspended within a welding rod and then bonded directly to the cutting tool, by melting of the welding rod onto the cutting tool. In either method, it is impossible to control the orientation of each particle of tungsten carbide relative to the cutting tool. Therefore, it is impossible to control the angle at which the leading face or leading edge of each particle is ultimately presented to the workpiece. Further, it is difficult to arrange the particles in a uniform pattern on the cutting tool, since the particles are not of uniform size and shape. Even though the technician typically attempts to pack the crushed particles together for good coverage, some areas will have a higher concentration of smaller carbide particles, with few open spaces therebetween, while other areas will have a lower concentration of larger particles, with larger open spaces therebetween. Therefore, it is impossible to ensure that the various particles will achieve a uniform cutting pattern on the workpiece. The result is a relatively inefficient cutting tool.
The flat sided pyramid cutting insert is not particularly well suited to this cutting tool application, because each pyramid insert will almost certainly rest on one flat face, projecting a single point in the direction of rotation of the cutting tool. In this orientation, the three exposed flat side faces would be oriented at less than optimum angles for achieving the chip breaking effect.
Because of the relative inefficiency of the crushed tungsten carbide aggregate, the use of whole inserts arranged in a uniform pattern, with some type of chip breaking feature being employed, has come to be the industry standard for downhole milling and cutting. This efficiency has a price, however, in that the arrangement of cutting inserts in a uniform pattern, and the orientation of each insert at the optimum attack angle, add some expense and complexity to the cost of manufacturing the cutting tool. It is desirable to have a cutting element, and a method for applying cutting edges to a cutting tool, which will combine the simplicity of an aggregate cutting structure with the cutting efficiency of a unif
Baker Hughes Incorporated
Lillis Eileen D.
Singh Sunil
Spinks Gerald W.
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