Grinding surfaces for treating aqueous suspension

Abstract

Grinding element (2) having a grinding surface (4) for a grinding arrangement, grinding bars (21), and grooves (22) extending between the grinding bars (21). Dams (23) are located in the grooves. Each dam connects two adjacent grinding bars (21) to one another. At one end of the dam (23), the connected grinding bar (21) extends only radially outwards. An opening (26) is formed radially inwards of the dam (23) in the grinding bar (21) as a passage for fibers.

Description

[0001] File: 28629 WO / PSA - 1 -

[0002] Grinding surfaces for the treatment of aqueous suspension

[0003] The invention relates to grinding elements with grinding surfaces for grinding an aqueous suspension, preferably for grinding suspended cellulose fibers, between two grinding surfaces forming a grinding gap and rotating relative to each other. The grinding surfaces have grinding ridges and grooves running between them, and dams arranged in the grooves.

[0004] It has long been known to mill cellulose fibers, i.e., virgin pulp and / or recycled paper fibers, to achieve the desired properties in the resulting fiber web, particularly regarding strength, structure, and surface. The proportions of fiber suspensions of varying quality, especially long fibers, have a decisive influence on the resulting product. Long fibers are defined as those with a length exceeding 1.5 mm, and particularly 2.0 mm. Such long fibers are predominantly obtained from softwood.

[0005] In fiber treatment involving grinding, machines called refiners are used. The grinding surfaces in refiners are subject to significant wear and are therefore replaceable. Grinding plates are typically screwed to a support surface provided in the refiner. The opposing grinding plates create a treatment gap. The grinding plates or elements used to create this treatment gap are also referred to as a grinding assembly.

[0006] To achieve the desired fiber properties, especially the degree of refining, the grinding attachments must be optimally adapted to the fiber material being processed. Furthermore, minimizing the energy required for this process is always a priority.

[0007] Minimizing idle power consumption reduces the energy required for processing. File: 28629 WO / PSA -2 -

[0008] The requirements for grinding sets are differentiated between the application cases of low-consistency (LC) and high-consistency (HC) treatment. HC is defined as a suspension concentration of at least 6% by weight of solid material, particularly fibers. During HC treatment, the problem of gas formation frequently arises. The gas is discharged radially through designated openings in the grinding bars. Specifically, the provision of channels for vapor discharge is known from US 5,373,995. Furthermore, a grinding set with channels for radially inward vapor discharge is known from EP 3 450 624 B1.

[0009] EP 2722433 shows grinding plates or grinding plate segments with grooves and ridges. The grooves of the grinding plate segments are either substantially completely blocked by full-height ridges or partially blocked by full-height ridges. In some designs, the ridges are only located in the radially outer area between the grinding ridges.

[0010] US Patent 259,974 discloses a fiber treatment device with two facing grinding discs and an eccentrically arranged pulp feed. In the radially inner region, the grinding surface is concave and features radially extending ridges. In the radially outer region, cutting edges are arranged in a zig-zag pattern to prevent excessively rapid radial outward flow and to allow processing by the cutting edges in this area. The zig-zag arrangement of the grinding surface's cutting edges includes circumferential openings for material passage.

[0011] From EP 1 670 592 B1, grinding plate segments with grinding guides are known. The grinding guides are radially aligned. This allows these grinding plate segments to be used independently of the direction of rotation, and the direction of rotation can be changed during operation. File: 28629 WO / PSA - 3 -

[0012] EP 3 450 624 shows grinding plates with dams. The dams are arranged at an angle to the ridges to allow any steam that forms to be returned radially inwards. Recesses are provided for the steam to pass through, so that the steam can take its path radially inwards within the grinding surface and does not enter the gap formed between the grinding surfaces.

[0013] From US 12,031,270 it is known to provide a pressure equalization system between at least two adjacent boxes arranged radially at the outermost points, each formed by two grinding bars and two dams.

[0014] A grinding surface for a pulp treatment device is known from CN 116657436 A. The grinding surface has radially oriented ridges connected by circumferentially extending ridges. Partially height-filling blocks are provided radially inside the ridges to facilitate pulp passage and to counteract excessive wear, e.g., from sand, in front of the ridges. The blocks have a height of at least 1 / 3 to 3 / 4 of the height of the grinding ridges / ridges. This results in a stepped structure for easier passage over the ridges / ridges. Such treatment surfaces are subject to significant wear, so that with wear, the reduced height of the blocks reaches the height of the ridges and ridges, and the stepped structure disappears.

[0015] The invention is based on the objective of providing grinding elements for a refiner, thereby ensuring treatment quality and keeping energy consumption low.

[0016] In particular, the invention aims to improve the quality of long-fiber treatment in granites while requiring less energy. File: 28629 WO / PSA - 4 -

[0017] The problem is solved according to the invention by grinding elements according to the independent claim. Further advantageous embodiments of the present invention are found in the dependent claims.

[0018] Idle power consumption can be reduced by incorporating dams. Therefore, the inclusion of dams is of great importance in energy-optimized grinding elements. However, tests have shown that conventional dams cause a significant fiber shortening effect during grinding with high edge loads, which is generally undesirable. By providing the openings according to the invention radially inside at one end of the respective dam, a passage for the suspension is provided. This allows dams to be incorporated even in grinding elements used with high edge loads, resulting in a positive effect on reduced idle power consumption.

[0019] In a preferred embodiment, each dam has a radially internal opening for the passage of long fibers. This ensures that the undesirable fiber shortening effect frequently caused by dams is counteracted at every dam. Such grinding elements are advantageous for processing fiber grades with a high proportion of long fibers.

[0020] In a preferred embodiment, the dams are provided with an opening at only one end. This ensures that the dams have a beneficial effect on idle power consumption, thereby minimizing the energy required for treatment.

[0021] In one embodiment, the dams are only formed in the radially outer region. It is precisely in this radially outer region that undesirable backflow frequently occurs, which has a negative effect on energy consumption. File: 28629 WO / PSA - 5 -

[0022] In one embodiment, dams are distributed across the entire grinding surface. This counteracts unwanted backflow across the entire grinding surface, particularly in the radially inner area.

[0023] In a preferred embodiment, a circumferential dam is formed radially inside, connecting all the starting grinding bars. Such a circumferential dam can significantly contribute to reducing backflow when used on the stator and thus improves efficiency.

[0024] In one possible embodiment, the opening in the grinding bar is smaller than the width of the respective groove measured perpendicular to the grinding bar. This ensures that the suspension in the grooves can pass through the opening, while the edge length of the grinding bar is only slightly reduced.

[0025] In a preferred embodiment, the free end of a grinding bar defining the opening is provided with a chamfer. This reduces fiber adhesion to the edges of the opening. The opening can have a greater extent in the region of the chamfer than the groove width in the circumferential direction. The chamfer leads to an opening that narrows towards the bottom of the groove.

[0026] In a preferred embodiment, the narrowest point of the opening is smaller than the groove width when a chamfer is formed. This minimizes the reduction in edge length caused by the opening. The chamfer can extend right up to the dam.

[0027] Preferably, the groove widths n are in the range of 2.0 to 6.0 mm. Particularly preferably, the groove widths n are in the range of 3.8 to 5.0 mm. File: 28629 WO / PSA - 6 -

[0028] In a preferred embodiment, the chamfers are formed in the range of 15° to 60° and particularly preferably in the range of 30° to 45°. This prevents, or at least reduces, the accumulation of fiber material in the area of ​​the opening and minimizes the reduction in edge length.

[0029] In one embodiment, the connection between the dam and the grinding bar has a radius of at least 3 mm, particularly preferably at least 4 mm, radially inside the dam. Preferably, the radius at this connection point is a maximum of 7 mm. A maximum radius of 6 mm is particularly preferred.

[0030] In one embodiment, the opening on the dam is provided to have a radially inward curve with a radius in the range of 1mm to 3mm.

[0031] In one embodiment, it is provided that the end of the respective grinding bar pointing towards the opening is formed with a curve, preferably with a semicircle as a curve.

[0032] In a preferred embodiment, the connection point between the dam and the base plate is formed at least on the radially outer side of the dam with a radius in the range of 2 mm to 6 mm.

[0033] Such designs of the opening help to prevent the opening from becoming clogged with fibrous material, or at least to reduce this risk.

[0034] In one design variant, an opening is provided on only one side of the dam. Such grinding elements are particularly suitable for processing long fibers. File: 28629 WO / PSA - 7 -

[0035] In an alternative design variant, openings are formed radially inwards at both ends of the dam. This design variant can be particularly advantageous for the treatment of short fibers.

[0036] In one embodiment of a grinding element, dams are arranged in a radially outward extending groove at a distance greater than 10 mm, preferably less than 80 mm. In a preferred embodiment, the dam spacing is at least 35 mm. Spacings in this range have proven particularly suitable for maximizing the effect associated with the dams.

[0037] In a preferred embodiment, dams are provided in the grooves, preferably in the radially outer region extending over two-thirds of the radial extent of the grinding element. This allows for improved fiber treatment. The dams optimize the hydraulic capacity. It has been shown that with reduced height of treatment elements, the flow direction in the stator can reverse from backflow to forward flow. Providing dams in the grooves prevents this potential forward flow.

[0038] Grinding elements are used in grinding arrangements, particularly in refiners, for grinding aqueous-suspended cellulose fibers and must be replaced regularly due to wear. For processing, the grinding elements form two grinding surfaces that create a grinding gap and rotate relative to each other. At least one of the grinding surfaces has at least one of the previously described grinding elements.

[0039] The grinding elements can be used for processing both short and long fibers. These fibers can be either virgin or recycled. File: 28629 WO / PSA - 8 -

[0040] It has proven advantageous to provide grinding elements according to the invention, in particular for the stator of a grinding assembly.

[0041] In an advantageous grinding assembly, a cutting angle of 60° ±10° is provided by the grinding bars and / or dams of the rotor grinding surface and the stator grinding surface for the processing of long fibers. The dams provided can also contribute to the processing of the suspension in conjunction with the grinding bars and dams of the opposing grinding surface. The dams can also function as cutting edges through appropriate arrangement.

[0042] In an advantageous grinding assembly for the treatment of short fibers in particular, it is provided that a cutting angle of 35° + / - 10° is provided by the grinding elements / dams of the opposing grinding surfaces.

[0043] It has proven advantageous to use the grinding elements for treating a suspension in the LC range with a maximum concentration of 6% by weight of the suspension. In particular, the grinding elements allow a high proportion of long fibers to be maintained.

[0044] In a grinding arrangement, at least one grinding surface is preferably provided with dams. Fibers can pass through radially arranged openings within the dams and are retained. This makes it possible to process fibers under high edge loads on grinding surfaces provided with dams.

[0045] The flow direction of the suspension is determined by the relative movement of the grinding surfaces and, in the case of radial inward feeding, always has a flow component towards the radial outward.

[0046] In a preferred application, when the grinding elements are used in the stator, the openings are provided in the direction of rotation of the rotor, and when the grinding elements are used in the rotor, the openings are formed against the direction of rotation of the rotor on the respective grinding element. File: 28629 WO / PSA

[0047] The invention will be explained below with the aid of figures. The figures show, in detail:

[0048] Fig. 1: Grinding element

[0049] Fig. 2: Sectional view of an opening of the grinding element

[0050] Fig. 3: Schematic representation of a refiner

[0051] Fig. 4: Sectional view of the grinding bars starting radially inwards

[0052] Fig. 5: Sectional view of a design of a grinding surface with a one-sided opening

[0053] Fig. 6: Sectional view of a design of a grinding surface with openings on both sides

[0054] Fig. 7: Sectional view of a design of a grinding surface with a one-sided opening radially inside the dam and rounded connection points of the dam on the radially outer side of the dam. Fig. 8: with variants a) to g) of a possible embodiment of the grinding bar radially limiting the opening with a chamfer.

[0055] Fig. 9: Angle of inclination of dam

[0056] Fig. 10: Opening 26 with residual height of the grinding bar

[0057] Fig. 11: Circumferential dam at the stator

[0058] Figure 3 shows a grinding arrangement of a refiner. In the grinding arrangement 1, a grinding gap 3 is formed by a stationary grinding surface 4 coupled to the housing and a grinding surface 4 rotating about a rotational axis 10. Refiners are used particularly in the fiber processing of cellulose fibers.

[0059] The two annular grinding surfaces 4 run parallel to each other, with the distance between them typically being adjustable. In addition to the flat grinding surfaces 4 shown here, conical grinding surfaces, also known as treatment surfaces, are possible. The rotating grinding surface 4 is moved in the direction of rotation by a shaft 12, which is rotatably mounted in the housing. This shaft 10 is driven by a drive mechanism (not shown). File: 28629 WO / PSA - 10 -

[0060] In the example shown, the fiber suspension 1 to be ground enters a grinding gap 3 between the two grinding surfaces 4 via an inlet 5 through the center. However, feeding via openings 26 in the grinding surface is also possible. The fiber suspension S passes radially outwards through the interacting grinding surfaces 4 and exits the subsequent annular space through an outlet 6.

[0061] Not shown are the means, known per se, by which a force is generated to press the two grinding surfaces 4 against each other. Each grinding surface 4 is formed by several circular segment or annular segment-shaped grinding segments 8 as grinding elements according to Figure 2. However, the grinding surface 4 could also be formed by a single grinding element 2. The grinding elements 2 have a base plate 18. Treatment elements 20, here grinding bars 21 and dams 23, are provided on the base plate.

[0062] Figure 1 shows a grinding element 2. The grinding element 2 is a ring segment and extends over a 90° angle. The grinding bars 21 extend predominantly in the radial direction R. Grooves 22 are formed by adjacent grinding bars 21. Dams 23 are arranged in the grooves 22. The dams 23 extend predominantly in the circumferential direction U. The dams extend in a straight line between two grinding bars. Two adjacent grinding bars 21 are connected to each other by the dams 23. An opening 26 is formed radially inward below the dam 23, directly adjacent to a connection with a grinding bar 21. Thus, the connection of the grinding bar 21 at one end of the dam 23 is formed as an angled connection 27. At the opposite end of the dam 23, the connection with the grinding bar is formed as a T-shaped connection 28. The angled connection 27 is rounded on the side facing the opening 26.The grinding bar 23, which limits the opening 26, is also provided with a curve 29 on the side facing the opening 26. The opening 26 widens towards the side facing away from the dam 23. File: 28629 WO / PSA - 11 -.

[0063] The opening 26 will be arranged on a grinding element for the stator 17 at the stator dam in the direction of rotation of the rotor. Theoretically, backflow could occur through the interruptions in the grinding bars 21 in the stator 17; however, this is strongly restricted by the resulting labyrinth shape and by the opening direction of the slots 22 via the opening 26, which is opposite to the direction of rotor rotation.

[0064] If dams 23 and openings 26 are also used on the rotor 16, the opening 26 on the rotor grinding element, from the perspective of the forward flow (flow direction from radial inside to radial outside), is opposite to the direction of rotation of the rotor 16. Thus, with appropriate alignment of the grinding bars, the exact same design (casting pattern) can be used for stator 17 and rotor 16.

[0065] This arrangement of the openings 26 of the grinding bars directly on the dam 23 allows a fiber flake to escape into the adjacent groove 22 at the dam 23 when the rotor grinding bar 21' and stator grinding bar 21' overlap (Fig. 2) and is not retained there. This avoids locally excessive shear forces and prevents, or at least reduces, undesirable shortening.

[0066] If a grinding assembly with grinding elements 2 without dams is provided for the rotor 16 and grinding elements with dams 23 and openings 26 are provided for the stator, different casting models are required for the rotor and stator.

[0067] The provision of dams 23 has the disadvantage that the effective cutting edge length of the grinding bars 21 is lost. To compensate for these losses and even increase the cutting edge length, these dams 23 are positioned such that the desired cutting angle is achieved between the dams 23 of the stator 17 and the grinding bars 21' of the rotor 16. The cutting angle α is shown in Fig. 2. The relative movement between rotor 16 and stator 17 causes the cutting angle between the grinding bars 21' of the rotor 16 and the dams 23 of the stator 17 to close in the direction of the inner diameter. The dams 23 thus also take over the function of the grinding bars 21 of the stator. In the illustrated embodiment, the cutting angle is 60°. File: 28629 WO / PSA - 12 -

[0068] Angles are shown. The angle of intersection between a grinding bar 21' of the rotor 16 and a dam 23 of the stator 17 is denoted by a. The angle of intersection between a grinding bar 21' of the rotor and a grinding bar of the stator 21 is denoted by ß.

[0069] Optimizing Hydraulic Capacity:

[0070] It has been shown that a reduced height of the grinding bars 21 due to wear can reverse the flow direction in the stator 17 from backflow to forward flow. The dams 23 at grinding element 2 of the stator 17 prevent this forward flow, and thus a reduction in hydraulic capacity can occur towards the end of the service life. For this reason, the inner area of ​​the stator 17 is not equipped with dams 23 in treatment elements used for organic chlorinated filtration (OCC). This allows suspension to flow in the conveying direction and, especially in cases of advanced wear of the grinding bars 21, contribute to the capacity.

[0071] Figure 4 shows grinding bars 21. The grinding bars 21 have an axially extended extent 31, also referred to as the height of the grinding bar 21. The volume of the grooves 22 bounded between the grinding bars is thereby increased in this region. The grinding element 2 has a constant axial extent 9. The gap width remains unchanged. The base plate 18 supporting the grinding bars 21 has a reduced thickness 19 in its radially inner region. The reduced thickness of the base plate 18 compensates for the greater extent of the grinding bars 21 in this inner region. This results in improved suspension flow in the radially inner region.

[0072] The hydraulic capacity of the grinding segments typically decreases with increasing wear, and premature replacement of the grinding elements 2 may be necessary due to insufficient hydraulic capacity. To increase the hydraulic capacity, e.g., with a remaining grinding bar height of, for example, 2 mm in the radially outer third of the grinding element 2, the open area in the inner region of the grinding element 2 can be significantly increased by increasing the height of the grinding bars 21 radially inwards, for example, by 1 mm to a maximum of 3 mm, and in particular by 1.5 mm. The heights of the grinding bars 21 are shown in File: 28629 WO / PSA - 13 -

[0073] The radial outer area typically has an initial height of 10 mm, 8 mm, or 6 mm. With a continuous increase of 1.5 mm radially inwards, a grinding bar 21 height of 8 mm at the outer radius would initially result in a height of 9.5 mm on the inside.

[0074] Figures 5 to 7 show various designs of grinding surfaces with dams and openings.

[0075] In the embodiment shown in Figure 5, an opening 26 with width b is formed radially inside the dam. The edges 29, 33 bounding the opening 26 are rounded. The width b of the opening 26 is the narrowest point of the opening 26 in the grinding bar 21, which extends radially outwards. The width b of the opening 26 is smaller than the width n of the grooves 22, where the width n of the grooves 22 is measured perpendicular to one of the grinding bars laterally bounding the groove. If the two grinding bars bounding the groove have different values, the smaller value is used as the width n of the groove. The radially inward-facing surface of the connection between the dam 23 and the grinding bar 21 is rounded. The radius of the rounding is at least 3 mm. The maximum radius of the surface is 7 mm.At the junction of the dam and the grinding bar, which defines the opening, the radially inward-facing surface 29 is also formed with a radius. The radius of this radius can be smaller than that of surface 33. It is possible for the radius of surface 9 to be only half the radius of the curved surface 33. On the radially outer side, the connection between the dam 23 and the base plate 18 is formed with a radius 34. Here, a radius in the range of 2 mm to 6 mm is provided.

[0076] Figure 6 shows one embodiment. In this embodiment, the dams are connected to the adjacent grinding bars on both sides by an angled connection. Radially on the inside of the dam, openings 26, 126 are formed at both ends. The widths of the openings 26, 126 are b and b'. The widths b, b' can be of different sizes. File: 28629 WO / PSA - 14 -

[0077] In the embodiment shown in Figure 7, the connections 31, 32 from dam 23 to grinding bar 21 are rounded. The radii 31, 32 are formed on the radially outward-facing side of the dam, with a radius ranging from R = 2 mm to 7 mm. The radii formed on the two sides 31, 32 can have different radii, as also shown in Figure 7.

[0078] Figure 8 shows various possible configurations of openings 26 with a phase with an angle of inclination. <p an der die Öffnung radial innen begrenzenden Mahlleiste 21. Die Phase kann über die gesamte Höhe der Öffnung ausgebildet sein, wie in den Varianten 8b), 8d) und 8f) gezeigt. In den Ausführungsvarianten 8a), 8c) und 8e) erstreckt sich die Phase nur über den äußeren Teilbereich der Mahlleiste. Der äußere Teilbereich ist auf der dem Nutgrund abgewandten Seite der Mahlleiste. Bei den hier dargestellten Ausführungsvarianten verbleibt im Bereich der Öffnung keine Mahlleiste und damit keine Erhebung über dem Nutgrund.

[0079] However, from a manufacturing perspective, it can be advantageous to allow a remaining portion of a grinding bar with a maximum height h of 2 mm, preferably 1 mm. Figure 10 shows such an opening 26 with a chamfer and a residual height h of a grinding bar 21 in the area of ​​the opening 26.

[0080] Figure 9 shows the inclination angle y of the dams as an example. The angle is measured tangentially in the circumferential direction. The angle is in the range of up to + / - 25°, preferably in the range of up to + / - 10°. The dam is still inclined radially outwards, so that an opening is formed radially inwards at the radially outward end of the dam. It is possible for the inclination angle of the dams to vary radially outwards.

[0081] Figure 11 shows a radially circumferential dam 24. Assemblies with such a circumferential dam 24 are particularly suitable for use on the stator. This circumferential dam represents a flow obstruction and influences the flow in the slots. File: 28629 WO / PSA

[0082] - 15 -

[0083] Reference symbol list

[0084] 1 Grinding arrangement

[0085] 2 grinding element

[0086] 3 grinding gap

[0087] 4 grinding surfaces

[0088] 5 Inlet

[0089] 6 Procedure

[0090] 8 grinding segment

[0091] 9 Axial extension of grinding element

[0092] 10 Rotation axis

[0093] 16 Rotor

[0094] 17 Stator

[0095] 18 Base plate

[0096] 19 Axially reduced thickness of the base plate

[0097] 20 treatment elements (walkways, dams)

[0098] 21 grinding bars

[0099] 22 Nut

[0100] 23 Dam

[0101] 24 Circumferential dam

[0102] 26 Opening

[0103] 126 Further opening

[0104] 27 angled connection

[0105] 28 T-shaped connection

[0106] 29 Rounding of the angled connection

[0107] 30 Radial curvature inside the dam at the T-junction 31 Radial curvature outside the T-junction

[0108] 32 Rounding angle connection radial outside

[0109] 33 Rounding of the grinding bar at the opening

[0110] 34 Rounding of dam base plate

[0111] S fiber suspension file: 28629 WO / PSA

[0112] - 16 -

[0113] R Radial direction

[0114] U circumferential direction

[0115] A axial direction

[0116] a cutting angle grinding bar dam

[0117] ß Cutting angle grinding bar-grinding bar

[0118] Y Inclination of the dam to the circumferential tangent cp Inclination angle of the phase of the opening 26 n Width of the groove

[0119] b Width of the opening

[0120] h Height of grinding bar in the area of ​​opening 26

Claims

File: 28629 WO / PSA - 17 - Patent claims 1. Grinding element (2) with a grinding surface (4) for a grinding arrangement, in particular a refiner, with grinding bars (21) and grooves (22) extending between the grinding bars (21) and with dams (23) arranged in the grooves, wherein two adjacent grinding bars (21) are connected to each other by a dam (23), characterized in that at one end of the respective dam (23) the connected grinding bar (21) extends only radially outwards and an opening (26) is formed radially inwards from the dam (23) in the grinding bar (21) as a passage for fibers, wherein the opening (26) preferably extends almost over the entire height of the grinding bar.

2. Grinding element (2) according to claim 1 , characterized in that the opening (26) for the passage of long fibers is provided radially inside each dam (23).

3. Grinding element (2) according to one of the preceding claims, characterized in that the opening (26) is limited by rounded walls (29, 33).

4. Grinding element (2) according to one of the preceding claims, characterized in that the dam (23) is arranged inclined radially outwards and the opening (26) at the radially outward end of the dam (23) is formed radially inwards from the dam (23).

5. Grinding element (2) according to claim 4, characterized in that the dam (23) is arranged inclined radially outwards at an angle y to the tangent in the circumferential direction of ±25°, preferably ±10°.

6. Grinding element (2) according to one of the preceding claims, characterized in that the dam (23) at the connection (28) with the grinding bar (21) on the radially inwardly pointing limiting edge (30) has a radius at least twice as large compared to the file: 28629 WO / PSA - 18 - The opening (26) is provided with a radially inner boundary (29) formed on the dam.

7. Grinding element (2) according to one of the preceding claims, characterized in that the connection point (28) of the dam and the grinding bar has a radius of at least 3 mm, preferably of a maximum of 7 mm, radially inside the dam (23).

8. Grinding element (2) according to one of the preceding claims, characterized in that the dams (23) are provided with an opening (26) only at one end.

9. Grinding element (2) according to one of the preceding claims, characterized in that the dams (23) are provided with an opening (26) radially inside at both ends.

10. Grinding element (2) according to one of the preceding claims, characterized in that the connection point from the dam (23) to the base plate (18) is rounded, wherein the rounding (34) has a radius in the range of 2 mm to 6 mm, preferably the rounding is formed at least on the radially outer side of the dam (23).

11. Grinding element (2) according to one of the preceding claims, characterized in that the dams (23) are formed only in the radially outer region.

12. Grinding element (2) according to one of the preceding claims, characterized in that dams (23) are provided distributed over the entire area of ​​the grinding surface (2).

13. Grinding element (2) according to one of the preceding claims, characterized in that the width (b) of the opening (26) in the grinding bar (21) is smaller than the width (n) of the grooves measured perpendicular to the grinding bar (21). File: 28629 WO / PSA - 19 - 14. Grinding element (2) according to one of the preceding claims, characterized in that dams (23) provided in a groove (22) extending radially outwards are arranged at a distance of greater than 10 mm, preferably at least 35 mm and preferably less than 80 mm.

15. Grinding element according to one of the preceding claims, characterized in that a grinding bar is preferably formed in the area of ​​the opening (26) with a maximum height (h) of 2mm above the base of the groove.

16. Grinding element according to one of the preceding claims, characterized in that the opening (26) extends over at least 80% of the maximum initial height of the grinding bar (21).

17. Grinding element (2) according to one of the preceding claims, characterized in that the free end of a grinding bar limiting the opening is formed with a phase (cp), wherein the phase preferably has an angle of 15° to 60°, particularly preferably an angle of 30° to 45°.

18. Grinding assembly comprising rotor grinding elements for forming a grinding surface (4) provided on a rotor (16) and stator grinding elements for forming a grinding surface (4) provided on a stator (17), characterized in that the grinding assembly comprises at least as stator grinding elements grinding elements (2) according to one of the preceding claims 1 to 13.

19. Grinding assembly according to claim 18, characterized in that the grinding bars (21', 21) of the rotor grinding surface and the stator grinding surface provide a cutting angle (β) of 60° ± 10°, preferably ± 5°, for long fibers, or a cutting angle (β) of 35° ± 10° is provided for short fibers by the grinding bars (21, 21'). File: 28629 WO / PSA -20 - 20. Grinding assembly according to one of claims 18 or 19, characterized in that the dams (23) of the stator (17) are arranged inclined radially outwards and that preferably a cutting angle (a) between grinding bar (21 ') of the rotor (16) to dam (23) of the stator (17) of 60° + / - 10° is provided or for short fiber a cutting angle (a) between grinding bar (21 ') of the rotor (16) to dam (23) of the stator (17) of 35° + / - 10° is provided.

21. Use of a grinding element (2) according to any one of claims 1 to 17 or a grinding assembly according to any one of claims 18 to 19 for the treatment of a suspension in the LC range with a maximum concentration of 6% by weight of the suspension.

22. Use of a grinding element (2) according to any one of claims 1 to 17 or a grinding assembly according to any one of claims 18 to 19 for the treatment of a suspension, characterized in that, when using the grinding element on a rotor, the openings are formed radially inside the dams in the grinding bars at least opposite to the direction of rotation of the rotor and / or, when using a grinding element on a stator, the openings in the grinding bars are formed at least in the direction of rotation of the rotor below each dam.

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