EP3781786A1

EP3781786A1 - Milling pick

Info

Publication number: EP3781786A1
Application number: EP19714560.0A
Authority: EP
Inventors: Heiko Friederichs; Ulrich Krämer
Original assignee: Betek GmbH and Co KG
Current assignee: Betek GmbH and Co KG
Priority date: 2018-04-17
Filing date: 2019-03-19
Publication date: 2021-02-24
Also published as: JP7474884B2; KR20200141085A; JP2023053987A; US11268382B2; AU2019254170A1; US20210095564A1; AU2019254170B2; CN112020596B; DE102018109150A1; JP2021522425A; WO2019201534A1; JP7269954B2; CN112020596A; TWI754810B; CA3097232A1; TW201943943A

Abstract

The present invention relates to a milling pick, in particular a straight shank pick with a pick head (40) comprising a pick bit (30) made of hard material as the cutting element, wherein a pick shaft (10) is further coupled directly or indirectly to the pick head (40), a wear protection disk (20) with a passage, in particular a bore, slipped on the pick shaft (11), wherein the wear protection disk (20) on the side facing the pick head (40) comprises a countersurface (23) designed to abut a support surface (41) of the pick head (40), the wear protection disk, away from the countersurface (23), comprising a bottom support surface (21) that is parallel to the countersurface (23), and having a disk thickness (d) between the countersurface (23) and the support surface (21), the milling pick being characterised in that the ratio between the diameter of the pick shaft (10) in the area of the passage (25) and the thickness (d) of the disk ranges from 1.5 to 3.75, preferably from 2 to 3.

Description

Tooth

The invention relates to a cutting bit, in particular a round shank bit having a chisel head, which has a chisel tip made of hard material as the cutting element, wherein furthermore a chisel shank is provided, which is coupled directly or indirectly to the chisel head, wherein a wear sheave is provided, which is provided with an opening, in particular a bore is pushed onto the drill collar, the wear protection disc having on its side facing the bit head a counter surface, which is adapted to come to rest on a bearing surface of the bit head, the wear plate facing away from the counter surface has a lower side support surface parallel is to the mating surface and wherein between the mating surface and the support surface a disc thickness is formed.

Such a bit is known from DE10 2014 104 040 A1. Starting from a cutting element, the diameter of the chisel head increases towards a collar, which is followed by a chisel shaft. The cylindrical chisel shaft is by means of a clamping sleeve in a bit holder in a Retained holding a chisel holder held. The fixing by means of the clamping sleeve allows a rotation of the bit about its central longitudinal axis, while an axial movement is blocked. Between the chisel head and the holding approach a wear protection disc is arranged, is guided by the central receiving bore of the drill collar. Towards the chisel head, the wear protection disc has a recess bordered by an edge, the bottom of which represents a support surface on which the chisel head rests with a bearing surface. Towards the bit holder, the wear protection disk forms a seat surface which merges with the center of the wear protection disk into a centering surface of a centering projection running obliquely to the central longitudinal axis of the bit. In the transition region between the centering surface and the seat surface, a groove is arranged. The upper side of the holding attachment of the chisel holder is formed towards the chisel head corresponding to the underside of the wear protection disk. It has a wear surface on which the seat surface of the wear protection disc rests. The centering shoulder of the wear protection disc is guided radially in a centering of the holding approach. Due to the wear of the wear surface during operation of the tool assembly with the chisel, a bead forms on the wear surface of the chisel holder in the region of the groove of the wear protection disk, which engages in the groove. Through this intervention, an additional lateral guidance of the wear protection disc is achieved. At the same time, the penetration of waste material into the area of the bit receptacle is at least reduced by the groove and the bead engaging therein, as a result of which the rotatability of the bit is preserved and wear is reduced.

In order to ensure the rotation of the bit about its central longitudinal axis a limited axial play of the bit in the bit holder is desired. It is intended for larger chisel a larger game than for smaller chisel. If the axial play exceeds the height of the centering shoulder, the lateral guidance of the wear protection disk is lost through the centering shoulder. This leads to increased wear of both the wear plate and the chisel holder. For this reason, DE 20 2017 006 713 U1 picks up on this solution and proposes a better toothing of the wear protection disc with the bit holder. With this measure, the crash behavior in the transverse direction can be improved. Overall, so radially acting forces can be better transferred from the milling bit in the bit holder. However, it is also true that, as a result, a greater load can be transmitted in the transition region between the bit head and the bit shaft. As the load increases, however, the risk of shaft fracture increases at this point.

It is therefore an object of the invention to provide a milling cutter of the type mentioned, which has an improved resistance to breakage.

This object is achieved in that the ratio of the arranged in the region of the aperture diameter of the drill collar to the disk thickness (d) in the range between 1, 5 and 3.75, preferably in the range between 2 and 3.

In this way, compared to common designs of milling tools constant absolute projection of the free end of the bit tip on the bit holder, the length of the chisel head can be shortened, in favor of a larger thickness of the wear plate. With a shorter length of the bit head, lower bending stresses occur in the transition area between the bit head and the bit shaft, which reduces the risk of shaft breakage. In the specified range between 1, 5 and 3.75, the stresses that occur in milling cutters, which are commonly used in road construction, especially in road milling machines and stabilizers, are taken into account in an optimized manner. In road milling machines, which are used for partial or full construction of road surfaces or the fine milling of road surfaces, the preferred specified range ratio between 2 and 3 is suitable.

Frequently, wear protection discs are used in modern milling chisels, which do not have a uniform cross-sectional geometry. According to the invention, it is preferably provided that the ratio of the in the region of the opening arranged diameter of the drill collar to the minimum disk thickness which is in the range between 1, 5 and 3.75, preferably between 2 and 3.

A preferred variant of the invention is such that recesses are introduced into the mating surface, wherein second surface portions of the counter surface are formed between the recesses, and that the second surface portions at least partially abut the bearing surface of the chisel head. During operation, the milling tool rotates relative to the wear protection disk. When the cutting bit engages in the substrate to be machined, milling material is removed. This milling material can reach into the area between the chisel head and the wear protection disc and then into the area of the receiving bore of the chisel holder in which the chisel is mounted. Occasionally, it may occur that this milling material accumulates in the receiving bore and limits the free rotation of the cutting bit or blocks it. The recesses, in cooperation with the raised areas opposite the recesses, form a kind of grinder. With this penetrating particles can be crushed. The finer components are then transported away radially outward, so that they can not get into the area of the receiving bore of the chisel holder.

In this case, it can be provided, in particular, that the mating surface has, subsequent to the opening, a first surface section which runs around the opening in an annular manner, to which the second surface sections adjoin and wherein the first surface section bears against the contact surface of the chisel head at least in regions. The annular surface portion forms a kind of sealing portion, which also prevents penetration of the comminuted fine particles in the region of the receiving bore.

According to a further preferred variant of the invention, it can be provided that the recesses pass over inclined lateral flanks into the second surface sections. Flierdurch the grinding effect is improved. In order to improve the removal of the penetrated or comminuted particles, provision may be made for the recesses to have the greatest recessing dimension with respect to the mating surface at their radially outer region and to merge into the first surface section in their radially inner region. In order not to unduly reduce the stability of the wear protection disc, it is recommended that the recesses have a Eintiefungsmaß of at most half the thickness of the disc at its radially outer region, more preferably at most 30% of the thickness of the disc.

According to a conceivable variant of the invention, it may be provided that on the underside of the wear protection disc projecting a centering approach, which is arranged circumferentially around the aperture around and projects over the support surface at least partially. The centering approach improves the lateral guidance and support of the wear protection disc relative to the bit holder in the radial direction. In this case, an exact guidance of the wear protection disc with respect to the bit holder is achieved in a simple manner in that the centering projection is cone-shaped.

A preferred embodiment of the milling bit is such that the centering approach merges into a, preferably circumferential groove which is recessed in the support surface. The wear shield grinds during operation in an associated surface of the chisel holder. In this case, an annular circumferential and bead-shaped projection is produced in this area in the region of the circumferential groove in cooperation with the groove and the centering approach results in an improved transverse support of the wear protection disc relative to the bit holder in the radial direction. It has been found that for conventional road milling applications, the ratio of the distance between the groove bottom of the groove and the free end of the centering shoulder relative to the slice thickness is ideally selected in the range between 30% and 70%.

According to a possible variant of the invention it can also be provided that between the wear protection disk and the chisel head and / or the Chisel shank is provided a form-fitting connection in the circumferential direction.

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 plate 20 can be formed 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 portion of the cutting bit. 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 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 made with a constant outside diameter in the region of its base part 42. The shortened design of the bit head leads to a smaller bending stress in the fracture-prone area between the bit head and the bit shaft 10. 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 preload 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 spigot 21.2 and the circumferential groove 21.1 thus leads to longer service 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 forms Surface portion 23 is a type of sealing area which minimizes the risk of penetration of space material into the area of retaining element 14. Between the bearing 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 depression 31.1 can be incorporated into this lower surface, which in particular can be formed 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, in particular tungsten carbide. 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 that during the Operational use is reduced 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.

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 the road milling area, it has been found that, with the angles of attack selected here, the milling tool has a particular advantage over a milling drum on which the milling tools are mounted. 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. 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 α is selected in the range between 30 ° and 60 °, preferably between 40 ° and 50 °, particularly preferably the angle, as shown here is 45 °. The concave area therefore has one, the Ellipse E following geometry. 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 generated by a radius-shaped geometry, ie a circle. It becomes clear that a significant thickening of the bit tip 30 is effected in relation to the material region B. This improves the strength in the critical bit tip 30 with respect to the variant with the material region B. (oblique ellipse E) not 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

1. Milling cutter, in particular a round shank bit with a chisel head (40) having a chisel tip (30) made of hard material as a cutting element, wherein further a chisel shank (10) is provided which directly or indirectly coupled to the chisel head (40), wherein a Wear protection disc (20) is provided, which is pushed with an opening, in particular a bore on the drill collar (10), wherein the wear protection disc (20) on its the chisel head (40) facing side has a counter surface (23) which is formed to come to rest on a support surface (41) of the bit head (40), the closure disc (20) facing away from the counter surface (23) having an underside support surface (21) which is preferably parallel to the counter surface (23) and between the counter-surface (23) and the support surface (21) a disc thickness (d) is formed,

characterized,

in that the ratio of the diameter of the drill collar (10) to the slice thickness (d) in the region of the opening (25) is in the range between 1.5 and 3.75, preferably in the range between 2 and 3.

2. Milling cutter according to claim 1,

characterized,

in that the ratio of the diameter of the cutter shank (11) arranged in the region of the aperture (25) to the minimum slice thickness (d) is in the range between 1.5 and 3.75, preferably between 2 and 3.

3. A milling cutter according to claim 1 or 2, characterized in that in the mating surface (23) recesses (24) are introduced, wherein between the recesses (24) second surface portions (23.2) of the counter surface (23) are formed, and that the second Surface portions (23.2) at least partially abut the support surface (41) of the chisel head (40).

4. A milling cutter according to claim 3, that the counter surface (23) following the opening (25) has an annular around the opening (25) encircling first surface portion (23.1) to which connect the second surface portions (23.2), and wherein the first surface portion (23.1) on the support surface (41) of the chisel head (40) at least partially abuts.

5. Milling cutter according to one of claims 3 or 4, characterized in that the recesses (24) pass over inclined lateral flanks in the second surface portions (23.2).

6. Milling cutter according to one of claims 3 to 5, characterized in that the recesses (24) at their radially outer region have the largest Eintiefungsmaß relative to the counter surface (23) and in its radially inner region in the first surface portion (23.1) pass.

7. A cutting bit according to claim 6, that the recesses (24) have at their radially outer region a Eintiefungsmaß of a maximum of half the thickness of the disc (d), more preferably at most 30% of the thickness of the disc (d).

8. A cutting bit according to one of claims 1 to 7, characterized in that on the underside of the wear protection disc (20) a centering projection (21.2) protrudes, which is arranged circumferentially around the opening (25) and about the support surface (21) at least partially protrudes.

9. Milling cutter according to claim 8, characterized in that the centering projection (21.2) is cone-shaped.

10. A cutting bit according to claim 8 or 9, characterized in that the centering projection (21.2) merges into a preferably circumferential groove (21.1), which is recessed in the support surface (21).

1 1. Milling cutter according to one of Claims 1 to 10, characterized in that the ratio of the distance between the groove base of the groove (21.1) and the free end of the centering projection (21.2) in the axial direction of the cutter shank (10) relative to the sheave thickness (d) in the Range is between 30% and 70%.

12 milling cutter according to one of claims 1 to 11, characterized in that between the wear protection disc (20) and the chisel head (40) and / or the chisel shank (10) is provided a form-fitting connection in the circumferential direction.