Center cutters and tunnel boring machines

Abstract

To provide a center cutter allowing an underground obstacle to be cut well.SOLUTION: A center cutter 3 placed at a rotational center of a cutter head of a tunnel excavator includes a shank 4 fixed on the cutter head and a plurality of tips 51, 52 attached on the shank 4. The tips 51, 52 are aligned on the same circumference of which center is the rotational center of the cutter head. Further, the tips 51, 52 are placed at positions in point symmetry with respect to the rotational center of the cutter head.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a center cutter provided on a cutter head of a tunnel boring machine, and to a tunnel boring machine including the center cutter. [Background technology]

[0002] Conventionally, various cutters and bits have been provided on the cutter head of a tunnel boring machine. For example, Patent Document 1 discloses a center cutter (referred to as a "rotation center bit" in Patent Document 1) that is placed at the rotation center of the cutter head and is suitable for cutting underground obstacles (referred to as an "obstacle" in Patent Document 1).

[0003] The center cutter disclosed in Patent Document 1 is semi-cylindrical and centered on the rotation center of the cutter bit. Specifically, the center cutter includes a shank (referred to as a "bit body" in Patent Document 1) with a semi-circular cross section that is fixed to the cutter head, and five tips are attached to the shank and arranged on the same circumference centered on the rotation center of the cutter head. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-141545 Summary of the Invention [Problem to be solved by the invention]

[0005] However, underground obstacles are unstable and therefore prone to movement. When the semi-cylindrical center cutter disclosed in Patent Document 1 is used to cut such underground obstacles, as shown in FIG. 8, the tip 121 of the center cutter 120 presses the underground obstacle 130 on only one side of the cutter head's rotation center 110, which can cause the underground obstacle 130 to move and tip toward a portion where the center cutter 120 is not present. This makes it difficult to cut the underground obstacle 130 well. Furthermore, the load on the tip 121 becomes uneven, which can lead to damage to the tip 121.

[0006] Therefore, an object of the present invention is to provide a center cutter that can effectively cut underground obstacles, and to provide a tunnel boring machine that includes such a center cutter. [Means for solving the problem]

[0007] In order to solve the above problem, the center cutter of the present invention is a center cutter that is placed at the center of rotation of the cutter head of a tunnel boring machine, and is characterized in that it comprises a shank that is fixed to the cutter head, and a plurality of tips attached to the shank that are arranged on the same circumference centered on the center of rotation of the cutter head, and the plurality of tips are arranged in positions that are point-symmetric with respect to the center of rotation of the cutter head.

[0008] According to the above configuration, the tips are positioned symmetrically about the center of rotation of the cutter head, so that underground obstacles can be pressed evenly around the center of rotation of the cutter head. This allows underground obstacles to be cut well. In addition, the load on the tips is uniform, which helps prevent tip damage.

[0009] The tunnel boring machine of the present invention is characterized in that it comprises the above-mentioned center cutter and a bit including a plurality of fourth tips positioned radially outward of the plurality of third tips and arranged circumferentially around the center of rotation of the cutter head, and the trajectories of the plurality of fourth tips when the cutter head rotates overlap with the trajectories of the plurality of third tips when the cutter head rotates.

[0010] If the tip trajectories do not overlap, large burrs may be created on the underground obstacle when it is cut. In contrast, if the trajectory of the third tip of the center cutter and the trajectory of the fourth tip of the bit overlap, the burrs created on the underground obstacle can be reduced. [Effects of the Invention]

[0011] According to the present invention, there are provided a center cutter that can effectively cut underground obstacles, and a tunnel boring machine that includes the center cutter. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a cross-sectional view of a part of a tunnel boring machine including a cutter head provided with a center cutter according to a first embodiment of the present invention. FIG. [Figure 2] FIG. 2 is a front view of the tunnel boring machine shown in FIG. [Figure 3] FIG. 3 is an enlarged view of a main part of FIG. 2. [Figure 4] FIG. 2 is a perspective view of a center cutter and a first bit. [Figure 5] FIG. 5 is a cross-sectional view taken along line VV in FIG. [Figure 6] FIG. 6 is a cross-sectional view taken along line VI-VI in FIG. [Figure 7] FIG. 2 is a diagram showing a state in which the center cutter of the first embodiment abuts against an underground obstacle. [Figure 8] FIG. 10 is a diagram showing a state in which a conventional center cutter abuts against an underground obstacle. [Figure 9] FIG. 2 is a rear view of the first bit. [Figure 10] FIG. 10 is a rear view of the first bit of the modified example. [Figure 11] FIG. 10 is a perspective view of a center cutter and a first bit according to a second embodiment of the present invention. [Figure 12] FIG. 12 is a cross-sectional view taken along line XII-XII in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0013] (First embodiment) 1 and 2 show a tunnel boring machine 1 including a cutter head 2 provided with a center cutter 3 according to a first embodiment of the present invention. The cutter head 2 is rotatably supported on an excavator body 11. In this embodiment, the cutter head 2 has a circular shape when viewed from the front, but the shape of the cutter head 2 is not limited to this and may, for example, be rectangular when viewed from the front.

[0014] In this embodiment, the cutter head 2 includes a disk portion 21 located in the center, a peripheral wall 23 that forms the outer circumferential surface of the cutter head 2, and a plurality of cutter spokes 22 that connect the disk portion 21 and the peripheral wall 23. However, the configuration of the cutter head 2 is not limited to this and can be changed as appropriate.

[0015] The disk portion 21 is provided with a center cutter 3 and a plurality of bits 6. A plurality of bits 6 is also provided on each cutter spoke 22. In this embodiment, as shown in Fig. 2, six bits 6 are provided on the disk portion 21. However, the number of bits 6 provided on the disk portion 21 can be changed as appropriate.

[0016] The center cutter 3 is disposed at the rotation center 20 of the cutter head 2. The bits 6 provided on the disk portion 21 are disposed so as to surround the center cutter 3, as shown in Fig. 3. Note that in Fig. 3, the positions of the tips, which will be described later, are indicated by hatching so that they can be seen at a glance (the same applies to Figs. 7 and 8).

[0017] More specifically, the bits 6 provided on the disk portion 21 include a first bit 61 closest to the center of rotation 20 of the cutter head 2, a second bit 62 second closest to the center of rotation 20 of the cutter head 2, a third bit 63 third closest to the center of rotation 20 of the cutter head 2, a fourth bit 64 fourth closest to the center of rotation 20 of the cutter head 2, a fifth bit 65 fifth closest to the center of rotation 20 of the cutter head 2, and a sixth bit 66 sixth closest to the center of rotation 20 of the cutter head 2. The sixth bit 66 is provided across the disk portion 21 and the cutter spokes 22.

[0018] 4, the center cutter 3 includes a shank 4 fixed to the disk portion 21, and a plurality of first tips 51, a plurality of second tips 52, and a plurality of third tips 53 attached to the shank 4. In addition, a center tip 50 located on the rotation center 20 of the cutter head 2 is also attached to the shank 4.

[0019] The first tip 51 and the second tip 52 are arranged on the same circumference centered on the rotation center 20 of the cutter head 2. The third tip 53 is positioned radially outward of the first tip 51 and the second tip 52.

[0020] The first tip 51 and the second tip 52 are arranged at positions that are point-symmetric with respect to the rotation center 20 of the cutter head 2. In other words, each of the first tips 51 is located on the opposite side of the corresponding second tip 52 across the rotation center 20.

[0021] In this embodiment, the number of first chips 51 and the number of second chips 52 are three. However, the number of first chips 51 and the number of second chips 52 may be two or four or more, as long as they are the same.

[0022] The shank 4 includes a columnar core portion 41 centered on the rotation center 20 of the cutter head 2 and a curved-wall-like bit portion 42 located outside the core portion 41. As shown in FIG. 5 , the cross-sectional shape of the core portion 41 is oval and centered on the rotation center 20 of the cutter head 2, with a first arc-shaped side 41A and a second arc-shaped side 41B located on both sides of the core portion 41 in the longitudinal direction. That is, the first arc-shaped side 41A and the second arc-shaped side 41B are arc-shaped sides centered on the rotation center 20 of the cutter head 2 and are point-symmetric with respect to each other with respect to the rotation center 20 of the cutter head 2. The bit portion 42 is in contact with the first arc-shaped side 41A. The cross-sectional shape of the bit portion 42 is an arc-shaped side centered on the rotation center 20 of the cutter head 2.

[0023] As shown in FIG. 4, the first chip 51 is attached to a portion of the core portion 41 along the first arcuate side 41A, and the second chip 52 is attached to a portion of the core portion 41 along the second arcuate side 41B.

[0024] The first tips 51 located at both ends of the core portion 41 are bonded to the core portion 41 while being exposed from the core portion 41. The remaining first tip 51 located in the center is bonded to the core portion 41 while being inserted into a groove formed in the core portion 41. The first tips 51 are bonded by brazing, for example.

[0025] Similarly, the second tips 52 located at both ends of the second tips 52 are bonded to the core part 41 while being exposed from the core part 41. The remaining second tip 52 located in the center is bonded to the core part 41 while being inserted into a groove formed in the core part 41. The second tips 52 are bonded by brazing, for example.

[0026] The third tips 53 are attached to the bit portion 42 in a state where they are lined up in the extending direction of the arc-shaped cross section of the bit portion 42. In other words, the third tips 53 are lined up in the circumferential direction around the rotation center 20 of the cutter head 2.

[0027] In this embodiment, the number of third chips 53 is four. However, the number of third chips 53 may be two, three, or five or more.

[0028] The third tips 53 located on both ends of the third tips 53 are joined to the bit portion 42 while being exposed from the bit portion 42. The remaining third tips 53 located on the inside are joined to the bit portion 42 while being inserted into grooves formed in the bit portion 42. The third tips 53 are joined by brazing, for example.

[0029] In this embodiment, the third tips 53 located at both ends of the third tips 53 are arranged at the same angular position as the first tips 51 located at both ends of the first tips 51. The third tip 53 located at one end is integrated with the first tip 51 located at the other end, and the third tip 53 located at the other end is integrated with the first tip 51 located at the other end. However, the third tips 53 located at both ends of the third tips 53 and the first tips 51 located at both ends of the first tips 51 may be separate bodies.

[0030] The core portion 41 of the shank 4 has a tip surface 43 facing in the traveling direction of the tunnel boring machine 1. The above-mentioned center tip 50, first tip 51, and second tip 52 protrude slightly forward (in the traveling direction of the tunnel boring machine 1) from this tip surface 43. The core portion 41 of the shank 4 also has a pair of parallel side surfaces 44 that connect both ends of the above-mentioned first arc-shaped side 41A and both ends of the second arc-shaped side 41B. Furthermore, the core portion 41 has a pair of inclined surfaces 45 that incline toward each other from the pair of side surfaces 44 toward the tip surface 43.

[0031] As shown in Fig. 6, each of the first tip 51, second tip 52, and third tip 53 is pointed in the direction of travel of the tunnel boring machine 1. In this embodiment, the shape of each of the first tip 51, second tip 52, and third tip 53 is symmetrical about the center line of the tip. Therefore, the distance a from the center of rotation 20 of the cutter head 2 to the apex of the first tip 51 (or its center if the apex is flat) is equal to the distance a from the center of rotation 20 of the cutter head 2 to the apex of the second tip 52 (or its center if the apex is flat).

[0032] The shape of the third tip 53 is substantially the same as the shapes of the first tip 51 and the second tip 52. However, the apex of the third tip 53 is located slightly behind the apex of the first tip 51 (in the opposite direction to the traveling direction of the tunnel boring machine 1) so as to be located on a tapered surface at a predetermined angle θ from the locus circle of the apex of the first tip 51. The apex of the third tip 53 may also be located on the same plane as the apexes of the first tip 51 and the second tip 52.

[0033] The distance b from the center of rotation 20 of the cutter head 2 to the apex of the third tip 53 (or its center if the apex is flat) is the sum of the distance a from the center of rotation 20 of the cutter head 2 to the apex of the first tip 51 and the width of the first tip 51 (the radial dimension centered on the center of rotation 20 of the cutter head 2).

[0034] 4, the first bit 61 is located on the opposite side of the core portion 41 of the shank 4 of the center cutter 3 from the bit portion 42. The first bit 61 includes a curved, wall-shaped shank 61a fixed to the disk portion 21, and a plurality of fourth tips 61b attached to the shank 61a.

[0035] In this embodiment, the number of fourth chips 61b is four. However, the number of fourth chips 61b may be two, three, or five or more.

[0036] 5, the cross-sectional shape of the shank 61a is an arc centered on the rotation center 20 of the cutter head 2. The radius of curvature of this arc is larger than the radius of curvature of the cross-sectional shape of the bit portion 42 of the shank 4 of the center cutter 3. In other words, the fourth tip 61b of the first bit 61 is located radially outward of the third tip 53 of the center cutter 3.

[0037] 4, the fourth tips 61b are attached to the shank 61a and lined up in the direction of extension of the arc-shaped cross section of the shank 61a. In other words, the fourth tips 61b are lined up in the circumferential direction around the rotation center 20 of the cutter head 2. If the number of fourth tips 61b is an even number, there will be no fourth tips 61b located at the center of the shank 61a, and if the number of fourth tips 61b is an odd number, there will be fourth tips 61b located at the center of the shank 61a.

[0038] The fourth tips 61b located at both ends of the fourth tips 61b are joined to the shank 61a while being exposed from the shank 61a. The remaining fourth tips 61b located on the inside are joined to the shank 61a while being inserted into grooves formed in the shank 61a. The fourth tips 61b are joined by brazing, for example.

[0039] The fourth tip 61b protrudes slightly forward (in the traveling direction of the tunnel boring machine 1) from the tip face of the shank 61a. The apex of the fourth tip 61b, like the third tip 53, is located slightly rearward of the apex of the third tip 53 (in the opposite direction to the traveling direction of the tunnel boring machine 1) so as to be located on a tapered surface at a predetermined angle θ from the locus circle of the apex of the first tip 51. Note that when the apex of the third tip 53 is located on the same plane as the apexes of the first tip 51 and the second tip 52, the apex of the fourth tip 61b may also be located on the same plane as the apexes of the first tip 51 and the second tip 52.

[0040] The width of the fourth tip 61b is equal to the widths of the first tip 51, the second tip 52, and the third tip 53. Also, as shown in FIG. 6, the difference between the distance c from the rotation center 20 of the cutter head 2 to the apex of the fourth tip 61b (or its center if the apex is flat) and the distance b from the rotation center 20 of the cutter head 2 to the apex of the third tip 53 is narrower than the widths of the third tip 53 and the fourth tip 61b. Therefore, the trajectory of the fourth tip 61b when the cutter head 2 rotates overlaps with the trajectory of the third tip 53 when the cutter head 2 rotates.

[0041] Furthermore, in this embodiment, all of the fourth tips 61b are inclined so that the gap between adjacent fourth tips 61b narrows toward the tip, as shown in Fig. 9. When the number of fourth tips 61b is odd, the fourth tips 61b located in the center of the shank 61a are not inclined, and the remaining fourth tips 61b are inclined.

[0042] In this way, if all of the fourth tips 61b are inclined except for the fourth tip 61b located at the center of the shank 61a, an external force acts on the fourth tips 61b located at both ends so as to press them against the shank 61a when the tunnel boring machine 1 moves forward. This prevents the fourth tips 61b located at both ends from peeling off. Also, since the exposed area of the shank 61a is small at the tip of the first bit 61, wear on the shank 61a can be reduced. Furthermore, since the dimensions of the shank 61a between the fourth tips 61b are large at the bases of the fourth tips 61b, the strength of the shank 61a can be ensured.

[0043] However, like a first bit 61' of a modified example shown in FIG. 10, all of the fourth tips 61b may be parallel to the plane passing through the rotation center 20 of the cutter head 2 without being inclined.

[0044] 3, the second bit 62 is disposed at a position facing one side surface 44 of the core portion 41 of the shank 4 of the center cutter 3. The second bit 62 includes a curved, wall-shaped shank 62a fixed to the disk portion 21, and a plurality of fifth tips 62b attached to the shank 62a. Note that the configuration of the second bit 62 is similar to the configuration of the first bit 61, and therefore a description thereof will be omitted.

[0045] 6, the width of the fifth tip 62b is equal to the widths of the first tip 51, the second tip 52, the third tip 53, and the fourth tip 61b. Furthermore, the difference between the distance d from the rotation center 20 of the cutter head 2 to the apex of the fifth tip 62b (or its center if the apex is flat) and the distance c from the rotation center 20 of the cutter head 2 to the apex of the fourth tip 61b is narrower than the widths of the fourth tip 61b and the fifth tip 62b. Therefore, the trajectory of the fifth tip 62b when the cutter head 2 rotates overlaps with the trajectory of the fourth tip 61b when the cutter head 2 rotates.

[0046] Although not shown in the figure, the third to sixth bits 63 to 66 are configured in the same manner as the first bit 61 and the second bit 62.

[0047] As described above, in the center cutter 3 of this embodiment, the first tip 51 and the second tip 52 are arranged in positions that are point-symmetrical with respect to the rotation center 20 of the cutter head 2, so that the underground obstacle 7 can be pressed evenly around the rotation center 20 of the cutter head 2, as shown in FIG. 7. This allows the underground obstacle 7 to be cut well. In addition, because the load on the first tip 51 and the second tip 52 is uniform, damage to the first tip 51 and the second tip 52 can also be suppressed.

[0048] However, if the shank 4 of the center cutter 3 consists of only the core portion 41 and a bit is placed near the center cutter 3, a gap that prevents cutting may occur between the center cutter 3 and the bit. In contrast, in this embodiment, the shank 4 of the center cutter 3 includes not only the core portion 41 but also the bit portion 42, and the third tip 53 is attached to the bit portion 42, so it is possible to prevent such a gap that prevents cutting.

[0049] In addition, in this embodiment, the third tips 53 located at both ends are integrated with the first tips 51 located at both ends, which reduces the number of times that the tips need to be attached to the shank 4. Furthermore, if the first tips 51 and the third tips 53 are integrated, they will be aligned in the radial direction around the rotation center 20 of the cutter head 2, which makes it easier to discharge cut earth and sand, underground obstacles, etc., radially outward.

[0050] Furthermore, in this embodiment, the core portion 41 of the shank 4 has a pair of inclined surfaces 45, so that the soil, sand, underground obstacles, etc. cut by the first tip 51 and the second tip 52 can be smoothly flowed along the inclined surfaces 45 to the periphery of the center cutter 3 (the area circled in FIG. 3). Moreover, if the first to fourth bits 61 to 64 are arranged as shown in FIG. 3, the soil, sand, underground obstacles, etc. can be smoothly flowed radially outward from the periphery of the center cutter 3, as shown by the arrows in FIG. 3.

[0051] However, if the trajectories of the tips do not overlap, large burrs may be generated on the underground obstacle when it is cut. In contrast, if the trajectory of the third tip 53 of the center cutter 3, the trajectory of the fourth tip 61b of the first bit 61, and the trajectory of the fifth tip 62b of the second bit 62 overlap as in this embodiment, the burrs generated on the underground obstacle can be reduced.

[0052] (Second embodiment) 11 and 12 show a center cutter 3A according to a second embodiment of the present invention. In this embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and redundant explanations will be omitted.

[0053] In this embodiment, the shapes of the first tip 51 and the second tip 52 are not symmetrical with respect to the center line of the tip. More specifically, the apex of each first tip 51 is located closer to the center of rotation 20 of the cutter head 2 than the center line of the first tip 51, and the apex of each second tip 52 is located farther from the center of rotation 20 of the cutter head 2 than the center line of the first tip 51. Therefore, the distance a1 from the center of rotation 20 of the cutter head 2 to the apex of the first tip 51 is different from the distance a2 from the center of rotation 20 of the cutter head 2 to the apex of the second tip 52.

[0054] In this embodiment, the apex of the third tip 53 is located slightly rearward of the apex of the second tip 52 so as to be located on a tapered surface at a predetermined angle θ from the locus circle of the apex of the second tip 52. Similarly, the apex of the fourth tip 61b is located slightly rearward of the apex of the third tip 53 so as to be located on a tapered surface at a predetermined angle θ from the locus circle of the apex of the second tip 52.

[0055] This embodiment can also achieve the same effects as those of Embodiment 1. Furthermore, with a configuration like this embodiment, the cutting pitch, which is the distance between the apexes of the tips in the radial direction of the cutter head 2, can be narrowed.

[0056] (Other embodiments) The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the gist of the present invention.

[0057] (summary) The center cutter of the present invention is a center cutter that is placed at the center of rotation of the cutter head of a tunnel boring machine, and is characterized in that it comprises a shank that is fixed to the cutter head, and a plurality of tips attached to the shank that are arranged on the same circumference centered on the center of rotation of the cutter head, and the plurality of tips are arranged in positions that are point-symmetric with respect to the center of rotation of the cutter head.

[0058] According to the above configuration, the tips are positioned symmetrically about the center of rotation of the cutter head, so that underground obstacles can be pressed evenly around the center of rotation of the cutter head. This allows underground obstacles to be cut well. In addition, the load on the tips is uniform, which helps prevent tip damage.

[0059] The shank may have a core portion having a cross-sectional shape with a first arcuate side centered on the center of rotation of the cutter head and a second arcuate side point-symmetrical to the first arcuate side with respect to the center of rotation of the cutter head, and a bit portion tangent to the first arcuate side and having an arcuate cross-sectional shape centered on the center of rotation of the cutter head. The tips may include a plurality of first tips attached to a portion of the core portion along the first arcuate side and a plurality of second tips attached to a portion of the core portion along the second arcuate side, and a plurality of third tips attached to the bit portion aligned in the direction of extension of the arcuate shape. If the shank of a center cutter consists of only the core portion and a bit is placed near the center cutter, a gap that cannot cut may occur between the center cutter and the bit. In contrast, if the shank of the center cutter includes not only the core portion but also the bit portion and a third tip is attached to the bit portion, the occurrence of such a gap that cannot cut can be prevented.

[0060] At least one of the plurality of third tips may be integral with one of the plurality of first tips. This configuration reduces the number of times that tips must be attached to the shank. Furthermore, if the first tip and the third tip are integral, they will be aligned radially around the center of rotation of the cutter head, making it easier to discharge cut earth and sand, underground obstacles, etc., radially outward.

[0061] The core portion may have a tip surface facing the traveling direction of the tunnel boring machine, a pair of parallel side surfaces connecting both ends of the first arc-shaped side and both ends of the second arc-shaped side, and a pair of inclined surfaces inclined toward each other from the pair of side surfaces toward the tip surface. With this configuration, earth and sand, underground obstacles, etc. cut by the first tip and the second tip can be made to flow smoothly around the center cutter along the inclined surfaces.

[0062] For example, each of the plurality of first tips and the plurality of second tips may be pointed in the direction of travel of the tunnel boring machine, and the distance from the center of rotation of the cutter head to the apex of the plurality of first tips may be equal to the distance from the center of rotation of the cutter head to the apex of the plurality of second tips.

[0063] The plurality of first tips and the plurality of second tips may each be pointed in the direction of travel of the tunnel boring machine, and the distance from the center of rotation of the cutter head to the apex of the plurality of first tips may be different from the distance from the center of rotation of the cutter head to the apex of the plurality of second tips. With this configuration, the cutting pitch, which is the distance between the apexes of the tips in the radial direction of the cutter head, can be narrowed.

[0064] The tunnel boring machine of the present invention is characterized in that it comprises the above-mentioned center cutter and a bit including a plurality of fourth tips positioned radially outward of the plurality of third tips and arranged circumferentially around the center of rotation of the cutter head, and the trajectories of the plurality of fourth tips when the cutter head rotates overlap with the trajectories of the plurality of third tips when the cutter head rotates.

[0065] If the tip trajectories do not overlap, large burrs may be created on the underground obstacle when it is cut. In contrast, if the trajectory of the third tip of the center cutter and the trajectory of the fourth tip of the bit overlap, the burrs created on the underground obstacle can be reduced. [Explanation of symbols]

[0066] 1. Tunnel boring machine 2 cutter heads 20 Rotation Center 3,3A Center Cutter 4 shank 41 Core 41A First arc edge 41B Second arc edge 42-bit section 43 Tip surface 44 Side 45 Slope 51 First Chip 52 Second Chip 53 Third Chip 61 1st bit 61b 4th chip

Claims

1. A center cutter disposed at the rotation center of the cutter head of a tunnel boring machine, a shank fixed to the cutter head, the shank having a core portion whose cross-sectional shape has a first arc side centered on the rotation center of the cutter head and a second arc side that is point-symmetrical to the first arc side with respect to the rotation center of the cutter head, and a bit portion that is in contact with the first arc side and has an arc-shaped cross-sectional shape centered on the rotation center of the cutter head; a plurality of first tips attached to a portion of the core portion along the first arc side and arranged on the same circumference centered on the rotation center of the cutter head; a plurality of second tips attached to a portion of the core portion along the second arc side and arranged on the same circumference centered on the rotation center of the cutter head, the plurality of first tips and the plurality of second tips are arranged at positions that are point-symmetric with respect to a rotation center of the cutter head, The center cutter has a plurality of third tips attached to the bit portion and aligned in the direction of extension of the arc shape.

2. The center cutter according to claim 1 , wherein at least one of the plurality of third tips is integral with any one of the plurality of first tips.

3. 3. The center cutter according to claim 1, wherein the core portion has a tip surface facing the direction of travel of the tunnel boring machine, a pair of parallel side surfaces connecting both ends of the first arc side and both ends of the second arc side, and a pair of inclined surfaces that incline toward each other from the pair of side surfaces toward the tip surface.

4. each of the plurality of first tips and the plurality of second tips is pointed toward a traveling direction of the tunnel boring machine; The distance from the center of rotation of the cutter head to the vertices of the plurality of first tips is equal to the distance from the center of rotation of the cutter head to the vertices of the plurality of second tips. A center cutter according to any one of claims 1 to 3.

5. each of the plurality of first tips and the plurality of second tips is pointed toward a traveling direction of the tunnel boring machine; The distance from the center of rotation of the cutter head to the vertices of the plurality of first tips is different from the distance from the center of rotation of the cutter head to the vertices of the plurality of second tips. A center cutter according to any one of claims 1 to 3.

6. The center cutter according to any one of claims 1 to 5, a bit including a plurality of fourth tips positioned radially outward of the plurality of third tips and arranged in a circumferential direction around the rotation center of the cutter head; a trajectory of the plurality of fourth tips when the cutter head rotates overlaps a trajectory of the plurality of third tips when the cutter head rotates.

Images