AU2008307767B2

AU2008307767B2 - Method and grinding appliance for grinding

Info

Publication number: AU2008307767B2
Application number: AU2008307767A
Authority: AU
Inventors: Mats Eriksson; Goran Stenberg
Original assignee: Epiroc Drilling Tools AB
Current assignee: Epiroc Drilling Tools AB
Priority date: 2007-10-03
Filing date: 2008-10-02
Publication date: 2014-06-19
Anticipated expiration: 2028-10-02
Also published as: SE0702215L; AU2008307767A1; CA2701017C; WO2009045142A1; CA2701017A1; SE531596C2; EP2205396A1; EP2205396A4

Abstract

This invention relates to a grinding appliance for grinding of button drill bits which comprise a drilling head with a plurality of buttons, and a method for manufacturing such a grinding appliance. The grinding appliance comprises a first element provided with an abrasive facing comprising diamonds as the abrasive medium and adapted to grinding a button to an intended end profile shape, and a second element adapted to grinding the drilling head. At least one section of the second element is provided with an abrasive facing comprising diamonds as the abrasive medium, the average grain size for the diamonds in the second abrasive facing being of a different average grain size from those in the first abrasive facing.

Description

WO 2009/045142 PCT/SE2008/000538 1 Method and grinding appliance for grinding Technical field The present invention relates to a grinding appliance for grinding of button drill bits which comprise a drilling head with a plurality of buttons, and a method for 5 manufacturing such a grinding appliance. State of the art A button drill bit intended for rock drilling comprises usually a plurality of buttons which are made of, for example, hard metal and are embedded in a drilling head which is made of a relatively softer material, e.g. steel. Each button usually has a cylinder-like 10 portion partly embedded in the steel, a cupola-shaped end profile shape protruding from the steel. The end profile shape of the button may be of various shapes, e.g. semi ballistic, as depicted in the drawings in this specification, hemispherical or semi cylindrical or some other desired shape. Such a button is often made of a hard metal, usually a material comprising tungsten carbide grains combined with a binding phase 15 which comprises cobalt or material with similar characteristics. During the drilling process, the button becomes worn in such a way that it becomes flat, thereby substantially reducing the drilling effectiveness of the button drill bit. As button drill bits are expensive to purchase, the button is therefore reground to restore its original shape so that the button drill bit can be reused instead of being scrapped. 20 Swedish patent specification SE434356 refers to a grinding facility for grinding of drill bits. The grinding facility comprises a grinding appliance comprising an abrasive wheel fastened to a powered spindle, and a rotatable table with a holder for the button drill bit. In this specification, a spindle is a machine part which, via a shaft, transmits a rotary motion to a tool, in this case the abrasive wheel, fastened in the shaft. The abrasive 25 wheel has running round it a profile groove corresponding to an intended end profile for the button drill bit. The end profile is obtained by rotating the tool about the geometric axis of symmetry of the button. The abrasive wheel is also fastened in such a way that it can grind a button to its original shape in conjunction with the button drill bit being held firmly on the rotating table. 30 Such an abrasive wheel for grinding of button drill bits with the object of restoring a worn button to its original shape is known from European patent EP397955. The abrasive wheel according to that patent takes the form of a pulley with a groove situated WO 2009/045142 PCT/SE2008/000538 2 between two flanks, with the shape which the drilling button originally had and which is to be recreated by the abrasive wheel. The groove on the abrasive wheel is provided with a grinding agent, usually a diamond facing, intended to be able to grind away the hard metal which the drilling button is 5 made of. In grinding with such an abrasive wheel, the situation is aggravated by the fact that the hard metal button is fastened in a softer material, usually steel, with the result that, in cases where the hard metal button is severely worn down or has been reground more than once, both the hard metal and the drilling head, which is made of the softer 10 material, e.g. steel, have to be ground on the same occasion. However, this is a difficult material combination to grind simultaneously, in that the tools and grinding methods used also cause severe wear of the edges of the abrasive wheel, which are caused to grind down the surrounding steel, thereby also reducing the service life of the abrasive wheel. During the removal of the material round the hard metal buttons of button drill 15 bits, the abrasive wheel quickly becomes clogged because of the relatively soft material of the button drill bit's drilling head in which the hard metal button is fastened. To solve this problem, a grinding appliance according to Swedish patent SE458425 is used. The grinding appliance according to that patent takes the form of a disc-shaped abrasive wheel provided with an abrasive facing of boron nitride adapted to grinding the 20 steel material of the drilling head. Using such an abrasive wheel for grinding the button of the drill bit makes it possible for the shape of the button to be restored, thereby greatly lengthening the service life of the drill bit. In normal use, a drill bit can be reground about 8-10 times. A problem is that if a boron nitride facing intended for grinding the steel of the drilling 25 head comes unintendedly into contact with a hard metal button, the abrasive facing is very-quickly destroyed and the abrasive wheel has to be scrapped. Moreover, the boron nitride facing used as the abrasive medium for grinding the drilling head, e.g. cubic boron nitride (c-Bn), functions badly in the grinding of hard metal. Dividing the grinding process into two stages, firstly steel grinding and thereafter hard metal 30 grinding, is also a time-consuming process. There is therefore within the industry a desire to improve the grinding process and make it more efficient.

3 Summary of the Invention A first aim of the invention is to propose a grinding appliance of the kind indicated in the introduction which at least ameliorates some of the above problem. A further aim is to indicate a method for manufacturing such a grinding appliance. 5 In accordance with a first aspect, the present invention provides a grinding appliance for grinding a button drill bit which has a drilling head provided with a plurality of buttons, the appliance comprising (ie including) a first element provided with a first abrasive facing comprising diamonds of a first average grain size as the abrasive medium adapted to grinding a button to an intended end profile shape, and at least one second element 10 adapted to grinding the drilling head, at least one section of the second element being provided with a second abrasive facing comprising diamonds of a second average grain size adapted to grinding the material of the drilling head, wherein the average grain size of the diamonds in the second abrasive facing is larger than average grain size of the diamonds in the first abrasive facing. 15 Manufacturing a grinding appliance in such a way that it comprises a plurality of separate but mutually assembled parts made of different materials makes it possible for each part of the abrasive wheel to have a function of its own, i.e. for each part to be adapted to grinding different portions of the drill bit. This makes it possible for each part to be adapted according to the material, e.g. hard metal or steel, which is ground by the various 20 parts of the grinding appliance. It is also possible to change the parts separately if they become worn at different rates. Using an abrasive facing which comprises coarser diamond grains on the abrasive wheel's flanks adapted to grinding the material of the drill bit causes the abrasive facing to last for more grinding operations than is the case with an abrasive facing which comprises finer 25 diamond grains, since the coarser abrasive facing will grind away larger material fragments, thereby making the grinding process quicker. This makes it possible for the abrasive wheel to be not worn down as quickly as one used with an abrasive facing which comprises finer diamond grains on all the abrasive surfaces. Nor are large material fragments trapped as easily in the coarser abrasive facing as smaller material fragments. A 30 further advantage is that the second element adapted to grinding the drilling head is diamond-faced, since diamond grains are more durable than, for example, boron nitride, 4 making it possible for the second element not to become worn prematurely if the grinding appliance inadvertently comes into contact with the hard metal of the button, thus allowing for careless handling. As noted, the average grain size of the diamonds in the second abrasive facing is different from that in the first abrasive facing, since the 5 respective abrasive facings are thereby adapted to grinding materials which have different characteristics. In an embodiment according to the invention, the diamonds in the second abrasive facing have an average grain size within the range 210-500 pm, corresponding to US mesh 70/80 - 35/40. In a preferred embodiment, the diamonds in the second abrasive facing have an 10 average grain size of 250-354 pzm, corresponding to US mesh 60/70 -45/50. The diamond grain size of the abrasive medium determines the amount of material which can be removed with a certain amount of abrasive media. The material of the drilling head is softer than that of the drilling button. The material of the drilling head is ground by the second abrasive facing. The material of the drilling head is, for example, steel or a 15 material with characteristics similar to steel, e.g. titanium alloys, aluminium alloys and bronzes. The larger the diamond grains, the more steel can be removed per unit time. Larger diamond grains increase the amount of material removed, and the drill bit is ground quicker. The abrasive wheel also lasts for more grinding operations with coarser diamond grains. 20 In an embodiment according to the invention, the diamonds in the first abrasive facing have an average grain size within the range 37-320 tim, corresponding to US mesh 400/500 - 45/60. In another embodiment according to the invention, the diamonds in the first abrasive facing have an average grain size within the range 37-229 pim, corresponding to US mesh 400/500 - 60/80. The size of the diamond grains is less 25 significant as regards grinding speed and wear resistance when grinding the button made of, for example, hard metal than when grinding the drill bit made of, for example, steel. For certain applications, however, diamond abrasive grains which are too large may cause deep scratches in hard metal, which may lead to the hard metal cracking during the grinding process. Smaller diamond grains limit surface roughness and result in small 30 depth of scratches, thereby increasing the durability, and allowing more regrindings, of the button.

4a An advantage of using an abrasive facing comprising coarser diamond grains on the flanks of the abrasive wheel is that the abrasive wheel does not become worn down as quickly on the flanks as when diamonds with a smaller average grain size are used as abrasive facing, with the result that more grinding operations can be effected with a WO 2009/045142 PCT/SE2008/000538 5 grinding appliance according to the invention. Another advantage of using an abrasive facing comprising coarser diamond grains on the flanks of the abrasive wheel than in the abrasive facing on the waist is that the flanks of the abrasive wheel can inadvertently reach the button without the abrasive medium on the flanks being damaged, since 5 coarser diamond grains have better durability than finer diamond grains, making it possible for more grinding operations to be done with the same grinding appliance without the abrasive facing becoming worn or clogged and the abrasive flank having to be scrapped. In an embodiment according to the invention, the first element is a first separate 10 component, the second element is a second separate component, and these components are connected for joint rotation so that a complete profile groove with an intended end profile shape is formed. This is an advantage in that the elements can be produced separately. It is also an advantage in that they can be changed separately. In an embodiment according to the invention, the grinding appliance is an abrasive 15 wheel and the first element has running round it a concave profile groove corresponding to the intended end profile shape, and the second element is a concentric circular flank, a concentrically circular side portion. The elements with the profile groove and the flank are connected for joint rotation so that a complete profile groove with an intended end profile shape is formed. The circular profile groove is provided with the first 20 abrasive facing intended for grinding the button. The concentric circular flank is provided with the second abrasive facing intended for grinding the drilling head. The abrasive wheel is with advantage mounted on a spindle in a grinding facility. In a preferred embodiment, the profile groove has a shape such that a button with a convex shape corresponding to the through-section of a substantially spherical zone of a 25 trapezoid can be ground. In an embodiment according to the invention, the grinding appliance comprises a third separate element connected for joint rotation with the first element and opposite to the second element, which third element is provided with a third abrasive facing comprising diamonds as the abrasive medium adapted to grinding the drilling head. In a preferred 30 embodiment, the third element is a second concentric circular flank. In this embodiment, the abrasive wheel comprises a middle portion made of one material and separate flanks made of another material. The grinding appliance is thus specially adapted to grinding a soft material, e.g. steel or a material with similar characteristics to 6 steel, with the flanks of the abrasive wheel while at the same time the hard metal button is ground by the middle portion, the waist of the abrasive wheel. In an embodiment according to the invention, the first element is an inner portion of a grinding cup and the second element is an adjacent firmly connected outer portion of the 5 grinding cup intended to grind the drilling head. The inner portion of the grinding cup is provided with the first abrasive facing intended to grind the button to an intended end profile shape. The second element of the adjacent firmly connected outer portion of the grinding cup, is provided with the second abrasive facing adapted to grinding the drilling head. This embodiment makes it possible for the grinding cup to rotate while the button is 10 stationary, or vice versa. This is also an advantage in that the parts can be changed separately. In an embodiment according to the invention, at least one of the abrasive facings comprises diamonds with protrusions. The diamonds with protrusions have preferably only one layer of diamonds so that a thin abrasive layer with a well-controlled surface 15 profile can be applied. The diamonds with protrusions will grind steel or a material with characteristics similar to steel quicker, without the abrasive wheel being destroyed, than if boron nitride is used as the abrasive facing, resulting in more efficient grinding. In an embodiment according to the invention, at least one of the abrasive facings comprises matrix diamonds. An advantage of matrix diamonds is that the diamonds will 20 be in two or more layers, so the layer can be made thicker. This is particularly an advantage in the manufacture of a homogeneously made second element for grinding the drill bit, in which the shape of the drill bit is of no great importance and it is therefore not important if the flank becomes worn down. In the manufacture of grinding cups, a thick layer is also of advantage for longer service life of the grinding cup. 25 In accordance with a second aspect, the present invention provides a method for manufacturing a grinding appliance for grinding of button drill bits which comprise a drilling head with a plurality of buttons, including the following steps: 7 - providing a first element of the grinding appliance with an abrasive facing comprising diamonds as the abrasive medium of a first average grain size adapted to grinding a button to an intended profile shape, - providing at least one section of a second element of the grinding appliance with an 5 abrasive facing comprising diamonds as the abrasive medium, - the average grain size for the diamonds in the second abrasive facing being of a different average grain size adapted to grinding the drilling head. In an embodiment, the method further comprises: -joining the first element and the second element together for joint rotation so that a 10 complete profile groove is fonned. Advantageous further developments and features of the invention are indicated in the following description of preferred embodiments of the invention which is provided with reference to the drawings. Brief Description of the Drawings 15 Figure I depicts a side view of a grinding facility intended for grinding of drill bits, Figure 2 A depicts a through-section of an abrasive wheel according to the invention, Figure 2B depicts an exploded diagram of a through-section of the abrasive wheel in Figure 2A, Figure 2C depicts a side view of the abrasive wheel in Figure 2A, 20 Figure 2D depicts a perspective view of the abrasive wheel in Figure 2A, Figure 3 depicts another through-section of an abrasive wheel according to the invention, Figure 4 depicts further through-section of an abrasive wheel according to the invention, WO 2009/045142 PCT/SE2008/000538 8 Figure 5 depicts a through-section of a grinding cup according to the invention, Figure 6 depicts a detail of a through-section of an abrasive facing intended for a grinding appliance according to the invention, Figure 7 depicts a further detail of a through-section of an abrasive facing 5 intended for a grinding appliance according to the invention, and Figure 8 depicts a method according to the invention for manufacturing a grinding appliance according to the invention. Description of embodiment examples The following description refers to both the method and the device. 10 Figure 1 depicts a grinding facility intended to grind buttons of a button drill bit with a grinding appliance according to the invention. The grinding facility is in this case intended to be mounted on a drilling rig and includes a supporting frame 1 intended to be fastened in the drilling rig, not depicted in the drawing. The supporting frame I has an upper arm 2 running outwards which supports a grinding machine 3 via a supporting 15 structure 4 which is movable in the horizontal plane. The grinding machine 3 can be raised and lowered in the supporting structure, i.e. it is adapted to pivoting to and fro in the vertical plane. The supporting frame 1 also comprises a fastening means 5 situated below the grinding machine 3. The fastening means 5 is adapted to firmly holding a drill bit 6. The drill bit 6 can easily be fitted into and locked in the fastening means 5 by 20 means of a locking handle 7. The drill bit comprises a number of buttons 8, the size and positioning of which on the bit 6 may vary. The grinding machine 3 comprises also a grinding unit 9 which includes a motor unit 10 and a spindle 11 which is driven by the motor. The grinding unit 9 is thus also adapted to pivoting to and fro about a vertical axis which coincides with the geometric axis of symmetry of the button 8. A grinding 25 appliance, in this case an abrasive wheel 12, is supported at the end of the spindle 11. The abrasive wheel 12 is adapted to grinding the buttons of the drill bit. The grinding unit 9 is so arranged that the spindle 11 will slope somewhat relative to the horizontal plane, so that the abrasive wheel 12 rotates about the spindle. The grinding unit is supported by a supporting means 13 on the grinding facility and can be pivoted about a 30 substantially vertical axis 14 by means of a pivot cylinder 15. The geometric axis about which the grinding unit 9 moves forwards and rearwards is a generally vertical axis which coincides with the geometric centre of the button 8 when the grinding machine 3 is adjusted relative to the button drill bit. During the grinding process, the grinding unit WO 2009/045142 PCT/SE2008/000538 9 moves forwards and rearwards in a pendulum movement in the horizontal plane when the button 8, which protrudes substantially vertically, is being ground. The original shape of the button can be recreated by moving the abrasive wheel towards the button while at the same time the grinding tool rotates about its own axis. 5 A grinding appliance according to the invention may also be used in other variants of grinding facilities intended for drilling rigs, not depicted. Such a grinding appliance may also be used in a fixed station, not depicted, for grinding of button drill bits. Figure 2A depicts a grinding appliance 20 for grinding a button 8A of a button drill bit 6A. In this case the grinding appliance is an abrasive wheel 20. The grinding appliance 10 comprises a first element 22 and the second element 24 which are connected to one another for joint rotation with respect to the axis of rotation of the spindle so that a complete profile groove with an intended end profile shape is formed. The first element 22 is a first separate component and the second element 24 is a second separate component. The first element 22 has running round it a profile groove in the form of a 15 concave surface corresponding to an end profile shape 26 intended for the button 8A. The profile groove thus forms a waist round the first element 22. The waist is limited to the cap-shaped end profile shape of the hard metal button. The first element 22 is thus adapted to grinding the button 8A to, for example, a spherical or fully ballistic end profile shape. The grinding appliance also comprises a second element 24 which is a 20 concentric circular flank situated at one of the planar outsides of the grinding appliance. The flank has running round it an outer portion with a substantially arcuate cross section adapted to grinding the drilling head 28 round the button 8A. The grinding appliance further comprises a third separate element 29 connected for joint rotation with the first element and opposite to the second element. The third element 29 is a second 25 concentric circular flank. The first element is provided with, running round it, an outer layer 30 with an abrasive facing comprising diamonds as the abrasive medium. The abrasive facing 31 of the second element is depicted in the same Figure 2A in a first embodiment illustrated on the second element 24. The second element 24 is provided 30 with, running round it, an outer layer with an abrasive facing 31 comprising diamonds as the abrasive medium. On the second element 24, the abrasive facing is applied on the circular outer portion 32 with a substantially arcuate cross-section.

WO 2009/045142 PCT/SE2008/000538 10 Figure 2A depicts a further embodiment on the third element 29, the second flank. The third element 29 is a component which is homogeneously made of the second abrasive facing 32 so that the whole flank comprises the abrasive medium. It should be noted that both flanks in the two embodiments illustrated in Figure 2A may 5 have an abrasive facing of the same kind. The hatched portions which follow the waist 30 and the flanks 31, 32 in Figure 2A show where the diamond facing is applied on the first element 22 and the second element 24 respectively. The average grain size for the diamonds in the first abrasive facing 30 is adapted to grinding of hard metal. The average grain size for the diamonds 10 in the second and third abrasive facings is of an average grain size adapted to grinding the drill bit. The diamonds are, for example, fastened in a layer which is nickel-based or chrome-based or a mixture of these materials or some other material with similar characteristics, so that the layer is softer than hard metal but nevertheless retains its shape and tolerates impacts. 15 The grinding appliance in Figure 2A is firmly clamped to a grinding facility, not depicted, by a screw 33 and a nut 34. They may also be joined together by, for example, adhesive bonding or welding or by bolts, not here depicted, or by other similar fastening devices. Within the industry, diamonds are sold in, for example, dimensions stated in US mesh 20 size specifications. US mesh sizes are defined by the mesh apertures of the sieves used for the separation of diamond grains. The sieve sizes are graded and defined according to the number of wires per inch of the respective sieve, e.g. 50 wires per inch or 20 wires per inch. The diamonds are then sold in overlapping mesh sizes. The bodies which set out and monitor the US mesh dimension specifications are the American 25 National Standards Institute (ANSI) and the Florida Emergency Preparedness Association (FEPA). The specifications for the sizes are entirely interchangeable. ANSI indicates a US mesh size, whereas FEPA indicates a DIN size. In an embodiment, the diamonds have in the first abrasive facing an average grain size within the range of 37-320 pim, corresponding to US mesh 400/500 - 45/60. The 30 average grain size for the diamonds in the second abrasive facing is adapted to grinding of drilling steel. In an embodiment according to the invention, the diamonds in the second abrasive facing have an average grain size within the range 210-500 pm, corresponding to US WO 2009/045142 PCT/SE2008/000538 11 mesh 70/80 - 35/40. In another embodiment, the diamonds in the second abrasive facing have an average grain size of 250-354 pm, corresponding to US mesh 60/70 45/50. The average grain size for the diamonds in the second abrasive facing is adapted to grinding the drill bit, so it is preferable that the average grain size for the diamonds 5 in the second abrasive facing be larger than the average grain size in the first abrasive facing. Figure 2B depicts an exploded diagram of a through-section of the drawing in Figure 2A. It shows the separate elements of the grinding appliance before they are joined together. The first element 22 is a first separate component, the second element 24 is a 10 second separate component and the third element 29 is a third separate component. The second element 24 is a first concentric circular flank. The third element 29 is a second concentric circular flank. The first element 22 has running round it a concave profile groove 26 corresponding to an end profile shape intended for the button 8A. The second element 24 is a concentric circular flank and is adapted to being joined 15 together with the first element 22, the respective end portions 22A, 24A being adapted in size to one another so that the continuous end profile shape 26 is formed. Similarly, the third element 29 is adapted to being joined together with the first element 22, the respective end portions 22B, 29B being adapted in size to one another so that the continuous end profile shape 26 is formed. The second element 24 has in this 20 embodiment a smaller outside diameter than the largest diameter of the first element 22. The third element 29 has a larger outside diameter than the largest diameter of the first element 22. Thus the grinding appliance is adapted to being angled during the grinding of a button so that the device, not depicted, fastening the grinding appliance to the grinding facility will be clear of the other buttons in the button drill bit. It should be 25 noted that the second element 24 and the third element 29 may also be equal in size, not depicted. Figure 2C depicts a side view of the abrasive wheel in Figure 2A. It shows the second element 24 as a concentric circular flank. The outer layer 31 with abrasive facing comprising diamonds is applied to the concentrically outermost portion of the flank. 30 Figure 2D depicts a perspective view of the abrasive wheel in Figure 2A. The grinding appliance 20 comprises the first element 22, the second element 24 and the third element 29 connected for joint rotation with respect to the spindle's axis of rotation A. The first element 22 has running round it a profile groove 26 in the form of a concave WO 2009/045142 PCT/SE2008/000538 12 surface corresponding to an end profile shape intended for the button 8A. The second element 24 and the third element 29, the flanks, each have running round them an outer portion with a substantially arcuate cross-section adapted to grinding the drilling head round the button. The first element 22 is provided with, running round it, an outer layer 5 30 with a first abrasive facing comprising diamonds adapted to grinding of hard metal buttons. The second element 24 and the third element 29 are provided with, running round them, an outer layer with a second abrasive facing 31 and a third abrasive facing 32 comprising diamonds with an average grain size adapted to grinding a soft material, e.g. steel or a material with characteristics similar to steel, as the abrasive medium. 10 Figure 3 depicts a further embodiment of a grinding appliance for grinding a button 8B of a button drill bit 6 comprising a drilling head 6B with a plurality of buttons. In this case the grinding appliance is an abrasive wheel 40. The grinding appliance comprises a first element 41 and a second element 42 adapted to being joined together for joint rotation with one another with respect to the spindle's axis of rotation C so that a 15 complete profile groove with an intended end profile shape 43 is formed. The first element 41 is a first separate component and the second element 42 is a second separate component. The first element 41 has running round it a concave profile groove with an end profile shape 43 corresponding to an end profile shape intended for the button 8B. The first element 41 is thus adapted to grinding the button 8B to, for example, a 20 spherical or fully ballistic end profile shape. The second element 42 of the grinding appliance is a concentric circular flank. The flank has running round it in this embodiment an outer concentric ring homogeneously made of the abrasive facing adapted to grinding the drilling head, and an inner concentric ring 44 adapted to being fastened to the grinding facility. The outer ring has a substantially convex cross-section 25 adapted to grinding the drilling head 28 round the button 8B. The flank may also have an outer circular shaped portion of a ring made of abrasive media and with a substantially convex cross-section. The flank may also have an inner ring of other than concentric shape adapted to being fastened to the grinding facility. The profile groove 43 on the first element 41 is provided with a first abrasive facing 46 30 comprising diamonds with an average grain size adapted to grinding of hard metal, as the abrasive medium. The second element 42 is provided with a second abrasive facing 48 comprising diamonds as the abrasive medium with an average grain size adapted to grinding a soft material, e.g. steel or a material with characteristics similar to steel. It WO 2009/045142 PCT/SE2008/000538 13 should be noted that this abrasive wheel also has an undepicted embodiment in which the second element 42 is homogeneously made of the abrasive medium 48 comprising diamonds as the abrasive medium with an average grain size adapted to grinding a soft material, e.g. steel or a material with characteristics similar to steel. 5 Figure 4 depicts another embodiment of a grinding appliance for grinding a button drill bit 6C comprising a drilling head with a plurality of buttons 8C. In this case the grinding appliance is a half abrasive wheel 50. The grinding appliance comprises a first element 52 and a second element 54 adapted to being joined together for joint rotation with one another with respect to the spindle's axis of rotation D so that a complete profile groove 10 is formed. The first elenient 52 is a first separate component and the second element 54 is a second separate component. The first element 52 has running round it a profile groove 53 corresponding to a half end profile shape intended for the button 8C. The grinding appliance also comprises a second element 54 which is a concentric flank with a parabolic shape. By rotating the abrasive wheel about the button's geometric axis of 15 symmetry B the first element 52 is thus adapted to grinding the button 8C to, for example, a spherical or fully ballistic end profile shape while at the same time the second element 54 is adapted to grinding the drilling head 6C round the button 8C. The flank has running round it an outer convex portion with a substantially arcuate cross section adapted to grinding the drilling head 28 round the button 8C. 20 The first element 52 is provided with an abrasive facing comprising diamonds with an average grain size adapted to grinding the button 8C. The second element 54 is provided with an abrasive facing comprising diamonds with an average grain size adapted to grinding the drilling head 6C. The profile groove on the first element 52 is thus provided with a first abrasive facing 56 comprising diamonds as the abrasive 25 medium with an average grain size adapted to grinding of hard metal. The second element 53 is thus provided with an abrasive medium which is a second abrasive facing 58 comprising diamonds with an average grain size adapted to grinding a soft material, e.g. steel or a material with characteristics similar to steel. It should also be noted that this abrasive wheel also has a undepicted embodiment in which the second element 54, 30 the flank, is homogeneously made of the abrasive medium 48 comprising diamonds with an average grain size adapted to grinding a soft material, e.g. steel or a material with characteristics similar to steel.

WO 2009/045142 PCT/SE2008/000538 14 Figure 5 depicts a further grinding appliance, in this case a grinding cup 60, for grinding a button 8D of a button drill bit 6D. The first element 62 is a grinding cup filled with an abrasive facing comprising diamonds as the abrasive medium. The second element 64 is an outer portion applied round part of the grinding cup 62. The profile groove on the 5 first element 62 is filled with an abrasive medium with a first abrasive facing 66 comprising diamonds with an average grain size adapted to grinding of hard metal. The second element 64 is provided with a second abrasive facing 68 comprising diamonds as the abrasive medium with an average grain size adapted to grinding a soft material, e.g. steel or a material with characteristics similar to steel. The second abrasive facing 10 may also comprise boron nitride, silicon carbide, aluminium oxide, titanium carbide and titanium nitride, or similar material. The grinding cup 60 or the button 8D is rotated during grinding or both the grinding cup and the button are rotated. Figure 6 depicts a detail of an abrasive facing 70 intended for a grinding appliance as described above. The abrasive facing 70 comprises an abrasive medium with a single 15 layer of diamonds 72A, 72B, 72C, 72D , 72E, 72F fastened in a layer which is nickel based or chrome-based or a mixture of these or some other material with similar characteristics, such that the layer is softer than hard metal but nevertheless retains its shape and tolerates impacts. The diamonds in this abrasive facing have a protrusion, which means that one portion of each diamond is fastened in the layer and the other 20 portion protrudes. This abrasive facing is applied preferably on the first element for grinding the hard metal of the button. This abrasive facing may also be applied on the second and third elements for grinding the layer of a soft material, e.g. steel or a material with characteristics similar to steel. Figure 7 depicts a further detail of an abrasive facing 80 intended for a grinding 25 appliance as described above. The abrasive facing 80 comprises an abrasive medium with diamonds 82A, 82B, 82C, 82D, 82E, 82F, fastened in this case in a nickel-based layer. Some other material with similar characteristics may also be used. The diamonds in this abrasive facing comprise matrix diamonds. The matrix diamonds are situated in two or more layers in the abrasive facing so that a layer of diamonds may be ground 30 away and uncover a new layer of diamonds. This abrasive facing is applied preferably on the second and third elements for grinding the drilling head made of, for example, steel.

15 Figure 8 depicts a method for manufacturing a grinding appliance 90 for grinding of button drill bits which comprise a drilling head with a plurality of buttons. The method comprises: a) providing a first element of the grinding appliance with an abrasive facing comprising 5 diamonds as the abrasive medium of a first average grain size adapted to grinding a button to an intended profile shape (92), b) providing at least one section of a second element of the grinding appliance with an abrasive facing comprising diamonds as the abrasive medium of a second average grain size adapted to grinding a drilling head (94), 10 c) joining the first element and the second element together for joint rotation so that a complete profile groove is formed (96). The invention is not limited to the embodiment examples referred to but one skilled in the art can of course modify it in a plurality of ways within the scope of the invention defined by the claims. Equally, it will be noted that the terms 'comprises' and 'comprising' are 15 used herein and the claims in their inclusive meaning of 'including' or 'having'.

Claims

1. A grinding appliance for grinding of button drill bits which comprise a drilling head with a plurality of buttons, which grinding appliance comprises a first element provided with a first abrasive facing comprising diamonds of a first average grain size 5 adapted to grinding a button to an intended end profile shape, and characterized in that the grinding appliance also comprises a second element adapted to grinding the drilling head, wherein at least one section of the second element is provided with a second abrasive facing comprising diamonds of a second average grain size adapted to grinding the material of the drilling head, the average grain size of the diamonds in the second 10 abrasive facing being larger than the average grain size in the first abrasive facing, and the diamonds in the second abrasive facing having an average grain size within the range 210 500 ym, corresponding to US mesh 70/80 - 35/40.

2. A grinding appliance in accordance with claim 1, wherein the diamonds in the second abrasive facing have an average grain size of 250-354 pm, corresponding to US 15 mesh 60/70 - 45/50.

3. A grinding appliance in accordance with claim I or 2, wherein the diamonds in the first abrasive facing have an average grain size within the range 37-320 pm, corresponding to US mesh 400/500 - 45/60.

4. A grinding appliance in accordance with any one of claims 1-3, wherein the 20 diamonds in the first abrasive facing have an average grain size within the range 37-229 ym, corresponding to US mesh 400/500 - 60/80.

5. A grinding appliance in accordance with any one of claims 1-4, wherein the first element is a first separate body, wherein the second element is a second separate body, and wherein these separate bodies are connected for joint rotation so that a complete 25 profile groove with an intended end profile shape is fonned.

6. A grinding appliance in accordance with any one of claims 1-5, wherein the grinding appliance is an abrasive wheel, the first element comprising a profile groove 17 running around it and corresponding to an intended end profile shape and the second element being a concentric circular flank.

7. A grinding appliance in accordance with claims 5 or 6, wherein the grinding appliance comprises a third separate element connected for joint rotation with the first 5 element and opposite to the second element, which third element is provided with an abrasive facing comprising diamonds with a third average grain size.

8. A grinding appliance in accordance with claim 7, wherein the third element is a second concentric circular flank.

9. A grinding appliance in accordance with any one of claims 1-4, wherein the first 10 element is an inner portion of a grinding cup and the second element is an adjacent firmly connected outer portion of the grinding cup, so that a complete profile groove with an intended end profile shape is fonned.

10. A grinding appliance in accordance with any one of claims 1-9, wherein at least one abrasive facing comprises diamonds with protrusions. 15

11. A grinding appliance in accordance with any one of claims 1-10, wherein at least one abrasive facing comprises matrix diamonds.

12. A grinding facility for grinding of button drill bits which comprise a drilling head with a plurality of buttons, which grinding facility comprises a grinding appliance according to any one of claims 1-11. 20

13. A method for manufacturing a grinding appliance for grinding of button drill bits which comprise a drilling head with a plurality of buttons, wherein the method comprises providing a first element of the grinding appliance with an abrasive facing comprising diamonds as the abrasive medium of a first average grain size adapted to grinding a button to an intended profile shape, characterized in that the method further comprises 25 providing at least one section of a second element of the grinding appliance with an abrasive facing comprising diamonds as the abrasive medium, and the average grain size for the diamonds in the second abrasive facing is of a second average grain size adapted to 18 grinding the drilling head, and the average grain size for the diamonds in the second abrasive facing is larger than the average grain size in the first abrasive facing, the diamonds in the second abrasive facing having an average grain size within the range 210 500 pm, corresponding to US mesh 70/80 - 35/40. 5

14. A method according to claim 13, which method further comprises joining together for joint rotation the first element and the second element so that a complete profile groove is formed.

15. Using a grinding appliance according to any one of claims 1-11 for grinding of buttons of a button drill bit which comprises a drilling head with a plurality of buttons. 10 ATLAS COPCO SECOROC AB WATERMARK PATENT AND TRADE MARKS ATTORNEYS P32894AU00