HK1248174B - Agitator ball mill - Google Patents

Description

Agitator ball mill

Technical Field

The present invention relates to an agitator ball mill and to an agitator disk for the agitator ball mill.

Background Art

In a stirrer ball mill with a horizontally arranged grinding chamber, known from DE 1 632 424, a stirrer disk is known with a circular entrainment profile, which can be formed by openings, grooves, or flat grooves. The entrainment profile is circular and has a radius of curvature of 50% to 100% of the disk radius. The inclination angle increases by 30% to 50% from the disk edge toward the center of the disk. This is to achieve a substantial increase in the efficiency of the dispersion without damaging the grinding bodies. Due to the large radius of curvature, the correspondingly shaped entrainment profile ends at a large radial distance from the stirrer shaft, effectively lateral to the stirrer shaft. At its radially inner end, the entrainment profile extends essentially tangentially to the central longitudinal axis of the stirrer shaft (and therefore tangentially to the torque vector). Overall, the entrainment of the grinding bodies in the interior of the stirrer disk (corresponding to a radial extension of 50% between the inner and outer circumferential limits of the surface of the stirrer disk within the grinding chamber) is unsatisfactory. Agitator ball mills equipped with such a stirrer disk are only suitable for filling the grinding chamber to a minimal degree, with grinding media representing 40% to 60% of the grinding chamber volume. At the outer circumference of the stirrer disk, the grinding media are displaced radially outward in the plane of the stirrer disk and perpendicular to the stirring axis by the rear wall of the entrainment profile. Such agitator ball mills achieve only low efficiencies and, moreover, lack uniform distribution within the grinding chamber. Consequently, for such a grinding process, the relatively high specific energy requirements result in low throughput in terms of space and time consumption.

Summary of the Invention

The object of the present invention is therefore to achieve a more efficient grinding process at lower peripheral speeds of the agitator disk and furthermore to achieve improved energy efficiency of the grinding process for the production of a narrower particle size distribution of the processed ground material and to obtain a higher yield.

This object is achieved according to a first aspect with respect to agitator ball mills and according to a second aspect with respect to agitator disks. The basic approach of the present invention to the formation of a particularly intense circulation flow in the grinding units for more effective entrainment of the grinding bodies is to form an acceleration rear wall of the entrainment profile, which already begins at right angles to the central longitudinal axis at the agitator shaft in its interior and curves back further outward without continuing the entrainment profile to the disk periphery (i.e., the outer edge of the agitator disk). Surprisingly, it has been shown that under comparable conditions in other conventional agitator ball mills, the grinding quality is improved with a narrower particle distribution in the processed grinding material when the entrainment profile terminates before reaching the outer edge of the agitator disk. One explanation is therefore that the grinding bodies accelerated outward by the entrainment profile in the radially outer portion of the entrainment profile are redirected toward the upstream grinding unit by the front surface of the respective agitator disk and toward the downstream grinding unit by the rear surface of the respective agitator disk relative to the overall direction of the flow through the agitator ball mill. The result is that the grinding bodies that are accelerated outwards are fanned out in a defined manner on both sides of the agitator disk, instead of being compressed only in the area between the outer edge of the agitator disk and the wall of the grinding chamber, as in the prior art. No secondary vortices are generated near the outer edge of the agitator disk (i.e. in the annular portion or gap between the outer edge of the agitator disk and the wall of the grinding container). This provides a significantly improved smooth operation of the agitator ball mill, together with a significantly reduced wear of the agitator disk and the walls of the outer grinding unit. Due to the entrainment profile of the agitator disk formed according to the invention, those parameters that can be used to achieve a predetermined grinding quality can be set with a significantly reduced specific energy required for the grinding process. These parameters are in particular a high filling degree of the grinding bodies and a simultaneously low rotational speed of the agitator.

The further aspects specify advantageous aspects of the agitator ball mill according to the invention and correspondingly apply to the agitator disk according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages and details of the invention become apparent from the further dependent claims and from the following description of embodiments of the invention with the aid of the accompanying drawings. These drawings show:

FIG1 is a schematic representation of an embodiment of an agitator ball mill according to the invention in a partial sectional side view;

FIG2 is a top view of a first embodiment of a stirring plate according to the present invention;

FIG3 is a partial cross-sectional view of the stirring plate according to FIG2 ;

FIG4 is a detail of FIG1 with a stirring disk according to FIG2 and FIG3 , which is enlarged in size relative to FIG1 ;

FIG5 is a top view of a second embodiment of a stirring plate according to the present invention;

FIG6 is a partial cross-sectional view of the stirring plate according to FIG5;

FIG7 is a detail of FIG1 with a stirring plate according to FIG5 and FIG6 , which is enlarged in size relative to FIG1 ;

FIG8 is a top view of a third embodiment of a stirring plate according to the present invention;

FIG9 is a partial cross-sectional view of the stirring plate according to FIG8;

FIG10 is a top view of a fourth embodiment of a stirring plate according to the present invention; and

FIG. 11 is a partial cross-sectional view of the stirring plate according to FIG. 10 .

DETAILED DESCRIPTION

FIG1 shows a horizontal agitator ball mill. A stirrer ball mill generally comprises a stand 1 supported on the ground 2. A drive motor 3 with a controllable rotational speed is arranged within the stand 1 and is equipped with a V-belt pulley 4, by which a drive shaft 7 of the stirrer ball mill can be driven via a V-belt and a further V-belt pulley 6. The drive shaft 7 is supported in the upper part of the stand 1 by a plurality of bearings 9.

A substantially cylindrical grinding container 10 is releasably mounted to the upper portion 8 of the support 1. The cylindrical grinding container 10 comprises an inner wall 11 and is closed by a first cover 12 at the end facing the upper portion 8 and by a second cover 13 at the opposite end. The grinding container encloses a grinding chamber 14. The inner wall 11 thus forms the outer boundary of the grinding chamber.

A stirring shaft 16 is arranged in the grinding chamber 14 concentrically with the common central longitudinal axis 15 of the grinding container 1 and the drive shaft 7 and is connected to the drive shaft 7 in a manner fixed against rotation relative to the longitudinal axis 15. The grinding chamber 14 is sealed by a gasket 17 located between the first cover 12 and the drive shaft 7. The combination of the drive shaft 7 and the stirring shaft 16 is supported in a cantilevered manner and is therefore not supported in the region of the second cover 13. The stirring shaft 16 is equipped with stirring means located in the grinding chamber 14 and extending over the entire length of the stirring shaft 16, which stirring means is embodied as a circular stirring disk 18.

The agitator disk 18 is mounted on the agitator shaft 16 and is typically held on the agitator shaft 16 in a manner fixed against rotation relative to the agitator shaft 16, for example by means of a key and groove connection, and is held axially spaced apart by means of a spacer sleeve 19. The agitator shaft 16, together with the spacer sleeve 19 and the agitator disk 18, forms an agitator 20. The spacer sleeve 19 internally delimits the generally cylindrical grinding chamber 14 and thus forms the inner boundary of the grinding chamber.

A grinding material inlet 21 opens into the grinding chamber 14 in the region of the first cover 12 . A grinding material outlet 22 opens out of the second cover 13 at the end of the grinding container 10 opposite the end of the grinding material inlet 21 .

A cylindrical holder 23 is formed at the outer circumference of the last agitator disk 18 adjacent to the second cover 13. The holder includes openings 24 distributed over its entire circumference. A sieve 26 mounted on the second cover 13 and connected to the ground material outlet 22 is arranged in a separator space 25 defined by the last agitator disk 18 and the holder 23. These parts form a ground material/grinding body separator unit 27 known from EP 2 178 642 A1, into which the ground material (e.g., ground suspension) and the grinding bodies 33 enter through the openings 28.

Adjacent agitator disks 18 have the same axial distance from one another. Furthermore, adjacent agitator disks 18 define a separation angle α, which is formed by a line 29 between an outer edge 30 of an agitator disk 18 and a base of an adjacent agitator disk 18 on the agitator shaft 16 (i.e., on the corresponding spacing sleeve 19) and a line 31 parallel to the axis 15. The following applies: 30°≤α≤60°.

The width b of the annular gap 32 between the outer edge 30 and the wall 11 does not exceed 20% of the free radius R14 of the grinding chamber 14 between its inner edge and its outer boundary, ie b≦0.2·R14.

The grinding chamber 14 is primarily filled with grinding bodies 33, preferably made of a high-density material (e.g., high-performance ceramic made of _ZrO₂ (zirconium dioxide) with a solid density of 6.0 g/ ^cm³ ). The degree of filling with grinding bodies is in the range of 50% to 90%, particularly in the range of 80% to 90%. A high solid density of grinding bodies 33 relative to the density of the grinding suspension is important for the desired effect (i.e., transporting grinding bodies 33 from the surface of each agitator disk 18 outwards into the zone where the agitated material has already accumulated at a relatively low agitator rotational speed). Grinding cells 34 (see, for example, FIG. 4 ) are formed between each adjacent agitator disk 18.

The agitator disks 18 include entrainment profiles 35 for the grinding bodies 33 (see, for example, FIG. 2 ). These entrainment profiles are integrated into the respective agitator disk 18 and therefore do not protrude from the surface of the agitator disk 18 . The profiles begin directly at the inner wall of the grinding chamber (i.e., at the spacing sleeve 19 ). For the effects described below to occur optimally, the width c of the entrainment profiles 35 preferably corresponds to 0.5 to 1.5 times the thickness d of the agitator disk 18 . This means that 0.5·d≤c≤1.5·d.

In the embodiment according to Figures 2 and 3, the entrainment profile 35 forms flat, trough-like channels 36, which are formed uniformly on both sides of each agitator disk 18, so that, as can be seen in Figure 3, thin-walled sections 37 remain between the channels. Each channel 36 comprises a rear wall 39, relative to the direction of rotation 38 of the agitator disk 18, which extends parallel to the central longitudinal axis 15, which is also the central longitudinal axis 15 of the respective agitator disk 18. As can be seen in Figure 2, this channel 36 comprises a straight inner channel portion 40 extending radially outward at right angles to the central longitudinal axis 15, and an outer channel portion 41 adjoining the inner channel portion 40 and facing radially outward, which curves against the direction of rotation 38 and ends at a distance e from the outer edge 30 of the agitator disk 18. The outer channel portion 41 thus ends at an annular outer circumference 42 of the agitator disk 18. The distance e or radial extent e of the enveloping annular outer circumference 42 is preferably 0.5 to 1.5 times the thickness d of the agitator disk 18. This means that 0.5·d≤e≤1.5·d.

As can be further seen in FIG. 2 , the grinding bodies 33 are entrained tangentially by the rear wall 39 in the direction of rotation 38 and are thus centrifugally accelerated in the respective channels 36. The tangential velocity, and therefore the resulting outwardly directed centrifugal acceleration, increases radially outward (as indicated by the radially outwardly increasing length of the velocity arrows 43). Due to the relatively low tangential velocity near the agitator shaft 16 or the respective spacer sleeves 19, it has been shown that the power input into the grinding chamber 14 is more efficient if the wall 39, which accelerates the grinding bodies 33 to the local circumferential velocity, is oriented perpendicular to the moment vector (i.e., perpendicular to the central longitudinal axis 15). This is achieved due to the straight, radially arranged inner channel sections 40. The corresponding centrifugal acceleration is generated by the circumferential velocity of the grinding bodies 33.

According to the invention, the straight inner channel portion 40 has a length f that is 25% to 60%, preferably 30% to 50%, of the free radius R18 of the agitator disk 18 from the spacing sleeve 19 to the outer edge 30. This means that R18 ≤ f ≤ 0.6·R18, and preferably 0.3·R18 ≤ f ≤ 0.5·R18. It has been shown that radial portions 40 of the entrainment profile 35 that significantly exceed 60% of the free radius R18 of the agitator disk 18 lead to undesirable turbulence in the grinding body 33, which cannot be used in the grinding process.

Due to the channel section 41, which is curved backwards against the direction of rotation 38 and in particular due to its rear wall 39 as an entrainment surface, a tangential-radial entrainment of the grinding bodies 33, which are in contact with the wall 39, is generated by the local peripheral speed and occurs in addition to centrifugal acceleration. The grinding bodies are actively transported outwards. The radial entrainment component advantageously increases continuously outwards. In order to achieve an active and beneficial grinding process, a radius of curvature r41 of less than 40% of the radius r18 of the agitator disk 18 has proven to be advantageous. It must be taken into account that the channel 36 and in particular the channel section 41 at the outer end extend over its entire width c. The rear wall 39 merges into the outer boundary of the channel section 41, which extends concentrically with respect to the outer edge 30 of the agitator disk 18 and is formed by the annular outer circumference 42 with a very small merging radius r41/42 (i.e., at an acute angle). The merging radius r41/42 should preferably be less than 20% of the width c of the entrainment profile 35. This means that r41/42 ≤ 0.2·c. The rear wall 39 embodied according to the invention thus exerts an exclusively outwardly directed acceleration on the grinding bodies 33 up to its outermost end. This embodiment has proven particularly advantageous for generating an unimpeded circulation flow, i.e., an interwoven flow 44 (see, for example, FIG. 4 ), while avoiding secondary vortices within the grinding unit 34, which in turn is a prerequisite for efficient operation at high filling levels of the grinding bodies.

As can be seen in FIG4 , a double circulation flow (so-called interwoven flow 44) is formed within the individual grinding units 34. In the region of the agitator disks 18, the grinding bodies 33, together with the grinding material to be processed and the grinding suspension, flow outwards due to the tangential acceleration caused by the agitator disks 18 in the direction of the inner wall 11 delimiting the grinding chamber 14 on the outside, and then return inwards in the axial central region of the grinding unit 34 towards the agitator shaft 16. Radially outside the entrainment profile 35, which forms the groove-like channel 36, the agitator disks 18 actually act as a double-sided deflection device. In the outer circumference 42 of the agitator disks 18, the thickness of the agitator disks 18 is the same as in the region of the spacer sleeves 19, and this outer circumference 42 of the agitator disks 18 ensures the fanning out and the change of direction of the mixture of grinding bodies 33 and the outwardly accelerated grinding material. The upstream side of the outer circumference 42 of the individual agitator disks 18, relative to the overall direction of the flow 45 through the agitator ball mill, redirects the mixture of grinding bodies and grinding material upstream. This effect on the grinding bodies 33, which are directed counter to the general direction of the flow 45, means that even at a high filling level of grinding bodies and at typical grinding suspension flow velocities, these grinding bodies cannot be carried along with them to the next downstream grinding unit 34 due to the grinding suspension flow velocity. This results in a smoother distribution of the grinding bodies throughout the grinding chamber 14. However, the downstream side of the outer periphery 42 of the agitator disk 18, which delimits the grinding units 34, causes a corresponding deflection in the downstream direction. Due to the agitator disk 18 embodied according to the invention, the grinding suspension flows through the annular portion of the gap 32, in which only a reduced amount of grinding bodies is present, and is sucked into the downstream circulating flow 44 in the grinding units 34. As can be seen in FIG. 4 , the outer channel section 41 can be provided with a guide bevel 46 at the transition to the outer periphery 42 in order to support the corresponding deflection.

For the description of the embodiment according to Figures 5 to 7 , the following applies: identical parts are identified by the same reference numerals, and similar parts are identified by the same reference numerals followed by a, without requiring a repetition of the detailed description. The agitator disk 18a according to Figures 5 and 6 differs from the agitator disk 18 according to Figures 2 and 3 in that the channels 36a are not embodied as grooves with walls 37 separating the channels from one another, but are instead formed as continuous grooves as an entrainment profile, comprising walls 39 extending from one side of the agitator disk 18a to the other. The mechanism of action is generally equivalent to that of the embodiment according to Figures 2 to 4 . The significantly increased surface area of the walls 39, which accelerate the grinding bodies 33 due to the omission of the walls 39, further increases the efficiency of the agitator ball mill or allows for a previously constant output at reduced agitator speed. Of course, the ground material can be transferred directly from a grinding unit 34 to an adjacent grinding unit 34 downstream via the channels 36a embodied as continuous continuous grooves with corresponding channel sections 40a and 41a. The extent to which this generally undesirable effect occurs depends on the selected operating parameters, in particular on the volume throughput of the grinding suspension per unit time and the filling degree of the grinding bodies. It can be seen in FIG7 (similar to FIG4 ) that the density of the grinding bodies decreases sharply towards the agitator shaft 16 and increases sharply towards the wall 11.

A mixed embodiment of closed trough-like channels and channels embodied as continuous through-grooves is possible, which can lead to further advantages in terms of the teaching of the present invention.

For the description of the embodiments according to Figures 8 and 9 , the following applies: identical parts are identified by the same reference numerals, and similar parts are identified by the same reference numerals followed by a "b." A detailed description need not be repeated. In the agitator disk 18b according to Figures 8 and 9 , the wall 37b separating the two identical channels 36b is broken over substantially the entire length of the straight channel portion 40b, while the wall 37b remains in the radially outer, groove-shaped channel portion 41 that curves against the direction of rotation 38. This embodiment has the advantage that, due to the omission of the dividing wall, the entrainment of the grinding bodies 33 is enhanced in areas of low peripheral speed (i.e., precisely where they are particularly needed). In the outer circumference, where there are more grinding bodies in the area of the curved channel portion 41, the dividing wall 37b prevents the uncontrolled migration of grinding suspension and grinding bodies 33 from one grinding unit 34 to an adjacent one. This measure contributes to a narrower particle size distribution and thus increases the grinding quality or efficiency. Otherwise, the explanations regarding the mechanism of action described above apply here as well.

Furthermore, for the description of the embodiment according to Figures 10 and 11, the following applies: For identical parts, the reference numerals of Figures 2 and 3 are used. For similar parts, the same reference numerals of Figures 2 and 3 with a successor c are used. In this case, no further detailed description is necessary. In the agitator disk 18 according to Figures 10 and 11, the grinding material passage opening 47 is formed in the wall 37c of the groove-shaped channel 36c in the immediate vicinity of the agitator shaft 16 (and therefore in the immediate vicinity of the spacing sleeve 19), and due to the low density of the grinding bodies 33 in the immediate vicinity of the agitator shaft 16, essentially only grinding material can be transferred through the grinding material passage opening 47 from one grinding unit 34 to the adjacent grinding unit 34 in the general direction of the flow 45. The ratio of the radial extension R47 (i.e., the extension of the grinding material passage opening 47 from the inner boundary of the grinding chamber in the radial direction of the agitating disk 18c) to the radial extension R18 of the agitating disk 18c from the inner boundary of the grinding chamber (i.e., the spacing sleeve 19) to the outer edge 30 is: 0.05·R18≤R47≤0.25·R18. Preferably, the condition R47≤0.20·R18 applies, and particularly preferably R47≤0.15·R18.

The grinding material passage opening 47 is arranged in close proximity to the spacing sleeve 19 (inner boundary of the grinding chamber). The term "close proximity" means that either the radial inner boundary of the grinding material passage opening 47 is bounded by the spacing sleeve 19; or the radial inner boundary of the grinding material passage opening is arranged at a short radial distance from the spacing sleeve 19, so that substantially this distance is either zero (boundary) or can be close to one tenth of the radial extension R18 of the agitating disk 18c or 18b (≤0.1·R18).

Due to the very low flow resistance compared to the conditions in the area of the accumulation of grinding bodies in the region adjacent to the outer edge 30 of the agitator disk 18 c, this embodiment is also suitable for the highest grinding body filling levels and particularly high total flow rates while maintaining a uniform distribution of grinding bodies along the grinding chamber 14. High efficiency can be achieved even at reduced agitator speeds. Due to the well-defined boundaries of the grinding cells 34, uncontrolled migration of grinding suspension from one grinding cell 34 to an adjacent grinding cell 34 is completely eliminated. This embodiment results in a particularly high grinding quality with respect to homogeneity, which can be verified by the narrow particle size distribution of the processed grinding suspension. Apart from this, the mechanism of action here is also the same as that described above.

Claims (18)

1. A stirrer-type ball mill The agitator-type ball mill has a horizontally arranged grinding container (10). The grinding container (10) encloses a cylindrical grinding chamber (14) with a free radius R14, the grinding chamber being defined by the grinding container wall (11) and by the inner boundary of the grinding chamber, the grinding chamber containing grinding media and grinding materials in operation; An abrasive material supply port (21) is provided at one end of the abrasive container (10) to enter the abrasive container, and An abrasive material outlet (22) is located at the other end of the abrasive container (10) and extends to the outside of the abrasive container, wherein a separator unit (27) for separating the abrasive material from the abrasive body is arranged upstream of the abrasive material outlet; The agitator-type ball mill has an agitator (20) arranged inside the grinding chamber (14), and the agitator has: A stirring shaft (16) having a central longitudinal axis (15), the stirring shaft (16) being rotatably driven in the direction of rotation (38); and The mixing discs (18, 18a, 18b, 18c) are mounted to the mixing shaft (16) in a manner that prevents them from rotating relative to the mixing shaft (16) and are arranged at an axial distance a from each other. The stirring discs (18, 18a, 18b, 18c) have an outer edge (30) and a thickness d. The stirring discs (18, 18a, 18b, 18c) have a free radius R18 located between the boundary of the grinding chamber and the outer edge (30). Wherein, a gap (32) having a radial width b is formed between the outer edge (30) of the stirring discs (18, 18a, 18b, 18c) and the grinding container wall (11). Among them, two adjacent stirring discs (18, 18a, 18b, 18c) respectively define the grinding unit (34), and The mixing discs (18, 18a, 18b, 18c) include entrainment profiles (35, 35a, 35b, 35c) for the grinding media (33), the entrainment profiles being formed in the mixing discs (18, 18a, 18b, 18c), each entrainment profile being formed by a rear wall (39) of a channel (36, 36a, 36b, 36c) formed in the mixing disc relative to the direction of rotation (38), the rear wall extending parallel to the central longitudinal axis (15), the rear wall being formed by a curved channel portion (41, 41a, 41b, 41c) bent radially outward of the channel relative to the central longitudinal axis (15), the curved channel portion (41, 41a, 41b, 41c) bending against the direction of rotation (38). The channels (36, 36a, 36b, 36c) having a rear wall (39) relative to the direction of rotation (38) each include an inner channel portion (40, 40a, 40b, 40c) extending radially straight relative to the central longitudinal axis (15) and having a length f, and include a curved channel portion (41, 41a, 41b, 41c) that bends against the direction of rotation (38) in the next stage. Furthermore, the curved channel portions (41, 41a, 41b, 41c) are radially closed relative to the outside by the outer periphery (42) of the stirring disc (18, 18a, 18b, 18c) having a radial width e. 2. The agitator-type ball mill according to claim 1, wherein the agitator discs (18, 18a, 18b, 18c) include channels (36, 36a, 36b, 36c) formed on both sides of the agitator discs (18, 18a, 18b, 18c), wherein, in each case, two channels (36, 36a, 36b, 36c) formed on different sides of the agitator discs (18, 18a, 18b, 18c) are arranged in pairs. 3. The agitator-type ball mill according to claim 2, wherein the channels (36, 36b, 36c) arranged in pairs are formed in the form of grooves and separated by the walls (37, 37b, 37c) of the agitator discs (18, 18b, 18c). 4. The stirrer-type ball mill according to claim 3, wherein the wall portion (37b, 37c) is opened in the region of the inner channel portion (40a, 40b) by means of abrasive material through-holes (47) having a radial extension R47 in the radial direction of the stirring disc (18b, 18c). 5. The agitator-type ball mill according to claim 2, wherein the channels (36, 36a) arranged in pairs are connected in a groove manner. 6. The stirrer-type ball mill according to any one of claims 1 to 5, wherein the channels (36, 36a) are provided with guide ramps (46, 46a) at the locations where they transition to the outer periphery (42) of the stirring disc (18, 18a), the guide ramps (46, 46a) redirecting the grinding media (33) to the grinding unit (34) facing the channels (36, 36a). 7. The agitator-type ball mill according to any one of claims 1 to 5, wherein the ratio of the radial width b of the gap (32) to the free radius R14 of the grinding chamber (14) is: b ≤ 0.2·R14. 8. The stirrer-type ball mill according to any one of claims 1 to 5, wherein the ratio of the thickness d of the stirring disc (18, 18a, 18b, 18c) to the radial width e of the outer periphery (42) of the stirring disc (18, 18a, 18b, 18c) is: 0.5·d≤e≤1.5·d. 9. The stirrer-type ball mill according to any one of claims 1 to 5, wherein the ratio of the free radius R18 of the stirring discs (18, 18a, 18b, 18c) to the length f of the straight-extending inner channel portion (40, 40a, 40b, 40c) is: 0.25·R18≤f≤0.6·R18. 10. The stirrer-type ball mill according to any one of claims 1 to 5, wherein the curved channel portions (41, 41a, 41b, 41c) are incorporated into the outer periphery of the stirring discs (18, 18a, 18b, 18c) with a radius r41/42, and the relationship between the radius r41/42 and the width c of the channel (36) is: r41/42 ≤ 0.2·c. 11. The stirrer-type ball mill according to claim 4, wherein the grinding material through holes (47) are arranged only adjacent to the inner boundary of the grinding chamber. 12. The agitator-type ball mill according to claim 4, wherein, calculated from the boundary of the grinding chamber, the ratio of the radial extension R47 of each grinding material through hole (47) to the radial extension R18 of the agitator discs (18, 18a, 18b, 18c) is: 0.05·R18≤R47≤0.25·R18. 13. The stirrer-type ball mill according to claim 9, wherein the ratio of the free radius R18 of the stirring discs (18, 18a, 18b, 18c) to the length f of the straight-extending inner channel portion (40, 40a, 40b, 40c) is: 0.3·R18≤f≤0.5·R18. 14. The stirrer ball mill according to claim 12, wherein the ratio of the radial extension R47 of each grinding material through hole (47) to the radial extension R18 of the stirring disc (18, 18a, 18b, 18c) is: R47 ≤ 0.20·R18. 15. The stirrer-type ball mill according to claim 14, wherein the ratio of the radial extension R47 of each grinding material through hole (47) to the radial extension R18 of the stirring disc (18, 18a, 18b, 18c) is: R47 ≤ 0.15·R18. 16. A mixing disc for a stirrer-type ball mill according to any one of the preceding claims, the mixing disc (18, 18a, 18b, 18c) comprising an outer edge (30) and a thickness d, and the mixing disc (18, 18a, 18b, 18c) comprising entrainment profiles (35, 35a, 35b, 35c) for grinding media (33), the entrainment profiles being formed by channels (36, 36a, 36b, 36c) formed in the mixing disc (18, 18a, 18b, 18c) relative to the grinding media (33). A rear wall (39) is formed with respect to the rotation direction (38) of the stirring discs (18, 18a, 18b, 18c), the rear wall (39) extending parallel to the central longitudinal axis of the stirring discs (18, 18a, 18b, 18c), the rear wall being formed by curved channel portions (41, 41a, 41b, 41c) that are bent relative to the central longitudinal axis (15) in the radially outer part of the channel, the curved channel portions (41, 41a, 41b, 41c) being bent against the rotation direction (38). The channels (36, 36a, 36b, 36c) having a rear wall (39) relative to the direction of rotation (38) each include inner channel portions (40, 40a, 40b, 40c) extending radially straight relative to the central longitudinal axis (15), and include curved channel portions (41, 41a, 41b, 41c) that bend in the opposite direction of rotation (38) in the next stage. Furthermore, the curved channel portions (41, 41a, 41b, 41c) are radially closed relative to the outside by the outer periphery (42) of the stirring disc (18, 18a, 18b, 18c). 17. The mixing pan according to claim 16, wherein the mixing pan (18, 18a, 18b, 18c) includes channels (36, 36a, 36b, 36c) formed on both sides of the mixing pan (18, 18a, 18b, 18c), wherein, in each case, two channels (36, 36a, 36b, 36c) formed on different sides of the mixing pan (18, 18a, 18b, 18c) are arranged in pairs. 18. The mixing tray according to claim 16 or 17, wherein the channels (36, 36a) are provided with guide ramps (46, 46a) at the locations where they transition to the outer periphery (42).