WO2019201536A1

WO2019201536A1 - Milling pick

Info

Publication number: WO2019201536A1
Application number: PCT/EP2019/056867
Authority: WO
Inventors: Heiko Friederichs; Ulrich Krämer
Original assignee: Betek Gmbh & Co. Kg
Priority date: 2018-04-17
Filing date: 2019-03-19
Publication date: 2019-10-24
Also published as: DE102018109148A1; TW201943945A

Abstract

The invention relates to a milling pick, in particular a straight shank pick with a pick head (40) and a pick bit (30) consisting of a hard material, wherein the pick bit (30) comprises a fastening region where it is connected to the pick head (40), the pick bit (30) comprises at its end opposite the pick head (40) in the longitudinal direction an end section (39) located around the pick bit (3) and comprising a tapering section (39.1) and an end cap (39.2), wherein the tapering section (39.1) has a maximum first radial extension (e1) in a first end region facing the pick head (40) and a maximum second radial extension (e2) in its end region away from the pick head, and wherein the end cap (39.2) that forms the free end of the pick bit (30) is coupled to the tapering section (39.1). According to the invention, improved wear properties of the milling pick are obtained when the end cap (39.2) is formed by a spherical dome having a base circle with a diameter (306), and the ratio between double the maximum first extension (twice e1) and the diameter of the base circle (306) ranges between 1.25 and 2.25.

Description

Tooth

The invention relates to a cutting bit, in particular round shank bit having a chisel head and a chisel tip, consisting of a hard material, wherein the chisel tip has a mounting portion, where it is connected to the chisel head, the chisel tip at its longitudinal end facing away from the chisel head one, the The chisel tip has a circumferential end portion having a taper portion and an end cap, wherein the taper portion at its first end portion facing the chisel head, a maximum first radial extent and at its end remote from the bit head has a maximum second radial extent, and wherein the Rejuvenation area of the end cap is coupled, which forms the free end of the chisel tip.

Such a milling cutter is known from DE 10 2007 009 711 A1. In this document are described as a cutting chisel round shank chisel, as used for example in mining or road milling machines use. These Round shank chisels have a cup-shaped recess on their chisel head, into which a carbide chisel tip is soldered.

The chisel tip has a base with a mounting boss. With the attachment lug the chisel tip is received in the cup-shaped depression. The base is followed by a concavely tapered area. The concave tapered portion merges into a cylindrical portion and the cylindrical portion joins the tip of the bit. This is formed by a tapered portion, which is merged in the form of a truncated cone in an end cap. The chisels described in DE 10 2007 009 711 A1 are particularly powerful when used in road milling machines. Nevertheless, there is a continuous need for effecting an increased service life with a consistent use of material for the chisel tip and with the same effect or better cutting action.

It is therefore an object of the invention to provide a milling cutter of the type mentioned above, which is characterized by an improved service life.

This object is achieved in that the end cap is formed by a spherical cap, which has a diameter at its base circle, and that the ratio of twice the maximum first extent to the diameter of the base circle is in the range between 1, 25 and 2.25.

This diameter ratio ultimately defines, in conjunction with the usual axial extensions of such chisel tip in the axial direction, the taper dimension of the connecting portion. It has been found that with such a diameter ratio, an optimized wear behavior is established. The inventors have recognized that the main wear pressure is distributed throughout the tapering area during the machining operation. With a larger diameter ratio, the main wear pressure shifts in the direction of the coupling point between the connecting portion and the subsequent cylindrical portion. As a result, too fast length wear of the chisel tip is effected. If, on the other hand, the diameter ratio <1.25 is selected, the main Wear pressure in the direction of the coupling region of the tapering section to the end cap. The consequence of this is that the chisel tip becomes dull and therefore is no longer so willing to cut. Overall, therefore, a chisel tip according to the invention is offered, which is particularly suitable for use in road milling machines and thereby shows an optimized wear behavior with the greatest possible chopping versatility. The use of materials of expensive hard material, in particular carbide than, for such a chisel tip is minimized.

According to a preferred embodiment variant of the invention, it may be provided that a connecting line from a point of the first maximum extension to a point of the second maximum extension is at an angle between 45 ° and 52.5 ° to the central longitudinal axis. These angular geometries result in particular in the above-mentioned effect, according to which a uniform distribution of the main wear pressure over the rejuvenation region results.

It has proved to be advantageous if it is provided that a connecting line from a point of the first maximum extent to a point of the second maximum extent at an angle between 47.5 ° and 52.5 °, to the central longitudinal axis, and wherein the Rejuvenation section is truncated cone-shaped or concave.

Alternatively, it may also be provided that a connecting line from a point of the first maximum extension to a point of the second maximum extension is at an angle between 45 ° and 50 ° to the central longitudinal axis, and wherein the tapering section is convex. With this geometry results in an improved length-wear behavior, the possible life of the cylindrical portion can be better and optimized exploited.

A possible embodiment of the invention may be such that adjoins the tapering portion, on the side facing the bit head, a connecting portion which is cylindrical or conical with a cone angle of 20 ° maximum that the connecting portion in Transition region to the tapering section has a cross-sectional extension, and that the ratio of this cross-sectional extension to twice the maximum second extension is <2. The connecting section serves as a wear-active area within which a length wear can take place. Over the life of the chisel tip, the length of this wear-active area is reduced continuously. About the cylindrical or slightly conical design can be maintained approximately uniform and sufficient overall cutting action.

For a material-optimized design of the chisel tip, it may be provided that the concave region preferably has an elliptical contour. As a result, the use of expensive hard material, in particular carbide is reduced.

In order to provide a sufficient service life in the milling cutters according to the invention when used in road milling, it may be provided within the scope of the invention that the transition section has an axial extent in the direction of the central longitudinal axis of the chisel tip in the range between 2.7 mm and 7.1 mm having. This also ensures that the chisel tip is sufficiently break-resistant.

For this purpose it can also be provided that the ratio of the maximum extent of the bit tip (30) in the direction of the central longitudinal axis of the bit tip to the maximum first radial extent is in the range between 3.5 and 4.25.

A further conceivable embodiment of the invention may be such that recesses are introduced into the concave area, and / or protrude elevations from the concave area, which are arranged distributed over the circumference of the bit tip and preferably spaced from each other at equal pitch. The recesses or elevations improve the rotational behavior of the milling bit, if this is designed as a round shank chisel. In addition, an improved dissipation of milled during operation of the material is achieved. In order not to cause excessive weakening of the chisel tip, can In particular, it can be provided that the recesses have a depth opposite the surface of the concave region between 0.3 and 1.2 mm.

A milling cutter according to the invention may also be such that the bit tip consists of hard metal and is preferably soldered to the bit head, in particular preferably fixed in a cup-shaped receptacle of the bit head by means of a solder joint. Instead of chisel tips made of hard metal, of course, other chisel tips made of hard material can be used within the scope of the invention. For example, as a hard material then a super hard material, such as ceramic material, a polycrystalline diamond, cubic boron nitride or the like can be used.

A particularly preferred variant of the invention is such that the tapering section is convex, preferably spherical, in the direction of the central longitudinal axis. This creates an optimized wear behavior

When it is envisaged that a tangent to the bit tip and through the point of maximum second extension includes a tangent angle with the central longitudinal axis, and that this tangent angle is greater than the angle that the connecting line from a point of the first maximum extension to a point the second maximum extent includes with the central longitudinal axis, then the transition region between the taper portion and the subsequent wear in the direction of the chisel head wear is formed. Then, the wear pressure distributes more evenly on the actually intended tapering section

An optimally designed for road milling applications designed cutting tool according to the invention may be characterized in that the ratio of the total length of the bit tip to the maximum diameter of the bit tip in the range between 0.8 to 1, 2.

The invention will be explained in more detail below with reference to exemplary embodiments illustrated in the drawings. Show it FIG. 1 is a perspective side view of a milling cutter in a first embodiment,

FIG. 2 a perspective side view of a milling cutter in a second embodiment variant,

FIG. 3 is a side view of a bit tip (30) for use on one of the milling bits according to FIGS. 1 or 2,

FIG. 4 shows the bit tip (30) according to FIG. 3 in a side view and partly in section

5 shows a wear protection disk (20) in a perspective view from above for use on one of the milling tools according to FIGS. 1 or 2, FIG.

6 shows the wear protection disc (20) according to FIG. 5 in a perspective view from below and FIG

Figure 7 is a comparative image in side view, in which a chisel tip (30) is shown.

FIG. 1 shows a milling bit, namely a round shank bit. This milling cutter has a drill collar 10, to which a chisel head 40 is integrally formed. Also conceivable is a design variant in which the chisel head 40 is not integrally formed on the chisel shank 10, but is manufactured as a separate component and connected to the chisel shaft 10.

The drill collar 10 has a first portion 12 and an end portion 13. Between the first portion 12 and the end portion 13 extends a circumferential groove 11. Both the first portion 12 and the end portion 13 are cylindrical. The groove 11 is arranged in the region of the free end of the drill collar 10. On the drill collar 10 is a clamping element 14, which is in the present case in the form of a clamping sleeve, mounted. It is also conceivable to attach another clamping element 14 to the drill collar 10. The clamping element 14 serves to set the cutting bit in a receiving bore of a chisel holder. By means of the clamping sleeve of the cutting bit can be set in the receiving bore of the bit holder so that the clamping sleeve with its outer periphery to the inner wall of the receiving bore exciting applies.

The clamping element 14 has Flalteelemente 15. These flap elements 15 engage in the circumferential groove 11. Thus, the milling cutter is freely rotatable in the clamping element 14 in the circumferential direction, but held captive in the axial direction.

The clamping element 14 may, as I said, be designed as a clamping sleeve. For this purpose, the clamping sleeve may consist of a rolled sheet metal section. The flap elements 15 may be embossed in the direction of the groove 11 above, in the sheet metal section. It is also conceivable that the sheet elements are partially cut free from the material of the sheet metal section and bent in the direction of the groove 11 out.

On the drill collar 10 a wear protection disc 20 is mounted. The wear protection disk 20 is arranged in the region between the associated end of the tensioning element 14 and a chisel head 40. The wear shield 20 is rotatable relative to both the tension member 14 and the bit head 40.

The design of the wear protection disk 20 can be seen in more detail in FIGS. 5 and 6. As these illustrations show, the wear shield 20 may be annular. The wear plate 20 has a central opening 25, which may be formed as a bore. Also conceivable is a polygonal opening. The wear protection disc 20 has an upper counter surface 23 and the counter surface 23 facing away on the underside a support surface 21. The support surface 21 may be aligned parallel to the counter surface 23. It is also conceivable that these two surfaces are at an angle to one another. Recesses 24 may be recessed from the mating surface 23 or be recessed into the mating surface 23. In the present embodiment, the recesses 24 are circumferentially spaced from each other in the same pitch grid. It is also conceivable that a varying division is provided. The recesses 24 divide the counter surface 23 into individual surface sections 23.1, 23.2. In this case, a first surface portion 23.1 is first formed, which is annular and which rotates about the opening 25. At the first surface portion 23.1 close the second surface portions 23.2 radially. The second surface portions 23.2 are arranged on the recesses 24 spaced from each other. As can be seen from FIG. 5, the recesses 24 can pass via flanks 24.1 into the adjacent second surface sections 23.2. In this case, the flanks 24.1 are inclined and at an obtuse angle to the respective subsequent second surface section 23.2. As can be seen further from FIG. 5, the recesses 24 run continuously towards the first surface section 23.1. The surface portions 23.1, 23.2 form a flat support surface for a chisel head 40th

FIG. 6 shows the underside of the wear protection disk 20. Here, the support surface 21 is clearly recognizable. In the support surface 21 a circumferential groove 21.1 is recessed. The circumferential groove 21.1 is adjoined indirectly or directly by a centering projection 21.2. The spigot 21.2 is cone-shaped. It is arranged circumferentially around the bore-shaped opening 25.

On its outer periphery, the wear plate 20 is bounded by an annular peripheral edge 22.

The wear protection disk 20 can be pushed with its opening onto the drill collar 10. In the assembled state, which is shown in Figures 1 and 2, the wear plate 20 encloses with its opening 25 a cylindrical section of the milling cutter. This cylindrical portion may be formed by the first portion 12 of the drill collar 10. Preferably, however, a further portion is connected to the first portion 12, which forms the cylindrical portion. The cylindrical portion is enlarged in diameter relative to the first portion 12 and arranged concentrically thereto.

It is also conceivable to use the wear protection disk 20 as a simplification of assembly. In this case, the wear shield 20 is mounted on the outer periphery of the clamping element 14. In the present embodiment, the clamping element 14 is formed as a longitudinally slotted clamping sleeve. The opening 25 has a smaller diameter than the clamping sleeve in its spring-loaded, shown in Figures 1 and 2 state. Now, if the wear plate 20 is mounted with its opening 25 on the outer circumference of the clamping sleeve, it is brought into a bias state. In this case, this bias state is chosen so that the clamping sleeve can be inserted without or with little effort in the receiving bore of a chisel holder. The insertion movement into the bit holder is then limited by the wear protection disk 20. This then strikes with its underside support surface 21 on an associated wear surface of the chisel holder. Subsequently, the milling cutter, for example, by Flammerschläge be driven further into the receiving bore of the bit holder. In this case, the wear protection plate is deported from the clamping sleeve until it reaches the position shown in Figure 1 or 2. The clamping sleeve can then rebound more freely radially, wherein the cutting tool clamped in the receiving bore by means of the clamping sleeve. In this state, the chisel with the clamping sleeve is jammed in the receiving bore. The drill collar 10 can be freely rotated in the clamping sleeve in the circumferential direction. By means of the flap elements 15 it is held axially captive.

The wear protection disk 20 has a disk thickness d between the support surface 21 and the mating surface 23. The ratio of this disk thickness d to the diameter of the opening 25 and to the diameter of the opening 25 associated cylindrical portion of the drill collar 10 is located in the range between 2 and 4.5. In the present embodiment, this ratio is 2.8, with a slice thickness d of 7 mm. The slice thickness d is preferably selected in the range between 4.4 mm and 9.9 mm. With such disc thicknesses d, an improvement can be achieved compared to the milling tools known from the prior art. In particular, the bit head 40 of the milling bit in the axial direction of the milling bit can be made shorter, the reduction of the bit head 40 is compensated by the larger thickness of the wear plate 20. However, the shorter bit head 40 can then be designed with a constant outer diameter in the region of its base part 42. The shortened design of the chisel head results in a fracture-endangered area between the chisel head and the chisel shank 10 to a smaller bending stress. Accordingly, the comparison voltage applied here also decreases in favor of improved head and shaft breakage behavior.

By arranged in the region of the support surface 21 circumferential groove 21.1 an improved Querabstütz behavior is offered. During operation, the support surface 21 works in an associated bearing surface of the chisel holder. On the bit holder, a circumferential bead in the form of a negative is produced in the region of the circumferential groove 21.1, corresponding to the circumferential groove 21.1. It is also conceivable initially to provide a bearing surface with a corresponding bead already in the new state on the bit holder. So it is so that then engages the spigot 21.1 in a corresponding centering of the chisel holder. The circumferential groove 21.1 comes to rest in the region of the bead. As a result, the improved Querabstütz behavior is achieved. An improved transverse support has the consequence that the surface pressures in the upper region of the clamping sleeve, ie in the region facing the chisel head 40 decrease. This prevents that the clamping sleeve is excessively worn in this area. The inventors have recognized that excessive wear here can lead to a loss of the bias of the clamping sleeve. As a result of this bias loss of the cutting bit from the receiving bore of the chisel holder can accidentally slip out and get lost. The improved support in the radial transverse direction, due to the Centering lug 21.2 and the circumferential groove 21.1 thus leads to longer life for the milling cutter. When using the milling bits in road milling, the range of the disk thickness d given above has proven to be advantageous. In that case, it is the case that the wear protection disks 20 reliably fulfill their function over the entire, extended service life of the cutting chisel or the chisel does not have to be changed prematurely due to a worn clamping sleeve.

As described above, with the circumferential groove 21.1 during operation, a better Querabstützverhalten for the wear plate 20. This also means that in the radial direction larger forces between the wear plate 20 and the bit holder can be transferred. A larger pane thickness d in the manner indicated above results in that the opening in the wear plate 20 offers the drill collar 10 a larger contact surface. In conjunction with the specified wheel thickness d and the circumferential groove 21.1 in the underside of the wear plate 20 so that larger lateral forces can be transmitted, as is possible in the prior art. In conjunction with the shorter design of the chisel head but this also means that can drive higher feed speeds with the novel design, or alternatively, in favor of a material saving, the chisel head or the drill collar 10 can be constructed according to optimized voltage.

The dimensional relationships between the holding element 14 and the drill collar 10 are set so that a limited axial displacement of the drill collar 10 relative to the holder element 14 is possible. As a result, a pump effect in the axial direction of the milling cutter is effected during operation. If milled material enters the area between the bearing surface 41 of the bit head 40 and the mating surface 23 during operation, the annular first surface portion 23 forms a type of sealing area which minimizes the risk of penetration of scrap material into the area of the retaining element 14. Between the support surface 41 of the chisel head 40 and the surface portions 23.2 and in conjunction with the flanks 24.1 forms a kind of mill effect. penetrating larger particles are crushed and removed via the inclined design of the recesses 24 again to the outside. This also reduces the risk of penetration of removed material in the area of the drill collar 11.

The cutting bit has a chisel head 40 as mentioned above. The chisel head 40 has a lower contact surface 41. With this contact surface 41 of the chisel head can be placed on the counter surface 23. In this case, the contact surface 41 covers the annular first surface portion 23.1 and the second surface portions 23.2 at least partially, as shown in Figures 1 and 2. Following the support surface 41, the chisel head 40 has a base part 42. The base part 42 is formed bead-shaped in the present embodiment. However, other geometries are also conceivable. For example, it is conceivable to provide a cylindrical geometry, a frusto-conical geometry or the like for the base part 42. The base part 42 is followed by a wear surface 43. The wear surface 43 is in the present embodiment wear-optimized at least partially concave. The wear surface 43 merges into an end region of the chisel head 40, which forms a receptacle 45 for a chisel tip 30. In this case, as shown in the drawings, in the end region of the chisel head 40, the receptacle 45 may be incorporated as a cap-shaped recess. In the cap-shaped recess, a chisel tip 30 can be attached. It is conceivable to use a solder joint for fastening the chisel tip 30.

The shape of the bit tip 30 is detailed in the drawings 3 and 4. As these illustrations illustrate, the bit tip 30 has a mounting portion 31. This is formed in the present embodiment as a lower surface 31 of the chisel tip 30. As can be seen in FIG. 4, a recess 31.1 can be incorporated in this lower surface, which can be formed in particular a trough-shaped. The recess 31.1 forms a reservoir in which excess solder material can accumulate. In addition, the required material for manufacturing the chisel tip 30 is reduced via the recess 31.1. Usually, the chisel tip 30 is made of a hard material, especially made of hard metal. This is a relatively expensive material. About the recess 31.1 so the parts cost can be reduced.

In the area of the underside of the chisel tip 30 31 projections 32 are present on the mounting portion. The adjustment of the thickness of the solder gap between the planar attachment section 31 and an associated surface of the chisel head 40 can be set via these extensions 32.

The attachment portion 31 merges via a chamfer 33 into a collar 34. Also conceivable is another transition between the attachment portion 31 and the collar 34. In particular, an immediate transition of the attachment portion 31 may be provided in the collar 34. The collar 34 is cylindrical in the present embodiment. It is also conceivable to perform the collar 34, for example convexly curved and / or bead-shaped. The collar 34 can pass directly or indirectly into a concave area 36. In the embodiment shown in the drawings, the design of an intermediate junction is shown. Accordingly, the collar 34 merges into the concave region 36 via a conical or convexly curved transition section 35.

The concave region 36 can pass directly or indirectly into a connecting section 38. In the present case, the design of an immediate transition into the connecting section 38 is selected. The connecting portion 38 may, as shown in the present embodiment, be cylindrical. It is also conceivable to choose a frusto-conical design for the connecting portion 38. Also, slightly convex or concave shapes of the connecting portion 38 may find use. A cylindrical connecting portion 38 has the advantage of a material and simultaneously strength-optimized design. In addition, the connecting portion 38 forms a wear area which is reduced during operation while the bit tip 30 wears. In this respect, a uniform cutting effect is achieved via the cylindrical design of the connecting portion 38. The connecting section 38 is adjoined indirectly or directly by an end section 39. In the present case, an indirect transition is selected, whereby the transition over a chamfer-shaped contour 39.3 is created. The end portion 39 has a taper portion 39.1 and an end cap 39.2. With the taper portion 39.1, the cross section of the bit tip 30 is tapered toward the end cap 39.2. In this respect, in particular the end cap 39.2, the cutting-active element of the chisel tip 30 forms.

In the present embodiment, the outer contour of the end cap is formed by a spherical cap. The base circle of this spherical cap has a diameter 306. In order to achieve the sharpest possible cutting action and at the same time to achieve a fracture-resistant design of the bit tip 30, it is advantageous if it is provided that the diameter 306 of the base circle is selected in the range between 1 and 20 millimeters.

The tapering section 39.1 has at its first, the chisel head 40 facing end region on a maximum first radial extent e1. At its end remote from the bit head 40, the tapering section 39.1 has a second maximum radial extension e2. FIG. 3 shows a connection line from a point of the first maximum extent e1 to a point of the second maximum extent e2 in dashed lines. This connecting line is to the central longitudinal axis M of the bit tip 30 at an angle ß / 2 between 45 ° and 52.5 °. Preferably, an angle of 50 ° is selected. Figure 4 also illustrates, that a tangent T to the bit tip 30 and through the point of the maximum second extension e2 with the central longitudinal axis M includes a tangent angle m, and that this tangent angle m is greater than the angle β / 2 which the connecting line of a point of the first maximum extension e1 to a point of the second maximum extension e2 with the central longitudinal axis M includes.

In the present case, a spherical geometry of the tapering section 39.1 is selected. However, it is also conceivable to choose a slightly convex or concave geometry, which tapers in the direction of the end cap 39.2. During the machining operation, the bit tip 30 wears off, shortening in the direction of the central longitudinal axis M. When used in Straßenfräsbreich has been shown that at the selected angles of attack of the cutting bit compared to a milling drum on which the cutting tools are fixed, the present angular range of the connecting line proves to be particularly advantageous. If a larger angle is chosen, too great a penetration resistance is caused during the milling process. This affects a higher required drive power of the milling machine. In addition, the main pressure point for the wear attack then acts on the bit tip 30 in the transition region between the connecting section 38 and the tapering section 39.1. Flierdurch creates an increased risk of edge breakage and premature failure of the chisel tip 30. If a smaller angle is selected, the chisel tip 30 is initially too willing to cut, resulting in a high initial length wear. This reduces the possible maximum service life. With the angular range according to the invention, the pressure action is evenly distributed during the milling process on the surfaces of the tapering section 39.1 and the end cap 39.2. This results in an ideal tool life for the chisel tip and at the same time a sufficiently cutting-active chisel tip 30.

The chisel tip 30 has an axial extent 309 in the direction of the central longitudinal axis M in the range between 10 and 30 mm. This extension range is optimized for the road milling application. It may be provided in particular that the ratio of the total length 309 of the bit tip 30 to the maximum diameter of the bit tip 30 is in the range between 0.8 to 1.2. The main wear portion forming connecting portion 38 may have an axial extent in the range between 2.7 and 7.1 millimeters

The concave portion 36 of the bit tip 30 has an elliptical contour. The elliptical contour generating ellipse E is shown in dashed lines in Figure 3. The ellipse E is arranged so that the large semiaxis 302 of the ellipse E and the central longitudinal axis M of the chisel tip 30 include an acute angle a. in the present embodiment, the angle a in the range between 30 ° and 60 °, preferably selected between 40 ° and 50 ° °, more preferably the angle, as shown here 45 °. The concave area therefore has a geometry following the ellipse E. Preferably, the length of the major semi-axis 302 is selected in the range between 8mm and 15mm. In the embodiment shown in FIG. 3, the length of the large semiaxis 302 is 12 mm. The length of the small half-axis is chosen in the range between 5 mm and 10 mm. In the present case, a length of 9 mm for the small semiaxis 301 is selected in FIG.

As illustrated in FIG. 3, the midpoint D of the ellipse E is preferably located in the direction of the central longitudinal axis M at a distance from the transition point between the concave portion 36 and the connecting portion 38, with the midpoint D offset towards the chisel head 40 opposite this joint. As a result, a wear-optimized geometry of the concave region 36 is generated.

In Figure 7, the effect of the inclination of the ellipse E is illustrated. FIG. 7 shows a bit tip 30, in which, according to the prior art, as known from DE 10 2007 009 711 A1, a concave contour in the concave region 36 of the bit tip 30 is selected, in which the large semiaxis of the generating ellipse E is arranged parallel to the central longitudinal axis M of the chisel tip 30. As a result of the inclination of the ellipse E, an additional circumferential material region B results. This additional peripheral material region B reinforces the contour of the bit tip 30 in the most heavily loaded region of the bit tip 30. This is the region in which the highest comparison stress occurs. Thus, therefore, the chisel tip 30 is reinforced in the relevant area due to the inclination of the generating ellipse E, without a significantly higher proportion of material is required here. The chisel tip 30 remains slender and schneidfreudig.

On the left side in FIG. 7, on the other hand, a contour of the concave region 36 is shown, which has an additional peripheral material region C in relation to the chisel tip 30. The contour of this additional circumferential material region C is of a radius-shaped geometry, ie a circle generated. It becomes clear that a significant thickening of the bit tip 30 is effected in relation to the material region B. As a result, the strength in the critical of the chisel tip 30 with respect to the variant with the material region B (oblique ellipse E) does not improve or only insignificantly. At the same time, however, a significantly higher proportion of material of the expensive hard material is required and the bit tip 30 becomes less cutting friendly.

Also illustrated in Figure 7 is how the feature described above provides that in cross-section of the bit tip 30 is a connecting line from a point of the first maximum extent e1 to a point of the second maximum extent e2 at an angle β / 2 of between 45 ° and 52.5 ° to the central longitudinal axis M of the bit tip 30 is illustrated. As the illustration shows, the employment of the connecting line generates an additional circulating material region A. This additional material area A brings on the one hand additional wear volume in the main loaded cutting area and beyond the advantages described above.

Claims

claims

A milling cutter, in particular a round head bit having a bit head (40) and a bit point (30), consisting of a hard material, wherein the bit point (30) has a mounting area where it is connected to the bit head (40),

the bit tip (30) having at its longitudinal end remote from the bit head (40) an end portion (39) encircling the bit tip (30) and having a tapered portion (39.1) and an end cap (39.2),

wherein the tapered portion (39.1) has a maximum first radial extent (ei) at its first end portion facing the bit head (40) and a maximum second radial extent (62) at its end portion facing away from the bit head,

and wherein the end cap (39.2), which forms the free end of the bit tip (30), is coupled to the tapering region (39.1),

characterized,

the end cap (39.2) is formed by a spherical cap which has a diameter (306) at its base circle,

and that the ratio of twice the maximum first extent (2 times e1) to the diameter of the base circle (306) is in the range of between 1.25 and 2.25.

2. Milling cutter according to claim 1, characterized in that a

Connecting line from a point of the first maximum extent (e1) to a point of the second maximum extent (e2) at an angle (ß / 2) between 45 ° and 52.5 °, to the central longitudinal axis (M).

3. Milling cutter according to claim 2, characterized in that a

Connecting line from a point of the first maximum extent (e1) to a point of the second maximum extent (e2) at an angle (β / 2) between 47.5 ° and 52.5 °, to the central longitudinal axis (M), and wherein the tapering portion is frusto-conical or convex.

4. Milling cutter according to claim 2, characterized in that a

Connecting line from a point of the first maximum extent (e1) to a point of the second maximum extent (e2) at an angle (ß / 2) between 45 ° and 50 °, to the central longitudinal axis (M), and wherein the tapered portion is convex ,

5. Milling cutter according to one of claims 1 to 4, characterized in that adjoins the tapering portion (39.1), on the side facing the bit head (40) side, a connecting portion (38), the cylindrical or conical with a cone angle of 20 maximum Is formed such that the connecting portion (38) in the transition region to the taper portion (39) has a cross-sectional extension (diameter 305), and that the ratio of this cross-sectional extension (diameter 305) to twice the maximum second extension (62) ^ 2.

6. A cutting bit according to any one of claims 1 to 5, characterized in that the connecting portion (38) facing the bit head (40) merges into a concave portion (36),

and that the concave portion (36) preferably has an elliptical contour.

7. A milling cutter according to one of claims 1 to 6, characterized in that the transition section (38) has an axial extent in the direction of the central longitudinal axis (M) of the chisel tip (30) in the range between 2.7 mm and 7.1 mm.

8. A chisel according to one of claims 1 to 7, characterized in that the ratio of the maximum extent (309) of the chisel tip (30) in Direction of the central longitudinal axis (M) of the chisel tip (30) to the maximum first radial extent (ei) is in the range between 3.5 and 4.25.

9. A cutting bit according to any one of claims 1 to 8, characterized in that in the concave portion (36) recesses (37) are introduced, and / or projections project from the concave portion (39), over the circumference of the chisel tip (30). arranged distributed and preferably spaced from each other in the same pitch are arranged.

10. A cutting bit according to claim 9, characterized in that the recesses (37) have a depth relative to the surface of the concave portion (36) between 0.3 and 1, 2 mm.

11.Fräsmeißel according to one of claims 1 to 10, characterized in that the chisel tip (30) consists of flamed metal and preferably with the chisel head (30) soldered, more preferably in a cup-shaped receptacle (45) of the chisel head (40) by means of a solder joint is attached.

12. Milling cutter according to one of claims 1 to 11, characterized in that the tapering portion (39.1) in the direction of the central longitudinal axis (M) is convex, preferably spherical.

13. A cutting bit according to any one of claims 1 to 12, characterized in that a tangent (T) to the bit tip (30) and through the point of the maximum second extension (e2) with the central longitudinal axis (M) includes a tangent angle (m), and that said tangent angle (m) is smaller than the angle (β / 2) included by the connecting line from a point of the first maximum extension (e1) to a point of the second maximum extension (e2) with the central longitudinal axis (M)

14. A cutting bit according to any one of claims 1 to 13, characterized in that the ratio of the total length (309) of the chisel tip (30) to the maximum diameter of the chisel tip (30) in the range between 0.8 to 1, 2.