JP6589374B2 - 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. This application claims priority about Japanese Patent Application No. 2014-167601 for which it applied to Japan on August 20, 2014, and uses the content here.

  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. And the engaged portion that is engaged with the tool rotating direction during the drilling, a first contact portion which is contactable against increased diameter was the bit head to the tip side in the axial line direction provided Te A small-diameter portion whose inner diameter is reduced by one step is formed at the inner peripheral portion of the front end of the casing pipe, and the outer peripheral portion of the pilot bit is abutted against the small-diameter portion from the rear end side in the axial direction. A contactable second contact portion is formed, and a third contact portion capable of contacting the surface of the ring bit facing the rear end side in the axial direction is provided at the tip of the casing pipe. It is characterized by.

  In such a drilling tool, the bit head provided at the outer peripheral portion of the tip 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.

  In addition, a small-diameter portion whose inner diameter is reduced by one step is formed on the inner peripheral portion of the front end of the casing pipe, and a second end that can contact the small-diameter portion from the rear end side in the axial direction is formed on the outer peripheral portion of the pilot bit. An abutting portion is formed, and the striking force and thrust toward the tip end in the axial direction applied to the pilot bit are applied to the casing pipe through this small diameter portion in the same manner as the drilling tool described in Patent Documents 1 and 2. The casing pipe is inserted into the excavation hole. Further, since the third abutment portion that can abut against the surface of the ring bit facing the rear end side in the axial direction is provided at the front end portion of the casing pipe, the impact force transmitted to the casing pipe in this way. And the thrust can be reliably transmitted to the ring bit.

  Therefore, even if the outer diameter of the ring bit is made larger than the outer diameter of the casing pipe, a sufficient rotational force can be transmitted to the ring bit by the bit head whose radius from the axis is enlarged. At the same time, the striking force and thrust can be reliably transmitted from the casing pipe to the ring bit, thereby ensuring the drilling performance.

  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. Therefore, for example, the inner diameter of the ring bit can be made larger than the inner diameter of the small diameter portion within a range not exceeding the outer diameter of the third contact portion. For this reason, since the volume of the ring bit can be reduced to reduce the necessary material, the construction cost can be reduced even when the bit head is rotated in the opposite direction after excavation to leave the ring bit in the excavation hole. The increase can be suppressed.

  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. In this case, for example, the front end surface of the ring bit adjacent to the concave portion is used as the first contact portion, and the diameter of the first contact portion is increased so that the surface facing the rear end side of the bit head faces the first contact portion. However, by forming a bottom surface facing the front end side in the axial direction in the recess and using this as the first abutting portion, in the unlikely event that the diameter of the expanded bit head is reduced in the drilling hole, Even if they are displaced, it is possible to avoid a situation in which the ring bit falls off.

  In order to form the small-diameter portion as described above in the inner peripheral portion of the tip of the casing pipe, a casing top is attached to the tip of the casing pipe, and the inner diameter of the casing top is made smaller than the inner diameter of the casing pipe. When forming the small diameter portion, the mounting portion of the casing top to the casing pipe is located on the rear end side in the axial direction with respect to the rear end surface facing the rear end side in the axial direction of the small diameter portion. It is desirable. When the mounting portion is positioned on the front end side with respect to the rear end surface of the small diameter portion, the striking force is transmitted from the second contact portion of the pilot bit to the ring bit via the small diameter portion of the casing pipe (casing top). Passing through the mounting part of the casing top to the casing pipe during this time, the mounting part may be damaged by the impact or load, but the mounting part is located on the rear end side in the axial direction from the rear end surface of the small diameter part It is possible to avoid the striking force from passing through the mounting portion by being positioned in the position.

  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, efficient drilling can be performed by transmitting sufficient rotational force, striking force and thrust to the ring bit.

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. It is a fragmentary sectional side view which shows the 1st modification of embodiment shown in FIG. It is a fragmentary sectional side view which shows the 2nd modification of embodiment shown 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. In the casing top 1A, the rear end portion is fitted from the front end side of the casing pipe 1, and the surface facing the rear end side (right side in FIG. 1) in the axis O direction of the front end portion is the front end surface of the casing pipe 1. By being joined by welding or the like, it is integrated with the casing pipe 1 coaxially.

  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. Furthermore, the front end surface of the casing top 1A is a plane perpendicular to the axis O, and serves as the third contact portion 1C in the present embodiment. In FIG. 1, reference numeral 1D denotes an attachment portion formed by joining the casing top 1A to the casing pipe 1, and this attachment portion 1D is the front end side in the axis O direction with respect to the rear end face of the small diameter portion 1B in this embodiment. Is located.

  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 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 is directed to the front end side. The bottom surface 3A is perpendicular to the axis O, and extends from the inner periphery 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. It is chamfered by the inclined surface 2D.

  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 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, and the outer peripheral portion of the enlarged head main body 4B serves as an engaging portion that engages with an engaged portion of a ring bit described later.

  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 as shown in FIGS. 1 and 3 with the bit head 4 having an enlarged diameter. The pilot bit 2 is formed so as to protrude on the outer periphery from the second abutting portion 2 </ b> B and to be positioned on a cylindrical surface with the axis O as the center. Further, in this embodiment, the second side surface 4b directed in the tool rotation direction T in the state in which the bit head 4 is expanded in diameter is slightly inclined toward the opposite side to the tool rotation direction T in the present embodiment. ing.

  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 end 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. The intersecting ridge line portion between the fourth side surface 4d and the second side surface 4b is chamfered in a planar shape, and the fifth wall portion of the housing recess 3 with the bit head 4 having a reduced diameter as shown in FIG. It is located inside 3e.

  Furthermore, the intersecting ridge line portion between the fourth side surface 4d and the tip end surface of the head body 4B is formed on the side of the center line C so as to form a truncated cone surface centered on the axis O in a state where the bit head 4 is expanded in diameter. It is set as the multi-step (2 steps in this embodiment) inclined surface which goes to the front end side as it goes. 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. In this embodiment which inclines toward the front end side as it goes, it is set as the 1 step | paragraph inclined surface. In addition, the arc centering on the axis O which the intersection ridgeline of the front-end | tip inclined surface and head surface of the head main body 4B makes is a pilot bit 2 in the state where the bit head 4 is expanded in diameter as shown in FIG. The diameter is slightly larger than the outer diameter of the tip of the second contact portion 2B and smaller than the outer diameter of the second contact portion 2B.

  Further, the tip surfaces of the pilot body 2 and the head body 4B of the bit head 4 excluding these inclined surfaces are flat surfaces perpendicular to the axis O and the center line C, respectively. Furthermore, the length of the head main body 4B in the direction of the center line C is made 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 is larger than the outer diameter of the further expanded bit head 4. On the other hand, the inner diameter of the ring bit 7 is smaller than the outer diameter of the second contact portion 2B of the pilot bit 2, and in this embodiment, is equal to the inner diameter of the small diameter portion 1B formed in the casing pipe 1 by the casing top 1A. The tip of the pilot bit 2 on the tip side of the second abutting portion 2B can be inserted. Furthermore, as shown in FIG. 1, the thickness of the ring bit 7 in the direction of the axis O is made smaller than the width between these inner and outer diameters, and the second contact portion 2B is brought into contact with the small diameter portion 1B. Thus, the distance between the front end surface of the casing top 1A and the rear end surface of the head body 4B in a state where the diameter of the bit head 4 is expanded is made larger.

  Further, the inner peripheral portion of the ring bit 7 is formed with three concave portions recessed on the outer peripheral side at equal intervals in the circumferential direction, and the concave portions are expanded in diameter as shown in FIG. The engaged portion 7A is engaged with the bit head 4 in the tool rotation direction T during excavation. In this embodiment, the engaged portion 7A is formed as a bottomed concave portion that is recessed from the front end surface of the ring bit 7 to the rear end side, that is, retreats from the inner peripheral portion of the ring bit 7 to the one-step outer peripheral side. A first wall surface 7a facing the inner circumferential side, a second wall surface 7b facing the opposite side of the tool rotation direction T extending from the first wall surface 7a to the inner circumferential portion, a third wall surface 7c facing the tool rotation direction T, and these A bottom surface 7d extending between the first to third wall surfaces 7a to 7c and facing the distal end side having the same inner diameter as the inner peripheral portion of the ring bit 7 is provided.

  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 fourth side surface 4d facing the outer peripheral side of the head body 4B of the expanded bit head 4. The circumferential length of the first wall surface 7a is slightly longer than the circumferential length of the fourth side surface 4d. 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. An angle formed by the second side surface 4b of the bit head 4 having a diameter with respect to the radial direction with respect to the axis O is made equal.

  Further, the third wall surface 7c is the center 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 bit head 4 whose diameter is increased as shown in FIG. It is formed so as to form a concave cylindrical surface centered on the line C. Further, the bottom surface 7d of the engaged portion 7A is located behind the head main body 4B of the bit head 4 whose diameter has been expanded in a state where the rear end surface of the ring bit 7 is in contact with the front end surface of the casing top 1A as shown in FIG. The first abutting portion is disposed so as to face the end face with a slight gap and is capable of abutting on the distal end side in the axis O direction with respect to the enlarged bit head 4.

  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 8 </ b> A is opened in the mounting hole 3 </ b> C in the receiving recess 3 of the pilot bit 2 so as to face the notch 4 </ b> C in the shaft portion 4 </ b > A of the bit head 4. The first blow hole 8A extends perpendicularly to the axis O and opens to the outer peripheral surface of the pilot bit 2, and branches to the tip side along the center line C and opens to the center of the mounting hole 3C. You may do it. 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. is 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 When 2B contacts the rear end surface of the casing top 1A, it is positioned in the direction of the axis O. 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. As shown in FIG. 1, the rear end face is brought into contact with the front end face of the casing top 1A, which is the third contact portion 1C.

  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 side surface 4b of the head main body 4B, which is a joint portion, is engaged by being in close contact with the second wall surface 7b of the engaged portion 7A of the ring bit 7, and the third side surface 4c of the head main body 4B is engaged. 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 3 b of the receiving recess 3.

  Further, in the direction of the axis O, as shown in FIG. 1, the bottom surface 7d as the first contact portion in the engaged portion 7A of the ring bit 7 is formed on the rear end surface of the head main body 4B of the bit head 4 whose diameter has been expanded. The ring bit 7 is prevented from coming off to the tip side by being able to contact each other with a slight gap. Further, the front end surface of the casing top 1A, which is the third abutting portion 1C, abuts on the rear end surface of the ring bit 7 and is supported on the front end side, whereby the casing pipe 1 and the ring bit 7 are connected to the pilot bit 2 and the bit. The head 4 can be moved forward together with the head 4 in the direction of the axis O.

Accordingly, from this state, the down-the-hole hammer H applies a striking force toward the front end side in the axis O direction on the pilot bit 2 and the bit head 4 and the ring bit 7 via the second and third contact portions 2B and 1C. In addition to transmitting the thrust and the rotational force in the tool rotation direction T from the excavator, the excavator tip 6 provided on the tip surface of the pilot bit 2, the bit head 4 and the ring bit 7 is used. Drilling work is performed, and the casing pipe 1 is inserted into the formed excavation hole. During the drilling, compressed air is jetted from the supply hole 8 through the first to third blow holes 8A to 8C , and the dust produced by the excavation tip 6 is passed through the casing pipe 1 from the discharge groove 2C. While discharging | emitting, the biting of the dusting to the accommodation recess 3 and the mounting hole 3C 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 so as to be rotatable, and the inner diameter thereof is larger than the outer diameter of the third contact portion 1C of the tip portion of the casing pipe 1 (the tip surface of the casing top 1A in this embodiment). Can be increased while being a small range. 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, the bottom surface 7d of the engaged portion 7A formed as a recessed portion with a bottom that is recessed from the inner peripheral portion of the ring bit 7 toward the outer peripheral side is used as the first contact portion. Even if the bit head 4 is slightly displaced in the direction in which the diameter of the bit head 4 is reduced at the time of drilling, the ring bit 7 is prevented from falling off to the tip side if the bottom surface 7d faces the head body 4B. Can do. However, for example, the second side surface 4b of the head body 4B of the bit head 4 in an expanded state is extended to the tip surface of the ring bit 7 on the tool rotation direction T side with respect to the engaged portion 7A. The tip surface portion of the ring bit 7 that faces the protruding portion may be used as the first contact portion. In this case, a recessed portion that penetrates in the direction of the axis O without forming the bottom surface 7d in the engaged portion 7A is covered. It is good also as an engaging part.

  By the way, in this embodiment, as mentioned above, the surface facing the rear end side of the front end portion of the casing top 1A is attached to the front end surface of the casing pipe 1 by welding or the like, and the attachment portion 1D by this joining is attached. Although it is located on the front end side in the axis O direction from the rear end surface of the small diameter portion 1B of the casing pipe 1 by the casing top 1A, in such a case, when an excessive striking force is applied to the pilot bit 2 from the down-the-hole hammer H, Since the impact force is transmitted from the second abutting portion 2B of the pilot bit 2 to the ring bit 7 via the small diameter portion 1B, the mounting portion 1D is damaged, and the mounting portion 1D is damaged by the impact. In some cases, the casing pipe 1 may not be inserted into the excavation hole.

  Therefore, in order to prevent such damage of the attachment portion 1D, the attachment portion 1D of the casing top 1A to the casing pipe 1 as in the first and second modifications of the above-described embodiment shown in FIGS. Is positioned further to the rear end side in the axis O direction than the rear end surface facing the rear end side (right side in FIGS. 6 and 7) of the small diameter portion 1B of the casing pipe 1 by the casing top 1A. Good. In these modified examples shown in FIGS. 6 and 7, elements common to the embodiment shown in FIGS. 1 to 5 are denoted by the same reference numerals and description thereof is omitted, and the illustration of the bit head 4 is also omitted. To do.

  Among these, in the first modification shown in FIG. 6, the outer diameter of the multi-stage cylindrical casing top 1A is made larger than the outer diameter of the casing pipe 1, and the small-diameter portion 1B is formed at the inner periphery of the tip. In addition, the inner diameter of the rear end portion is set such that the front end portion of the casing pipe 1 can be fitted, and the rear end portion has a plurality of penetrating holes on the rear end side in the axis O direction from the rear end surface of the small diameter portion 1B. Holes 1E are formed at intervals in the circumferential direction. Further, a portion extending from the rear end surface of the small diameter portion 1B to the inner periphery of the rear end portion on the outer peripheral side (lower side in FIG. 6) and the front end surface of the casing pipe 1 are formed in a planar shape perpendicular to the axis O.

  The casing top 1A according to the first modified example has a casing pipe 1 in which the tip end portion of the casing pipe 1 is fitted on the inner periphery of the rear end portion, and the portion extending from the rear end surface of the small diameter portion 1B to the inner periphery of the rear end portion. 1 is brought into contact with the front end surface of the casing 1, the entire rear end surface of the rear end portion and the outer peripheral surface of the casing pipe 1 are welded, and the through-hole 1 </ b> E portion is the outer peripheral surface of the casing pipe 1. And is welded to the casing pipe 1. Accordingly, the entire circumference welded portion and the plug welded portion indicated by reference numeral 1D in FIG. 6 are the attachment portions in the first modification, and these attachment portions 1D are located closer to the rear end side in the axis O direction than the rear end surface of the small diameter portion 1B. Will be located.

  Further, in the second modified example shown in FIG. 7, the outer diameter of the casing top 1A is made equal to the outer diameter of the casing pipe 1, and the small diameter portion 1B is formed on the inner peripheral portion of the tip, and the rear The inner diameter of the end portion is made equal to the inner diameter of the casing pipe 1, and the rear end surface of the rear end portion and the front end surface of the casing pipe 1 are butt welded over the entire circumference, so that the casing top 1 </ b> A becomes the casing pipe 1. It is attached to the tip. Accordingly, the butt weld portion indicated by reference numeral 1D in FIG. 7 is an attachment portion in the second modified example, and this attachment portion 1D is also located on the rear end side in the axis O direction from the rear end surface of the small diameter portion 1B.

  In such first and second modified examples, the mounting portion 1D of the casing top 1A to the casing pipe 1 is located on the rear end side in the axis O direction with respect to the rear end surface of the small diameter portion 1B. It is possible to avoid a striking force directed from H to the distal end side in the direction of the axis O transmitted to the small diameter portion 1B via the second contact portion 2B of the pilot bit 2 through the mounting portion 1D. Therefore, it is possible to prevent breakage or the like in the welded portion due to the impact or load when the striking force passes through the attachment portion 1D directly acting on the attachment portion 1D, and the casing pipe 1 can be reliably inserted into the excavation hole. It becomes possible to insert.

  In the above embodiment and the first and second modifications, the casing top 1A is attached to the tip of the casing pipe 1 by welding or the like. For example, as in the above embodiment, the casing top 1A is When the end portion is fitted into the inner circumference of the casing pipe 1 or when the front end portion of the casing pipe 1 is fitted into the inner circumference of the rear end portion of the casing top 1A as in the first modification, they face each other. The outer periphery of the rear end of the casing top 1A and the inner periphery of the front end of the casing pipe, or the inner periphery of the rear end of the casing top 1A and the outer periphery of the front end of the casing pipe are formed to engage with each other and fasten these screw portions. You may make it attach the casing top 1A by.

  Even in such a case, the male and female screw portions to be the attachment portion 1D are positioned on the rear end side in the axis O direction from the rear end surface of the small diameter portion 1B as in the first modification shown in FIG. If so, it is possible to avoid the striking force from the down-the-hole hammer H from passing through the mounting portion 1D, and to prevent the male and female screw portions from being damaged and preventing the casing pipe 1 from being inserted into the excavation hole. it can.

  As mentioned above, although embodiment of this invention and its modification were demonstrated, each structure in these embodiment and its modification, those combinations, etc. are examples, and within the range which does not deviate from the meaning of this invention, of composition. Additions, omissions, substitutions, and other changes are possible. Further, the present invention is not limited by the embodiments, and is limited only by the scope of the claims.

  As described above, according to the drilling tool of the present invention, even when forming a drilling hole having a larger inner diameter than the outer diameter of the casing pipe, the drilling performance is reduced, the construction cost is increased, or the tool is damaged. Therefore, efficient drilling can be performed by transmitting a sufficient rotational force, striking force, and thrust to the ring bit without incurring the above. Therefore, industrial use is possible.

DESCRIPTION OF SYMBOLS 1 Casing pipe 1A Casing top 1B Small diameter part 1C 3rd contact part 1D Mounting 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 5 Pin 6 excavation tip 7 ring bit 7A engaged portion 7d bottom surface of engaged portion 7A (first contact portion)
8 Supply hole O Axis line of casing pipe 1 T Tool rotation direction during excavation C Center line of mounting hole 3C H Down the hole hammer

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 front end 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 has an engaged portion that is engaged with the enlarged bit head in the direction of rotation of the tool during excavation and an axially forward end side of the enlarged bit head. A first abutting portion that can be contacted, and
A small-diameter portion having a smaller inner diameter is formed at the inner peripheral portion of the tip of the casing pipe, and a rear end outer peripheral portion of the pilot bit is a first portion that can contact the small-diameter portion from the rear end side in the axial direction. 2 contact portions are formed,
The excavation tool according to claim 1, wherein a third abutting portion capable of abutting on a surface of the ring bit facing the rear end side in the axial direction is provided at a front end portion of the casing pipe.   The excavation tool according to claim 1, wherein an inner diameter of the ring bit is set to be equal to or larger than an inner diameter of the small diameter portion.   The excavation tool according to claim 1 or 2, wherein a concave portion that is recessed toward an outer peripheral side is formed in an inner peripheral portion of the ring bit, and the concave portion serves as the engaged portion.   The excavation tool according to claim 3, wherein a bottom surface facing the tip end side in the axial direction is formed in the recess, and the bottom surface serves as the first contact portion.   A casing top is attached to a tip portion of the casing pipe, the small diameter portion is formed on the casing top, and an attachment portion of the casing top to the casing pipe is arranged in the axial direction of the small diameter portion. The excavation tool according to any one of claims 1 to 4, wherein the excavation tool is located on a rear end side in the axial direction with respect to a rear end surface facing the rear end side.

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