The present invention relates to a grinding wheel, in particular a diamond grinding wheel for the grinding of drill bits in rock drill crowns.

Grinding wheels for the grinding of drill bits in rock drill crowns are normally designed as a wheel with two sides that surround an inner surface, where the inner surface demon- strates the same curved form as it is intended that the drill bits are to have when they have been ground. The grinding wheels are used in special grinding machines for rock drill crowns, and they are arranged during grinding with their axis in a plane that lies perpendicular to the direction of the axis of the bit that is to be ground. The grinding wheel is arranged such that it can be turned forwards and backwards, or rotated, with the aid of the grinding machine, around the axis of the bit that is to be ground, in addition to being able to be rotated around its own axis. The drill bits can in this way be given the correct domed form as they originally had.

The grinding wheels described above are effective in the processing of not only the dome form of the actual drill bits, but also the embedding steel around the drill bits in the drill crown.

These grinding wheels, however, have the disadvantage that they are complicated to manufacture, since it is difficult to obtain an even structure of the coating of diamonds of the curved inner surface of the grinding wheel. The design of the grinding wheel also leads to a high production of heat around the drill bit during use of the grinding wheel, with the drill bit enclosed to a great extent by the grinding wheel

during grinding. The design leads also to the fact that in principle a fixed contact angle to the drill bit that is to be ground is always obtained, something that often leads to the grinding wheel being worn in a "strip" where the contact to the worn drill bit takes place.

The aim of the present invention is thus to achieve a new grinding wheel that is simpler to manufacture with a more even structure of the diamond coating, which makes the grind- ing operation simpler, and that furthermore is designed such that the development of heat will be lower.

The aim described above of the invention is achieved with a grinding wheel that demonstrates a flange at one end of a principally cylindrical body, which flange protrudes radially from the body and that comprises an oblique side that extends between a radial outer edge of the flange and the outer surface of the principally cylindrical body, and where the side passes into the outer surface through a curve, and where the oblique side, the radial outer edge and the curve are all coated with an abrasive agent.

The invention will now be described in more detail in the form of a non-limiting embodiment, illustrated with the aid of the attached drawings, where Figure 1 shows a cross- section through a grinding wheel of known type, Figure 2 shows a plan of the grinding wheel in Figure 1, Figure 3 shows a cross-section through a grinding wheel according to the invention according to its fundamental principles, Figure 4 shows a plan of the grinding wheel in Figure 3, Figure 5 shows a cross-section through a first variant of a grinding wheel according to the invention, Figure 6 shows a cross- section through a second variant of a grinding wheel according to the invention, and Figure 7 shows a cross-section

through a third variant of a grinding wheel according to the invention.

Figure 1 thus shows a grinding wheel 1 of known type. This known grinding wheel comprises a cylindrical part 2, or wheel, with a penetrating central hole 3 for attachment to the axle of a grinding machine (not shown in the drawing) . A flange 4, 5 protrudes at each end of the cylindrical part 2, which flanges form a curved concavity 6 between them. The two flanges 4, 5 demonstrate oblique sides 7, 8 on the surfaces that face each other that form the walls of the concavity 6, which also demonstrates a bottom 9. The sides 7 ^" , 8 and the bottom 9, which thus form the concavity, demonstrate together a form that is the negative form of the dome that the drill bits that are to be ground are to have.

Both the sides 7, 8, which face each other; the bottom 9; and the outer edges 10, 11 of the flanges 4, 5 that face outwards away from the cylindrical part 2 are coated with an abrasive agent, such as diamonds. This coating of abrasive agent is suggested in Figure 1 by dashed lines.

Figure 3 and Figure 4 show a grinding wheel 12 according to the invention. This grinding wheel comprises a principally cylindrical body 13, with a penetrating hole 14. The grinding wheel 12 is provided in this case with only one flange 15 that protrudes from the principally cylindrical part 13, arranged axially at a first end of the principally cylindrical part 13. This protruding flange 15 demonstrates an oblique side 16 that extends from the radial outer edge 17 of the flange, inwards towards the principally cylindrical part 13, and this side 16 passes through a curve 18 into an outer surface 19 of the principally cylindrical part 13, which

outer surface 19 extends away from the flange 15 to a corresponding second end of the principally cylindrical part 13.

The oblique side 16 of the flange 15 is coated with an abra- sive agent, such as diamonds, as are the radial outer edge 17 of the flange and the curve 18, such that it is possible to use the grinding wheel 12 according to the invention to grind the drill bits of rock drilling crowns.

The form of the side 16, the curve 18 and the part of the outer surface 19 that makes contact with it are adapted to the form that the drill bits are to have when they have been ground, normally the form that they had originally. The radial outer edge 17 of the flange 15 of the grinding wheel 12 is also coated with an abrasive agent in order to make it possible to grind down the steel around the drill bit, and in which the drill bit is embedded.

The critical aspect of the design of the grinding wheel ac- cording to the invention is that the part of the grinding wheel that is coated with abrasive agent extends from the radial outer edge 17, through the oblique side 16 and the curve 18 sufficiently far towards the outer surface 19 that the coating extends over the complete top of the hardened metal bit that is to be ground with the grinding wheel.

Figure 5 shows a first variant of a grinding wheel according to the invention in which the outer surface 19a is arranged obliquely downwards from the free end of the outer surface towards the curve 18a and the side 16. The risk that the outer surface will grind the drill bit in an erroneous manner is reduced by designing the outer surface 19a in this manner, reducing for example, the risk that the drill bit will be given a flattened outer end.

Figure 6 shows a second variant of a grinding wheel according to the invention, where the outer surface 19b is arranged extending primarily in a circular manner from the free end of the outer surface towards the curve 18b and the side 16. The curve 18b and the outer surface 19b to which it is connected are formed such that a depression is formed at the transition between the curve 18b and the outer surface 19b, such that the bottom of the depression or curve lies lower than the connecting outer surface 19b, and in this manner forms a depression between the outer surface 19b and the side 16. Also this design of the outer surface 19b and the curve 18b reduces the risk that the outer surface will grind the drill bit in an erroneous manner, reducing, for example, the risk that the drill bit will be given a flattened outer end.

Figure 7 shows a third variant of a grinding wheel according to the invention, where the outer surface 19c is arranged obliquely upwards from the free end of the outer surface towards the curve 18c and the side 16. The risk that the outer surface will grind the drill bit in an erroneous manner is reduced also by this design of the outer surface 19c, reducing, for example, the risk that the drill bit will be given a flattened outer end.

Also other variants are possible.

Grinding wheels according to the invention can be used to grind drill bits of rock drilling crowns. The grinding wheel is arranged on the axle of a grinding machine, and rotates with the rotation of the axle. The grinding machine is arranged in a plane that is essentially perpendicular to the direction of the axle of the drill bit that is to be ground, and it is arranged in turn to rotate, or to be turned for-

wards and backwards over a region of 360°, arpund the centre of the drill bit that is being ground. It is possible in this way to recreate the shape of a domed drilling bit with the aid of the simple grinding wheel according to the invention.

It is simpler to manufacture a grinding wheel according to the invention in that the surfaces that are to be coated with an abrasive agent are located more openly, such that it is easier to coat the surfaces.

The new grinding wheel according to the invention has also a shorter axial length than the grinding wheel that has previously been available, and this means that more units can be coated at the same time, when they are packed into a fitting. The shorter length means also that the consumption of diamonds per grinding wheel is reduced. Also the consumption of chemicals is reduced.

It is easier to obtain an even and good structure for the coating with the new grinding wheels according to the invention.

Through the new grinding wheel according to the invention being more open, and through it not enclosing the drill bit that is to be ground to the same extent as previous grinding wheels, the same high development of heat during grinding does not take place, and this makes possible either a higher rate of feed or a higher contact pressure, or both, and this means that the grinding will be more efficient, and further- more that the grinding wheels will achieve a longer lifetime than the grinding wheels that have been used until now.

Grinding wheels according to the invention allow also a greater flexibility in the contact between the grinding wheel

and the drill bit that is to be ground, such that a more distributed area of contact is obtained, such that a more even wear of the grinding wheel takes place, and also this contributes to the grinding wheel according to the invention achieving a greater lifetime.

It has proved to be the case that it is possible to obtain a lifetime that is double as long with the new grinding wheels as that obtained with the previously known grinding wheels.

Grinding wheels according to the invention may also be coated with another abrasive material than diamonds. Boron nitride, for example, can be used, and other materials that can be used for the grinding of hardened metal drilling bits can be used for coating grinding wheels according to the invention.