grinder

Abstract

The present invention relates to a grinding mill (1) having a grinding space (7) containing grinding bodies and an agitator (3) therein surrounding a horizontal axis, the agitator carrying a plurality of grinding discs (8) non-rotatably connected thereto and spaced apart from each other along the horizontal axis, the grinding discs causing the grinding bodies to move, wherein the grinding discs (8) preferably have slits or notches, characterized in that adjacent grinding discs (8) are arranged on the agitator (3) such that the ratio of the length (b) of the grinding chamber to the radial height (a) of the grinding chamber is greater than or equal to 2:3, and such that the radial distance (c) between the outer surface of the grinding discs (8) and the inner wall of the grinding container (2) defining the grinding space (7) is greater than 20% of the radial height (a) of the grinding chamber.

Description

TECHNICAL FIELD

[0001] The invention relates to a stirred mill having a grinding space comprising grinding bodies, a stirring shaft and a plurality of stirring bodies. BACKGROUND

[0002] First of all, the basic principle of a stirred mill, which is also called a ball mill, is explained. In Figure 1 The basic principle of a stirred mill, which is also called a ball mill, is explained. In Figure 1 A stirred mill 1 having a horizontal stirring shaft 3 is shown schematically in Fig. 1. The schematic representation of the grinding bodies, which are usually embodied as steel or ceramic balls, located in the grinding vessel 2 is omitted therein. During operation of the stirred mill 1, the material to be ground is pumped via an inlet 5 of the stirred mill 1 into or through a grinding space 7, which is surrounded by the grinding vessel 2. The material to be ground is usually a suspension consisting of water and solid substances.

[0003] By the rotational movement of the stirring shaft 3, the stirring bodies 8, which are also called grinding discs, are brought into a rotational state, which are connected non-rotatably to the stirring shaft 3. In addition, a sleeve-like stirring shaft bushing 12, which serves as a spacer for the stirring bodies 8 and as a protection for the stirring shaft 3, is usually mounted on the stirring shaft 3, in particular between the stirring bodies 8, which is not explicitly shown in the figures.

[0004] For generating the rotational movement, the stirring shaft 3 is driven, for example, via a belt drive 10 by an electric motor 9. Herein, the drive of the stirred mill 1 is mostly located in a housing 11, which adjoins the grinding vessel 2.

[0005] By the rotation of the stirring bodies 8, the grinding bodies located in the grinding space 7 in the vicinity of the stirring bodies 8 are moved in the direction of the grinding vessel 2. The moving grinding bodies flow back again in the intermediate region between every two stirring bodies 8 from the grinding vessel 2 in the direction of the stirring shaft 3. A circulating movement of the grinding bodies is thus generated between every two stirring bodies 8.

[0006] By the movement of the grinding bodies, collisions between the solid substances in the grinding material suspension pumped through the grinding space 7 and the grinding bodies are caused. This collision leads to the fact that fine particles are broken off the solid substances in the grinding material suspension, so that the solid substances reaching the outlet 6 of the stirred mill 1 are ultimately significantly smaller than the solid substances introduced at the inlet 5.

[0007] In order to ensure that the grinding bodies do not leave the grinding space 7, a separation system 4 in the form of a screen or filter, for example, is also installed before the outlet 6.

[0008] In practice, variations in the size of the stirring bodies and / or their relative position to each other are known, the aim of which is to improve the effectiveness of the stirred mill.

[0009] Therefore, in patent EP 2 178 643 B1, a grinding pan is proposed which is inclined at an angle of 30° to 60° with respect to the axis of the stirring shaft and is therefore not approximately perpendicular to the axis of the stirring shaft. Therefore, the circulating movement of the grinding bodies needs to be improved.

[0010] Furthermore, in patent DE 34 34 155 A1, it is proposed to extend the grinding pan such that it has a minimum radial spacing to the inner wall of the grinding container, whereby this radial spacing is smaller than the diameter of the grinding bodies used. It is therefore primarily to be prevented that individual grinding bodies can move between a plurality of intermediate regions which are formed between two grinding pans, respectively.

[0011] However, the aforementioned proposals do not achieve the desired degree of utility increase. Therefore, on the one hand, the circulating movement of the grinding bodies needs to be improved. On the other hand, the effective grinding space which is not occupied by the components needs to be reduced by a structural change of the grinding pan. This leads to the fact that only less of the material to be ground can be ground simultaneously in the grinding space, which tends to impair the effectiveness of the attrition mill. SUMMARY

[0012] Against this background, it is an object of the present application to provide a device which further increases the effectiveness of an attrition mill.

[0013] According to the application, an attrition mill of the known type is proposed, which has a grinding space containing grinding bodies and a stirring shaft which is arranged in the grinding space about a horizontal axis. The stirring shaft carries a plurality of grinding pans which are connected to it in a rotationally fixed manner and are spaced apart from one another in the direction of the horizontal axis. The grinding pans can be configured in one piece or in multiple pieces. The grinding pans cause a movement of the grinding bodies. In order to be as efficient as possible, the grinding pans generally have recesses and / or continuous slits or notches, respectively. According to the application, it is proposed that adjacent grinding pans are arranged on the stirring shaft such that the ratio of the grinding chamber length b measured in the axial direction along the so-called horizontal axis to the radial grinding chamber height a is greater than or equal to 2:3. This technical measure is based on the knowledge gained from system simulations, which have repeatedly shown that too many grinding pans per axial length unit and too small a spacing between the pans result in a more severe reduction of the grinding body fluctuations than intended in the solutions so far.

[0014] The inventive technical measure works in combination with other technical measures, such that the radial spacing c between the outer side of the grinding pan and the inner wall of the grinding container which delimits the grinding space is greater than 20% of the radial grinding chamber height a. If the grinding pan is not a complete cylinder along its circumferential side, for example because the grinding pan has recesses, slits or notches, the ratio is maintained along a large part of the circumference and ideally along substantially the entire circumference or along the entire circumference.

[0015] Systematic dimensional testing has revealed that the ratio of grinding chamber length *b* to grinding chamber height *a* is greater than or equal to 2:3, and that the increased spacing between the two grinding discs, compared to conventional agitators, results in a surprisingly significant amplification of grinding volume fluctuations within the gap between the discs. The increased volume of the grinding chamber between two adjacent discs is certainly one reason for this result. However, this is not the only contributing factor. The effect occurs precisely when there is interaction between the grinding disc's end-side configuration via grooves, gaps, or notches, and the significantly increased radial spacing between the grinding discs and the inner surface of the grinding container.

[0016] The latter results in a gradual increase in grinding body undulation on the grinding discs, which intensifies the grinding body undulation within the gap between the discs. Simultaneously, due to increased friction between the grinding body, the inner surface of the grinding space, and the grinding discs, the grinding body is further propelled circumferentially before tipping over and falling back into the intermediate region between the two grinding discs defining the grinding chamber. This produces a synergistic effect: better grinding body mobility is achieved within the enlarged grinding chamber between the two discs, forcing the grinding body's motion to be intensified, allowing the grinding body to truly utilize the newly acquired degrees of freedom within the grinding chamber.

[0017] Another synergistic improvement is achieved when the grinding discs have grooves, slits, and / or notches. This results in a further improved carrying effect for the grinding body in the circumferential direction. However, in some cases, the grinding body also receives additional pulses in a direction parallel to the rotation axis of the stirring shaft when passing through grooves, slits, or notches. As a result, the grinding body moves again toward the middle of the grinding chamber defined by the two grinding discs, which, overall, enhances the circulation within the grinding chamber by being transverse to or inclined to the direction of rotation.

[0018] In this case, the grinding chamber height 'a' is a measure between the inner wall of the grinding container that defines the grinding space 7 and the maximum envelope diameter of the stirring shaft or the stirring shaft bushing that may be mounted on the stirring shaft.

[0019] The grinding chamber length b is a measure of the distance between two adjacent grinding discs, where the distance is between the edges pointing towards and thus opening the grinding chamber.

[0020] There are a number of possibilities for designing the invention to further improve its effectiveness or usability. Attached Figure Description

[0021] Figure 1 The schematic diagram illustrates the construction and connections of a typical agitator.

[0022] Figure 2A first variant of the agitator is shown, which has the indicated grinding chamber height a, grinding chamber length b, and radial spacing c.

[0023] Figure 3 A second variant of the agitator according to the invention is shown, having the indicated grinding chamber height a, grinding chamber length b, and radial spacing c.

[0024] Figure 4 The schematic illustration shows one option for the shape of the rotor disc, which demarcates the various grinding chambers 14 of the grinding space 7 from the separation system 4.

[0025] Preferred Implementation

[0026] Figure 2 A first variant of the agitator 1 with a stirring shaft bushing 12 is shown, which is indicated here only by the unemphasized and therefore dotted term "dummy bushing". The grinding container 2, stirring shaft 3, separation system 4, inlet 5, outlet 6, grinding disc 8, and horizontal axis 13 of the stirring shaft are also visible. The grinding space 7 refers to the entire space inside the grinding container occupied by the material to be ground. However, in this case, the grinding chamber 14 is a subcategory of the grinding space and is indicated by dashed lines.

[0027] In addition, the grinding chamber height a, grinding chamber length b, and radial spacing c are also shown.

[0028] according to Figure 2 It is clearly visible that a rotor disc 15 is formed on the end of the stirring shaft facing the separation system 4, which demarcates the actual grinding space from the separation system. For this purpose, the rotor disc 15 is provided with rotor rods 16 that extend generally in a finger-like manner and are spaced apart from each other in the circumferential direction, forming gaps between them. The rotor rods 16 span the separation system 4 and generally form a cavity that accommodates the separation system 4. The rotor disc 15 can be advantageously slotted into the slot region 17 radially below the rotor rod, i.e., if necessary, also having axially permeable notches radially below the rotor rod 16, extending directly into the actual shaft. The shape of the rotor disc with rotor rods 16 is schematically illustrated by... Figure 2 As shown. This design makes a significant further contribution to improving the motion of the grinding media.

[0029] In all cases, it is advantageous that the rotor disc 15 has a smaller diameter than the grinding disc 8 or the hypothetical rotating body composed of the units that form the grinding disc (such as blades).

[0030] Figure 3A second variant of the mill 1 is shown. A quadrilateral stirring shaft bushing 12 is used. The shape of the grinding disc can also be seen on the left side of the sectional view. The rest of the mill's construction corresponds to that of the first variant.

[0031] In addition, the figure also shows the grinding chamber height a, grinding chamber length b, and radial spacing c.

[0032] It is clearly visible that each grinding disc consists of multiple blades arranged sequentially along the circumferential direction within the range of rotational motion. These blades are separated from each other circumferentially by continuous gaps. This is coordinated with the dimensions of the grinding body, because the gap size, the dimensions of the grinding body, and the radial clearance between the grinding disc and the inner wall or circumferential surface of the grinding container must be selected so that the grinding body remains movable despite friction and self-locking forces and does not lock the blades.

[0033] List of reference numerals

[0034] 1. Grinding machine

[0035] 2. Grinding container

[0036] 3. Stirring shaft

[0037] 4. Separation System

[0038] 5 entrances

[0039] 6 Exports

[0040] 7. Grinding space

[0041] 8. Mixing block or grinding disc

[0042] 9 Electric motors

[0043] 10. Belt drive mechanism

[0044] 11. Driver Housing

[0045] 12. Stirring shaft bushing

[0046] 13. Horizontal axis of the stirring shaft

[0047] 14 Grinding chamber

[0048] 15 rotor discs

[0049] 16 Rotor rod

[0050] 17. Gap area (axial gap)

[0051] a. Length of the grinding chamber along the longitudinal axis

[0052] b. Radial grinding chamber height

[0053] c. Radial spacing

Claims

1. A stirred mill (1) having a grinding space (7) comprising grinding bodies; a stirring shaft (3) oriented in the direction of the horizontal axis, which is rotatably mounted in the grinding space (7); a plurality of grinding discs (8) non-rotatably connected with the stirring shaft (3) and spaced apart from each other in the direction of the horizontal axis, wherein the grinding discs (8) each having: a plurality of slits or circumferential notches arranged to create a controlled grinding body flow pattern; a radial spacing (c) between the outer side of each grinding disc (8) and the inner wall of the grinding vessel (2) defining the grinding space (7) is greater than 20% of the radial grinding chamber height (a); a separation system (4) located at the axial end of the grinding space (7), wherein the separation system (4) has: a rotor disc (15) coaxially mounted on the stirring shaft (3); a plurality of rotor bars (16) extending radially or obliquely from the rotor disc (15), wherein the rotor bars (16) are spaced apart from each other to form a flow gap for separating ground particles from grinding bodies; wherein the ratio of the axial grinding chamber length (b) to the radial grinding chamber height (a) is greater than or equal to 2:3; and wherein the grinding discs (8) and the structure for flow guidance are arranged to enhance the uniformity of particle dispersion and reduce energy consumption.

2. The attrition mill (1) according to claim 1, characterized in that The slits and / or notches are arranged in a helical or staggered pattern to cause a helical flow of grinding bodies.

3. The attrition mill (1) according to claim 1, characterized in that, The separation system (4) is integrated into the flow path of the grinding bodies to enable continuous separation during operation.

4. The attrition mill (1) according to claim 3, characterized in that The rotor bars (16) are arranged as a filter structure having a defined cut-off size for particle separation.

5. A stirred mill (1) according to claim 3 or 4, characterized in that, The rotor disc (15) and the rotor bars (16) are configured to create a centrifugal flow to improve separation efficiency.

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