FIELD OF THE INVENTION [0001] The invention relates to a rock drill shank that is an elon- gated piece and comprises at least : a first end and a second end; connecting elements at the first end of the shank for fastening a drilling tool to the shank; an impact surface for providing impact pulses to the shank, and rotating ele- ments for providing rotation torque to the shank to rotate it around its longitudi- nal axis.

[0002] The invention further relates to a rock drill comprising at least : a body; a shank that is an elongated piece and comprises a first end and a second end, connecting elements at said first end for fastening a drilling tool, an impact surface and rotating elements; a percussion device having a per- cussion element for providing impact pulses to the impact surface of the shank; and a rotating device that is arranged to provide rotation torque and to act on said rotating elements for rotating the shank around its longitudinal axis.

[0003] The invention further relates to a method for rock drilling, wherein rock is drilled with a rock drill having a body, a shank for fastening a drilling tool, a percussion device and a rotating device; the method comprising: providing impact pulses to the impact surface of the shank with the percussion element of the percussion device of the rock drill ; rotating the shank around its longitudinal axis with the rotating device of the rock drill ; and transmitting the impact pulses and rotation torque from the shank to the drilling tool and on to the rock being drilled.

BACKGROUND OF THE INVENTION [0004] A typical rock drill comprises a shank, percussion device and rotating device. A tool can be fastened to the shank, to which rotation torque is transmitted from the rotating device by means of the shank and impact pulses are transmitted from the percussion device. The percussion device generally comprises a reciprocating percussion piston arranged to provide impacts to an impact surface located outermost at the back end of the shank. This type of drill has a certain minimum length and, in practice, it cannot be made shorter than the minimum length. The minimum length is determined by the length of the percussion piston and shank, the stroke length of the percussion piston and the remaining structure of the drill, such as the end covers. When quarry- ing in low spaces, for instance in tunnels, it is advantageous to use as short a

drill as possible so as to be able to use tools of a practical length. However, the length of the drill cannot be shortened without shortening the length of the per- cussion piston and shank. If the percussion piston is made very short, it is no longer possible to provide therewith the impact pulses needed to break rock, and the performance of the drill is substantially reduced. The shank, too, should have a certain length so that tools can be firmly fastened to it and that it can be firmly supported to the body of the drill. In addition, the rotation torque required to rotate the shank should be transmitted to it. The stroke of the per- cussion piston also cannot be shortened very much without a harmful effect on the impact pulses transmitted to the shank.

BRIEF DESCRIPTION OF THE INVENTION [0005] It is an object of the present invention to provide a novel and improved rock drill shank, rock drill and method for rock drilling.

[0006] The shank of the invention is characterized in that said im- pact surface is located at a predefined distance from the outermost section of the second end of the shank as seen longitudinally.

[0007] The rock drill of the invention is characterized in that the im- pact surface of the shank is located at a predefined distance from the second end of the shank; and that the percussion element is arranged at least partly to overlap the shank.

[0008] The method of the invention is characterized by striking the shank with the percussion element in such a manner that the percussion ele- ment and the shank are at least at the time of impact disposed at least partly inside each other.

[0009] The essential idea of the invention is that the impact surface of the shank is formed at a distance from the back end of the shank, i. e. the outermost end on the percussion device side. Further, the percussion element, which is arranged to transmit the impact pulses from the percussion device to the shank, and the back end of the shank are arranged to overlap at least partly.

[0010] The invention provides the advantage that because the per- cussion element of the percussion device and the shank overlap at least partly, the entity formed by the percussion device and shank can be relatively short in length. In spite of this, the percussion device and its percussion element can be designed so as to provide impact pulses of sufficient strength. Further, due

to the invention, the shank can be dimensioned such that it can be well sup- ported to the body.

[0011] The essential idea of an embodiment of the invention is that the rotating elements of the shank are formed on the outer rim of the second- end area of the shank. The impact surface in turn resides on the centre axis of the shank. The second end of the shank is cuplike in shape. The impact sur- face forms the bottom of the cuplike section. The percussion element then overlaps the rotating elements at least when transmitting the impact pulse.

With the rotating elements thus arranged at the second end of the shank, there is a free section on the arm of the shank, whereby it is easier to arrange the support of the shank. Further, it is easier to arrange the supply of a flushing medium and the sealing arrangements it requires in such a construction.

BRIEF DESCRIPTION OF THE FIGURES [0012] The invention will be described in greater detail in the at- tached drawings, in which Figure 1 is a schematic view of a section of a prior-art rock drill, Figure 2 is a sectional schematic view of a rock drill of the invention, Figure 3 is a sectional schematic side view of a shank of the inven- tion, Figure 4 is a schematic side view of the shank of Figure 3, Figure 5 is a sectional schematic side view of a second shank of the invention, Figure 6 is a schematic view of the shank of Figure 5 from direction A, and Figure 7 is a schematic view of a possible rock drill construction.

[0013] In the figures, the invention is shown in a simplified manner for the sake of clarity. Similar parts are marked with the same reference nu- merals in the figures.

DETAILED DESCRIPTION OF THE INVENTION [0014] Figure 1 shows a conventional rock drill having a percussion piston 1 arranged to strike an impact surface 3 at the back end of a shank 2, forming impact pulses. The shank 2 transmits the impact pulses on to a tool 4 fastened to the shank 2 and on through a drill bit or the like to the rock being drilled. The shank 2 is connected with rotating elements 5 to a rotating device 6 in such a manner that the shank 2 and too 4 can be rotated around their

longitudinal axes. The conventional drill has a minimum length Lmin that is formed of the lengths of the percussion piston 1 and shank 2 arranged con- secutively, the stroke length Lper of the percussion piston 1 and further, the casing and body structure of the rock drill ; in this case, the thickness Li of an end cover 7. It is very difficult to design this kind of drill to be substantially shorter without the shortening of the structure affecting harmfully the properties of the drill. If the length of the percussion piston 1 is shortened, its percussion dynamics decrease significantly. This is due to the fact, for instance, that the shortening of the percussion piston reduces its mass. The percussion power and, through it, the performance of the drill decreases. It is also difficult to shorten the shank, since the flushing medium channel, the channel seals, and the bearings and rotating elements 5 of the shank require that the shank 2 have a certain length.

[0015] Figure 2 shows a rock drill 21 according to the idea of the in- vention. The back end of the shank 2 is cuplike, whereby the percussion piston 1 does not strike the outermost end of the shank 2 but the impact surface 8 that is at a distance L2 from the back end of the shank 2. Depending on the stroke length LPER and the length of the cuplike section, the percussion piston 1 and the shank 2 are partly inside each other either during the stroke only or during the entire percussion cycle. The rotating elements 5 are formed on the outer rim of the cuplike section of the shank 2, whereby there remains a rela- tively long free section on the arm 18 of the shank 2, to which the flushing me- dium channel 9, seals 10 and shank 2 bearings 11 can be arranged. Because the percussion piston 1 or a corresponding percussion element is arranged partly inside the shank 2, the minimum length Lmin of the drill can be shorter than in the known drills. The body 22 of the drill 21 is marked with a dashed line in the figure. Control elements and pressure medium channels belonging to the percussion device 23 are not shown in Figure 2 for the sake of clarity.

[0016] Figure 3 is a sectional view and Figure 4 a side view of a shank 2 of the invention that comprises a first end 12, i. e. front end, and a sec- ond end 13, i. e. back end. The front end 12 has connecting elements 14, such as threads, by means of which tools 4 can be fastened to the drill. Instead of threads, it is naturally possible to use other connection elements suitable for the purpose. As shown in Figure 3, the back end 13 of the shank 2 is cuplike in shape and consequently has longitudinal edges 15 that form a circular cross- section at the back end 13 of the shank 2. The impact surface 8 is a transverse

surface with respect to the longitudinal axis of the shank 2 and resides at a distance L2 from the outermost surface 16 of the back end 13 of the shank 2, thus forming the bottom of the cuplike section. The impact surface 8 is located on the longitudinal axis of the shank 2. In the area of the back end 13 of the shank 2, there may be rotating elements 5 to transmit rotation torque to the shank 2 from the rotating device 6. As Figure 4 shows, the rotating elements 5 can comprise gearing on the outer rim of the edges 15, to which the rotating device 6 can be geared through a gear wheel. It is clear that instead of gear- ing, it is possible to use any other suitable transmission elements for transmit- ting rotating torque to the shank 2. Further, the shank 2 can have at least one flushing medium channel 9, the first end of which extends to the connection surface between the shank 2 and tool 4 and the second end 17 of the channel 9 extends to the arm 18 of the shank 2. Flushing medium can then be supplied through the shank 2 to a second flushing medium channel in the tool 4. On the arm 18 of the shank 2, there is space for suitable collars or surfaces 19 and 20 for seals 10 and bearings 11.

[0017] Figures 5 and 6 show a shank 2 having female connection elements 14 at its first end 12. The tool 4 is then arranged to the shank 2 by pushing it partly inside the connection elements 14 of the shank 2. The tool 4 may have an angular connection head, for instance hexagonal, and the shank 2 may have a recess corresponding to the cross-profile of said connection head. The shank 2 and tool 4 then connect to each other by shape. The con- nection can yet be secured in the longitudinal direction of the tool by means of a suitable screw, pin, wedge or another fastening element. Instead of the an- gular shape, the cross-profile of the shank recess and the connection head of the tool 4 can also be some other non-circular shape, such as oval. It is natu- rally possible to have an internal thread in the connection elements 14 of the shank 2, to which a threaded pinlike connection head of the tool 4 can be ar- ranged.

[0018] Figure 7 further shows in a very simplified manner the cross- section of the structure of a rock drill. At least in principle, it is possible to con- struct a rock drill in such a manner that the percussion piston 1 or a corre- sponding percussion element surrounds the back end 13 of the shank 2 to a predefined extent. The front end of the percussion element 1 can then be cup'- like and the impact surface 8 of the shank 2 can be formed to a collar 25 in the

shank 2, at a distance L2 from the back end of the shank 2. Rotating elements 5 can be formed on the outer rim of the collar 25.

[0019] It should be noted that in this application, the percussion element also refers to other components generating an impact pulse than the reciprocating percussion piston shown in Figures 1 to 7. It can thus be said that the percussion element is a part of the percussion device that is arranged to transmit the impact pulse provided by the percussion device in one way or another to the impact surface of the shank.

[0020] It should further be noted that in some cases, the rock drill does not comprise the conventional type of pressure medium-operated or elec- trically operated rotating device, but the shank and drilling tool are rotated around their longitudinal axes for instance by transforming part of the impact pulse energy to rotation torque. Thus, the shank of such a drill does not neces- sarily have rotating elements.

[0021] The drawings and the related description are only intended to illustrate the idea of the invention. The invention may thus vary in detail within the scope of the claims.