Roller mill with inclined grinding rollers

Description

[0001] The present invention relates to a roller mill, a method for operating a roller mill and the use of a roller mill for crushing particulate bulk material.

[0002] In the prior art, roller mills with a grinding plate and grinding rollers are known, wherein the grinding rollers may be twisted by a set angle. For example, EP 2 252 403 B1 discloses that when one of several drives of a grinding plate is deactivated, one or more grinding rollers are disengaged from the grinding plate, and the remaining grinding rollers are set to set to further reduce the radial force. In particular, the prior art teaches setting rollers to the opposite direction of rotation of the grinding plate, for example in US 1,661,297 or DE 32 40 931 A1.

[0003] Furthermore, prior art often describes quite large angles of rotation, for example in DE 10 2007 009 723 A1, DE 10 2008 039 541 A1, or CN 105 080 665 A. According to CN 105 080 665 A, the angle of rotation generates a frictional force towards the edge of the grinding disc; the grinding roller is thus rotated by an angle opposite to the direction of rotation of the grinding disc. JP 11 156 220 A discloses an angle of rotation range from 3 degrees opposite to 0.7 degrees in the direction of rotation of the grinding disc. It is explained that for angles of rotation exceeding 3 degrees opposite to the direction of rotation of the grinding disc, the motor torque would be too high. Angles of rotation exceeding 0.7 degrees in the direction of rotation of the grinding disc are discouraged, as vibrations are then to be expected.

[0004] The object of the present invention is to provide a roller mill, as well as a method and a use for operating roller mills, which enable a more uniform grinding result and an increased grinding performance without significantly increasing wear.

[0005] The invention provides a roller mill with a grinding plate and grinding rollers, wherein the grinding plate is rotatable relative to the grinding rollers about a central axis of the grinding plate in a grinding plate rotation direction, so that the grinding rollers roll on a grinding track of the grinding plate about a roller rotation axis. At least one of the grinding rollers is rotated by a set angle in the direction of rotation of the grinding plate, such that the roller rotation axis is at a radial distance from the central axis of the grinding plate. According to the invention, the set angle is between 1 degree and 9 degrees.

[0006] In one embodiment, the angle of rotation lies between 1 degree and 4.5 degrees.

[0007] In preferred embodiments, the angle of rotation is between 1 and 3 degrees, between 1 and 2 degrees, between 2 and 3 degrees, between 2.5 and 3.5 degrees, between 3 and 4.5 degrees, between 2 and 9 degrees, between 3 and 8 degrees, or between 4 and 7 degrees. Angles of rotation greater than 9 degrees, and particularly greater than 4.5 degrees, can lead to an unnecessarily high drive torque of the at least one drive of the grinding plate without improving the grinding result.

[0008] The roller mill is specifically designed to grind material in the form of particulate bulk material. This particulate bulk material includes, in particular, ground rock material such as limestone, gypsum, coal, or claystone; mineral bulk material such as cement or cement raw materials; or recycled bulk material such as recycled gypsum concrete slab material, blast furnace slag, flue gas desulfurization gypsum, or fly ash.

[0009] A set angle in the area according to the invention for rotating the grinding roller in the direction of rotation of the grinding disc increases the shear forces between the grinding roller and the grinding disc, since relative velocities, i.e., slippage, now also occur between the grinding roller and the grinding disc in the radial direction. These shear forces generate additional friction, which in turn creates damping and thus reduces vibrations. This enables the formation of a uniform grinding bed thickness, and in particular prevents the grinding bed from becoming too thin in certain areas. This also reduces the wear of the grinding rollers and the grinding disc. The set angle according to the invention allows the roller mill to run more smoothly, meaning that fewer fluctuating normal forces act between the grinding disc and the grinding rollers, thus enabling a more uniform and efficient grinding process.The normal force is the force that acts in the normal direction to the surface of the grinding track from the grinding roller onto the grinding plate.

[0010] The material being ground is broken down in the roller mill, but the grinding pressure can compress it back into agglomerates, which, due to their size, are then returned to the grinding process or the grinding plate via the classifier. The additional shear forces resulting from the offset design prevent the formation of agglomerates. These shear forces break up larger components in the material being ground, especially agglomerates and / or flakes, allowing their individual particles to leave the grinding area more quickly via the classifier. In particular, the offset design causes shear forces to act in the radially inward direction of the grinding plate, resulting in a more thorough grinding process.

[0011] The ground particles are captured radially outside the grinding plate by an airflow and conveyed to a classifier. In the classifier, fines that have already reached the desired particle size are separated and removed, while coarser material that requires re-grinding is returned to the grinding plate. However, agglomerates are also returned to the grinding plate due to their size. The classifier according to the invention can at least reduce the formation of agglomerates and prevent further re-grinding. Overall, this increases grinding efficiency.

[0012] In particular, the roller mill is designed so that the grinding plate can only be driven in the direction of rotation relative to the grinding rollers. This can be achieved, for example, by a drive gearbox designed solely for operation in the direction of rotation of the grinding plate. Alternatively or additionally, an electronic control system is provided, which is configured to control at least one drive of the grinding plate only in such a way that the grinding plate rotates in its intended direction of rotation. This prevents the roller mill from being operated against the intended direction of rotation of the grinding plate, which would have a negative impact on the grinding result.

[0013] In one embodiment, the grinding roller is cylindrically shaped in the contact area with the grinding track. In particular, the grinding track is then correspondingly flat. The cylindrical shape makes it possible, in particular, to generate shear forces in the circumferential direction of the grinding disc between the grinding disc and the grinding roller. Furthermore, the flat grinding area between a cylindrical grinding roller and the flat grinding track is advantageous with regard to the transport of the material being ground on the grinding disc. In particular, the cylindrical shape of the grinding roller can enable a constant slip velocity in the transverse direction of the grinding roller.

[0014] Advantageously, the grinding roller is cylindrically shaped at least over 70%, advantageously 80%, or even advantageously 90% of its axial extension and may only be provided with rounded edges in its axial edge regions.

[0015] The ratio of the grinding roller's diameter to its width is advantageously 1.5 to 6; in preferred embodiments, the ratio can be 2 to 5, 3 to 5, 3.5 to 5, or 2 to 4; and in even more preferred embodiments, 3 to 4. The grinding roller thus has a relatively large diameter relative to its width, making it a comparatively narrow grinding roller. This allows, in particular, a high local grinding pressure or a high specific surface pressure to be applied, while preventing the generation of vibrations or excessive drive torque.

[0016] In preferred embodiments, the ratio between the radial distance from the central axis of the grinding plate to the axial center of the grinding roller and the width of the grinding roller is between 1.5 and 6. In other embodiments, this ratio can also be between 1.5 and 5. In further preferred embodiments, the ratio is between 1.75 and 5 or 3.5 and 5. These ratios particularly allow for relatively small grinding rollers with respect to fairly large grinding plate diameters, which, in combination with the offset according to the invention, can provide an advantageous grinding result without increasing vibrations. In particular, the specific energy requirement, i.e., drive energy (kWh) per mass (kg), can be reduced. This is due, among other things, to the fact that energy input for breaking up agglomerates, for unnecessary over-grinding, for elastic deformation, and / or for vibrations can be avoided.

[0017] Preferably, the ratio between the radial distance from the central axis of the grinding plate to the axial center of the grinding roller and the diameter of the grinding roller is between 0.5 and 1.5. In other embodiments, this ratio can also be between 0.6 and 1.3.

[0018] Advantageously, the grinding path is formed by a flat area of ​​the grinding plate; in particular, the areas of the grinding plate adjacent to the grinding path radially inside and radially outside are also flat. In particular, the entire grinding plate can be flat. The flat area allows for advantageous transport of the material to be ground through the grinding gap between the grinding roller and the grinding plate. In particular, advantageous transport of the material to be ground towards the interior of the grinding plate can be achieved by combining this with the angles of rotation according to the invention.

[0019] In one embodiment, the grinding roller is rotatable about an axially central contact point on the grinding track. This has the advantage that a twist can be achieved without having to change the contact point of the grinding roller. This keeps the introduction of the normal force between the grinding roller and the grinding disc at the same location, which can be advantageous with regard to the mounting of the grinding disc. Alternatively, it is also possible to linearly displace the grinding roller in a direction deviating from the radial direction of the grinding disc, in particular in a direction orthogonal to the radial direction of the grinding disc. This also achieves a twist of the grinding roller. The rotatability of the grinding roller can be achieved, in particular, by a circular segment-shaped guide. Linear adjustment can be achieved, in particular, by a linear guide. The guides can, in particular, be designed as guide slots.In particular, fastening can be achieved by friction or form-fitting using screws.

[0020] In one embodiment, several grinding rollers are provided, with only a subgroup of the grinding rollers being offset. In particular, all grinding rollers in the subgroup are rotated by the offset angle in the direction of rotation of the grinding plate. If only a subgroup of the grinding rollers is offset, then non-offset grinding rollers are also in contact with the grinding plate. In another embodiment, all grinding rollers can also be rotated by the offset angle in the direction of rotation of the grinding plate.

[0021] In one embodiment, the roller's axis of rotation is parallel to the surface of the grinding plate. In particular, the roller's axis of rotation can be orthogonal to the axis of rotation of the grinding plate. In particular, the axis of rotation of the grinding plate is vertical. In particular, the roller's axis of rotation is horizontal. The orthogonality of the roller's axis of rotation to the axis of rotation of the grinding plate ensures that slippage occurs relative to the grinding plate in the circumferential direction of the grinding roller, starting from the axial center of the grinding roller. Shear forces act in the radially outer region of the grinding path opposite to the direction of rotation of the grinding plate, and in the radially inner region of the grinding path in the direction of rotation of the grinding plate.

[0022] In an alternative embodiment, the axis of rotation of the grinding roller can be inclined at an angle of 0.5 degrees to 20 degrees to the surface of the grinding plate. In particular, the axis of rotation of the grinding roller is inclined at an angle of 0.5 degrees to 10 degrees or 10 degrees to 18 degrees, advantageously 12 degrees to 15 degrees, relative to the surface of the grinding plate. This inclination of the axis of rotation can be combined, in particular, with conically shaped rollers. Additionally or alternatively, the grinding track can also be inclined relative to the radial direction of the grinding plate. By influencing the axis of rotation, especially in combination with conical rollers and / or an inclined grinding track, the slippage, and thus the shear forces, between the grinding rollers and the grinding track can be controlled.In particular, it is possible to eliminate circumferential slippage between the grinding roller and the grinding track, allowing only the radial slippage generated by the angle of rotation of the grinding plate. This can achieve a particularly uniform grinding result in some applications. Specifically, the axis of rotation of the grinding roller is inclined such that, without the angle of rotation, it would intersect a radial vector originating from the grinding track at the axis of rotation of the grinding plate.

[0023] In one embodiment, a rocker arm is provided, wherein the rocker arm is pivotably mounted about a bearing axis. The grinding roller is rotatably mounted in the rocker arm about the roller's axis of rotation, with the bearing axis of the rocker arm advantageously being parallel to the roller's axis of rotation. This achieves height compensation of the grinding roller for varying material thicknesses, whereby the roller's axis of rotation is shifted parallel to the rocker arm. Thus, the grinding gap can remain parallel, and only its thickness can be changed. This allows for a uniform grinding result.

[0024] In one embodiment, the rocker arm is mounted radially outside the grinding plate in a bracket which is supported in the foundation. Thus, the forces acting on the grinding roller can be transferred directly into the foundation via the rocker arm.

[0025] The invention further provides a method for operating a previously described roller mill, wherein the grinding plate is rotated at a rotational speed such that a radial acceleration of at least 1 g acts radially outwards on the material being ground in the region of the radial center of the grinding path. g is the acceleration due to gravity of 9.81 m / s² (9.81 meters per second squared).

[0026] In further embodiments of the method, the grinding plate is rotated at a rotational speed such that a radial acceleration of at least 1.1 g or at least 1.2 g acts on the material being ground in the area of ​​the radial center of the grinding path.

[0027] In advantageous embodiments of the method, the grinding plate is rotated at a rotational speed such that a radial acceleration of at least 1.3 g, at least 1.4 g or at least 1.5 g acts on the material to be ground in the area of ​​the radial center of the grinding path.

[0028] The comparatively high rotational speeds are made possible because at least one grinding roller, which is twisted by an angle in the direction of rotation of the grinding plate, exerts a shear force on the material being ground, which acts radially inwards, and thus counteracts the acceleration force acting radially outwards on the material being ground due to radial acceleration.

[0029] This ensures that, despite high grinding disc speeds and correspondingly high radial accelerations, there is always sufficient material to be ground in the grinding gap between the grinding roller and the grinding disc, thus achieving high grinding performance and reducing wear.

[0030] The invention further provides a method for operating a roller mill in which grinding rollers roll on a grinding plate, the slip velocity in the transverse direction of the grinding rollers being constant over at least one contact area across the width of the grinding rollers. This allows for a reduction in vibrations and an improvement in the grinding result. The method advantageously counteracts the formation of agglomerates. The method comprises the step of providing at least one grinding roller which is rotated by an angle of rotation in the range of 1 degree to 9 degrees, or in one embodiment, 1 degree to 4.5 degrees, in the direction of rotation of the grinding plate. Advantageously, the grinding roller is cylindrically shaped in the contact area with the grinding track.

[0031] In particular, the slip velocity in the transverse direction of the grinding roller transports the material to be ground towards the center of the grinding plate. The transverse direction of the grinding roller is the axial direction of the grinding roller. Because the grinding rollers transport the material to be ground inwards, the slip velocity counteracts the centrifugal forces that transport the material outwards due to the rotation of the grinding plate. This allows for a longer residence time of the material in the area of ​​the grinding rollers at simultaneously high grinding plate rotation speeds, resulting in an improved grinding result.

[0032] Finally, the invention provides for the use of a roller mill for grinding particulate bulk material, wherein, by offsetting at least one grinding roller by an angle of 1 to 9 degrees in the direction of rotation of a grinding disc, the vibrations of the roller mill are reduced compared to the state with unoffset grinding rollers. In the prior art, vibrations are increased in corresponding applications compared to the unoffset state. The inventive method and use, however, enable the reduction of vibrations while maintaining or even improving the grinding result, particularly through the operation of the previously defined embodiments of roller mills.

[0033] The invention will now be explained in more detail with reference to exemplary embodiments, which are illustrated in the following figures. These figures show: Figure 1a perspective view of a roller mill according to an embodiment of the present invention; Figure 2 a top view of the embodiment of a roller mill according to the invention; Figure 3 a schematic view of the grinding plate and the grinding roller in an embodiment of a roller mill according to the invention, showing the slip speeds in the direction of rotation of the grinding plate; and Figure 4 a schematic view of the grinding plate and the grinding roller in an embodiment of a roller mill according to the invention, showing the slip velocities in the radial direction of the grinding plate.

[0034] In Fig. 1Figure 1 shows a roller mill according to an exemplary embodiment of the invention. The roller mill has a grinding plate 2 and four grinding rollers 3. The grinding plate 2 is driven about its central axis 100 in a grinding plate rotation direction 200. At least one grinding plate drive 4 is provided for this purpose. The grinding roller 3 is mounted about a roller rotation axis 300 in a rocker arm 5. The rocker arm 5 is pivotably mounted about a bearing axis 400 in a bracket 6. The bracket 6 is directly attached to the foundation. Furthermore, hydraulic cylinders 7 can be provided, which are spaced apart from the bearing axis 400 and connected to the rocker arm 5, and which can apply a force to the rocker arm 5 from the foundation. This can serve to pivot the grinding rollers 3 out of engagement with the grinding plate 2, or to adjust the normal force between the respective grinding roller 3 and the grinding plate 2.

[0035] In the inner area of ​​the grinding plate 2, particulate bulk material is introduced, which then moves radially outwards on the grinding plate 2, so that it is ground between the grinding rollers 3 and the grinding plate 2. The ground bulk material is then exposed to an airflow via a nozzle ring 8 arranged radially outside the grinding plate. The airflow carries the ground bulk material to a classifier (not shown), which can return coarse components to the grinding plate 2 and remove sufficiently fine particles from the roller mill 1.

[0036] In Fig. 2Figure 1 shows a top view of the grinding plate 2, the grinding rollers 3, and their bearings. The grinding rollers 3 are shown in dashed lines in their unskewed arrangement and in solid lines in their skew arrangement. The grinding rollers are rotated by an angle of 50° in the direction of rotation 200° of the grinding plate. This results in the roller axis of rotation 300 being at a radial distance 60° from the central axis 100° of the grinding plate 2. In the area of ​​a grinding track 9, the grinding rollers 3 form a grinding gap in which particulate bulk material resting on the grinding plate 2 is ground by means of normal and shear forces.

[0037] The axial center of the grinding rollers 3 is at a radial distance of 700 from the central axis 100 of the grinding plate 2. The axial center of the grinding roller 3 also defines, in particular, the radial center of the grinding track 9. According to Figure 2The offset is achieved by rotating the grinding roller 3 about its axial center of contact with the grinding plate 2. For this purpose, a semicircular guide can be provided in the bracket 6, allowing the oscillating lever 5 to move relative to the bracket 6. Alternatively or additionally, the offset can be achieved by linearly moving the grinding roller 3, particularly in its radial direction. However, this changes the position of the grinding roller 3's axial center of contact with the grinding plate 2.

[0038] In Fig. 3 and Fig. 4 The slippage between a set grinding roller 3 and the grinding plate 2 is shown. How Fig. 3As can be seen, the circumferential speed of the grinding plate is calculated as a linear function of the radius. The speed of the cylindrical grinding roller 3, which is mounted parallel to the grinding plate 2 and orthogonal to its central axis 100, is, however, constant along its axial extent. Consequently, the grinding roller 3, driven solely by the grinding plate 2, rotates faster at its radially inner end (with respect to the grinding plate) than the corresponding section of the grinding track 9. In its radially outer section 11 (with respect to the grinding plate 2), the grinding roller 3 rotates more slowly than the grinding plate 2. This creates slippage between the grinding roller 3 and the grinding plate 2, which in each case leads to shear forces that can be beneficial to the grinding process.By offsetting the grinding wheel by an angle of 500° in the direction of rotation 200°, a constant slip 90° in the radial direction of the grinding wheel 2 is achieved, according to the geometry and arrangement described above. The slip velocity is constant along the entire axial extent of the grinding wheel 3, i.e., across the entire contact area across the width of the grinding wheel 3. This generates shear forces that act inwards in the radial direction of the grinding wheel 2, thus counteracting the centrifugal force acting on the particle-like bulk material rotating with the grinding wheel 2. This enables improved grinding of the bulk material, with particularly lower vibrations being generated compared to offsets not designed according to the invention.The uniform grinding process allows more material to pass through the classifier, thereby reducing the proportion of material that needs to be re-ground, resulting in an overall increase in the capacity of the roller mill.

[0039] In one embodiment of the method according to the invention, the roller mill 1 described above is operated by rotating the grinding plate 2, causing the grinding rollers 3 to roll on it. A constant slip velocity of 900 in the transverse and axial directions of the grinding rollers 3 is generated by offsetting the grinding rollers 3. In particular, the slip velocity of 900 transports the material to be ground towards the radial interior of the grinding plate 3 and counteracts the centrifugal force in certain areas, thus enabling improved grinding. Therefore, the roller mill can be used to reduce vibrations within the mill through offsetting, while simultaneously producing an improved grinding result.

Claims

1. A roller grinding mill (1) comprising: a grinding plate (2) and grinding rolls (3), wherein the grinding plate (2) is rotatable relative to the grinding rolls around a central axis (100) of the grinding plate (2) in a rotational direction (200) of the grinding plate such that the grinding rolls (3) roll over a grinding path (9) of the grinding plate (2) around a rotational direction of the grinding rolls, characterized in that at least one of the grinding rolls (3) is tilted by a set angle (500) towards the grinding plate rotation direction (200) such that the roller rotation axis (300) extends in a radial distance (600) to the centre axis (100) of the grinding plate (2), wherein the set angle (500) is between 1° and 9°.

2. The roller grinding mill according to anyone of the preceding claims, wherein the ratio between the diameter of the grinding roll (3) and the width of the grinding roll is between 1.5 and 6.

3. The roller grinding mill according to anyone of the preceding claims, wherein the ratio between the radial distance from the centre axis (100) of the grinding plate (2) to the axial centre of the grinding roll (3) and the width of the grinding roll (3) is between 1.5 and 6.

4. The roller grinding mill according to anyone of the preceding claims, wherein the ratio between the radial distance from the centre axis (100) of the grinding plate (2) to the axial centre of the grinding roll (3) and the diameter of the grinding roll (3) is between 0.5 and 1.5.

5. The roller grinding mill according to anyone of the preceding claims, wherein the grinding path (9) is defined by a plane area of the grinding plate (2).

6. The roller grinding mill according to anyone of the preceding claims, wherein the grinding roll (3) can be tilted around its centre contact point on the grinding path (9).

7. The roller grinding mill according to anyone of the preceding claims, wherein a plurality of grinding rolls (3) is provided and only a subset of the grinding rolls (3) is set.

8. The roller grinding mill according to anyone of the preceding claims, wherein the roller rotation axis (300) is orthogonal to the rotation axis (100) of the grinding plate (2) and / or parallel to the surface of the grinding plate (2).

9. The roller grinding mill according to anyone of the preceding claims, wherein the roller rotation axis (300) is tilted by an angle between 0.5° and 20° to the surface of the grinding plate (2).

10. The roller grinding mill according to anyone of the preceding claims, wherein a pivoting lever (5) is provided, wherein the pivoting lever (5) is supported pivotably around a bearing axis (400), wherein the grinding roll (3) is supported in the pivoting lever (5) rotatable around the roller rotation axis (300) wherein the bearing axis (400) of the pivoting lever (5) is parallel to the roller rotation axis (300) and the pivoting lever (5) is supported radially outside the grinding plate (2) in a bracket (6) pivotal around the bearing axis (400) and the bracket (6) is supported in the substructure.

11. A method for operating a roller grinding mill (1) according to anyone of the preceding claims, wherein the grinding plate (2) is rotated with a rotation speed such that on the grinding plate (2) in the radial centre of the grinding path (9) a radial acceleration of at least 1g affects the material to be ground, wherein g is the standard acceleration of 9.81 m / s2.

12. The method according to claim 11, wherein the radial acceleration is at least 1.3 g, advantageously at least 1.4 g.

13. A method for operating a roller grinding mill (1) comprising: rolling grinding rolls (3) over a grinding plate (2), wherein the transverse slip speed between the grinding plate (2) and at least one of the grinding rolls (3) across at least a widthwise contact region of the at least one grinding roll (3) is constant, and wherein the method further comprises: providing at least one grinding roll (3) tilted by a set angle between 1° and 9° towards the grinding plate rotation direction.

14. The method according to claim 13, wherein material (3) to be ground is transported towards the inside of the grinding plate (2) by means of the slip speed in the transverse direction of the grinding roll.

15. Usage of a roller grinding mill (1) for grinding particulate bulk material, wherein by tilting at least one grinding roll (3) by a set angle between 1° and 9° in the rotational direction (200) of a grinding plate the vibrations of the roller grinding mill (1) are reduced compared to untilted grinding rolls (3).