WO2012038428A1

WO2012038428A1 - A rock drill bit for percussive drilling and a rock drill bit button

Info

Publication number: WO2012038428A1
Application number: PCT/EP2011/066323
Authority: WO
Inventors: Mauri Esko; Markku Keskiniva; Juha Piispanen; Pauli Lemmetty
Original assignee: Sandvik Intellectual Property Ab
Priority date: 2010-09-22
Filing date: 2011-09-20
Publication date: 2012-03-29
Also published as: AU2011304461B2; AU2015238819A1; AU2011304382B2; EP2619396A1; KR20140005880A; KR20140009149A; CA2812600A1; EP2434086B1; WO2012038342A1; RU2013118269A; BR112013006623A2; CN103339339A; BR112013006621A2; RU2571783C2; AU2011304382A1; ZA201302143B; US20130180785A1; EP2434086A1; AU2011304461A1; CA2811674A1

Abstract

A button and a rock drill bit (30, 50) for percussive drilling comprising a bit head (39) configured to be attached at an end of a drill element (33, 53) of a drilling assembly, said bit head having at a front end (38, 60) as seen in the intended drilling direction a plurality of buttons (41, 42, 56, 59, 80, 90) distributed over said bit head and configured to engage material to be crushed, at least one of said buttons having a shank portion (41', 56', 80', 90') of a substrate material, comprising particles of a first material embedded in a binder phase, said first material being harder than the binder phase. The shank portion (41', 56', 80', 90') comprises at least partially a bearing portion, the material of which is harder than the binder phase. At least one of said buttons (41, 42, 56, 80, 90) is allowed to rotate about its own symmetry axis.

Description

A ROCK DRILL BIT FOR PERCUSSIVE DRILLING AND A

ROCK DRILL BIT BUTTON

TECHNICAL FIELD OF THE INVENTION AND BACKGROUND ART

The present invention relates to a rock drill bit for percussive drilling and a rock drill bit button according to the preambles of the independent claims.

The invention is not restricted to any type of drilling assembly for use of a said rock drill bit, but the former may be a down-the- hole hammer drill just as well as a top hammer drill, although the rock drill bit shown is especially intended for the latter type.

Furthermore, said rock drill bit may have any conceivable size and has normally a diameter of 30 mm - 300 mm. The same ab- sence of limitations applies to the intended percussion frequency and rotational speed of the rock drill bit in operation, although it may be mentioned that these are typically within the ranges 20 Hz - 100 Hz and 20 - 500 revolutions per minute, respectively, but the invention does not exclude the use of the rock drill bit in high frequency assemblies operating at a frequency above 250 Hz and which may reach more than 1 kHz.

A known so-called standard rock drill bit 1 of the type defined in the introduction will now be described while referring to both Fig 1 and Fig 2. The drill bit has a bit head 2 configured to be attached at an end of a drill element, for example in the form of a drill tube or drill rod, of a drilli ng assembly and having a diameter larger than that of a said drill element. This drill element is not shown in these figures but may be intended to be received in a so-called ski rt 3 integ ral with a bit head and having a smaller diameter than the bit head. Other ways of connecting the dril l bit to the dril l element are conceivable and known with in the art. The bit head has at a front end 4 as seen i n the intended dril ling direction a plu rality of pressed-in gauge buttons 5 distributed along the circu mference of the bit button head 2. The gauge buttons are config ured to engage material to be crushed and to determine the diameter of a hole 6 (see Fig 1 ) to be drilled by the rock drill bit. These gauge buttons are made of hard

material , such as cemented carbide or tungsten carbide. Front buttons 7 also of hard material are pressed into a front surface 8 for engagi ng material to be crushed. It is also i ndicated how a flush chan nel opens at the front by a flushi ng hole 9 in the front surface.

In operation the gauge buttons 5 will engage and break rock close to the walls of a hole 6 in which the rock drill bit with said rod is located and the front buttons 7 will break rock closer to the centre of such a hole by impacts carried out by the rock drill bit in the direction of the arrow A. The drill bit wi ll rotate somewhat, typically about 5 °, between each such i mpact.

The operation efficiency of a rock dril l bit of th is type is of course an important featu re and th is may be expressed as the penetration speed of the rock dril l bit defined as the length of a hole drilled per time unit (meter/m inute) . The penetration speed of known rock drill bits of this type is dependent upon the wear of said buttons, especially the gauge buttons. It is i ndicated in Fig 2 that duri ng the operation of such a rock drill bit material is abraded at the periphery of the gauge buttons resulting in a flat surface 1 0 there, which makes them less sharp and reduces the penetration speed. These flat surfaces 1 0 will during the operation of the rock dri ll bit grow and finally result in a diameter of a hole drilled determi ned by said gauge buttons being so m uch reduced that the rock drill bit has to be replaced. It is of course an on-goi ng attempt to increase the penetration speed and prolong the l ife time of a rock drill bit of the type defined in the introduction .

SUMMARY OF TH E INVENTION

The object of the present invention is to provide a rock drill bit of the type defined in the introduction being improved in at least some aspect with respect to such rock dril l bits al ready known .

This object is according to the invention obtained by providing such a rock dri ll bit in which at least one of said buttons having a shank portion at least partially comprising a beari ng portion , the material of which is harder than the bi nder phase, and allowi ng the button to rotate about its own symmetry axis. By rotatably fitting at least one said button in the bit head this button wil l whi le drilling be i nfluenced by the impacts thereof and rotation of the rock drill bit to rotate about its own symmetry axis, so that the parts of said button engaging rock will vary and the button will be evenly worn and by that self-sharpened. This means that this button will thanks to the self-sharpening effect maintain its contribution to the penetration speed of the rock drill bit longer than would it be fixed in the bit head. The provision of a bearing portion on the button wil l substantially avoid any grinding action on the hole wall .

According to an embodiment of the invention the material of the beari ng portion is substantially homogenous or stated another way it comprises a material generally free from particles that are harder than the su rrounding material so as to avoid exposure of abrasive particles towards the hole wall . According to another embodiment of the invention the bearing portion is at least partially coated with a barrier coating, which substantially stops dissolution of binder phase. According to another embodiment of the invention the bearing portion can have a friction coefficient against steel which is less than 0.5 that will substantially avoid wear on the hole wall.

According to another embodiment of the invention the bearing portion may have a microhardness (HV 0.05) of at least 3000 to make the bearing portion endure abrasion.

According to another embodiment of the invention the bearing portion comprises anyone of or several of titanium-aluminium nitride (TiAIN), aluminum-chromium nitride (AICrN), titanium carbide (TiC), titanium nitride (TiN), chromium nitride (CrN), zirconium nitride (ZrN) and/or diamond coatings to achieve non- abrasive effect on the hole. According to another embodiment of the invention the button comprises button retaining means such that the button may be reliably held in the rock drill bit while being allowed to rotate.

According to another embodiment of the invention a base portion of at least one button rests against or contacts a bottom of a button hole to transfer impact forces to the button while allowing the base portion to move thereon when rotating.

The invention also relates to a rock drill bit button according to the invention for percussive rock drilling into earth material, such as rock.

The invention also relates to a use of a rock drill bit according to the invention for percussive rock drilling into earth material, such as rock. Further advantages as well as advantageous features of the invention will appear from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the appended drawings, below follows a specific description of embodiments of the invention cited as examples. In the drawings:

Fig 1 is a very simplified view of a rock drill bit according to prior art in operation

Fig 2 is a perspective view of a rock drill bit according to prior art after some time of operation,

Fig 3 is a perspective view illustrating the principle of a rock drill bit according to the present invention,

Fig 4 shows a longitudinal section through a part of a rock drill bit according to a first embodiment of the invention in operation,

Fig 5 is an exploded view of the rock drill bit according to

Fig 4,

Fig 6 is a view corresponding to Fig 4 of a rock drill bit according to a second embodiment of the invention,

Fig 7 is an exploded view of the rock drill bit according to

Fig 6,

Fig 8 is a simplified view corresponding to Fig 4 of a rock drill bit according to a third embodiment of the invention, Fig 9 is a simplified view of a button allowed to rotate i n a bit head of a rock dril l bit according to a fourth embodiment of the i nvention , and

Fig 1 0 is a very simplified view of a drilling assembly for percussive rock drill ing according to an embodiment of the present invention in operation . Fig . 1 1 is a graph showing drilled meters versus drill

penetration speed, wherei n dril l bits B and C represent the present invention .

DETAI LED DESCRI PTION OF EMBODIM ENTS OF TH E INVENTION

Fig 3 shows very schematical ly the principle of a rock drill bit according to the present invention , in which all gauge buttons 20 and all front buttons 21 are allowed to rotate about thei r own symmetry axis by bei ng received in holes 22 in a dril l bit body in a substantially circumferential ring su rface 23 defini ng a substantially frusto-conical shape as seen in the intended drilli ng di rection and in a front surface 24, respectively. Each button may be man ufactured from pressed and sintered cemented carbide. By the term "cemented carbide" is here meant WC, TiC, TaC, NbC, etc. , in sintered combination with a binder metal such as, for instance, Co or Ni . The button is preferably at least partially coated with a barrier coating which will be discussed more in detail . In certai n cases, it may be justified that at least the exposed part of the button comprises superhard materials such as polycrystalline diamond or cubic boron nitride.

A rock dril l bit 30 according to a first embodiment of the present invention will now be described while maki ng reference to Figs. 4 and 5. The rock drill bit comprises a first member 31 having a substantially circu mferential ring surface 32 defining a substantially frusto-conical shape as seen in the i ntended drilling direction . This first member 31 is provided with means configured to secure this member to a dril l element 33, i n which th is securi ng means is formed by a sleeve-like portion 34 of the first member 31 provided with engagement means in the form of an internal thread 35 configured to engage engagement means i n the form of an external thread 36 on the drill element.

The rock drill bit fu rther comprises a second member 37 defini ng a front end 38 of a bit head 39 of the rock dri ll bit. This second member is provided with a plurality of throug h holes 40 receiving the gauge buttons 41 and front buttons 42 while allowing these to rotate about their own sym metry axis. Each gauge button 41 comprises a shank portion 41 ' preferably integral with a tip portion . Preferably, the shank portion 41 ' defines a larger diameter than any chosen diameter of the tip portion . The through-holes 40 each have a diameter slightly exceedi ng

(suitably by a diameter difference in the order of 30-80 μιη) the diameter of the respective shank portion received therei n for allowi ng the button to move with respect to walls 43 in the second member 37 defini ng said hole when rotating . However, this difference in diameter has been exaggerated in this figu re and also i n the embodiment shown in Fig 6 and described below for better illustrati ng th is feature. The gauge buttons as well as the front buttons are provided with a base portion 44 with larger cross-section than the rest of the button and also than the respective hole 40 so as to maintain the button received in the second member.

A gauge button 41 rests by the base portion 44 thereof on said ring surface 32 configu red to transfer impact forces to the gauge button and allow the base portion to move thereon when rotat- ing . This means that impact forces are transferred to the gauge buttons from a surface 32 located inside the dri ll bit. The first member has also surfaces 45 directed in an intended drilling direction for supporti ng base portions of front buttons and

transferring impact forces thereto whi le allowing these base portions to move on these su rfaces 45 when rotating . Further- more, the bit head 39 wil l through a shoulder 47 on the first member 31 provide a clearance C with respect to this member 31 , so that the button 41 may rotate freely without jamm ing .

Particular measures are taken for flushing the surfaces and spaces surrounding the button , which will be explained more in detai l below.

The rock drill bit comprises means 46 config ured to secure the second member 37 to the first member 31 . The securi ng means is preferably configured to releasably secure these members to each other, for instance by m utual ly securi ng them by engagement of th reads. This would then mean that it would be possible to remove said second member with buttons for replacement while keeping the first member after the buttons have been that much worn that they have to be replaced. Welding or press fitting are other possible alternatives of said securing means 46 easier to accomplish .

When carrying out percussive dril ling with the rock drill bit shown in Fig 4 and 5 as illustrated in Fig 4 the buttons thereof will be allowed to rotate about their own axes, which means that the gauge buttons 41 wil l be worn evenly and maintain their sharpness, so that a high penetration speed may be mai ntained over a long period of time and the diameter of the hole defined by the gauge buttons wil l be reduced more slowly than would the gauge buttons be fixedly arranged in the bit head.

Figs. 6 and 7 i llustrate a rock dril l bit 50 according to a second embodiment of the invention . This rock dri ll bit has a fi rst member 51 in the form of a ring configured to be supported on and/or secured to an end 52 of a drill element 53 and havi ng a ring surface 54 form ing a support for a base portion 55 of each gauge button 56 in the same way as the correspondi ng surface 32 in the embodiment shown in Figs. 4 and 5. Each gauge button 56 comprises a shank portion 56' preferably integral with a tip portion . Preferably, the shank portion 56' defi nes a larger diameter than any chosen diameter of the tip portion . I mpact forces will be transferred by the ring surface 54 to the gauge buttons wh ile the base portions thereof are allowed to move thereon when rotating . A second member 57 of the rock dri ll bit has through holes 58 receiving said gauge buttons and allowing them to move with respect to walls of these holes when rotati ng . The front buttons

59 are, as an example, in this embodiment fixedly secured to a front end 60 of the second member 57.

The second member 57 is in this embodiment provided with means for secu ring this member to a drill element 53 by having a sleeve-l ike portion 61 designed to receive a dril l element and having engagement means in the form of an internal th read 62 for engagi ng with engagement means i n the form of an external thread 63 on the drill element for releasably securing said second member to the drill element and by that also keeping said ring 51 , a so-called pusher ring , in place. The first member 51 is provided with a col lar 64, so that the first 51 and second 57 members are fixed with respect to each other while leaving a clearance 66 therebetween for the button to freely rotate. Proper flushi ng of a button allowed to rotate is also important. It is indicated in Fig 6 that the rock drill bit has a conventional flush channel 67 extendi ng th roug h the bit head. The flush channel has also at least one fl ushing hole 68 (see the arrows F

indicating the flow of flushing medium) opening at the first end

60 and passing the clearance 66 and the circumference of the button 56 allowed to rotate. This will keep said clearance 66 clear and elimi nates wear problems whi le the button rotates inside the hole 58. The function of this embodiment of the invention in operation appears clearly from the above discussion of inter al ia the first embodiment of the present i nvention .

A part of a rock dri ll bit according to a third embodi ment of the invention is very schematical ly shown i n Fig 8. This rock drill bit is provided with alternative means to lock a button 80 to a dri ll bit head 81 wh ile allowing the button to rotate. Each gauge button 80 comprises a shank portion 80' preferably integral with a tip portion . Preferably, the shank portion 80' defi nes the largest diameter of the button . A blind hole 82 in the bit head desig ned to receive the button 80 is provided with an annular groove 83, and the shank portion 80' is provided with a corresponding ann ular groove 84 receivi ng an elastic lock ring 85, for example a ring , such as a C-ri ng , made from steel . When the button 80 is pushed into the hole 82 the lock ring wi ll first be compressed until reachi ng the groove 83 in the bit head. It will then expand outwards into that g roove and lock the button to the bit head 81 wh ile allowing the button to rotate. Fig 9 illustrates an alternative way of locki ng a button 90 to a bit head not shown in a rock dril l bit according to a fourth embodiment of the invention wh ile allowi ng the button to rotate. This is achieved by providing a shank portion 90' with an annular groove 91 as i n the embodiment shown in Fig 8. However, a lock pin 92 is used instead of a lock ring , and this lock pin is after pushi ng the button 90 i nto a corresponding hole in the bit head pushed into the groove 91 while locking the button in place and still allowing it to rotate about its own sym metry axis. The base portions 44, 55 and the ann ular groove 91 are all examples of button retain ing means and each said portion may define a largest diameter of the button .

Fig 1 0 illustrates very schematical ly a drilling assembly for per- cussive rock drilling according to the present invention having a rock drill bit 70 accordi ng to an embodiment of the invention provided with gauge buttons 71 . This drilli ng assembly is a so- called top ham mer drill acting upon the rock drill bit from a location above the ground and has power means 72, such as diesel engine and hydrau lic pu mp, configured to drive the rock dril l 76, which in turn makes said dril l element 73 and the rock drill bit to rotate and carry out percussions and by that crush the rock. A desig n of the drilli ng assembly as a down-the-hole hammer equipment is also within the scope of the present i nvention . The drilling assembly has also means 74, such as a compressed air generator, configured to flush cuttings resulted from engagement of the gauge buttons and the front buttons of the drill bit away from the region occupied by the drill bit. The drilling assembly has a control arrangement 75 configured to control the operation of the power means 72 so as to adapt the frequency of impacts and the rotational speed of the drill bit. It has turned out that drill bits according to the present invention with buttons allowed to rotate about their own symmetry axis are particu larly wel l suited to be used i n dril ling assemblies controlled to have frequencies above 250 Hz, preferably above 350 Hz and most preferred in the range of 350 Hz - 1 000 Hz.

Drilli ng with a drilli ng assembly according to Fig 8 with a rock drill bit according to the present i nvention will be more efficient than with rock drill bits already known , since the penetration speed may be kept at a high level longer and the stops needed for replaci ng the rock drill bit or parts thereof wil l be less frequently occurring . The i nventors of the present invention fou nd during tests that button hole wear is of major importance. Numerous experiments were made to avoid hole wear includi ng harden ing of the steel bit body, different flushing solutions for avoiding cutti ngs to enter into the holes, pol ishi ng of the buttons, etc. The results of the tests regarding button hole wear showed that su rface hardness of the dri ll bit body and entrance of rock cuttings into the hole clearance have no significant effect on wear rate. The inventors surprisingly found that tungsten carbide grains are responsible for the steel wear in the button holes. Surface quality of the button has tremendous effect on wear rate but the wear rate increases rapidly after a certain time of use of polished buttons. It is believed that after a certain period of drilling time the cobalt binder of the cemented carbide dissolves from the button surface thereby exposing abrasive wolfram carbide grains and the button surface quality is lost so that the wear rate in the hole increases rapidly.

The aim of the further tests was to maintain the integrity of the envelope surface of the button. One way of achieving that aim is to coat at least the shank portion 41', 56', 80', 90' of the button with a barrier such as a barrier coating to substantially eliminate cobalt dissolution. The button will then substantially maintain the surface quality and the button hole wear is substantially eliminated. It is preferable that also the button retaining means and/or the exposed portions of the rotatable buttons are coated.

Two coating materials were used in tests, i.e. one material comprising TiAIN and one material comprising AICrN.

Fig. 11 is a graph showing drilled meters versus drill penetration speed of A - a drill bit with fixed, uncoated gauge buttons, B - a drill bit with coated, rotatable gauge buttons, the coating being BALINIT® FUTURA NANO, i.e. titanium-aluminium nitride

(TiAIN), and C - a drill bit with coated, rotatable gauge buttons, the coating being BALINIT® ALCRONA PRO, i.e. aluminum- chromium nitride (AICrN). The coating thickness was about 3 micrometers in both cases. All bits had fixed, i.e. pressed-in, front buttons during the drilling tests. Each drilled hole was about 4.1 m deep. The drill bits all had conical button tips and were made for hole diameter of 48 mm. They all had five 10 mm buttons on gauge and three uncoated 9 m m buttons fixed to the front surface.

Both drill bits B and C with coated gauge buttons outperformed the drill bits A with uncoated gauge buttons. While drill bit A only could dril l about 40 m , drill bit B managed about 80 m and drill bit C about 1 70 m . Thus with a suitable barrier agai nst binder phase dissolution the life of a drill bit can be extended up to at least 400 %. After drill ing about 1 43 m with dri ll bit C the feed was i ncreased since by then the buttons became blu nt and a further 20 m could be drilled. The latter action is depicted i n Fig . 1 1 as "Hig her power".

Properties for a su itable coating can be that the bearing portion has a friction coefficient against steel which is less than 0.5, preferably in the range of 0.1 - 0.5, most preferably in the range of 0.2-0.4. The bearing portion may have a microhardness (HV 0.05) of at least 3000, preferably in the range of 3000-3500, most preferably in the range of 31 00-3400. The coating

thickness at the bearing portion can be thi n such as 1 -5 micrometers, preferably 2-4 micrometers, most preferably about 3 micrometers.

The coatings form diffusion barriers which prevent the

interaction between the hole wall and the button substrate material . Other coatings that can be used are titani um carbide (TiC) , titanium nitride (TiN) , chrom ium n itride (CrN) , zi rcon ium nitride (ZrN) and diamond coatings. A material generally free from particles that are harder than the surrounding material is here called substantially homogenous.

It is preferable that the base portion of each rotatable button rests agai nst or contacts the bottom of the hole to transfer impact forces to the button and while allowing the base portion to move thereon when rotating . The i nvention is of course not in any way restricted to the embodiments described above, but many possibilities to modifications thereof would be apparent to a person with skill i n the art without departi ng from the scope of the invention as defined in the appended clai ms. For example, the rotatable button can be provided with bearing portion in the shape of a sleeve secured to its shank portion instead of a coating such that the substrate does not reach the hole wall in the drill bit.

The n umber and positions of the buttons of the rock drill bit may differ a lot with respect to the embodi ments shown in the figures. "Substantially" used in the expressions "substantial ly a frusto- conical shape" and "substantially circumferential ring" also cover the case when cutting recesses or grooves and/or gauge buttons intersect the ri ng , as shown i n the fig ures. The disclosures in EP Patent Appl ication No. 1 01 78387.6, from which this appl ication claims priority, are i ncorporated herei n by reference.

Claims

A rock drill bit (30, 50) for percussive drilling comprisi ng a bit head (39) config ured to be attached at an end of a drill element (33, 53) of a drill ing assembly, said bit head having at a front end (38, 60) as seen in the intended dri lling direction a plural ity of buttons (41 , 42, 56, 59, 80, 90) distributed over said bit head and configured to engage material to be crushed, at least one of said buttons having a shank portion (41 ', 56', 80', 90') of a substrate material , comprisi ng particles of a first material embedded i n a binder phase, said first material being harder than the bi nder phase, characterized in that the shank portion (41 ', 56', 80', 90') at least partial ly comprises a bearing portion , the material of which is harder than the binder phase, and i n that at least one of said buttons (41 , 42, 56, 80 , 90) is allowed to rotate about its own sym metry axis.

A rock drill bit according to claim 1 , characterized in that the material of the bearing portion is substantial ly homogenous.

A rock drill bit according to claim 1 or 2, characterized in that the bearing portion comprises a material generally free from particles that are harder than the surrou nding material .

A rock drill bit according to anyone of claims 1 to 3,

characterized in that the bearing portion at is at least partially coated with a barrier coating .

A rock drill bit according to anyone of claims 1 to 4,

characterized in that the bearing portion has a friction coefficient against steel wh ich is less than 0.5, preferably i n the range of 0.1 - 0.49, most preferably in the range of 0.2- 0.4.

6. A rock drill bit according to anyone of claims 1 to 5,

characterized in that the bearing portion has a

microhardness (HV 0.05) of at least 3000, preferably in the range of 3000-3500, most preferably in the range of 3100- 3400.

7. A rock drill bit according to anyone of claims 1 to 6,

characterized in that the bearing portion comprises anyone of or several of titanium-aluminium nitride (TiAIN), aluminum- chromium nitride (AICrN), titanium carbide (TiC), titanium nitride (TiN), chromium nitride (CrN), zirconium nitride (ZrN) and/or diamond coatings.

8. A rock drill bit according to anyone of claims 1 to 7,

characterized in that the button comprises button retaining means (44, 55, 91 ).

9. A rock drill bit according to anyone of claims 1 to 8,

characterized in that a base portion (44, 55) of at least one button (41, 42, 56, 80, 90) rests against or contacts a bottom of a button hole to transfer impact forces to the button while allowing the base portion to move thereon when rotating.

10. A rotatable rock drill bit button, said button (41, 42, 56, 59, 80, 90) having a shank portion (41', 56', 80', 90') of a substrate material, comprising particles of a first material embedded in a binder phase, said first material being harder than the binder phase, characterized in that the shank portion (41', 56', 80', 90') at least partially comprises a bearing portion, the material of which is harder than the binder phase.

11. A rock drill bit button according to claim 10, characterized in that the material of the bearing portion is substantially homogenous.

12. A rock drill bit button according to claim 10 or 11 ,

characterized in that the bearing portion comprises a material generally free from particles that are harder than the surroundina material.

13. A rock drill bit button according to anyone of claims 10 to 12, characterized in that the bearing portion has a friction coefficient against steel which is less than 0.5, preferably in the range of 0.1 - 0.5, most preferably in the range of 0.2- 0.4.

14. A rock drill bit button according to anyone of claims 10 to 13, characterized in that the bearing portion has a

15. A rock drill bit button according to anyone of claims 10 to 14, characterized in that the bearing portion comprises anyone of or several of titanium-aluminium nitride (TiAIN), aluminum- chromium nitride (AICrN), titanium carbide (TiC), titanium nitride (TiN), chromium nitride (CrN), zirconium nitride (ZrN) and/or diamond coatings. 16. A rock drill bit button according to anyone of claims 10 to 15, characterized in that the button comprises button retaining means (44, 55, 91 ).

17. Use of a rock drill bit (30, 50) according to any of claims 1-9 for percussive drilling into earth, such as rock.