ROTARY DRILL BIT

Abstract: A bearing system in rotary drill bits for rotatably carrying a roller cutter (12) on a bearing shaft (11) comprises a bearing element (14) connected to the roller cutter or the bearing shaft. For purposes of rigidly connecting the bearing element (14) to the roller cutter (12) or the bearing shaft (11) the bearing element (14) is adapted to be wedgingly secured the roller cutter (12) or the bearing shaft (11) upon a limited turning of the bearing element (14) relative to the roller cutter (12) or the bearing shaft (11).

Description: Rotary drill bit The present invention relates to bearing means in rotary drill bits of the type comprising a main body and at least one bearing shaft associated therewith. A roller cutter provided with cutting means is rotatably carried on the bearing shaft by means of a bearing system which comprises at least one bearing element connected to the roller cutter or the bearing shaft. In rotary drill bits of this type the radial and axial forces are often taken up by means of friction bearings. In U.S. patent specification No. 3.721.307 a rotary drill bit is disclosed which has a radial friction bearing in form of a floating bushing. For purposes of obtaining a wear distribution as even as possible the radial friction bearing, however, is usually connected to the bearing shaft or, more commonly, to the roller cutter, for in¬ stance by welding or press-fitting. Such typical mounting technique is described in U.S. patent specification Nos. 4.176.724 and 3-862.762, respectively. The object of the present invention is to provide a simpli¬ fied mounting technique for rigid connection of the bearing element. The above and other Ob ects of the invention are attained by giving the invention the characterizing features stated in the appending claims. The invention is described in detail in the following with reference to the accompanying drawings in which various embodiments are shown by way of example. It should be understood that these embodiments are only illustrative of the invention and that various modifications thereof may be made within the scope of the claims. In the drawings, Fig. 1 shows, partly in section, one embod ment of a rotary drill bit provided with a bearing means accordin *go to the invention. Fig. 2 shows in section another embodiment of a drill bit provided with a bearing means according to the invention. Fig. 3 shows in section a bearing element included in the embodiments according to Figs. 1 and 2. Fig. 4 is an end view of the bearing element in Fig. 3. Figs. 5 and 6 show in section two further embodiments of a bearing means according to the invention. Corresponding details in the various figures are given the same reference numeral. Fig. 1 shows a rotary drill bit having three separate legs extending from a bit body one of which is shown in section and designated by 10. The end of the leg is shaped as a bearing shaft or lug 11, on which a roller cutter 12 having cutting means, such as inserts, is rotatably mounted. The inserts 13 are pressed into the outer surface of the roller cutter 12 for ' the purpose of crushing the rock when the bit is rotated and fed forward in the drill hole. The bearing system necessary for the rotation of the roller cutter 12 comprises a radial friction bearing 14, a ball bearing 15, a radial friction bearing 16 and an axial bearing 17. For insertion of the balls in the ball bearing 15 there is a channel 18 provided in the bearing lug 11 having a plug 19 inserted therein for retaining the separate balls. The Q?'PI main task of the ball bearing 15 is to retain the roller cutter 12 without actually absorbing any force. The axial forces on the roller cutter 12 are in the main absorbed by the axial bearing 17 » but moreover the roller cutter 12 is provided with a shoulder 20 adapted to abut against a shoulder 21 on the bearing lug 11, thus absorbing part of the axial load. The axial bearing 17 consists of a support plate 22 of hardened steel which is pressed into the top of the roller cutter 12 and is applied in supporting abutment against the axial end surface of the bearing lug 11. Also the bearing lug is usually made of hardened steel but its axial bearing surface is covered with a hard-facing deposit material such as Stellite. Fluid for cooling and flushing the bearing system 14, 15, 16, 17 is supplied through passages 23, 24, 25. The radial friction bearing 14 comprises a bearing element in form of a bushing and is provided with a cylindrical mounting surface 26, Fig. 3 and 4, intended to cooperate with a mounting surface 27 in the roller cutter 12. The mounting surfaces 26, 27 are concentric relative τo the rotational axis 28 of the roller cutter 12. The bearing element 14 is provided with a further mounting surface 29, which is intended to cooperate with a mounting sur¬ face 30 in the roller cutter 12. The bearing element 14 is also provided with a surface 41 which is opposed to the mounting surface 29. According to the invention the dis¬ tance between the mounting surface 29 and the surface 41 varies in the circumferential direction of the bearing element 14. In the illustrated embodiment the mounting surfaces 29, 30 are eccentric relative to the rotational axis 28 of the roller cutter 12, the eccentricity being designated by e in Fig. 4-, Thus, the bearing element 14 is wedgingly secured at the mounting surfaces 29, 30 upon a limited turning of the bearing element relative to the roller cutter 12. According to the invention the eccentricity of the mounting surfaces 29, 30 is within the interval 0,5 mm to 3,0 mm, with preference for values in the order of 1,0 mm to 2,0 mm. When the bearing element 14 is turned relative to the roller cutter 12, then its turning, as counted along the surfaces 26, 29, is less than 30 mm, preferably less than 20 mm. The mounting surfaces 26, 29 of the bearing element 14 are separated by a transverse surface 31 so that a stepped outer surface is formed on the bearing element. The eccen¬ tric surface 29, then, has the largest diameter and is lo¬ cated nearest to the periphery of the drill bit. In the illustrated embodiment the mounting surfaces 26, 29 are of substantially equal widths. The ratio of the widths of the surfaces is chosen with regard to the size of the eccentricity, the demand for a firm attachment of the bearing element and thε demand for a small out-of-truth or non-alignment of the centre hole of the bearing element. In the embodiment according to Fig. 1 the bearing system is continuously flushed. Due to the continuous flushing there are no seals in the gap between the roller cutter 12 and the leg 10. Fig. 2 shows the invention applied in a rotary drill bit where the bearing system is sealed. Lubricant is then supplied to the bearing system 14, 15, 16, 17 through passages 33, 34 from a lubricant reservoir 32 in the leg 10. Sealing of the gap between the roller cutter 12 and the leg 10 may be obtained.by the bearing element 14- Normally, however, a separate sealing element is placed in the gap. As above-described the bearing element 14 is according to the invention bound by force to the roller cutter 12 v/hen being turned relative thereto. In Figs. 5 and 6 there is shown alternative connectionswhere the roller cutter 12 is bound by force as well as by shape. In the embodiment according to Fig. 5 the eccentric mounting surface 35 of the bearing element 14 is located on a coiler 37 and formed conical along a fraction of its circumference. The coni- city, then, has such a direction that the conical surface 35 and the rotational axis 28 converge toward the peri¬ phery of the drill bit. The roller cutter 12 is provided with a recess of such size as to permit insertion of the coller 37 therein. Upon a limited turning of the bearing element 14 the conical surface 35 is caused to rest against a corresponding conical surface 36 in the roller cutter 12. In the embodiment according to Fig. 6 the eccentric sur¬ face 38 is formed on a collar 39, which is located bet¬ ween the ends of the bearing element 14. When the bearing element 14 is secured to the roller cutter its eccentric surface 38 is caused to rest against a corresponding eccen¬ tric surface 40 in an inner groove in the roller cutter 12. In the illustrated embodiments the bearing element 14 is provided with two axially spaced mounting surfaces 26, 29. It is believed that a bearing element having only the eccentric mounting surface 29 would work satisfactorily. In this case, preferably, the bearing element should be shrink fitted in the roller cutter 12. In the previously described embodiments the bearing ele¬ ment is secured to the roller cutter by radially acting forces. Within the scope of the invention, however, the bearing element could be designed such that axially acting 'BUKLATT clamping forces arise. In this case a bearing element havin a cylindrical outer surface is inserted into a recess in the roller cutter to abutment against a radially extending inner surface therein. Upon insertion of the bearing ele¬ ment a lock ring is inserted into the recess outwardly of the bearing element and secured to the roller cutter, pre¬ ferably by welding. The bearing element and the lock ring are provided with one or several cooperating wedge sur¬ faces. The wedge surface is designed such that the distance between the inner surface and the wedge surface increases in the circumferential direction of the bearing element. Preferably, the wedge surface is inclined in such a way that this distance, when measured in an arbitrary section, increases from the radially innermost end toward the ra¬ dially outermost end. In all the illustrated embodiments the bearing element 14 is secured to the roller cutter 12. Alternatively, how¬ ever, the mounting surfaces of the bearing element may be provided on the inner side thereof, thus cooperating with corresponding surfaces on the bearing shaft 11. Within the scope of the invention also the other bearings in the bearing system, such as the front radial bearing 16 and the axial bearing 17, may be applied in the roller cutter or on the bearing shaft according to the improved mounting technique.

Claims: Claims 1. A rotary drill bit comprising a main body (10), at least one bearing shaft (11), a roller cutter (12) rotatab¬ ly mounted on the shaft (11), cutting means (13) carried by the roller cutter (12), bearing means (14, 15, 16, 17) for rotatably supporting the roller cutter on the shaft, said bearing means including a bearing element (14) which is connected to either of the roller cutter and the shaft, said bearing element and the one of the roller cutter and ' shaft attached thereto being provided with first cooperat¬ ing mounting surfaces (29, 30) and said bearing element being provided with a surface (41) opposed to its mounting surface (29)., c h a r a c t e r i z e d in that the distance between the mounting surface (29) of the bearing element (14) and the opposed surface (41) varies in the circumferential direction of the bearing element (14) and the cooperating mounting surfaces (29 . , 30.) are mutually designed in such a way that the bearing element (14) is wedgingly secured at said mounting surfaces (29, 30) upon a limited turning of the bearing element (14) relative to said one of the roller cutter (12) and shaft (11). 2. Rotary drill bit according to claim 1 , wherein the cooperating mounting surfaces (29, 30) are similarly de¬ signed with respect to the bearing shaft (11) in a pre¬ determined mutual angular turning position between the bearing element (14) and the roller cutter (12). 3. Rotary drill bit according to claim 1 or 2, wherein the bearing element (14) is a radial friction bearing attached to the roller cutter (12). 4. Rotary drill bit according to any of the preceding claims, wherein the bearing element (14) is bound by shape to either of the roller cutter (12) and the bearing shaft (11) in at least its secured position. 5. Rotary drill bit according to any of the preceding claims, wherein the first cooperating mounting surfaces (29, 30) are eccentric relative to the rotational axis (28) of the roller cutter, and the bearing element (14) and either of the roller cutter (12) and the bearing shaft (11) is provided with second cooperating mounting surfaces (26, 27), which are concentric relative to the rotational axis (28). 6. Rotary drill bit according to claim 5, wherein the first and second mounting surfaces (29, 26) of the bearing element (14) are separated by a transverse surface (31), thereby providing a stepped surface on the bearing element (14), the mounting surface which has the largest diameter being located nearest to the periphery of the drill bit. 7. Rotary drill bit according to claim 6, wherein the first, eccentric, mounting surface (29) of the bearing •element (14) is provided with the largest diameter. 8. Rotary drill bit according to any of claims 5-7, wherei the first, eccentric, mounting surface (35) of the bearing element (14) is conical along at least a fraction of its axial extent, said conical surface (35) and the rotational axis (28) converging toward the periphery of the drill bit. 9. Rotary drill bit according to any of claims 5-8, wherei the first and second mounting surfaces (29, 26) are of sub¬ stantially equal width. 10. Rotary drill bit according to any of claims 5-9, wherein the eccentricity of the first mounting surface (29, 30) is in the range of 0,5 mm to 3,0 mm, with preference for values in the range of 1,0 mm to 2,0 mm, and wherein the bearing element (14) is turned less than 30 mm, as counted along its mounting surfaces, preferably less than 20 mm, relative to the roller cutter (12) or the bearing shaft (11) upon turning between not secured and fully clamped position.

Inventors: KLING K
Applicants: KLING K, SANDVIK AB
Application year: 1981
Main classification: E21B10
IPC codes: E21B10