Improved tooth design using cylindrical diamond cutting elements

Description

[0001] The present invention relates to a rotatable bit for use in earth boring as claimed in the pre- charactering portion of claim 1.

[0002] A rotatable bit of the kind referred to (US-A-4 373 593) comprises cutting member connected to a bit body by soldering or adhesion without any embedding into the the matrix material of bit body. Each of the cutting members consist of a supporting portion and a cutting portion disposed on the supporting portion. Each cutting member being formed as a wedge shaped cut-out segment of sintered body with a supporting portion surrounding the cutting portion as a casing at least at the periphery, said cutting portion being a material selected from compacted diamond and compacted cubic boron nitride.

[0003] EP-A-0 117 506 fifed priortothefiHng date of the present invention, but published thereafter discloses a bit comprising a matrix body member including a plurality of spaced synthetic polycrystalline diamond cutting elements mounted directly in the matrix during matrix formation, said matrix material forming a plurality of spaced teeth, and at least some of said teeth including a trailing support contacting the rear of the associated cutting element.

[0004] Object of the invention is to provide a rotatable drill bit of the kind referred to in the pre-characterising portion of claim 1, which can be manufactured at reasonable costs, and will perform well in terms of length of bit life and rate of penetration.

[0005] The present invention is an improvement in a rotatable bit as claimed in claim 1, and further embodiments of the bit according to the invention being claimed in claims 2-12.

[0006] The present invention affixes thermally-stable cutting elements securely in a protected manner in the bit in a one-step process, providing accurate orientation without any laborious post-furnacing cutter affixation. The present invention also provides improved cutting efficiency with less use of diamond material, improved cleaning and cooling efficiency and less tendency to dull or to polish.

[0007] The present invention and its various embodiments are better understood by first considering the following drawings wherein like elements are referenced by like numerals.

Brief Description of the Drawings

[0008] 

Figure 1 is a cross-sectional view of a tooth incorporating a cylindrical diamond segment according to the present invention.

Figure 2 is a plan view of three teeth of the type shown in Figure 1.

Figure 3 is a cross-sectional view through a rotating bit showing the area of a gage-to-shoulder transition incorporating the teeth of Figure 1.

Figure 4 is a plan view in reduced scale showing a coring bit incorporating the teeth of Figures 1 and 2.

Figure 5 is a half profile view of the coring bit of Figure 4.

Figure 6 is a plan view of the gage-to-shoulder transition of the coring bit in Figure 4 in conformity with the teaching of Figure 3.

Figure 7 is a cross-sectional view in enlarged scale of a tooth incorporating a second embodiment of the present invention.

Figure 8 is a plan view of three teeth devised according to the second embodiment shown in Figure 7.

The present invention and its various embodiments may be better understood by viewing the above figures in light of the following detailed description.

Detailed Description of the

Preferred Embodiments

[0009] The present invention is an improvement in a tooth design used in rotating bits, particularly rotary bits, wherein the tooth includes a diamond cutting element and in particular a diamond cutting element derived from cylindrical polycrystalline synthetic diamond (PCD). Such full cylindrical elements are generally commercially available but not is segment form. Such synthetic diamond is formed in the shape of a full circular cylinder having one planar end perpendicular to the longitudinal axis of the cylindrical shape and an opposing domed end, generally formed in the shape of a circular cone. Such elements are typically available in a variety of sizes with the above described shape.

[0010] According to the present invention, the full cylindrical diamond element is segmented to form a cylindrical segment wherein the segment is then axially disposed within a bit tooth. Such segmented or split cylindrical elements thus provide a cutting element with improved cutting efficiency with less use of diamond material and less tendency to dull or polish. The present invention and its various embodiments may be better understood by now turning to Figure 1.

[0011] Figure 1 is a cross-sectional view of a first embodiment of the present invention showing a tooth, generally denoted by reference numeral 10, incorporating a diamond cutting element, generally denoted by reference numeral 12. Element 12 is axially disposed within the tungsten- carbide matrix material 14 of the rotating bit. In other words, longitudinal axis 16 of element 12 is oriented to be approximately perpendicular to bit surface 18 atthe location of tooth 10. Bit surface 18 may be bit face of a crown of a rotating bit or may be the superior surface of a raised land or pad disposed upon a bit crown. In either case, but surface 18 is taken in the present description as the basal surface upon which tooth 10 is disposed.

[0012] As better seen in Figure 2, element 12 is approximately a quarter section or 90 degrees of the full cylindrical shape of the PCD element normally available. Element 12 is cut using a conventional laser cutter. For example, deep cuts are made every 90 degrees parallel to the longitudinal axis 16 of a full cylindrical diamond element. Although the laser could be used to completely cut through the diamond element, it has been found possible that with deep scoring, the diamond can then be fractured with propagation of the fracture lying approximately along the continuation of the plane of the laser cut. For example, the laser may cut a millimeter or less into and along the length of the full cylindrical diamond element. A diametrically opposed cut of equal depth is also provided on the cylinder. Therafter, the cylinder may be split in half and then later quartered on another laser cut by fracturing the diamond element using an impulsive force and chisel.

[0013] Diamond element 12 is disposed within tooth 10 as is shown in Figure 2 so that the apical edge 20 of diamond 12 formed by the cleavage planes or laser cuts which have formed radial surfaces 22, is oriented in the leading or forward direction of tooth 10 as defined by the rotation of the bit upon which tooth 10 is disposed.

[0014] Turning again to Figure 1, it can be seen that a portion of element 12 is fully exposed above bit surface 18 and in particular, that apical edge 20 forms the foremost portion of diamond element 12 as the tooth moves forwardly in the plane of the figure. Surfaces 22 define a dihedral angle and the tangential direction of movement of tooth 10 during normal cutting operation is generally along the direction of the bisector of the dihedral angle. In the illustrated embodiment a channel 24 is defined immediately in front of apical edge 20 to serve as a waterway or collector as appropriate. Thus, leading surfaces 22 and edge 20 can be placed virtually in channel 24 or immediately next thereto, forming as shown in Figure 1, one wall of channel 24 or a portion thereof, whereby hydraulic fluid supplied to and flowing through channel 24 during normal drilling operations will serve to cool and clean the cutting face of tooth 10 and in particular the leading edge and surfaces of diamond element 12.

[0015] Further, in the illustrated embodiment, tooth 10 is shown as having a trailing support 26 of matrix material integrally formed with matrix material 14 of the bit and extending above bit surfaces 18 to the trailing surface of diamond element 12. The slope of trailing support 26 is chosen so as to substantially match the slope of the top conical surface 28 of element 12 with the opposing end of element 12, which is a right circular plane, being embedded within matrix material 14. However, it must be understood that the exact shape and placement of trailing support 26 can be varied without departing from the spirit and scope of the present invention: For example, with larger diameter elements 12, cut from larger diameter synthetic cylinders, no trailing support 26 may be provided at all and element 12 may be totally free standing above bit surface 18 like an embedded stud. In the cases of thinner cylindrical elements 12, trailing support 26 may be even more substantial than that shown in Figure 1 and may assume a slope different from surface 28 of element 12 to thereby provide additional matrix reinforcing material behind and on top of conical surface 28 and leading surfaces 22.

[0016] Figure 2 illustrates a plan view the tooth of Figure 1 in a double row or triad configuration. In other words, a first row of teeth including teeth 10a and 10b is succeeded by a trailing tooth or second row of teeth including tooth 10c, wherein tooth 10c is placed halfway between the spacing of teeth 10a and 10b. Therefore, it can be appreciated that as the teeth 10a-c move forward during cutting of rock formation, the diamond cutting elements incorporated within each of the teeth effectively overlap and provide a uniform annular swath cut into the rock formation as the bit rotates. Figure 4, which shows in plan view a coring bit incorporating the teeth of Figures 1 and 2 illustrates the disposition of such a double row of configured teeth, collectively denoted by reference numeral 32, on pad 30.

[0017] Bit 34 also includes an inner gage 44 wherein the inner and outer gage are connected by waterways 31. Each pad 30 begins at or near inner gage 44 and is disposed across the bit face in a generally radial direction as seen in Figure 4 and splits into two pads which then extend to outer gage 36. The bifurcated pads are separated by a collector 33 which communicates with a gage collector 35 or junk slot 37 as may be appropriate. Clearly, other types of coring bits and petroleum bits could have been illustrated to show the use of the teeth of Figures 1-3 other than the particular bit illustrated in Figure 4. Therefore, the invention is not to be limited to any particular bit style or in fact, even to rotating bits.

[0018] Turning now to Figure 3, a cross-sectional view of the shoulder-to-gage transition utilizing the teeth of Figures 1 and 2 is illustrated. The bit, generally denoted by reference numeral 34, is characterized by having a vertical cylindrical section or gage 36 which serves to define and maintain the diameter of the bore drilled by bit 34. Below gage 36, bit 34 will slope inwardly along a designed curve toward the center of the bit. In the example of coring bit of Figure 4, a half profile is shown in Figure 5 and is a simple elliptical cross section characterized by an outer shoulder 38, nose 40 and inner shoulder 42. Inner diameter of the core is then defined by inner gage 44. Turning again to Figure 3, outer gage 36 is shown as incorporating a half cylindrical segment 46, which is surface set and embedded into gage 36 so that the rounded cylindrical surface 48 is exposed above bit surface 50 of gage 36 with the flat longitudinal face 52 of the half cylindrical segment embedded within matrix material 54 of bit 34. Half cylindrical diamond crystalline element 46 is more clearly depicted in cross-sectional view in Figure 4 on gage 36.

[0019] Moving from gage 36 to outer shoulder 38, teeth 32 as shown in Figure 4 include quarter cylindrical segments, shown in rear view in Figure 3 as exemplified by diamond elements 56 and 58. Each element 56 is disposed within bit 34 so as to extend therefrom in a prependicular direction as defined by the normal to bit surface at each point where such element is located.

[0020] In the preferrred embodiment each element 56 and 58 is exposed by a uniform amount, namely, 2.7 mm (0.105") above the bit face. Element 56 which is the diamond element closest to gage 36 is placed upon shoulder 38 at such a position next to the beginning of gage 36 so that its outermost radially extending point, namely, apex 60, extends radially from the longitudinal axis of rotation of bit 34 by an amount equal to the radial distance from the longitudinal axis of bit 34 by the gage diamonds, in particular diamond 46. For example, in the preferred embodiment, gage diamond 46 extends above bit surface 50 by 0.64 mm (0.025"). While element 56 extends above bit face 50 by 2.7 mm (0.105") it is placed as the first tooth on the bit face at such a distance from the gage 36 that the radially outermost exposed portion of diamond element 56 will equal the radial distance of the gage diamonds 46 from the axis of rotation of bit 34.

[0021] Thus, as illustrated in Figure 6, which shows a plan view of the gage of the bit of Figure 4, a double row of gage diamonds 46a is disposed at and slightly below gage level 62 on a type I gage column corresponding to a type I pad 30 shown in plan view in Figure 4. Gage diamonds 46b are thus placed adjacent to a pad of type II and gage diamonds 46c placed on a gage section corresponding to a type III pad. Gage diamonds 46a-c thus form a staggered pattern as best illustrated in Figure 6 which effectively presents a high cutting element density as the bit rotates. Above gage diamonds 46a-46b are conventional natural diamonds surface set in broaches, namely, kickers which are typical of the order of 6 per carat in size. Whereas the double row of diamonds within one gage section are offset from each other by approximately half a unit spacing, a unit spacing being defined as the length of a gage diamond 46, the adjacent row of teeth on the next adjacent gage section begins at a quarter spacing displaced from the corresponding row of gage diamonds on the adjacent pad. In other words, while type pad corresponds to gage diamonds 46a having two rows with each row offset by half a space between each other, pad II corresponds to gage diamonds 46b which are similarly offset with respect to each other and are spaced down the gage one quarter of a spacing as compared to gage diamonds 46a on pad type 1.

[0022] Turning now of Figure 7, a second embodiment of the present invention is illustrated wherein a tooth, generally denoted by reference numeral 66, incorporates a half cylindrical segment diamond element 68 extending from and embedded in matrix material 14 in much the same manner as illustrated in connection with the first embodiment of Figures 1 and 2. As better seen in plan view of Figure 8, PCD element 68 is characterized by a half cylindrical surface 70 and a planar leading surface 72, which is formed as described above by cleaving a full cylinder along the diameter.

[0023] Turning again to Figure 7, diamond element 68 also includes a conical or domed upper surface 74 forming the apical point 76 of element 68. A trailing support 78 of integrally formed matrix material is smoothly fared from surface 74 to bit face 18 to provide tangential reinforcement and support for diamond element 68 against the cutting forces to which element 68 is subjected. As better seen in plan view of Figure 8, trailing supports 78 are tapered to a point 80 on bit face 18 thereby forming a teardrop shaped plan outline for tooth 66.

[0024] As shown in Figure 7, diamond element 68 is placed immediately adjacent to and forms one side of a channel 80 formed into matrix material 14 which channel 80 serves as a conventional waterway or cellector as may be appropriate with the same advantages as described in connection with the first embodiment of Figure 1.

[0025] As described in connection with Figure 2, the second embodiment of Figure 8 similarly consists of two rows of teeth 66a and 66b followed by a second row represented by tooth 66c. Tooth 66c as defined with respect of the direction of tangential movement during normal drilling operations. The double row of teeth are disposed on a petroleum or coring bit in the same manner as illustrated in connection with the first embodiment of the invention in Figure 4. Teeth 66 are thus disposed within matrix material 14 and used on a bit in the same manner as are teeth 10 of Figures 1 and 2. However, teeth 66 as shown in Figure 8, clearly provide a broader cutting surface and a diamond element 68 containing twice the diamond material and structural bulk as compared to diamond elements 12 of the first embodiment. Therefore, in those applications where a larger cutting bite is required or where greater structural strength is needed in the diamond element, the half cylindrical split elements 68 of the second embodiment may be more advantageously used than the quarter split diamond elements of the first embodiment.

[0026] Many alterations and modifications may be made to the present invention without departing from its spirit and scope. For example, although the split cylindrical segment has been shown a perpendicularly embedded into the matrix material, it is clearly contemplated that it may be eitherforwardly or rearwardly raked if required by design objectives. Therefore, the illustrated embodiment must be understood as presented only as an example of the invention and should not be taken as limiting the invention as set forth in the following claim.

Claims

1. A rotatable bit (34) having a bit face (18) and a plurality of teeth (10; 66) disposed thereon and each comprising a polycrystalline. diamond cutting element (12; 68) said cutting element (12; 68) having the form of a segment of a cylinder, said segment of said cylinder shape of said cutting element (12; 68) providing at least one planar surface (22; 72), said planar surface of said cutting element being oriented within said tooth (10; 66) to provide at least in part a leading surface of said tooth (10; 66) as defined by the direction of movement of said tooth (10; 66) during normal cutting operation when said bit (34) rotates, characterized in that one end of said cylindrical shape being formed into a conical segment, each cutting element (12; 68) being mounted directly in the matrix of the bit (34) during matrix formation, and trailing support means (26; 78) being provided integrally formed with said bit face (18) and extending in a tapered fashion from said bit face (18) to a trailing surface (28; 74) of said cutting element (12; 68), the slope of said cone shaped segment approximately matching the slope of said trailing support (26; 78).

2. A rotatable bit as set forth in claim 1 wherein said segment of said cylindrical shaped cutting element is a half cylindrical segment (68), thereby defining a planar leading surface (72) lying along a diameter of said cylindrical shape.

3. A rotatable bit as set forth in claim 1 wherein said segment of said cylindrically shaped cutting element is a quarter segment (12), thereby defining an apical edge (20) and two leading surfaces (22) forming a dihedral angle behind said edge, said dihedral angle being approximately 90 degrees.

4. A rotatable bit as set forth in claim 3 wherein said cylindrically shaped cutting element having a longitudinal axis (16) lying along said apical edge (20) and wherein said cutting element (12) is oriented with respect to said bit face (18) so that longitudinal axis (16) is approximately perpendicular thereto.

5. A rotatable bit as set forth in claim 3 or 4 wherein a channel (24) is defined into said bit face (18) immediately in front of said diamond cutting element (12; 68) and wherein said apical edge (20) is disposed on and serves at least as part of an adjacent wall of said fluid channel (24).

6. A rotatable bit as set forth in any of claims 1-5 wherein a plurality of rows of said teeth (10; 66) are disposed on said bit (34) and wherein said rows are paired to form a first and second related row, the distance of spacing between teeth (10a; 10b; 10c) within said first and second row being substantially constant, said teeth (10c) of said second row being disposed behind said teeth (10a, 10b) of said first row as defined by tangential motion of said teeth during rotation of said bit (34) during normal cutting operations, said teeth (10c) of said second row being readily disposed halfway between said teeth (10a; 10b) of said first row, whereby said teeth (10a, 10b; 10c) of said first and second rows cut a uniform annular swath as said bit (34) rotates of a higher effective tooth density than achievable by tooth density within said first or second row alone, said teeth (10c) of said second row following behind said teeth (10a, 10b) of said first row in the gaps between and behind said teeth (10a, 10b) of said first row.

7. A rotatable bit as set forth in claim 1 wherein said bit (34) includes a gage (36) and a sloping shoulder (38), said teeth (56, 58) being disposed on said shoulder (38) near said gage (36) and extending above said bit face (18) by a first predetermined distance, said gage (36) including cutting elements disposed above said bit face (18) of said gage (36) by a second predetermined distance, and said bit (34) further having a long- tiduinal axis of rotation, the radial distance from said longitudinal axis rotation of said cutting elements (46) disposed and extending above said gage (36) being approximately equal to the radial distance from said longitudinal axis of rotation of an uppermost one (56) of said diamond cutting elements (56, 58) disposed on said shoulder (38), said uppermost cutting element (56) on said shoulder (38) being positioned on said shoulder (38) next to said gage (36) at a location such that said radial distances from said longitudinal axis of rotation of said cutting elements (46) on said gage (36) and of said uppermost cutting element (56) are set approximately equal.

8. A rotatable bit as set forth in any of claims 1-7 wherein said cylindrical shape of said cutting element is a circular cylinder.

9. A rotatable bit as set forth in any of claims 3 through 6 wherein said segment of cylindrically shaped cutting element is a quarter segment (12) of a full cylinder and wherein said apical edge (20) lies along said longitudinal axis (16).

10. A rotatable bit as set forth in claims 1 or 9 wherein said cutting element (12) is disposed within each tooth (10) so that each apical edge (20) provides the leading portion of said cutting element (12).

11. A rotatable bit as set forth in claim 10 wherein the tangential direction of movement of said tooth (10) lies approximately along the bisector of said dihedral angle defining said apical edge (20).

12. A rotatable bit as set forth in claim 1 or 2 wherein said cutting element (12) forms one wall of an adjacent fluid channel (24) defined into said bit face (18) in front of said tooth (10).

Ansprüche

1. Drehbohrmeißel (34) mit einer Meißeloberfläche (18) und einer Mehrzahl von auf dieser angeordneten Zähnen (10; 66), von denen jeder ein polykristallines Diamantschneidelement (12; 68) umfaßt, das die Form eines Segmentes eines Zylinders aufweist, wobei das Segment der Zylinderform des Schneidelements (12; 68) zumindest eine ebene Fläche (22; 72) darbietet und die ebene Fläche des Schneidelementes innerhalb eines Zahns (10; 66) derart orientiert ist, daß sie zumindest teilweise eine Vorlauffläche des Zahns (10; 66) bildet, wie sie durch die Bewegungsrichtung des Zahns (10; 66) während eines normalen Schneidvorgangs bei rotierendem Meißel (34) definiert ist, dadurch gekennzeichnet, daß ein Ende der zylindrischen Gestalt zu einem konischen Segment geformt ist, jedes Schneidelement (12; 68) direkt in der Matrix des Meißels (34) während der Matrixbildung angebracht ist, und ein nachlaufendes Stützmittel (26; 78) vorgesehen ist, das integral mit der Meißeloberfläche (18) ausgefuhrt ist und sich in spitz zulaufender Form von der Meißeloberfläche (18) zu einer Nachlauffläche (28; 74) des Schneidelements (12; 68) erstreckt, wobei die Schräge des konisch geformt Segments annähernd mit der Schräge der Nachlaufstütze (26; 78) zusammenfällt.

2. Drehbohrmeißel nach Anspruch 1, bei dem das Segment des zylindrisch geformten Schneidelementes ein Halbzylindersegment (68) bildet, das dementsprechend eine entlang einem Durchmesser der Zylinder verlaufende Vorlauffläche (72) definiert.

3. Drehbohrmeißel nach Anspruch 1, bei dem das Segment des zylindrisch geformten Schneidelementes ein Viertelsegment (12) bildet, das dementsprechend eine Scheitelkante (20) und zwei Vorlaufflächen (22) definiert, die einen spitzen Winkel hinter der Scheitelkante bilden, der annahernd 90° beträgt.

4. Drehbohrmeißel nach Anspruch 3, bei dem das zylindrisch geformte Schneidelement eine Längsachse (16) aufweist, die sich entlang der Scheitelkante (20) erstreckt, und bei dem das Schneidelement (12) derart zur Meißeloberfläche (18) ausgerichtet ist, daß die Längsachse (16) annähernd senkrecht zu ihr verläuft.

5. Drehbohrmeißel nach Anspruch 3 oder 4, bei dem ein Kanal (24) in der Meißeloberfläche (18) unmittelbar vor dem Diamantschneidelement (12; 68) ausgebildet ist und die Scheitelkante (20) an der benachbarten Wand des Flüssigkeitskanals (24) gelegen ist und wenigstens als Teil derselben dient.

6. Drehbohrmeißel nach einem der Ansprüche 1 bis 5, bei dem eine Mehrzahl von Reihen von Zähnen (16; 66) auf dem Meißel angeordnet sind und die Reihen paarweise zusammengefaßt sind und eine erste und zweite zugehörige Reihe bilden, der räumliche Abstand zwischen Zähnen (10a, 10b; 10c) innerhalf der ersten und der zweiten Reihe im wesentlichen konstant ist, die Zähn (10c) der zweiten Reihe hinter den zähnen (10a, 10b) der ersten Reihe angeordnet sind, und zwar hinter im Sinne der tangentialen Bewegung der Zähne während des Umlaufens des Meißels (34) bei normalen Schneidvorgängen, die Zähne (10c) der zweiten Reihe etwa mittig zwischen den Zähnen (10a; 10b) der ersten Reihe angeordnet sind, wodurch die Zähnen (10a; 10b; 10c) der ersten und der zweiten Reihen einen gleichförmigen Ringbereich schneiden, da der Meißel (34) mit höher wirksamer Zahndichte rotiert, als sie durch die Zahndichte innerhalb der ersten oder zweiten Reihe alleine erreichbar ist, und bei dem die Zähne (10c) der zweiten Reihe den Zähnen der ersten Reihe (10a, 10b) im Zwischenraum zwischen und hinter den Zähnen (10a; 10b) der ersten Reihe nachfolgen.

7. Drehbohremeißel nach Anspruch 1, bei dem der Meißel einen Kalibrierbereich (36) und eine schräge Schulter (38) aufweist, die Zähne (56, 58) auf der Schulter (38) nahe dem Kalibrierbereich (36) angeordnet sind und sich über der Meißeleberfläche (18) mit einem ersten vorbestimmten Abstand erstrecken, der Kalibrierbereich (36) Schneidelemente aufweist, die sich über der Meißeloberfläche (18) des Kalibrierbereiches (36) mit einem zweitenvorbestimmten Abstand erstrekken, der Meißel (34) ferner eine längsgerichtete Rotationsachse aufweist, die radiale Entfernung der auf dem Kalibrierbereich angeordneten und sich vorerstreckenden Schneidelemente (46) zur längsgerichteten Rotationsachse gleiche ist dem radialen Abstand eines zuoberst auf der Schulter (38) angeordneten Schniedelements (56) der Diamantschneidelemente (56, 58) zur längsgerichtent Rotationsachse, das oberste Schneidelement (56) auf der Schulter (38) auf dieser nächst dem Kalibrierbereich (36) an einer Stelle angeordnet ist, bei der die radialen Entfernungen der Schniedelemente (46) auf dem Kalibrierbereich (36) und des obersten Schneidelements (56) zur längsgerichteten Rotationsachse annähernd gleich sind.

8. Drehbohrmeißel nach einem der Ansprüche 1 bis 7, bei dem die Zylinderform des Schneidelementes ein Kreiszylinder ist.

9. Drehbohrmeißel nach einem der Ansprüche 3 bis 6, bei dem das Segment des zylindrisch geformten Schneidelements ein Viertelsegment (12) eines Vollzylinders ist und die Scheitelkante (20) entlang dessen Länngsachse (16) verläuft.

10. Drehbohrmeißel nach einem der Ansprüche 1 oder 9, bei dem das Schneidelement (12) in jedem Zahn (10) so angeordnet ist, daß jede Scheitelkante (20) den Vorlaufbereich des Schneidelementes (12) bildet.

11. Derhbohrmeißel nach Anspruch 10 bei, dem die tangentiale Bewegungsrichtung des Zahns (10) sich annähernd entlang der Winkelhalbierenden des die Scheitelkante (20) definieren spitzen Winkels verläft.

12. Drehbohrmeißel nach Anspruch 1 oder 2, bei dem das Schneidelement (12) eine Wandung eines benachbarten, in der Meißeloberfläche (18) vor dem Zahn angeordneten Flüssigkeitskanals (24) bildet.

Revendications

1. Trépan rotatif (34) comportant une face de trépan (18) et une pluralité de dents (10, 66) disposée sur cette face de trépan et comprenant chacune un élément de coupe en diamant poly- cristallin (12, 68), l'élément de coupe (12, 68) ayant la forme d'un segment de cylindre, le segment de forme cylindrique de l'élément de coupe (12,68) présentant au moins une face plane (22, 72), la face plane de l'élément de coupe étant orientée dans la dent (10,66) de manière à former au moins en partie une face antérieure de la dent (10, 66) définie par la direction de mouvement de la dent (10, 66) pendant une opération de forage normale lorsque le trépan (34) tourne, caractérisé en ce qu'une extrémité de la forme cylindrique est façonnée en un segment conique, chaque élément de coupe (12, 68) étant monté directement dans la matrice du trépan (34) pendant la formation de cette matrice, et un support traînant (26, 78) étant prévu d'une seule pièce avec la face de trépan (18) et s'etendant en pente à partir de la face de trépan (18) jusqu'à une face traînante (28, 74) de l'élement de coupe (12, 68), la pente du segment conique correspondant approximativement à celle du support traînant (26, 78).

2. Trépan rotatif suivant la revendication 1, dans lequel le segment de l'élément de coupe de forme cylindrique est un segment semi-cylindrique (68), définissant ainsi une face antérieure plane (72) disposée suivant un diamètre de la forme cylindrique.

3. Trépan rotatif suivant la revendication 1, dans lequel le segment de l'élément de coupe de forme cylindrique est un segment en forme de quartier, définissant ainsi une arête (20) et deux faces antérieures (22) formant un angle dièdre derrière l'arêtel, l'angle dièdre étant d'environ 90°.

4. Trépan rotatif suivant la revendication 3, dans lequel l'élément de coupe de.forme cylindrique présente un axe longitudinal (16) situé le long de l'arête (20) et dans lequel l'élément de coupe (12) est orineté par rapport à la face de trépan (18), de telle sorte que l'axe longitudinale (16) y soit approximativement perpendiculaire.

5. Trépan rotatif suivant la revendication 3 ou 4, dans lequel un canal (24) est ménagé dans la face de trépan (18) immédiatement en avant de l'élément de coupe en diamant (12, 68) et dans lequel l'arête (20) est disposée sur le canal à fluide (24) et forme au moins une partie d'une paroi adjacente de ce canal.

6. Trépan rotatif suivant l'une quelconque des revendications 1 à 5, dans lequel une pluralité de rangées des dents (12, 68) est disposée sur le trépan (34) et dans lequel les rangées sont appariées pour former une première et une seconde rangée associées, l'espacement entre les dents (10a, 10b, 10c) dans la première et la deuxième rangée étant en substance constant, les dents (10c) de la seconde rangée étant disposées der- mière les dents (10a, 10b) de la première rangée par rapport au mouvement tangentiel des dents pendant la rotation du trépan (34) durant des opérations de forage normales, les dents (10c) de la seconde rangée étant facilement disposées au milieu entre les dents (10a, 10b) de la première rangée, de sote que les dents (10a, 10b, 10c) de la première et de la seconde rangée taillent, lorsque le trépan (34) tourne, une bande annulaire uniforme d'une densité de dents effective supérieure à celle qui peut être obtenue par la densité des dents dans la première ou la seconde rangée seule, les dents (10c) de la seconde rangée suivant les dents (10a, 10b) de la première rangée dans les interstices séparant les dents (10a, 10b) de la première rangée et derrière ceux- ci.

7. Trépan rotatif suivant la revendication 1, dans lequel le trépan (34) comprend une partie de calibrage (36) et un épaulement incliné (38), les dents (56, 58) étant disposées sur l'épaulement (38) près de la partie de calibrage (36) et s'étendant au-dessus de la face de trépan (18) d'une première distance prédéterminée, la partie de calibrage (36) comprenant des éléments de coupe disposés au-dessus de la face de trépan (18) de la partie de calibrage (36) d'une seconde distance prédéterminée, et le trépan (34) présentant, en outre, un axe de rotation longitudinal, la distance radiale séparant cet axe de rotation longitudinal des éléments de coupe (46) disposés et s'étendant au-dessus de la partie de calibrage (36) étant approximativement égale à la distance radiale séparant ledit axe de rotation longitudinal d'un élément supérieur (56) parmi les éléments de coupe en diamant (56, 58) disposés sur l'épaulement (38), l'élément de coupe supérieur (56) sur l'épaulement (38) étant positionné sur cet épaulement (38) à proximité de la partie de calibrage (36) à un endroit tel que les distances radiales séparant l'axe de rotation longitudinal des éléments de coupe (46) sur la partie de calibrage (36) et de l'élément de coupe supérieur (56) sont réglées approximativement égales.

8. Trépan rotatif suivant l'une quelconque des revendications 1 à 7, dans lequel la forme cylindrique de l'élément de coupe est celle d'un cylindre circulaire.

9. Trépan rotatif suivant l'une quelconque des revendications 3 à 6, dans lequel le segment d'élément de coupe de forme cylindrique est un segment en forme de quartier (12) d'un cylindre complet et dans lequel l'arête (20) est disposée le long de l'axe longitudinal (16).

10. Trépan rotatif suivant la revendication 1 ou 9, dans lequel l'élément de coupe (12) est disposé dans chaque dent (10), de telle sorte que chaque arête (20) forme la partie antérieure de l'élément de coupe (12).

11. Trépan rotatif suivant la revendication 10, dans lequel la direction de mouvement tangentiel de la dent (10) est disposée approximativement le long de la bissectrice de l'angle dièdre définissant l'arête (20).

12. Trépan rotatif suivant la revendication 1 ou _'2, dans lequel l'élément de coupe (12) forme une paroi d'un canal de fluide adjacent (24) défini dans la face de trépan (18), devant la dent (10).

Drawing