1. Field of the Invention
Embodiments disclosed herein relate generally to manufacturing methods for roller cone drill bits.
2. Background Art
Historically, there have been two main types of drill bits used drilling earth formations, drag bits and roller cone bits. The term “drag bits” refers to those rotary drill bits with no moving elements. Drag bits include those having cutters attached to the bit body, which predominantly cut the formation by a shearing action. Roller cone bits include one or more roller cones rotatably mounted to the bit body. These roller cones have a plurality of cutting elements attached thereto that crush, gouge, and scrape rock at the bottom of a hole being drilled.
Roller cone drill bits typically include a main body with a threaded pin formed on the upper end of the main body for connecting to a drill string, and one or more legs extending from the lower end of the main body. Referring now FIGS. 1 and 2, a conventional roller cone drill bit, generally designated as 10, consists of bit body 12 forming an upper pin end 14 and a cutter end of roller cones 16 that are supported by legs 13 extending from body 12. Each leg 13 includes a journal (not shown) extending downwardly and radially inward towards a center line of the bit body 12, with cones 16 mounted thereon. Each of the legs 13 terminate in a shirttail portion 22. The threaded pin end 14 is adapted for assembly onto a drill string (not shown) for drilling oil wells or the like.
Conventional roller cone bits are typically constructed from at least three segments. The segments are often forged pieces having an upper body portion and a lower leg portion. The lower leg portion is machined to form the shirttail section and the journal section. Additionally, lubricant reservoir holes, jet nozzle holes, ball races are machined into the forgings. Cones are mounted onto the formed journals, and the leg segments are be positioned together longitudinally with journals and cones directed radially inward to each other. The segments may then be welded together using conventional techniques to form the bit body. Upon being welded together, the internal geometry of each leg section forms a center fluid plenum. The center fluid plenum directs drilling fluid from the drill string, out nozzles to cool and clean the bit and borehole, etc.
While roller cone bits have had a long presence in the market due to their overall durability and cutting ability (particularly when compared to previous bit designs, including disc bits), fixed cutter bits gained significant growths, particularly in view of the rates of penetration achievable. Accordingly, there exists a continuing need for developments in roller cone bits, as well as manufacturing techniques, that may at least provide for increased rates of penetration.