PDC (Polycrystalline Diamond Compact) self-updating rotary tooth drill bit based on hydraulic reversing wheel structure

Abstract

A PDC (Polycrystalline Diamond Compact) self-updating rotary tooth drill bit based on a hydraulic reversing wheel structure relates to the technical field of petroleum drilling and production equipment, and comprises a drill bit joint, a drill bit body and a hollow shaft, the hollow shaft is positioned in the center of the drill bit body, the outer side of the hollow shaft is fixedly connected with a reversing wheel, the outer side of the reversing wheel is sleeved with a hydraulic starting sleeve, and the outer wall of the reversing wheel is provided with a guide rail; a guide pin is arranged on the inner wall of the hydraulic starting sleeve, when the hydraulic starting sleeve axially reciprocates relative to the reversing wheel, the reversing wheel circumferentially rotates relative to the hydraulic starting sleeve under the cooperation of the guide pin and the guide rail, an installation opening is formed in the lower end of the drill bit body, and a tooth drum is installed in the installation opening in a rolling mode. Rotation of the hollow shaft is converted into rotation of the gear drum through the two bevel gears, a spring is arranged between the lower portion of the drill bit body and the hydraulic starting sleeve indirectly, the hollow shaft is sleeved with a limiting ring in a sliding mode, and the upper end face of the limiting ring can abut against the lower end face of the drill bit connector. The hydraulic pneumatic sleeve can be driven to slide only when the drilling hydraulic pressure is multiplied.

Description

Technical Field

[0001] This invention belongs to the field of oil drilling and production equipment technology, and particularly relates to a PDC self-renewing rotary tooth drill bit based on a hydraulic reversing wheel structure. Background Technology

[0002] In oil and gas exploration and geological drilling, the drill bit, as the core tool that directly contacts the rock formation, directly determines drilling efficiency, construction costs, and operational safety. PDC drill bits, due to their high hardness, high wear resistance, and excellent rock-breaking efficiency, have gradually replaced traditional roller cone drill bits and become one of the mainstream drilling tools. However, existing PDC drill bits still face many technical bottlenecks in practical applications, hindering their further promotion and efficiency improvement.

[0003] In existing PDC drill bits, the PDC teeth are mostly connected to the drill bit body via fixed inlay or welding, resulting in relatively fixed tooth angles, cutting directions, and working faces. During drilling operations, the continuous friction and impact between the PDC teeth and the rock formation can lead to tooth surface wear, cracking, or detachment. Furthermore, due to uneven stress distribution, PDC teeth near the drill bit center or specific cutting areas typically wear much faster than those in other areas, leading to PDC tooth failure. When some PDC teeth fail, even if the remaining teeth are still functional, the overall rock-breaking efficiency of the drill bit will significantly decrease, manifesting as reduced drilling speed and increased torque fluctuations. In such cases, tripping out and replacing the drill bit is necessary, resulting in extended non-productive time and a significant increase in drilling costs. Statistics show that the tripping out and tripping operations related to drill bit replacement, along with the purchase cost of the drill bit itself, account for approximately 15%-25% of the total drilling cost, with this percentage being even higher in deep and ultra-deep well operations.

[0004] To address the aforementioned issues, existing patents have proposed some "self-renewing" or "rotatable" PDC drill bit solutions. Compared to ordinary PDC drill bits, "self-renewing" or "rotatable" PDC drill bits offer higher rock-breaking efficiency, longer service life, higher mechanical energy conversion rate in drilling rigs, and are more energy-efficient, representing a low-carbon mining technology.

[0005] Existing technologies have proposed solutions for "self-renewing" or "rotatable" PDC drill bits, which are implemented as follows: One solution uses a hydraulically driven ratchet to rotate the teeth, allowing worn teeth to be replaced. However, this approach suffers from drawbacks such as difficulty in precisely controlling the rotation angle and frequency, complex structure, high failure rate, and poor reliability. Another solution uses an electric device to drive tooth renewal. However, this approach is susceptible to damage to electrical components due to environmental factors, and has high manufacturing and cost.

[0006] Meanwhile, the shape design of PDC teeth in existing technologies is relatively simple, mostly cylindrical or wedge-shaped, which has poor adaptability to different rock types. The single shape of PDC teeth is prone to slippage when breaking hard rock and mud packing when breaking soft rock, further reducing drilling efficiency.

[0007] Therefore, a self-renewing PDC drill bit technology with stable driving force and high reliability is needed to solve the problems of rapid local wear, unreliable self-renewal mechanism, and low rock breaking efficiency of existing PDC drill bits. Summary of the Invention

[0008] This invention provides a PDC self-renewing rotary tooth drill bit based on a hydraulic reversing wheel structure, which aims to solve the problems of rapid local wear, unreliable self-renewal mechanism, and low rock breaking efficiency of existing PDC drill bits. The self-renewal mechanism of this invention can precisely control the rotation angle and frequency of the tooth body, and the stability of the tooth drum after tooth body renewal is very high, which can withstand rock breaking torque.

[0009] The technical solution provided by this invention is: a PDC self-renewing rotary toothed drill bit based on a hydraulic reversing wheel structure, comprising a drill bit connector and a drill bit body. The drill bit connector is threadedly connected to the upper end of the drill bit body, and the two are further securely connected by a first connecting pin. A hollow shaft is provided in the center of the drill bit body, and a reversing wheel is fixedly connected to the outer side of the hollow shaft. The hollow shaft rotates synchronously with the reversing wheel. A hydraulic starting sleeve is fitted with a clearance sleeve on the outer side of the reversing wheel. A guide rail is provided on the outer wall of the reversing wheel, and a guide pin is provided on the inner wall of the hydraulic starting sleeve, which cooperates with the guide rail. The guide pin is located inside the guide rail. When the hydraulic starting sleeve performs axial reciprocating motion relative to the reversing wheel, the reversing wheel rotates circumferentially relative to the hydraulic starting sleeve under the cooperation of the guide pin and the guide rail. A first bevel gear is fixedly connected to the lower end of the hollow shaft, and a through mounting port is provided at the lower end of the drill bit body. A toothed drum is rolled in the mounting port, and a second bevel gear is installed synchronously with the toothed drum. The second bevel gear meshes with the first bevel gear, and the power of the reversing wheel and hollow shaft rotation is transmitted to the gear drum through the two bevel gears, driving the gear drum to rotate. A limit platform is fixed to the inner side of the lower part of the drill bit body. A spring is set between the limit platform and the hydraulic starter sleeve. A limit ring is slidably fitted on the hollow shaft above the hydraulic starter sleeve. The upper end face of the limit ring can abut against the lower end face of the drill bit joint. Under normal drilling conditions, the drilling hydraulic pressure cannot overcome the spring force to push the limit ring. Therefore, under normal conditions, the hydraulic starter sleeve cannot undergo axial reciprocating motion. Only when the drilling hydraulic pressure is increased several times can the spring force be overcome to push the limit ring, forcing the hydraulic starter sleeve to move axially. After the pressure is released, the hydraulic starter sleeve returns to its original position under the action of the spring. Thus, the reciprocating motion of the hydraulic starter sleeve is achieved by alternating high pressure and low pressure, thereby realizing the rotation of the reversing wheel, hollow shaft, two bevel gears, and gear drum.

[0010] A further technical solution is as follows: the guide rail includes an upper vertical section, a lower right sloping section, a lower vertical section, and an upper right sloping section, which are connected sequentially and repeat in a cycle.

[0011] A further technical solution is as follows: the hydraulic starting sleeve and the drill bit body are connected by an axial key, so that the hydraulic starting sleeve can only slide axially relative to the drill bit body and cannot rotate circumferentially; a limiting block is fixedly connected to the hollow shaft, and the limiting block abuts against the limiting platform, so that the hollow shaft cannot move axially relative to the limiting platform and the drill bit body.

[0012] A further technical solution is: the lower part of the drill bit body is equipped with a cutter wing, and the cutter wing is inlaid with main PDC teeth, which include alternating conical PDC teeth, wedge-shaped PDC teeth and cylindrical PDC teeth.

[0013] A further technical solution is: the toothed drum is inlaid with secondary PDC teeth, which include alternating conical PDC teeth, wedge-shaped PDC teeth and cylindrical PDC teeth.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] 1. Existing technology includes a downhole electric self-renewal device, but its drawbacks include difficulty in ensuring the sealing of electrical components downhole, difficulty in guaranteeing the service life of electrical components in the high-temperature environment downhole, extremely high failure rate, and the layout of electrical components downhole is also limited by the wellbore size. In contrast, this invention is a purely mechanical self-renewal device. Whether considering environmental tolerance, failure rate, or cost (economic efficiency), this invention is significantly superior to existing technologies.

[0016] 2. Existing technology also includes a ball-throwing type mechanical self-renewal device, which has the drawbacks of ball-throwing failure and waiting time after ball dissolution. In contrast, this invention has an extremely high success rate, and the entire renewal process has no waiting time, making its work efficiency far superior to existing technologies.

[0017] 3. During the operation of the updating device of this invention, because the drilling hydraulic pressure is manually increased once, the rotation angle of the reversing wheel is fixed, so there is no problem of inaccurate or imprecise rotation angle. Furthermore, after the update is completed, the guide pin of the hydraulic starting sleeve falls within the lower vertical section of the guide rail. The lower vertical section firmly restricts the rotation of the reversing wheel, which in turn firmly restricts the rotation of the hollow shaft, the two conical teeth, and the tooth drum, ensuring that the updated tooth drum will not rotate even under strong torque, thus ensuring the reliability of the PDC tooth update.

[0018] 4. The conventional drilling hydraulic pressure of this invention differs significantly from the drilling hydraulic pressure during "self-renewal," thus eliminating the possibility of misoperation and ensuring that the "self-renewal" frequency is controllable.

[0019] 5. This invention alternately embeds PDC teeth of different shapes on the cutter blades and tooth drum. Conical PDC teeth are used for hard rock breaking, utilizing the tip effect to increase rock-breaking pressure; wedge-shaped PDC teeth are used for shearing and breaking medium-hard rocks, reducing rock-breaking torque; cylindrical PDC teeth are used for soft rock and abrasive rock formations, improving wear resistance. The alternating arrangement of the teeth ensures that suitable teeth are involved in drilling different rock types, while achieving a uniform distribution of the wear surface. Attached Figure Description

[0020] Figure 1 This is an isometric view of the present invention.

[0021] Figure 2 This is the front view of the present invention.

[0022] Figure 3 This is the left view of the present invention.

[0023] Figure 4 This is the right view of the present invention.

[0024] Figure 5 This is a top view of the present invention.

[0025] Figure 6 This is a bottom view of the present invention.

[0026] Figure 7 This is a sectional view of [the object].

[0027] Figure 8 This is a cross-sectional view showing the fit between the drill bit body and the hydraulic starter sleeve in this invention.

[0028] Figure 9 This is an axonometric view of the commutator wheel in this invention.

[0029] Figure 10 This is an unfolded view of the guide rail on the outer wall of the commutator wheel in this invention.

[0030] In the diagram: 1. Drill bit connector; 2. Hollow shaft; 3. Limiting ring; 4. Hydraulic starting sleeve; 5. Reversing wheel; 6. Guide pin; 7. First elastic retaining ring; 8. Spring; 9. Limiting platform; 10. Second connecting pin; 11. Gear drum; 12. First rotating shaft; 13. Secondary PDC gear; 14. Main PDC gear; 15. Second bevel gear; 16. Second elastic retaining ring; 17. First bevel gear; 18. First flat key; 19. Second flat key; 20. Drill bit body; 21. First connecting pin; 22. Upper vertical section; 23. Lower right inclined section; 24. Lower vertical section; 25. Upper right inclined section; 26. Through hole. Detailed Implementation

[0031] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0033] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0034] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0035] The present invention includes a drill bit connector 1 and a drill bit body 20. The drill bit connector 1 is threaded to the upper end of the drill bit body 20, and the two are further securely connected by a first connecting pin 21.

[0036] A hollow shaft 2 is provided in the center of the drill bit body 20. A reversing wheel 5 is fitted on the outer side of the hollow shaft 2. The reversing wheel 5 cooperates with the hollow shaft 2 through the second flat key 19, so that the hollow shaft 2 rotates synchronously with the reversing wheel 5. The reversing wheel 5 is fitted onto the hollow shaft 2 from the lower end of the hollow shaft 2. The upper end of the hollow shaft 2 is limited by a step, and the lower end of the hollow shaft 2 is limited by the first elastic retaining ring 7, thereby fixing the reversing wheel 5 on the hollow shaft 2. A hydraulic starter sleeve 4 is fitted onto the outer side of the reversing wheel 5 with clearance. A guide rail is provided on the outer wall of the reversing wheel 5. A guide pin 6, which mates with the guide rail, is located on the inner wall of the hydraulic starter sleeve 4. When the hydraulic starter sleeve 4 reciprocates axially relative to the reversing wheel 5, the reversing wheel 5 rotates circumferentially relative to the hydraulic starter sleeve 4 due to the interaction between the guide pin 6 and the guide rail. In other words, the axial reciprocating motion of the hydraulic starter sleeve 4 is converted into the circumferential rotation of the reversing wheel 5 through the interaction between the guide rail and the guide pin 6. To transmit the rotational motion of the hollow shaft 2, a first bevel gear 17 is provided at the lower end of the hollow shaft 2. (The first bevel gear 17 mates with the hollow shaft 2 via a first flat key 18. The upper end of the first bevel gear 17 is limited on the hollow shaft 2 by a step, and the lower end of the first bevel gear 17 is limited by a second elastic retaining ring 16, thereby fixing the first bevel gear 17 to the hollow shaft 2.) Figure 6As shown, the lower end of the drill bit body 20 has a through mounting port, in which a toothed drum 11 is rolled. A portion of the toothed drum 11 extends beyond the drill bit body 20. A second bevel gear 15 is mounted synchronously (coaxially) with the toothed drum 11. The mounting shaft of the toothed drum 11 is called the first rotating shaft 12. The first rotating shaft 12 is rotatably connected to the drill bit body 20. The second bevel gear 15 meshes with the first bevel gear 17, thereby transmitting the power of the reversing wheel 5 and the hollow shaft 2 to the toothed drum 11 via the two bevel gears, driving the toothed drum 11 to rotate. A limiting platform 9 is provided on the lower inner side of the drill bit body 20. The limiting platform 9 is fixedly connected to the drill bit body 20 by a second connecting pin 10. A spring 8 is provided between the limiting platform 9 and the hydraulic starting sleeve 4. In the initial state, the spring 8 is in a compressed state, and the stored elastic potential energy acts on the lower end of the hydraulic pneumatic sleeve, pushing the hydraulic starting sleeve 4 to generate an upward movement tendency. A limiting ring 3 slides on the hollow shaft 2 above the hydraulic starter sleeve 4. The upper end face of the limiting ring 3 can abut against the lower end face of the drill bit connector 1, forming a seal. The conventional drilling hydraulic pressure is around 2 MPa. Because the downward thrust generated by the drilling hydraulic pressure at this intensity on the limiting ring 3 cannot overcome the thrust of the spring 8, the hydraulic starter sleeve 4 cannot perform axial reciprocating motion under normal conditions. The drilling fluid can only reach the drill bit body 20 by descending through the hollow shaft 2. To rotate the toothed drum 11 (to replace the PDC teeth), manual intervention is required. The hydraulic pressure of the drilling fluid is increased (to about 6 MPa) to overcome the elastic force of the spring 8 and push the limit ring 3, forcing the hydraulic starter sleeve 4 to move axially. After the pressure is released, the hydraulic starter sleeve 4 returns to its original position under the action of the spring 8. Thus, the axial reciprocating motion of the hydraulic starter sleeve 4 is achieved by alternating high pressure and low pressure, which in turn realizes the rotation of the reversing wheel 5, the hollow shaft 2, the two bevel gears and the gear drum 11. Since the PDC teeth are embedded on the gear drum 11, the PDC teeth are finally renewed.

[0037] like Figure 9 and Figure 10 As shown, the guide rail includes an upper vertical section 22, a lower right sloping section 23, a lower vertical section 24, and an upper right sloping section 25. The lower right sloping section 23 refers to the section of the guide rail whose direction, viewed from left to right, is downward to the right, and the upper right sloping section 25 refers to the section of the guide rail whose direction, viewed from left to right, is upward to the right. In the entire guide rail, the upper vertical section 22, lower right sloping section 23, lower vertical section 24, and upper right sloping section 25 are sequentially connected and repeat in a cycle. In this way, the reciprocating motion of the guide pin 6 can be achieved through… Figure 9 or Figure 10 The guide rail is converted into the rotational motion of the commutator wheel 5.

[0038] In this invention, on the one hand, it is necessary to ensure that the hydraulic starting sleeve 4 can only slide axially relative to the drill bit body 20, and cannot rotate circumferentially relative to the drill bit body 20. Specifically, as... Figure 8As shown, the hydraulic starting sleeve 4 and the drill bit body 20 can have a polygonal fit, which restricts the rotation of the hydraulic starting sleeve 4 relative to the drill bit body 20. On the other hand, it is necessary to ensure that the hollow shaft 2 can only rotate relative to the drill bit body 20 in the circumferential direction and cannot move axially relative to the drill bit body 20. To limit the axial movement of the hollow shaft 2 and ensure transmission reliability and working stability, the shaft end connection structure design needs to be carried out specifically according to the specific structural form of the upper connecting drill tool. The existing design in this application is only a schematic structure of the drill bit connection part. The specific shaft end locking and anti-movement structure will be further optimized and determined according to the interface form of the matching drill tool.

[0039] The lower part of the drill bit body 20 is equipped with a cutter wing, on which main PDC teeth 14 are inlaid. The main PDC teeth 14 include alternating conical PDC teeth, wedge-shaped PDC teeth and cylindrical PDC teeth.

[0040] The toothed drum 11 is inlaid with secondary PDC teeth 13, which include alternating conical PDC teeth, wedge-shaped PDC teeth and cylindrical PDC teeth.

[0041] Conical PDC teeth are used for hard rock breaking, utilizing the tip effect to increase rock-breaking pressure; wedge-shaped PDC teeth are used for shearing and breaking medium-hard rocks, reducing rock-breaking torque; cylindrical PDC teeth are used for soft rock and abrasive rock formations, improving wear resistance. The alternating arrangement of the teeth ensures that suitable teeth are involved in drilling different rock types, while achieving a uniform distribution of the wear surface.

[0042] The working process of this invention is as follows:

[0043] Connect the upper end of drill bit connector 1 to the drilling string and lower it into the well for drilling. When it is necessary to replace the PDC teeth, first manually increase the hydraulic pressure of the drilling fluid, forcing the hydraulically driven limit ring 3 and hydraulic starting sleeve 4 to descend. At this time, the guide pin 6 moves from the upper dead point of the upper vertical section 22 of the guide rail through the lower right inclined section 23 to the lower dead point of the lower vertical section 24. After depressurization, under the elastic force of the spring 8, the hydraulic starting sleeve 4 moves upward to reset, and the guide pin 6 moves from the lower dead point of the lower vertical section 24 through the upper right inclined section 25 to the upper dead point of the next upper vertical section 22. If one upper vertical section 22 and one right... The lower inclined section 23, a lower vertical section 24, and a right upper inclined section 25 form a group, and this embodiment has six groups. So, each time the drilling fluid is pumped up and then depressurized, the reversing wheel 5 rotates by 60 degrees, and the first bevel gear 17 rotates by 60 degrees. If the first bevel gear 17 and the second bevel gear 15 have the same specifications, then the second bevel gear 15 also rotates by 60 degrees. Since the second bevel gear 15 rotates coaxially with the toothed drum 11, the toothed drum 11 also rotates by 60 degrees, and the PDC teeth on the toothed drum 11 are updated.

[0044] After the hydraulic starter sleeve 4 descends, in order to allow the drilling fluid to flow downwards, a flow passage hole 26 is provided axially upwards on the hydraulic starter sleeve 4.

[0045] In summary, this invention is a purely mechanical self-renewing rotary tooth PDC drill bit. Through its mechanized structural design, the transmission components are simple in structure, easy to manufacture, and low in cost. Because the hydraulic pressure required for self-renewal differs significantly from that of conventional drilling, the problem of accidental renewal is largely avoided, ensuring a controllable renewal frequency. The toothed drum 11 of this invention has a precise rotation angle, and the renewed toothed drum 11 also acts as a lock, ensuring that it can withstand strong torque.

Claims

1. A PDC self-renewing rotary-tooth drill bit based on a hydraulic reversing wheel structure, comprising a bit joint (1) and a bit body (20), the bit joint (1) being connected to the upper end of the bit body (20), characterized in that: The central part of the drill bit body (20) is provided with a hollow shaft (2), the outer side of the hollow shaft (2) is fixedly connected with a reversing wheel (5), the outer side gap of the reversing wheel (5) is sleeved with a hydraulic starting sleeve (4), the outer wall of the reversing wheel (5) is provided with a guide rail, the inner wall of the hydraulic starting sleeve (4) is provided with a guide pin (6) matched with the guide rail, when the hydraulic starting sleeve (4) reciprocates axially relative to the reversing wheel (5), the reversing wheel (5) rotates circumferentially relative to the hydraulic starting sleeve (4) under the cooperation of the guide pin (6) and the guide rail, the lower end of the hollow shaft (2) is fixedly connected with a first bevel gear (17), the lower end of the drill bit body (20) is provided with a through mounting opening, a tooth drum (11) is rotatably installed in the mounting opening, a second bevel gear (15) is synchronously rotatably installed with the tooth drum (11), and the second bevel gear (15) is engaged with the first bevel gear (17); the inner side of the lower part of the drill bit body (20) is fixedly connected with a limiting table (9), a spring (8) is arranged between the limiting table (9) and the hydraulic starting sleeve (4), and a limiting ring (3) is slidably sleeved on the hollow shaft (2) above the hydraulic starting sleeve (4), and the upper end surface of the limiting ring (3) can abut against the lower end surface of a drill bit joint (1).

2. The PDC self-cleaning rotary tooth drill bit based on the hydraulic reversing wheel structure according to claim 1, characterized in that: The guide rail comprises an upper vertical section (22), a right lower inclined section (23), a lower vertical section (24) and a right upper inclined section (25), and the upper vertical section (22), the right lower inclined section (23), the lower vertical section (24) and the right upper inclined section (25) are sequentially connected and repeatedly circulated.

3. The PDC self-cleaning rotary tooth drill bit based on the hydraulic reversing wheel structure according to claim 1, characterized in that: The hydraulic starting sleeve (4) and the drill bit body (20) are axially keyed, so that the hydraulic starting sleeve (4) can only slide axially relative to the drill bit body (20) and cannot rotate circumferentially; the hollow shaft (2) is fixedly connected with a limiting stopper, and the limiting stopper abuts against the limiting table (9), so that the hollow shaft (2) cannot move axially relative to the limiting table (9) and the drill bit body (20).

4. The PDC self-cleaning rotary tooth drill bit based on the hydraulic reversing wheel structure according to claim 1, characterized in that: The lower part of the drill bit body (20) is provided with a blade wing, and the blade wing is inlaid with a main PDC tooth (14); the main PDC tooth (14) comprises alternately arranged conical PDC teeth, wedge-shaped PDC teeth and cylindrical PDC teeth.

5. The PDC self-cleaning rotary tooth drill bit based on the hydraulic reversing wheel structure according to claim 1, characterized in that: The tooth drum (11) is inlaid with a secondary PDC tooth (13), and the secondary PDC tooth (13) comprises alternately arranged conical PDC teeth, wedge-shaped PDC teeth and cylindrical PDC teeth.

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