Roller Mill Having Grinding Rollers Set At An Angle

Abstract

A roller mill, having a grinding table and grinding rollers, wherein the grinding table is rotatable relative to the grinding rollers about a center axis of the grinding table in a grinding table rotation direction, such that the grinding rollers roll on a grinding track of the grinding table about a roller rotation axis. At least one of the grinding rollers is rotated to be set at a set angle in the direction of the grinding table rotation direction, such that the roller rotation axis extends at a radial distance from the center axis of the grinding table. The set angle is between 1 degree and 9 degrees. A method for operating a roller mill, and the use of a roller mill for comminuting particulate bulk material are also disclosed.

Claims

1. A roller mill (1), comprising: a grinding table (2) and grinding rollers (3); wherein the grinding table (2) is rotatable relative to the grinding rollers about a center axis (100) of the grinding table (2) in a grinding table rotation direction (200), such that the grinding rollers (3) roll on a grinding track (9) of the grinding table (2) about a roller rotation axis (300); wherein at least one of the grinding rollers (3) is oriented at a set angle (500) in the direction of the grinding table rotation direction (200), such that the roller rotation axis (300) of the at least one grinding roller (3) extends at a radial distance (600) from the center axis (100) of the grinding table (2); wherein the set angle (500) is between 1 degree and 9 degrees.

2. The roller mill according to claim 1, wherein the set angle (500) is between 1 degree and 4.5 degrees.

3. The roller mill according to claim 1, wherein the at least one grinding roller (3) is of a cylindrical shape in a contact region with the grinding track (9).

4. The roller mill according to claim 1, wherein a ratio of a diameter of the at least one grinding roller (3) to a width of the grinding roller is 1.5 to 6.

5. The roller mill according to claim 1, wherein a ratio between the radial distance from the center axis (100) of the grinding table (2) to an axial center of the at least one grinding roller (3) and a width of the at least one grinding roller (3) is between 1.5 and 6.

6. The roller mill according to claim 1, wherein a ratio between the radial distance from the center axis (100) of the grinding table (2) to an axial center of the at least one grinding roller (3) and a diameter of the at least one grinding roller (3) is between 0.5 and 1.5.

7. The roller mill according to claim 1, wherein the grinding track (9) is formed by a plane region of the grinding table (2).

8. The roller mill according to claim 1, wherein the at least one grinding roller (3) is rotatable about its axially central contact point on the grinding track (9).

9. The roller mill according to claim 1, wherein the grinding rollers (3) comprise at least two grinding rollers (3) and only a subset of the at least two grinding rollers (3) is oriented at a set angle (500) in the direction of the grinding table rotation direction (200), such that the roller rotation axis (300) of each grinding roller (3) of the subset extends at a radial distance (600) from the center axis (100) of the grinding table (2).

10. The roller mill according to claim 1, wherein the roller rotation axis (300) of the at least one grinding roller (3) is orthogonal to the rotation axis (100) of the grinding table (2) and/or parallel to a surface of the grinding table (2).

11. The roller mill according to claim 1, wherein the roller rotation axis (300) of the at least one grinding roller (3) is inclined at an angle of 0.5 degree to 20 degrees with respect to a surface of the grinding table (2).

12. The roller mill according to claim 1, further comprising a rocker arm (5), wherein the rocker arm (5) is pivotally mounted about a bearing axis (400), wherein the at least one grinding roller (3) is rotatably mounted to the rocker arm (5) about the roller rotation axis (300), and wherein the bearing axis (400) of the rocker arm (5) is parallel to the roller rotation axis (300).

13. The roller mill according to claim 12, wherein the rocker arm (5) is mounted radially outside the grinding table (2) to a bracket (6) so as to be pivotable about the bearing axis (400), wherein the bracket (6) is mounted to a base.

14. A method for operating a roller mill (1) according to claim 1, wherein the grinding table (2) is rotated at a rotational speed such that on the grinding table (2) in a radial center of the grinding track (9), a radial acceleration of at least 1 g acts on grinding stock, wherein g is the normal gravity acceleration of 9.81 m/s{circumflex over ( )}2.

15. The method according to claim 14, wherein the radial acceleration is at least 1.3 g, advantageously at least 1.4 g.

16. A method for operating a roller mill (1), comprising: rolling grinding rollers (3) on a grinding table (2), wherein a slippage speed in a transverse direction is constant between the grinding table (2) and at least one of the grinding rollers (3) over at least one contact region in a width of the at least one grinding roller (3).

17. The method according to claim 16, further comprising transporting grinding stock (3) in a direction of an interior of the grinding table (2) due to the slippage speed in the transverse direction of the at least one grinding.

18. A method for using a roller mill (1) for comminuting particulate bulk material, wherein due to a set angle of at least one grinding roller (3) in a rotation direction (200) of a grinding table, vibrations of the roller mill (1) are reduced compared to a state of the roller mill (1) with grinding rollers (3) not set at the set angle.

Description

[0033] The invention will be further illustrated below with reference to exemplary embodiments which are represented in the following figures. In the drawings:

[0034] FIG. 1 shows a perspective view of a roller mill in accordance with one embodiment of the present invention;

[0035] FIG. 2 shows a plan view onto of a roller mill according to an embodiment of the invention;

[0036] FIG. 3 shows a schematic view of the grinding table and the grinding roller of a roller mill according to an embodiment of the invention with a representation of the slippage speed in the circulation direction of the grinding table; and

[0037] FIG. 4 shows a schematic view of the grinding table and the grinding roller of a roller mill according to an embodiment of the invention with a representation of the slippage speed in the radial direction of the grinding table.

[0038] In FIG. 1, a roller mill according to an exemplary embodiment of the invention is shown. The roller mill has a grinding table 2 and four grinding rollers 3. The grinding table 2 is driven about its center axis 100 in a grinding table rotation direction 200. For this, at least one grinding table drive 4 is provided. The grinding roller 3 is mounted in a rocker arm 5 about a roller rotation axis 300. The rocker arm 5 is mounted in a bracket 6 so as to pivot about a bearing axis 400. The bracket 6 is directly attached to the base. Furthermore, hydraulic cylinders 7 can be provided which are connected, spaced apart from the bearing axis 400, with the rocker arm 5 and can apply a force onto the rocker arm 5 starting from the base. This can serve to deflect the grinding rollers 3 from the engagement with the grinding table 2, or to adjust the normal force between the respective grinding roller 3 and the grinding table 2.

[0039] In the inner region of the grinding table 2, particulate bulk material is introduced which then moves radially outwards on the grinding table 2, so that it is ground between the grinding rollers 3 and the grinding table 2. Then, the ground bulk material is subjected to an air flow through a nozzle ring 8 disposed radially outside the grinding table. The air flow supplies the ground bulk material to a non-depicted classifier, which can return coarse components back to the grinding table 2 and discharges sufficiently fine particulates from the roller mill 1.

[0040] In FIG. 2, a plan view onto the grinding table 2, the grinding rollers 3, and their mounting is represented. The grinding rollers 3 are represented in dashed lines in their arrangement without set angles, and in solid lines in their set angle arrangement. Here, the grinding rollers are rotated to be set at a set angle 500 in the direction of the grinding table rotation direction 200. Thereby, the roller rotation axis 300 extends at a radial distance 600 from the center axis 100 of the grinding table 2. The grinding rollers 3 form a grinding gap in the region of a grinding track 9 in which particulate bulk material lying on the grinding table 2 is ground by means of normal and shearing forces.

[0041] The axial center of the grinding rollers 3 is at a radial distance 700 from the center axis 100 of the grinding table 2. The axial center of the grinding roller 3 in particular also defines the radial center of the grinding track 9. According to FIG. 2, the set angles are achieved by a rotating of the grinding roller 3 about the axial central contact point of the grinding roller 3 on the grinding table 2. For this, a guide having the shape of a graduated circle can be provided in particular in the bracket 6 by which the rocker arm 5 can be moved with respect to the bracket 6. As an alternative or in addition, the set angles can be achieved by linearly moving the grinding roller 3, in particular in its radial direction. Thereby, however, the position of the axial central contact point of the grinding roller 3 with respect to the grinding table 2 is changed.

[0042] In FIG. 3 and FIG. 4, the slippage between a grinding roller 3 at a set angle and the grinding table 2 is represented. As can be taken from FIG. 3, the speed of the grinding table in the circumferential direction is calculated as a linear function in response to the radius. The speed of the cylindrical grinding roller 3 mounted in parallel to the grinding table 2 and orthogonally to its center axis 100, however, is equal along its axial extension. Consequently, the grinding roller 3 only driven by the grinding table 2 runs faster at its radially inner end with respect to the grinding table than the corresponding region of the grinding track 9. In its radially outer region 11 with respect to the grinding table 2, the grinding roller 3 runs slower than the grinding table 2. This causes slippage between the grinding roller 3 and the grinding table 2, which respectively leads to shearing forces that could serve the grinding operation. By the rotated arrangement at the set angle 500 in the direction of the grinding table rotation direction 200, according to the above illustrated geometry and arrangement, a constant slippage 900 is caused in the radial direction of the grinding table 2, wherein the slippage speed is constant along the total axial extension of the grinding roller 3, that means over the total contact region in the width of the grinding roller 3. Thereby, shearing forces are generated which act to the inside in the radial direction of the grinding table 2 and thus counteract the centrifugal force acting on the particulate bulk material rotating with the grinding table 2. This allows to achieve an improved grinding of the bulk material, where in particular less vibrations are generated than by set angles not designed according to the invention. By the uniform grinding, more grinding stock can pass the classifier, whereby the proportion of grinding stock that has to be reground is reduced, so that altogether an increase of the capacity of the roller mill is achieved.

[0043] In one embodiment of the method according to the invention, the above illustrated roller mill 1 is operated by rotating the grinding table 2, so that the grinding rollers 3 roll thereon, wherein by set angles of the grinding rollers 3, a constant slippage speed 900 is achieved in the transverse direction or axial direction of the grinding rollers 3. In particular, by the slippage speed 900, grinding stock is transported in the direction of the radial interior of the grinding table 3 or counteracts the centrifugal force in some regions, so that a better grinding effect is permitted. Thus, the roller mill can be used for reducing the vibrations in the roller mill by the set angles, and wherein simultaneously, an improved grinding result is generated.