DRILL BIT AND ROLLER CUTTER FOR SAID DRILL BIT

Abstract: The invention relates to a drill bit (10) having saddles (12) for a number of roller cutters (16-38) having two along the circumference of the roller cutter extending rows (41,42) of cutting means, said rows (41,42) being displaced internally in the axial direction of the roller cutter. A saddle (12) and adherent roller cutter (20) are so designed that the roller cutter is reversibly mountable in the saddle (12). The rows (41,42) of cutting means are locaed on each side of the transverse symmetry plane (45) of the roller cutter (16-32) . The distance (B) of the first row (42) is bigger than the distance (A) between the second row (41) and the symmetry plane (45) . The rows (41,42) of cutting means of a roller cutter (20) are arranged to move along a first series of circles (46,47) when the roller cutter (20) is mounted in a first position in its saddle (12) and along a second series of circles (48,49) when the roller cutter (20) is mounted in a reversed position in the saddle (12) in relation to said first position.

Description: The present invention relates to a drill bit comprising a body whereon saddles are mounted for a number of roller cutters, said roller cutters having rows of cutting means, e g hard metal inserts, extending along the circumference of the roller cutter, said rows being spaced in the axial direction of the roller cutter, the drill bit being provided with a first and a second collection of saddles, the first collection carrying a first set of roller cutters and the second collection carrying a second set of roller cutters identical with the roller cutters of said first set, the roller cutters of both sets being cylindrical and reversibly mountable in their saddles and exhibiting two rows of cutting means located on either side of a centre plane, wherein for the roller cutters of both sets the distance B between the first row of cutting means and a centre plane is longer than the distance A between the second row of cutting means and the centre plane. The invention also relates to a method of adjusting the cutting pattern of said drill bit. When drilling with such a drill bit the hardness of the rock varies between different drill holes. An aim of the present invention is to optimize the drilling in order to achieve the highest possible penetration rate regardless of the hardness of the rock formation. This means that in softer rock formations a bigger distance between the rows should be used than in harder rock formations. At the same time the invention intends to make it possible to optimize the drilling without having to change the type of roller cutters of the drill bit. These and other aims have been achieved by giving the invention the characteristics of the appending claims. From DE-A-2838154 a drill bit for raise boring is previously known. Said drill bit has a roller cutter having two rows of cutting means located on opposite sides of a centre plane, said rows of cutting means being located at different distances from said centre plane. However, said document is silent about any adjustment of the cutting pattern of said drill bit. From DE-A-3001788 a drill bit is previously known. In said drill bit the distance between the rows of the cutting means can be varied by exchange of a roller cutter of a first collection for a roller cutter of a second collection. This known drill bit arrangement however requires two collections of roller cutters while the present invention intends to make it possible to vary the distance between rows by one single type of roller cutters. From DE-A-1805336 a drill bit is previously known, said drill bit makes it possible to vary the distane between rows by removing a supporting arm carrying a number of roller cutters and thus also removing said roller cutters. In this known drill bit the roller cutters are not selectively exchangeable for one another. The invention will be described more in detail in the following, reference being made to the accompanying drawings, disclosing an embodiment by way of example. The embodiment is only intended to illustrate the invention that can be varied within the scope of the claims. In the drawings Fig. 1 shows a top view of a drill bit according to the invention. Fig. 2 shows a vertical projection of the drill bit in Fig. 1, the roller cutters have been rotated from their positions in Fig. 1 and superpositioned relative each other in order to illustrate the profile that the drill hole is given. Fig. 3 shows a top view of the drill bit in Fig. 2, however only two roller cutters are disclosed, illustrating the circles along which the cutting means of said roller cutters move when the drill bit is rotating. Fig. 4 shows in detail the superposition in Fig. 2 of the roller cutters and thus the distance between the rows that is achieved during drilling. Figs. 5-8 correspond to Figs. 1-4 with the exception that the distance between the rows is bigger. Fig. 9 illustrates the superposition of the roller cutters in a drill bit having the same distance between the rows as the drill bit according to Figs. 5-8 with the exception that there are a smaller number of roller cutters. Fig. 10 shows a roller cutter according to the invention. Fig. 11 shows the roller cutter of Fig. 10 in a reversed position. The drill bit in the drawings generally designated by the reference number 10 comprises a frame 11. A number of roller cutters 13-38, in the disclosed embodiment twenty-six, are mounted in brackets or saddles, the saddles 12 for the roller cutters 16-31 being identical to each other. When drilling the drill bit 10 is by means of a raise boring or tunnelling machine pressed towards the frontal face 39 of the raise or tunnel. In the disclosed embodiment the roller cutter 13 is of a type disclosed in DE,B, 3521159 and the roller cutters 14, 15 have a conventional conical design. The roller cutters 13-15 are intended to machine the portion of the frontal face 39 that is closest to the rotational axis 40 of the drill bit. The roller cutters 16-38 are designed with two rows 41,42 of cutting means, e g hard material inserts, said rows being displaced in the axial direction of the roller cutter. The roller cutters 16-38 are cylindrical and their shaft journals 43, 44 are identical. This means that the roller cutters are reversibly mountable in their saddles 12 and that the cutting means of the roller cutters are engaging the frontal face 39 even if the roller cutters are reversed. According to the invention the rows 41, 42 of cutting means are located on each side of the transverse centre plane 45 of the roller cutter 16-38. The distance B between one row 42 and the centre plane 45 is longer than the distance A between a second row 41 and the centre plane 45. In the prferred embodiment the distance B is essentially three times the distance A. This means that the row 41 of cutting means, if the roller cutter 16-38 is reversed, will cut a groove that is located halfway between the grooves that are cut by the rows 41, 42 of cutting means before the roller cutter 16-38 was reversed, see Figs. 10 and 11. The rows of cutting means of the roller cutters 13-38 are arranged to move along concentric circles when the drill bit 10 rotates around the axis 40 of rotation. For the sake of simplicity only two roller cutters 19, 20 are disclosed in Fig. 3, the rows 41', 42' of cutting means of the roller cutter 20 move along a first series of circles 46, 47 and the rows 41", 42" of cutting means of the roller cutter 19 move along a second series of circles 48, 49. The saddles 12 of the roller cutters 19, 20 are located at such distance from the axis 40 of rotation that, in the preferred embodiment, the distance B is three times the distance A, the circles 46-49 being located at the same distance from the axis 40 of rotation and in the order 48, 47, 49, 46 from said axis. In Fig. 4 is disclosed four at radial distance from the centre axis 40 adjacent each other located roller cutters 19-22, said roller cutters being superpositioned, the roller cutters 19 and 21 being mounted in the position of Fig. 11 and the roller cutters 20 and 22 in the position of Fig. 10. As can be seen from Fig. 4 each of the rows 41, 42 of cutting means on the roller cutters 20, 22 moves along an own circle in the first series of circles when the drill bit is rotating and that each of the rows 41, 42 of cutting means on the roller cutters 19, 21 moves along an own circle in the second series of circles, said distance between two consecutive circles being 2A. In the drill bit of Fig. 1 the saddles for the roller cutters 16-32 are arranged in such a way that the distance between the rows can be varied by these roller cutters, said each row of cutting means on all roller cutters 16-32 move along an own circle in the first and the second resp series of circles. The drill bit of Fig. 1 is provided with a first and a second collection internally alike saddles 12, the first collection of saddles carrying the roller cutters, 16, 18, 20, 22, 24, 26, 28, 30 and 32 and the other collection of saddles carrying the roller cutters 17, 19, 21, 23, 25, 27, 29 and 31. These saddles are consequently located at such distance from the axis 40 of rotation that the rows 41, 42 of cutting means on the roller cutters 16, 18, 20, 22, 24, 26, 28, 30 and 32 move along the first series of circles when these roller cutters are mounted in the first position, i e in the position of Fig. 10, and the rows 41, 42 of cutting means on the roller cutters 17, 19, 21, 23, 25, 27, 29 and 31 move along the other series of circles when the last-mentioned roller cutters are mounted in the other position, i e the position of Fig. 11. In Fig. 5 it is disclosed how the roller cutters 16, 18, 20, 22, 24, 26, 28, 30 and 32 have been reversed from the first position of Fig. 10 to the second position of Fig. 11. As can be seen from Fig. 8, the four adjacent located roller cutters 19-22 being superpositioned, the distance between two consecutive circles are A + B or 4A, the rows 41, 42 of cutting means moving along said circles. This means that each of the rows 41, 42 of cutting means of the roller cutters 16, 18, 20, 22, 24, 26, 28, 30 and 32 will move along circles that are included in that series of circles along which the cutting means of the roller cutters 17, 19, 21, 23, 25, 27, 29 and 31 are moving. This is illustrated in Fig. 7 disclosing for the sake of clearness only the roller cutters 19, 20. The distance between rows of the drill bit according to Fig. 5 is thus twice as big as the distance between rows of the drill bit according to Fig. 1, the number of rows of cutting means that are in engagement with the frontal face 39 being unchanged. Alternatively it is possible to achieve the bigger distance between rows according to Fig. 8 by removing the roller cutters 16, 18, 20, 22, 24, 26, 28, 30 and 32. In order to achieve both as few roller cutters as possible and also to counterbalance the drill bit 10 the roller cutters 15, 34 and 36 are preferably deleted. This means that only one row 41, 42 of cutting means will move along a given circle. The invention can also have application for other types of roller cutters, e g roller cutters having cutting means in the shape of steel discs. Also the invention can be applied in raise boring when a pre-drilled pilote hole is reamed by a drill bit having a large diameter. In such a drill bit no centre roller cutters 13, 14, 15 are needed.

Claims: Drill bit (10) comprising a body whereon saddles (12) are mounted for a number of roller cutters (16-32), said roller cutters (16-32) having rows (41,42) of cutting means, e g hard metal inserts, extending along the circumference of the roller cutter (16-32), said rows (41,42) being spaced in the axial direction of the roller cutter (16-32), the drill bit (10) being provided with a first and a second collection of saddles (12), the first collection carrying a first set of roller cutters (16-32 even numbers) and the second collection carrying a second set of roller cutters (17-31 uneven numbers), identical with the roller cutters (16-32 even numbers) of said first set, the roller cutters (16-32) of both sets being cylindrical and reversibly mountable in their saddles (12) and exhibiting two rows (41,42) of cutting means located on either side of a centre plane (45), wherein for the roller cutters (16-32) of both sets the distance B between the first row (42) of cutting means and a centre plane (45) is longer than the distance A between the second row (41) of cutting means and the centre plane (45), characterized in that the distance in radial direction of the drill bit (10) between a saddle (12) in the first collection and a radially adjacent saddle (12) in the second collection is equal to the distance between the rows (41,42) of cutting means on each roller cutter (16 - 32) of both sets. Drill bit as in claim 1, characterized in that the roller cutters (16-32) of both sets either face away from the centre line (40) of the drill bit (10) or toward it. Drill bit as in claim 1, characterized in that the roller cutters of one set face away while the other set faces toward the centre line (40) of the drill bit (10). Drill bit according to any of the previous claims, characterized in that for all roller cutters (16-32) the distance (B) between the first row (42) and the centre plane (45) is essentially three times the distance (A) between the second row (41) and the centre plane (45). A method of adjusting the cutting pattern of a drill bit (10) according to anyone of claims 1 - 4, characterized in that said method comprises the steps of reversing the roller cutters of one set from a position facing toward the centre line (40) of the drill bit to a position facing away from the centre line of the drill bit, or reversing the roller cutters of one set from a position facing away from the centre line of the drill bit to a position facing toward the centre line of the drill bit, while the roller cutters of the other set are maintained in their positions, the saddles (12) not being moved.

Inventors: MATTSSON, MICHAEL, TUNELL, LARS-ERIK
Applicants: SANTRADE LTD.
Application year: 1986
Main classification: E21B10
IPC codes: E21B10