EP4093550A1

EP4093550A1 - Stirred ball mill, stirred ball mill stirring mechanism, and method for comminuting milling material

Info

Publication number: EP4093550A1
Application number: EP21701526.2A
Authority: EP
Inventors: Falk SILBERMANN
Original assignee: FLSmidth AS
Current assignee: FLSmidth AS
Priority date: 2020-01-24
Filing date: 2021-01-22
Publication date: 2022-11-30
Also published as: DE102020200878A1; CN114945427A; WO2021148623A1; JP7566915B2; US20220410170A1; JP2023511383A

Abstract

The present invention relates to a stirred ball mill (1) comprising a milling container (2), at least three stirring shafts (3) and a drive (4), the milling container (2) being arranged in a main direction and having a milling chamber (5) which is suitable for receiving milling material and milling aids. Each of the at least three stirring shafts (3) has a centre axis (X) arranged parallel to the main direction of the milling container (2) and is designed as a screw fixed to the frame in the milling container (2) and rotatable about the centre axis (X). The drive (4) is designed to rotate the at least three stirring shafts (3) about their respective centre axes (X), wherein the at least three stirring shafts (3) do not touch each other, and the centre axes (X) of the at least three stirring shafts (3) are arranged as side edges of a prism. The invention also relates to a stirred ball mill stirring mechanism for such a stirred ball mill (1) and to a method for comminuting milling material.

Description

Agitator ball mill, agitator ball mill agitator and process for comminuting millbase

The invention is in the field of comminution technology and relates to agitator ball mills comprising grinding containers, agitator shafts and drives. In such an agitator ball mill, a grinding container is arranged in one main direction and has a grinding chamber for receiving material to be ground, an agitating shaft has a central axis arranged parallel to the main direction of the grinding container and is designed as a screw rotatable about the central axis, and a drive is set up which To rotate the agitator shaft around its central axis. Furthermore, the invention relates to an agitator ball mill stirrer for such an agitator ball mill and a method for comminuting millbase, the method comprising slurrying the millbase to be milled in a grinding aid liquid, a millbase dispersion being obtained, continuous introduction of the millbase dispersion into a lower section of a millbase filled with grinding accessories Grinding chamber of an agitator ball mill, continuous vertical conveying of part of the grinding stock dispersion from the lower section of the grinding chamber into an upper section of the grinding chamber, whereby a prepared grinding stock dispersion is obtained in which at least part of the grinding stock dispersed in the auxiliary grinding liquid is comminuted, continuous feeding out of a part the prepared grist dispersion from the upper section of the grinding chamber, and a final separation of the comminuted grist from the processed grist dispersion that has been diverted out n.

An agitator ball mill (agitator ball mill, agitator mill, agitator mill) is a device for comminuting and / or homogenizing solids as ground material. For this purpose, the grinding stock is mixed with auxiliary grinding bodies (grinding bodies, grinding balls) and this mixture is set in motion with the aid of an agitator in the grinding chamber of the agitator ball mill. During this movement, the auxiliary grinding bodies and the material to be ground repeatedly collide with one another and against the boundary walls of the grinding chamber. As a result of the forces that occur during movement - the impact forces due to impact stress and the shear forces that occur between the material to be ground and the auxiliary grinding bodies and also between the material to be ground and the agitator ball mill - the material to be ground is comminuted, so that the agitator ball mill is a special form of the ball mill. Such grinding units get about at the Processing of mineral raw materials and pigments for use, but also in the processing of vegetable raw materials, for example in the paper industry or in the food industry. Agitator ball mills naturally offer many advantages when grinding stock that exhibits brittle fracture behavior is to be comminuted.

Agitator ball mills have grinding containers that can be arranged vertically or horizontally. The interior (grinding chamber) of the grinding container often has the shape of a cylinder, a polygonal prism or shapes derived therefrom. During operation, the interior is predominantly filled with auxiliary grinding bodies with a spherical or ball-like basic shape, typically to about 70% to 90% of the volume of the interior. As a rule, the auxiliary grinding bodies consist of a ceramic, metallic or mineral material, which should be chemically inert, wear-resistant and wear-resistant with respect to the material to be comminuted. The intensive movement and mixing of the auxiliary grinding bodies and the ground material is carried out by the agitator shaft of an agitator, which has suitable agitating elements.

Grinding containers arranged horizontally (horizontally or horizontally) are preferably used for wet grinding of grist dispersions with high mobility. Grinding containers arranged vertically (vertically or upright) can also be used for systems with poor mobility and poor flow behavior. Depending on the specific application, vertically arranged grinding containers can be used in “wet” mode (wet operation) for grinding stock dispersions or in “dry” mode (dry mode) for finely divided regrind. Agitator ball mills with vertically arranged grinding containers are preferably used for grinding tasks in which grinding stock with certain fineness is to be obtained economically on an industrial scale.

In the wet operation of agitator ball mills with vertically arranged grinding containers, the ground material to be ground (in the form of particles or lumps - the terms "particles" or "lumps" are used synonymously here) are introduced into the grinding container as a dispersion (suspension, slurry, slurry). The material is introduced as a rule continuously, for example on the base of the grinding chamber via an inlet in the lower end wall of the grinding container. The solids content distributed in such a grist dispersion is determined with the aid of Grinding aids comminuted and dispersed. Depending on the particular configuration of the agitator ball mills, the comminuted ground material is discharged above the inlet, usually in the upper area of the grinding container. The auxiliary grinding bodies are typically separated from the comminuted ground material at the outlet of the grinding container, for example with the aid of a sieve. When the process is carried out in this way, the product, i.e. the comminuted ground material, is present in a size distribution due to the process.

The impact forces and shear forces required for comminuting the ground material are entered into the agitator ball mill by the agitator. The agitator typically has an agitator shaft and a drive. The agitator shaft comprises agitating elements such as axially arranged threads (as single-start or multi-start screws), a multiplicity of disks aligned parallel on the agitator shaft with passage openings or on pins aligned radially on the agitator shaft. The stirring elements are set in rotary motion via the agitator shaft, which results in an intensive mixing of the auxiliary grinding bodies and the ground material distributed in the grinding material dispersion, during which the ground material is deagglomerated and comminuted. The rotary movement of the agitator shaft is ensured by a suitable drive which has a drive unit, usually a suitable motor.

During the operation of the agitator ball mill, the auxiliary grinding bodies are subject to high mechanical loads due to the intensive mixing and must therefore be replaced from time to time. In order to keep the abrasion on the inner wall of the grinding container and on the agitator shaft as well as on the agitator elements low, the inner wall and agitator shaft usually have high-strength linings or coatings made of wear-resistant and wear-resistant materials.

For the fine grinding of mineral regrind such as ores, agitator ball mills with vertically arranged grinding containers are used, the agitator of which comprises an agitator shaft that has one or more threads as a stirring element, so that the agitator shaft also acts as a vertically arranged screw (screw, helix, helix, spiral) is designed, often as a multi-thread screw. This screw rotates out in a ball bed Auxiliary grinding bodies, the grinding stock dispersion with the grinding stock to be comminuted being in the space between the individual auxiliary grinding bodies. As a result of the rotary movement of the screw, the auxiliary grinding bodies are set in motion, as a result of which a force is exerted on the grinding stock dispersion, which leads to a comminution of the grinding stock. For such applications in particular, agitator ball mills with agitators are required which ensure high drive powers.

Drive units suitable for agitators in agitator ball mills typically have a maximum drive power of around 1,500 hp (corresponding to 1,120 kW) - for special applications, agitators with drive powers of up to 4,500 hp (corresponding to 3,360 kW) can be used in isolated cases. However, the power of such drive units is not sufficient to allow a variation of the throughput in the agitator ball mill within certain limits if the batches of auxiliary grinding bodies and grinding stock dispersions are difficult to move (e.g. batches with a high solids content, with grinding auxiliary bodies or grinding stock particles of large diameter and irregular shapes and / or in which the total mass of the batch to be moved is high - in contrast to easily movable batches, i.e. batches in which the volume fraction of the liquid phase is relatively high, in which both the dispersed grist particles and the auxiliary grinding bodies are relatively smooth and sufficiently small and in which the total mass of the mixture to be moved is sufficiently low); Such mixtures can occur in particular in the processing of mineral raw materials. Particularly with such heavily agitated batches, more powerful agitator ball mills can therefore not be easily realized with currently commercially available drive units: In order to be able to design an agitator ball mill with an input of particularly high grinding energies or grinding capacities and with a particularly high throughput for such heavy-moving batches, the Increased the diameter of the agitator shaft, namely the diameter of the thread of the screw. However, the mass of a screw increases with the square of the screw diameter, which is why significantly more powerful drive units are required to drive a larger screw. The selection of such powerful drive units on the market is small, which is why mostly on here Custom orders must be used. If agitator ball mills with higher performance can be realized at all from a technical point of view, this is therefore associated with disproportionately high costs.

Alternatively, instead of increasing the screw diameter of the agitator shafts, there is also the possibility of increasing the throughput of the agitator ball mill by using a drive unit which can drive the agitator shaft at higher rotational speeds. To change the rotational speed of the drive unit, in addition to more powerful drive units, correspondingly variable frequency converters would also be required. However, due to the costs associated with such more powerful drive units, the use of variable frequency converters does not make sense for economic reasons. For this reason, only drive units with a fixed rotational speed are used in current agitator ball mills, which makes process control more difficult.

Accordingly, it is the object of the present invention to provide an agitator ball mill which eliminates these disadvantages, which enables a particularly high throughput and / or an input of particularly large grinding energies or grinding capacities in a simple manner, especially when using conventional drive units for difficult-to-move batches which, above all, also allows the speed of rotation to be regulated.

This object is achieved by an agitator ball mill, an agitator ball mill agitator and a method for comminuting millbase with the features specified in the independent claims. Advantageous further developments result from the subclaims, the following description and the drawings.

The invention includes an agitator ball mill comprising a grinding container, at least three agitator shafts and a drive, wherein the grinding container is arranged in a main direction and has a grinding chamber which is adapted to receive grist and auxiliary grinding bodies, each of the at least three agitator shafts one parallel to the main direction of the Has the grinding container arranged central axis and mounted as placed in the grinding container and rotatable about the central axis Screw is formed, wherein the drive is set up to rotate the at least three stirring shafts about their respective central axes, and wherein the at least three stirring shafts do not touch each other and the central axes of the at least three stirring shafts are arranged as side edges of a prism.

Agitator ball mills are understood to mean all constructions known to the person skilled in the art for comminuting and / or homogenizing solids as grinding stock, in which the grinding stock is set in motion inside a grinding container together with auxiliary grinding bodies by means of an agitator with agitator shafts and at least one drive. Agitator ball mills of this type can be operated discontinuously (for example in batch operation), continuously (for example with constant or variable inflow and outflow) or also quasi-continuously.

The grinding container is a housing, the interior of which is designed as a grinding chamber and is therefore adapted to receive a mixture of ground material or grinding material dispersion on the one hand and auxiliary grinding bodies on the other hand (in addition, depending on the grinding task, the mixture can also have other components, for example function-changing components such as additives in cement production or Auxiliary materials). The grinding container - and thus the grinding chamber - has a main direction (main direction of extent) in which it is arranged. With a horizontally arranged grinding container, the main direction of the grinding container is horizontal (or at least essentially horizontal with a maximum deviation of 10 ° from the horizontal), with a vertically arranged grinding container the main direction of the grinding container is vertical (or at least essentially vertical with a maximum deviation of 10 ° to the vertical). In addition, other arrangements are also possible, such as an “inclined” orientation of the grinding container, in which the main direction of the grinding container deviates from the vertical and the horizontal, or arrangements with an orientation that changes over the extent of the grinding chamber. Basically, the grinding container can be designed in any way, for example its housing jacket can be formed from individual segments or can be made in one piece. The grinding container can be designed for wet operation or dry operation. The invention preferably relates to agitator ball mills with vertically arranged grinding containers, in particular those which are designed for wet operation. Usually, a grinding chamber has the shape of a cylinder or a polygonal prism (the main direction of the grinding chamber runs in the direction of the axis of these geometrical structures) or shapes derived therefrom, but in principle it can also have other shapes. For continuous operation or quasi-continuous operation, the grinding chamber can have an inlet and an outlet. "Fresh" ground material is fed into the grinding chamber via the inlet, and comminuted ground material is discharged from the grinding chamber via the discharge. In agitator ball mills with vertically arranged grinding containers in wet operation, the grinding stock is fed in in dispersed form and the grinding stock dispersion with the comminuted grinding stock is discharged. The grinding stock dispersion discharged from the grinding chamber with the comminuted grinding stock can be fed to a size separation. During size separation, regrind particles that have at most the desired target size are separated from larger regrind particles and the latter are returned to the grinding chamber. In the event that the regrind dispersion discharged from the grinding chamber or a part of it is to be branched off from the outlet stream and returned to the milling chamber again, the regrind dispersion to be returned can be mixed with fresh regrind - usually in the form of a dispersion - before it is returned , the combined material flows then being introduced into the grinding chamber via a common inlet; Of course, the fresh ground material can also be fed in separately and a separate return inlet can be provided for the material flow to be returned. In the case of vertically arranged grinding containers, the inlet is often in the lower area of the grinding chamber (for example in the bottom of the grinding chamber or in the side wall of the grinding chamber near the bottom) and the discharge in the upper area of the grinding chamber (for example in the side wall of the grinding chamber). In the grinding chamber, the mixture of grinding stock dispersion and auxiliary grinding bodies is conveyed from bottom to top against gravity. In other configurations of vertically arranged grinding containers, the inlet can also be located in the upper area of the grinding space and the discharge in the lower area of the grinding space.

The discharge can have a sieve device, in which the auxiliary grinding bodies are separated from the grinding stock dispersion to be discharged, consisting of comminuted grinding stock and auxiliary grinding liquid, and retained in the grinding chamber; In principle, such a separation can also only take place outside the grinding container, for which purpose, however, a separate return of the diverted auxiliary grinding bodies would be required. Fresh auxiliary grinding bodies can be added to the grinding chamber via a separate feed opening, but other arrangements are also possible; for example, the grinding material dispersion can be mixed with the auxiliary grinding bodies before it is introduced into the grinding chamber and the mixture of the grinding material dispersion and auxiliary grinding bodies can then be introduced into the grinding chamber via the inlet.

Furthermore, the agitator ball mill has at least three agitator shafts and a drive. The drive has at least one drive unit and can also include further elements, for example one

Rotational speed change unit (e.g. frequency converter), a control unit for controlling the drive unit (e.g. by means of control electronics or logic circuits) or machine elements for changing movement variables (e.g. gearbox). The drive is actively connected to the agitator shafts so that the drive power provided by the drive is transmitted to the agitator shafts. The operative connection between the agitator shaft and drive can be designed as desired, for example it can include a direct coupling (in that the agitator shaft is flanged to the shaft or the axis of the drive) or a coupling via a gear. A coupling can take place, for example, at one end section of the agitator shaft or via both end sections of the agitator shaft. In principle, any engine can be provided as the drive unit which is set up and - in particular with regard to the design of its power - suitable to set the agitator shaft or agitator shafts operatively connected to it in a rotary movement about an axis of rotation, for example a motor.

The agitator shafts are elongated elements that are designed to be rotatable about the axis of rotation and are suitable for transferring rotary movements and torques from the drive to the mixture of auxiliary grinding bodies and grinding material or grinding material dispersion in the grinding chamber of the grinding container. The axis of rotation of a stirrer shaft is usually arranged parallel to its main direction of extent and represents the central axis of the stirrer shaft. The stirrer shaft has a stirrer section which is adapted for immersion in the mixture of auxiliary grinding bodies and ground material or grinding material dispersion and whose outer enveloping shape is often similar that of a cylinder or cone section is formed. The rotatable mounting of an agitator shaft can take place at one point or at several points, in the case of agitator shafts of agitator ball mills With a vertically arranged grinding container, the agitator shafts are often only supported at their upper end, but here, too, other configurations are fundamentally possible.

An agitator shaft has agitator elements as essential functional components, which transfer the drive energy introduced by the drive when the agitator shaft rotates around the central axis designed as a rotation axis to the medium to be mixed in the grinding chamber, i.e. to the mixture of auxiliary grinding bodies and ground material or grinding material dispersion. The mixture is set in motion so that the constituents of the mixture are mixed. In the present case, the stirring elements are shaped in such a way that the stirring shaft is designed as a screw that can be rotated around the central axis of the stirring shaft, so that the central axis of the screw coincides with the central axis / axis of rotation of the stirring shaft (the two central axes therefore have at most a slight positional deviation of a few percent of the outer diameter of the screw, in particular less than 5% of the outer diameter of the screw). Basically, all common designs are suitable as screws (worm, helix, spiral, spiral), be it single-thread screws or multi-thread screws - for example double-thread screws, three-thread screws or four-thread screws - the aforementioned ones with a cylindrical basic shape and those with a slightly tapered (conical ) Basic shape, with a filled middle area or with an unfilled middle area ("with core" or "without core"), right-hand screws as well as left-hand screws with a suitable screw line, screw surface or helical surface, pitch and pitch angle, depending on the available drive power, composition of the mixture and the mixing to be achieved can be suitably selected in a manner known to the person skilled in the art. The at least three screws can be designed the same or different, for example with regard to the screw type, screw geometry (thread geometry) or the screw dimensions, that is to say, for example, their total length or their diameter. To improve the wear behavior, the areas of the agitator shaft that are particularly stressed during the power transmission can be designed to be wear-resistant, for example they can have a high-strength thread coating and / or tip coating. It has now been found that the ground material is not comminuted evenly over the entire extent of the grinding chamber or the screw, but that the stress area in question for the grinding processes is primarily located in a narrow area on the outside of the screw. It was also found that the grinding energy introduced into the mixture of ground material / grinding material dispersion and auxiliary grinding bodies by the drive via the agitator shaft is proportional to the outer circumference of the agitator shaft designed as a screw. The entered grinding energy therefore increases linearly with the diameter of the screw, while the space requirement (the required base side, i.e. the base area for agitator ball mills with vertically arranged grinding containers) of such an agitator increases with the square of the diameter of the screw. For a high energy input, an efficient torque transmission between the drive unit and agitator shaft on the one hand and a mixture of ground material / grinding material dispersion and auxiliary grinding bodies on the other hand is required, which is why the agitator shafts must be installed in the grinding container, the interior of which is designed as the grinding chamber. A shaft whose position does not change relative to the frame (the machine frame, that is to say the supporting parts of the agitator ball mill and its grinding container, in particular the grinding chamber) is referred to as placed; this of course does not preclude a rotary movement of the shaft about its central axis. For this reason, the agitator shafts cannot be revolving shafts and must therefore not revolve in the machine frame on circular paths within the grinding chamber, so that an arrangement of the shafts on the revolving part of a planetary gear (epicyclic gear) is basically not possible here.

When comparing the energies entered for agitator shaft systems with the same space requirement but different agitator shaft diameters, it can be seen that it is more advantageous to use several smaller agitator shafts than one larger agitator shaft: For example, for a first system with four small screws as agitator shafts, each with a diameter ds , k = D, the total circumference Us, k of the four smaller agitator shafts to Us, k = 4 x (p D), while a second system consisting of a large screw as agitator shaft with the diameter ds, g = (2D), which has the same Like the first system, it takes up space, Us, g of the agitator shaft of Us, g = 1 x (p (2D)). Since the energy input is proportional to the total circumference of the agitator shafts, the energy input for the first system drops with the same space requirement twice as large as that for the second system. If particularly large grinding energies or grinding capacities are to be achieved in a grinding chamber with a given base and volume, then it makes sense to use several smaller agitator shafts instead of a single larger agitator shaft in the available milling chamber, so that, as a result of the division into several smaller agitator shafts, the Can increase performance efficiency.

In such an arrangement, the agitator ball mill therefore has more than two agitator shafts, i.e. at least three agitator shafts, but more agitator shafts can also be provided, for example four agitator shafts, five agitator shafts or six agitator shafts. The stirrer shafts are designed as screws, which can be designed in any suitable form; for example, the agitator shafts can have a hollow shaft or a solid shaft. The drive is set up to rotate the at least three agitator shafts about their respective central axes; for this purpose, each agitator shaft can have a separate drive unit, but several or even all of the agitator shafts can have a common drive unit. The agitator shafts do not touch each other, so that there is a gap between two adjacent agitator shafts; Adjacent screws can in particular also be arranged in such a way that their threads do not interlock or penetrate one another. In an agitator ball mill, the gaps between the various agitator shafts can each be of the same size or also be of different sizes. The central axes of the agitator shafts are arranged in the grinding chamber of the grinding container in each case parallel to the main direction of the grinding container, so that the central axes of the at least three agitator shafts also run parallel to one another; A parallel course is regarded here as a course which has at most a deviation of 5 ° from an exactly parallel alignment. The central axes of these at least three agitator shafts are arranged as side edges of a prism (as a polygonal arrangement). In the present case, a prism is understood to be a polyhedron, the shape of which is obtained in the parallel displacement of a flat, regular or irregular polygon as a base area along a straight line as a displacement line, the straight line not lying in the plane of the polygon; in the case of a straight prism, the shift takes place perpendicular to the plane of the polygon; in the case of an inclined prism, the shift takes place at an angle deviating from the vertical. The polygon represents the base area and also represents the top surface of such a prism, the remaining boundary surfaces form the jacket surfaces, two jacket surfaces being connected to each other via a side edge which extends from a corner of the base surface to a corner of the top surface. The side edges are parallel to each other and are all the same length. As a rule, the base area and top area are congruent, but in exceptional cases they can also be rotated relative to one another (so that the term prism can also include prismatoids). The prism, as the side edges of which the at least three agitator shafts are arranged, can have a regular structure (the base area therefore represents a regular polygon, for example an equilateral triangle, a square, a regular pentagon, a regular hexagon or the like) or also an irregular structure (the base of which represents an irregular polygon, for example an unequal-sided triangle, in particular an isosceles triangle, an unequal-sided square, in particular an unequal-sided rectangle, a parallelogram or a trapezoid, as well as other non-regular closed polygonal curves), so that the prism also Cuboid, triangular prisms, pentagonal prisms, hexagonal prisms and the like. The arrangement of the center axes of the at least three agitator shafts as side edges of a prism is necessary in order to be able to use the torques of the three agitator shafts as effectively as possible for the grinding process, which is possible with a purely linear arrangement due to the smaller number of approach zones between adjacent agitator shafts (in the "gap"). between adjacent agitator shafts, where the outsides of adjacent screws approach each other and ground material and auxiliary grinding bodies are exposed to the influence of different agitator shafts) and would therefore not be possible due to the smaller total area of all approach zones.

The adaptation of the grinding chamber to accommodate ground material and grinding auxiliary bodies includes, in addition to a suitable geometric configuration, generally also the use of suitable chemically inert and mechanically resilient materials that are resistant to abrasion and wear-resistant with respect to the material to be ground. For this purpose, the inner wall of the interior space is typically provided with a corresponding high-strength coating or lining, with the latter being able to be segmented or designed as a full cladding element. A corresponding high-strength lining or coating is also used for the agitator shaft, in particular for its central axis, its thread and their tip. The material for such linings or coatings is generally selected in accordance with the material of the auxiliary grinding bodies in order to minimize the mutual wear effects. Typically, the surface of such elements subject to wear consists of metals or alloys, such as steels such as high-alloy steels, in particular chromium steels, of ceramic materials or minerals, such as carbidic materials, in particular tungsten carbide, chromium carbide, tantalum carbide, niobium carbide, titanium carbide, hafnium carbide or mixed carbides thereof , in particular corundum (especially sintered corundum), titanium dioxide or zirconium dioxide (in a stabilized form - for example with yttrium oxide or scandium oxide or in non-stabilized form), agate or flint, and made of composite materials such as flart metals.

The auxiliary grinding bodies themselves are not an integral part of the agitator ball mill, but are essential in operation. Typically, auxiliary grinding bodies are used, the outside of which has a rounded shape to make the movement behavior more uniform, for example spherical or ball-like auxiliary grinding bodies, cylindrical auxiliary grinding bodies ("Cylpebs"), and ellipsoidal, ovoid or spindle-shaped auxiliary grinding bodies and the like. During operation, these typically fill up the volume of the grinding chamber to around 70% to 90%, with this quantitative ratio having a significant influence on the product quality. The size distribution of the ground material ultimately achieved depends primarily on the size and shape of the grinding aid as well as on the ground material itself (e.g. on its density, hardness, brittle fracture behavior, crystallinity and crystal morphology as well as the size of the ground material supplied). The choice of material for the auxiliary grinding bodies is generally chosen to match the material of the coating.

In the simplest embodiment, all of the at least three agitator shafts are driven by the same drive unit. According to a further aspect, the agitator ball mill is designed in such a way that the drive for each of the at least three agitator shafts comprises its own drive unit. In this way, each agitator shaft can be controlled individually, which enables particularly versatile process control. If a rotational speed control is additionally provided in at least one drive unit - possibly also in all drive units - then even with grinding conditions that are not constant over time - for example a changing nature of the fed regrind - dynamically ensure a constant morphology for the comminuted regrind. In addition, by using separate drive units for each agitator shaft, it is possible to achieve the highest possible total energy input with commercially available drive units, so that a particularly high grinding capacity can be achieved. The drive units can be designed identically or differently. The latter can also be useful if, for example, not all agitator shafts have the same screw diameter or the same screw geometry, but at least two different types are to be assigned with regard to diameter or geometry.

Instead, the agitator ball mill can also be designed such that the drive for at least two of the at least three agitator shafts comprises a common drive unit, so that at least two drive units are provided for each agitator ball mill. In the case of an agitator ball mill with three agitator shafts, two agitator shafts are then driven by a common drive unit, the last agitator shaft has its own drive unit. In an agitator ball mill with four agitator shafts, three agitator shafts are driven by a common drive unit and the remaining agitator shaft then has its own drive unit or two agitator shafts are driven by a common drive unit and the other two agitator shafts either have their own drive unit or are instead driven by a second common drive unit; The same applies to agitator ball mills with more than four agitator shafts, that is to say with five agitator shafts, with six agitator shafts or with seven agitator shafts. In such a configuration, it is sufficient to set up only one of the at least two drive units for operation at a controllable rotational speed (speed) in order to ensure a change in the loading speed within the mixture of ground material / grinding material dispersion and auxiliary grinding bodies in the grinding chamber. Such a configuration has fewer drive units than the configuration in which each agitator shaft has its own drive unit, which is why the space requirement can be lower and this configuration can also be more cost-effective due to the smaller number of drive units. At the same time, however, this configuration already offers a process control that is significantly more powerful than an agitator ball mill with at least three agitator shafts, all of which are driven by a single drive unit, which is why this variant represents a sensible compromise.

According to a further aspect, the agitator ball mill is designed such that the drive is set up to drive at least one agitator shaft of the at least three agitator shafts at a rotational speed that can be regulated independently of the rotational speeds of the other agitator shafts of the at least three agitator shafts. This can be achieved, for example, by using individual drive units or agitator shaft gears that can be switched independently of one another. In this way, a special, individual process control can be achieved.

According to a further aspect, the agitator ball mill is designed in such a way that the agitator ball mill has at least one inner agitator shaft in addition to the at least three agitator shafts, which each has a central axis arranged parallel to the main direction of the grinding container and the screw mounted in the grinding container and rotatable around the central axis is formed, wherein the at least one inner stirring shaft does not touch the at least three stirring shafts and the central axis of the at least one inner stirring shaft is arranged within the prism formed by the central axes of the at least three stirring shafts. The at least one inner agitator shaft is therefore not arranged on a side edge of the prism, the jacket of which is spanned by the at least three — outer — agitator shafts. The at least one inner agitator shaft can be designed identically with one agitator shaft or with several agitator shafts from the at least three (outer) agitator shafts or different from these, for example with regard to the screw type, screw geometry (thread geometry) or the screw dimensions, i.e. about their total length or their diameter . If more than one inner agitator shaft is provided (for example two inner agitator shafts or three inner agitator shafts), then these can be designed the same or different. This configuration offers the advantage that the inner area between the outer agitator shafts does not become depleted of ground material as a result of the rotation of the outer agitator shafts, so that no “empty inner area” arises as a dead volume or dead zone. An arrangement with at least one inner agitator shaft is all the more useful if there are more than four outer agitator shafts are provided, since then the volume of the inner area is also larger, so for example in agitator ball mills with five agitator shafts, with six agitator shafts, with seven agitator shafts or with eight agitator shafts.

In this case, the agitator ball mill can additionally comprise a braking device which is set up to reduce the rotational speed of the at least one inner agitator shaft or to prevent a rotational movement. Any suitable braking device can in principle be used for this purpose, for example mechanical braking systems, magnetic braking systems, electrical braking systems, fluid braking systems or the like. In this way, the rotatable inner agitator shaft can be braked in a targeted manner during operation, which makes it possible to directly influence the flow of the mixture of ground material / grinding material dispersion and auxiliary grinding bodies in the interior between the at least three (outer) stirring shafts in order to localize the formation of dead zones there to counteract this or to be able to influence the energy input and torque transmission through additional turbulence (for example when starting up or shutting down the agitator ball mill or to force or prevent a transition to cascade movement, cataract movement or centrifugation for the batch during operation).

The agitator ball mill can be designed in such a way that the drive has a drive unit in order to rotate the at least one inner agitator shaft about its central axis. This drive unit can be a separate drive unit or a common drive unit, via which at least one or more of the outer agitator shafts and also the inner agitator shaft are driven, for example this common drive unit can be connected to the inner agitator shaft directly or via a corresponding gear. With this configuration, energy can also be introduced via the inner drive shaft; in addition, this enables the flow of the mixture of ground material / grinding material dispersion and auxiliary grinding bodies in the grinding chamber to be influenced in an even more targeted manner in order to be able to avoid dead zones. Instead, the agitator ball mill can also be designed in such a way that the at least one inner agitator shaft is not connected to a drive. A rotation of the inner agitator shaft around its central axis is then passively achieved in this embodiment by the inner agitator shaft running along in the flow movement of the mixture of millbase / millbase dispersion and Grinding aids. In this way, the inner agitator shaft serves to equalize a flow of material circulating in the grinding chamber and can thus lead to a passive stabilization of the grinding operation; in addition, the formation of dead zones can be counteracted.

In principle, the at least three agitator shafts can be adapted for a rotary movement in the same direction of rotation (in each case clockwise or counterclockwise) or in different directions of rotation. The adaptation of the agitator shaft for certain directions of rotation primarily concerns its screw shapes, the design as a right-hand screw or as a left-hand screw; In addition, a corresponding adaptation also relates to the structural design of the drive for the respective directions of rotation, i.e. the control unit, the drive units and / or any elements for power transmission and / or torque transmission (for example of gears that are arranged between the drive unit and agitator shaft).

If the at least three agitator shafts are adapted for different directions of rotation, at least one agitator shaft of the at least three agitator shafts is a right-hand screw and at least one agitator shaft of the at least three agitator shafts is a left-hand screw. As a result, with an even number of agitator shafts, it is then possible for each agitator shaft to have a direction of rotation that differs from the directions of rotation of the two adjacent agitator shafts. If adjacent agitator shafts have different directions of rotation, then the outer sides of their screws run where they approach each other (i.e. in the “gap” between adjacent agitator shafts) in the same direction, so that especially uniform grinding conditions prevail locally at these points. Instead, the agitator ball mill can also be designed in such a way that the at least three agitator shafts are adapted for a rotary movement in the same direction of rotation. If adjacent agitator shafts have the same directions of rotation, then the outer sides of their screws run in different directions in relation to one another in the approach zone. As a result, the solid constituents - i.e. the ground material and the auxiliary grinding bodies - which are exposed to the influence of different agitator shafts, have local relative speeds in the approach zone relative to one another that are almost twice as high as the speed of the solid constituents in the flow of the agitator shafts outside the approach zone. This results in significantly higher local impact forces and shear forces in this zone and thus also a considerably higher input of grinding energy without requiring a larger area for the unit than with conventional single-shaft agitator ball mills, so that such a design has considerable advantages.

In the case of agitator ball mills with at least three (outer) agitator shafts, which have the same direction of rotation, the risk is particularly high that dead zones will develop in the inner area between the agitator shafts (roughly equivalent to the formation of a vortex due to the donut effect). If an agitator ball mill therefore has at least three (outer) agitator shafts which are adapted for a rotary movement in the same direction of rotation, then - as described above - it can be useful if at least one inner agitator shaft is also provided. The at least one inner agitator shaft can be adapted for a rotary movement in the same direction of rotation as the at least three (outer) agitator shafts (wherein the at least one inner agitator shaft can have a different rotational speed than the at least three (outer) agitator shafts). In this way, the energy input can be increased even further, since additional proximity zones are created compared to an arrangement without an inner agitator shaft. Instead, the agitator ball mill can also be designed so that the at least three agitator shafts are adapted for a rotary movement in the same direction of rotation, and the at least one inner agitator shaft is adapted for a rotary movement in the direction of rotation different from the direction of rotation of the at least three agitator shafts. In this way, the same high grinding energy input is offered as in an agitator ball mill with at least three (outer) agitator shafts with the same direction of rotation, the formation of dead zones being counteracted.

According to a further aspect, the agitator ball mill can be designed such that the outer diameter of each of the at least three agitator shafts is at most half the maximum inner width of the grinding chamber. This ensures that the majority of the energy input does not take place via a single agitator shaft, but essentially via each of the at least three agitator shafts to similar parts, so that an optimal increase in throughput and / or grinding energy or grinding performance can be achieved. The invention further comprises an agitator ball mill agitator for the agitator ball mill described above, the agitator ball mill agitator comprising at least three agitator shafts and a drive, each of the at least three agitator shafts having a central axis, being designed as a screw rotatable about the central axis and being set up for frame-fixed installation in a grinding container , wherein the drive is set up to rotate the at least three agitator shafts about their respective central axes, and the at least three agitator shafts do not touch each other and the central axes of the at least three agitator shafts are aligned parallel to one another and are arranged as side edges of a prism, in particular the drive for each of the at least three agitator shafts can comprise its own drive unit or can comprise a common drive unit for at least two of the at least three agitator shafts and can in particular be set up to include at least one of the at least three To drive agitator shafts at a rotational speed that can be regulated independently of the rotational speeds of the other of the at least three agitator shafts, wherein in particular the agitator ball mill agitator in addition to the at least three agitator shafts can have at least one inner agitator shaft, which each has a central axis arranged parallel to the main direction of the grinding container, as Rotatable screw is formed around the central axis and is set up for a fixed installation in a grinding container, wherein the at least one inner agitator shaft does not touch the at least three agitator shafts and the center axis of the at least one inner agitator shaft is arranged within the prism formed by the center axes of the at least three agitator shafts is, and in particular the drive cannot be connected to the at least one inner agitator shaft or can have a drive unit in order to rotate the at least one inner agitator shaft about its central axis, and i In particular, it can comprise a braking device which is set up to reduce the rotational speed of the at least one inner agitator shaft or to prevent a rotational movement, wherein in particular the outer diameter of each of the at least three agitator shafts can be at most half the maximum inner width of the grinding chamber.

Accordingly, the agitator ball mill agitator comprises at least three agitator shafts and a drive. Each of the at least three agitator shafts has a central axis and is designed as a screw that can be rotated about the central axis. Furthermore, each of the at least three agitator shafts set up for the most posed assembly in a grinding container. The drive is set up to rotate the at least three agitator shafts about their respective central axes. The at least three stirring shafts do not touch one another, and the central axes of the at least three stirring shafts are aligned parallel to one another and are arranged as side edges of a prism.

Optionally, the drive can comprise a separate drive unit for each of the at least three agitator shafts or can comprise a common drive unit for at least two of the at least three agitator shafts. Furthermore, the drive can optionally be set up in particular to drive at least one of the at least three agitator shafts at a rotational speed that can be regulated independently of the rotational speeds of the other of the at least three agitator shafts. Also optionally, the agitator ball mill agitator can have at least one inner agitator shaft in addition to the at least three agitator shafts, each of which has a central axis arranged parallel to the main direction of the grinding container. In this case, the at least one inner agitator shaft is designed as a screw that can be rotated about the central axis and is designed for a fixed installation in a grinding container, whereby it does not touch the at least three agitator shafts; the central axis of the at least one inner stirring shaft is arranged within the prism which is formed by the central axes of the at least three stirring shafts. Furthermore, the drive can optionally have a drive unit in order to rotate the at least one inner agitator shaft about its central axis, or it can not be connected to the at least one inner agitator shaft. Likewise optionally, the drive can also comprise a braking device which is set up to reduce the rotational speed of the at least one inner agitator shaft or to prevent a rotational movement. Finally, the outer diameter of each of the at least three agitator shafts can optionally also be at most half the maximum inner width of the grinding chamber. A corresponding agitator has already been explained in more detail in connection with the description of the agitator ball mill.

Finally, the invention comprises a method for comminuting millbase in an agitator ball mill with a vertically arranged grinding container in wet operation, the method comprising (i) slurrying the millbase to be comminuted in a grinding aid liquid, a millbase dispersion being obtained, (ii) a continuous Introducing the grinding stock dispersion into a lower section of a grinding chamber filled with auxiliary grinding bodies of an agitator ball mill, in particular the agitator ball mill described above, (iii) a continuous vertical conveying of a part of the grinding stock dispersion from the lower section of the grinding chamber into an upper section of the grinding chamber by at least three rotating, positionally mounted vertical stirring shafts which do not touch one another, are at least substantially vertically parallel to one another and whose central axes are arranged as side edges of a prism, a prepared grinding stock dispersion being obtained in which at least part of the grinding stock dispersed in the auxiliary grinding liquid is comminuted, (iv) a continuous removal of part of the prepared grinding stock dispersion from the upper section of the grinding chamber, and (v) a final separation of the comminuted grinding stock from the processed grinding stock dispersion which has been conducted out.

Accordingly, the ground material to be comminuted is first slurried in a grinding aid liquid, a grinding material dispersion being obtained. All suitable liquids can be used as the auxiliary grinding liquid, pure substances, solutions, mixtures and disperse systems, in particular liquids which are chemically inert to the constituent of the ground material to be comminuted; This is not opposed to the fact that the auxiliary grinding liquid can optionally also be used for cleaning and processing the ground material, for example by decomposing any impurities in it or detaching it from the ground material, adsorbing it or otherwise binding it and thus separating it from the ground material.

If the ground material is a mineral raw material, it is often broken rock, which has previously been broken up in a breaking device (e.g. in a rotary crusher) and fed to a separating device for classification (e.g. a sifter or sieve), the broken stone being included the desired particle size is optionally fed to a further pre-comminution, for example a horizontal ball mill or roller mill, before it is finally introduced as grinding stock into a grinding stock dispersion. The slurry can then take place immediately when it is introduced into the grinding chamber of the agitator ball mill or shortly before it, for example in a mixing chamber or a grist dispersion tank. If the grinding of the ground material in the agitator ball mill is preceded by further process steps, such as those for Preparation of the millbase, cleaning or pre-comminution, the slurrying of the millbase in the auxiliary milling liquid can take place in the process before the introduction of the millbase dispersion into the agitator ball mill. Typically, the grinding stock dispersion is subjected to a pre-classification (for example in a centrifugal separator, such as a hydrocyclone) before it is introduced into the agitator ball mill, in order to separate off grinding stock that already has the desired target size. After separation, the grinding stock dispersion with the grinding stock, which already has the desired target size, can be discharged as a product dispersion from the agitator ball mill system and fed to further use.

After slurrying, the grinding stock dispersion (or its coarse fraction) is continuously introduced into the lower section of the grinding chamber of an agitator ball mill. For this purpose, the grinding stock dispersion is typically conveyed by means of pumps upstream of the agitator ball mill through pipelines to the inlet of the grinding container and from there fed into the grinding chamber. The auxiliary grinding bodies are already located in the grinding chamber (together with product dispersion that was fed to the grinding chamber at an earlier point in time and has not yet left it). The auxiliary grinding bodies are often chosen so that they have larger dimensions than the material to be ground. The actual agitator ball mill can have one of the configurations already described in detail above.

In the grinding chamber, as the agitator shafts rotate around their respective central axes, the grinding stock dispersion is continuously conveyed from the lower section of the grinding chamber in the vertical direction into an upper section of the grinding chamber. For this purpose, the at least three agitator shafts are aligned at least substantially vertically parallel to one another and are mounted in such a way that they do not touch one another, the central axes of the at least three agitator shafts being arranged as side edges of a prism. If the at least three agitator shafts are set in a rotary movement around their central axes, part of the grinding stock dispersion is conveyed upwards and is crushed by the auxiliary grinding bodies as a result of the impact and shear stresses that occur. This gives a prepared millbase dispersion in which at least a portion of the millbase dispersed in the auxiliary milling liquid is obtained comminuted (based on the particle size of the originally supplied grist). Above all, those parts of the ground material that already have smaller particle sizes are conveyed upwards; the parts of the ground material with the larger particle sizes, like the auxiliary grinding bodies, remain mainly in the lower part of the grinding chamber. In many agitator ball mills, a pump for the grinding stock dispersion is only provided in the inlet system, whereas the removal of the grinding stock dispersion takes place passively via an overflow system, without another pump being provided in the discharge system. Therefore, the average dwell time of the grist in the grinding chamber can be regulated primarily through the adjustable pump output of the pump in the feed stream.

After passing through the vertical transport path, part of the prepared grinding stock dispersion is continuously passed out of the upper section of the grinding chamber. The discharge (outlet, drain) typically has a sieve device so that the larger auxiliary grinding bodies cannot leave the milling chamber via the discharge, but rather remain in the milling chamber. Alternatively or in addition, the discharge in the grinding chamber can also be arranged above the grinding volume at a sufficient distance from the actual grinding volume (the sub-area of the grinding chamber where the stirring elements of the agitator shaft are arranged and result in a strong mixing of the mixture of grinding stock dispersion and auxiliary grinding bodies), so that the auxiliary grinding bodies Due to their mass, do not leave the grinding chamber via the discharge, but rather remain in the grinding chamber. Since the auxiliary grinding bodies are also subject to wear, new auxiliary grinding bodies can be introduced into the grinding space, for which purpose a separate auxiliary grinding body inlet can be provided in the upper section of the grinding space, for example.

After being discharged from the grinding chamber, the prepared millbase dispersion with the comminuted millbase is then fed to a secondary classification in which the portions of the comminuted millbase that already have the desired target sizes (fines) are separated off in order to be discharged from the agitator ball mill as a product stream. The proportions of the comminuted ground material which do not yet have the desired target sizes, but which are still too large (coarse material), are usually fed back into the grinding chamber. In terms of apparatus, it has proven to be favorable if the pre-classification and the Post-classification can be carried out together: For this purpose, the entire regrind suspension with the crushed regrind is fed directly into a tank, into which the fresh regrind suspension with the not yet crushed regrind is fed. The two millbase suspension streams are mixed with one another there and fed together to the single classifying device (such as the aforementioned hydrocyclone), in which the pre-classification then takes place simultaneously with the post-classification.

The aforementioned process sequence can be supplemented and modified in accordance with the respective framework conditions for the separation task in a manner known to the person skilled in the art, without deviating from the invention, as long as the aforementioned steps (i), (ii), (iii), (iv ) and (v) are implemented, step (iii) being the most important.

The invention is to be described in more detail below with reference to the accompanying drawings of particularly advantageous examples without restricting the general inventive concept on which these examples are based, which also results in further advantages and possible applications. It each show schematically

1 shows different schematic representations of a conventional agitator ball mill, namely FIG. 1a a side sectional view of a conventional agitator ball mill, FIG. 1b a simplified symbolic representation

Side view of a conventional agitator ball mill, FIG. 1c a detailed side view of the agitator shaft of a conventional agitator ball mill and FIG. 1d a simplified horizontal section through a conventional agitator ball mill; FIG. 2 shows schematic representations of agitator ball mills with three agitator shafts, namely FIG. 2a a simplified symbolic side view of a

Agitator ball mill with three agitator shafts and FIG. 2b a simplified horizontal section through an agitator ball mill with three agitator shafts;

3 shows schematic, simplified horizontal sections through agitator ball mills with four agitator shafts which differ with regard to the directions of rotation of the four agitator shafts, namely FIG. 3a for a first embodiment, FIG. 3b for a second embodiment, FIG. 3c for a third embodiment and FIG. 3d for a fourth embodiment; and 4 shows schematic, simplified horizontal sections through agitator ball mills with five outer agitator shafts, namely FIGS. 4a, 4b and 4c, FIG. 4c additionally having an inner agitator shaft.

In Fig. 1 different schematic representations of a conventional agitator ball mill from the prior art and details thereof are shown. In Fig. 1a a conventional agitator ball mill T is shown in a sectional side view. The agitator ball mill T is an agitator ball mill with a vertically aligned screw. The agitator ball mill T has a grinding container 2 ‘, which is arranged vertically, with an interior designed as a grinding chamber 5‘. In the grinding chamber 5 ‘a single agitator shaft 3‘ is arranged, the central axis of which is also oriented vertically as the axis of rotation. At the top, the grinding chamber 5 ‘is covered by a cover on which the drive 4‘ for the individual agitator shaft 3 ‘is located. The drive 4 ‘has for this purpose a drive unit 6‘, which is designed as an electric motor and the top end of the

Agitator ball mill T represents. In addition, the drive has a vertical axis via which the drive unit 6 ‘is operatively connected to the individual agitator shaft 3.. The upper end of the individual agitator shaft 3 ‘is attached to the lower end of the axle by means of a flange connection in such a way that the torque provided by the drive unit 6‘ is transmitted to the individual agitator shaft 3 ‘. The individual agitator shaft 3 ‘is designed as a screw, namely as a screw of a cylindrical basic shape with a filled central area. The screw has two threads 8 ‘, so that this is a two-start screw. The drive 4 ‘and the agitator shaft 3‘ together form the

Agitator ball mill agitator. Near the bottom of the grinding container 2 ', which is designed as a base area, an opening is provided in the side wall of the grinding container 2', which opening forms the inlet 9 'of the grinding chamber 5'. A mixture of grinding stock dispersion and auxiliary grinding bodies (not shown) is continuously fed through this opening to the grinding chamber 5 'during operation. As a result of the rotational movement of the agitator shaft 3 ', the mixture of grinding stock dispersion and auxiliary grinding bodies in the grinding chamber 5' is conveyed in the vertical direction from bottom to top and is exposed to strong shock and shear stresses, with the grinding stock being comminuted. To reduce the wear and tear on the agitator ball mill T, the wall of the grinding chamber 5 'is provided with a grinding chamber lining 1 T made of a high-strength material lined. In its upper area, the grinding container 2 'has a further opening which forms the discharge 10' of the grinding space 5 '. This opening is arranged outside the grinding volume. A sieve is located in front of this opening so that the auxiliary grinding bodies are retained in the grinding chamber 5 'and only the grinding stock dispersion with the at least partially comminuted grinding stock is passed out of the grinding chamber via the discharge 10'.

FIG. 2b shows a simplified symbolic side view of the conventional agitator ball mill 1 'shown in FIG. 1a. In Fig. 1b, for the sake of clarity, many construction elements are omitted, only the agitator ball mill 1 'with the grinding container 2' is shown, in whose interior 5 'there is the individual agitator shaft 3' with the thread 8 ', which via the drive 4' , which is arranged on the grinding container 2 ', is set in a rotational movement. Here, too, the drive 4 ‘and the agitator shaft 3‘ together form the agitator ball mill agitator.

FIG. 1c shows a detailed side view of the agitator shaft 3 'of the conventional agitator ball mill shown in FIG. 1a. The agitator shaft 3 ‘is designed as a two-start screw of a cylindrical basic shape with a filled central area. On the shell side of the central middle area, which holds the central axis of the agitator shaft 3, two threads 8 ‘are arranged, which are provided with an abrasion-resistant coating. At the upper end of the agitator shaft 3 ‘the flange connection is indicated, via which the agitator shaft 3‘ is directly connected to the axis of the drive.

FIG. 1d shows a simplified horizontal section through the conventional agitator ball mill 1 'shown in FIG. 1a. As in FIG. 1b, a simplified representation was chosen here in which, for reasons of clarity, most of the construction elements are not shown, so that essential differences to the present invention can be seen more clearly. 1d shows a horizontal section through the agitator ball mill 1 'on the fleas of the agitator shaft 3'. The agitator 2 ', the interior of which is designed as a grinding chamber 5', has a square cross-section (floor plan). For the single agitator shaft 3 ', the thread is not shown separately in Fig. 1d, only the maximum cross-sectional area is shown, which is from the agitator shaft 3 'is stressed, so the outer edge of the screw of the agitator shaft 3' (so this is not the cross-sectional area of the agitator shaft 3 'itself, but rather the projection of the agitator shaft 3' on the plane of the drawing). Furthermore, the effective diameter of the agitator shaft 3 'is shown as a double arrow and the central axis of the agitator shaft 3' running perpendicular to the plane of the drawing is shown as a cross, the agitator shaft 3 'rotating around this central axis in the direction of rotation (here: clockwise).

2 shows schematic representations of agitator ball mills according to an embodiment of the present invention, the agitator ball mills having three agitator shafts. 2a shows a simplified symbolic side view of such an agitator ball mill with three agitator shafts, the representation being selected analogously to the representation in FIG. 1b, so that many construction elements are not shown for the sake of clarity. In Fig. 2a, the agitator ball mill 1 can be seen with the vertically aligned grinding container 2, in the interior 5 of which there are three agitator shafts 3, each with a thread 8. The agitator shafts 3 are arranged in the form of a triangle, with two agitator shafts 3 being positioned in the same plane and parallel to the plane of the drawing and a further agitating shaft 3 being positioned centrally in front of it in the viewing direction. A drive 4 is arranged on the grinding container 2, by means of which the three agitator shafts 3 are set in rotation about their central axes. The drive 4 here comprises three separate drive units, but instead a common drive unit can also be provided, which is connected to the three agitator shafts 3 via gears, or two drive units, of which one drive unit drives two of the three agitator shafts 3 and the third drive unit drives the third agitator shaft 3 drives. Each drive unit can have its own regulation, but a common regulation can also be provided, which also includes regulation of the rotational speeds of the three agitator shafts. The central axes of the three agitator shafts 3 are aligned parallel to one another and do not touch one another.

FIG. 2b shows a simplified horizontal section through an agitator ball mill according to the embodiment of the present invention described above. As in FIG. 1d, this is a simplified representation in which, for reasons of better clarity, most of the construction elements are not are shown, whereby essential differences to the conventional agitator ball mill shown in Fig. 1d become more clearly recognizable. Accordingly, Fig. 2b is also a horizontal section through an agitator ball mill 1 on the fleas of the three agitator shafts 3. The agitator 2, the interior of which is designed as a grinding chamber 5, has a square cross-section for the sake of better distinguishability, but in principle all other suitable shapes are also possible, for example a circular or oval cross section, a regular or irregular polygonal cross section, for example a triangle, diamond, pentagon, hexagon, heptagon, octagon and the like. For the three agitator shafts 3, the threads are not shown separately in Fig. 2b, but only the maximum cross-sectional areas that are claimed by the agitator shafts 3, i.e. the outer edges of the screws (i.e. a projection of the outer edges of the threads onto the plane of representation). Furthermore, the central axes of the agitator shafts 3, which run perpendicular to the plane of representation, are shown as crosses, around which the agitator shafts 3 rotate in the directions of rotation indicated by simple arrows. In Fig. 2b, all three agitator shafts 3 have the same direction of rotation in the clockwise direction, but all three agitator shafts 3 can also have the same direction of rotation counterclockwise or two of the three agitator shafts have a common direction of rotation and the third an opposite direction of rotation. The central axes of the three agitator shafts 3 are arranged as side edges of a trigonal prism.

Apart from the design of the agitator with three agitator shafts, the other elements of an agitator ball mill 1 according to the invention can basically be chosen similar to the elements of conventional agitator ball mills; possible configurations have already been mentioned in connection with the general description of the invention and with the description of FIG.

Thus, the agitator ball mill can in particular have a horizontally arranged grinding container or a vertically arranged grinding container and be set up for a discontinuous, continuous or quasi-continuous process control in wet operation or in dry operation. The grinding container arranged in the downward direction (vertical or horizontal) can, for example, be formed from individual segments or be designed in one piece. Typically the Grinding chamber has a shape that is derived from that of a cylinder or a polygonal prism, the inner wall of which can have high-strength cladding or coatings made of wear-resistant and wear-resistant materials. A vertically arranged grinding container set up for continuous operation generally has one or more inlets, for example on the base or in the vicinity of the base, whereas an outlet above the inlet can be provided, for example in the upper area of the grinding container. In addition, the grinding container can have further elements, for example a separate feed opening for fresh auxiliary grinding bodies, sieve units for holding back the auxiliary grinding bodies, maintenance openings and the like.

The agitator ball mill agitator comprises the three agitator shafts 3 and the drive 4. The drive has at least one suitable drive unit, such as a motor, and other components such as units for changing the rotational speed, for example frequency converters, or other control units, such as those with control electronics or logic circuits, or machine elements for changing movement variables, for example gearboxes. A separate drive unit can be provided for each agitator axis, but several or even all of the agitator shafts can have a common drive unit, with the different drive units being controlled via a common control system or via separate control systems.

The three agitator shafts each have a central axis which is arranged parallel to the downward direction of the grinding container and around which the agitator shafts are designed to be rotatable without the three agitator shafts touching each other. The agitator shafts are installed in the grinding container and have threads as agitator elements, so that the agitator shafts are designed as screws, for example as axially arranged single-start or multi-start screws, for example as double-start screws, three-start screws or four-start screws, these screws being for example such with a cylindrical basic shape and those with a slightly conical (conical) basic shape, can have a filled central area or a non-filled central area and right-hand screws or left-hand screws with a suitable screw line, screw surface or Helical surface, pitch and pitch angle can be. The screws - especially their thread turn and tip - can also have high-strength linings or coatings made of wear-resistant and wear-resistant materials. As shown in the following explanations, more than three agitator shafts can in principle also be provided (for example four agitator shafts, five agitator shafts or six agitator shafts), the central axes of which then represent the side edges of prisms that have different base areas, for example a triangle, a square, a pentagon, a hexagon or the like. The agitator shafts can be chosen to be the same or different and thus also have different diameters and screw geometries.

When grinding stock in such an agitator ball mill with a vertically arranged grinding container in wet operation, the grinding stock to be comminuted is first slurried in an auxiliary grinding liquid, a grinding stock dispersion being obtained. The grinding stock dispersion is then continuously introduced into a lower section of the grinding chamber of the agitator ball mill described above, which is filled with auxiliary grinding bodies. The resulting mixture of grinding material dispersion and auxiliary grinding bodies is stirred / mixed by the rotational movement of the three vertically mounted stirrer shafts, which do not touch one another and are at least substantially vertically parallel to one another, their central axes being arranged as side edges of a prism, namely a trigonal prism . During the rotational movement, the grinding stock is comminuted and, at the same time, part of the grinding stock dispersion is continuously conveyed from the lower section of the grinding chamber vertically into an upper section of the grinding chamber. The processed grinding stock dispersion obtained in this way, in which at least part of the grinding stock dispersed in the auxiliary grinding liquid has already been comminuted, is finally passed continuously out of the upper section of the grinding chamber. The auxiliary grinding bodies can be separated from the grinding stock dispersion, for example with the aid of a sieve, before it is discharged from the agitator ball mill. Finally, the comminuted millbase is separated from the pulverized millbase dispersion. Possible configurations of such a comminution process have already been mentioned in connection with the general description of the invention. 3 shows schematic, simplified horizontal sections through agitator ball mills according to further embodiments of the present invention, each agitator ball mill shown there having four agitator shafts. Here, too, the form of simplified representations was chosen, each showing horizontal sections through an agitator ball mill 1 at the level of the four agitator shafts 3. In FIGS. 3a, 3b, 3c and 3d each agitated container 2 is shown, the interior of which is designed as a grinding chamber 5 which has a square cross section. For each of the four agitator shafts 3, the threads are not shown separately, but only the outer edges of the screws. The central axes of the agitator shafts 3, which run perpendicular to the plane of representation, are indicated as crosses, around which the agitator shafts 3 rotate in the directions of rotation represented by the simple arrows. The central axes of the four agitator shafts 3 are each arranged as side edges of a prism with a square base. The four partial representations in Fig. 3 differ only in the direction of rotation of the four agitator shafts 3: In Fig. 3a all four agitator shafts 3 have the same direction of rotation (here clockwise), in Fig. 3b three agitator shafts 3 each have the same direction of rotation ( here counterclockwise) and an agitator shaft 3 has a different direction of rotation (here clockwise), in Fig. 3c and Fig. 3d two agitator shafts 3 each have one direction of rotation and the other two agitator shafts 3 have the other direction of rotation, in Fig. 3c, the two agitator shafts 3 with the same direction of rotation are each arranged adjacent to one another, whereas in Fig. 3d adjacent agitator shafts 3 each have different directions of rotation. Apart from the use of four agitator shafts 3 instead of three agitator shafts, the considerations given in connection with FIG. 2 regarding the structural design and any design leeway also apply to the further embodiments shown in FIG. 3; the same applies to the method of crushing regrind.

4 shows schematic, simplified horizontal sections through agitator ball mills according to further embodiments of the present invention, each agitator ball mill having five agitator shafts 3, the central axes of which are arranged as side edges of a prism with a regular pentagonal base. Here, too, the form of simplified representations was chosen, each showing horizontal sections through an agitator ball mill 1 at the level of the agitator shafts 3. In FIGS. 4a, 4b and 4c there are each stirred tank 2 shown, the interior of which is designed as a grinding chamber 5, which has a square cross-section. In Fig. 4a an agitator ball mill 1 is shown, which has only five agitator shafts 3 in a pentagonal arrangement, the agitator ball mills 1 shown in Fig. 4b and 4c also have a sixth agitator shaft, which as an inner agitator shaft 7 in the interior of the five outer agitator shafts 3 spanned pentagon is arranged. For all agitator shafts 3, 7, the threads are not shown separately in FIG. 4, but only the outer borders of the screws. The central axes of the agitator shafts 3, 7, which run perpendicular to the plane of the drawing, are indicated as crosses, around which the agitator shafts 3, 7 rotate in the directions of rotation indicated by simple arrows. The directions of rotation for the five outer agitator shafts 3 in FIGS. 4a, 4b and 4c are each selected to be the same, but these can in principle also be selected to be different. In Fig. 4b the direction of rotation of the inner agitator shaft 7 is different from the directions of rotation of the five outer agitator shafts 3, while in Fig. 4c the direction of rotation of all six agitator shafts 3, 7 is the same. In Fig. 4b and 4c the inner agitator shafts 7 also have diameters which differ from the diameters of the five outer agitator shafts 3 (in Fig. 4b the inner agitator shaft 7 has a smaller diameter than the five outer agitator shafts 3, in Fig. 4c, on the other hand, has a larger diameter. Instead, the inner agitator shaft can of course also have the same diameter as the outer agitator shafts. In principle, more than one inner agitator shaft can be provided in the interior of the prism spanned by the central axes of the outer agitator shafts. Alternatively or additionally, the (at least one ) the inner agitator shaft can be connected to the drive (for example with a separate or a common drive unit) or have no drive, so that it can only be set into rotation passively via the flow movement of the mixture of grinding material dispersion and auxiliary grinding body. Furthermore, the (at least one) inner agitator shaft also has a braking device sen, such as mechanical brake systems, magnetic brake systems, electrical brake systems, fluid brake systems or the like. Apart from that, the considerations given in connection with FIG. 2 regarding the structural design and any design leeway are also valid for the further explanations shown in FIG. 4; the same applies to the method of crushing regrind. List of reference symbols

1 agitator ball mill

V conventional agitator ball mill

2 grinding containers

2 ‘grinding container of a conventional agitator ball mill

3 (outer) agitator shaft

3 ‘(single) agitator shaft of a conventional agitator ball mill

4 drive

4 ‘Drive of a conventional agitator ball mill

5 grinding chamber

5 ‘grinding chamber of a conventional agitator ball mill

6 ‘Drive unit of a conventional agitator ball mill

7 inner agitator shaft

8 thread turn

8 ‘thread of a conventional agitator ball mill

9 ‘inlet

10 ‘discharge

11 ‘Grinding chamber lining X central axis

Claims

Expectations

1. Agitator ball mill (1) comprising a grinding container (2), at least three agitator shafts (3) and a drive (4), the grinding container (2) being arranged in one main direction and having a grinding chamber (5) which is adapted to receive it of ground material and auxiliary grinding bodies, each of the at least three agitator shafts (3) having a central axis (X) arranged parallel to the main direction of the grinding container (2) and designed as a screw mounted in the grinding container (2) and rotatable about the central axis (X) , wherein the drive (4) is set up to rotate the at least three stirring shafts (3) about their respective central axes (X), and wherein the at least three stirring shafts (3) do not touch one another and the central axes (X) of the at least three stirring shafts ( 3) are arranged as side edges of a prism.

2. agitator ball mill (1) according to claim 1, wherein the drive (4) comprises a separate drive unit for each of the at least three agitator shafts (3).

3. agitator ball mill (1) according to claim 1, wherein the drive (4) for at least two of the at least three agitator shafts (3) comprises a common drive unit.

4. agitator ball mill (1) according to any one of claims 1 to 3, wherein the drive (4) is set up to drive at least one agitator shaft of the at least three agitator shafts (3) at a rotational speed that is independent of the rotational speeds of the other agitator shafts of the at least three agitator shafts (3) is adjustable.

5. agitator ball mill (1) according to one of claims 1 to 4, wherein the agitator ball mill (1) in addition to the at least three agitator shafts (3) has at least one inner agitator shaft (7), each of which is arranged parallel to the main direction of the grinding container (2) Has central axis (X) and mounted as placed in the grinding container (2) and rotatable about the central axis (X) Screw is formed, wherein the at least one inner agitator shaft (7) does not touch the at least three agitator shafts (3) and the central axis (X) of the at least one inner agitator shaft (7) within that of the central axes (X) of the at least three agitator shafts (3 ) formed prism is arranged.

6. agitator ball mill (1) according to claim 5, wherein the agitator ball mill (1) comprises a braking device which is designed to reduce the rotational speed or to prevent a rotational movement in the at least one inner agitator shaft (7)

7. agitator ball mill (1) according to one of claims 5 or 6, wherein the at least one inner agitator shaft (7) is not connected to the drive (4).

8. agitator ball mill (1) according to any one of claims 5 or 6, wherein the drive (4) has a drive unit to rotate the at least one inner agitator shaft (7) about its central axis (X).

9. agitator ball mill (1) according to any one of claims 5 to 8, wherein the at least three agitator shafts (3) are adapted for a rotary movement in the same direction of rotation, and wherein the at least one inner agitator shaft (7) for a rotary movement in the direction of rotation at least three agitator shafts (3) are adapted to different directions of rotation.

10. agitator ball mill (1) according to one of claims 1 to 8, wherein the at least three agitator shafts (3) are adapted for a rotary movement in the same direction of rotation.

11. agitator ball mill (1) according to any one of claims 1 to 8, wherein at least one agitator shaft of the at least three agitator shafts (3) is a right-hand screw and at least one agitator shaft of the at least three agitator shafts (3) is a left-hand screw.

12. agitator ball mill (1) according to one of claims 1 to 11, wherein the outer diameter of each of the at least three agitator shafts (3) is at most half the maximum inner width of the grinding chamber (5).

13. Agitator ball mill agitator for an agitator ball mill (1) according to one of claims 1 to 12, the agitator ball mill agitator comprising at least three agitator shafts (3) and a drive (4), each of the at least three agitator shafts (3) having a central axis (X) as The screw is designed to be rotatable about the central axis (X) and is designed for a fixed installation in a grinding container (2), the drive (4) being arranged to rotate the at least three agitator shafts (3) about their respective central axes (X), and wherein the at least three agitator shafts (3) do not touch each other and the central axes (X) of the at least three agitator shafts (3) are aligned parallel to one another and are arranged as side edges of a prism, in particular the drive (4) for each of the at least three agitator shafts ( 3) can comprise its own drive unit or can comprise a common drive unit for at least two of the at least three agitator shafts (3) and in particular can include a drive unit can be icht to drive at least one of the at least three agitator shafts (3) at a rotational speed that can be regulated independently of the rotational speeds of the other of the at least three agitator shafts (3), in particular the agitator ball mill agitator in addition to the at least three agitator shafts (3) at least one inner stirrer shaft (7), each having a central axis (X) arranged parallel to the main direction of the grinding container (2), designed as a screw rotatable about the central axis (X) and designed for frame-fixed installation in a grinding container (2) , the at least one inner stirring shaft (7) not touching the at least three stirring shafts (3) and the central axis (X) of the at least one inner stirring shaft (7) within the prism formed by the central axes (X) of the at least three stirring shafts (3) is arranged, and in particular the drive (4) not be connected to the at least one inner agitator shaft (7) or a drive can have iebsaggregat to rotate the at least one inner agitator shaft (7) about its central axis (X), and in particular can include a braking device which is set up to reduce the speed of rotation of the at least one inner agitator shaft (7) or a Prevent rotational movement, wherein in particular the outer diameter of each of the at least three agitator shafts (3) can be at most half the maximum inner width of the grinding chamber (5).

14. A method for comminuting millbase, the method comprising slurrying the millbase to be comminuted in an auxiliary grinding liquid, whereby a millbase dispersion is obtained, continuously introducing the millbase dispersion into a lower section of a grinding chamber (5) of an agitator ball mill (1) filled with auxiliary milling bodies, in particular an agitator ball mill (1) according to one of claims 1 to 12, continuous vertical conveying of part of the grinding stock dispersion from the lower section of the grinding chamber (5) into an upper section of the grinding chamber (5) by at least three rotating, vertically mounted vertical stirring shafts (3) ), which do not touch one another, are aligned at least essentially vertically parallel to one another and whose central axes (X) are arranged as side edges of a prism, a prepared millbase dispersion being obtained in which at least part of the millbase dispersed in the auxiliary milling liquid is comminuted, a continuous removal of part of the prepared grinding stock dispersion from the upper section of the grinding chamber (5), and - a final separation of the comminuted grinding stock from the processed grinding stock dispersion conducted out.