US 3158214 A
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1954 A. E. WISLER ETAL SHIRTTAIL HARDFACING Filed March 15, 1962 TEETH 1 SHANK m i LC w m l v 5m WL m LT AS E s R U m U D P m U 0 F mum m GE m GW E NCL B QM T ADE RW M R 1 A Z MHZ B32 2 2 03m 125 M 022910 wmom m 252 ad; .2
TORNEY United States Patent 3,158,214 SZERTTAIL HARBFAQKN'G Allen E. Wisler and Stanley R. Scales, Houston, 'li'ex., assignors to Hughes Tool ilornpany, Houston, Tex, a corporation of fielaware Filed Mar. 15, 1362, Ser. No. 179,557 9 Claims. (Ci. 175-375) The present invention relates to hardfacing structures on earth penetrating tools, particularly on the outer surfaces of the bit legs of rolling cone rock bits. Such surfaces extend to full gage or only slightly less, and are consequently exposed to considerable abrasive Wear. In mud drilling, such exposure ordinarily produces no very marked amount of wear, and the bit legs consist of alloy steels which are hardened by heat treating but usually have no hardfacing on their outer surfaces. However, in the more recently introduced and now often used air and mist drilling techniques, aggravated erosive wear on such surfaces does result from drillin through certain types of hard formations, e.g., those containing siliceous material.
The observed Wear may take place over most of the outer surface of the bit leg, and has heretofore been anticipated and minimized in a number of ways. Since one result was wear of the now commonly used weld metal used to retain the ball plug in position, hardfacing has been added around the weld metal plu This hardfacing has typically been in a reverse .5 pattern, i.e., a band of welded hardfacing having a vertical leg between the ball plug weld metal and the leading edge of the leg and a generally horizontal leg between the weld metal and the tip of the shirttail (lower end) of the leg. In Hugheset, type bits, i.e., those using cylindrical compacts or inserts of a hard material such as tungsten carbide in place of the more conventional steel cutting teeth, similar compacts with flat outer ends are ofen used to protect the weld metal, most often in a U pattern wherein the cross-arm is disposed in the shirt-tail and the compacts in one vertical leg lie betwee the compacts in the other vertical leg so that no nar ow horizontal band is left unprotected. This structure has also been modified by using shallower holes than those used to retain compacts and welding tube hardfacingin such holes.
While such harufacing str ctures have proven adequate to protect the weld plug and he niaior partof the bit leg surface from erosion, the have not successfully cornbated erosion of the shirttail at d the area above the shirttail and below the ball plug weld. This area is particularly important because it constitutes one side of a fairly sharp corner, the other side of which is defined by a machined annular surface surrounding the bearing pin or" the bit leg. The latter surface serves to retain a set of rollers in place, and it wi l be apparent from the accompanying drawing that erosion of the sharp corner will expose such rollers and ultimately cause them to fall out and prevent normal functioning of the rolling cone.
This result has indeed obtained on occasion and is undesirable for several reasons. lthough the cutting structure of the bit is often still relatively sharp, drilling must be halted while repairs or replacements are made. A cone left in the hole will interfere with subsequent drilling, and may have to be removed with fishing tools. In deep well drilling, the cost of a premature round trip to replace the bit, with the time-consuming and costly raising, uncoupling and stacking of drill stem sections (and reverse in putting the new bit on bottom) far exceeds the cost of hardfacing necessary to insure bit leg protection.
In approaching the present invention of furnishing hard facing extending to the lower tip of a shirttail, the present inventor first tried extending the reverse J hardiacing mentioned above to a point /2" above the tip of the shirt- 3,158,2l4 Patented Nov. '24, 1%64 tail. When this caused some improvement in abrasion resistance but still permitted premature erosion and loss of rollers, the gap between shirttail tip and hardfacing was reduced to /2". Despite the narrowness of this gap, there was only a slight increase in performance, excessive wear of the unprotected metal in the gap and loss of rollers still taking place before full dul-ling of the cone cutting structure.
It appeared to be necessary to extend the hardfacing all the Way down the shirttail, but this created obvious problems. The metal at the shirttail tip is so thin that there is Very little back-up material to support the relatively brittle hardfacing. In addition, it was known from prior experience that hardfacing extending to the very edge of a surface and exposed to the type of abrasion here involved (continuous grinding) would be quickly undermined and washed out.
The essence of the present invention lies in providing a very narrow head of hard, tough metal adjacent the periphcry of the shirttail and providing hardfacing extending upwardly from the upper surface of such hard, tough metal head. The metal bead may be of any of a number of compositions of reasonable toughness and having an in situ hardness of 25 to 35 Rockwell C, or any greater hardness which may be achieved Without sacrifice in toughness. Suitable met s, hardfacing materials and techniques are described below in the example To better understand and appreciate the present invention, this application includes a drawing in which:
FIGURE 1 is an elevation of a three-cone rock'bit in inverted position, looking directly at one of the bit leg outer surfaces here involved, and
FEGURE 2 is a partial vertical section looking in the direction of the arrows marked 2-2 in FIGURE 1 1'0- tated clockwise.
Fl'GURE 1 shows in inverted position a conventional three-cone rotary bit comprising the threaded and tapered shank ll integrally extending from head 2, three bit legs 3 integral with the head extending in the opposite direction, and three rolling cones 4 mounted on bearing pins 5 of bit legs 3 extending inwardly toward the bit axis and axially away from shank 1. Steel teeth 6 are illustrated, though it is believed to be apparent that the present invention may be used with any type cutting structure and with bits or reamers, etc., having any number of rolling cutters. H
As may be seen from FIGURE 2, the now commonly used cone mounting structure includes rollers 7 and balls 3 mounted in appropriate spaces between cone 4 and bearing pin 5. Cone 4 is mounted on pin 5 with rollers '7 in place, after which balls 8 are loaded through bore 9 from its opening it) in the outer surface of bit leg 3. When all of the balls llnecessary to fill the ball race definedby cone l and bearing pin 5 have, been added, bzdl plug 11 is inserted to prevent the escape of any balls, thus locking cone 4 to the bit. Movement of plug 11 is prevented by welding it to hit leg 3 with weld metal 12. The shirttail of bit leg 3 is indicated by the numeral 13, and is generally regarded as that portion lying between tip 14 and the dashed line 15.
The material added to the above described structure by the present invention is indicated by metal bead 21 and hardfac ing 22. Metal head 21 extends from shirttail or hit leg-tip l4 and need be of only relatively smdl thickness and width. Hardfacing 22 consists of particles 23 of a hard metal such astungsten carbide dispersed'in a suit-v able binder 24. Both materials are applied to bit leg 3 by a variety of well known welding methods, depending on the state of assembly ofthe bit. [Whenthe bit has been completely assembled with cones, fbearings, ball plug, etc, or when an unassembled third of a bit head has already been heat treated, metal arc welding methods are preferred because relatively little heat is dissipated throughout the bit, while if the hardfacing is done prior to the heat treatment of the unassembled bit third the greater heat of an atomic hydrogen torch can be tolerated. (A bit third includes a bit leg 3 with bearing pin and a /3 portion of head 2 and shank 1, three such thirds being welded together in forming a Tri-Cone rock bit.)
The complete hardfacing shown in FIGURE 1 is in the aforementioned reverse 'J pattern including horizontal leg 22 and vertical leg 25, it being understood that the contribution of the present invention is steel head 21 at the periphery and that part of hardfacing 22 and 25 immediately adjacent thereto, in particular the generally horizontal hardfacing 22 and portion of steel head 21. In this connection it should be noted that the generally vertical portion of steel bead 2.1 and hardfacing 25 are desirable but not necessary to the practice of the present invention. So long as the horizontal portion are em ployed, any of the aforementioned prior art methods of protecting ball plug weld 12 are adequate.
Attention is invited to the fact that the hardfacing 22. and 25 of the drawing extends radially somewhat beyond the outside surface of bit leg 3. This permissable in drilling shallow holes used for seismograph work, blast holes, and the like, but is generally objectionable in deep holes such as production-seeking oil well holes wherein it is often necessary to lower a bit to the bottom of the hoie through the bore of a casing. For the latter type employment, it is apparent that the bit leg 3 may be designed and fabricated with an appropriate groove to receive metal bead 21 and hardfacing 22. The deposit in such cases may be ground flush with the outer surface of bit leg 3, as has been done with ball plug weld 12.
New Bit Example An example of using the present invention on a bit third on which no cone or hearing structure has been mounted and prior to heat treatment is:
A metal bead (ll) is laid down along the periphery of the bit leg 3 using an atomic hydrogen torch and a inch diameter 3501 steel welding rod and the backhand welding method to deposit a bead of about 3%;; inch thickness and A3 inch with. This rod has a weight percent composition of Si=0.200.35 Ni=3.253.75 Mo=0.200.30 S=0.04 max. P=0.04 max. Balance essentially Fe On subsequent heat treating of the assembled bit by furnace soaking, oil quenching and tempering, it has a Rockwell C hardness of 25 to 35, although any greater hardness without loss of toughness is desirable. The metal bead is applied to the lower edge of the bit leg surface and to the rising edge on the leading side of the bit leg, i.e., the side facing the direction of rotation.
Hardfacing 22 and 25 is then applied with the same atomic hydrogen torch, preferably by a tube application. One tube used successfully has been designated 230 A and consists of a hollow steel tube filled with cast tungsten carbide particles. The wall of the tube is of low carbon steel (0.15 w/o C. max), and the particulate carbide filling includes sufficient ferromolybdcnum and ferromanganese powders (screened through 80 mesh US. sieve) to make a binder of a composition of approximately 2 weight percent (W/o), Mn, 0.5 w/ o Mo, balance low carbonsteel. The tube is about /5 inch in outside diameter and has a wall thickness such that the binder is about 30 w/o of the combined weight of binder and tungsten carbide filler.
, The tungsten carbide particles in the tube are of the cast type, produced by reacting powders of tungsten and carbon in a graphite crucible under high heat, and tapping the molten mixture into an oil bath. The quantities used, giving due regard to carbon pick-up from the crucible, are preferably such as to produce a eutectic of WC and W C containing about 4 w/o combined carbon. The relatively large particles obtained from the oil bath are crushed and screened, in the present example to a size range of 14 to mils. V
The hmdfacing band or bead 22 and 25 thus deposited is of about ,1 inch thickness above surface 3 and varies in Width from inch to inch, the horizontal portion 22 preferably being wider than vertical portion 25. There is no particular point for the upward termination of portion 2 5, and terminations co-extcnsive with weld plug 12 have provcn adequate.
Assembled Bi! Example In this procedure, the welder is working on a bit or bit third in which the bearing surfaces of the bit legs have already been heat treated and in which a cone 4 has been mounted on a bearing pin 5 with rollers 7 in place. Balls 8 have already been loaded through opening 10 and bore 9, ball plug 11 has been added and fixed in place by weld 12.
It is necessary to observe special precautions to prevent overheating of the assembly, in particular the rollers and bearing surfaces. A copper shield is inserted between cone and bit leg, the cone or cones are immersed in water throughout the process, and the bit head is cooled in water between successive steps of depositing successive weld beads or portions thereof. The other precautions lie in the type welding torch and the materials used.
A metal bead 21 is deposited around the periphery of bit leg 3 using a shielded metal arc Welding method with a welding current of 100 to 110 ampercs of direct current, the workpiece serving as the positive electrode. The welding electrode material may be of any of several so-callcd air hardening" materials, two of which successfully employed in the present invention are Race and Airco 91. The first of these is a product of the Reed-Avery Company and has a typical deposit composition by weight percent of 0.26 C, 1.17 Mn, 0.50 Si, 0.71 Ni, 2.15 Cr, balance essentially Fe. The Airco 91 rod is a product of the Air Reduction Company and has a typical deposit composition by weight percentage of 0.33 C, 1.76 Mn, 0.10 Si, 2.80 Cr, balance essentially Fe. Each is deposited from a Vs inch diameter electrode to form a bead about 7 inch high and W inch to M1 inch Wide, preferably with a cooling step between depositing the horizontal and vertical legs.
The same welding method is employed for depositing the hardfacing bands 22 and 25, and the cgnsumable electrode used for the hardfacing is similar to that used for hardfacing new bits above in that it consists of a hollow tube filled with tungsten carbide particles, the tube wall again being a low carbon steel. The tungsten carbide particles are of 20 and 30 mesh U. S. Standard Sieve and comprise about w/o of the total weight of binder plus hardfacing particles. Such rods or electrodes are commercially available as the Stoody Companys Stoody Tube Borium and the Victor Equipment Companys Coated Victortube Electric welding rods.
In contrast with the preferred single ha-rdfacing head 22 of the new bit technique above and as shown in the drawing, it is preferable in the rework of assembled bits to apply hardfacing 2.2 (and 25) in two or more narrow beads, each 1 to /2 inch wide by about inch high. This is done to minimize the heat which must be dissipated by the bit, and again has the purpose of avoiding damage to the bearings. It is also highly desirable to pause and cool the bit between the depositing of bead segments and after completing each head.
The complete hardfacing bands 22 and 25 may be laid down by the described metal are technique, and indeed this technique is most convenient when the hardfacing is being applied in the field. When the bit is being factory reworked a final bead may be added above the electric distance between the tip 14 of shirttail 13 and the line where the first atomic hydrogen head is to join the electric tube bead, about /2 inch. Substantially all of the vertical hardfacing portion 25 may be deposited by the atomic hydrogen torch. The total width of all beads is about /1 inch for the horizontal portion and /2 inch for the vertical portion.
Bits with shirttail hardfacing as in these examples have been extensively field tested and have resulted in increases in footage drilled averaging more than 70%. As one example, a number of bits with prior art hardfacing on the bit leg averaged 588 feet per bit before it was necessary to pull them for loss of shirttail metal. At the same location and in the same formation, the same type and size bits with the shirttail hardfacing of the present invention drilled 1029 feet per bit, an increase of 75%.
While the present invention has been described in connection with rolling cone rock bits, it will be appreciated that it is not necessarily limited thereto, but may be generally applied to structures having sharp corners subject to abrasion, e.g., other types of rock bits, reamers and the like. Broadly the invention comprises a structure on the outer surface of the rotating part consisting of a narrow bead of a hard, tough metal at the edge of such surface immediately adjacent the sharp corner and a band of hardfacing material adjacent the metal bead in contact therewith. The metal bead should be of a minimum final hardness of about 25 on the Rockwell C scale and may have any greater hardness consistent With toughness. The hardfacing band may consist of sintered or cast particles dispersed in a suitable binder, and may be of other suitable hard particles as well as tungsten carbide.
In addition, while it has been indicated above that exposure to abrasive conditions ordinarily produce no severe wear on shirttails and bit legs used in mud drilling, there are exceptions. The shirttail hardfacing of the present invention is equally applicable to earth penetrating tools used in such mud drilling, including rock bits, reamers and shaft cutters, Le, a rolling cutter mounted on the bearing pin of a bit leg with a construction similar to that described above and with the same sharp corner at the tip of the shirttail.
What is claimed is:
1. A hardfacing structure on a member subject to abrasion on the outer surface thereof and terminating at a corner, such member having a portion at and adjacent such corner so relatively thin as to require strengthening prior to hardfacing but being otherwise relatively thick, such hardfacing structure comprising: a narrow head of a tough, hard, homogeneous metal alloy on said surface immediately adjacent said corner and a substantially discrete band of hardfacing material on said surface immediately adjacent said hard metal bead and in contact therewith, said hardfacing material being a heterogeneous combination of wear resistant particles in a tough alloy binder.
2. The hardfacing structure of claim 1 in which said hard metal is an alloy steel having a minimum hardness of about 25 Rockwell C.
3. The hardfacing structure of claim 2 in which said hardfacing band comprises tungsten carbide particles in a binder of a low carbon steel.
4. The hardfacing structure of claim 3 in which said metal bead has a width of about A; inch and said hardfacing band has a minimum Width of about inch.
5. A hardfacing structure on the shirttail and bit leg of a rock bit or other tool comprising a narrow bead ,of a tough, hard, homogeneous metal alloy welded on the outer surface of said shirttail immediately adjacent the corner thereof and a band of hardfacing material welded on said surface above said metal bead and in contact therewith, said hardfacing material being a heterogeneous combination of Wear resistant particles in a tough alloy binder.
6. The hardfacing structure of claim 5 in which said metal bead has a minimum hardness of about 25 on the Rockwell C scale.
7'. The hardfacing structure of claim 6 in which said metal bead is an air hardening steel head.
8. A hardfacing structure for rock bit legs and shirttails and Welded to the outer surfaces thereof including a narrow band of a tough hard metal extending generally horizontally across the tip of said shirttail and generally vertically along the leading edge of the periphery of said shirttail and bit leg, and a hardfacing band similarly extending horizontally across said shirttail and vertically along said periphery, said hardfacing band being in supporting contact with said hard metal bead and extending vertically to the top of any ball plug Weld metal in said bit leg, said hard metal bead being composed of a homogeneous alloy steel whereas said hardfacing bead is a heterogeneous combination of tungsten carbide particles dispersed in a steel binder.
9. The hardfacing structure of claim 8 in which said hard metal has a minimum hardness of about 25 Rockwell C.
References Cited by the Examiner UNITED STATES PATENTS 1,733,241 10/29 Scott 175411 X 1,855,330 4/32 Zublin 175411 X 2,057,209 10/36 Schlurnpf l-4l1 X 2,086,682 7/37 Scott 175341 X FOREIGN PATENTS 1,244,3 9/60 France.
CHARLES E. OCONNELL, Primary Examiner.