Abstract:
A dual blade cutter head for a rotary cutting tool which consists of two identical blades disposed in opposed position, each blade having an outer arcuate edge movable into cutting contact and having suitable hard facing affixed to the arcuate edge oriented for right-turn cutting rotation. In one form the hardface is an arcuate inlay block faced with thermally stable polycrystalline diamond.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to downhole rotary cutting tools and, more particularly, but not by way of limitation, to a clean-out tool cutting blade of the butterfly or expansible type that is capable of cutting different diameter bores within a tubing section without cutting the tubing. 
     2. Prior Art 
     The prior art known to Applicant is well characterized in Applicant&#39;s previously filed U.S. Pat. No. 4,809,793 as issued on Mar. 7, 1989. This patent describes a rotary clean-out tool of the type that would use the cutting blade that is described in the present application. Thus, the tubing clean-out tool includes fluid pressure responsive linear actuators that function above the cutting blade assemblies to expand and retract the blade to operational attitude. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a particular type of cutting blade of the expandable type, i.e. a double blade combination, that is of particular shape and is hardface reinforced at particular points around the cutting edge. Each of the two cutting blades is identical as they function in pairs in opposed position with right-turn edge surfaces formed with selected hardfacing. For example, a synthetic diamond facing pre-formed in a fused block is bonded into an insert space milled around the right-turn edge of the blade. 
     Therefore, it is an object of the present invention to provide a cutting blade that is rugged and reliable for use in selected tubing clean-out applications. 
     It is also a object of the present invention to provide a cutting blade combination that can cut through different inner diameters without cutting the inner wall of the tubing containing such restrictive formations. 
     Finally, it is an object of the present invention to provide a cutting blade having a reinforced hardface of arcuate shape that enables effective abrasion at varying radial distances from the axis of the rotary clean-out tool. 
     Other objects and advantages of the present invention will be apparent from an understanding of the drawings and detailed descriptions which illustrate the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a vertical section of a portion of clean-out tool illustrating the cutting blade assembly when in closed position; 
     FIG. 2 is a similar section showing the cutting blades in the outward open position; 
     FIG. 3 is a plan view of the right-turn side of a single cutting blade; 
     FIG. 4 is an end view of the cutting blade shown in FIG. 3; and 
     FIG. 5 is a side view of a hard-facing insert block as used in the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is an idealized sectional view of a portion of rotary clean-out tool 10 such as that described in detail in Applicant&#39;s U.S. Pat. No. 4,809,793. Thus, the rotary tool 10 is formed from a cylindrical body member 12 having an axial bore 14 and counterbore 16 with piston 18 and piston rod end 20 received reciprocally therein. The piston 18 is in opposition to drilling fluid under pressure present in axial bore 14. A narrow slotway or transverse cavity 22 then retains a pair of cutting blades 24a and 24b in opposed disposition as retained on a pivot pin 26. 
     FIG. 2 shows an attitude when fluid pressure has been increased sufficiently above piston 18 to force the piston downward such that rod end 20 contacts the upper angle edges 28a and 28b forcing a spread of the opposite ends 38a and 38b of blades 24a and 24b, thus presenting an open position for maximum radius cutting. As illustrated, the right-turn facings of blades 28a and 28b are each inset with a hardface block 30a and 30b, respectively. It should be understood that there is additional fluid control detail and sealing arrangement provided in tool 10 as well as internal fluid passages that lead around the cavity 22, and such detail is readily apparent from a study of the U.S. Pat. No. 4,809,793. 
     Referring to FIGS. 3, 4 and 5, the various components and configurations of a blade 24 are shown. Thus, the blade 24 consists of a base plate 32 which is formed with a straight side 34, an upper angle edge 28, and an arcuate edge 36 coming to a bottom point 38. A hole 40 receives pivot pin 26. A raised corner surface 42 provides an interlocking surface for contact with the counterpart blade 24, as does a raised facing 44 adjacent the arcuate outer edge 36. An arcuate cut-out of rectangular cross section is formed as milled inset 46 which is formed to receive the hardface insert 30 therein. 
     The hardface 30 is formed as an insert having an upper, wider portion 50 that tapers to a narrower lower portion 52 while defining a continuous outer surface 54. The insert 30 is a heat/pressure molded formation of suitable sintered or powdered metallic substance and a bonding agent that forms a base for overlay of thermally stable polycrystalline diamond (TSP) 55 which extends completely around the outer surface 54 of wide portion 50 and narrow portion 52. The insert 30 is secured within the inset 46 with silver solder 56, and the blade 32 is then in final form and ready for use with right-turn rotation. 
     In operation, the rotary tool 10 may be lowered downhole to a work area through existing tubing and, once at a work site, the attendant fluid pressure may be adjusted to compress the piston 18 downward to force rod end 20 against the angle edges 28a, 28b  thereby to expand outward the lower points 38a and 38b of respective cutter blades 24a and 24b. The increasing fluid pressure will force the cutter blades 24a, 24b outward against the existing sediment or deposit at that point and pressure will be maintained until the blades 24 have progressed outward to the inner wall of the tubing whereupon the rotary tool 10 can be moved upward or downward with repetition of the same sequence. 
     The foregoing discloses a novel cutter blade that is specifically designed in shape and hardfacing to provide abrading function at selected places along a tubing string. It should be understood that other types of hardfacing or cutter elements such as natural diamonds, tungsten carbide inserts, etc. can be employed in substitution. Also, the placement and depth of hardfacing along the arcuate edge of the blades is subject to change, particularly for cutting certain deposits that may be encountered. 
     Changes may be made in the combination and arrangement of elements as heretofore set forth in the specification and shown in the drawings; it being understood that changes may be made in the embodiments disclosed without departing from the spirit and scope of the invention as defined in the following claims.