EP2257687A1

EP2257687A1 - Drilling unit, method for slot drilling and slotting device

Info

Publication number: EP2257687A1
Application number: EP08736810A
Authority: EP
Inventors: Maunu MÄNTTÄRI
Original assignee: Sandvik Mining and Construction Oy
Current assignee: Sandvik Mining and Construction Oy
Priority date: 2008-04-03
Filing date: 2008-04-03
Publication date: 2010-12-08
Also published as: AU2008353952A1; JP5167404B2; JP2011516760A; WO2009122001A1; CN101981269A; CA2714983A1; CA2714983C; US20110017513A1; ZA201006643B; AU2008353952B2

Abstract

A slotting device (100) to be used with a rock drilling apparatus (1) to drill closely together a plurality of parallel intersecting holes so as to form a slot in a brittle material, such as rock, masonry or concrete. The slotting device (100) includes a guide portion (110) connected to a body portion (120) with at least one strut (130). The guide portion (110) is disposed in a previously drilled hole, and the body portion (120) and a rotary percussion tool (7) mutually define a variable volume chamber (140) that contains flushing fluid that damps transmission of impact stress waves from a percussion device (4) of the drilling apparatus (1) to the slotting device (100).

Description

DRILLING UNIT, METHOD FOR SLOT DRILLING AND SLOTTING DEVICE

FIELD OF THE INVENTION

[0001] The present invention relates to a drilling unit and method for slot drilling and a slotting device. In the slot drilling a plurality of holes are drilled closely together so as to form a slot in a rock material. A slot may be formed in a rock surface or into rock mass by drilling a plurality of holes in the surface at a pitch substantially equal to the diameter of the holes. In the slot drilling a special slotting device is needed for guiding the drilling tool along a previously drilled hofe. The object of the invention is disclosed more closely in the preambles of the independent claims.

BACKGROUND OF THE INVENTION

[0002] Slot drilling is a method used in underground and surface mining. In the slot drilling holes are successively drilled very close to each other and when a new hole is drilled next to a previously drilled hole, the wall of rock between the holes is broken. In this manner, a continuous slot is formed by the holes as they are successively drilled. Such continuous slots i.e. elongated voids can be used in the surface blasting to protect buildings near a blasting site. In this manner propagation of the Shock waves outside the blast- ing site is prevented. In the underground mining elongated voids or slots can be drilled in solid rock for example in a tunnel face in order to form a primary open space whereto a broken rock material can expand in blasting. This is needed e.g. in stope opening or drifting.

[0003] When a single hole is drilled into rock, the fully circumferen- tial wall of the hole remains intact and radial forces acting from the wall of the hole on the drill bit tend to cancel each other. However, in the slot drilling, when a plurality of holes are formed in a row so as to form a slot, the wall of rock between a previously drilled hole and a new hole being drilled is broken as the new hole is being drilled, and the radial forces acting from the partially circumferential waif of the new hole on the drill bit result in a net force that is directed toward the previously drilled hole.

[0004] Therefore, the drill bit as it drills the new hole tends to be displaced radially off a desired course under the combination of radial forces thus applied. To prevent the drill bit from being displaced, it has been a con- ventional practice to use a guide rod supported parallel to the drill rod and hav- ing a diameter, which is substantially the same as or slightly smaller than the diameter of holes to be formed. Before a new hole is drilled, the guide rod is inserted into a previously drilled hole next to the position of the new hole so as to stabilize the support for the drill rod. By placing the guide rod in the previ- ously drilled hole, the support for the drill rod is prevented from shifting position even when large radial forces are imposed on the drill rod as it drills the new hole.

[0005] US Patent No. 5690184 discloses a rock drilling unit for slot drilling. The drilling unit includes a guide rod fixed to a support for the drill rod at the front end of the feeding beam, whereby the guide rod extends to the front of the feeding beam. Thus, the drilling unit is designed only for slot drilling.

[0006] WO 99/45237 discloses a slotting device, which includes a down-hole rock drilling machine inside a body portion of the slotting device and a parallel guide tube arranged by means of a strut to the body portion. One disadvantage of the disclosed slotting device is that stress waves generated by a percussion device of the drilling machine are transmitted not only to a tool but also to the body structure and to the guide tube. The stress waves may cause serious damages to the body and the guide of the slotting device. This said disadvantage concerns especially top hammer applications.

BRIEF DESCRIPTION OF THE INVENTION

[0007] The object of the invention is to provide a new and improved drilling unit and method for slot drilling and further a new and improved slotting device. [0008] The drilling unit of the invention is characterized in that between the body portion of the slotting device and the tool there is at lest one axial volume chamber containing fluid so as to dampen transmission of the impact stress waves from the percussion device to the slotting device.

[0009] The slotting device of the invention is characterized in that the slotting device is provided with at least one axial volume chamber between the body portion and the tool; and wherein the slotting device comprises at least one flow channel for directing fluid into the chamber, whereby the fluid in the chamber is arranged to transmit axial forces from the tool to the body portion. [0010] The method of the invention is characterized in that it comprises the steps of transmitting the feed force to the body of the slotting device in the drilling direction by means of fluid in at lest one axial volume chamber between the tool and the body portion; and dampening transmission of the im- pact stress waves from the percussion device to the slotting device by means of the fluid in the at least one axial volume chamber.

[0011] According to the present invention the slotting device comprises an axial volume chamber that contains flushing fluid so as to dampen transmission of the impact stress waves from a percussion device to the slot- ting device. Accordingly, impact stress waves are transmitted to a tool, but their transmission to a slotting device attached to the tool is damped. Further, during driiling feed force in the drilling direction is transmitted to the body of the slotting device by means of fluid.

[0012] An advantage of the invention is that in normal drilling situa- tion there is an axial gap in drilling direction between the mechanical counter surfaces of the tool and the body of the slotting device, whereby the energy of the stress waves generated by a percussion device are not transmitted to the body and to the guide of the slotting device. Thanks to this, stress waves do not damage the structure of the slotting device and the operating life of the slotting device may longer.

[0013] It is the idea of an embodiment that the slotting device is a dismountable auxiliary device connected to a shank of the rock drilling machine or to a drill rod connected to the shank. This being so, the slotting device can be easily connected and disconnected to a standard rock drilling machine according to the need. When the slotting device is disconnected, the rock drilling machine can be used in drilling normal single holes.

[0014] It is the idea of an embodiment that fluid is provided to flush drilling waste from a hole being drilled. Preferably, the fluid flows through an axial volume chamber that is defined between a body portion of a slotting de- vice and the tool, and the flushing fluid damps transmission to the slotting device of impact stress waves generated by a percussion device.

[0015] It is the idea of an embodiment that the slotting device is capable of dislodging itself in the event the slotting device becomes jammed in the slot. [0016] It is the idea of an embodiment that the slotting device provides valve means regulating a flow of fluid through the axial volume chamber. The valve means restricts the fluid flow thereby increasing fluid pressure and providing additional force to move the slotting device if it becomes jammed.

[0017] It is the idea of an embodiment that the guide portion comprises a tube that is spaced from and parallel to the body portion. Further the tube may comprise a cutout in which an edge of the bit may rotate. This eliminates the risk that the drill bit comes in contact with the tube.

[0018] It is the idea of an embodiment that the guide portion comprises at least one elongated guiding flange extending longitudinally along a peripheral surface of the guide portion. These elongated guide flanges ensure that the distance of the hole being drilled is correct in relation to the previous hole.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In the following the invention will be described in greater detail by means of exemplary embodiments with reference to the attached draw- ings, in which

Figure 1a is a schematic illustration of a rock drilling rig; Figure 1b is a schematic illustration of a rock drilling unit- Figures 2a - 2c are schematic illustrations showing how a slot is formed by successively drilling closely together a plurality of holes; Figure 3 is a first perspective view of a first embodiment of a slotting device according to the present invention;

Figure 4 is a plan view of the slotting device shown in Figure 3; Figure 5 is a partial cross-section view of the slotting device shown in Figure 3; Figure 6 is a partial cross-section detail view of an area indicated in

Figure 5 and showing a first condition of the slotting device shown in Figure 3;

Figure 7 is a partial cross-section detail view similar to Figure 6 but showing a second condition of the slotting device shown in Figure 3;

Figure 8 is a second perspective view of the slotting device shown in Figure 3;

Figure 9 is a schematic illustration showing a second embodiment of a slotting device according to the present invention;

Figure 10 is cross-section view taken along line X-X in Figure 9; Figure 11 is a cross-section view taken along line Xl-Xl in Figure 10; and Figure 12 is a schematic illustration of a hold device through which the slotting device can be pushed.

[0020] In the Figures, some embodiments are shown in a simplified manner for the sake of clarity. In the Figures, like parts are denoted with like reference numerals.

DETAILED DESCRIPTION OF THE INVENTION

[0021] Figure 1a is a schematic illustration of a rock drilling rig 1 , that includes a boom 2, at the end of which there is a rock drilling unit 60. The rock drilling unit 60, which is shown more detailed in Figure 1b, comprises a feed beam 3 with a rock drilling machine 6 including a percussion device 4 and possibly a rotating device 5. In general, the percussion device 4 comprises a percussion piston that is operated by a pressure medium, and strikes the upper end of a tool 7 or a connecting piece arranged between the tool 7 and the percussion device 4, such as a drill shank 61. Naturally, it is possible to gener- ate impact pulses in the percussion device 4 in some other manner, for example electrically or without a reciprocating striking piston. The proximal end of the tool 7 is connected to the rock drilling machine 6 by means of the shank

61 , and at the distal end of the tool 7 there is a fixed or detachable bit 8 for breaking rock. Typically, the bit 8 is a drill bit with buttons 8a, but other bit structures are also possible. The rotating device 5 may transmit to the tool 7 continuous rotating force to cause the bit 8 connected to the tool 7 to change its position after an impact of the percussion device 4 and with a subsequent impact strikes a new spot in the rock. The rock drilling machine 6 is arranged movably on the feed beam 3 in drilling direction D and in reverse direction R and during drilling the tool 7 is thrust with a feeding device 9 against the rock

62. The feeding device 9 can be for example a pressure-medium-operated cylinder. When deep holes are drilled, i.e. in so-called extension rod drilling, drill rods 10a, 10b, 10c (the number of which depends on the depth of the hole to be drilled and which constitute the tool 7) are arranged between the bit 8 and the drilling machine 6. The drilling machine 6 may comprise a flushing device 11 for supplying a flushing fluid through the tool 7 and the bit 8 to a bored drill hole so as to flush loose drilling waste there from. For the sake of clarity, Figure 1a does not show the flushing channels of the tool 7. The rock drilling rig 1 may also be provided with at least one control unit 63 for controlling the drilling. Further, at the outermost end section of the feed beam 3 there may be a hold- ing device 64 through which the tool 7 is arranged. The hold 64 includes means for supporting the tool 7 during drilling. There may be also a drilling component magazine 65 for storing drilling components such as drill bits 8, slotting devices and drilling rods 10. The component magazine 65 may be pro- vided with a manipulator for transferring drilling components between the drilling axis and the magazine. Thereby drilling components, such as the slotting device, can be connected and disconnected to the drilling machine according to the need.

[0022] Referring more particularly to Figure 1b, a feed pump 12 drives the feeding device 9, an impact pump 13 drives the percussion device 4, and a rotation pump 14 drives the rotating device 5. The pumps 12, 13, 14 supply pressurized fluid, preferably hydraulic oil, to the respective dedicated devices 9, 4, 5 that they drive. The pumps 12, 13, 14 are disposed along supply conduits 15, 16, 17 respectively connected to the devices 9, 4, 5 and through which pressurized fluid is supplied to the devices in the direction indicated by arrows A. Alternatively the needed pressure fluid is supplied from one single pump to the devices. The fluid is returned from the devices 9, 4, 5 along respective return conduits 18, 19, 20 in the direction indicated by arrows B back to a tank. The drilling machine 6 also comprises a flushing pump 21 that is disposed along a supply conduit 22 that is connected to the flushing device 11. A flushing agent, which is typically water, is supplied to the flushing device 11 in the direction of arrow A.

[0023] The feed pump 12, impact pump 13, rotation pump 14 and flushing pump 21 are typically driven by motors 12a, 13a, 14a, 21a, respec- tively. For the sake of clarity, Figure 1 b does not show control valves used for the control of the devices 4, 5, 9 and 11. The structure and operation of the rock drilling rig 1 and machine 6 are known per se to the person skilled in the art, and therefore they are not discussed here in greater detail.

[0024] Referring now to Figures 2a - 2c, a slot S is formed in a rock surface by drilling a plurality of holes at a pitch substantially equal to the diameter of the holes. Since the holes are successively drilled very closely to each other, when a new hole is drilled next to a previously drilled hole, the wall of rock between these holes is broken. In this manner, a slot is formed along the holes as they are successively drilled. [0025] As shown in Figure 2a, when a single hole 50 is drilled in a rock surface, the fully circumferential wall 50a of the hole 50 is left intact. The radial forces F (four of which are shown in Figure 2a) acting from the wall 50a on the drill bit cancel each other, and the sum of the radial forces F is negligible. However, as shown in Figure 2b, when a new hole 52 is drilled adjacent to the previously drilled hole 50 so as to form a slot, a partition 51 of rock be- tween the previously drilled hole 50 and the hole 52 being drilled is broken (this is indicated with a broken line in Figure 2b). Consequently, the broken partition 51 does not provide a radial force -F, and the sum of radial forces F acting on the drill bit do not cancel each other. Instead, there is a resultant force directed toward the previously drilled hole 50 and, as the new hole 52 is drilled, the drill bit tends to be displaced radially off from its desired course, i.e., parallel and intersecting the previously drilled hole 50.

[0026] Referring now to Figure 2c, the utilization of a slotting device 100 according to the present invention will be described. The hole 50 is initially drilled with a normal drill bit. Thereafter, the slotting device 100 is fitted to the rock drilling machine 6, and the holes 52 and 54 are successively drilled. When hole 52 is being drilled, it is parallel to and intersects previously drilled hole 50, and when hole 54 is being drilled, it is parallel to and intersects previously drilled hole 52. After completing hole 54, the tool 7 including the bit 8 is withdrawn and positioned such that a guide portion 110 of the slotting device 100 will extend into the previously drilled hole 54. A body portion 120 of the slotting device 100, which is fitted with respect to the tool 7 and connected to the guide portion 100 by at least one strut 130, maintains the desired course for the new hole being drilled.

[0027] The guide portion 110 may be provided with one or more longitudinally extending elongated guiding flanges 112a, 112b. Preferably, the guiding flanges 112a, 112b are disposed on the peripheral surface of the guide portion and are positioned on either side of the broken partition between the two previously drilled holes 52, 54. The guiding flanges 112a, 112b facilitate locating the guide portion 110 in the previously drilled hole 54, particularly with regard to the absence that results from the broken partition. Alternatively, a single flange that extends on the peripheral surface of the guide portion 110 beyond the opposite ends of the broken partition may also facilitate locating the guide portion 110 in the previously drilled hole.

[0028] Referring now to Figures 3 - 8, a first preferred embodiment of the slotting device 100 are described in detail. Preferably, the guide portion 110, which is to be disposed in a previously drilled hole, is tubular and extends longitudinally between a tapered leading edge 114 and a trailing end 116, which may also be tapered to facilitate extraction of the guide portion from the previously drilled hole. A cutout 118 may be provided so as to avoid contact between the guide portion 110 and the bit 8 as it works in the hole being drilled. As was previously described, the guiding flanges 112a, 112b may be disposed on the peripheral surface of the guide portion 110.

[0029] The slotting device 100 comprises one or more struts 130 for connecting the guide portion 110 to the body portion 120. The strut 130 provide a structural link to convey movement of the body portion 120 to the guide portion 110, i.e., the guide portion 110 is displaced in the previously drilled hole in response to movement of the body portion 120. Thus, the connection between the guide portion 110 of the slotting device 100 and the rock drilling apparatus 1 is, preferably, solely via the strut 130 and the body portion 120 of the slotting device 100. [0030] The body portion 120 of the slotting device 100 is disposed in the hole being drilled, and is coupled to the tool 7 via a mutually defined axial volume chamber 140 that contains flushing fluid to damp transmission of the impact stress waves from the percussion device 4 to the slotting device 100.

[0031] The body portion 120 includes a sleeve 122 that defines a bore 124 in which extends the tool 7. The bore 124 includes a first diameter portion 124a, a second diameter portion 124b that is smaller than the first diameter portion 124a, a shoulder portion 124c that extends between and couples the first and second diameter portions 124a, 124b, and a third diameter portion 124d that is smaller than the second diameter portion 124b. The por- tion of the tool 7 that extends through the bore 124 includes a piston portion 7a and a rod portion 7b, which is proximal to the bit 8. Preferably, the piston and rod portions 7a, 7b are mechanically coupled between the drill rods 10a, 10b, 10c, if any, and the bit 8; but may alternatively be integrally formed as part of the tool 7. Thus, the impact stress waves generated by the percussion device 4 are transmitted via a direct mechanical coupling, i.e., via the tool 7 including the piston and rod portions 7a, 7b, to the bit 8.

[0032] The first diameter portion 124a of the bore 124 slidingly receives the piston portion 7a of the tool 7, and the second diameter portion 124b of the bore receives the rod portion 7b of the tool 7. Thus, the variable axial volume chamber 140 has an annular shape that is defined radially between the first diameter portion 124a of the bore 124 and the rod portion 7b of the tool 7, and is defined axially between the piston portion 7a of the tool 7 and the shoulder portion 124c of the bore 124. Preferably, flushing fluid is prevented from flowing between first diameter portion 124a and the piston portion 7a, such as with a seal 126. [0033] The variable volume chamber 140 may contain flushing fluid, which is supplied via a flow passage 142 that connects a first internal passageway 144 that extends through the tool 7 and a second internal passageway 146 that also extends through the tool 7. With respect to the bit 8, the first internal passageway 144 is distally disposed, and the second internal pas- sageway 146 is proximally disposed. Preferably, the second internal passageway 146 provides flushing fluid flow to the bit 8. The flow passage 142 includes an axial flow passage 142a, a first generally radial How passage 142b, and a second generally radial flow passage 142c. The axial flow passage 142a is disposed radially between the rod portion 7b of the tool 7 and the second di- ameter portion 124b of the bore 124. The first generally radial flow passage 142b connects the first internal passageway 144 of the tool 7 to a first axial end of the axial flow passage 142a, and a second generally radial flow passage 142c connects a second axial end of the axial flow passage 142a to the second internal passageway 146 of the tool 7. The first and second generally radial flow passages 142b, 142c may extend obliquely or perpendicularly with respect to the axial flow passage 142a and to the first and second internal passageways 144, 146.

[0034] The third diameter portion 124d of the bore 124 in the sleeve 122 slidingly receives the rod portion 7b of the tool 7. Preferably, flushing fluid is prevented from flowing between third diameter portion 124d and the rod portion 7b, such as with a seal.

[0035] In Figure 6 is shown a first relationship between the body portion 120 of the slotting device 100 and the tool 7. Flushing fluid is supplied to the variable volume chamber 140 via the first generally radial flow passage 142b. The flushing fluid contained in the variable volume chamber 140 serves to damp transmission to the slotting device 100 of impact stress waves generated by the percussion device 4 of the rock drilling apparatus 1. Specifically, the impact stress waves generated by the percussion device 4 are transmitted through the tool 7, but the slotting device 100 is generally isolated from the impact stress waves by virtue of the coupling via the flushing fluid contained in the axial vofume chamber 140. Because of the fluid in the axial volume cham- ber 140 there is a gap G between the pressure surfaces 70 and 71 , whereby there is no mechanical axial contact between the tool 7 and the sleeve 122. Additional flushing fluid continues to flow from the first internal passageway 144, via the first generally radial flow passage 142b, the axial flow passage 142a and the second generally radial flow passage 142c, to the second internal passageway 146, through the bit 8 and into the hole being drilled.

[0036] The slotting device 100 is advanced, i.e., the guide portion 110 is displaced in the previously drilled hole and the body portion 120 is displaced along with the tool 7, in accordance with the operation of the feeding device 9 and the flow of the flushing fluid along the tool 7 that fills the axial volume chamber 140. The flushing fluid in the axial volume chamber 140 affects on the first and second working pressures surfaces 70 and 72 generating a force in drilling direction D and further on a third working pressure surface 71 generating a force in reverse direction R. Thus the fluid transfers the force that is supplied from the feeding device 9, via the piston portion 7a of the tool 7, to the sleeve 122 of the body portion 120, via the working pressure surfaces 70, 72, and on to the guide portion 110 via the strut 130. But the flushing fluid contained in the axial volume chamber 140 damps transmission to the slotting device 100 of impact stress waves generated by the percussion device 4 of the rock drilling apparatus 1.

[0037] In Figure 7 is shown a second relationship between the body portion 120 of the slotting device 100 and the tool 7. In the event that the slotting device 100 becomes jammed, e.g., the guide portion 110 becomes stuck in the previously drilled hole, a second relationship develops. Resistance to the slotting device 100 advancing, in combination with the operation of the feeding device 9, causes flushing fluid flow through the axial flow passage 142a to be restricted by virtue of the third diameter portion 124d at least partially closing the second generally radial flow passage 142c. This raises fluid pressure in the axial volume chamber 140, and thus increases the force acting to dislodge the slotting device 100. At the extreme of the second relationship, the second generally radial flow passage 142c is completely closed and the How of flushing fluid is blocked, which can be detected by the control unit 63 or the operator of the rock drilling rig 1 , and the tool 7 and slotting device 100 can be extracted from their respective holes. [0038] Preferably, the first generally radial flow passage 142b feeds into the variable volume chamber 140 during the first relationship between the body portion 120 of the slotting device 100 and the tool 7 of the rock drilling apparatus 1. As the piston portion 7a of the tool 7 is displaced relative to the sleeve 122 of the body portion 120 during the second relationship between the body portion 120 and the tool 7, the first generally radial flow passage 142b may feed into the axial flow passage 142a rather than the variable volume chamber 140, thus the primary flow of flushing fluid bypasses the variable volume chamber 140, which is also reduced in capacity. The reduced capacity of the variable axial volume chamber 140 enhances the ability to increase the fluid pressure for dislodging the slotting device 100, and by limiting flushing fluid communication between the variable volume chamber 140 and the flow passage 142, the flushing fluid provides less damping whereby impact stress waves generated by the percussion device 4 may be transmitted to the slotting device 100 to assist in dislodging the guide portion 110 with respect to the previously drilled hole. [0039] Thus, the third diameter portion 124d and the second generally radial flow passage 142c act like a valve to automatically control the position of the sleeve 122 with respect to the tool 7, thereby automatically reacting to feeding resistance of the guide portion 110. When the guide portion is jammed in the previously drilled hole, the flow through the slotting device is blocked and the fluid pressure is increased. This can be monitored by means of one or more pressure sensor. Measuring results can be transmitted from the sensor to the control unit 63 including a control strategy. When a predetermined pressure limit is exceeded the control unit 63 may stop drilling and reverse the feed direction of the drilling machine. [0040] Referring now to Figures 9 - 11 , a second preferred embodiment of the slotting device 100 is described. The same reference numbers are used to indicate substantially identical features in both preferred embodiments, and no further explanation will be given.

[0041] Whereas the variable volume chamber 140 of the first pre- ferred embodiment is in the shape of an annulus, with the tool 7 defining the piston portion 7a, the variable volume chamber 140a according to the second preferred embodiment has a generally cylindrical shape with a sleeve portion 122 and a dampening piston 128 disposed within a flow passage 142 that extends through the tool 7. The flow passage 142 includes at least one axial flow passage 142a (four are shown in Figure 10), a first generally radial flow passage 142b, and a second generally radial flow passage 142c. The first gener- ally radial flow passage 142b connects a first portion of the flow passage 142 to a first axial end of the axial flow passage 142a, and the second generally radial flow passage 142c connects a second axial end of the axial flow passage 142a to the second portion of the flow passage 142 through the tool 7. [0042] The piston 128 includes an interior portion 128a, an exterior portion 128b, and at least one coupling portion 128c. The exterior portion 128b may comprise two halves the inner surfaces of which include protrusions for forming coupfing portions 128c, and wherein the halves are arranged against each other and coupled with the interior portion 128a for example by screw joints. Each coupfing portion 128c defines a web that extends between and fixes together the interior and exterior portions 128a, 128b of the piston 128. The interior portion 128a defines a first working pressure surface 80 affecting in drilling direction D and a second working pressure surface 81 affecting in reverse direction R when pressure fluid is arranged to flow through the slotting device 100. During the first relationship, the same pressure affects to the working pressure surfaces 80, 81 having the same surface area, whereby forces affecting the piston 128 are in equilibrium and the piston is positioned in its middle position. The exterior portion 128b slidingly receives the tool 7 and contiguously engages the sleeve portion 122 during the first relationship between the slotting device 100 and the tool 7. There are axial gaps G in drilling direction D and in reverse direction R between the tool 7 and the damping piston 128 so as to prevent mechanical axial contact between them.

[0043] When the feeding resistance of the guide portion 110 increases the dampening piston 128 moves in reverse direction R in relation to the tool 7, as shown in Figure 11. During the second relationship between the slotting device 100 and the tool 7, the flushing fluid flow through the axial flow passage 142a is restricted by virtue of the piston 128 at least partially closing the first generally radial flow passage 142b. Because of this, the fluid pressure affecting on the first working pressure surface 80 increases and the fluid pres- sure affecting on the second working pressure surface 81 decreases, whereby a greater force is generated towards the drilling direction D. The piston 128 also restricts the fluid flow in case the piston 128 moves in drilling direction D in relation to the tool 7. This situation may take place when drilling downwards. Thus, the dampening piston 128 automatically adjusts the feed force transmit- ted to the guide portion 110. [0044] During the normal slot drilling the dampening piston 128 is not in mechanical axial contact with the tool 7. Forces affecting on the pressure working surfaces 80, 81 of the piston 128 ensure that no axial mechanical surfaces between the tool 7 and the piston 128 are against each other. The feed force is transmitted to the piston 128 by means of the fluid in the axial volume chamber 140a. Thereby the transmission of stress pulses to the slotting device is dampened.

[0045] Let it be mentioned that it is possible to conduct any other fluid than flushing fluid to one or more axial volume chamber of the slotting de- vice. The fluid can be for example hydraulic fluid led from the feed pump 12, the impact pump 13 or the rotation pump 14. In this embodiment the tool 7 has to be provided with a special fluid channel and an axial volume chamber separated from the flushing system.

[0046] Figure 12 shows a hold device 64 having an opening 66 through which the sfotting device 100 can be pushed. Dimensions and form of the opening 66 is designed according to a cross sectional profile of the slotting device 100, whereby it includes two intersecting minor openings. The opening 66 may be provided with a flexible sealing material 67 such as rubber and having several cuts 68 for facilitating the penetration. [0047] It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

Claims

CLAIMS:

1. A rock drilling unit for slot drilling, comprising a feed beam (3); a rock drilling machine (6) arranged on the feed beam (3), and com- prising a percussion device (4) and a flushing device (11 ); a tool (7) connected to the rock drilling machine (6); and wherein the percussion device (4) is arranged to produce impact stress waves directed to the tool (7), and the flushing device (11) is arranged to supply flushing fluid through the toof (7) for flushing drilling waste from a hole being drilled (52); a feeding device (9), which is arranged to move the drilling machine (6) on the feed beam (3) and to feed the tool (7) in the hole being drilled (52); and further a slotting device (100) connected to the rock drilling machine (6) and comprising a guide portion (110), a body portion (120) and at least one strut (130) extending between and coupling the guide portion (110) and body portion (120), and wherein the guide portion (110) is disposed in a previously drilled hole (50), and wherein the tool (7) is arranged slidingly through the body portion (120); characterized in that between the body portion (120) of the slotting device (100) and the tool (7) there is at lest one axial volume chamber (140) containing fluid so as to dampen transmission of the impact stress waves from the percussion device (4) to the slotting device (100).

2. The rock drilling unit according to claim 1, characterized in that the axial volume chamber (140) is connected to the flushing device

(11 ) by means of at least one flow channel; and the axial volume chamber (140) contains flushing fluid.

3. The rock drilling unit according to any one of claims 1 and 2, characterized in that the slotting device (100) is a dismountable auxiliary device connected to a shank (61) of the rock drilling machine (6) or to a drill rod (10) connected to the shank (61).

4. The rock drilling unit according to any one of the preceding claims, characterized in that the body portion (120) of the slotting device (100) and the tool (7) mutually define the at least one axial volume chamber (140) containing fluid.

5. The rock drilling unit according to claim 4, characterized in that the body portion (120) of the slotting device (100) comprises a sleeve (122) including a bore (124) through which the tool (7) extends; the bore (124) of the sleeve (122) comprises a first diameter portion (124a), a second diameter portion (124b) smaller than the first diameter portion (124a), and a shoulder portion (124c) extending between and coupling the first diameter portion (124a) and second diameter portion (124b); the first diameter portion (124a) of the bore (124) slidingly receives a piston portion (7a) of the tool (7), and the second diameter portion (124b) of the bore (124) receives a rod portion (7b) of the tool (7); the axial volume chamber (140) comprises an annulus that is defined radially between the first diameter portion (124a) of the bore (124) and the rod portion (7b) of the tool (7), and is defined axially between the piston portion (7a) of the tool (7) and the shoulder portion (124c) of the bore (124); the slotting device further comprises a flow passage (142) supplying the flushing fluid along the tool (7), the flow passage (142) comprises an axial flow passage (142a) disposed radially between the rod portion (7a) of the tool (7) and the second diameter portion (124b) of the bore (124), a first generally radial flow passage (142b) connecting a first internal passageway (144) of the tool (7) to a first axial end of the axial flow passage (142a), and a second generally radial flow passage (142c) connecting a second internal passageway (146) of the tool (7) to a second axial end of the axial flow passage (142a); the bore (124) of the sleeve (122) comprises a third diameter portion

(124d) smaller than the second diameter portion (124b), the third diameter portion (124d) slidingly receives the rod portion (7b) of the tool (7); and relative axial displacement of the tool (7) with respect to the body portion (120) restricts fluid flow through the second generally radial flow pas- sage (142c) and increases fluid pressure moving the body portion (120) with respect to the tool (7).

6. The rock drilling unit according to any one of the claims 1 to 3, characterized in that between the tool (7) and the body portion (120) there is a dampen- ing piston (128), which is in axial connection to the body portion (120) and is in the axial direction separated by means of fluid from the tool (7).

7. The rock drilling unit according to claim 6, characterized in that the body portion (120) of the slotting device (100) comprises a sleeve (122) including a bore (124) through which the tool (7) extends; the tool (7) comprises a flow passage (142) that extends through it; the dampening piston (128) comprises an interior portion (128a) arranged within the flow passage (142), an exterior portion (128b) around the tool (7) and at least one coupling portion (128c) coupling the interior portion and exterior portion together; the piston (128) is arranged slidingly movably with respect to the tool (7); the interior portion (128a) comprises a first working pressure surface (80) affecting towards the drilling direction (D) and a second working pressure surface (81) affecting towards the reverse direction (R); a first axial volume chamber (140a) is on the first working pressure surface (80) side of the piston (128) and the fluid therein is transmitting the feed force from the tool (7) via the piston (128) to the sleeve (122); and a second axial volume chamber (140b) is on the second working pressure surface (81) side of the piston (128) and the fluid therein prevents mechanical axiaf contact between the tool (7) and the piston (128) in the drilling direction (D).

8. The rock drilling unit according to claim 7, characterized in that the flow passage (142) of the tool (7) comprises at least one axial flow passage (142), which connects the axial volume chambers (140a, 140b); and wherein an axial movement of the piston (128) relative to the tool (7) in the reverse direction (R) is arranged to restrict the pressure of the fluid affecting the first working pressure surface (80) thus increasing the feed force transmitted via the piston (128) to the sleeve (122).

9. The rock drilling unit according to any one of the preceding claims, characterized in that the guide portion (110) comprises at least one elongated guiding flange (112) extending longitudinally along a peripheral surface of the guide portion (110).

10. The rock drilling unit according to any one of the preceding claims, characterized in that the feed beam is provided with a hold device (64) at the distal end of the feed beam (3); and the hold device (64) comprises an opening (66), which is dimensioned according to a cross sectional profile of the slotting device (100) allow- ing the slotting device (100) to be pushed through the hold device (64).

11. A slotting device comprising: an elongated tool (7) including a first end and a second end, and wherein the first end is provided with first coupling means (90) for attaching the slotting device (100) to a shank (61) of a drilling machine (6) or to a drill rod (10) connected to the shank (61), and wherein the second end is provided with a drill bit (8); a body portion (120) through which the tool (7) is arranged; a guide portion (110) disposable in a previously drilled hole (50); and at least one strut (130) extending between and coupling the guide portion (110) and body portion (120); characterized in that the slotting device (100) is provided with at least one axial volume chamber (140) between the body portion (120) and the tool (7); and wherein the slotting device (100) comprises at least one flow chan- nel for directing fluid into the chamber (140), whereby the fluid in the chamber (140) is arranged to transmit axial forces from the tool (7) to the body portion (120).

12. The slotting device according to claim 11 , characterized in that the slotting device (100) comprises at least one feed channel for feeding flushing fluid from the rock drilling machine into the axial volume chamber (140) and at least one discharge channel for discharging flushing fluid from the axial volume chamber (140) to the hole being drilled, whereby flushing fluid is arranged to flow through the axial volume chamber (140).

13. The slotting device according to claim 11 or 12, characterized in that the slotting device (100) comprises means for monitoring axial forces opposing the disposal of the guide portion (110) into the previously drilled hole (50); and means for increasing pressure of the fluid affecting in drilling di- rection (D) on at least one working pressure surface (70, 80) of the at least one axial volume chamber (140, 140a) as a response to the monitored opposing forces, whereby axial force transmitted to the guide portion (110) is increased.

14. The slotting device according to claim 12 and 13, characterized in that the slotting device (100) comprises valve means for affecting the volume flow through the axial volume chamber as a response to the relative axial position of the tool (7) and the body portion (120).

15. A method for slot drilling, comprising: drilling closely together a plurality of holes (50 - 54) so as to form a slot (S) in a rock material (62); using in drilling a rock drilling machine (6) comprising a percussion device (4) for generating percussion pulses to a tool (7) connected to a rock drilling machine (6); connecting a slotting device (100) to the rock drilling machine (6), the slotting device (100) comprising: a body portion (120) through which the tool (7) is arranged; a guide portion (110); and at least one strut (130) extending between and coupling the guide portion (110) and body portion (120); disposing a guide portion (110) in a previously drilled hole (50) for maintaining the course of the previously drilled hole (50) for the new hole being drilled (52); and transmitting during drilling a feed force towards the drilling direction (D) from the tool (7) to the body portion (120) of the slotting device (100) and further to the guide portion (110); comprising transmitting the feed force to the body portion (120) of the slotting device in the drilling direction (D) by means of fluid in at least one axial volume chamber (140, 140a) between the tool (7) and the body portion (120); and dampening transmission of the impact stress waves from the percussion device (4) to the slotting device (100) by means of the fluid in the at least one axial volume chamber (140, 140a).

16. A method as claimed in claim 15, comprising influencing pressure of the fluid in the axial volume chamber (140, 140a) in response to the axial movement between the body portion (120) and the tool (7) arranged to slide longitudinally relative to each other.

17. A method as claimed in claim 16, comprising arranging fluid flow through the axial volume chamber (140, 140a); and restricting the fluid flow through the axial volume chamber (140, 140a) when the movement of the guide portion (110) in the previously drilled hole (50) is hindered, whereby the feed force transmitted to the guide portion (110) is increased.

18. A method as claimed in claim 17, comprising arranging fluid flow through the axiaf volume chamber (140, 140a); closing the discharge fluid flow through the axial volume chamber (140, 140a) when the movement of the guide portion (110) in the previously drilled hole (50) is stopped, whereby the pressure of the fluid in the axial vol- ume chamber increases; monitoring the pressure of the fluid affecting in the axial volume chamber; and reversing the feed movement of the rock drilling machine (6) when the pressure of the fluid in the axiaf volume chamber exceeds a predetermined pressure limit.

19. A method as claimed in any of the previous claims 15 - 18, comprising connecting at least one drill rod (10) to a shank (61) of the drilling machine (6); and connecting the slotting device (100) to a distal end of an outermost drill rod (10).

20. A method as claimed in any of the previous claims 15 - 18, comprising connecting the slotting device (100) to a shank (61) of the drilling machine (6).

21. A method as claimed in any of the previous claims 15 - 20, comprising supporting the guide portion (110) to surfaces of the previously drilled hole (50) by means of at least one elongated guiding flange (112) ex- tending longitudinally along a peripheral surface of the guide portion (110).

22. A method as claimed in any of the previous claims 15 - 21 , comprising conveying flushing fluid into the axial volume chamber (140, 140a).