A grinding machine and a method for grinding buttons of a rock drill bit .

Background of the Invention The present invention relates to a grinding machine and a method for grinding buttons of a rock drill bit according to the preambles of the independent claims.

By, for example, WO0204169, a grinding machine is previously known for grinding buttons of a rock drill bit, the grinding machine comprising a grinding head having a rotatably mounted spindle, which carries a grinding cup. Upon use of the grinding machine, muscular strength is required for operating the grinding head, which is suspended in a link-lever system. This complicates the design of the grinding machine and decreases the accuracy during grinding. Furthermore, the task is physically heavy for the operator.

Objects of the Invention

An object of the present invention is to provide a grinding machine and a method for easy grinding of buttons of rock drill bits.

Another object of the present invention is to provide a grinding machine and a method for obtaining good repetition accuracy upon grinding of buttons of rock drill bits.

Another object of the present invention is to provide a grinding machine and a method for obtaining accurate centering of the grinding cup upon grinding of buttons of rock drill bits. Still another object of the present invention is to provide a grinding machine and a method for enabling the return to one and the same position after grinding of the respective button of a rock drill bit.

These and other objects have been attained by means of a grinding machine and a method according to the present invention having the features according to the characterizing parts of the appended independent claims.

Brief Description of the Drawings

Below, an embodiment example of a grinding machine according to the present invention is described, reference being made to the drawings, wherein: Fig. 1 shows parts of a grinding machine according to the present invention in side view in a first position in connection with grinding of a rock drill bit. Fig. 2 shows parts of the grinding machine in side view in a second position. Fig. 3 schematically shows within which area parts of the grinding machine can move.

Detailed Description of the Invention

As is seen in Figs. 1 and 2, the grinding machine according to the present invention comprises a grinding head 10, which comprises a driving source 12, preferably an electric motor. Alternatively, the driving source may be arranged outside the grinding head. The grinding head 10 can be displaced vertically in relation to a frame 11 , i.e., downward and upward, by means of an arrangement, not shown. The frame 11 is intended to constitute a stand for holding and guiding the grinding head. The grinding head in Figs. 1 and 2 comprises the driving source 12 along the longitudinal axis of which a rotatable grinding spindle 13 extends. The grinding spindle is intended to rotate around a first rotational axis CL1. The free end 14 of the grinding spindle 13 is intended to drive and to replaceably carry a grinding cup 15. The rotary grinding spindle 13 executes, via the grinding cup 15, the grinding of the selected cemented- carbide button 36. The other end 16, not shown, of the grinding spindle 13, facing away from the free end 14 of the grinding spindle 13, can assume different positions in relation to a fixed, second rotational axis CL2. The other end 16 is arranged to assume at least two separate positions, one of which positions is intersected by the second rotational axis CL2. This means that the grinding spindle also is intended to rotate around the second axis CL2, so that the first rotational axis CL1 qf the grinding spindle is arranged to assume at least two separate positions in relation to the second rotational axis CL2, one of which positions is collinear with the second rotational axis CL2. Here, by "collinear" is meant that the axes CL1 and CL2 coincide with each other

irrespective of which view they are regarded in. Thus, the other end 16 of the grinding spindle 13 is arranged to assume at least two separate positions, one of which positions is intersected by the second rotational axis CL2.

A rotation unit 17 is rotatably mounted via bearing members 18 to a part 19 of the grinding head 10 that is not rotatable in relation to the frame 11. The part 19 is via a support member 20 vertically adjustably connected to the frame 11. A motor 21 is attached in the support member 20 and coupled to the rotation unit 17 in order to drive the last-mentioned one. The rotation unit 17 comprises a support shaft 22, which extends through the part 19. Said support shaft 22 is intended to rotate around the rotational axis CL2 when the motor 21 is activated. The support shaft 22 is fixedly connected to a position indicator member 23. The position indicator member 23 comprises, in the embodiment illustrated, two plane-parallel sheet-metal plates or sides 24, which are connected to each other via an upper sheet-metal plate or side 25. Each side 24 comprises a curved groove 26, the centre line 27 of which may be described by a radius R having a radius centre C. Said radius centre coincides substantially with a radius centre of a cavity 28 of the grinding cup 15. The ends 28, 29 of the groove 26 may constitute fixed stops for the slanting of a motor bracket 30. Alternatively, an adjustable stop may be provided near at least one of the ends of the groove. The driving source or the motor 12 is rotatably mounted in the motor bracket 30, for example via a co-operating journal 31 in the motor and bearing members 32, so that the driving source in its entirety can rotate in relation to the motor bracket and the first axis CL1. The above- mentioned journal may alternatively be arranged on an intermediate part, which holds the motor in a way similar to what is shown in the figures. The motor bracket 30 comprises two pairs of wheels or two pairs of followers 33 intended to be guided by the grooves 26 along a curved path when the motor bracket is actuated by an actuator 34. The actuator 34 is tumably fixed in the position indicator member 23 as well as turnably connected to the motor bracket 30, so that when the length of the actuator is altered, the motor bracket follows the path of the grooves 26. The actuator 34 may be an air cylinder, an electric motor or the like. The upper portion of the support shaft 22 in the shown

embodiment has recesses for receiving connections for air. When the actuator 34 is extended (Fig. 1), the axes CU and CL2 can coincide, wherein a starting position has been assumed. When the actuator 34 is contracted (Fig. 2), the same can be arranged substantially perpendicularly to the second axis CL2, wherein a working position has been assumed. Thus, the position indicator member 23 is arranged to rotate around the second axis CL2. Hence, the position indicator member 23 or the rotation unit 17 comprises members 26, 30, 33 and 34 for adjusting the rotational axis CL1 of the grinding spindle in relation to the second axis CL2. Thus, the members 26, 33 and 34 for adjusting the rotational axis CL1 of the grinding spindle in relation to the second axis CL2 are arranged to lock the other end 16 of the grinding spindle in a path, which substantially may be described by a radius R. Members 35 for supplying flush medium to the grinding spindle 13 are mounted on the part of the grinding spindle 13 that is situated outside the driving source 12. The other end 16 of the grinding spindle 13 can be displaced within an area that may be defined by a spherical cone Z, schematically shown in Fig. 3. The spherical cone Z has a cone angle of 1° to 90°. For instance, a smaller cone angle is used upon grinding of acute buttons.

As typical values, it may be mentioned that if the spindle 13 rotates by >10000 r/min, the position indicator member 23 rotates by approx. 60-100 r/min.

The grinding machine according to the present invention described above operates in the following way. The grinding head 10 is lowered and simultaneously the drill bit 37 is displaced until the recess 28 in the grinding cup 15 is correctly orientated in relation to the button 36 that is to be ground. After that, the drill bit is locked in the position thereof. Position the grinding cup 15 in a starting position so that the rotational axis CL1 of the grinding spindle substantially coincides with the centre axis of the button that is to be ground. Start rotation of the grinding spindle around the first rotational axis CL1 and around the second axis CL2. Feed the grinding cup 15 toward the button until the grinding cup abuts against the button 36 that is to be ground, in accordance with Fig. 1. Grind the button under simultaneous slanting of the grinding cup,

from a position where the first axis CL1 of the grinding spindle is collinear with the second rotational axis CL2 to a position where the axes CL1 and CL2 form an angle with each other, for instance 10°, in accordance with Fig. 2. Then, after a certain time of grinding, the grinding cup 15 is guided back to the starting position. It is an advantage to guide the grinding cup so that it returns to the starting position or a standby position where the axes CL1 and CL2 become collinear, since the drill bit or the grinding head then can be indexed or moved, respectively, wherein a new button can be ground without any adjustment work needing to be made. When the driving source 12 starts, simultaneously the supply of flush medium, preferably water, to the flushing head 35 begins and then mouths in the recess 28 of the grinding cup 15 for providing flushing and cooling of the button that is to be ground.

Thus, the present invention relates to a grinding machine and a method for easy grinding of buttons of rock drill bits, good repetition accuracy and accurate centering of the grinding cup being obtained.