Feeding device with metering device for a roller press

Description

[0001] The invention relates to a feeding device for feeding brittle ground material onto a roller gap formed between two rollers of a roller press, comprising a material feeding chute above the roller gap and a metering device with a metering body for metering the stream of brittle ground material emerging from the material feeding chute and flowing to the roller gap, wherein the metering body has a lower boundary surface which defines a space between the metering body and the roller surface of a first of the two rollers for the passage of the brittle ground material.

[0002] Roller presses (high-pressure roller presses) are used to crush granular, brittle ground material, for example, cement clinker sintered from cement raw meal in a rotary kiln in the cement production process, in the nip between two counter-rotating rollers of this roller press (high-pressure roller press) by applying material to the material bed under high pressure. Typically, one of the two rollers is designed as a fixed roller, supported against the machine frame, while the other roller is designed as a floating roller. The floating roller is typically supported by associated bearing blocks against hydraulic cylinders of a hydropneumatic system, which generates the roller pressing force.

[0003] However, the desired effective material bed comminution and problem-free operation of the roller press cannot be achieved with every feed quantity per unit of time into the upper area of the roller gap, nor with every arbitrary load distribution on the roller gap along its longitudinal extent, the direction of which corresponds to the axial extent of the roller press determined by the rotational axes of the rollers (at rest),. A disadvantage is, for example, if uneven distribution of the particles of the ground material in the material bed, which are drawn into the roller gap by gravity and, above all, due to friction, leads to locally different forces acting on the rollers and, as a result, to temporary misalignment of the loose roller. The roller gap then gaps open in the sense that the roller surfaces in the roller gap area, or the rotational axes of the rollers, are no longer parallel.This not only leads to varying comminution effectiveness along the gaping roller gap, but also to disadvantageously high loads on the bearings and pressure cylinders of the loose roller. In addition to the problems with the material feed behavior due to disadvantageous, particularly asymmetric, feeding of the roller gap, in the case of the ground material in the form of cement clinker, the high pressure in the material bed partially compresses the clinker into agglomerated material, so-called flakes. Although these can be processed further in the subsequent process without any problems, at the same time air that was originally contained in the bulk material is forced out of the material bed. Air thus escapes from the area of material bed stress in the roller gap, counter to the direction of the material flow, and on its way upwards, loosens the ground material in the feed area of the rollers.Especially if a high column of material has formed in the intake area, this is disadvantageous in terms of material intake, throughput and degree of comminution.

[0004] For a more controlled feeding of the ground material into the upper area of the roller nip of the roller press, it is known, for example from the publications DE 33 05 339 A1 and DE 102 33 811 B4, to use a material feed chute. Ground material is fed into the upper material inlet opening in a suitably preset quantity per unit of time. This material is released at the bottom through a material outlet opening in a geometrically predetermined manner to feed the roller nip. Typically, the material feed chute is arranged above the roller nip, so that the ground material flows into the intake area of the roller nip under the influence of gravity in a manner determined in particular by the shape of the material feed chute and its height above the rollers.The publication DE 20 2010 009 151 U1 discloses an example of a special geometric design for the outlet opening of the material feed chute. This design achieves an advantageous equalization of the impact along the roll gap, particularly avoiding an excessive amount of feed material in the axial center of the roll gap, under the aspects mentioned therein—namely, avoiding roller vibrations and evening out wear on the roll surfaces and bearings. For this purpose, the lower opening of the material feed chute has a shape that tapers toward the axial center.

[0005] From patent DE 102 33 811 B4, for example, it is known to arrange the material feed chute above the roller gap, but not vertically directly above it, but rather laterally, i.e., transversely to the axial direction of the roller gap. This ensures that the ground material is fed onto the roller press at least predominantly on the side of one of the two rollers, allowing the air pressed out of the material bed to escape more easily upwards, past a large portion of the material flow.

[0006] To further improve the effectiveness of material bed comminution and the grinding operation of the rollers by controlling the flow of material to be ground for feeding to the roller press, it is also known to meter the flow of material to be ground emerging from the feed chute. Dosing devices in the material feed chute have been proposed for this purpose – for example, in the publication DE 33 05 339 A1, which teaches an adjustable, rotatable and / or pivoting metering tongue inside the feed chute, where it is subject to significant wear.

[0007] Dosing devices that are arranged downstream of the material feed chute and upstream of the roller gap in the direction of material flow have proven to be even more suitable for dosing. For example, patent DE 102 33 811 B4 discloses a movable, height-adjustable dosing slide after the laterally offset material feed chute. This is essentially plate-shaped and forms a gap-like space between its lower edge or underside on the one hand and the roller surface of one of the rollers on the other, such that the ground material flow emerging downwards from the material feed chute must flow through this space. By lowering or raising the dosing slide, the amount of ground material flow per unit of time and thus the amount of material fed to the roller gap following in the direction of flow is suitably reduced or increased. A comparable enlargement orAccording to the teaching of the document DE 42 26 182 A1, the reduction of a corresponding passage area for the grinding material flow to be fed in is achieved by adjustable or pivotable dosing flaps which are arranged at the lower end of the material feed chute.

[0008] While the spatial axial distribution of the brittle ground material to be fed into the roller gap is predetermined in a first step by appropriate size and shape design as well as arrangement of the material feed chute, the flow rate, i.e. the amount of ground material fed into the roller gap per unit of time, is typically only roughly pre-adjustable and generally requires the described, controlled or even regulated dosing adapted to the operating sequence. However, the dosing devices known from the prior art with the above-mentioned dosing flaps or dosing slides as dosing bodies generally change the distribution of the ground material to be fed in axially along the roller gap, whereby the corresponding influence also depends, within certain limits, on the position of the dosing flap orof the dosing slide, which is why this cannot be easily and sufficiently compensated for by a previously modified geometry of the material feed chute. The known basic shape of these dosing bodies is such that for each position of the dosing element, there is a constant distance along the axial length between the lower edge of the dosing body (dosing slide, flap) and the corresponding roller surface. It has been shown that dosing with dosing elements of this type leads to a change in the quantity distribution along the roller gap in such a way that relatively more ground material is fed into the roller gap at the axial ends and relatively less in the axial middle than without dosing.This leads to a number of disadvantages in the operation of the roller press: The edge areas of the rollers are subjected to heavy loads, particularly with regard to wear, the force acting on the limiting elements usually provided at the axial ends of the roller gap, which are intended to prevent axial escape of ground material from the roller gap, is increased and the resulting uneven distribution along the roller gap, further aggravated by random temporary asymmetries in the loading of the two axial end areas of the roller gap, increases the probability of the disadvantageous misalignments of the rollers relative to one another as described above.

[0009] The object of the invention is therefore to provide a feeding device of the type mentioned at the outset for feeding brittle ground material onto the roller gap formed between the two rollers of the roller press, in which the aforementioned disadvantages of the prior art are overcome or at least reduced.

[0010] The object of the invention is achieved by a feeding device for feeding brittle ground material onto a roller gap formed between two rollers of a roller press, having the features of claim 1. Further advantageous embodiments are specified in the subclaims to claim 1.

[0011] According to the invention, the lower boundary surface of the metering body protrudes at each outer section relative to the longitudinal extent of the roller gap, so that in the region of these two outer sections, the space between the metering body and the roller surface of the first roller is narrower than the space between the metering body and the roller surface of the first roller in the region of the central section of the lower boundary surface of the metering body located between the two outer sections. The metering body, as part of the metering element, which, in addition to the metering body, typically also comprises a mechanism for adjusting the metering body and a drive or a manual adjustment device, forms a space through its spacing from one of the two rollers (first roller), through which the ground material flowing from the material outlet opening of the material feed chute passes on its way to the roller gap.As is typical, the position of the dosing body of the dosing system is adjustable, allowing the size of the gap and thus the amount of material passing through per unit of time to be changed or controlled. This gap extends in the longitudinal direction of the roller gap, i.e., in the axial direction (always relative to the axial direction resulting from the idle mode of the roller press), over the entire length of the dosing body. For reasons of symmetry, the dosing body can be positioned vertically directly above the roller gap, or, like the material feed chute, can be offset laterally toward the first roller for the advantages described above, particularly regarding the trouble-free extraction of extruded air from the material to be ground.

[0012] The shape of the dosing body according to the invention can be described in simplified terms as follows: the dosing body is extended downwards at the bottom, i.e. on its side oriented towards the first roller, in each case in the outer region - formulated in relation to its longitudinal extent. It therefore has downwardly projecting partial regions (in short: parts) in which the distance to the roller surface of the first roller is smaller in a normal position of the dosing body, i.e. position suitable for the dosing process, than in the middle region, which here refers to the entire region between these two outer partial regions. In relation to the lower boundary surface orThe underside of the dosing body therefore has three sections: two outer sections and one middle section. The outer sections project in such a way that each geometric point on the lower boundary surface in the region of the middle section is farther away from the surface of the first roller than each point on the outer sections is from the roller surface. In terms of these distances—and not necessarily in terms of volume—the space in the region of the outer sections of the lower boundary surface is narrower than the space between the dosing body in the middle section and the roller surface of the first roller in the region of the middle section.The entire and, as such, connected space between the metering body and the roller surface of the first roller is understood as being composed of three parts, namely the two spaces in the outer regions of the metering body with the projecting parts, defined by the outer sections of the lower boundary surface, and the space in the central region. Within such a section, there is not necessarily a constant distance to the roller surface, i.e., a constant gap height or opening width. It should be noted that, particularly in the case of plate-shaped metering slides as the metering body, the lower boundary surface or underside can also be a comparatively narrow surface (lower end face) and, in this sense, can also be referred to as the lower edge or bottom edge.Typically, the dosing body is symmetrical with respect to a vertical center plane in terms of its profile on the underside, but one projecting outer section of the lower boundary surface of the dosing body can be made larger than the other - in relation to its extension in the axial direction and / or its extension vertically transverse to the axial direction, thus corresponding to a more strongly reduced height or opening width of the space there.

[0013] The inventive profile of the lower region of the metering body results in the narrowing of the passage area for the grinding material flow in the outer regions compared to the gap in the middle section, in the direction of the distance vector, resulting in a relatively reduced grinding material flow in the outer sections compared to the middle section. During operation of the roller press, therefore, less grinding material reaches the axially outer regions of the roller gap and more grinding material reaches its middle region than would be the case when using the known metering bodies that define a gap with a uniform opening width without the inventive profile design, without the outer projecting parts of the metering body.This relieves the outer edge zones of the rollers (particularly with regard to wear) and reduces the impact of the grinding material in the direction of the longitudinal extension of the roller gap on the limiting devices usually present at the ends of the roller gap (to prevent material from escaping there). Particularly in combination with a quantity distribution of the grinding material to be fed into the roller gap over the axial extension of the roller gap, which is already suitably preset by the geometry of the feed chute, a reduction in the frequency of the disadvantageous misalignment processes of the loose roller described above has also been observed. Surprisingly, it has been shown that the effect of this protection of the axially outer areas of the roller press and the more trouble-free roller operation is valid for every position of the dosing body, i.e.each achieved dosage level, within the limits of the dosage levels normally required in practice, to a considerable extent.

[0014] Since, in the typical dosing function, no ground material is to flow around the dosing body, but only through the space between the dosing body and the roller surface of the first grinding roller, in a preferred embodiment the dosing body extends in its axial direction over the entire length of the roller gap. In an advantageous embodiment of the invention, it is then provided that each of the two projecting outer sections of the lower boundary surface of the dosing body extends in the direction of the longitudinal extent of the roller gap from the respective end of the dosing body to the center over a length of up to 25% of the total length of the dosing body. This information relates to the fact that the ends of the dosing body each lie in a plane perpendicular to the horizontal plane running through the rotational axes of the rollers, which plane runs at each end of the roller gap and perpendicular to this.Any additional parts on the dosing body, particularly in its upper area, may exist (for example, with a holding function), but are irrelevant for the above description of the extension. In a symmetrical limiting case, the length of each outer section in this embodiment can be a quarter of the total length of the dosing body in its longitudinal extension, and the length of the middle section can thus be half the total length.

[0015] In a further advantageous embodiment of the subject matter of the invention, it has surprisingly been found that for typical grinding scenarios with roller presses in which cement clinker is subjected to pressure, the aforementioned advantageous effects are particularly pronounced and, at the same time, an economical throughput of ground material is achieved if each of the two projecting outer sections of the lower boundary surface of the dosing body extends in the direction of the longitudinal extent of the roller gap from the respective end of the dosing body to the center over a length of up to 10% of the total length of the dosing body.

[0016] In one embodiment of the invention, the metering element is provided as a slide metering element, wherein the metering body is present as a substantially plate-shaped metering slide, or the metering element is provided as a flap metering element, wherein the metering body is present as a substantially plate-shaped metering flap. A metering slide is characterized in that it has a degree of freedom for translational movements, manually or typically by means of a mechanical drive. For example, it can be moved up and down in a vertical direction, so that the opening width of the intermediate space between the metering body and the roller surface increases or decreases accordingly. A metering flap is characterized in that it can be rotated or pivoted by rotation and likewise varies the opening width of the intermediate space accordingly. The respective adjustment mechanism and, if applicable,A corresponding gear mechanism is well known to those skilled in the art from the practice of feeding devices with conventionally designed metering slides or metering flaps, more specifically from parts of the prior art described above. The movement of the metering flaps or slides can be controlled or regulated depending on the grinding efficiency and quality. Essentially plate-shaped metering bodies can also be used for metering elements, which allow both translational and rotational movement. The designation of the metering bodies in this embodiment as essentially plate-shaped refers to the flat and planar basic shape of the metering body with a narrow lower boundary surface or edge. The downwardly projecting extension parts or regions present according to the invention are then also plate-shaped.In addition to technically insignificant deviations from an ideal plate shape, the dosing body may have functional elements that deviate from the plate shape, particularly in the upper area but not in the extension areas, in addition to its basic shape, in particular for the holder and for the drive mechanism.

[0017] The profile of the lower boundary surface of the dosing body determines the geometry of the gap between the dosing body and the roller surface and thus influences the characteristics of the grinding material flow in its axial longitudinal direction, i.e., approximately perpendicular to the mean flow direction. In the case where the dosing body is designed as a slide or a flap, i.e., with a plate-like basic shape, further embodiments of the subject matter of the invention provide, among other advantageous alternatives.

[0018] In a first alternative, the lower boundary surface of the dosing body runs essentially parallel to the horizontal center plane of the two rollers in the area of the two projecting outer sections, based on an imaginary vertical alignment of the dosing body. The aforementioned vertical alignment of the slide or flap, in which the plate-like basic shape is directed vertically downwards with the lower boundary side, does not indicate any technical function and does not need to be actually realized in operation, but serves as at least an imaginary position as a geometric reference for specifying the aforementioned parallelism. In the case of slides, this can be realized in any position; in the case of flaps, the spatial position of the flat underside changes through pivoting. This implicitly assumes that the underside of the dosing body is flat, at least in the outer sections.The aforementioned horizontal center plane is determined by the fact that the rotation axes of the two rollers lie within it. The course is essentially parallel in that, for example, rounded transitions in the stepped course of the lower boundary surface are irrelevant. In the case of a metering flap, when pivoted outside of a vertical position, the lower profile line, which results from a central longitudinal section through the plate, is parallel to the horizontal center plane of the two rollers in the area of the outer sections. The lower boundary surface or profile line of the metering body in the central area can typically also run parallel as a straight line, but can also, for example, be symmetrically concavely curved along its longitudinal course on the streamside, so that the largest opening width of the gap is in the axial center. The first alternative, in particular, allows for simple production of the metering body.

[0019] A second alternative is characterized in that the lower boundary surface of the dosing body in the area of the two projecting outer sections slopes downwards towards the outer ends of the dosing body, so that in this area the distance between the lower boundary surface of the dosing body and the roller surface of the first roller decreases outwards. The advantage here is that the stepped profile of the dosing body is somewhat, but not completely, smoothed out on the underside. The reducing effect on the ground material flow along the longitudinal extent is therefore not caused by a single 'jump', but increases outwards in the area of the outer sections. This can occur linearly, based on an imaginary vertical position of the dosing body, or by a corresponding curve of the associated profile line.The choice between the alternatives and the specific implementation of the second alternative will be made by the expert in each individual case through empirical tests.

[0020] In a further embodiment of the subject matter of the invention, the projecting parts of the dosing body, defined by the two projecting outer sections of the lower boundary surface of the dosing body, are movably connected to the remaining part of the dosing body. The movable connection can be provided, for example, by a hinge. Although this must be adjusted to be stiff with high resistance, it nevertheless allows for a vibrating yielding of these projecting parts in the event of exceptionally strong and peak-like impulse inputs in the area of the extension parts, which prevents rapid material fatigue or even breakage of these extensions and also reduces wear there.The protruding parts of the dosing body are given to the person skilled in the art by the fact that the profile line of the underside continues from the central area in a natural manner, for example smoothly, outwards, which leads to an imaginary definition of the protruding sections or parts.

[0021] To counteract a movement component of the ground material particles toward the axial ends of the roller gap, an at least partial deflection of this direction of movement can be achieved by a suitably curved or arched design of the extension parts of the metering slide. Thus, in one embodiment of the invention, the projecting parts of the metering body, defined by the two projecting outer sections of the lower boundary surface of the metering body, each have a concavely curved profile on their inner side facing the oncoming flow of brittle ground material flowing between the material feed chute and the metering body, in the direction of the longitudinal extent of the roller gap toward the respective end of the metering body.

[0022] In the case of a plate-shaped, non-curved metering slide or a plate-shaped metering flap, the metering body can be equipped with vane-like guide vanes at its axial ends to achieve a similar effect. However, these must be coordinated with the limitation of freedom of movement, which is predetermined by any side parts already arranged at the axial ends of the roll gap to prevent material from escaping.

[0023] The invention is not limited to the use of only one feed chute and only one metering element in total or per feed chute in a roller press (high-pressure roller press). The design of the metering element according to the invention then applies to at least one metering element or at least one metering element.

[0024] Dosing elements designed according to the invention, e.g., dosing slides or dosing flaps, can also be easily retrofitted to existing feed devices for roller presses where the existing feed chute already causes a disadvantageous asymmetric distribution of the ground material along the roller gap, namely a disadvantageously large amount in the axially outer regions. Any dosing flaps or slides already in use can be replaced with those designed according to the invention, or, if a dosing element is currently missing, a dosing element designed according to the invention can be retrofitted.

[0025] The invention is explained in more detail with reference to the following figures. Fig. 1 is a schematic cross-sectional sketch through a roller press with a feeding device according to the invention with a metering slide, Fig. 2 is a metering body according to the invention above a roller of a roller press, Fig. 3 is an embodiment of a metering body according to the invention, Fig. 4 is a further embodiment of a metering body according to the invention, and Fig. 5 is a schematic cross-sectional sketch through a further embodiment of a metering slide above the rollers of a roller press.

[0026] In Figure 11 shows a schematic cross-sectional view of a feeding device 1 according to the invention for feeding brittle ground material 2 onto the roller nip 3 of a roller press 4. The ground material 2 enters a material feed chute 5 through a material feed opening at the top. Due to gravity and the pressure of additional ground material 2 fed in from above, the ground material 2 moves downwards out of the material outlet opening of the material feed chute 5 and flows towards the roller nip 3 to a first roller 6, preferably the fixed roller, above which the material feed chute 2 is arranged laterally offset from the center. The flow of ground material 2 can be metered by adjusting a metering body 8 of a metering element 9, designed as a metering slide 7 in the illustrated embodiment, upwards or downwards. The flow of ground material 2 passes through the gap 10 between the surface of the first roller 6 and the metering slide 7.The opening width of this intermediate space 10 typically controls or regulates the amount of grinding material 2 flowing through per unit of time.

[0027] An auxiliary line drawn in the lower area of the metering slide 7 indicates one of the downwardly projecting parts 11 of the metering slide 7 according to the invention, in which the opening width of the intermediate space 10 is smaller than that between the central area of the metering slide 7 and the surface of the first roller 6, which leads to the intended advantageous distribution of the quantity of ground material 2 fed in along the roller gap 3 in its axial extension, which here runs perpendicular to the plane of the illustration. The ground material 2 is then drawn into the roller gap 3 and comminuted in the material bed between the first roller 6 and the second roller 12 rotating in the opposite direction to the first roller, preferably the loose roller, by compressive stress and, if necessary,agglomerated, whereby any air pressed from the ground material 2 flows partly upwards against the material flow, but laterally past the dosing device 9 and the material feed chute 5 and, for example, into a ventilation duct (not shown).

[0028] The dosing device 9 with the dosing body 7, 8 is attached, for example, to the machine frame of the roller press 4 and contains an adjusting mechanism and typically a gear (not shown) for adjusting the dosing body 7, 8. The dosing body 7, 8 could also be mounted on the material feed chute 5 or on a specially provided rod assembly. Without changing the schematically illustrated basic structure of the system, the dosing body 8 of the dosing device 9 could also be designed as a rotatable or pivotable dosing flap 13. Cover elements (not shown) are advantageous at the axial ends of the roller gap 3, which prevent or reduce the axial escape of ground material 2 from the roller gap 3 before the compressive stress is applied.

[0029] In Figure 21 shows a schematic, three-dimensional oblique view of a dosing body 8 of a feeding device 1 according to the invention. The flow of ground material 2, the direction of movement of which is indicated by arrows, comes from the material feed chute 5 between the dosing body 8 and the only first roller 6 shown here, in the direction of the roller gap 3 (not shown), which adjoins the viewer. The (geometric) rotation axis 14 of the roller 6 is shown. According to the inventive design of the dosing body 8, there is a further intermediate space 17 in the area of the central section 15 of the lower boundary surface 16 of the dosing body 8 and a narrower intermediate space 19 in the area of the outer sections 18 towards the roller 6. This design of the dosing body 8 with its projecting parts 11 advantageously reduces the throughput of ground material 2 in the area of the outer sections 18.The length of the outer sections 18, which are of equal length in the illustrated embodiment, in the axial direction is each up to 25% of the total length of the dosing body 8, which here extends over the entire roller gap length; (illustration not to scale).

[0030] Figure 3 and Figure 4 show two embodiments of the metering body 8 according to the invention above the first roller 6 in a schematic sketch. The metering body 8 can be designed as a height-adjustable metering slide 7 or a rotatable metering flap 13 and in each case has a plate-like basic shape. Its lower profile line resulting in this longitudinal section is composed of two outer sections 18 and a middle section 15. While in the embodiment of the Figure 3 in the outer sections 18 there is a constant distance A to the surface of the roller 6, in the embodiment of the Figure 4The lower boundary surface 16 in the outer sections 18 is not parallel to the horizontal center plane of the rollers 6, 12. Instead, it slopes downwards toward the outer ends of the metering body 8, located here on the left and right. The profile line shown slopes downwards linearly. As a result, the distance between the lower boundary surface 16 and the surface of the roller 6 decreases outwards: A1 < A2 , which has an outwardly increasing reducing effect on the grinding material stream 2.

[0031] In Figure 51 shows a schematic cross-sectional sketch through a further design of the dosing body 8 according to the invention, wherein the section in the lower region of the dosing body 8 is parallel to the horizontal plane containing the axes of rotation 14 of the two rollers 6, 12. In this plan view, the underlying rollers 6, 12 as well as the roller gap 3 formed between them are also shown. The dosing body 8 has, in its outer sections 18 in the region of the downwardly projecting parts 11, a concavely curved profile 20 on the side facing the ground material stream 2 coming from the material feed chute 5 (i.e., not the underside 16), wherein the ground material 2 has previously emerged from the material feed chute 5. This concave curvature 20 of the extension parts has an effect against any escaping of ground material 2 at the axial ends of the upper roller gap region 3.The expert will carry out the precise design of the concavely curved profile 20 with reference to a frequently set, possibly central, setting position of the dosing body 8 in practice. LIST OF REFERENCE SYMBOLS 1 Feeding device 14 axis of rotation 2 Ground material 15 middle section 3 roller gap 16 lower boundary surface 4 roller press 17 Space (in the middle section) 5 Goods feed chute 6 Roller (first) 18 outer section 7 Dosing slide 19 Space (in the area of an outer section) 8 Dosing body 20 concave curved course 9 Dosing device 10 Gap (between dosing body 8 and surface of roller 6) 11 protruding part 12 Roller (second) A, A1, A2 Distance 13 Dosing flap

Claims

1. Feeding device (1) for feeding brittle grinding stock (2) onto a roll gap (3) formed between two rollers (6, 12) of a roller press (4), comprising - a material feed chute (5) above the roll gap (3), and - a feed control device (9) with a control element (8) for controlling the flow of brittle grinding stock (2) emerging from the feed chute (5) and flowing towards the roll gap (3), wherein the control element (8) has a lower delimiting surface (16) which defines a clearance (10) between the control element (8) and the roller surface of a first of the two rollers (6) for the passage of the brittle grinding stock (2), characterized in that the lower delimiting surface (16) of the control element (8) projects at each outer section (18), relative to the longitudinal extent of the roll gap (3), such that in the region of these two outer sections (18), the clearance (19) between the control element (8) and the roller surface of the first roller (6) is narrower than the clearance (17) between the control element (8) and the roller surface of the first roller (6) in the area of the central section (15) of the lower delimiting surface (16) of the control element (8) located between the two outer sections (18).

2. Feeding device (1) according to claim 1, characterized in that each of the two projecting outer sections (18) of the lower delimiting surface (16) of the control element (8) extends from the respective end of the control element (8) towards the center in the direction of the longitudinal extent of the roll gap (3) over a length of up to 10% of the total length of the control element (8).

3. Feeding device (1) according to one of claims 1 or 2, characterized in that the feed control device (9) is provided - as a slide-type feed control device (9), wherein the control element (8) is embodied as an essentially plate-shaped dosing slide (7), or - as a flap-type feed control device (9), wherein the control element (8) is embodied as an essentially plate-shaped dosing flap (13).

4. Feeding device (1) according to claim 3, characterized in that the lower delimiting surface (16) of the control element (8), in the area of the two projecting outer sections (18), extends essentially parallel to the horizontal central plane of the two rollers (6, 12), with reference to an assumed vertical orientation of the control element (8).

5. Feeding device (1) according to claim 3, characterized in that the lower delimiting surface (16) of the control element (8), in the area of the two projecting outer sections (18), descends towards the outer ends of the control element (8), so that in this area, the distance between the lower delimiting surface (16) of the control element (8) and the roller surface of the first roller (6) decreases outwardly.

6. Feeding device (1) according to one of claims 1 to 5, characterized in that the projecting parts (11) of the control element (8) defined by the two projecting outer sections (18) of the lower delimiting surface (16) of the control element (8) are movably connected to the remaining part of the control element (8).

7. Feeding device (1) according to one of claims 1 or 2, characterized in that the projecting parts (11) of the control element (8) defined by the two projecting outer sections (18) of the lower delimiting surface (16) of the control element (8) each have a concavely curved profile (20) on their inner side facing the flow of the brittle grinding stock (2), in the direction of the longitudinal extent of the roll gap (3), towards the respective end of the control element (8).