Center drill bit and chambering drilling tool

Abstract

The invention relates to the technical field of construction drilling tools, in particular to a center drill bit and a reaming drilling tool. The center drill bit comprises a bottom plane, a bottom inclined plane and a wave impedance discontinuous groove formed in the center drill bit, a stress wave discontinuous medium is arranged in the wave impedance discontinuous groove, a first set included angle is formed between the wave impedance discontinuous groove and the bottom plane, and a second set included angle is formed between the bottom inclined plane and the bottom plane. The wave impedance discontinuous groove is used for reflecting stress waves to the bottom inclined face and entering hole wall rock drilled by the center drill bit. By arranging the wave impedance discontinuous grooves, crushing and crack development of rocks in the reaming area are remarkably enhanced, the damage diameter of the rocks in the reaming area can reach several times of the damage diameter of the rocks in the reaming area after impact drilling of a conventional center drill bit, the strength of the rocks in the reaming area is reduced, the reaming drilling speed is increased, and the drilling efficiency is improved. The rock breaking collaboration and the mechanical drilling efficiency of the combined reaming drilling tool are enhanced, the hard rock drilling speed of the combined reaming drilling tool is increased, and the service life of a drill bit is prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of construction drilling tools, in particular to a center drill bit and a hole enlarging drilling tool. Background Art

[0002] Prefabricated pipe piles have the advantages of low cost, environmental protection, high strength and stable quality. In particular, large-diameter prefabricated pipe piles can better meet the higher requirements of various large-scale buildings for single pile bearing capacity, and have great development potential and application prospects. For large-diameter prefabricated pipe piles with a diameter of more than 800 mm, the existing soil squeezing construction method has problems such as difficulty in sinking piles in hard strata, easy damage to the pile body, limited construction pile length and difficulty in achieving rock embedding at the pile end. The drilling-pipe pile technology uses a long spiral telescopic reaming drilling equipment to achieve simultaneous drilling-soil discharge-pile sinking, effectively solving the problem of large-diameter pipe piles being difficult to sink in hard strata and easy damage to the pile body. And by embedding the pile end in rock, the high bearing capacity characteristics of large-diameter prefabricated pipe piles can be fully utilized. Rock-embedded prefabricated pipe piles require that the pipe piles be embedded in a certain depth in medium-slightly weathered rock strata or unweathered rock strata. At present, the drilling-pipe pile technology uses a long spiral pick reaming drilling method for drilling, which has problems such as difficulty in drilling in hard rock strata, low drilling efficiency, slow pile sinking construction, and easy wear of the drill bit.

[0003] The Chinese invention patent application with application number 202011030400.9 proposes a rock-entry reaming drill, which consists of a central down-the-hole hammer drill bit and a retractable reaming wing drill bit. The down-the-hole hammer drill bit is used to pilot drill into the rock, which reduces the difficulty of reaming and cutting rock and improves the efficiency of reaming drilling in hard rock formations. However, since the impact drilling speed is significantly higher than the spiral reaming drilling speed, the two drilling methods lack synergy, the impact drill bit is easily damaged by empty hitting, and the service life of the drill is low, which restricts the efficiency of large-diameter drilling and pile embedding in the rock. Summary of the invention

[0004] The purpose of the present invention is to provide a center drill bit and a hole-reaming drill tool to increase the service life of the drill tool and improve the drilling speed of the drill tool.

[0005] The center drill bit of the present invention comprises a bottom plane, a bottom inclined surface and a wave impedance discontinuity groove arranged in the center drill bit, wherein the wave impedance discontinuity groove has a stress wave discontinuity medium, a first set angle is formed between the wave impedance discontinuity groove and the bottom plane, a second set angle is formed between the bottom inclined surface and the bottom plane, and the wave impedance discontinuity groove is used to reflect the stress wave to the bottom inclined surface and enter the hole wall rock drilled by the center drill bit.

[0006] Furthermore, the second set angle is greater than or equal to 1.4 times the first set angle and less than or equal to 2 times the first set angle.

[0007] Furthermore, a sealing section for sealing the wave impedance discontinuity groove is provided at a notch of the wave impedance discontinuity groove close to the bottom inclined surface.

[0008] Furthermore, an enlarged circular groove is provided at a position of the bottom inclined surface corresponding to the wave impedance discontinuity groove, a welding area is provided in the enlarged circular groove to form the sealing section, and a plurality of ball teeth are provided in the enlarged circular groove.

[0009] Furthermore, the stress wave interruption medium is air.

[0010] Furthermore, the center drill bit has a center air channel, and the center air channel is communicated with the wave impedance discontinuity groove.

[0011] Furthermore, the wave impedance discontinuity groove is filled with a metal material as the stress wave discontinuity medium, and the wave impedance of the metal material is smaller than the wave impedance of the material of the center drill bit.

[0012] Furthermore, the stress wave interrupter medium is a thin plate made of the same material as the center drill bit, and the surface of the thin plate is provided with an undulating structure for reducing the contact rate with the inner wall surface of the wave impedance interrupter groove.

[0013] Furthermore, the bottom inclined surface is provided with drill teeth, and the drill teeth are planar teeth.

[0014] The present invention also provides a reaming drill tool, comprising a fixedly connected reaming drill bit and a center drill bit as described in any one of the above technical solutions, wherein the center drill bit is located at the lower part of the reaming drill bit.

[0015] Compared with the prior art, the present invention has at least the following beneficial effects: This application greatly improves the transmission ratio of stress wave energy to the rock in the expansion area outside the center drill bit by setting the wave impedance discontinuity groove. The compression stress wave generated by the impact is reflected by the wave impedance discontinuity groove and becomes a tensile stress wave entering the rocks on both sides. The tensile stress wave can better cause crack expansion and damage to the rock, significantly enhancing the fragmentation and crack development of the rock in the expansion area. The damage diameter of the rock in the expansion area can reach several times the damage diameter of the rock in the expansion area after the impact drilling of the conventional center drill bit, reducing the strength of the rock in the expansion area, thereby improving the expansion drilling speed. At the same time, the stress wave diversion effect, on the one hand, appropriately reduces the impact drilling speed of the center drill bit, and on the other hand, improves the drilling speed of the expansion drill bit, thereby reducing the difference in mechanical drilling speed between impact drilling and expansion cutting drilling, thereby enhancing the rock breaking synergy and mechanical drilling efficiency of the combined expansion drill, which is conducive to greatly improving the hard rock drilling speed and drill bit service life of the combined expansion drill.

[0016] Furthermore, by reasonably setting the wave impedance discontinuity groove angle and the bottom slope angle, the reflected stress wave is shot into the center drill bit and rock interface at an incident angle within 0° (vertical injection) -30°, so that most of the stress wave enters the rock in the hole expansion area, and a small part of the stress wave is reflected, thereby increasing the energy and amplitude of the stress wave that finally enters the hole wall rock. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic diagram of a state of an embodiment of the reaming drill of the present invention in a rock formation; Figure 2 for Figure 1 A schematic diagram of the structure of the center drill bit of the hole expansion drilling tool; Figure 3 for Figure 1 A schematic structural diagram of the center drill bit of the hole expansion drilling tool from another perspective; Figure 4 for Figure 1 Schematic diagram of the three-dimensional structure of the wave impedance discontinuity slot; Figure 5 A diagram showing the damage state of rock when the reaming drill of the present invention is drilling in a rock formation; Figure 6 This is a diagram of the damage state of rock when a conventional hole-reaming drill is drilling in a rock formation; Figure 7 for Figure 2 A schematic structural diagram of the wave impedance discontinuity groove of the center drill bit of the first embodiment of the hole expansion drilling tool of the present invention; Figure 8 for Figure 2 A schematic structural diagram of the wave impedance discontinuity groove of the center drill bit of the second embodiment of the hole expansion drilling tool of the present invention; Fig. 9 for Figure 2 A schematic structural diagram of the wave impedance discontinuity groove of the center drill bit of the third embodiment of the reaming drilling tool of the present invention; Reference numerals: 1. Center drill bit; 101. Bottom plane; 102. First bottom slope; 1021. Second bottom slope; 103. First wave impedance discontinuity groove; 1031. Second wave impedance discontinuity groove; 1032. Support; 1033. Air; 1034. Welding area; 1035. Enlarged circular groove; 1036. Top fillet; 104. Center air channel; 105. Drill teeth; 106. Rock damage diameter in lateral enhanced hole expansion area; 107. Rock damage diameter in conventional hole expansion area; 108. Ball teeth; 2. Reaming drill bit; 3. Rock strata; 31. Rock cracks; 4. Stress waves; 5. Metal materials; 6. Thin plates. DETAILED DESCRIPTION

[0018] The center drill bit and reaming drill of the present invention will be described below in conjunction with schematic diagrams, wherein preferred embodiments of the present invention are shown, and it should be understood that those skilled in the art may modify the present invention described herein while still achieving the advantageous effects of the present invention. Therefore, the following description should be understood as being widely known to those skilled in the art and not as a limitation of the present invention.

[0019] The serial numbers assigned to the components herein, such as "first", "second", etc., are only used to distinguish the objects described and do not have any order or technical meaning. The "connection" and "coupling" mentioned in this application, unless otherwise specified, include direct and indirect connections (couplings). In the description of the present invention, it should be understood that the orientation or position relationship indicated by the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc. are based on the orientation or position relationship shown in the accompanying drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present invention.

[0020] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0021] The present invention is described in more detail in the following paragraphs by way of example with reference to the accompanying drawings. The advantages and features of the present invention will become more apparent from the following description and claims. It should be noted that the drawings are in very simplified form and in non-precise proportions, and are only used to facilitate and clearly assist in illustrating the purpose of the embodiments of the present invention.

[0022] The following is attached to the instruction manual Figure 1 To Attachment Fig. 9 , the center drill bit and reaming drill tool of the present invention are introduced.

[0023] In one embodiment, if Figure 1 , Figure 2 and Figure 3As shown, the reaming drill tool comprises a reaming drill bit 2 and a center drill bit 1 which are fixedly connected, and the center drill bit 1 is located at the lower part of the reaming drill bit 2. The center drill bit 1 and the reaming drill bit 2 are detachably fixedly connected, so when the center drill bit 1 or the reaming drill bit 2 is damaged, it can be repaired or replaced by disassembly. Preferably, the reaming drill bit 2 is a retractable structure, specifically, the reaming drill bit 2 can be an impact reaming drill bit 2, or a pick reaming drill bit 2.

[0024] Wherein, the center drill bit 1 is an impact drill bit, such as Figure 2 As shown, the center drill bit 1 comprises a bottom plane 101, a bottom bevel and a wave impedance discontinuity groove arranged in the center drill bit 1, wherein the wave impedance discontinuity groove has a stress wave discontinuity medium, a first set angle α is formed between the wave impedance discontinuity groove and the bottom plane 101, and a second set angle β is formed between the bottom bevel and the bottom plane 101, and the wave impedance discontinuity groove is used to reflect the stress wave 4 to the bottom bevel and enter the hole wall rock drilled by the center drill bit 1. Preferably, the first set angle α is in the range of 0°-90°, and the second set angle β is in the range of 90°-180°.

[0025] When drilling, Figure 5 As shown, the center drill bit 1 drills forward, and the stress wave 4 generated by the impact of the impactor hitting the center drill bit 1 propagates toward the lower part of the center drill bit 1. When the stress wave 4 reaches the wave impedance discontinuity groove, the stress wave 4 is reflected at the wave impedance discontinuity groove at a certain incident angle, and the reflected stress wave 4 is shot into the bottom slope of the center drill bit 1 and enters the rock of the hole wall drilled by the center drill bit 1. Most of the stress waves 4 enter the rock layer 3 in the lateral expansion area of ​​the center drill bit 1, and a small part of the stress waves 4 is reflected due to the difference in wave impedance between the center drill bit 1 and the rock.

[0026] Due to the reflection of the wave impedance discontinuity groove, most of the stress wave 4 that should have entered the rock directly below the center drill bit 1 is diverted and propagated to the rock layer 3 in the expansion area around the center drill bit 1, and under the action of the stress wave 4, the rock cracks 31 in the rock layer 3 in the expansion area are fully developed, forming a rock layer 3 damage zone in the expansion area with a rock damage radius larger than the center drilling radius, thereby improving the drillability of the rock layer 3 in the expansion area. In addition, the stress wave 4 generated by the impact is a compression stress wave, which becomes a tensile stress wave after being reflected by the wave impedance discontinuity groove, and the tensile stress wave enters the rocks on both sides, and the tensile stress wave can better cause crack expansion and damage to the rock.

[0027] Therefore, the present application greatly improves the transmission ratio of the stress wave 4 energy to the rock in the hole expansion area outside the center drill bit 1 by setting the wave impedance discontinuity groove. The stress wave 4 generated by the impact is reflected by the wave impedance discontinuity groove and becomes a tensile stress wave entering the rocks on both sides. The tensile stress wave can better cause crack expansion and damage to the rock, significantly enhancing the crushing and crack development of the rock in the hole expansion area. By comparison Figure 5 and Figure 6 It can be found that after using the reaming drill of the present application, the rock damage diameter 106 of the lateral enhanced reaming area can reach several times the rock damage diameter 107 of the conventional reaming area obtained after impact drilling of the conventional reaming drill, which reduces the strength of the rock in the reaming area, thereby improving the reaming drilling speed. At the same time, the shunting effect of the stress wave 4, on the one hand, appropriately reduces the impact drilling speed of the center drill bit 1, and on the other hand, improves the drilling speed of the reaming drill bit 2, thereby reducing the difference in mechanical drilling speed between impact drilling and reaming cutting drilling, thereby enhancing the rock breaking synergy and mechanical drilling efficiency of the combined reaming drill, which is conducive to significantly improving the hard rock drilling speed and drill bit service life of the combined reaming drill.

[0028] In one embodiment, the bottom slope and the wave impedance discontinuity groove are provided in plurality, and the two correspond to each other. By providing a plurality of wave impedance discontinuity grooves at different angles, more stress waves 4 can be transmitted to the rock in the hole expansion area outside the center drill bit 1, thereby further reducing the strength of the rock in the hole expansion area and improving the hole expansion drilling speed.

[0029] In one of the embodiments, in order to increase the energy of the stress wave 4 entering the rock in the expansion area outside the center drill bit 1, the second set angle is greater than or equal to 1.4 times the first set angle and less than or equal to 2 times the first set angle, so that the reflected stress wave 4 is incident on the interface between the center drill bit 1 and the rock at an incident angle within 0° (vertical injection)-30°, thereby causing most of the stress wave 4 to enter the rock in the expansion area, and a small part of the stress wave 4 is reflected, thereby increasing the energy and amplitude of the stress wave 4 that finally enters the rock on the hole wall.

[0030] Preferably, the first set angle is in the range of 45°-75°.

[0031] In this embodiment, if Figure 2As shown, there are two bottom slopes, namely the first bottom slope 102 and the second bottom slope 1021. Correspondingly, there are two wave impedance discontinuity grooves, namely the first wave impedance discontinuity groove 103 and the second wave impedance discontinuity groove 1031. The first set angle between the first wave impedance discontinuity groove 103 and the bottom plane 101 is 67.5°, and the second set angle between the first bottom slope 102 and the bottom plane 101 is 135°. The first set angle between the second wave impedance discontinuity groove 1031 and the bottom plane 101 is 50°, and the second set angle between the second bottom slope 1021 and the bottom plane 101 is 90°.

[0032] When the center drill bit 1 drills forward, the stress wave 4 generated by the impact of the impactor on the center drill bit 1 propagates toward the lower part of the center drill bit 1, such as Figure 5 As shown, when the stress wave 4 reaches the first wave impedance discontinuity groove 103 and the second wave impedance discontinuity groove 1031 , the stress wave 4 is reflected and transmitted respectively in the wave impedance discontinuity grooves at a certain incident angle.

[0033] For the first wave impedance discontinuity groove 103, since the first set angle between the first wave impedance discontinuity groove 103 and the bottom plane 101 is 67.5°, and the second set angle between the first bottom slope 102 and the bottom plane 101 is 135°, the corresponding incident angle is 67.5°, and the incident angle of the stress wave 4 reflected by the first wave impedance discontinuity groove 103 to the first bottom slope 102 is 0°, that is, the stress wave 4 enters the second bottom slope 1021 vertically, and the stress wave 4 will not be reflected due to the angle, thereby improving the transmission energy of the stress wave 4 at the interface between the second bottom slope 1021 of the center drill bit 1 and the rock, and entering the lateral hole wall rock layer 3.

[0034] For the second wave impedance discontinuity groove 1031, since the first set angle between the second wave impedance discontinuity groove 1031 and the bottom plane 101 is 50°, and the second set angle between the second bottom slope 1021 and the bottom plane 101 is 90°, the corresponding stress wave 4 incident angle is 50°, and the stress wave 4 reflected by the second wave impedance discontinuity groove 1031 reaches the second bottom slope 1021 at 10°. At this time, the incident angle is less than 30°, and most of the energy is transmitted at the second bottom slope 1021 and enters the lateral hole wall rock layer 3.

[0035] Therefore, under the action of the stress wave 4, the rock cracks 31 of the rock layer 3 in the hole expansion area are fully developed, forming a rock layer 3 damage zone in the hole expansion area with a rock damage radius greater than the central drilling radius, thereby improving the drillability of the rock layer 3 in the hole expansion area.

[0036] In one embodiment, if Figure 2 and Figure 4As shown, the wave impedance discontinuity groove is in the shape of a truncated cone side surface. In other embodiments, the wave impedance discontinuity groove may also be in the shape of a trapezoidal surface. The wave impedance discontinuity groove may be realized by micro casting, wire cutting, laser processing or electric spark processing, and may also be realized during the process of casting the central brick.

[0037] Preferably, the width of the wave impedance discontinuity groove ranges from 2 mm to 5 mm, for example, 3 mm or 4 mm.

[0038] Furthermore, a sealing section for sealing the wave impedance discontinuity groove is provided at a notch of the wave impedance discontinuity groove close to the bottom inclined surface.

[0039] Specifically, an enlarged circular groove 1035 is provided at a position of the bottom inclined surface corresponding to the wave impedance discontinuity groove, a welding area 1034 is provided in the enlarged circular groove 1035 to form the sealing section, the welding area 1034 is located at the position where the enlarged circular groove 1035 and the wave impedance discontinuity groove are connected, and the wave impedance discontinuity groove can be effectively sealed, and a plurality of ball teeth 108 are provided in the enlarged circular groove 1035, which can be specifically arranged in the enlarged circular groove 1035 by inlaying or welding. The use of this design can significantly reduce the stress concentration at the bottom end of the wave impedance discontinuity groove, improve the fatigue resistance, and prevent cuttings and drilling fluid from entering the wave impedance discontinuity groove to change the interface wave impedance of the wave impedance discontinuity surface or chemical corrosion.

[0040] Preferably, in order to reduce stress concentration at some positions of the wave impedance discontinuity groove, top fillets 1036 are provided at the corners of the wave impedance discontinuity groove to improve the structural strength and fatigue resistance of the drill bit body.

[0041] In the first embodiment, if Figure 7 As shown, the stress wave 4 interruption medium is air 1033.

[0042] Specifically, there is only air 1033 in the wave impedance discontinuity groove, and both sides of the wave impedance discontinuity groove are the same solid material, so that the stress wave 4 passes through the air 1033 with extremely low wave impedance from the fixed material with high wave impedance, thereby generating a strong discontinuity in the material wave impedance. The stress wave 4 is mainly reflected in the wave impedance discontinuity groove, thereby enhancing the transmission energy of the stress wave 4 at the interface between the second bottom slope 1021 of the center drill bit 1 and the rock, and entering the lateral hole wall rock layer 3.

[0043] Furthermore, when the stress wave discontinuity medium is air 1033, in order to improve the deformation resistance and fatigue life of the wave impedance discontinuity groove structure, a plurality of support members 1032 may be spaced apart in the wave impedance discontinuity groove, and the support members 1032 may be metal blocks.

[0044] Furthermore, the center drill bit 1 has a center air channel 104, and the center air channel 104 is connected to the wave impedance discontinuity groove. By passing compressed air into the center air channel 104, the compressed air can enter the wave impedance discontinuity groove, thereby cooling the bottom plane 101 of the center drill bit 1 and the drill teeth 105 on the bottom inclined surface.

[0045] In the implementation where the stress wave interruption medium is air, the maximum final velocity v of the impactor of the reaming drill is max Calculated according to the following formula: (1) In the formula, is the dynamic yield limit of the material of the center drill 1, k is the safety factor, is the material density of center drill 1, is the longitudinal wave velocity of the center drill bit 1 , and θ is the angle between the wave impedance discontinuity groove and the bottom plane 101 .

[0046] In this embodiment, the material of the center drill bit 1 is 40Cr steel, and the longitudinal wave velocity of the center drill bit 1 is is 5000m / s, the material density of center drill 1 The dynamic yield limit of the material of the center drill 1 is 7850 kg / m3. The maximum terminal velocity of the impactor is 23 m / s. The maximum terminal velocity of the impactor can be adjusted according to the material properties and structural safety factor requirements during design, but the design limit value must be less than the maximum terminal velocity calculated by the above formula (1).

[0047] In the second embodiment, if Figure 8 As shown, the wave impedance discontinuity groove is filled with metal material 5 as the stress wave 4 discontinuity medium, and the wave impedance of the metal material 5 is smaller than the wave impedance of the material of the center drill bit 1. Filling the metal material 5 can improve the deformation resistance and fatigue life of the wave impedance discontinuity groove structure.

[0048] For example, the material of the central brick is steel, the metal material 5 filled is aluminum, the wave impedance ratio of the wave impedance discontinuous groove composed of the two materials is 2.86, the stress wave 4 enters the low wave impedance material from the high wave impedance material, and a considerable part of the stress wave 4 is reflected, and the angle of the reflected wave is also controlled by the setting angle of the wave impedance discontinuous groove. By fully filling the low wave impedance material, the deformation resistance and fatigue life of the wave impedance discontinuous groove structure can be greatly improved.

[0049] In the third embodiment, if Fig. 9As shown, the stress wave 4 interrupting medium is a thin plate 6 made of the same material as the center drill bit 1, and the surface of the thin plate 6 is provided with an undulating structure for reducing the contact rate with the inner wall surface of the wave impedance interrupting groove.

[0050] Specifically, a thin plate 6 made of the same material as the center drill bit 1 is embedded in the wave impedance discontinuity groove as a stress wave 4 discontinuity medium, and at the same time, an undulating structure is processed on the surface of the thin plate 6 to form an uneven surface. The undulating structure can be regular or irregular. For example, the undulating structure can be formed by processing grooves on the surface of the thin plate 6, thereby reducing the contact rate between the thin wall and the inner wall surface of the wave impedance discontinuity groove, improving the wave impedance ratio of the wave impedance discontinuity groove, and then effectively improving the energy proportion of the stress wave 4 reflected at the wave impedance discontinuity groove. While greatly improving the deformation resistance and fatigue life of the wave impedance discontinuity groove structure, it can also avoid the problem of the stress wave 4 discontinuity medium at the wave impedance discontinuity groove falling off due to the uncoordinated deformation under high temperature conditions. In addition, it can also improve the ability of the center brick to resist electrochemical corrosion in a corrosive environment, and significantly improve the service life of the center drill bit 1 under harsh working conditions.

[0051] In one embodiment, if Figure 3 As shown, the bottom inclined surface is provided with drill teeth 105, and the drill teeth 105 are plane teeth. Setting the drill teeth 105 as plane teeth can improve the stress wave 4 transmission coefficient between the bottom inclined surface of the center drill bit 1 and the rock interface, thereby improving the transmission ratio of the stress wave 4 energy to the rock in the hole expansion area outside the center drill bit 1, and significantly enhancing the crushing and crack development of the rock in the hole expansion area.

[0052] Compared with the prior art, this application has the following beneficial effects: This application greatly improves the transmission ratio of stress wave energy to the rock in the expansion area outside the center drill bit by setting the wave impedance discontinuity groove. The compression stress wave generated by the impact is reflected by the wave impedance discontinuity groove and becomes a tensile stress wave entering the rocks on both sides. The tensile stress wave can better cause crack expansion and damage to the rock, significantly enhancing the fragmentation and crack development of the rock in the expansion area. The damage diameter of the rock in the expansion area can reach several times the damage diameter of the rock in the expansion area after the impact drilling of the conventional center drill bit, reducing the strength of the rock in the expansion area, thereby improving the expansion drilling speed. At the same time, the stress wave diversion effect, on the one hand, appropriately reduces the impact drilling speed of the center drill bit, and on the other hand, improves the drilling speed of the expansion drill bit, thereby reducing the difference in mechanical drilling speed between impact drilling and expansion cutting drilling, thereby enhancing the rock breaking synergy and mechanical drilling efficiency of the combined expansion drill, which is conducive to greatly improving the hard rock drilling speed and drill bit service life of the combined expansion drill.

[0053] Furthermore, by reasonably setting the wave impedance discontinuity groove angle and the bottom slope angle, the reflected stress wave is shot into the center drill bit and rock interface at an incident angle within 0° (vertical injection) -30°, so that most of the stress wave enters the rock in the hole expansion area, and a small part of the stress wave is reflected, thereby increasing the energy and amplitude of the stress wave that finally enters the hole wall rock.

[0054] The present application also provides a center drill bit, the structure of which is the same as that of the center drill bit in the above-mentioned reaming drill tool embodiment, and will not be repeated here.

[0055] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A center drill bit, characterized in that: It includes a bottom plane, a bottom inclined surface and a wave impedance discontinuity groove arranged in the center drill bit, wherein the wave impedance discontinuity groove has a stress wave discontinuity medium, a first set angle is formed between the wave impedance discontinuity groove and the bottom plane, a second set angle is formed between the bottom inclined surface and the bottom plane, and the wave impedance discontinuity groove is used to reflect the stress wave to the bottom inclined surface and enter the hole wall rock drilled by the center drill bit.

2. The center drill bit according to claim 1, characterized in that: The second set angle is greater than or equal to 1.4 times the first set angle and less than or equal to 2 times the first set angle.

3. The center drill bit according to claim 1, characterized in that: A sealing section for sealing the wave impedance discontinuity groove is arranged at the notch of the wave impedance discontinuity groove close to the bottom inclined surface.

4. The center drill bit according to claim 3, characterized in that An enlarged circular groove is arranged at a position of the bottom inclined surface corresponding to the wave impedance discontinuity groove, a welding area is arranged in the enlarged circular groove to form the sealing section, and a plurality of ball teeth are arranged in the enlarged circular groove.

5. The center drill bit according to claim 1, characterized in that: The stress wave interruption medium is air.

6. The center drill bit according to claim 1, characterized in that: The center drill bit has a center air channel, and the center air channel is communicated with the wave impedance discontinuity groove.

7. The center drill bit according to claim 1, characterized in that The wave impedance discontinuity groove is filled with a metal material as the stress wave discontinuity medium, and the wave impedance of the metal material is smaller than the wave impedance of the material of the center drill bit.

8. The center drill bit according to claim 1, characterized in that The stress wave interrupter medium is a thin plate made of the same material as the center drill bit, and a surface of the thin plate is provided with an undulating structure for reducing the contact rate with the inner wall surface of the wave impedance interrupter groove.

9. The center drill bit according to claim 1, characterized in that: The bottom inclined surface is provided with drilling teeth, which are plane teeth.

10. A hole-reaming drill, characterized in that: It comprises a reaming drill bit and a center drill bit as claimed in any one of claims 1 to 9 which are fixedly connected, wherein the center drill bit is located at the lower part of the reaming drill bit.

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