Roller mill and method for operating the same

Abstract

The invention relates to a roller mill, in particular a vertical roller mill, having a rotatable grinding table and a plurality of grinding roller units (1) which are arranged around a grinding track of the grinding table and which each carry a grinding roller (10) in such a way that the grinding roller (10), when in a working position, is associated with the grinding track such that a grinding gap is formed. Each of the grinding roller units (1) has a bearing lever, in particular a rocker lever (20), on which the grinding roller (10) is mounted for rotation about a rotation shaft (12) of the grinding roller. The bearing lever, in particular rocker lever (20), is mounted for movement, in particular for pivoting about a pivot shaft (3), on a roller stand (2) by means of a bearing block / bearing housing (21) in such a way that the grinding roller (10) can be moved, in particular pivoted, into the working position associated with the grinding track. The bearing lever, in particular rocker lever (20), can be selectively mechanically fastened / fixed by a support mechanism (30) in order to hold the grinding roller (10) in the set working position at least against a grinding pressure which is exerted on the grinding roller (10) by a grinding bed during the grinding process.

Description

[0001]

[0002] L 2341

[0003] Rolling mill and method for operating the same

[0004] The invention relates to a rolling mill, in particular a vertical or vertical roller mill, and to a method for operating this rolling mill.

[0005] Vertical roller mills, also known as vertical roller bowl mills (the terms are used synonymously in the context of this disclosure, and the term "roller mill" is used as a representative term), are used for grinding brittle materials, for example, in the cement industry and also in coal-fired power plants. Materials to be ground can include, in particular, raw meal (a raw material for cement production), cement clinker, limestone, coal, clay, gypsum, blast furnace slag (granulated blast furnace slag), ores, and others.

[0006] Roller mills essentially consist of a rotatable grinding bowl (which can also be called a "grinding plate") and several grinding roller units arranged around a grinding track of the grinding bowl. Each grinding roller unit carries a grinding roller such that the grinding roller is positioned in a working position relative to the grinding track, forming a grinding gap. Grinding tools can, in principle, also be spheres, but within the scope of the present invention, cylindrical, convex, or, most preferably, conical rollers are preferred. The grinding roller units of a roller mill can be interconnected in a common mill structure by being mounted on a common foundation or base.

[0007] Each of the grinding roller units has a rocker arm on which the grinding roller is rotatably mounted at one end about a pivot axis. The rocker arm is further mounted on a roller stand via a bearing block or bearing housing so as to pivot about a horizontal pivot axis, such that the grinding roller can be moved, i.e., pivoted, into the working position associated with the grinding path. In a top view, the pivot axis of the grinding roller extends perpendicular to the pivot axis. A roller mill of this type is disclosed, for example, in WO 2020 / 200455 A1. Designs with a vertical roller guide are also known. The material to be ground is generally fed from above or obliquely from above onto the center of the grinding bowl. The material is moved towards the edge of the bowl by the centrifugal forces. In doing so, the material is gripped by the grinding rollers, rolled over once or several times, and thereby ground.A circulating mixture of coarsely and finely ground material is created, the so-called "grinding bed" on the grinding track of the grinding bowl.

[0008] A jet ring at the edge of the grinding bowl directs an upward flow of process gas into the grinding chamber. This gas carries lighter, ground material upwards to a classifier or separator, where coarse and fine material are separated. The fine material is discharged, and the coarse material falls back onto the grinding bowl (it is recirculated). Particularly coarse material can fall out of the grinding bowl as overflow or effluent and can be returned to the mill via an external recirculation system, possibly using a bucket elevator.

[0009] In conventional roller mills, the grinding rollers are pressed against the material being ground in the grinding bed during operation. This is achieved, for example, by means of a spring-loaded hydraulic system that allows the rocker arm to be movably mounted at an end of the rocker arm opposite the pivot axis and preloaded against the material being ground. Such a hydropneumatic suspension system is also provided in the roller mill of the generic type disclosed in WO 2020 / 200455 A1.

[0010] In the past, the necessity of roller suspension and a movable arrangement during grinding operations was derived from the assumption that the grinding bed presents an extremely hard surface with inconsistent height for the rollers. Accordingly, the suspension system is intended to ensure that the roller can follow the changing grinding bed height without noticeably altering the grinding pressure.

[0011] Measurements of mill dynamics indicate that the grinding bed should be understood as a relatively soft particle stream that adapts to the roller position. A compressive force builds up between the roller and the particle stream, supporting the roller. Under these conditions, the oscillating roller-rocker arm suspension structure can generate system vibrations that are constantly energized by the torque at the bowl. With this understanding of the grinding bed's behavior, it must also be recognized that the comminution process is comparable to a forming process. While in a roller press all the material fed into the grinding gap must pass through the gap, in a vertical mill it can bypass the roller laterally—either over the outer edge or towards the center of the mill.A conical roller shape is helpful for the inward flow, whereby material that cannot be drawn in through the gap is deflected to the side towards the center of the mill.

[0012] The suspension systems used so far in roller kinematics are, among other things, the cause of process-damaging vibrations that can lead to damage and emergency stops, as well as the starting point for reduced efficiency due to insufficient utilization of the grinding parts because of inadequate control over the roller position.

[0013] In the operation of roller mills of this type, the grinding bed is almost always higher than the parallel gap, causing the rocker arm and, consequently, the grinding roller to deflect around its pivot axis. This results in reduced utilization of the rollers and grinding track width, as different grinding pressures are generated in certain areas. The uneven distribution of grinding pressure leads to corresponding wear patterns on the roller surfaces.

[0014] The complexity of the interrelationships explains why it is very difficult for a mill operator to accurately control and influence the optimal roller position. This is further complicated by the fact that vibrations, in most cases, limit the adjustment options for some parameters, and low-frequency vertical vibrations, due to the hydraulics, superimpose large amplitudes on the set mean roller position.

[0015] Since the roller position has a very strong impact on grinding efficiency, this lack of control is a major disadvantage. Furthermore, constant changes in the height of the grinding bed lead to a lower grinding speed and higher energy consumption.

[0016] It is known that a high rotational speed of the internal material flow in the roller mill also negatively impacts energy consumption. This correlation, along with the roller vibrations observed during measurements, suggests that comminution occurs primarily through surface abrasion between the particles and less through pressure comminution. This necessitates multiple passes through the comminution zone beneath the rollers, which explains the high rotational speed and longer processing times, and thus the energy consumption.

[0017] The hydropneumatic suspension system presses the roller onto the grinding bed with spring force. According to the usual, statically oriented conception of the rolling process, as it occurs in an edge-mill mill, similar to a wheel on an uneven road, the grinding bed would not permit large-amplitude oscillations of the roller. Nevertheless, such oscillations have been observed in practice.

[0018] The entire vibration sequence in modern roller mills represents a relatively complex, self-excited vibration state. In particular, the higher-frequency (approx. 5–25 Hz) harmonic vibrations of the heavy, moving components limit the possibilities of the grinding process, as they restrict increases in grinding pressure and throughput. They make grinding a sensitive and costly process that requires continuous balancing, and they place a heavy load on the machine, necessitating a robust and therefore expensive design, as well as extensive maintenance and repair work. They can also reduce the quality of the ground material (e.g., cement) if water spraying of the grinding bed becomes necessary for stabilization.

[0019] The objective of the invention is therefore to eliminate or at least mitigate at least some of the aforementioned problems in the prior art and to improve the grinding efficiency of a roller mill and the controllability of the grinding process.

[0020] To solve this problem, the invention proposes a roller mill with the features of claim 1 and a method with the features of claim 15. Preferred embodiments of the roller mill are specified in the dependent claims.

[0021] The invention relates in particular to a roller mill, especially a vertical roller mill, with a rotatable grinding bowl and several grinding roller units arranged around a grinding track of the grinding bowl, each of which carries a grinding roller such that the grinding roller is positioned in a working position relative to the grinding track, forming a grinding gap. Each of the grinding roller units has a bearing lever, in particular a rocker arm, on which the grinding roller is rotatably mounted about an axis of rotation aligned with an axis of symmetry. The bearing or rocker arm is movable via a bearing block on a roller stand, in particular pivotally mounted about a pivot axis, such that the grinding roller can be moved, in particular pivoted, into the working position relative to the grinding track. The bearing lever can also be additionally or alternatively mounted to allow linear or vertical deflection.The roller mill according to the invention is characterized in that the bearing lever can be selectively mechanically locked or fixed by a support mechanism in order to hold the grinding roller in the set working position at least against a grinding pressure exerted on the grinding roller by a grinding bed during the grinding process and thereby to essentially maintain a grinding gap height defined in the working position.

[0022] The fundamental concept of the invention, and its differentiation from, in particular, conventional roller mills with hydropneumatic suspension systems for the grinding rollers, lies in the provision of a roller mill, especially a vertical roller mill, which has grinding rollers that are rigidly supported or lockable in the working position. Measurements demonstrate that vertical movement of the rollers during the grinding process is not necessary. A mill with a lockable conical roller has the advantage that the grinding gap required and set for optimal utilization and efficiency is maintained throughout the grinding process and is not passively altered, for example, by the material being ground. The grinding force can thus be indirectly, but clearly, controlled via the roller position and grinding bed properties.

[0023] The grinding process in roller mills, especially vertical roller mills, has always been described as a combination of pressure and abrasive comminution. However, operational experience and observations suggest that the actual comminution occurs primarily through grinding processes on the grain surfaces of the individual particles, resulting in deformation processes.

[0024] ■ - Circulation rates of the material in the grinding chamber;

[0025] ■ - the grinding bed exhibits more characteristics of a flow than those of a hard-compacted roller surface (roller movements and roller force primarily follow harmonic vibrations); ■ - the correlation between grinding pressure and product quantity / quality is often low in practice due to emerging vibrations;

[0026] ■ - the grinding gap that arises in practice is generally too large for pure pressure grinding; and

[0027] ■ - the comminution of very hard, brittle material components (e.g. quartz), which respond more readily to pressure comminution, is difficult in a vertical roller mill.

[0028] The mill concept with a rigid, fixed, or fixable roller position at the grinding gap now opens up new possibilities, as direct control over the set grinding gap height and maintenance of that height creates the condition that all particles, even those with larger dimensions, must shatter under the roller if they are not plastically deformable.

[0029] The inventive mill concept with rigid roller support allows for increased use of pressure comminution, thereby increasing overall efficiency. This mill concept with rigidly supported grinding rollers is particularly suitable for milled products with a narrow particle size range. With an optimally adjusted, fixed grinding gap, the highest grinding efficiency can be achieved. Thus, the requirements of both the construction materials and ore industries are ideally met by improving costs, grinding efficiency, and machine dynamics.

[0030] A roller mill with a lockable (and preferably conical) grinding roller has the advantage that the grinding gap required and set for optimal utilization and efficiency is rigidly maintained. Control over the grinding force at each roller can now be ensured in a simpler, more controllable, and more immediate manner through other means, namely by adjusting parameters that are set on the one hand during assembly work outside of mill operation (such as the height of the support ring or the rim of the grinding bowl and the height of the parallel gap) and on the other hand by adjusting parameters that are regulated during mill operation (such as roller position within a limited range, bowl rotation speed, material feed rate, and classifier speed).

[0031] With the possibility of the rollers moving in conjunction with a suspension system as in the prior art, direct control over the roller position is not possible. Furthermore, every suspension or spring force system is also capable of oscillation, and therefore the roller position can be subject to vibrations that may necessitate control intervention, even leading to the shutdown of the roller mill.

[0032] According to the invention, the support mechanism can have a sufficiently stiff / rigid lever support on which the bearing lever, in particular the rocker lever, can be selectively supported in order to maintain the working position against the grinding pressure.

[0033] According to the invention, the grinding roller can have a cylindrical, convex, or, even more preferably, a conical roller shell. In addition to the advantageous material guidance already described in the introduction, the principle of the conical, cylindrical, or convex roller in the vertical mill also serves to reduce the shear force between the roller and the grinding path over a relatively large roller width.

[0034] Based on this principle, the idea is to support the grinding pressure of the roller with a rigid lever support. The spring force system used in the prior art is eliminated from the design or can at least be deactivated, while the roller position remains pivotable and adjustable around a rotary axis, provided the rigid support mechanism can be temporarily released and the lever support adjusted accordingly during operation.

[0035] In a preferred embodiment of the invention, the lever support can have a support block which can be moved by a first actuator into a support position relative to the bearing or rocker lever, in particular to set different working positions of the grinding roller.

[0036] Furthermore, the lever support can have a support block, particularly a wedge-shaped one, which can be moved by a first actuator into several different support positions (in a limited range, also steplessly) relative to the bearing or rocker lever. These support positions define different working positions of the grinding roller, allowing it to be adjusted very precisely within the adjustment range. The first actuator can be a first screw or spindle drive or a first hydraulic cylinder.

[0037] Based on the measurement findings described above, stable mill operation is possible even when the grinding roller is fixed in a set working position relative to the grinding gap and can no longer move. There are still possibilities for movement on the material flow side. The comminution process is very similar to a forming process, in which the grinding force does not experience peak loads originating from the material and can be controlled by the intensity of the forming action. In this mill concept, a speed control for the bowl can be a helpful parameter.

[0038] According to the invention, a second actuator, in particular a second spindle drive or a second hydraulic cylinder, can be provided which acts on the bearing lever, in particular a rocker arm, and can move it, in particular pivot it about the pivot axis, so that the grinding roller is moved into a maintenance position raised from the grinding bowl. Previously, the grinding roller was moved into the raised position, in which the grinding roller typically stands vertically upwards, exclusively by means of a hydraulic cylinder acting on the rocker arm. According to the invention, it is advantageous if the grinding roller is raised into the maintenance position by pivoting the rocker arm with a spindle actuator, because this is more cost-effective to implement, especially with regard to the relatively large travel distance required.The second actuator can also be used to simply lift the roller slightly when starting the mill, in order to reduce the necessary torque.

[0039] According to the invention, a bearing block / bearing housing of the rocker arm, on which the rocker arm is pivotably mounted on the roller stand about the pivot axis, can be designed as a separate component that is detachably and adjustably connected to a lever arm of the rocker arm in order to adjust the distance of the axis of rotation of the grinding roller from the pivot axis and thus to adjust the size of the roller gap in the working position of the grinding roller with the same pivot position of the rocker arm.

[0040] The connection between the bearing block / bearing housing and the lever arm of the rocker arm can be a friction-fit (flange) screw connection, preferably with a friction-enhancing element, for example a friction-enhancing coating or an intermediate layer such as a sheet with a friction-enhancing coating, in between and / or a slotted guide.

[0041] To date, no cost-effective solution has been found to adjust the height position of the roller pivot axis (the height of the bearing block or pivot axis determines the height of the parallel grinding gap). According to the invention, this adjustment can now be achieved very simply by designing the previously one-piece rocker arm with a separate bearing block / bearing housing and an adjustable flange connection between the rocker arm's lever arm (on which the grinding roller is rotatably mounted at one end) and the bearing block / bearing housing, preferably using friction-enhancing measures.

[0042] As a preferred measure to increase the frictional forces between the flanges and to ensure the holding forces required for very high grinding pressures, a friction-enhancing element such as a coating on the contact surfaces of the flanges or an intermediate layer such as a sheet with such a coating to increase the coefficient of friction between them can be inserted, while at the same time providing defined overload protection through the possibility of slippage.

[0043] Instead of a coating to increase friction, the contact surfaces can also be roughened directly or a piece of material with a higher coefficient of friction can be inserted.

[0044] Each of the grinding roller units can have a pressing element, in particular containing a hydraulic cylinder, which can act on the rocker arm to load it to press the grinding roller in the direction of the grinding track and to overcome the grinding pressure during grinding operation and to lower the grinding roller, at least to set the working position of the grinding roller.

[0045] While raising the roller position can potentially be achieved solely by the first actuator (the first screw or spindle drive or the first hydraulic cylinder) of the support mechanism, particularly if it is designed as a wedge-shaped support block, lowering the grinding roller during operation to adjust to a lower working position requires overcoming the increase in grinding pressure. This is accomplished by initiating the change in the grinding roller's position with the pressing element, which overcomes the increased grinding pressure via the rocker arm. The support mechanism, for example, the wedge-shaped support block, is then adjusted accordingly to re-establish or fix the lowered working position. The pressing element can then be retracted.Each of the grinding roller units can have a stop buffer, preferably adjustable, which acts on the rocker arm to limit its downward movement and define a minimum roller gap. The lowest position the roller can assume is determined by the stop buffer. Its height can also be adjusted, for example, by means of a spindle drive. The grinding roller automatically assumes this position due to gravity when the mill is emptied and there is no grinding pressure beneath the roller. The stop buffer can also be used to slightly raise the roller when starting the mill, thus reducing the torque required for startup.

[0046] The stop buffer can be designed so that it is pivotably mounted away from an engagement position with the rocker arm, in order to allow further / unhindered pivoting of the rocker arm upwards around the pivot axis, for example to move the grinding roller into a maintenance position clearly raised from the grinding bowl (for example in a vertical orientation of the axis of rotation).

[0047] According to the invention, the multiple grinding roller units of the roller mill can have different natural frequencies.

[0048] Currently, the grinding rollers and grinding roller units in a roller mill are all identical and therefore exhibit essentially the same natural frequencies. To take a first step towards diversifying the roller natural frequencies, the use of at least two different roller sizes in one mill is being considered. However, this is undesirable because it would entail greater part variation and increased inventory, particularly for this wear part.

[0049] The innovative design of the new mill concept, with its rigidly supported grinding roller, allows for variations in local stiffness at appropriate points. This influences the natural frequency of both horizontal and vertical vibration patterns.

[0050] The different natural frequencies can be adjusted in particular by one or more of the following structural differences or measures:

[0051] - different foundation or base height above a machine base and / or - mass and / or - stiffness of the roller stands, - different mass and / or stiffness of the bearing or rocker arms, further in particular of the bearing blocks / bearing housing, whereby the structural differences are always chosen so that the several grinding rollers in grinding operation do not perform equally oscillating amplitudes of movement with horizontal movement in the same phase and / or vertical movement in the same or opposite phase.

[0052] In practice, it has been shown that the bearing block or housing, to which the rocker arm is screwed, is the central component that significantly influences the natural frequencies in both directions. Therefore, in this embodiment, with the bearing housing as a separate component of the rocker arm, it is possible to vary the natural frequencies of all grinding roller units by modifying only this one component (while maintaining the same roller size). In a mill, different versions of the bearing housing can be used, for example, with varying geometric shapes and materials with different stiffness (cast iron versus steel).This allows all the mill's rollers to be kept the same, but the connection of the rocker arm to the stand base can be made with varying degrees of stiffness, with the aim of distributing as many different natural frequencies as possible among the individual rollers.

[0053] This allows for a large diversification of natural frequencies without having to accept differently sized rollers and an excessively high number of component and assembly variants.

[0054] Even if other components of the grinding roller units are varied with respect to mass and / or stiffness to diversify the natural frequencies, the difference in mass and stiffness must be large enough so that a modal analysis does not show a "torsional vibration mode" in which all rollers oscillate horizontally in phase with each other.

[0055] The invention also relates to a method for operating a roller mill according to the invention, comprising the steps:

[0056] Driving the rotating grinding bowl with a variable speed drive, feeding a quantity of material to be ground onto the grinding bowl, preferably with a defined particle size range,

[0057] Setting a working position of the grinding rollers of the grinding roller units to form a defined grinding gap with the grinding path, preferably a parallel grinding gap, and mechanically fixing / locking the grinding gap by fixing / locking the respective working position via the respective support mechanism, and

[0058] Measuring the grinding force at each grinding roller, for example by measuring the tension on a suitable surface of the bearing lever, and using the grinding force as a control variable for which a target range is specified, and adjusting and resetting / fixing the working position of the respective grinding roller as a control variable.

[0059] Up to now, the roll force has been a manipulated variable, and the roll position is a result of this setting and many other difficult-to-control boundary conditions. According to the invention, by enabling the fixed roll position, the roll gap size can be used as a precisely controlled and controllable manipulated variable, and the roll force as a measured target variable for operational control.

[0060] According to the invention, the measured value of the grinding force at each grinding roller can be used as a control variable, for which the target range is specified and which is to be maintained with the help of the following easier-to-control control parameters:

[0061] - Adjustment parameters that are set by assembly work outside of mill operation, such as the height of the support ring or the rim of the grinding bowl and / or the height of the parallel gap;

[0062] - Control parameters that can be regulated during grinding operation, such as roller position within a limited range, grinding bowl speed, material feed quantity and / or classifier speed.

[0063] The invention is described below by way of example using a schematic embodiment with reference to the accompanying drawings. These show: Fig. 1 a perspective view of a grinding roller unit for a roller mill, in particular a vertical roller mill, viewed from the rear and above;

[0064] Fig. 2 shows a partially cut-away side view of a detail of the grinding roller unit to illustrate the adjustment of the grinding roller between a lowest working position (top figure), in which a parallel grinding gap is set, and a higher working position (bottom figure) by adjusting a support mechanism, here in the form of a wedge-shaped support block;

[0065] Fig. 3 shows a side view of a detail of the grinding roller unit to illustrate further components;

[0066] Fig. 4 shows a partially cutaway side view of a detail of the grinding roller unit to illustrate an adjustment of the grinding roller between a working position (left figure) and a maintenance position (right figure).

[0067] The figures schematically show only one exemplary grinding roller unit 1, of which several, for example an even number such as 2, 4, or 6, are arranged around a grinding track of a rotatable grinding bowl (not shown here) that can be actively driven to rotate in a roller mill, particularly a vertical roller mill. Each grinding roller unit 1 carries a grinding roller 10 such that the respective grinding roller 10 can be selectively assigned to the grinding track in a working position, forming a grinding gap. A roller mill of this type is disclosed, for example, in WO 2020 / 200455 A1 and is included for the purpose of explaining the details of a basic structure of such a vertical roller mill that are not shown here.

[0068] Each of the grinding roller units 1 has a bearing lever, in particular a rocker arm 20, on which the grinding roller 10 is rotatably mounted about a rotational axis 12 of the same, which is aligned with an axis of symmetry of the grinding roller. The grinding roller can be actively driven or, as in the variant shown, freely rotatable in order to be passively carried along in interaction with the material being ground on the rotating grinding bowl.

[0069] The rocker arm 20 is mounted on a rigid roller stand 2 via a bearing block / bearing housing 21, and in particular pivotable about a pivot axis 3, such that the grinding roller 10, which is mounted at one end of a lever arm 22 of the rocker arm 20, can be moved, in particular pivoted, into the working positions associated with the grinding path. The roller stands 2 of the roller mill are fixedly or rigidly mounted on a base (not shown) of a machine base, so that the grinding forces occurring during operation can be introduced into and supported by the machine base.

[0070] The grinding roller 10 has a cylindrical, conical, or convex roller shell 11, with the conical roller shell 11 being preferred for the reasons already explained. This has the consequence that, in the case of a conical roller shell 11 as shown here, and preferably in conjunction with the pivotable mounting of the grinding roller at one end of the rocker arm 20, a change in the roller position (height distance to the grinding track) is always also associated with a change in the angle of the roller position, and the roller position is linked to a specific working position or a specific pivot position of the rocker arm 20 via a parallel gap (see also Fig. 2).

[0071] According to the invention, the rocker arm 20 can now be selectively mechanically fixed by a support mechanism 30 in order to hold the grinding roller 10 in the set working position at least against a grinding pressure exerted on the grinding roller 10 by a grinding bed during the grinding process, and thereby to essentially maintain a defined grinding gap height and orientation of the roller surface in the set working position.

[0072] In the embodiment shown, the support mechanism 30 has a sufficiently stiff / rigid lever support 31 on which the rocker arm 20 can be selectively supported in order to maintain the working position against the grinding pressure.

[0073] The lever support 31 has a support block which can be moved by a first actuator 32 into a support position relative to the bearing lever, in particular rocker lever 20, especially to set different working positions of the grinding roller.

[0074] It is particularly advantageous if the lever support 31, as shown in particular in Fig. 2, has a wedge-shaped support block which can be moved by a / the first actuator 32 into several support positions relative to the bearing lever, in particular rocker lever 20, which support positions define different stepless working positions of the grinding roller 10 in a limited range.

[0075] The first actuator 32 is here a first screw or spindle drive or a first hydraulic cylinder, which moves the support block with the lever support linearly horizontally towards and away from a corresponding support surface 24 at the opposite end of the lever arm 22 of the rocker arm 20. The first actuator 32 can also be inclined towards the corresponding support surface 24.

[0076] The support block can be guided on a support plate in rails or grooves, or along lateral stops, so that it can only be moved in a defined direction. When using a spindle drive, a geared motor (for example, a servo geared motor) can drive the spindle and travel the usable stroke.

[0077] Both the rocker arm 20 and the support block can be equipped with interchangeable support plates. The support plate on the rocker arm 20, as well as the one on the rocker arm 20, can have a curvature or radius in the contact area. A convex plate is also possible.

[0078] With the wedge-shaped support block, a wedge angle of 12°, for example, generates a sufficiently high self-locking effect through friction, so that the axial holding forces on the spindle are low. The drive torque is also sufficient to retract the support block even at maximum grinding pressure, thus relieving the grinding roller. With appropriate lever length selection, the adjustment range can, for example, achieve a height change of 3 to 6 cm for a 2° rotation angle of the roller position.

[0079] Although not shown, a rotating movement of the support block with the lever support under the corresponding support surface 24 of the swing arm would also be conceivable. Instead of a single support block, several support blocks can also be provided.

[0080] Figure 2 (lower illustration) also shows that the roller's working position can be raised solely by the actuator 32, which retracts the wedge-shaped support block. This allows the swing arm 20 to pivot counterclockwise around the pivot axis 3 (as shown in Figure 2) due to the rolling force at the roll gap during operation. To lower the working position during grinding, the change in position is initiated by a press element 60, indicated in Figure 3, which is designed to overcome the increase in grinding pressure. The support block of the lever support 31 can then be moved by the actuator 32 without resistance and positioned against the support surface 24, thus re-establishing / fixing the set (new, lower) working position of the grinding roller 10. The press element 60 can then be retracted.

[0081] The pressing element 60 can include one (or more) hydraulic cylinders for lifting and pivoting the rocker arm 20. These cylinders are arranged so that, when extended, they act on the rocker arm 20 to load it, at least to set the working position of the grinding roller 10, to press the grinding roller 10 towards the grinding path, and to overcome the grinding pressure during grinding operation (here by a clockwise pivoting movement of the rocker arm 20 about the pivot axis 3). The pressing element 60 can be provided on the support block of the lever support 31 and be horizontally movable with it via the first actuator 32, or it can be mounted in a fixed position on the roller stand 2.

[0082] The lowest position that the grinding roller 10 can assume is determined by a stop buffer 40. This is indicated in Fig. 3 and is preferably also adjustable in its height position by means of a spindle drive. The grinding roller automatically assumes this position under the influence of gravity when the mill is empty and there is no grinding pressure under the grinding roller. The stop buffer 40 can also be used to raise the grinding roller 10 slightly.

[0083] The stop buffer 40 is arranged on the roller stand 2 in such a way that it can act on the rocker arm 20 to limit the lowering of the grinding roller 20 due to gravity and to define a smallest roller gap in order to avoid metallic contact of the roller with the grinding track.

[0084] The highest possible roller position (see Fig. 2, lower figure) is predetermined during grinding operation by limiting the adjustability of the support block. In the illustrated embodiment, this corresponds to a roller stroke of 1.5° to 4° or 4 to 7 cm compared to the lowest roller position with a parallel gap. Further raising of the grinding roller 10, for example for maintenance purposes, is possible when the mill is stopped, if the stop buffer 40, which is designed to be pivotable away from an engagement position with the rocker arm 20 or retractable, is moved laterally out of the rocker arm's pivot range to allow further / unhindered pivoting of the rocker arm 20 upwards about the pivot axis 3 to move the grinding roller 10 into a maintenance position lifted from the grinding bowl. To allow the rocker arm 20 to pivot beyond the limited adjustment range into the maintenance position (see Fig. 2), the stop buffer 40 is also moved laterally out of the rocker arm's pivot range.4), the support mechanism 30 must also be retracted to such an extent (for example by means of the actuator 32 or another adjustment mechanism with a larger stroke, for example in the form of a rack and pinion mechanism, which can move the entire functional unit of the support mechanism out of the pivoting range of the rocker arm).

[0085] This further pivoting of the rocker arm 20 into the maintenance position can, as indicated in Fig. 4, be effected by a second actuator 50, which may in particular be a second spindle drive 51 or a second hydraulic cylinder and which engages a cantilever arm 52 at the rear end of the rocker arm 20 in order to move it, in particular to pivot it around the pivot axis 3, so that the grinding roller 10 is moved into the maintenance position lifted from the grinding bowl (for example, into the vertical orientation shown in Fig. 4, right-hand figure).

[0086] A further advantageous design aspect of the invention is that the bearing block / bearing housing 21 of the rocker arm 20, on which the rocker arm 20 is pivotably mounted on the roller stand 2 about the pivot axis 3, is designed as a separate component that is detachably and adjustably connected to the lever arm 22 of the rocker arm 20 (see Fig. 1). This allows for a basic setting of the parallel grinding gap height.

[0087] A connection between the bearing block / bearing housing 21 and the lever arm 22 of the rocker arm 20 can be designed as a detachable friction-fit screw connection 23, preferably a detachable flange screw connection 23 with a friction-enhancing element, for example a friction-enhancing coating or an intermediate layer with a friction-enhancing coating, and / or a slotted guide. By using the friction-enhancing element to increase the coefficient of friction in the contact area of ​​the screw connection, the holding forces required for very high grinding pressures can be achieved, while at the same time overload protection is provided by the possibility of slippage.

[0088] The division of the rocker arm 20 into the bearing block / housing 21 and the lever arm 22, and the detachable screw connection 23 between them by means of elongated holes, allows a defined adjustment of the distance of the axis of rotation 12 of the grinding roller 10 from the pivot axis 3, and thus an adjustment of the size of the parallel roller gap in the working position of the grinding roller 10 with the same pivot position of the rocker arm 20. The elongated holes in the rocker arm 20 and / or in the bearing block / housing 21 can, for example, allow the parallel grinding gap to be adjusted in the range of 5 to 15 cm.

[0089] In general, vertical roller mills are constructed such that a number of grinding rollers are arranged around the rotating grinding track of the grinding bowl. All associated grinding roller units are connected to each other within a common mill structure via a uniform machine base or foundation. From a machine dynamics perspective, it is desirable that the entire mill structure, as determined by modal analysis, does not exhibit a natural mode in which all rollers oscillate horizontally back and forth in phase (a "torsional mode" in top view). Furthermore, other local modes of vibration of the grinding rollers in a vertical orientation should also differ as much as possible in their natural frequencies. In this way, a fundamental characteristic of vertical roller mills can be structurally suppressed: their ability and tendency to generate self-excited vibrations between the mill structure and the drive train.

[0090] Therefore, according to the invention, it is also provided that the multiple grinding roller units 1 each have different natural frequencies. The different natural frequencies can be set by one or more of the following structural differences:

[0091] - different foundation or base height above a machine base and / or - mass and / or - stiffness of the roller stands 2, - different mass and / or stiffness of the bearing levers, in particular rocker arms 20, and further in particular of the bearing blocks / bearing housings 21 thereof,

[0092] - different mass and / or stiffness and / or dimensions of the grinding rollers 10.

[0093] The structural differences must always be chosen so that the multiple grinding rollers 10 do not perform equally oscillating movement amplitudes with horizontal movement in the same phase and / or vertical movement in the same or opposite phase during grinding operation.

[0094] The following summarizes some advantages of the roller mill according to the invention that are achievable in principle compared to the mill design according to the generic:

[0095] 1) Vibration-free grinding operation

[0096] => improved cement product quality, as no secondary measures to stabilize the grinding process, such as sprinkling the grinding bed with liquid, are required;

[0097] 2) Increase in grinding efficiency

[0098] => simple implementation of very high grinding pressure forces;

[0099] => Enabling targeted pressure crushing;

[0100] => lower energy consumption for the grinding process;

[0101] 3) Low costs

[0102] => Elimination of the hydropneumatic suspension and its components;

[0103] => The mill base is reduced in terms of part complexity and number;

[0104] 4) Quick and inexpensive installation

[0105] 5) Low maintenance requirements

[0106] 6) Reduced construction effort

[0107] 7) Wider range of applications for an individual mill => By varying the grinding gap height and the speed, the mill can easily be adjusted to very different materials to be ground;

[0108] => In principle, a mill can also be converted to a different inclination angle of the roller axis, so that the shearing effect can be changed;

[0109] 8) Lower risk of mill failure

[0110] => Damage to suspension components is eliminated;

[0111] => significantly lower dynamic load on all machine parts, including the drive train (transmission);

[0112] 9) Increased utilization of the grinding parts and reduced wear

[0113] => higher product throughput per set of milled parts and thus reduction of resource consumption.

Claims

II* Wunderlichs heim il PATENTANW Ä LTE L 2341 Practice 1. Roller mill, in particular vertical roller mill, comprising: a rotatable grinding bowl, and several grinding roller units (1) arranged around a grinding track of the grinding bowl, each of which carries a grinding roller (10) such that the grinding roller (10) is assigned to the grinding track in a working position, forming a grinding gap, wherein each of the grinding roller units (1) has a bearing lever, in particular a rocker arm (20), on which the grinding roller (10) is rotatably mounted about an axis of rotation (12) thereof, and wherein the bearing lever, in particular a rocker arm (20), is movably mounted on a roller stand (2) via a bearing block / bearing housing (21), in particular pivotably mounted about a pivot axis (3), such that the grinding roller (10) can be moved, in particular pivoted, into the working position assigned to the grinding track, characterized in that the bearing lever, in particular a rocker arm (20), can be selectively mechanically locked / fixed by a support mechanism (30).to hold the grinding roller (10) in the set working position, at least against a grinding pressure exerted on the grinding roller (10) by a grinding bed during the grinding process.

2. Roller mill according to claim 1, characterized in that the support mechanism (30) has a sufficiently stiff / rigid lever support (31) on which the bearing lever, in particular rocker lever (20), can be selectively supported in order to maintain the working position against the grinding pressure.

3. Roller mill according to claim 2, characterized in that the lever support (31) has a support block which can be moved by a first actuator (32) into a support position relative to the bearing lever, in particular rocker lever (20), in particular to set different working positions of the grinding roller.

4. Roller mill according to claim 2 or 3, characterized in that the lever support (31) has a support block, in particular a wedge-shaped one, which can be moved by a / the first actuator (32) into several support positions relative to the bearing lever, in particular rocker lever (20), which support positions define different working positions of the grinding roller (10).

5. Roller mill according to claim 3 or 4, characterized in that the first actuator (32) is a first screw or spindle drive or a first hydraulic cylinder.

6. Roller mill according to one of claims 1 to 5, characterized in that a second actuator (50), in particular a second spindle drive or a second hydraulic cylinder, is provided which acts on the bearing lever, in particular rocker lever (20) and can move it, in particular pivot about the pivot axis (3), so that the grinding roller (10) is brought into a maintenance position lifted from the grinding bowl.

7. Roller mill according to one of claims 1 to 6, characterized in that a bearing block / bearing housing (21) of the rocker arm (20), on which the rocker arm (20) is pivotably mounted on the roller stand (2) about the pivot axis (3), is designed as a separate component, which is detachably and adjustably connected to a lever arm (22) of the rocker arm (20) in order to adjust a distance of the axis of rotation (12) of the grinding roller (10) from the pivot axis (3) and thus to adjust the size of the roller gap in the working position of the grinding roller (10) with the same pivot position of the bearing lever, in particular rocker arm (20).

8. Roller mill according to claim 7, characterized in that a connection between the bearing block / bearing housing (21) and the lever arm (22) of the rocker arm (20) has a friction-fit screw connection (23), preferably a flange screw connection (23) with a friction-enhancing element, for example a friction-enhancing coating or an intermediate layer with a friction-enhancing coating, in between and / or a slotted guide.

9. Roller mill according to one of claims 1 to 8, characterized in that Each of the grinding roller units (1) has a pressing element (60), in particular comprising a hydraulic cylinder, which is arranged so that it can act on the rocker arm (20) to load it to press the grinding roller (10) in the direction of the grinding track and to overcome the grinding pressure during grinding operation, at least to set the working position of the grinding roller (10).

10. Roller mill according to one of claims 1 to 9, characterized in that each of the grinding roller units (1) has a stop buffer (40) which is preferably adjustable and can act on the rocker arm (20) to limit a lowering of the grinding roller (20) and to define a smallest roller gap.

11. Roller mill according to claim 10, characterized in that the stop buffer (40) is pivotable away from an engagement position with the rocker arm (20), retractable and / or removable in order to allow further / unhindered pivoting of the rocker arm (20) about the pivot axis (3) to bring the grinding roller (10) into a maintenance position lifted from the grinding bowl.

12. Roller mill according to one of claims 1 to 11, characterized in that the multiple grinding roller units (1) have different natural frequencies.

13. Roller mill according to claim 12, characterized in that the different natural frequencies are set by one or more of the following structural differences: - different foundation or base height above a machine base and / or mass and / or stiffness of the roller stands (2), - different mass and / or stiffness of the bearing levers, in particular rocker arms (20), and further in particular of the bearing blocks / bearing housings (21) thereof, - different mass and / or stiffness and / or diameter of the grinding rollers (10), wherein the structural differences are always chosen such that the multiple grinding rollers (10) do not perform equally oscillating amplitudes of movement with horizontal movement in the same phase and / or vertical movement in the same or opposite phase during grinding operation.

14. Roller mill according to one of claims 1 to 13, characterized in that the grinding roller (10) has a conical, cylindrical or convex roller shell (11).

15. Method for operating a roller mill according to any one of claims 1 to 14, comprising Driving the rotating grinding bowl with an adjustable drive of a certain speed, Feeding a quantity of material to be ground onto the grinding bowl, preferably with a defined particle size range, Setting a working position of the grinding rollers (10) of the grinding roller units (1) to form a defined grinding gap with the grinding path, preferably a parallel grinding gap, and mechanically fixing / locking the grinding gap by fixing / locking the respective working position via the respective support mechanism (30), and Measuring the grinding force at each grinding roller (10), for example by measuring the tension on a suitable surface of the bearing lever, in particular rocker arm (20), and using the grinding force as a control variable for which a target range is specified, and adjusting and resetting / fixing the working position of the respective grinding roller (10) as a control variable.

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