Pick having a supporting element with a centering extension

Abstract

A round-shank pick having a pick head and a pick shank that includes a supporting element pierced along its longitudinal center axis by a mounting hole with an inside diameter for receiving the pick shank. A collar height, measured in the direction of the longitudinal center axis between an end, facing away from the seat surface, of the centering extension and the seat surface or between the end of the centering extension and an inner termination of a recess that is integrally formed in the supporting element in an indented manner with respect to the seat surface, is configured such that the ratio between the inside diameter of the mounting hole in the supporting element and the collar height is less than 8, and/or that the collar height is greater than an axial clearance of the pick mounted in a pick holder.

Claims

1. A pick holder for a tool system, the pick holder comprising: a base part having a pick receptacle defined therein, the pick receptacle having a longitudinal central axis and an inside diameter; a wear surface defined on the base part and surrounding the pick receptacle; at least one extension integrally formed on and projecting beyond the wear surface; and an end of the pick receptacle adjacent the wear surface including a centering receptacle extending in an inclined manner relative to the longitudinal center axis and transitioning directly or indirectly into the wear surface, the centering receptacle having a centering height measured parallel to the longitudinal center axis, the centering height extending between an end of the centering receptacle facing away from the wear surface and a maximum point of projection of the at least one extension, a ratio of the inside diameter of the pick receptacle to the centering height being less than 8.0.

2. The pick holder of claim 1, wherein: the ratio between the inside diameter of the pick receptacle and the centering height is less than 7.5.

3. The pick holder of claim 1, wherein: the ratio between the inside diameter of the pick receptacle and the centering height is less than 7.0.

4. The pick holder of claim 1, wherein: the ratio between the inside diameter of the pick receptacle and the centering height is less than 6.5.

5. The pick holder of claim 1, wherein: the centering receptacle and the extension encircle the pick receptacle.

6. The pick holder of claim 1, wherein: transitions between the centering receptacle, the extension and the wear surface extend in a rectilinear or rounded manner.

7. The pick holder of claim 1, wherein: the extension has a height with respect to the wear surface greater than or equal to 0.3 mm.

8. The pick holder of claim 1, wherein: the extension has a height with respect to the wear surface between 0.3 mm and 2 mm.

9. The pick holder of claim 1 wherein: the extension has a height with respect to the wear surface between 0.5 mm and 1.5 mm.

10. The pick holder of claim 1, wherein: the inside diameter of the pick receptacle is about 20 mm, and the centering height is greater than 2.5 mm.

11. The pick holder of claim 1, wherein: the inside diameter of the pick receptacle is about 22 mm, and the centering height is greater than 2.75 mm.

12. The pick holder of claim 1, wherein: the inside diameter of the pick receptacle is about 25 mm, and the centering height is greater than 3.125 mm.

13. The pick holder of claim 1, wherein: the inside diameter of the pick receptacle is about 42 mm, and the centering height is greater than 5.25 mm.

14. The pick holder of claim 1, wherein: the at least one extension is one of a plurality of extensions; and the ratio between the inside diameter of the pick receptacle and the centering height is determined using the one of the extensions having a greatest centering height.

15. The pick holder of claim 1, wherein: the at least one extension surrounds the pick receptacle.

16. The pick holder of claim 1, wherein: the centering height is greater than an axial play of a round-shank pick installed in the pick holder.

17. A pick holder for a tool system, the pick holder comprising: a base part having a pick receptacle defined therein, the pick receptacle having a longitudinal central axis and an inside diameter; a wear surface defined on the base part and surrounding the pick receptacle; at least one extension projecting beyond the wear surface; and an end of the pick receptacle adjacent the wear surface including a centering receptacle extending in an inclined manner relative to the longitudinal center axis and transitioning directly or indirectly into the wear surface, the centering receptacle having a centering height measured parallel to the longitudinal center axis, the centering height extending between an end of the centering receptacle facing away from the wear surface and a maximum point of projection of the at least one extension, a ratio of the inside diameter of the pick receptacle to the centering height being less than 8.0; and wherein the pick holder includes a rib receptacle formed in the wear surface and surrounding the centering receptacle.

18. The pick holder of claim 17, wherein: the maximum point of projection is located between the centering receptacle and the rib receptacle.

19. The pick holder of claim 17, wherein: the at least one extension and the rib receptacle are formed on the wear surface by a shaping process during the production of the pick holder.

20. A pick holder for a tool system, the pick holder comprising: a base part having a pick receptacle defined therein, the pick receptacle having a longitudinal central axis and an inside diameter; a wear surface defined on the base part and surrounding the pick receptacle; at least one extension projecting beyond the wear surface; and an end of the pick receptacle adjacent the wear surface including a centering receptacle extending in an inclined manner relative to the longitudinal center axis and transitioning directly or indirectly into the wear surface, the centering receptacle having a centering height measured parallel to the longitudinal center axis, the centering height extending between an end of the centering receptacle facing away from the wear surface and a maximum point of projection of the at least one extension, a ratio of the inside diameter of the pick receptacle to the centering height being less than 8.0; and wherein the at least one extension is formed on the wear surface by a shaping process during the production of the pick holder.

21. A pick holder for a tool system, the pick holder comprising: a base part having a pick receptacle defined therein, the pick receptacle having a longitudinal central axis and an inside diameter; a wear surface defined on the base part and surrounding the pick receptacle; at least one extension projecting beyond the wear surface; and an end of the pick receptacle adjacent the wear surface including a centering receptacle extending in an inclined manner relative to the longitudinal center axis and transitioning directly or indirectly into the wear surface, the centering receptacle having a centering height measured parallel to the longitudinal center axis, the centering height extending between an end of the centering receptacle facing away from the wear surface and a maximum point of projection of the at least one extension, a ratio of the inside diameter of the pick receptacle to the centering height being less than 8.0; and wherein the pick holder includes a rib receptacle formed in the wear surface and surrounding the centering receptacle; and wherein the centering receptacle, the rib receptacle and the extension have an interrupted contour profile.

22. The pick holder of claim 21, wherein: interruptions in the contour profile have one or more radial longitudinal extents with different lengths.

23. A pick holder for a tool system, the pick holder comprising: a base part having a pick receptacle defined therein, the pick receptacle having a longitudinal central axis and an inside diameter; a wear surface defined on the base part and surrounding the pick receptacle; at least one extension projecting beyond the wear surface; and an end of the pick receptacle adjacent the wear surface including a centering receptacle extending in an inclined manner relative to the longitudinal center axis and transitioning directly or indirectly into the wear surface, the centering receptacle having a centering height measured parallel to the longitudinal center axis, the centering height extending between an end of the centering receptacle facing away from the wear surface and a maximum point of projection of the at least one extension, a ratio of the inside diameter of the pick receptacle to the centering height being less than 8.0; and wherein a transition between the centering receptacle and the maximum point of projection is continuous or rounded.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention is explained in more detail by way of an exemplary embodiment illustrated in the drawings, in which:

(2) FIG. 1 shows a side view of a tool system having a pick in its mounted position on a pick holder;

(3) FIG. 2 shows a detail labeled II. in FIG. 1;

(4) FIG. 3 shows a schematic illustration of the wear to a wear surface of a pick holder in the case of a known supporting element;

(5) FIG. 4 shows a lateral sectional illustration of a detail of a supporting element in a first embodiment; and

(6) FIGS. 5-14 each show schematic lateral sectional illustrations of a supporting element in further embodiments.

DETAILED DESCRIPTION OF THE INVENTION

(7) FIG. 1 shows a side view of a tool system according to the prior art, having a pick 10 in its mounted position on a pick holder 40. The pick 10, in the form of a round-shank pick, has a pick head 13 with a pick tip 14 made of a hard material, for example carbide. On the opposite side from the pick tip 14, a cylindrical centering portion 12 is integrally formed on the pick head 13, which transitions into a cylindrical pick shank 11 via a narrowing portion 12.1.

(8) The pick holder 40 has a base part 41 on which a plug-in extension 42 that protrudes from the underside is integrally formed. The base part 41 furthermore bears an integrally formed holding extension 43 into which a pick receptacle 46 is introduced as a cylindrical hole. In this case, the pick receptacle 46 is embodied as a through-hole which is open at both of its longitudinal ends. That end of the pick receptacle 46 that faces away from the plug-in extension 42 leads into a cylindrical portion 44 of the holding extension 43. Provided at the outer circumference of the holding extension 43 are wear markings 45 in the form of circumferential rings.

(9) The pick 10 is held on its pick shank 11 by means of a fastening sleeve 20 in the pick receptacle 46 of the pick holder 40. To this end, the fastening sleeve 20 has holding elements 21 which engage in a circumferential groove 15 in the pick shank 11. Furthermore, the fastening sleeve 20 has a clamping slot 23. This makes it possible for the fastening sleeve 20, produced from spring elastic material, to be pressed, on account of its residual stress, against the wall of the pick receptacle 46 and thus to be fixed against the latter. The pick 10 is thus rotatable about its longitudinal axis, but held axially and fixed in the pick receptacle 46. In this case, the axial mounting allows a defined axial clearance 50, indicated by a double arrow, of the pick 10, in order to allow smooth rotatability of the pick 10.

(10) Arranged between the pick head 13 and the pick holder 40 is a supporting element 30 in the form of a washer, as is shown in more detail in FIG. 2, wherein the external contour of the supporting element 30 in the form of a washer follows a geometric shape and/or an arbitrary shape.

(11) For operation, the pick holder 40 is mounted with its plug-in extension 42 in a corresponding holder on a milling drum (not shown) of a milling machine. The pick 10 is fastened to the holding extension 43 of the pick holder 40 by means of the fastening sleeve 20, together with the supporting element 30. During operation, the pick 10 is guided through the excavated material by a rotary movement of the milling drum. In this case, the pick 10 rotates automatically on account of acting forces, such that uniform radial wearing of the pick 10 is achieved.

(12) FIG. 2 shows a detail, labeled II. in FIG. 1, of the tool system having a pick 10 and a supporting element 30 according to the prior art. The pick head 13 is terminated by a flange 13.2 in the direction of the pick shank 11, the flange 13.2 forming a bearing surface 13.1. The latter rests on a supporting surface 32 of the supporting element 30. The supporting surface 32 is formed within a receptacle 31 on the top side of the supporting element 30. It is bounded externally in a corresponding manner by a rim 31.1. On the opposite side from the supporting surface 32, the supporting element 30 has a seat surface 33 by way of which it rests on a wear surface 47 of the cylindrical portion 44 of the holding extension 43. The supporting element 30 is constructed in a substantially rotationally symmetrical manner with respect to a longitudinal center axis (M) of the pick 10. The seat surface 33 transitions via a circumferential recess 35 into a centering surface 34.1, extending in an inclined manner with respect to the longitudinal center axis M, of a centering extension 34. As FIG. 2 clearly illustrates, the centering extension 34 of the supporting element 30 is inserted into a correspondingly formed centering receptacle 48 of the pick holder 40.

(13) Along the longitudinal center axis (M), the supporting element 30 has a mounting hole 39 which forms a guide region 36 for guiding the pick 10. In the mounted position, the centering portion 12 of the pick shank 11 is assigned to the guide region 36. In this way, rotary mounting arises between the guide region 36 and the centering portion 12. In this case, care should be taken to ensure that the outside diameter of the cylindrical centering portion 12 is matched to the inside diameter D.sub.i of the mounting hole 39 in the guide region 36, such that free rotatability remains between the supporting element 30 and the centering portion 12. The clearance between these two components should be selected such that as little lateral misalignment (transversely to the longitudinal center axis of the pick (10)) as possible arises. As already illustrated in FIG. 1, the centering portion 12 transitions into the cylindrical pick shank 11 after a narrowing region 12.1.

(14) The pick shank 11 is held in the holding extension 43 of the pick holder 40 by means of the fastening sleeve 20. At its upper end, the fastening sleeve 20 has a chamfer 22.

(15) During operation, the pick 10 can rotate about the longitudinal center axis. The free rotatability ensures that the pick 10 becomes worn uniformly over its entire extent. In this case, the loosely applied supporting element 30 held by the centering portion 12 of the pick shank 12 also rotates, with the result that the rotatability of the pick 10 overall is further improved. As a result of the rotation and the high mechanical load on the pick 10, wear to the pick holder 40 also takes place, mainly in the upper portion 44 of the holding extension 43. As a result of the load, the wear surface 47 is abraded. The wear present on the holding extension 43 can in this case be evaluated via the wear markings 45 shown in FIG. 1.

(16) As a result of the relative movement between the supporting element 30 and the holding extension 43, the wear surface 47, which is planar in the new state, of the holding extension 43 grinds into the recess 35 in the supporting element 30, as is shown in FIG. 2. By way of an extension 47.1 that forms the contour of the recess 35 in a corresponding manner, the supporting element 30 receives additional lateral guidance, this having a positive effect on the rotatability of the supporting element 30 and thus of the pick 10. The centering surface 34.1 transitions tangentially into the surface of the recess 35, such that no edges that impede the rotatability are formed. In a corresponding manner, the surface of the recess 35 transitions into the seat surface 33 via a rounding portion without sharp edges. With its radially outer surface portion, the recess 35 counteracts forces which act radially inward on the supporting element 30. Forces directed radially outward are counteracted by the radially inner surface portion. As a result, the force which has to be absorbed by the centering surface 34.1 is reduced, this resulting in reduced surface pressure and accordingly in reduced wear in this region. Furthermore, this support also counteracts a wobbling movement in the washer plane of the supporting element 30, bringing about a reduction in wear to the pick holder 40. Moreover, the recess serves, with its counterpart ground out of the wear surface 47, as a labyrinthine seal. Excavated material which passes between the seat surface 33 and the wear surface 47 is prevented from penetrating further by this seal and thus passes into the region of the pick shank 11 only to a reduced extent.

(17) FIG. 3 shows a schematic illustration of the wear to the wear surface 47 of the pick holder 40 in the case of a known supporting element 30 and in the case of an asymmetric load on the supporting element 30. The supporting element 30 in the form of a washer is bounded, in the embodiment shown, by a planar supporting surface 32 and an opposite seat face 33 that is likewise embodied in a planar manner. The centering extension 34 is integrally formed on the seat surface 33 with its centering surface 34.1 encircling the central mounting hole 39. The mounting hole 39 has an inside diameter D.sub.i 58. On the side of the supporting surface 32, the mounting hole 39 has an insertion chamfer 36.1.

(18) The asymmetric load is illustrated by two arrows of different lengths which symbolize a first force 55.1 and a larger second force 55.2. The asymmetric introduction of force can be brought about for example by the position of the pick holder 40 with respect to the direction of rotation of the milling drum. Such an irregular axial load results, in the case of a relatively large lateral movement (radial movement 54) of the supporting element 30, in asymmetric wear to the wear surface 47 of the pick holder 40. This is indicated by a profile of the wear surface 47 that is inclined at a wear angle 56 with respect to a plane extending perpendicularly to the longitudinal center plane M. The radial movement 54 is allowed in the case of insufficient lateral guidance of the supporting element 30. As a result of such asymmetric wearing of the wear surface 47, the supporting element 30 guiding the pick 10 rests on the wear surface 47 at an angle to the longitudinal center axis M. Thus, the mounting hole 39 is not aligned exactly with the longitudinal center axis M of the pick receptacle 46. As a result of this misalignment, the smooth rotatability of the pick 10 can be impeded or prevented.

(19) FIG. 4 shows a lateral sectional illustration of a detail of a supporting element 30 according to the present invention in a first embodiment.

(20) The supporting surface 32 is arranged in the receptacle 31 for mounting the pick head 13. In the opposing seat surface 33, a groove-like recess 35 is integrally formed in the supporting surface 32 at the transition to the centering surface 34.1 of the centering extension 34. The recess 35 has a first radius 35.1 in a range between 0.5 mm and 6 mm, in the present case 1.5 mm. The depth of the recess 35 with respect to the seat surface 33 is preferably in a range between 0.3 mm and 2 mm, preferably between 0.5 mm and 1.5 mm, in the present case 1.0 mm. The recess 35 transitions into the seat surface 33 via a rounded region with a second radius 35.2. The transition from the recess 35 to the centering surface 34.1 extends in a rectilinear manner. Thus, edges between the centering surface 34.1, the recess 35 and the seat surface 33 are avoided, with the result that free rotatability of the mounted supporting element 30 about the longitudinal center axis M is improved.

(21) A vertex 35.5 forms an inner termination 53 of the recess 35. Remote from the seat surface 33, the centering extension 34 is terminated by a rib-like end 34.2. A collar height 52 is illustrated by a double arrow. In the present exemplary embodiment, the collar height 52 represents the distance, measured in the direction of the longitudinal center axis M, between the end 34.2 of the centering extension 34 and the termination 53 of the recess 35.

(22) In the exemplary embodiment shown, the recess 35 is integrally formed in the seat surface 33 of the supporting element 30. In the mounted state, the supporting element 30 rests with its seat surface 33 on the wear surface 47, shown in FIG. 2, of the pick holder 40. If the wear surface 47 is embodied in a planar manner as far as its transition into the centering receptacle 48, the extension 47.1 grinds during use of the tool system and of the supporting element 30 rotating in the process about the longitudinal center axis M into the recess 35. Alternatively, provision can also be made for the extension 47.1 corresponding to the recess 35 to already be integrally formed on the wear surface 47 during the production of the pick holder 40. In this case, the extension 47.1 can already have its final contour matched to the recess 35. It is also possible for the extension 47.1 to be matched only approximately to the contour of the recess 35 during the production of the pick holder 40. The final contour of the extension 47.1 is then produced during the use of the tool system, in which the extension 47.1 grinds into the recess 35. According to a further possible embodiment, the seat surface 33 can be embodied without an integrally formed recess 35. Instead, the extension 47.1 is integrally formed on the wear surface 47 of the pick holder 40. During operation, the extension 47.1 now grinds into the wear surface 33 of the supporting element 30 and thus forms the recess 35.

(23) An outside diameter 51 of the supporting element 30 and the inside diameter 58 of the mounting hole 39 in the supporting element 30 are each marked by an arrow. The outside diameter 51 corresponds to an outside diameter 57 of the seat surface 33 in the exemplary embodiment shown.

(24) According to the present invention, the collar height 52 is designed such that the ratio between the inside diameter 58 of the mounting hole 39 in the supporting element 30 and the collar height 52 adopts a value of less than 8. The collar height 52 is in this case predefined by the axial dimensions of the centering extension 34 and the recess 35.

(25) At a ratio of less than 8 between the inside diameter 58 of the mounting hole 39 in the supporting element 30 and the collar height 52, good lateral guidance of the supporting element 30 and thus of the pick 10 is ensured. In particular, the collar height 52 is in this case designed so as to be greater than the axial clearance 50 of the pick 10 and thus of the supporting element 30. The dimensioning of the collar height 52 in dependence on the inside diameter 58 of the mounting hole 39 in the supporting element 30 takes into consideration the greater permissible axial clearance 52 in larger tool systems. Thus, regardless of the tool size, sufficient lateral guidance of the supporting element 30 and thus of the pick 10 is always ensured.

(26) On account of the centering surface 34.1 bearing against the centering receptacle 48, good radial guidance of the supporting element 30 is achieved even in the case of maximum deflection of the pick 10, within the permissible axial clearance 50, out of the pick receptacle 46. By way of the recess 35 and the extension 47.1, engaging therein, of the pick holder 40, further lateral guidance of the supporting element 30 is achieved. Lateral movements or wobbling movements of the supporting element 30 can thus be reliably avoided. As a result, the wear to the supporting element 30 and to the pick holder 40 can be reduced considerably. Asymmetric wear to the wear surface 47 given irregular loading of the supporting element 30, as is described with regard to FIG. 2, can be avoided or at least greatly minimized. On account of the remaining angular offset of the wear surface 47, as bearing surface of the supporting element 30 and thus of the pick 10, with regard to the longitudinal center axis M, consistently good rotation of the pick 10 and of the supporting element 30 is achieved. Likewise, exact lateral guidance of the pick 10 takes place as a result of its centering portion 12 of the pick shank 11 bearing against the guide region 36 of the supporting element 30. As a result of the exact lateral guidance of the supporting element 30 and thus of the pick 10 and the resultant reduced wear to the supporting element 30 and to the pick holder 40, stabilization of the rotational movement both of the supporting element 30 and of the pick 10 is achieved. As a result, the wear in particular to the pick 10 and to the pick head 13 can be reduced.

(27) Furthermore, at a ratio of less than 8 between the inside diameter 58 of the mounting hole 39 in the supporting element 30 and the collar height 52, an improved sealing action with respect to penetrating foreign matter by the mutually engaging contours of the supporting element 30 and the top side of the holding extension 43 of the pick holder 40 is achieved than in tool systems having a ratio of greater than or equal to 8. Thus, for example, less excavated material penetrates into the region of the pick receptacle 46, with the result that the wear in this region is reduced and the rotatability of the pick 10 is ensured.

(28) The easy rotatability of the supporting element 30 and of the pick 10 is furthermore maintained by the rounded or rectilinearly extending and thus edge-free transitions between the centering surface 34.1, the receptacle 35 and the seat surface 33. Sharp transitions easily result in the supporting element 30 tilting with respect to the pick holder 40 and rotation being prevented. This can be avoided by the rounded or rectilinearly extending transitions.

(29) FIGS. 5 to 14 each show schematic lateral sectional illustrations of a detail of a supporting element 30 in further embodiments.

(30) In the exemplary embodiments shown in FIGS. 5 to 11 and 13 and 14, the supporting elements 30 have a planar supporting surface 32. Alternatively, however, it is possible in each case, in a manner corresponding to the exemplary embodiment in FIG. 4, to provide a receptacle 31, bounded by a rim 31.1, on the top side of the supporting element 30. The receptacle 31 then forms the supporting surface 32 on which the pick head 13 rests with its bearing surface 13.1. At the transition from the supporting surface 32 into the guide region 36, an insertion chamfer 36.1 is arranged. Alternatively, the transition can also be embodied in a rounded manner.

(31) In the exemplary embodiments corresponding to FIGS. 5 to 12, the outside diameter 51 of the supporting element 30 corresponds to the outside diameter 57 of the respective seat surface 33. In the exemplary embodiments corresponding to FIGS. 13 and 14, a folded edge 38 is arranged encircling the seat surface 33. The outside diameter 51 of the supporting element 30 is accordingly greater than the outside diameter 57 of the associated seat surface 33 in these exemplary embodiments.

(32) In the exemplary embodiment of a supporting element 30 shown in FIG. 5, a guide rib 37 is arranged on the seat surface 33. The guide rib 37 extends at a distance from the centering extension 34. It has a trapezoidal contour with lateral surfaces extending at an angle to the seat surface 33. Toward the pick holder 40, the guide rib 37 is terminated by a seat-surface portion 33.1. The recess 35 is formed between the centering extension 34 and the guide rib 37. It, too, has a trapezoidal contour. The termination 53 of the recess 35 is formed by a bearing surface 35.3. In the exemplary embodiment shown, the bearing surface 35.3 is located in the same plane as the seat surface 33 to the side of the guide rib 37. Toward the longitudinal center axis M, the bearing surface 35.3 transitions into the centering surface 34.1, extending in an inclined manner, of the centering extension 34. The centering extension 34 is terminated toward the pick holder 40 by its rib-like end 34.2.

(33) The collar height 52 is measured in the direction of the longitudinal center axis between the end 34.2 of the centering extension 34 and the termination 53 of the recess 35, as is illustrated by a double arrow. The ratio between the inside diameter 58 of the mounting hole 39 in the supporting element 30 and the collar height 52 is selected to be less than 8, in the present case less than 6.5. As a result, good lateral guidance of the supporting element 30 and a good sealing action with respect to penetrating foreign matter is achieved with the described advantages. At a ratio of less than 6.5, sufficient lateral guidance is also achieved toward the end of the service life of the supporting element 30 and of the pick 10, when the axial clearance 50 of the pick 10 may have increased on account of the wear that has already occurred.

(34) It is conceivable to configure the collar height 52 at the centering extension 34 with a longitudinal extent which results in a ratio between the inside diameter 58 of the mounting hole 39 in the supporting element 30 and the collar height 52 of greater than 8. As a result, improved support of the centering surface 34.1 on the inner surface of the pick receptacle 46 and/or improved support of the outer surface of the collar height 52 with the outer surface of the free region of the pick shank can be achieved.

(35) In the mounted state, the guide rib 37 rests on the wear surface 47 of the pick holder 40. As a result of the rotation of the supporting element 30, it grinds into the wear surface 47 and thus forms a corresponding rib receptacle in the end face of the pick holder 40. As a result, both the lateral guidance of the supporting element 30 and the sealing action are improved considerably.

(36) Differing from the embodiment illustrated, the transition from the centering surface 34.1 to the bearing surface 35.3 and/or the transition from the bearing surface 35.3 to the adjoining lateral surface of the guide rib 37 and/or the transition from the opposite lateral surface of the guide rib 37 to the adjoining seat surface 33 can be rounded. Likewise, the transitions from the lateral surfaces to the seat-surface portion 33.1 can be embodied in a rounded manner. In this way, sharp edges can be avoided. This results in improved rotatability of the supporting element 30.

(37) In the case of the supporting element 30 shown in FIG. 6, a trapezoidal guide rib 37 is likewise arranged on that side of the supporting element 30 that faces the pick holder 40. A recess 35 formed between the guide rib 37 and the centering extension 34 has a contour in the form of a fillet. The radius of the recess 35 is in this case selected such that its surface transitions tangentially into the centering surface 34.1 and the adjoining lateral surface of the guide rib 37. The collar height 52 corresponds to the distance, extending in the direction of the longitudinal center axis M, between the end 34.2 of the centering extension 34 and the vertex 35.5 of the recess 35 in the form of a fillet. As a result of the immediately successive combination of centering extension 34, recess 35 and guide rib 37, a good sealing action with respect to penetrating material is achieved in conjunction with a correspondingly formed wear surface 47 of a pick holder 40.

(38) The seat surface 33 of the supporting element 30 shown in FIG. 7 transitions directly into the centering surface 34.1 of the centering extension 34. In the outer region of the seat surface 33, a groove-like recess 35 is let into the seat surface 33. The collar height 52 is measured along the longitudinal center axis M between the end 34.2 of the centering extension 34 and the vertex 35.5 of the groove-like recess 35. The recess 35 arranged comparatively far to the outside on the supporting element 30 results in particularly good stabilization of the rotational movement of the supporting element 30.

(39) FIG. 8 shows a supporting element 30 with a recess 35 embodied in a multilevel manner and a guide rib 37. The centering surface 34.1 extends into the recess 35 and transitions there into a bearing surface 35.3 arranged transversely to the longitudinal center axis M, in particular perpendicularly to the longitudinal center axis M. The bearing surface 35.3 is adjoined, as a further depression of the recess 35, by a groove-like region 35.4. The surface of the groove-like region 35.4 transitions tangentially into the adjoining lateral surface of the guide rib 37. The trapezoidally shaped guide rib 37 forms a seat-surface portion 33.1 which is connected to the further seat surface 33 via the external lateral surface of the guide rib 37. The bearing surface 35.3, the seat-surface portion 33.1 and the external seat surface 33 extend transversely, in particular perpendicularly to the longitudinal center axis M. In this case, the bearing surface 35.3 is integrally formed more deeply in the supporting element 30 than the seat surface 33. The collar height 52 is measured between the end 34.2 of the centering extension 34 and the vertex 35.5 as a termination 53 of the groove-like region 35.4 of the recess 35.

(40) The different planes in which the supporting surface 33, the supporting-surface portion 33.1 and the bearing surface 35.3 are arranged result both in good lateral guidance of the supporting element 30 and in a good sealing action.

(41) In the exemplary embodiment of the supporting element 30 shown in FIG. 9, concentrically arranged recesses 35 are integrally formed in the supporting element 30, around the centering extension 34. A wavy contour is thus formed, the surface of which represents the seat surface 33. Differing therefrom, provision can also be made for the recesses 35 to be formed by a channel encircling the centering extension 34 in a spiral shape. The collar height 52 is measured between the end 34.2 of the centering extension 34 and the vertex 35.5 of the innermost recess 35. In the case of adjacent recesses 35 with different depths, the collar height 52 is preferably determined as far as the termination 53 of the deepest recess 35. The recesses 35 arranged encircling the centering extension 34 ensure good rotatability of the supporting element 30. Furthermore, the engagement of corresponding extensions 47.1 of the pick holder 40 results in a good sealing action. As a result of the wavy contour, the area projected in the axial direction remains the same as a planar area, such that the axial supporting action is retained. The radially active area is enlarged considerably by the lateral flanks of the recesses 35. As a result, transverse forces can be absorbed better. On account of the wave shape, the contact area between the supporting element 30 and the pick holder 40 shown in FIG. 1 is enlarged. As a result, the surface pressure between the supporting element 30 and the pick holder 40 is reduced, resulting in reduced wear and in improved rotatability.

(42) FIG. 10 shows a supporting element with a planar seat surface 33, into which two concentrically extending, groove-like recesses 35 are incorporated. In this arrangement, too, good rotatability, good lateral stabilization and a good sealing action with respect to penetrating excavated material are achieved.

(43) The supporting element 30 illustrated in FIG. 11 has a seat surface 33 that extends in a rectilinear manner but is oriented at an angle to the longitudinal center axis M. In this case, the maximum depth into the supporting element 30 is formed in the transition region, embodied in a rounded manner, from the centering surface 34.1 into the wear surface 33. Both the centering surface 34.1 and the wear surface 33 have a radially stabilizing effect on the position of the supporting element 30 on account of their orientation at an angle to the longitudinal center axis M. The collar height 52 is measured from the end 34.2 of the centering extension 34 to the termination 53 in the transition region from the centering surface 34.1 to the wear surface 33.

(44) In the case of the supporting element 30 shown in FIG. 12, both the supporting surface 32 and the seat surface 33 extend at an angle to the longitudinal center axis M. The supporting surface 32 and the seat surface 33 are in this case arranged preferably in a plane-parallel manner to one another. The greatest distance, measured in the direction of the longitudinal center axis M, between the end 34.2 of the centering portion 34 and the seat surface 33 arises toward the outer rim of the supporting element 30, and so this distance forms the collar height 52. In this exemplary embodiment, too, both the centering surface 34.1 and the seat surface 33 oriented at an angle to the longitudinal center axis M act in a radially stabilizing manner on the supporting element 30.

(45) FIG. 13 shows a supporting element 30 with an outer folded edge 38. The centering surface 34.1 of the centering extension 34 transitions into the supporting surface 33 extending in a planar manner. The supporting surface 33 is preferably oriented perpendicularly to the longitudinal center axis M. The outside diameter 57 of the seat surface 33 is selected to be slightly greater than the diameter of the wear surface 47 of the pick holder 40. The folded edge 38, embodied in a rectangular manner in the exemplary embodiment shown, extends in the direction of the pick holder 40. In the mounted state, it engages around the upper portion 44 of the holding extension 43 and thus results in additional lateral stabilization of the supporting element 30. Furthermore, the folded edge 38 protects the region between the pick holder 40 and the supporting element 30 from penetrating material. In order to avoid tilting of the supporting element 30, the transitions from the centering surface 34.1 into the seat surface 33 and from the seat surface 33 to the folded edge 38 can be embodied in a rounded manner. The collar height 52, as the distance between the end 34.2 of the centering portion 34 and the seat surface 33, is marked by a double arrow.

(46) FIG. 14 also shows a supporting element 30 with a folded edge 38 engaging around the holding extension 43 of the pick holder 40. In this case, the seat surface 33 is embodied in an inwardly curved manner. As a result, compared with the exemplary embodiment shown in FIG. 13, improved lateral guidance and also improved rotatability about the longitudinal center axis M of the supporting element 30 are achieved. The distance between the end 34.2 of the centering extension 34 and the inner termination 53 of the seat surface 33 corresponds to the collar height 52.

(47) In all of the exemplary embodiments according to the present invention that are shown, the respective collar height 52 is designed to be greater than the permissible axial clearance 50 of the pick 10 and thus of the supporting element 30. As a result, even in the event of a maximum deflection of the pick 10 out of the pick receptacle 46, sufficient lateral guidance of the supporting element 30 is achieved. As a result of the different possible contours of that side of the supporting element 30 that faces the pick holder 40, and the top side, designed in a corresponding manner, of the pick holder 40, the lateral guidance and sealing with respect to penetrating foreign matter can be adapted to the applicable requirements. What is essential here is that the ratio between the inside diameter 58 of the mounting hole 39 in the supporting element 30 and the respective collar height 52 is less than 8, since, starting from this ratio, the radial movement of the supporting element 30 is blocked such that increased wear, as is caused by a radial movement of the supporting element 30, is ruled out.

(48) Tests by the applicant have revealed that, for example, the configuration of a centering extension 34, a guide rib 37 and/or a recess 35 with an interrupted contour profile, for example as a rib-like contour profile or a plurality of individual recesses 35 distributed over the contour profile, has a positive effect on the grinding behavior of a rotating pick on the end face of the holder shank. The result observed is that the ground-in centering extension 34 forms what is known as a labyrinth seal on the end face of the holder shank, in order in this way to protect the inner hole 39 from undesired contamination or in order to be able to remove contaminants in a targeted manner from the cavity forming between a centering extension 34, a guide rib 37 and/or a recess 35 and the end face of a holder shank on account of an axial displacement of the pick. In this case, such interruptions can be formed additionally in a radial longitudinal extent with different lengths, in order to further improve the removal of contaminants.

(49) Furthermore, the relief of the pressure that arises on account of the rotational movement of the pick in the holder can be improved.