HK1248173B - Agitator ball mill - Google Patents

Description

Agitator ball mill

Technical Field

The present invention relates to an agitator ball mill.

Background Art

Such an agitator ball mill is known from EP 2 178 641 A1. In such an agitator ball mill, a flowable grinding material or a grinding material suspension is ground or dispersed with the aid of grinding bodies. The grinding suspension consists of a carrier liquid and solids distributed therein, with the initial particle size ranging from a few micrometers to several hundred micrometers. The final size lies in the micrometer, submicrometer, and in special cases even nanometer ranges.

In the agitator ball mill known from EP2178642A1, relatively large openings are formed in the agitator disk that defines adjacent grinding units, which are arranged to be spaced a certain distance from the inner wall of the grinding chamber. The grinding bodies are accelerated outward on the surface of the agitator disk and in the outer area of the grinding unit relative to the axis by the agitator disk. Similar considerations apply to grinding suspensions. In the central area relative to the axial direction, the flow is redirected and directed toward the agitator axis. Two such roughly oppositely directed flows in the grinding unit are called braided flows or circular flows. The large openings formed in the agitator disk serve to pass the grinding material and the grinding bodies from the grinding unit to the downstream grinding unit viewed from the overall flow direction. In the corresponding openings, the grinding bodies are entrained in different directions by the walls that define the corresponding openings, so that completely uncontrolled passage of the grinding bodies and the grinding material occurs between adjacent grinding units, thereby strongly affecting the interlaced flow, so that the grinding bodies are very unevenly distributed throughout the grinding chamber and in each grinding unit. In addition, this results in a wide distribution of the residence time of the grinding material during its flow through the grinding chamber.

In known agitator ball mills, a grinding material/grinding body passage opening is formed in the downstreammost agitator disk, which forms part of the separator device, for the grinding material and grinding bodies to pass through and enter the separator device. In the downstreammost agitator disk, corresponding to the large opening already mentioned in the upstream agitator disk, a groove is arranged, through which the grinding bodies are entrained and accelerated outwards by centrifugal force. Due to this groove, the grinding material/grinding body passage opening is arranged relatively close to the agitator shaft, that is, for structural reasons.

The grinding bodies are moved within the active grinding chamber by means of stirring elements. The grinding suspension to be processed is supplied to the sealed grinding chamber by means of a suitable pump, which can operate at a pressure of up to approximately 5 bar, in particular up to 10 bar. The solids contained in the grinding suspension (i.e., the grinding material) are exposed to the grinding bodies moving relative to one another and are ground or dispersed, depending on their morphology.

Due to the viscosity of the grinding material, the entrainment forces imparted to the grinding bodies by the grinding material cause the latter to be transported towards the grinding material outlet. This leads to an uneven distribution of the grinding bodies along the axis of the grinding chamber. This is compounded by the uneven distribution of the grinding bodies caused by uncontrolled acceleration at the surface of the large opening of the agitator disc. For relatively high volumes of grinding material compressed and/or relatively high viscosities of the grinding bodies, increased wear can easily result. Furthermore, this often leads to excessive stress on the grinding material, potentially resulting in its destruction.

Summary of the Invention

The object of the present invention is therefore to ensure, in a particularly simple manner, a uniform distribution of the grinding bodies along the grinding chamber in an agitator ball mill of known type even at highest outputs and within a wide operating range, while producing a particularly uniform grinding result.

According to the present invention, this object is achieved by an agitator ball mill according to a first aspect.

Surprisingly, it has been shown that agitator ball mills can be operated at very high throughputs if agitator disks without through-holes have only small grinding material passage openings arranged in close proximity to the agitator shaft. The term "close proximity" should be understood to include situations in which the inner boundary of the grinding chamber and the radially inner boundary of the grinding material passage opening coincide, thus delimiting the inner boundary of the grinding chamber, as well as situations in which the radially inner boundary of the grinding material passage opening is at an even small distance from the inner boundary of the grinding chamber. For example, the radially inner boundary of the grinding material passage opening can be at a distance from the inner boundary of the grinding chamber that is within a range of up to one tenth (≤ 0.1) of the radial extension of the respective agitator disk from the inner boundary of the grinding chamber to the radially outer edge of the respective agitator disk. Such a small distance of the radially inner boundary of the grinding material passage opening from the inner boundary of the grinding chamber can be advantageous or even required for manufacturing reasons. An absolutely constant power consumption is achieved over a very wide throughput range, which is an indicator of a uniform distribution of the grinding bodies and is not adversely affected by an increase in throughput. Furthermore, a significantly narrower particle distribution is achieved over the entire operating range than is achieved in single-batch operation using agitator ball mills with conventionally large openings in radially outer regions. For the described effect, it is essential that the agitator disks delimiting adjacent grinding units have grinding material passage openings arranged in close proximity to the agitator axis. The grinding bodies are accelerated outward over the majority of the agitator disk surface, resulting in an increased density of the grinding bodies in the region of the grinding container's walls, which creates a correspondingly high flow resistance for the grinding material (i.e., the grinding suspension). Consequently, there are no bypasses, i.e., free passages, for the grinding material in the outer regions of the grinding chamber. This effect is particularly facilitated when the difference between the solid density and the density of the mixture of the grinding suspension (i.e., the grinding material consisting of solids and carrier liquid) is as high as possible, preferably equal to or greater than 2 g/ ^cm³ . Because the relatively small grinding material openings are located in regions with only a small number of grinding bodies, uncontrolled exchange of grinding material between adjacent grinding units, in particular, a large amount of grinding bodies passing through the grinding material openings, cannot occur.

Particularly advantageously, the relative radial extension of the grinding material passage openings of the agitator ball mill according to the invention is the subject matter of the second and third aspects.

In principle, there can be only a single grinding material through opening.In a fourth aspect, an advantageous arrangement of the grinding material through openings around the agitator shaft of the agitator ball mill according to the invention is specified.

The fifth to eighth aspects provide particularly advantageous further embodiments of the agitator ball mill according to the invention, in which different accelerations of the grinding bodies along the radial extension of the agitator disk can be achieved in a targeted manner, thereby achieving a directed outward transport of the grinding bodies.

By the ninth aspect, in the agitator ball mill according to the present invention, it is achieved that the grinding material flows from a circulating flow, ie, an interwoven flow, in one grinding unit into a similar flow in a downstream grinding unit.

BRIEF DESCRIPTION OF THE DRAWINGS

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

FIG1 is a schematic diagram of a partially cut-away side view of an embodiment of an agitator ball mill according to the present invention,

FIG2 is a top view of a first embodiment of an agitator plate of an agitator ball mill according to the present invention,

FIG3 is a detail of FIG1 on an enlarged scale of FIG1 ,

FIG4 is a top view of a second embodiment of an agitator plate of an agitator ball mill according to the present invention,

FIG5 is a partial cross-sectional view of the stirring plate of FIG4 ,

FIG6 is a top view of a third embodiment of an agitator plate of an agitator ball mill according to the present invention,

FIG7 is a partial cross-sectional view of the stirring plate of FIG6 ,

FIG. 8 is a view corresponding to FIG. 3 , with a modified inner boundary of the grinding chamber compared to FIG. 1 .

DETAILED DESCRIPTION

FIG1 shows a horizontal agitator ball mill. As is conventional, it comprises a support frame 1 supported on the ground 2. A drive motor 3 is arranged in the support frame. The drive motor 3 has a controllable rotational speed and may include a V-belt pulley 4 that rotatably drives a drive shaft 7 of the agitator ball mill via a V-belt 5 and another V-belt pulley 6. The drive shaft 7 is supported in an upper portion 8 of the support frame 1 by a plurality of bearings 9.

A generally cylindrical grinding container 10 is releasably mounted on the upper part 8 of the support 1. The cylindrical grinding container 10 has an inner wall 11 and is closed at the end facing the upper part 8 by a first cover 12 and at the opposite end by a second cover 13. It 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 10 and the drive shaft 7, and is connected to the drive shaft 7 in a torsionally fixed manner. The grinding chamber 14 is sealed by means of a gasket 17 arranged between the cover 12 and the drive shaft 7. The stirring shaft 16 is supported in a cantilevered manner, that is, it is not supported in the region of the second cover 13. A stirring tool in the form of an annular stirring disk 18 is provided along its entire length.

The agitator disks 18 are attached to the agitator shaft 16 and are held in a conventional manner on the agitator shaft 16 in a torsionally fixed manner, for example by means of a tongue and groove connection, and are held spaced apart from one another by means of a spacer sleeve 19. The agitator shaft 16 together with the spacer sleeve 19 and the agitator disks 18 form an agitator 20. The spacer sleeve 19 delimits the generally cylindrical grinding chamber 14 at its inner end, thereby forming the inner boundary of the grinding chamber.

In the region of the first cover 12 , a grinding material inlet 21 opens into the grinding chamber 14 . At the end of the grinding container 10 opposite the grinding material inlet 21 , a grinding material outlet 22 opens out of the second cover 13 .

A cylindrical holder 23 is formed at the outer periphery of the last agitator disc 18, adjacent to the second cover 13. It includes a plurality of openings 24 distributed along its circumference. In the separator space 25 surrounded by the most downstream agitator disc 18 and the holder 23, a sieve 26 is arranged, which is attached to the second cover 13 and connected to the ground material outlet 22. These components form a ground material/ground body separation device 27, which is known from EP 2 178 642 A1.

The agitating disc 18 (or 18a, 18b; see Figures 4 to 7) comprises one or more grinding material passage openings 28, which are circular in this embodiment. At their inner ends relative to the central longitudinal axis 15, the grinding material passage openings 28 are delimited to the spacing sleeve 19, i.e., the inner boundary of the grinding chamber. The grinding material passage openings 28 are arranged at uniform angular distances from one another, for example, six openings 28 are shown in Figure 2. Apart from the grinding material passage openings 28, the agitating disc 18 (or 18a, 18b) does not have any other openings; they are completely closed elsewhere.

The grinding material passage opening 28 includes a radial outer boundary, which is at a distance R28 from the spacer sleeve 19 (i.e., the inner boundary of the grinding chamber) in the radial direction of the agitator disk 18. With respect to the ratio of the distance R28 between the radial outer boundary of the grinding material passage opening 28 and the spacer sleeve 19 (i.e., the inner boundary of the grinding chamber) and the radial outer edge 30 of the agitator disk (the radial outer boundary), the following conditions apply:

0.05·R18≤R28≤0.25·R18, more preferably R28≤0.15·R18.

Adjacent agitator disks 18 each have the same axial distance a from one another. Furthermore, adjacent agitator disks 18 have a separator angle α defined by a line 29 extending from a radially outer edge 30 of an agitator disk 18 to the inner end of an adjacent agitator disk 18 at the agitator shaft 16 (i.e., at the corresponding spacer sleeve 19), and a line 31 extending parallel to the central longitudinal axis 15. The condition 30° < α < 60° applies.

The width b of the gap 32 between the radial outer edge 30 and the wall 11 amounts to a maximum of 20% of the free radius R14 of the grinding chamber 14 .

The grinding chamber 14 is substantially filled with grinding bodies 33, preferably made of a high-density material, such as a high-performance ceramic made of ZrO2 (zirconium dioxide) with a solid density of 6.0 g/ ^cm3 . The filling level (the bulk volume of the grinding bodies relative to the volume of the grinding chamber) is in the range of 50% to 90%, particularly in the range of 80% to 90%. The high solid density of the grinding bodies 33 relative to the density of the grinding suspension is important for the desired effect, namely, the outward transport of the grinding bodies 33 near the surface of the individual agitator disks 18 into the area where the grinding bodies accumulate.

Between adjacent agitator disks 18, grinding cells 34 are formed, wherein when the agitator shaft 16 is driven, an interwoven flow 35 is formed, as shown in FIG3 . As can be seen from the figure, the grinding bodies 33 and the grinding material to be processed (e.g., grinding suspension) flow outward in the region of the agitator disks 18 due to the tangential acceleration caused by the agitator disks, and flow inward toward the agitator shaft 16 in the axial center region of the grinding cells 34. The concentration of grinding bodies is lowest in the region of the grinding shaft 16. In this region, the grinding material flows from one grinding cell 34 into the adjacent grinding cell 34 through the grinding material passage opening 28. The flow of the grinding material through the grinding material passage opening 28 is indicated by the flow direction arrow 36 in FIG3 . The overall flow direction 37 through the agitator ball mill in FIG1 and FIG3 is from left to right, that is, from the grinding material inlet 21 to the grinding material outlet 22. However, in FIG3 , the grinding material passage opening 28 does not define the spacing sleeve 19, but rather the radial inner boundary of the corresponding grinding material passage opening 28 has a small distance A from the spacing sleeve 19 in the radial direction, which distance A can reach one tenth (≤0.1) of the radial extension R18 of the agitator disc 18 measured from the spacing sleeve 19 (inner boundary of the grinding chamber) to the outer edge 30 (radial outer boundary), so that the condition 0≤A≤R18 generally applies (when this distance is 0, the radial inner boundary of the corresponding grinding material passage opening 28 defines the isolation sleeve 19, see FIG2 ).

The acceleration of the grinding bodies 33 caused by the agitator disk 18 can be increased by forming groove-like channels 38a, 38b (see Figures 4 to 7) in the agitator disk 18. The groove-like channels 38a, 38b each begin at the agitator material passage opening and are directed to the radial outer edge 30 of the respective agitator disk 18 (or 18a, 18b), but do not penetrate the radial outer edge 30 of the respective agitator disk 18 (or 18a, 18b). Therefore, in the embodiment shown, the agitator disk outer ring 39 (in the embodiment shown in the figures) remains the same thickness c of the agitator disk 18 (or 18a, 18b). Moreover, the agitator disk 18 (or 18a, 18b) is not penetrated in a direction parallel to the central longitudinal axis 15. Therefore, each agitator disk 18 (or 18a, 18b) is completely closed, having only the agitator material passage opening 28 already described.

According to the first embodiment shown in Figures 4 and 5, the channels 38a extend radially relative to the central longitudinal axis 15 and have a width d corresponding to the diameter of the opening 28 through which the grinding material passes. The respective channels 38a are formed on both sides of the respective agitator disk 18a so that, as shown in Figure 5, a thin-walled portion 40a remains between them. As can be seen in Figure 4, the grinding bodies 33 are tangentially entrained by the respective rear channel walls 42a, viewed in the direction of rotation 41, and are thus accelerated by centrifugal force (centrifugation). The tangential velocity and the resulting radial acceleration increase radially outward, which is indicated by the radially increasing length of the velocity arrow 43a.

In the embodiment of the agitator disk 18b shown in Figures 6 and 7, the channel 38b has a width d (corresponding to the diameter of the grinding material passage opening 28) and is divided by a wall portion 40b, which includes an inner straight channel portion 44 starting at the corresponding grinding material passage opening 28, and is radially outwardly followed by an outer channel portion 45, which curves counter to the direction of rotation 41 of the agitator disk 18b and ends before the outer ring 39. Due to this design, the grinding body 33 experiences acceleration in different directions. In the inner channel portion 44, the entrainment of the grinding body 33 by the channel wall 42b is tangential, while in the radial outer channel portion 45, due to the orientation of the channel wall 42b, the entrainment is radial and tangential. In addition, the different lengths of the arrows 43b representing the velocity indicate the different directions and amounts of acceleration applied to the grinding body 33. It is worth noting that the channel 38b ends at the outer ring 39, having its full width. The rear channel wall 42b thus exerts an acceleration which is directed only outwards, all the way to the very outer end. The grinding body 33 engaged by the channel 38b is thus pushed precisely outwards.

8 shows a further development which can be applied to all the above-described embodiments, in which a redirection channel 46 is formed between the spacing sleeve 19 and the grinding material passage opening 28 of the upstream agitator disk 18, relative to the overall flow direction 37, which redirection channel redirects the grinding material flow from the upstream grinding unit 34 relative to the overall flow direction 37 and merges it into the radially outward interwoven flow 35 in the downstream grinding unit 34. The spacing sleeve 19b is embodied in such a way that the downstream grinding material passage opening 28 in the overall flow direction 37 can be reached unhindered by the grinding material flow in the grinding unit 34.

Claims (14)

1. A stirrer-type ball mill, The agitator-type ball mill has a horizontally arranged grinding container (10). The grinding container surrounds a cylindrical grinding chamber (14) defined by the wall (11) of the grinding container and the inner boundary (19) of the grinding chamber. The grinding container has an abrasive material inlet (21), which leads into one end of the grinding chamber, and The grinding container has an abrasive material outlet (22) that leads to the other end of the grinding chamber. An abrasive material/abrasive media separation device (27) is arranged upstream of the abrasive material outlet, which is a device for separating the abrasive media from the abrasive material. The agitator-type ball mill has an agitator (20) arranged in the grinding chamber (14), the agitator having: A rotatable stirring shaft (16) having a central longitudinal axis (15), and A mixing disc (18) is mounted to the mixing shaft (16) in an anti-torsional manner, and the mixing discs are spaced apart by a distance a. Two adjacent mixing discs (18) define the grinding unit (34) respectively. The stirring disc (18) includes an opening connecting adjacent grinding units (34), and The stirring disc (18) has a radial extension R18 from the boundary of the grinding chamber to the radial outer edge (30) of the stirring disc (18) relative to the central longitudinal axis (15). The opening is configured such that the grinding material passes through the opening (28) and is arranged only adjacent to the inner boundary (19) of the grinding chamber. The grinding material passing through the opening (28) has a radial outer boundary, which is a distance R28 from the inner boundary of the grinding chamber along the radial direction of the stirring disc (18). The ratio of the distance R28 of the abrasive material through the radial outer boundary of the opening (28) to the radial extension R18 of the stirring disc (18) is subject to the following condition: 0.05·R18≤R28≤0.25·R18. And in which the stirring pan (18) is enclosed in other parts. 2. The agitator-type ball mill according to claim 1, wherein the ratio of the distance R28 of the grinding material through the radial outer boundary of the opening (28) to the radial extension R18 of the agitator disc (18) is subject to the following condition: R28≤0.20·R18. 3. The agitator-type ball mill according to claim 1, characterized in that the ratio of the distance R28 of the grinding material through the radial outer boundary of the opening (28) to the radial extension R18 of the agitator (18) is subject to the following condition: R28≤0.15·R18. 4. The agitator-type ball mill according to any one of claims 1 to 3, wherein the grinding materials are arranged at uniform angular distances from each other through openings (28). 5. The stirrer-type ball mill according to any one of claims 1 to 3, characterized in that grooved channels (38a, 38b) are formed on both sides of the stirring discs (18a, 18b), the grooved channels (38a, 38b) starting from the opening (28) through which the grinding material passes and not passing through the corresponding stirring discs (18a, 18b) along the direction of the central longitudinal axis (15) of the stirring discs (18a, 18b), the grooved channels pointing towards the radial outer edge (30) of the stirring discs (18a, 18b) and being closed toward the radial outer edge (30) of the stirring discs (18a, 18b). 6. The stirrer-type ball mill according to claim 5, wherein the channels (38a, 38b) formed on different sides of the stirring disc (18a, 18b) and originating at the opening (28) through which the grinding material passes are arranged in pairs. 7. The stirrer-type ball mill according to claim 5, wherein the channels (38a) formed on both sides of the stirring disc (18a) extend straight and radially relative to the central longitudinal axis (15). 8. The stirrer-type ball mill according to claim 5, characterized in that the channels (38b) formed on both sides of the stirring disc (18b) include an outer channel portion (45) that is bent in the opposite direction to the rotation direction (41) of the stirring disc (18b). 9. The agitator-type ball mill according to claim 5, wherein the agitator disc (18a, 18b) includes an outer ring (39) of the agitator disc arranged radially outward. 10. The agitator ball mill according to any one of claims 1 to 3, characterized in that, when viewed along the overall flow direction (37) of the agitator ball mill, a redirection channel (46) is provided downstream of the opening (28) through which the grinding material connecting the upstream grinding unit (34) and the downstream grinding unit (34) passes, allowing it to enter the grinding unit (34) radially. 11. The stirrer-type ball mill according to any one of claims 1 to 3, wherein gaps (32) are formed between the radial outer edge (30) of the stirring disc (18) and the wall (11) of the grinding container (10), and the radial width b of the gap is at most 20% of the free radius R14 of the grinding chamber (14) between the inner boundary (19) of the grinding chamber and the wall (11) of the grinding container. 12. The agitator ball mill according to any one of claims 1 to 3, wherein the grinding chamber (14) is filled with grinding media (33), the total volume of the grinding media (33) corresponding to 50% to 90% of the volume of the grinding chamber (14). 13. The stirrer ball mill according to any one of claims 1 to 3, wherein the grinding media (33) has a solid density at least 2 g/ ^cm3 higher than the density of the grinding material. 14. The agitator ball mill according to any one of claims 1 to 3, wherein the grinding chamber (14) is filled with grinding media (33), the total volume of the grinding media (33) corresponding to 80% to 90% of the volume of the grinding chamber (14).