GB1591435A - Grinding fixture and method of grinding a button of a rock drilling button bit - Google Patents

Description

(54) GRINDING FIXTURE AND METHOD OF GRINDING A BUTTON OF A ROCK DRILLING BUTTON BIT (71) We, FAGERSTA AKTIEBOLAG, a Swedish Joint-Stock Company, of Fack, S-773 01 Fagersta, Sweden, do hereby declare the invention for which -we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement: The present invention relates to a grinding fixture and method for grinding the cutting buttons in rock drilling button bits.

In rock drilling technology rock drilling button bits are taking an ever-increasing place, due to their greater drilling capacity between grindings in comparison with bits having chisel-edge type cutting teeth. Not in the least with drifting and tunnelling has this meant a very large advance. In drilling holes of smaller diameter, the use of button bits is increasing as well. Button bits functioned as disposible products to begin with, and after becoming worn the bit was thrown away. Today however, attempts are being made to get greater drill sinking distances from button bits by grinding or dressing the buttons after they have become worn, so that they regain their hemispherical form, which is their ideal shape.

Up to now however, grinding the buttons is still a very primitive craft where the button bit is kept stationary and a small high-speed grinding wheel works with point contact on the buttons. Such a procedure can never give the button its exact hemispherical shape. Since the buttons in a drill bit sit very close together, it is also very difficult to get at the right places with the grinding wheel. The work takes a long time and the result will be far from a spherical surface. Only grinding wheels with very small diameters can be used, which means that the wheels are rapidly worn down. The whole procedure is a very expensive work process.

The object of the invention is to provide an apparatus and method by the aid of which an increase in the life of rock drilling button bits is enabled by repeated grindings without deterioration of the drilling function. At the same time, the work of grinding can be made very efficient. The fundamental idea is that grinding is best carried out if the button rotates while movement of the grinding machine is kept to a minimum. For this to be possible it must also be possible to center the button in question on a rotating grinding fixture in a simple way.

In one aspect the invention provides a grinding fixture for grinding the buttons of rock drilling button bits, which comprises a horizontally arranged disc, drive means for rotating the disc about a vertical axis through its centre, a displaceable centering means for centering a button of the bit so that that button is supported substantially coaxial with said disc axis, and grinding means arranged to be brought into contact with the button surface after the centering means has been disengaged from the button.

In another aspect the invention provides a method of grinding a button of a rock drilling button bit which comprises placing the button bit on a disc which is rotatable about its axis, centering the button so that it is coaxial with said axis of the disc, bringing a grinding surface into contact with the button and rotating the disc to grind the button.

A preferred embodiment of the invention will now be described while referring to the attached drawings, where Fig 1 shows a perspective view of the construction of the fixture, and Fig 2 shows a grinding wheel and a rock drilling button bit during grinding.

As shown in Fig 1, a disk 1 is mounted for rotation about its central vertical axis on a base frame 2, and can be driven at a continuously variable speed by the motor arrangement 3 via a belt 10. Attached to, and upstanding from, the frame there is a column 5, on which there is slidably mounted a centering arm 6. At the same distance from the chief axis of the column as this axis is from the center of the disk, a locating cup 7 has its center, the cup being attached to the centering arm.

On the disk there is placed a container 4, filled with a suitable particulate material, e.g. steel shot or grit, such as particles of white cast iron, granulated heat-treated malleable castings, granulated steel or cut steel wire. The bit is pressed into the particulate material so that the button 12 to be dressed is approximately over the center of the disk, and with the principal axis of the button substantially perpendicular to the surface of the disk. The cup is then moved down over the button and the button centered under it, which is facilited by moving the container. The position of the button is thus fixed coaxial with the axis of the disk, and the centering arm can be moved out of the way. The disk can now be brought into rotation by means of the foot pedal 9, whereat the button also rotates coaxially with the disk, and grinding can be carried out.

A cup-shaped grinding wheel 11 with a relatively large diameter is used for grinding, as is apparent from Fig 2. The button 12 will be easily accessible to such a wheel, and since its circumference is relatively large, the grinding wheel will suffice for many drill bits of the kind in question.

The work of grinding is easy to do, since the grinding machine only needs to be moved slightly for each button.

Although only one embodiment has been described and illustrated by way of an example, the invention is naturally not limited to this embodiment, but can be modified within the purview of the inven tive concept. For example, mechanical adjusting means can be utilized for positioning the cup and button. It is also possible to arrange for the grinding machine to have its motion mechanically controlled.

WHAT WE CLAIM IS: - 1. A grinding fixture for grinding the buttons of rock drilling button bits, which comprises a horizontally arranged disc, drive means for rotating the disc about a vertical axis through its centre, a displaceable centering means for centering a button of the bit so that the button is supported substantially coaxial with said disc axis, and grinding means arranged to be brought into contact with the button surface after the centering means has been disengaged from the button.

2. A grinding fixture as claimed in Claim 1 in which the centering means is an arm arranged to be displaceable along and swingable about a vertical column.

3. A grinding fixture as claimed in Claim 1 or Claim 2 in which the centering means includes a cup shaped recess at the end of an arm, the shape of the recess substantially corresponding to the shape of the button.

4. A grinding fixture as claimed in any of Claims 1 to 3 in which the grinding means has a cup shaped grinding surface of large diameter relative to the diameters of the buttons.

5. A grinding fixture as claimed in any of Claims 1 to 4 in which the speed of the drive means is continuously variable.

6. A method of grinding a button of a rock drilling button bit which comprises placing the button bit on a disc which is rotatable about its axis, centering the button so that it is coaxial with said axis of the disc, bringing a grinding surface into contact with the button and rotating the disc to grind the button.

7. A grinding fixture substantially as described herein with reference to and as illustrated in Figures 1 and 2 of the accompanying drawings.

8. A method of grinding a button of a button bit according to Claim 5 and substantially as described herein.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. 4, filled with a suitable particulate material, e.g. steel shot or grit, such as particles of white cast iron, granulated heat-treated malleable castings, granulated steel or cut steel wire. The bit is pressed into the particulate material so that the button 12 to be dressed is approximately over the center of the disk, and with the principal axis of the button substantially perpendicular to the surface of the disk. The cup is then moved down over the button and the button centered under it, which is facilited by moving the container. The position of the button is thus fixed coaxial with the axis of the disk, and the centering arm can be moved out of the way. The disk can now be brought into rotation by means of the foot pedal 9, whereat the button also rotates coaxially with the disk, and grinding can be carried out. A cup-shaped grinding wheel 11 with a relatively large diameter is used for grinding, as is apparent from Fig 2. The button 12 will be easily accessible to such a wheel, and since its circumference is relatively large, the grinding wheel will suffice for many drill bits of the kind in question. The work of grinding is easy to do, since the grinding machine only needs to be moved slightly for each button. Although only one embodiment has been described and illustrated by way of an example, the invention is naturally not limited to this embodiment, but can be modified within the purview of the inven tive concept. For example, mechanical adjusting means can be utilized for positioning the cup and button. It is also possible to arrange for the grinding machine to have its motion mechanically controlled. WHAT WE CLAIM IS: -

1. A grinding fixture for grinding the buttons of rock drilling button bits, which comprises a horizontally arranged disc, drive means for rotating the disc about a vertical axis through its centre, a displaceable centering means for centering a button of the bit so that the button is supported substantially coaxial with said disc axis, and grinding means arranged to be brought into contact with the button surface after the centering means has been disengaged from the button.

2. A grinding fixture as claimed in Claim 1 in which the centering means is an arm arranged to be displaceable along and swingable about a vertical column.

3. A grinding fixture as claimed in Claim 1 or Claim 2 in which the centering means includes a cup shaped recess at the end of an arm, the shape of the recess substantially corresponding to the shape of the button.

4. A grinding fixture as claimed in any of Claims 1 to 3 in which the grinding means has a cup shaped grinding surface of large diameter relative to the diameters of the buttons.

5. A grinding fixture as claimed in any of Claims 1 to 4 in which the speed of the drive means is continuously variable.

6. A method of grinding a button of a rock drilling button bit which comprises placing the button bit on a disc which is rotatable about its axis, centering the button so that it is coaxial with said axis of the disc, bringing a grinding surface into contact with the button and rotating the disc to grind the button.

7. A grinding fixture substantially as described herein with reference to and as illustrated in Figures 1 and 2 of the accompanying drawings.

8. A method of grinding a button of a button bit according to Claim 5 and substantially as described herein.