JP6330573B2 - Drilling tools - Google Patents

Description

  The present invention relates to a so-called double-pipe excavation tool that performs excavation using a ring bit disposed on the front end side of a casing pipe and a pilot bit inserted into the casing pipe.

  As such a double-pipe excavation tool, Patent Document 1 discloses that a ring bit is inserted at the tip of a casing pipe so that the inner and outer peripheral surfaces of the ring bit are opposed to each other, and is inserted into the casing pipe. An inner bit is attached to the tip of the transmission member, and the inner bit applies a striking force and thrust to the casing pipe and a rotational force in addition to the ring bit to drill the hole, forming a drilling hole to a predetermined depth After that, it has been proposed to remove the ring bit from the casing pipe and leave it in the excavation hole.

  Also, in Patent Document 2, a diameter expansion bit is attached to the outer periphery of the tip of a shank device that is rotated about an axis, and the diameter expansion bit is positioned in an expanded state during excavation and protrudes to the front end of the casing pipe. Thus, a so-called underreaming bit is described in which a drilling hole having a predetermined inner diameter is formed, and after completion of drilling, the diameter-enlarged bit is reduced and the shank device is collected through the casing pipe.

Japanese Patent No. 48878857 Japanese Patent No. 4501407

  Incidentally, in recent years, in a specific drilling operation using such a drilling tool, there is an increasing number of cases where a drilling hole having an inner diameter larger than an inner diameter sufficient to insert the casing pipe itself is formed. For example, when a steel pipe connection wall is buried, a casing pipe having a joint on the outer periphery of the steel pipe is inserted into the drilling hole, and the casing pipe is connected by a coupling having an outer diameter larger than the outer diameter of the steel pipe. In some cases, since the coupling is inserted into the excavation hole, an excavation hole having an inner diameter in consideration of the outer diameter up to the joint and the coupling must be formed. Furthermore, when cementing the periphery of a steel pipe to stop water in a water well or the like, a drilling hole having a larger inner diameter than the outer diameter of the steel pipe is required.

  When such a drilling hole having a large inner diameter is formed by the double pipe type drilling tool described in Patent Document 1, the outer diameter of the ring bit is increased. Since the bit is rotatably inserted with the outer peripheral surface of the rear end thereof facing the inner peripheral surface of the casing pipe, the inner diameter of the ring bit does not change, and the radial dimension increases. And since this ring bit is finally collected in the excavation hole without being collected, it results in an increase in construction cost. In addition, since the rotational force to the ring bit is transmitted by the inner bit inserted into the ring bit through the casing pipe, if the outer diameter of the ring bit becomes large, sufficient rotational force cannot be transmitted, and the drilling performance May decrease.

  On the other hand, when forming an excavation hole with a large inner diameter using the underreaming bit described in Patent Document 2, the radius from the axis of the diameter-expanded bit in the expanded state is increased. However, in order to reduce the diameter expansion bit after completion of excavation and collect the entire shank device, there is a limit to increasing the diameter expansion bit, and the load is increased to form a drilling hole with a larger inner diameter. There is also a possibility that damage may occur to the shaft that rotatably supports the diameter expanding bit. In addition, there is a limit to the amount of excavation tips installed in the diameter expansion bit, and the drilling performance decreases as the diameter of the excavation hole increases.

  The present invention has been made under such a background. When a drilling hole having a larger inner diameter than the outer diameter of the casing pipe is drilled, the drilling performance is deteriorated, damage is generated, and the construction cost is reduced. An object of the present invention is to provide a drilling tool capable of preventing an increase.

In order to solve the above-described problems and achieve such an object, the present invention provides a cylindrical casing pipe centering on the axis and a casing pipe coaxially disposed on the tip side of the casing pipe. An annular ring bit having a large outer diameter, and a pilot bit inserted through the casing pipe and into the inner periphery of the ring bit, the pilot bit being rotatable around the axis, A bit head is provided on the outer periphery of the tip of the pilot bit, and the bit head is rotatable around a center line eccentric from the axis, and when the pilot bit rotates in the tool rotation direction during excavation. The radius from the axis is expanded and supported by the pilot bit, and the ring bit is opposed to the expanded bit head. Te, engagement comprises a wall facing opposite to the wall surface facing the tool rotating direction during the drilling of this diameter was the bit head and the tool rotating direction during the drilling in contact with the tool rotating direction during the drilling An engaged portion to be engaged and a first abutting portion capable of abutting on the distal end side in the axial direction are provided.

  In such a drilling tool, the bit head provided at the outer peripheral portion of the tip end of the pilot bit expands during drilling, and the first contact portion provided in the ring bit with respect to the expanded bit head has an axis line Since the ring bit comes into contact with the front end in the direction, the ring bit can be prevented from coming off at the front end. And this ring bit is engaged in the tool rotation direction at the time of excavation with respect to the bit head whose engaged portion is expanded in diameter, so that the rotational force is transmitted from the pilot bit to the ring bit via the bit head. can do.

  Therefore, even if the outer diameter of the ring bit is made larger than the outer diameter of the casing pipe, the bit head whose radius from the axis is enlarged and transmitted is transmitted to the ring bit with a sufficient rotational force. Hole performance can be ensured. The ring bit engaged portion is engaged with the bit head whose diameter has been expanded in the tool rotation direction during excavation, so that the outer peripheral surface of the rear end of the ring bit faces the inner peripheral surface of the casing pipe. Since there is no need to insert the ring bit in a rotatable manner, the inner diameter of the ring bit can be increased, that is, the volume of the ring bit can be reduced and the required material can be reduced. Even when the ring bit is left in the excavation hole by rotating in the opposite direction, it is possible to suppress an increase in construction cost.

  On the other hand, in the pilot bit, a drill bit having a large inner diameter can be formed by the ring bit even if the radius from the axis of the bit head in the expanded state is not as large as the radius of the drill hole. It is possible to prevent the bit head from being damaged without applying a heavy load. Moreover, the installation amount of the excavation tip in the annular ring bit excavating the outer peripheral side of the excavation hole can be set relatively freely, and it is possible to prevent the drilling performance from being lowered due to the shortage of the tip.

  Here, if a concave portion recessed on the outer peripheral side is formed in the inner peripheral portion of the ring bit and this concave portion is used as the engaged portion, the volume of the ring bit can be further reduced, and the construction cost can be further reduced. Suppression can be achieved. At this time, the tip end surface of the ring bit adjacent to the recess may be the first contact portion, or a bottom surface facing the tip end in the axial direction is formed in the recess, and this is used as the first contact portion. Also good.

  In addition, in order to build the casing pipe in the excavation hole by the striking force and thrust to the axial tip provided to the pilot bit, the inner periphery of the end of the casing pipe is the same as the excavation tool described in Patent Documents 1 and 2. A small-diameter portion whose inner diameter is reduced by one step is formed on the portion, and a second abutting portion such as a step portion that can abut on the small-diameter portion from the rear end side in the axial direction on the outer peripheral portion of the pilot bit Is formed to transmit the striking force and thrust. At this time, by increasing the inner diameter of the ring bit to be equal to or larger than the inner diameter of the small-diameter portion, the volume of the ring bit can be reduced as described above, and the construction cost can be reliably suppressed.

  On the other hand, in order to transmit the striking force and thrust to the axial direction tip side to the ring bit, it may be transmitted directly from the pilot bit as in the excavation tool described in Patent Document 1, As described above, when a small diameter portion is formed on the inner periphery of the tip of the casing pipe so that the step portion of the pilot bit can be contacted, a small diameter portion having a smaller inner diameter than the small diameter portion of the casing pipe is formed on the ring bit. In this case, it is necessary to abut the pilot bit, and as described above, it may be difficult to reduce the inner diameter of the ring bit to reduce the construction cost.

  Therefore, particularly in such a case, by providing the bit head with a third abutting portion capable of abutting on the surface of the ring bit facing the rear end side in the axial direction in an expanded state, It is no longer necessary to form a small diameter portion having a smaller inner diameter than the small diameter portion of the casing pipe in the bit, so that the construction cost can be more reliably suppressed and the pilot bit can be connected via the third contact portion of this bit head. Thus, it is possible to reliably transmit the striking force and thrust from the axial direction to the tip end in the axial direction to the ring bit.

  Furthermore, in this case, the maximum radius from the axis of the third contact portion of the expanded bit head is made larger than the radius from the axis of the outer peripheral portion of the tip of the casing pipe. Can transmit striking force and thrust on the outer circumference side where drilling is performed, and when drilling holes with a larger inner diameter than the outer diameter of the casing pipe are formed, more efficient drilling can be performed At the same time, the thickness of the ring bit in the axial direction can be reduced, and the construction cost can be further reduced.

  As described above, according to the present invention, even when an excavation hole having a larger inner diameter than the outer diameter of the casing pipe is formed, the drilling performance is reduced, the construction cost is increased, or the tool is damaged. Therefore, it is possible to transmit a sufficient rotational force to the ring bit and perform efficient drilling.

It is a sectional side view which shows the state which the bit head expanded in one Embodiment of this invention. FIG. 2 is an enlarged front view of a state in which the bit head is reduced in diameter in the embodiment shown in FIG. 1 as viewed from the front end side in the axial direction (however, the casing pipe and the casing top are not shown). FIG. 2 is an enlarged front view of the state in which the diameter of the bit head is increased in the embodiment shown in FIG. 1 as viewed from the axial front end side (however, the casing pipe and the casing top are not shown). It is the enlarged front view which looked at the ring bit of embodiment shown in FIG. 1 from the axial direction front end side. It is ZZ sectional drawing in FIG.

  1 to 5 show an embodiment of an excavation tool of the present invention. In the present embodiment, the casing pipe 1 is formed in a cylindrical shape centering on the axis O with a metal material such as steel, and at the tip portion (left side portion in FIG. 1) of the casing pipe 1 is also steel or the like. A casing top 1 </ b> A formed in a multi-stage cylindrical shape is attached.

  The casing top 1 </ b> A has a constant inner diameter that is one step smaller than the inner diameter of the casing pipe 1, the outer diameter of the front end is the same as the casing pipe 1, and the outer diameter of the rear end is the casing pipe 1. It is the size which can be inserted in. The casing top 1 </ b> A is integrated coaxially with the casing pipe 1 by joining the rear end portion of the casing top 1 </ b> A from the front end side of the casing pipe 1 by welding or the like.

  By attaching the casing top 1 </ b> A in this way, a small diameter portion 1 </ b> B having a smaller inner diameter is formed on the inner peripheral portion of the tip of the casing pipe 1. The rear end surface of the small-diameter portion 1B is formed in a concave conical surface centered on the axis O that is inclined slightly toward the front end side as it goes toward the inner peripheral side.

  A pilot bit 2 is inserted into the casing pipe 1 from the rear end side (the right side in FIG. 1). The pilot bit 2 is also formed into a cylindrical shape having a multi-stage outer shape with a metal material such as steel, and the rear end portion is a small-diameter shank portion 2A. From the down-the-hole hammer H attached to the shank portion 2A A striking force directed toward the tip side in the direction of the axis O is transmitted.

  Further, a drill rod (not shown) is connected to the rear end side of the down-the-hole hammer H as necessary, and the rearmost drill rod is attached to a drilling device. From this excavator, the pilot bit 2 is transmitted through the excavating rod and the down-the-hole hammer H with a thrust directed toward the front end side in the axis O direction and a rotational force directed in the tool rotation direction T during excavation. The casing pipe 1 is also added to the rear end side as necessary and inserted into the excavation hole.

  A stepped portion having the maximum outer diameter is formed on the outer periphery of the pilot bit 2 on the tip side of the shank portion 2A, which is the second contact portion 2B of the present embodiment. The outer diameter of the second contact portion 2B is slightly smaller than the inner diameter of the casing pipe 1, and larger than the inner diameter of the small diameter portion 1B formed by the casing top 1A. Further, the distal end surface of the second contact portion 2B is formed in a convex conical surface shape that is inclined slightly toward the distal end side toward the inner peripheral side, and the inclination angle forms a concave conical surface shape. It is made equal to the inclination angle of the rear end face of the small diameter portion 1B.

  Therefore, when the pilot bit 2 is inserted from the rear end side of the casing pipe 1 and the second contact portion 2B contacts the small diameter portion 1B, the pilot bit 2 is coaxial with the casing pipe 1 and the casing top 1A and is in the axis O direction. It can be moved forward integrally with the distal end side, and can rotate relative to the casing pipe 1 and the casing top 1A around the axis O. Further, the outer diameter of the pilot bit 2 on the tip side of the second abutting portion 2B is a constant outer diameter slightly smaller than the inner diameter of the small diameter portion 1B by the casing top 1A. In a state where the contact portion 2B is in contact with the small diameter portion 1B, the tip end portion of the pilot bit 2 is formed so as to largely protrude from the tip end of the casing top 1A.

  In this manner, a housing recess 3 is formed on the outer periphery of the tip of the pilot bit 2 protruding from the tip of the casing top 1A so as to be located on the tip side of the casing top 1A. The receiving recess 3 is located on the front end side of the casing top 1A and has a bottom surface 3A that is perpendicular to the axis O facing the front end side, and extends from the inner peripheral edge of the bottom surface 3A to the front end side in parallel to the axis O. 2 and a wall surface 3B reaching the distal end surface of the pilot bit 2, and is formed so as to open to the outer peripheral surface and the distal end surface of the distal end portion of the pilot bit 2. In the present embodiment, a plurality (three) of such accommodating recesses 3 having the same shape and the same size are formed at equal intervals in the circumferential direction.

  The wall surface 3B of the receiving recess 3 is located on the opposite side of the first wall 3a of the pilot bit 2 to the outer peripheral side of the pilot bit 2 and the tool rotation direction T of the first wall 3a. A planar second wall portion 3b facing T, and a planar third wall portion 3c which is located on the tool rotation direction T side of the first wall portion 3a and faces away from the tool rotation direction T. Yes. The second and third wall portions 3b and 3c are formed such that the interval in the circumferential direction becomes larger toward the outer peripheral side, and among these, the second wall portion 3b is closer to the tool rotation direction T side toward the outer peripheral side. It extends to head.

  Further, the boundary portions of the first and second wall portions 3a and 3b and the boundary portions of the first and third wall portions 3a and 3c are in contact with the respective wall portions 3a to 3c around a straight line parallel to the axis O. A fourth wall portion 3d and a fifth wall portion 3e having a concave cylindrical surface are formed. The radius of the concave cylindrical surface formed by the fourth wall portion 3d formed at the boundary portion between the first and second wall portions 3a and 3b is the fifth radius formed at the boundary portion between the first and third wall portions 3a and 3c. It is made larger than the radius of the concave cylindrical surface which wall part 3e makes.

  Furthermore, from the tool rotation direction T side of the bottom surface 3A of each housing recess 3, it extends to the rear end side in parallel to the axis O, and reaches the outer peripheral side of the shank portion 2A beyond the second contact portion 2B. A powder discharge groove 2C is formed. The discharge groove 2C has a substantially square shape in a cross section perpendicular to the axis O and is open to the outer peripheral surface of the tip end portion of the pilot bit 2. The bottom surface of the discharge groove 2C facing the outer peripheral side of the pilot bit 2 is the second A concave curved surface is formed at the rear end of the abutting portion 2B and is slightly cut off to the outer peripheral side. A portion where the bottom surface and the bottom surface 3A of the housing recess 3 intersect with each other intersects at an obtuse angle. The chamfered surface 2D is chamfered.

  On the other hand, a mounting hole 3C having a circular cross section having a center line C parallel to the axis O is formed on the opposite side of the bottom surface 3A of each receiving recess 3 from the tool rotation direction T. The center line C of the mounting hole 3C is made to coincide with the center line of the concave cylindrical surface formed by the fourth wall portion 3d formed at the boundary between the first and second wall portions 3a and 3b. Is eccentric to the outer peripheral side. Further, the inner diameter (radius) of the mounting hole 3C is set to be approximately equal to or slightly smaller than the radius of the concave cylindrical surface formed by the fourth wall portion 3d.

  Bit heads 4 are respectively attached to the receiving recesses 3 of such pilot bits 2. In the bit head 4, a cylindrical shaft portion 4A that is slidably fitted into the mounting hole 3C and a head body 4B on the tip side of the shaft portion 4A are integrally formed of a metal material such as a steel material. The head body 4B is rotatably mounted around the center line C, and as shown in FIG. 2, the head main body 4B comes into contact with the first wall 3a and is housed in the housing recess 3 so that the radius from the axis O is reduced. As shown in FIG. 3, the head body 4B is positioned in a state where the radius from the axis O is enlarged when the head body 4B comes into contact with the second wall 3b. The rear end surface of the head main body 4B has a planar shape perpendicular to the center line C.

  The outer periphery of the shaft portion 4A has a semi-oval shape in the cross section along the center line C as shown in FIG. 1, and the cross section perpendicular to the center line C is almost as shown in FIGS. A notch 4C extending in an L shape is formed. On the other hand, at the front end portion of the pilot bit 2, the shaft portion 4A is inserted into the mounting hole 3C, the rear end surface of the shaft portion 4A is brought into contact with the bottom surface of the mounting hole 3C, and the rear end surface of the head body 4B is provided. A pin 5 is driven in a direction tangential to the mounting hole 3C in a cross section perpendicular to the axis O at a position facing the notch 4C in the direction of the axis O in a state of being in contact with the bottom surface 3A of the housing recess 3. The peripheral surface of the pin 5 is exposed in the mounting hole 3C and engaged with the notch 4C, so that the bit head 4 can be rotated around the center line C and is prevented from coming off on the tip side.

  Further, the first side surface 4a located on the extension of the outer peripheral surface of the shaft portion 4A among the side surfaces of the head body 4B is a convex cylinder centered on a center line C having an outer diameter that is flush with or slightly larger than the outer peripheral surface. It is formed in a planar shape and can be slidably contacted with the fourth wall portion 3 d of the wall surface 3 </ b> B of the housing recess 3. Further, the second and third side surfaces 4b and 4c with the first side surface 4a in between are formed in a flat shape, and the second side surface 4b is a state in which the bit head 4 has a reduced diameter as shown in FIG. The third side surface 4c faces the outer peripheral side of the pilot bit 2 and the third side surface 4c is expanded in diameter by the bit head 4 at this time. In this state, the second side surface 4b is directed in the tool rotation direction T.

  Further, the fourth side surface 4d located between the second and third side surfaces 4b and 4c on the side opposite to the first side surface 4a is a pilot bit 2 as shown in FIG. It is formed so that it may protrude on the outer periphery of this, and may be located on the cylindrical surface centering on the axis line O. FIG. The intersection ridge line portion between the fourth side surface 4d and the third side surface 4c has a diameter slightly smaller than the outer diameter of the tip portion of the pilot bit 2 in a state where the bit head 4 is reduced in diameter as shown in FIG. The head body 4B, which is formed to be chamfered by a cylindrical surface with the axis O as the center, is reduced in diameter and accommodated in the accommodation recess 3 is a cylindrical surface formed by the outer peripheral surface of the tip portion of the pilot bit 2. Located inside.

  Further, as shown in FIG. 1, the fourth side surface 4d is formed in a multi-stage shape (three stages in the present embodiment) that is uneven on the inner and outer circumferences with respect to the axis O in the direction of the center line C. The end step is protruded from the axis O to the outermost side, and the portion where the end step is formed is the third contact portion 4D in the present embodiment. The third abutting portion 4D has a flat surface perpendicular to the center line C, and a maximum radius R from the axis O when the bit head 4 is expanded. As shown in FIG. 1, it is made larger than the radius r from the axis O of the front-end | tip outer peripheral part of the casing pipe 1 and the casing top 1A.

  The intersecting ridge line portion between the fourth side surface 4d and the second side surface where the third contact portion 4D is formed is a convex having a radius substantially equal to the concave cylindrical surface formed by the fifth wall portion 3e of the housing recess 3. It is chamfered in the shape of a cylindrical surface, and as shown in FIG. The most advanced step of the fourth side surface 4d is slightly inclined so as to go to the inner peripheral side as it goes to the rear end side in the state where the bit head 4 is expanded.

  Furthermore, the fourth side surface 4d is formed so as to extend in parallel to the axis O in the middle stage located between the most advanced stage and the last stage where the third contact portion 4D is formed. . Furthermore, at the corner where the fourth side surface 4d and the second side surface 4b intersect in the middle stage, the engagement portion is cut out in a substantially L shape in a cross section perpendicular to the center line C. 4E is formed.

  The engagement portion 4E faces the first wall surface 4e facing the outer peripheral side in the state where the bit head 4 is expanded, the second wall surface 4f facing the tool rotation direction T, and the distal end side of the third contact portion 4D. It has a bottom surface 4g that is flush with the surface, and a ceiling surface 4h that faces the rear end side in parallel with the bottom surface 4g. Similarly, the first wall surface 4e is positioned on a cylindrical surface centered on an axis O having an outer diameter slightly larger than the second contact portion 2B of the pilot bit 2 in a state where the diameter of the bit head 4 is expanded. 2 wall surface 4f is formed so that it may go to the tool rotation direction T side slightly toward the outer peripheral side.

  Further, the intersecting ridge line portion between the foremost step of the fourth side surface 4d and the tip end surface of the head body 4B is centered so as to form a truncated cone surface with the axis O as the center when the bit head 4 is expanded in diameter. It is set as the inclined surface which goes to the front end side as it goes to the line C side. Further, the intersection ridge line portion between the front end surface and the outer peripheral surface of the pilot bit 2 also has a truncated cone surface shape with the axis O as the center, except for the portion notched by the receiving recess 3, and is on the inner peripheral side. It is set as the inclined surface which inclines toward the front end side as it goes.

  Furthermore, the tip surfaces of the head body 4B of the pilot bit 2 and the bit head 4 excluding these inclined surfaces are flat surfaces perpendicular to the axis O and the center line C, respectively. Further, the length of the head main body 4B in the direction of the center line C is equal to the depth from the bottom surface 3A of the receiving recess 3 to the tip end surface of the pilot bit 2, so that the bit head 4 is received in the receiving recess 3. In this state, the pilot bit 2 and the front end surface of the head body 4B are flush with each other.

  A plurality (many) of a hard metal or the like harder than the steel material or the like forming the pilot bit 2 or the bit head 4 is provided on the front end surface and each inclined surface of the head body 4B of the pilot bit 2 and the bit head 4. The excavation tip 6 is provided. These excavation tips 6 are formed by integrally forming, for example, a hemispherical head and a cylindrical body protruding from the tip surface and the inclined surface, and are formed perpendicular to the tip surface and the inclined surface, respectively. The body is fixed by press fitting, shrink fitting, cold fitting or brazing into the circular hole.

  Further, an annular ring bit 7 is disposed on the front end side of the casing pipe 1 so as to be coaxial with the axis O thereof. The ring bit 7 is also formed in a circular plate shape from a metal material such as steel, and the front and rear end faces facing the direction of the axis O are perpendicular to the axis O. However, the intersection ridge line between the tip and the outer peripheral surface is The inclined surface has a truncated cone shape with the axis O as the center. Similarly to the pilot bit 2 and the bit head 4, an excavation tip 6 made of a hard material such as a cemented carbide is provided on the outer peripheral portion of the inclined surface and the tip surface so as to protrude vertically.

  Further, the outer diameter of the ring bit 7 is larger than the outer diameters of the casing pipe 1 and the casing top 1 </ b> A and larger than the outer diameter of the expanded bit head 4. Further, the inner diameter of the ring bit 7 is slightly larger than the outer diameter of the second abutting portion 2B of the pilot bit 2, so that it is larger than the inner diameter of the small diameter portion 1B formed in the casing pipe 1 by the casing top 1A. In addition, the outer diameter of the bit head 4 in the expanded state is smaller than the outer diameter of the bit head 4 so that the first wall surface 4e of the engaging portion 4E can be fitted. Further, the thickness of the ring bit 7 in the direction of the axis O is made smaller than the width between the inner and outer diameters and slightly smaller than the distance between the bottom surface 4g of the engaging portion 4E and the ceiling surface 4h. Yes.

  Further, the inner periphery of the ring bit 7 is formed with three recesses recessed on the outer periphery side at equal intervals in the circumferential direction, the same number as the bit head 4, and these recesses are formed as shown in FIG. The engaged portion 4E and the engaged portion 7A engaged in the tool rotation direction T during excavation. The engaged portion 7A includes a first wall surface 7a that recedes from the inner peripheral portion of the ring bit 7 to the outer peripheral side and faces the inner peripheral side, and a tool rotation direction T extending from the first wall surface 7a to the inner peripheral portion. A second wall surface 7b facing the opposite side and a third wall surface 7c facing the tool rotation direction T are provided, and in this embodiment, the ring bit 7 is formed so as to penetrate in the axis O direction.

  Of these, the first wall surface 7a is located on a cylindrical surface centered on the axis O, and the radius from the axis O is the most advanced of the fourth side surfaces 4d facing the outer peripheral side of the expanded bit head 4. The radius is slightly larger than the radius from the axis O of the middle and middle stages, and smaller than the radius R of the third contact portion 4D. In addition, the circumferential length of the first wall surface 7a is slightly longer than the length of the middle circumferential length of the fourth side surface 4d excluding the engaging portion 4E.

  The second and third wall surfaces 7b and 7c extend in the tool rotation direction T toward the outer peripheral side, and the angle formed by the second wall surface 7b with respect to the radial direction with respect to the axis O increases. The second wall surface 4f of the engagement portion 4E of the diameter bit head 4 is made equal to the angle formed with respect to the radial direction with respect to the axis O. Further, the third wall surface 7c has a center line C of the mounting hole 3C in the receiving recess 3 of the pilot bit 2 in a state where the engaged portion 7A is engaged with the engaging portion 4E as shown in FIG. It is formed so as to form a concave cylindrical surface centered on.

  The pilot bit 2 is provided with a bottomed supply hole 8 along the axis O from the rear end of the shank portion 2A to the center of the receiving recess 3 in the direction of the axis O, and the down-the-hole hammer H Compressed air can be supplied from the side. From the supply hole 8, the first to third blow holes 8 </ b> A to 8 </ b> C, each having a smaller diameter than the supply hole 8, are obliquely branched so as to go to the distal end side toward the outer peripheral side.

  The first blow hole 8A opens to the distal end side of the second abutting portion 2B on the outer peripheral surface of the distal end portion of the pilot bit 2, and a fourth blow hole 8D having a smaller diameter extends from the first blow hole 8A. It branches in parallel with O and opens in the center of the bottom surface of the mounting hole 3C. Further, the second blow hole 8B branches from the first blow hole 8A on the tip side and opens substantially perpendicular to the inclined surface 2D between the bottom surface of the dust discharge groove 2C and the bottom surface 3A of the housing recess 3. doing. Further, the third blow hole 8C has a larger diameter than the first and second blow holes 8A, 8B, branches at the tip of the supply hole 8, and the fifth wall 3e of the first wall 3a of the housing recess 3. Open to the side.

  In such an excavation tool, the pilot bit 2 is inserted from the rear end side of the casing pipe 1 in a state where the diameter of the bit head 4 is reduced and the head main body 4B is accommodated in the accommodation recess 3, and the second abutting portion 2B Is positioned in the direction of the axis O when it contacts the rear end surface of the casing top 1A. Next, with the head main body 4B being accommodated, the ring bit 7 is inserted into the distal end portion of the pilot bit 2 from the distal end side by aligning the circumferential position of the engaged portion 7A with the accommodating recess 3 as shown in FIG. In the direction of the axis O, the head main body 4B is disposed at the position of the engaging portion 4E.

  Then, if the ring bit 7 is rotated relative to the side opposite to the tool rotation direction T during excavation while the bit head 4 is expanded in diameter from this state, the engagement of the expanded bit head 4 as shown in FIG. The second wall surface 4f in the joint portion 4E is engaged by being brought into close contact with and in contact with the second wall surface 7b in the engaged portion 7A of the ring bit 7, and the third side surface 4c in the head body 4B is in the housing recess 3. The ring bit 7 can be integrally rotated in the tool rotation direction T with respect to the pilot bit 2 and the bit head 4 by being brought into contact with and supported by the second wall portion 3b.

  Further, in the direction of the axis O, as shown in FIGS. 1 and 3, the portion on the tool rotation direction T side of the engaged portion 7A in the tip surface of the ring bit 7 is slightly on the ceiling surface 4h of the engaging portion 4E. The ring bit 7 is prevented from coming off to the tip side by being able to abut against each other with a gap. That is, in this embodiment, the portion of the engaged portion 7A on the tool rotation direction T side of the front end surface of the ring bit 7 can abut on the front end side in the axis O direction with respect to the enlarged bit head 4. The first abutting portion 7B is used. Further, the bottom surface 4g of the engaging portion 4E and the surface facing the front end side of the third contact portion 4D flush with the engaging portion 4E are in contact with the rear end surface of the ring bit 7 and supported on the front end side, whereby the casing pipe 1 and the ring bit 7 can be advanced together with the pilot bit 2 and the bit head 4 toward the front end side in the direction of the axis O.

  Accordingly, from this state, the down-the-hole hammer H transmits the striking force toward the front end side in the direction of the axis O to the pilot bit 2 and the bit head 4 and the ring bit 7 via the third contact portion 4D. Drilling work is carried out by the excavation tip 6 provided on the tip surface of the pilot bit 2, bit head 4 and ring bit 7 by transmitting thrust and rotational force in the tool rotation direction T from the excavator. The casing pipe 1 is inserted into the formed excavation hole. During the drilling, compressed air is ejected from the supply hole 8 through the first to fourth blow holes 8A to 8D, and the dust produced by the excavation tip 6 is passed through the casing pipe 1 from the discharge groove 2C. While discharging, the dusting into the mounting hole 3C and the small diameter portion 1B is prevented.

  After the excavation hole is formed to a predetermined depth in this way, in the excavation tool having the above configuration, the excavator rotates the pilot bit 2 in the direction opposite to the tool rotation direction T during excavation. Then, the diameter of the bit head 4 is reduced as shown in FIG. 2 by friction of the head body 4B with the excavation hole and the third wall surface 7c of the engaged portion 7A. By pulling the down-the-hole hammer H from the casing pipe 1, the pilot bit 2 and the bit head 4 can be recovered leaving the ring bit 7 in the excavation hole.

  Thus, according to the excavation tool having the above-described configuration, the rotational force in the tool rotation direction T is transmitted from the head body 4B of the bit head 4 whose diameter has been expanded to the engaged portion 7A of the ring bit 7. The rotational force can be efficiently transmitted at a position further away from the axis O that is the center of rotation of the bit 2 and the bit head 4. For this reason, even when a drilling hole having a larger inner diameter than the outer diameter of the casing pipe 1 is formed, a sufficient rotational force can be transmitted to the ring bit 7 to ensure drilling performance.

  In addition, in this embodiment, as shown in FIG. 1, the pilot bit 2 and the bit head 4 protrude one step toward the tip side of the ring bit 7, so that the inner periphery is formed by the excavation tip 6 of the pilot bit 2 and the bit head 4. The excavation tip 6 of the ring bit 7 excavates the outer peripheral portion of the excavation hole which has been easily crushed by drilling the portion. For this reason, more efficient drilling can be performed while suppressing the load on the ring bit 7. However, the front end surface of the pilot bit 2 and the bit head 4 and the front end surface of the ring bit 7 may be flush with each other, and the front end surface of the ring bit 7 protrudes from the front end surface of the pilot bit 2 and the bit head 4. It may be.

  Further, since the outer peripheral side of the excavation hole is drilled by the ring bit 7, in the pilot bit 2 and the bit head 4, it is necessary to increase the radius from the axis O of the enlarged head main body 4B to the inner diameter of the excavation hole. Therefore, the burden on the shaft portion 4A of the bit head 4 and the like can be reduced and damage can be prevented. Further, since the ring bit 7 has an annular shape, for example, as shown in FIG. 3, a drilling tip 6 is disposed in addition to the range where the bit head 4 whose diameter is increased in the circumferential direction is located. In addition, the installation amount and position of the excavation tip 6 can be set, and a decrease in drilling performance due to a partial deficiency of the excavation tip 6 can also be prevented.

  On the other hand, in the ring bit 7, the engaged portion 7A is engaged with the bit head 4 having an enlarged diameter as described above, and is supported so as to be integrally rotatable in the tool rotation direction T, and a rotational force is transmitted. Therefore, it is not necessary to support the casing pipe 1 and the inner diameter can be increased. For this reason, the volume of the ring bit 7 can be reduced to reduce the necessary material such as a steel material, and an increase in construction cost can be suppressed even when the ring bit 7 is left in the excavation hole after the excavation is completed.

  Further, as described above, the inner peripheral portion of the excavation hole is drilled by the excavation tip 6 of the pilot bit 2 and the bit head 4, so that the diameter is increased in the radial direction from the axis O in this embodiment. As shown in FIGS. 1 and 3, it is not necessary to provide the excavation tip 6 on the ring bit 7 in the range where the excavation tip is provided on the front end surface of the head body 4 </ b> B of the bit head 4. For this reason, it can be avoided that the ring bit 7 remaining in the excavation hole is provided with more excavation tips 6 made of an expensive cemented carbide than necessary, and the cost can be reduced.

  Furthermore, in this embodiment, the recessed part dented toward the outer peripheral side is formed in the inner peripheral part of the ring bit 7, and it is set as the to-be-engaged part 7A. In this regard, for example, it is also possible to form a convex portion as an engaged portion on the front end surface of the ring bit 7 and engage the head body 4B of the bit head 4 whose diameter is enlarged to the convex portion in the tool rotation direction T. However, in that case, the load due to the rotational force may be concentrated on the convex portion to cause damage, and the volume of the ring bit 7 is increased only by the convex portion, which increases the material cost. On the other hand, in this embodiment, while the rotational force can be received by the ring ring 7 itself, the volume and cost of the ring bit 7 can be further reduced.

  In the present embodiment, a portion of the distal end surface of the ring bit 7 adjacent to the tool rotation direction T side of the engaged portion 7A formed as a concave portion recessed from the inner peripheral portion toward the outer peripheral side is engaged. The striking force transmitted from the pilot bit 2 via the bit head 4 is, for example, a first abutting portion 7B that is opposed to the ceiling surface 4h of the portion 4E and is capable of abutting on the front end side in the axis O direction. Thus, even if the ring bit 7 collides with the ceiling surface 4h, the impact can be received by the entire thickness of the ring bit 7, and the occurrence of damage or the like can be prevented. However, the first contact portion 7B may be formed by forming a bottom surface facing the front end side of the recess so as to face the ceiling surface 4h.

  On the other hand, also in this embodiment, the casing pipe 1 is inserted into the excavation hole by the striking force and thrust force applied to the pilot bit 2 in the excavation hole. A casing top 1A is attached to the tip of 1 to form a small diameter portion 1B, and the second contact portion 2B of the pilot bit 2 is brought into contact with this small diameter portion 1B to transmit the striking force and thrust. . However, since the inner diameter of the ring bit 7 is increased in this embodiment with respect to the inner diameter of the small-diameter portion 1B, the inner diameter of the ring bit has to be reduced as described above. The construction cost can be surely reduced as compared with the excavation tool. The inner diameter of the ring bit 7 may be equal to the small diameter portion 1B.

  Furthermore, in this embodiment, the casing pipe 1 is provided with the small diameter portion 1B to transmit the striking force and thrust, whereas the pilot bit 2 transmits the striking force and thrust to the ring bit 7. The third contact portion that can contact the rear end surface of the ring bit 7 in a state where the diameter of the bit head 4 is expanded instead of being directly transmitted from the pilot bit 2 as in the excavation tool described in Patent Document 1. 4D is provided to transmit the striking force and the thrust from the third contact portion 4D. For this reason, when the small diameter portion 1B is provided as described above, it is not necessary to further reduce the inner diameter of the ring bit 7, and the construction cost can be more reliably reduced.

  Further, in the present embodiment, when the impact force and the thrust are transmitted to the ring bit 7 from the third contact portion 4D provided on the bit head 4 in this way, the third contact of the bit head 4 in the expanded state is achieved. The maximum radius R from the axis O of the portion 4D is set to be larger than the radius r from the axis O of the outer peripheral end of the casing pipe 1, that is, the radius of the casing top 1A. For this reason, it is possible to more reliably transmit the striking force and thrust to the ring bit 7 on the outer peripheral side where the hole is drilled, and excavation with a larger inner diameter than the outer diameter of the casing pipe 1 as in this embodiment. Even when holes are formed, it is possible to perform even more efficient drilling.

  When the impact force and thrust on the ring bit 7 are transmitted from the third abutting portion 4D having a radius R larger than the radius r of the outer peripheral portion of the casing pipe 1 as described above, Even if the thickness of the bit 7 in the direction of the axis O is made smaller than the width between the inner and outer diameters of the ring bit 7 as in the present embodiment, for example, the inner diameter is reliably increased without impairing the strength and rigidity of the ring bit 7. Drilling holes can be formed. Therefore, according to the present embodiment, it is possible to further reduce the volume of the ring bit 7 and to further suppress the construction cost.

DESCRIPTION OF SYMBOLS 1 Casing pipe 1A Casing top 1B Small diameter part 2 Pilot bit 2B 2nd contact part 2C Discharge groove 3 Accommodating recess 3C Mounting hole 4 Bit head 4A Shaft part 4B Head main body 4D 3rd contact part 4E Engagement part 5 Pin 6 Drilling tip 7 Ring bit 7A Engagement part 7B First contact part 8 Supply hole O Axis line of casing pipe 1 T Tool rotating direction during excavation C Center line of mounting hole 3C H Down the hole hammer R Expanded bit The maximum radius from the axis O of the third contact portion 4D of the head 4 r The radius from the axis O of the outer peripheral portion of the tip of the casing pipe 1

Claims (5)

A cylindrical casing pipe centering on the axis, an annular ring bit having an outer diameter larger than that of the casing pipe arranged coaxially on the tip side of the casing pipe, and the ring bit passing through the casing pipe A pilot bit inserted through the inner periphery of the
The pilot bit is rotatable around the axis, and a bit head is provided on the outer periphery of the pilot bit.
The bit head is rotatable about a center line that is eccentric from the axis, and when the pilot bit rotates in the tool rotation direction during excavation, the radius from the axis increases and is supported by the pilot bit. And
The ring bit faces the opposite side of the tool rotation direction at the time of excavation where the wall surface facing the tool rotation direction at the time of excavation of the diameter-expanded bit head comes into contact with the bit head having an enlarged diameter. characterized in that the engaged portion which is provided with a wall surface to engage in the tool rotating direction during the drilling, and a first contact portion which is contactable to the distal end side of the axial direction are provided And drilling tools.   The excavation tool according to claim 1, wherein a concave portion that is recessed toward the outer peripheral side is formed in an inner peripheral portion of the ring bit, and the concave portion serves as the engaged portion.   A small-diameter portion whose inner diameter is reduced by one step is formed on the inner peripheral portion of the tip of the casing pipe, and a rear end outer peripheral portion of the pilot bit is provided on the outer periphery of the pilot bit. The excavation tool according to claim 1 or 2, wherein two abutting portions are formed, and an inner diameter of the ring bit is equal to or greater than an inner diameter of the small diameter portion.   The bit head is provided with a third abutting portion capable of abutting on a surface of the ring bit facing the rear end side in the axial direction in an expanded state. The excavation tool according to any one of Items 3.   The maximum radius from the axis of the third contact portion of the expanded bit head is larger than the radius from the axis of the outer peripheral portion of the tip of the casing pipe. Drilling tools.

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