Boring or penetrating the earth – Bit or bit element – Specific or diverse material
Reexamination Certificate
2002-03-20
2004-04-13
Bagnell, David (Department: 3672)
Boring or penetrating the earth
Bit or bit element
Specific or diverse material
Reexamination Certificate
active
06719074
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to insert chips and a manufacturing method thereof. Insert chips are used as blades (teeth) of a tricone bit which is a tool for drilling an oil well (hereinafter referred to as oil-drilling tricone bit). Specifically, the insert chips refer to, for example, an inner chip for drilling a well in the vertical direction and a gage pad for drilling the well in the radial direction of the well. The present invention further relates to an oil-drilling tricone bit having the insert chips as described above.
2. Description of the Background Art
A tool called a tricone bit is used for drilling an oil well for example. The tricone bit is used for drilling subterranean rocks and thus the tricone bit generally has, as its cutting edges, insert chips made of WC—Co-based cemented carbide with good abrasion resistance.
Insert chips for the tricone bit are generally classified into two types, i.e., an inner chip for vertical drilling of an oil well and a gage pad for drilling the oil well in the radial direction. An inner chip and a gage pad are schematically shown in
FIGS. 9 and 10
respectively.
In recent years, oil wells are drilled at increasingly greater depths and accordingly rocks themselves at such great depths are hard to drill. Because of this, insert chips that are cutting edges of the tricone bit wear at earlier stages or some fragments of insert chips are broken (chipped) off from the insert chips (chipping of insert chips). A resultant problem is a shortened lifetime of the tricone bit. Moreover, a considerably costly work is necessary for lifting the tricone bit which reaches the end of its lifetime at several thousand meters below ground and for replacing the tricone bit with new one in order to proceed with drilling. Then, there is a need for further increase in the lifetime of insert chips.
Under the situation as described above, both of abrasion resistance and resistance to chipping (hereinafter chipping resistance) of insert chips must be improved. In general, cemented carbide has a higher hardness when it contains a smaller amount of Co and thus has an improved abrasion resistance, while the smaller amount of Co results in a higher brittleness of the cemented carbide which deteriorates the chipping resistance. In other words, the abrasion resistance and chipping resistance are not compatible with each other
Various arts have been well known that concern the need for increase in the lifetime of insert chips as detailed below.
Japanese Patent Laying-Open No. 5-209488 discloses a rock-drilling button having an &eegr; (eta)-phase core exposed at the top and a surface region having a high Co content that is formed to enclose the &eegr;-phase core, produced by adjusting sintering conditions of cemented carbide. According to the art disclosed, abrasion is alleviated since the exposed &eegr;-phase touches rocks from the start of drilling. On the other hand, the high Co content in the surface region enhances the chipping resistance. A problem with this art is that the cemented carbide composition containing the &eegr;-phase which is an embrittlement phase is requisite. In general, the &eegr;-phase included in the cemented carbide could be an origin from which the metal is likely to chip off, resulting in deterioration of reliability.
Japanese Patent Laying-Open No. 7-150878 discloses an art of improving peeling resistance of the outermost polycrystalline diamond layer of an insert. This insert has a substrate made of sintered tungsten carbide, the outermost surface of a cutting edge of the insert is covered with the polycrystalline diamond layer, and an intermediate layer is provided between the substrate of sintered tungsten carbide and the polycrystalline diamond layer. The intermediate layer is a composite-material layer made of sintered tungsten carbide and polycrystalline diamond. However, a problem with this art is that the polycrystalline diamond itself has a low toughness which causes any crack in the outermost polycrystalline diamond layer and consequently the crack becomes an origin from which the insert breaks off.
Japanese Patent Laying-Open No. 11-12090 discloses a similar art according to which CVD (chemical vapor deposition) is used for coating a surface of a drill bit made of cemented carbide with diamond. However, the diamond and cemented carbide are different in thermal expansion coefficient which could cause a problem of peeling.
Japanese Patent Laying-Open No. 8-170482 proposes a drill bit having a hardness gradient. Specifically, the lowest hardness of a substrate of an insert chip of the drill bit increases gradually toward the leading end of the insert chip. It is noted that the tricone bit includes cone sections in which respective insert chips are fit and a body holding the cone sections, and not only the cone sections rotate but also the body itself rotates for drilling. Accordingly, not only tips of cutting edges of the insert chips but also sides of the cutting edges contribute to drilling. If the art disclosed in Japanese Patent Laying-Open No. 8-170482 is applied to insert chips of a tricone bit, the cutting edge has its side where cemented carbide of low hardness, i.e., low abrasion resistance, is exposed, since the insert chip is formed of a stack including cemented carbide materials of different compositions bonded to each other. A resultant problem is that the side of the cutting edge predominantly wears to shorten the lifetime.
Japanese National Patent Publication No. 10-511432 proposes an insert chip having a substrate of a cemented carbide and a cutting edge coated with one coating layer of a cemented carbide different from that of the substrate. Specifically, the coating layer of the cemented carbide has a lower Co content than that of the substrate for improving the abrasion resistance of the insert chip and satisfying the chipping resistance requirement by the substrate. It is known that decrease of Co content of cemented carbide decreases thermal expansion coefficient thereof. Then, if the difference in Co content between the substrate and the coating layer with which the substrate is coated is excessively large, a resultant problem is that the coating cemented carbide layer is peeled off or any crack occurs, for example. Then, according to this art, the coating cemented carbide layer cannot have its Co content greatly different from that of the substrate and thus the improvement of abrasion resistance is limited.
As discussed above, various studies have been conducted on insert chips for drilling and drill bits. However, there is still a need for an insert chip, especially an insert chip of an oil-drilling tricone bit, that is suitable for drilling rocks which are at greater depths and accordingly difficult to drill and that has both of abrasion resistance and chipping resistance.
SUMMARY OF THE INVENTION
One object of the present invention is to provide an insert chip of an oil-drilling tricone bit and a method of manufacturing the insert chip, the insert chip having both of abrasion resistance and chipping resistance. It is also an object of the present invention to provide an oil-drilling tricone bit suitable for drilling rocks which are at greater depths and thus hard to drill.
An insert chip of an oil-drilling tricone bit according to the present invention includes, in order to achieve the above-described objects, an insert-chip substrate made of a cemented carbide of a first composition, the substrate including a cylindrical body and a cutting edge for drilling, and includes a cemented carbide coating layer formed of at least two stacked coating layers made of a cemented carbide of a composition different from the first composition, the cemented carbide coating layer covering at least 80% of the surface area of the cutting edge of the insert-chip substrate. The coating layers each have a thickness, at a tip portion of the cutting edge, ranging from 0.1 mm to 2.5 mm and, the total thickness of the cemented carbide coating layer ranges from 1 mm to 5
Mori Nobuyuki
Moriguchi Hideki
Tsuda Keiichi
Bagnell David
Fasse W. F.
Fasse W. G.
Japan National Oil Corporation
Smith Matthew J
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