The present invention relates to a rock drilling tool, a reamer means and a body element according to the preambles in the subsequent independent claims.

In known drilling tools of the above-captioned type the weak point is the threaded connection, for example between the guiding means and the part which carries the reamer. There are always energy losses in threaded joints which transfers impact energy.

Another known tool is shown in applicants US-A-5,284,216 wherein the shank and the drill bit constitutes a entity on which a guide are arranged. However it has bee experienced that the known tool comprises a number of drawbacks ; the reamer cannot easily be exchanged, the impact energy cannot be maximally utilized, the position of the grooves cannot be placed optimally and locking means for threads has poor strength and are troublesome to handle.

Obiects of the Invention One object of the present invention is to provide a rock drilling tool thereby eiiminating the above-captioned drawbacks.

Another object of the present invention is to provide a rock drilling tool wherein the reamer easily can be mounted and dismounted.

Still another object of the present invention is to provide a rock drilling tool wherein an optional reamer can be used.

Short description of the drawings The objects of the present invention are realized by a rock drilling tool, a body element and a reamer such as defined in the subsequent claims. Below embodiments of these are described with reference to the enclosed drawings, where Fig. 1A schematically shows a body element according to the present

invention in a perspective view; Fig. 1 B shows a cross-section through the body element; Fig. 2A schematically shows a reamer according to the present invention in a perspective view; Fig. 2B and 2C schematically show parts of the reamer in plan views, partly in section; Fig. 3 schematically shows a partly sectioned, side view of a rock drilling tool according to the present invention; Fig. 4 A and 4B show perspective views of the rock drilling tool in a penetration position respective in drilling mode, and Fig. 5 shows a end view of the rock drilling tool.

Detailed description of the invention The rock drilling tool 10 according to the present invention comprises a body element 11 and a reamer 12, Fig. 3. The drilling tool is provided in a known manner with a reamer 12 in drilling or operative mode, to expand a hole to allow a casing 13 to be displaced downwardly together with the drilling tool. By rotating the drilling tool around its rotational or center axis CL in a direction opposed to its operative direction the reamer 12 will rotate a limited angle relative to a bearing portion 14 and take an inactive position, the penetration position, which enables the drilling tool can be retracted, up through the casing 13. The bearing portion 14, which is substantially cylindrical with a diameter D3, has a rotational or center axis CL2 which is parallel with but eccentrically placed relative to the axis CL and carries the reamer 12. The reamer has at least partly a varying wall thickness along its circumference and has an internal smallest diameter D2 of the same order of magnitude as the diameter D3. The rock drilling tool is consequently provided to have a bigger diameter in the operative mode than in the inactive position.

The body element 11 according to the present invention is separately shown in Figs. 1A-1C. The body element 11 comprises a shank 15, a central pilot bit 16 and a guide 18, wherein the shank, the pilot bit and the guiding means constitutes an integral unit, which are not releaseable from each other. The pilot bit 16 comprises buttons 60 of cemented carbide (Fig. 5), possibly diamond coated, and are defined by a largest diameter D1. The guiding means 18 is

defined by a largest diameter D and comprises a driving portion 17, which is provided in connection with the shank 15 axially forwards of the guiding means 18. The driving portion 17 is eccentrically provided relative to the rest of the shank 11 and the guiding means 18 has a substantially corresponding eccentrical recess 19 at opposite sides relative to the central axis CL. The eccentrical recess 19 is bordered radially inwardly by a semi-cylindrical portion 22 and axially rearwardly by an essentially planar surface 20. A support surface 47 running around the bearing portion 14 is provided as an axial forward end of both the portion 22 and the driving portion 17. The support surface is perpendicular to the rotational axis CL. The portion 22 and the surface 20 connect to each other. A seat 21 for driving the reamer is provided at one circumferential end of the portion 22, i. e. at the trailing end in the rotational direction Y. A second end 48 is provided at the part of the portion 22 which comes first in the rotational direction Y. A system of flush channels are arranged in the body element, whereof one channel terminates in the seat 21 in order to rinse the seat and thereby guarantee a simple inwards pivoting of the reamer.

The guiding means 18 is provided with two external shoulders 23,24 which shall cooperate with an internal ledge on the casing 13. The shoulders 23,24 are somewhat conical in the direction of drilling as well as semi-circular in the direction of rotation. Through such an arrangement the casing 13 can be forced in the direction of drilling via impacts from the drilling tool when the drilling tool is displaced forwardly.

The guiding means 18 has two external flush channels 49,50, which space the shoulders 23,24 from each other. Alternatively, the fiushing channels can be arranged as flushing holes radially inside a circle which defines the radial position of the shoulders. Then only one contiguous shoulder is arranged.

The shank 15 is provided with external splines 25 which must be in engagement with internal splines of a down-the-hole hammer, not shown. The

down-the-hole hammer transfers rotation to the rock drilling tool via these splines. The shank 11 has a portion 15A with reduced diameter at its rear end, said portion 15A being used to allow the shank 15 to move axially a limited distance relative to the down-the-hole hammer.

In Figs. 2A, 2B and 2C the reamer 12 is shown, which in the preferred the embodiment consists of four portions, namely a button housing 26, a shackle 27 and two pins 28,29.

The button housing 26 is generally U-shaped. The button housing has an inner, semi-cylindrical bearing surface 30, which connects to upper 31 and lower surfaces, which are substantially perpendicular to the rotational axis CL of the drill, when mounted on the drilling tool. The bearing surface 30 is defined by a radius R, the center of which always lies on the central axis CL2 for the bearing portion 14. The upper surface 31 connects to an incline or substantially conical surface 32. The conical surface comprises a number of peripherally placed holes 33 for receiving buttons of cemented carbide. The buttons may be diamond coated. The surface 32 further connects to a jacket surface 34, which in the embodiment is defined by two different radii R1 and R2. The center of the radius R2 coincides with the rotational axis CL in the pivoted position, while the center of the radius R1 is arranged radially outside said rotational axis CL at the pivoted position. The radius R1 defines the jacket surface of the legs while the radius R2 defines the mid portion of the button housing. The radius R1 is smaller than the radius R2. The envelope surface 34 is, on the part which lies first in the direction of rotation, provided with holes 35 for receiving buttons of cemented carbide in order to minimize steel wash. The button housing has rounded free ends. Through-holes 36,37 are provided in the proximity of both free ends. The holes are parallel with the rotational axis CL. A recess or slot 38, 39 is provided in respective free end, which slot runs inwardly from respective free end a distance past the hole 36,37.

The shackle 27 is likewise generally U-shaped. The shackle has an inner, semi- cylindrical bearing surface 40, which connects to upper 41 and lower surfaces, which are essentially perpendicular to the axis of rotation CL of the drill, when mounted on the drilling tool. The bearing surface 40 is defined by a radius R identical to the radius for the bearing surface 30. The shackle preferably has no buttons. Through-holes 42,43 are provided in the proximity of both free ends.

The holes are parallel with the rotational axis CL. A lip 44,45 is provided at the respective free end, said lip carrying the holes 42,43 and runs from respective free end a distance past the holes 36,37. The thickness of the lip is somewhat less than the width of the connected stot 38,39. Each lip is surrounded in the height direction by a semi-cylindrical, concave surface adapted to follow the connected rounded free end of the button housing. The lip 44 is to be adapted to the slot 38 for constituting a hinge mounting. The lip has a rounded free end while the lip 45, which is to be adapted to the slot 39, has a planar free end.

The rock drilling tool 10 is mounted in the following manner, foremost with reference to Figs. 2A-2C and 4A. Firstly the lip 44 of the shackle is brought into the slot 38 of the button housing such that the holes 36 and 42 become aligned. Then the pin 28 is inserted through the holes 36,42 such that one end of the pin lies substantially flush with the surfaces 31 and 41. Said one end may include a head for axial positioning. The pin 28 is longer than the thickness of the hinge formed, and therefor its other end will project a distance L rearwardly in relation to the feed direction of the drill tool. The button housing and the shackle are thereby pivotably joined. Subsequently these are brought in an open condition towards the body element 11, in a position according to Fig. 4A i. e. in an inactive position, such that the bearing surface 30 of the button housing abuts against the bearing portion 14 of the body element.

Subsequently the shackle 27 is pivoted around the bearing portion 14 until the holes 39 and 43 align at a groove 46 for cuttings. The pin 29 is then inserted in the groove 46 for cuttings and into in the aligned holes 39 and 43. The end of the pin 29 comprises a head for axial positioning. The pin 29 is not longer than the thickness of the formed ring-shaped reamer, and therefor its other end does

not project relative to the reamer. The button housing and the shackle are thereby locked to each other around the bearing portion 14 which is eccentrical in relation to the axis of rotation CL of the drill. Thereby the position for the reamer according to Fig. 4A has been achieved, i. e. the reamer is eccentrically positioned relative to the rotational axis CL and can support either against the support surface 47 or an axially rear shoulder of the drill bit 16. The reamer 12 is consequently divided and has an inner diameter D2 which is smaller than the largest diameter D of the guiding means 18 and the diameter D1 of the pilot bit 16 in a mounted position. The inner diameter D2 of the reamer is somewhat bigger than the largest diameter D3 of the bearing portion.

In its mounted position the reamer 12 covers the bearing portion 14 and as is stated above the reamer 14 becomes rotatable a limited angle relative to the bearing portion 13. The angle which the reamer is admitted to rotate is defined by the projection L of the pin 28 and of the end positions 21 and 48 of the portion 22. The angle is about 180°.

Alternatively the pin 28 and seat 21 can be replaced by two axially extending planar shoulder surfaces on the button housing and the driving portion 17.

The drilling tool is thereby ready for mounting to a down-the-hole hammer for further transport through the casing against a casing shoe on the casing 13 whereafter drilling can be initiated in a known manner. When the drilling tool begins to drill the reamer will due to friction against the drilled hole rotate relative to the body element and thereby will be ejected outwardly until the pin 28 abuts against the seat 21, whereby further relative rotation is stopped, Fig.

4B.

When the rotation of the drill tool is reversed the reamer is retracted instead until the pin 28 abuts against the end surface 48, Fig. 4A, and the drilling tool can be retracted through the casing.

The flushing channels 49,50 are arranged on the same side of a normal to the rotational axis CL, i. e. on the side wherein the shackle 27 is arranged in operative position. Thereby the reamer will not cover the flushing channels in operative position, and therefor a good transport of drill cuttings is attained.

Since the reamer 12 normally wear out much faster than the body element 11 or bit 16 it is necessary to exchange the reamer 14. In such case the reamer 12 is easily dismounted in an inverted sequence compared to what has been described above.

In certain cases a bigger reamer is needed. Until now the user has been forced to purchase a bigger drilling tool but with the present invention only a bigger reamer needs to be stored as well as a intermediate ring for transfer of impacts to a casing with bigger diameter. In that case the intermediate ring follows between the reamer and the guiding means at retraction through the casing.

In the above-described embodiments is stated that the guiding means and the pilot bit constitutes a integral unit. However it is also possible within the inventive idea to have an arrangement where the guiding means, the shank and the pilot bit constitute separate parts but connected to each other for example by friction welding, i. e. the compounded unit has a design and function corresponding to an integral unit. For that reason was used the expression"... constitutes a one-piece unit, wherein the guiding means, the shank and the pilot bit cannot be dismounted relative to each other..."in claims 1 and 9.

In a drilling tool, a body element and a reamer according to the present invention the reamer can be easily exchanged. Further, the impact energy to the drill bit 16 is used to the maximum since this energy does not need to be guided via threads but rather by means of a solid body. Consequently also locking means for threads are avoided. According to an embodiment of the present invention the position of the grooves can be placed optimal such that removal of drill cuttings is not hindered.