Round-shank bit for a coal cutting machine

A round-shank bit for a coal cutting machine or the like, having a bit head and a bit shank, wherein the bit head has a bit tip, maintained by a base element in a receptacle of the bit head. Starting at the base element, the bit tip tapers in a direction toward the free end of the bit tip, wherein the base element forms a maximum diameter of the bit tip, and wherein the bit tip has recesses on its outer contour. In order to assure good rotational behavior over the entire length of the operating time, the base element has the recesses on an outer circumference forming the maximum diameter.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 This invention relates to a round-shank bit for a coal cutting machine or
 the like, having a bit head and a bit shank, wherein the bit head has a
 bit tip, maintained by a base element in a receptacle of the bit head, and
 starting at the base element, the bit tip tapers in a direction toward a
 free end of the bit tip, wherein the base element forms a maximum diameter
 of the bit tip, and the bit tip has recesses on an outer contour.
 2. Description of Prior Art
 A conventional round-shank bit is known from German Patent Publication DE
 34 42 546 A1.
 Such round-shank bits are installed in bit holders, which are fastened to a
 rotating body. When using the tool, the bit tips engage and penetrate the
 material to be removed, for example, rocks, coal, road covering and the
 like. The bit tip wears during this engagement. In order to obtain even
 wear over the entire circumference of the bit tip, the bit shank of the
 round-shank bit is rotatably held in a bit holder. For improving the
 rotational behavior of the round-shank bit known from German Patent
 Publication DE 34 42 546 A1, the bit tip has recesses on an outer
 circumference, which extend in a longitudinal direction of the round-shank
 bit. In this case the recesses extend from the bit tip as far as the bit
 head, where the recesses end continuously. Because of the cross-sectional
 weakening as a result of the recesses, rapid wear of the bit tip results
 when these conventional round-shank bits are used. The round-shank bit
 furthermore has a tendency for blockage when the lands formed between the
 recesses are worn out, but when the wear limit is not quite reached.
 SUMMARY OF THE INVENTION
 It is one object of this invention to create a round-shank bit of the type
 mentioned above, wherein a good rotational behavior over an entire length
 of wear is assured.
 This object is attained with a base element having recesses on its outer
 circumference, which constitutes the maximum diameter.
 With the arrangement of the recesses in accordance with this invention, the
 outer contour of the bit tip on a side facing the bit head has
 alternatingly recesses and intermediate elements located between the
 recesses. This results, for example, in a star-shaped or a tooth-shaped
 outer contour of the base element. When using the tool, the removed
 material is taken away in a definite manner via the recesses toward the
 bit head. Thus, an intentional wear of the bit head is caused, which
 carries the recesses on in the form of wash-outs in the bit head.
 In connection with the feed movement of the tool, the removed material
 introduces a force component in a circumferential direction into the
 round-shank bit via the recesses and wash-outs. Thus, the rotating
 property of the round-shank bit is assured up to the wear limit. The
 design of the bit tip in accordance with this invention also utilizes
 knowledge that in a not yet worn out state the bit tip must have
 sufficient support on the bit head in order to be able to dependably
 deflect occurring transverse forces. During increasing wear, however,
 lesser bending stresses are transmitted via the transition between the bit
 tip and the bit head because of the wear-induced shortening of the bit
 tip. At the beginning of use, the intermediate elements between the
 recesses assure sufficient support of the bit tip. With increasing wear
 the intermediate elements are also ground down, so that the contact
 surface of the bit tip on the bit head is reduced. Thus, with increasing
 shortening of the bit tip, the diameter of the base element and of the bit
 head are also reduced, so that the round-shank bit retains a
 cutting-friendly slim geometry up to the time it fails.
 In accordance with a preferred embodiment of this invention, the recesses
 are uniformly cut into the base element up to an interior graduated circle
 extended around the center longitudinal axis of the bit tip. In a plan
 view the bit tip is designed star-shaped on its outer contour defined by
 the base element. A uniform rotational behavior can also be assured
 because of the uniform erosion of the recesses.
 If the recesses terminate continuously and directly in the tapered area of
 the bit tip adjoining the base element, a precise flow of the removed
 material becomes possible. In order not to cause an unnecessary weakening
 of the bit tip and rapid wear, the recesses should terminate directly
 adjoining the base element.
 A preferred embodiment is distinguished because the receptacle in the bit
 head is enclosed by a collar around the circumference, and the recesses
 extend in the axial direction of the bit tip past the collar into the
 contact surface of the bit tip on the bit head. With a round-shank bit of
 this type the recesses do not contact or only partially contact the
 removed material at initial use of the tool. In this state the round-shank
 bit is capable of sufficient rotation because of its geometry alone. When
 used, the collar is ground off and the recesses are increasingly exposed.
 Thus, the support of the rotation in accordance with the invention then
 becomes effective.
 In another preferred embodiment of this invention, the area of a free end
 of the bit tip has a conical first area, which makes a transition into a
 second cylindrical transition area, and following the cylindrical
 transition area, the bit tip extends in a direction toward the base
 element over a truncated cone-shaped or concavely tapered area. A
 round-shank bit of this type has very good cutting properties and a long
 service life.
 Long service life can also be achieved if in the region of the free end the
 bit tip has a conical or approximately conical area, and if a second area
 in the shape of a truncated cone or nearly truncated cone adjoins the
 first area, having a cone opening angle less than the cone opening angle
 of the first area. The second area transitions into the base element via a
 further, third area in the shape of a truncated cone or nearly truncated
 cone, wherein the cone opening angle of the third area is greater than the
 cone opening angle of the second area.

DESCRIPTION OF PREFERRED EMBODIMENTS
 A round-shank bit is shown in a partial sectional side view in FIG. 1.
 Essentially, the round-shank bit comprises a bit tip 10, a bit head 20 and
 a bit shank 26. A clamping sleeve 31 is drawn on the cylindrical bit shank
 26. Tabs 33 are stamped out from the clamping sleeve 31 and are bent off
 in a direction toward the bit shank 26. The tabs 33 engage a
 circumferential groove 27 of the bit shank 26 and prevent the clamping
 sleeve 31 from being pulled off the bit shank 26. A bore in a
 wear-protection disk is pushed on the clamping sleeve 31 in the area of
 the tabs 33. The diameter of the bore is of such a size that the clamping
 sleeve 31 is maintained in a prestressed state. With the bit shank 26, the
 round-shank bit can be inserted into a bore of the bit holder. In this
 case, the diameter of the bore is of such a size that the clamping sleeve
 31 of the round-shank bit can be inserted with only a relatively small
 force. When the round-shank bit contacts the bit holder with its
 wear-protection disk 30, the insertion of the bit shank 26 can have an
 increased force. In the process, the wear-protection disk 30 is displaced
 in the direction toward the bit head 20 until there is no contact with the
 clamping sleeve 31. The clamping sleeve 31 then expands, and the
 longitudinal slit 32 is widened. The clamping sleeve 31 is then braced in
 the bore of the bit holder. The wear-protection disk 30 rests on the
 surface of the bit holder 26 and protects against wear created by rotation
 of the round-shank bit.
 The bit head 20 adjoins the bit shank 26 by means of a cylindrical element
 25. The cylindrical element 25 transitions into a constriction 24, which
 in turn terminates in a further cylindrical element 23. A tool can be
 inserted into the constriction, by means of which the round-shank bit can
 then be pulled out of the bore of the bit holder, when worn out.
 On an end remote from the shank bit, the bit head 20 has a receptacle 21
 bordered by a circumferential collar 22. The receptacle 21 has a flat
 contact surface, on which the bit tip 10 is placed and soldered.
 The bit tip 10 is designed as a hard metal insert. The bit tip 10 has a
 base element 16, which is inserted into the receptacle 21. Adjoining the
 base element 16, the bit tip 10 transitions via a tapered area 15 into a
 cylindrical transition area. The tapered area 15 is designed concave,
 wherein the bit tip 10 widens, starting at the cylindrical transition area
 13, in the direction toward the base element 16. Accordingly, the base
 element 16 has a maximum diameter of the dynamically balanced bit tip 10.
 Between tapered area 15 and cylindrical transition area 13 is a truncated
 conical area 14 of right circular cone shape. The bit tip 10 has a first
 area 12 in the shape of a truncated cone on the free end, which is closed
 off by a rounded portion 11.
 Recesses 17 are cut out of the exterior circumference of the bit tip 10 in
 the transition area between the base element 16 and the tapered area 15.
 In this case, the recesses 17 are cut into the base element 16 in a pocket
 shape and terminate continuously in the tapered area 15. Land-shaped
 intermediate elements 17a are formed between the individual recesses 17,
 by means of which the bit tip 10 is supported on the contact surface of
 the receptacle 21.
 The geometry of the bit tip 10 in the area of the collar 17 is evident from
 FIG. 2, which shows the round-shank bit in a top view. Together with the
 intermediate elements 17a, the recesses 17 provide the bit tip 10 with a
 star-shaped geometry.
 The round-shank bit represented in FIGS. 1 and 2 is shown in a perspective
 view in FIG. 3. As can be seen from this representation, the recesses 17
 form transition areas into the bit head 20.
 When the tool is in use, the material to be removed is cut off by the bit
 tip 21. The removed material then flows past the tapered area 15 toward
 the recesses 17, and in the process grinds past the bit head 20. When
 working, the recesses 17 continue in the bit head 20 in the form of
 wash-outs 18, as shown in FIG. 4. Since the round-shank bit rotates when
 in use, the wash-outs 18 are created in a twist-like manner around the
 center longitudinal axis of the round-shank bit. The recesses 17, and
 later on the wash-outs 18, make it possible for the removed material to
 introduce a force in the circumferential direction of the bit head 20. By
 means of this the rotating movement of the round-shank bit is assisted,
 for optimizing wear.
 The cutting-friendliness of the round-shank bit is also assisted by the
 recesses 17, in accordance with this invention.
 As FIG. 4 shows, the wash-outs 18 reduce the exterior cross section of the
 bit head 20 in a predeterminable manner. The intermediate elements 17a
 offer a sufficient support width on the contact surface of the receptacle
 21, so that the occurring transverse forces can be dependably absorbed.
 If, because of wear, the bit tip 10 experiences a shortening in the axial
 direction when used, the support width can then also be increasingly
 reduced. This invention compensates for continuous wear of the
 intermediate elements 17a after the wash-outs 18 are ground. Because of
 this simple measure the slim, cutting-friendly geometry of the round-shank
 bit 10 is always maintained over the entire length of the operation.