The present invention relates in general to earth boring bits, and in particular to rock bits having tungsten carbide inserts mounted in milled steel teeth.
Earth boring bits such as rock bits for the oil field and mining industries have long been provided by rotary drill bits having milled steel teeth formed on rotary cone cutters in circumferentially extending rows. The height of the milled teeth are measured from a base to a crest. The softer the rock, the larger the height of the teeth which may be used, providing for more aggressive rock bits capable of drilling more quickly through the softer earth formations. In harder formations less aggressive bits are used having teeth of smaller height. Cutting surfaces for rock bits have also been provided by embedding inserts into rotary cutters and bit bodies. Tungsten carbide inserts (“TCI”) and polycrystalline diamond compacts (“PDC”) have been used. The tungsten carbide inserts typically have a tungsten carbide insert body with one end formed to provide a cutting surface. The PDC inserts typically have an insert body formed of tungsten carbide with one end having a polycrystalline diamond cutting surface.
For rotary cone rock bits, the tungsten carbide insert bodies typically extend outward of the rotary cutters in a cantilevered arrangement. Compressive and torsional loads on the cantilevered insert bodies often lead to failure. Erosion of steel material of the rotary cutters from around the insert bodies is also a common failure mode. Increasing the amount of steel material of the rotary cutters around the insert bodies can provide more material for erosion and reduce the cantilevered length the insert bodies extend, reducing the compressive and torsional loads to provide longer service life for the bit. Although service life is increased, increasing the amount of cutter material around the insert bodies reduces an effective tooth height for the inserts which provides a less aggressive bit, reducing the speed at which the bit will move through earthen formations.
One example of an earth boring bit is the rotary cone rock bit. Rotary cone rock bits have a bit body with an upper end adapted for connection to a drill string and typically three bit legs which extend downward from the body to provide support arms. A bearing shaft extends inward and downward from each bit leg. A conventional rock bit bearing shaft is cylindrical and rotatably receives a rotary cutter provided by a cutter cone. The cutter cone is generally mounted on each bearing shaft and supported rotatably on bearings acting between the spindle and the inside of a spindle-receiving cavity in each cutter cone. The cutter cones have teeth, inserts or compacts on their exteriors for disintegrating earth formations as the cones rotate on the bearing shafts. One or more fluid nozzles are often formed on the underside of the bit body. The nozzles are typically positioned to direct drilling fluid passing downwardly from the drill string toward the bottom of the borehole being drilled. Drilling fluid washes away material removed from the bottom of the borehole and cleanses the cutter cones, carrying the cuttings and other debris radially outward and then upward within an annulus defined between the drill bit and the wall of the borehole.
An earth boring bit has cutters with embedded tungsten carbide inserts and milled steel teeth. The teeth are first milled into the cutters and grooves are milled to extend between bases of the teeth, parallel to the crests of the teeth. Hard facing is applied to surfaces of the teeth and the grooves, and then the cutters are heat treated. Insert sockets are drilled into the teeth, centrally disposed in crests of the teeth. The tungsten carbide inserts are secured in the insert sockets, aligned for forming cutting profiles with respective ones of the milled teeth. The cutters are preferably frustoconically shaped and used for a rotary cone rock bit, and the tungsten carbide inserts configured as chisel-shaped inserts having crests which are aligned parallel to the crests of the milled steel teeth.
For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying Drawings in which
Preferably, the longitudinal axes 86, 96 and 106 extend in adjacent relation to one another, in a generally parallel arrangement. It should be noted that the axes 86, 96 and 106 in general will be further from being parallel with increased curvature of the particular circumference of the cutter 20 on which the row of teeth 22 defining the axes 86, 96 and 106 are included. In some embodiments, the axes 86, 96 and 106 may extend perpendicular to the circumference 112 (shown in
The rotary cutters 20 are first formed by milling the teeth 34 into a conical cutter body. Then hard facing is preferably applied to the teeth 34. Next the cutter 20 will be heat treated followed by the holes being drilled to provide the insert sockets 110. The bases 100 of the tungsten carbide inserts 32 are then fixedly secured in the sockets 110.
The present invention provides advantages of a tungsten carbide rotary drill bit having milled teeth. The milled teeth are formed to be used as cutting surface in conjunction with the tungsten carbide inserts which provides a maximum amount of support metal around the insert. The additional metal limits stress on the insert, and also provides additional metal in the nose of the bit to deter bit failure due to erosion. The recesses extending in adjacent alignment with the teeth extend the effective height of the teeth, providing for a more aggressive geometry for the rotary cone drill bit.
Although the disclosed embodiment is for air drilling, other embodiments contemplate use of other drilling such as water based and oil based fluids. Sealed and lubricated bearings may be used, as is well known for rotary cone rock bits.
Although the preferred embodiment has been described in detail, it should be understood that various changes, substitutions and alterations can be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
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Number | Date | Country | |
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20170159366 A1 | Jun 2017 | US |