Milling surfaces for treating aqueous suspension

Abstract

The invention relates to a milling element (2) for a refiner. Milling strips (21) are arranged on a base plate (18) of the milling element (2). Adjacent milling strips (21) form grooves (22) extending between the milling strips (21). A hydraulic capacity is provided by the open area of the grooves in the peripheral direction. The height of the milling strips above the base plate (18) decreases from radially inwards to radially outwards, wherein, at a predetermined partial height, the open area of the grooves at the partial height at the inner radius approximately corresponds to the open area of the grooves at the partial height at the outer radius. The partial height is obtained by shortening all milling strips (21) by a predetermined amount (27).

Description

[0001] Grinding surfaces for the treatment of aqueous suspension

[0002] The invention relates to grinding plates 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 are formed by grinding ribs and grooves running between them. Dams can be arranged in the grooves.

[0003] It has long been known to grind cellulose fibers, i.e., virgin pulp and / or recycled paper fibers, in order to achieve the desired properties in the resulting fiber web, especially with regard to strength, formation and surface.

[0004] In the refiners used, the grinding surfaces are formed by replaceable grinding segments, also known as grinding assemblies, which are screwed to the corresponding support surface, due to the relatively rapid wear of the grinding elements. Several grinding segments can be used to form a grinding surface, or the grinding element can be formed as a single piece.

[0005] To achieve the desired fiber properties, especially the degree of grinding, the grinding sets must be adapted as closely as possible to the fiber material being treated, also to prevent excessive wear of the sets.

[0006] EP 2 722 433 shows grinding plates or grinding plate segments with grooves and ribs. The grooves of the grinding plate segments are either essentially completely blocked by full-height dams or partially blocked by full-height dams. In some designs, the dams are only located in the radially outer area between the grinding bars.

[0007] Grinding plate segments with grinding bars are known from EP 1 670 592 B1. The grinding bars 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.

[0008] EP 4063561 and EP 3450624 show grinding plates with dams. The dams are arranged at an angle relative to the ribs to allow the return of any steam that forms to the radial center. 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.

[0009] The invention is based on the objective of enabling a longer service life for the grinding elements.

[0010] The problem is solved according to the invention by an embodiment according to the independent claim. Further advantageous embodiments of the present invention are found in the dependent claims.

[0011] The service life can be extended by providing grinding elements where the height of the grinding bars above the base plate decreases from the radial inside to the radial outside. Improved operation can be achieved by matching the open area, and thus the hydraulic capacity, at the inner radius to the open area, and thus the hydraulic capacity, at the outer radius. This matching is based on a predetermined partial height of the grinding bars. Partial height means that, for the purposes of this analysis, the grinding bars are assumed to be reduced by a predefined amount. The design is therefore based on a predetermined residual height of the grinding bars. Such a reduction in the height of the grinding bars to a partial height occurs naturally during normal use of the grinding elements due to wear. This optimizes the hydraulic capacity of each grinding element.This optimization enables improved operation, particularly extended service life. If the remaining open area, and thus the hydraulic capacity radially inward for absorbing suspension during operation, is too small, the grinding element must be replaced, even if sufficient processing in the radially outer area would still be possible. A predetermined flow rate through the grinding assembly must be achieved to ensure smooth operation of the fiber processing system.

[0012] Partial height here means that the grinding bars are shortened by a predetermined amount. Any initial height difference in their radial path remains unchanged despite this predetermined reduction.

[0013] In a preferred embodiment, the open area at the inner radius is equal to the open area at the outer radius for a predetermined part height. This ensures sufficient treatment performance / flow capacity at the part height over an extended service life of the fitting.

[0014] The improved radial inner capacity allows for better utilization of the grinding surface. Special feed grooves can often be omitted, which has a beneficial effect on the edge length of the grinding bars.

[0015] It has been shown that it is advantageous to base the grinding element height on a maximum of 3 mm at the outer radius. This allows for improved functionality of the grinding element even when the grinding bars are worn down to a residual height of 3 mm at the outer radius, as this residual height corresponds to the partial height. This ensures that the hydraulic capacity is balanced between the inner and outer radii.

[0016] It has proven particularly advantageous to optimize the hydraulic capacities for a residual height of the grinding bars at the outer radius of 2 mm. This ensures the desired treatment even with this low residual height of the grinding bar and allows for a particularly long service life of the grinding element.

[0017] It has proven advantageous to compensate for the greater height of the grinding bars by reducing the thickness / incline of the base plate. This makes it possible to use the grinding elements in a refiner like conventional grinding elements, whereby the grinding gap can be adjusted to a predetermined value via its radial extent. An adapter or modification of the rotor and stator is not required for the use of the grinding elements according to the invention.

[0018] In one embodiment, it is provided that the height difference of the grinding bars in comparison from the inner radius to the outer radius is at least 1.0 mm, preferably at least 1.5 mm.

[0019] In a preferred embodiment, the grinding bars are radially inner and at least 10%, preferably 15%, taller than the grinding bars at the outer radius. Preferably, the variation in the height of the grinding bars is not greater than 50% of the height of the grinding bars at the radial outer radius.

[0020] In a preferred embodiment, the grinding bars are provided to have a greater height of 15% to 25% on the radial inside compared to the radial outside, relative to the height of the grinding bars at the radial outer radius.

[0021] In one embodiment, the decrease in the height of the grinding bars is continuous and radially outward, at least in an inner region. In particular, a linear decrease is possible. In a preferred embodiment, the height of the grinding bars decreases radially outward in an inner region until a minimum grinding bar height is reached.

[0022] To compensate for the grinding bars, which have a greater height radially inwards, the base plate supporting the grinding bars can be designed with a reduced thickness radially inwards. Alternatively, a sloping base plate can be used to compensate for the greater height of the grinding bars.

[0023] 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.

[0024] The invention will be explained below with the aid of figures. The figures show, in detail:

[0025] Fig. 1: Schematic cross-section through a grinding arrangement

[0026] Fig. 2: Grinding element in the form of a circular segment

[0027] Fig. 3: Sectional view of the inner radius with grinding bars

[0028] Figure 1 shows a grinding arrangement 1. 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. Such grinding arrangements 1 for treating fiber-containing suspensions are also called refiners. Refiners are used particularly in the fiber processing of cellulose fibers. In this highly simplified representation, the components forming the grinding gap 3 are shown in particular.

[0029] The two annular grinding surfaces 4 run parallel to each other, and the distance between them is generally adjustable. In addition to the flat grinding surfaces 4 shown here, conical grinding surfaces, also referred to as treatment surfaces 20, are also 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).

[0030] In the example shown, the fiber suspension 1 to be ground enters the grinding gap 3 between the two grinding surfaces 4 via an inlet through the center. However, feeding via openings 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.

[0031] 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 18. In the illustration according to Figure 2, the dams 23 formed between the grinding bars 21 are located in the radially outer region.

[0032] The grinding segments 8 extend circumferentially and are arranged side by side circumferentially. Each grinding segment 8 is formed by a base plate 18 with a plurality of treatment elements 20 and intervening grooves 22. The treatment elements 20 are grinding bars 21 and dams 23. Treatment elements consisting solely of grinding elements could also be provided.

[0033] Figure 2 shows a grinding segment with openings 35 for mounting in a grinding arrangement 1. In the embodiment shown, dams are provided between the grinding bars in the outer area. In an inner area 29, only grinding bars are provided.

[0034] Optimized edge length:

[0035] The provision of dams 23 has the disadvantage of reducing the cutting edge length of the grinding bars 21. To compensate for this loss and even increase the cutting edge length of the grinding bars, these dams 23 are positioned so 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 relative movement between the rotor 16 and the 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 thus also take over the function of the grinding bars of the stator.

[0036] Optimizing Hydraulic Capacity:

[0037] Figure 3 shows grinding bars 21 beginning at the inner radius 28. The grinding bars 21 have a greater height. The volume of the grooves 22 bounded between the grinding bars 21 is thereby increased in this area. The grinding bars 21 have a height 24. The greater height 25 of the grinding bars in this area 29 is compensated for by a reduced thickness of the base plate 18. The gap width 3, see Fig. 1, remains unchanged. This design achieves better suspension inflow in the radially inner area. The difference in the height of the grinding bars 21 decreases towards the radial outer edge. The decrease is linear, as shown here. The open area is the area of ​​the grooves into which suspension can flow. Thus, the open area along a circumferential section is calculated by multiplying the height of the grinding bar by the mean groove width 32 by the number of grooves.

[0038] The hydraulic capacity of the grinding segments 8 typically decreases with increasing wear, and premature removal of the grinding elements 2 may be necessary due to insufficient hydraulic capacity. To increase the hydraulic capacity, for example, with a remaining height 24 of the grinding bars 21 of, say, 2 mm at the outer radius of the grinding element 2, the open area in the inner region of the grinding element 2 can be significantly increased by a substantial increase in the height 24 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 24 of the grinding bars 21 in the radially outer region are generally initially 10 mm, 8 mm, or 6 mm. With a continuous increase of 1.5 mm radially inwards, a grinding bar height 24 of 8 mm at the outer radius 30 would thus initially result in a grinding bar height 24 of 9.5 mm on the inner side.The radially inward open area has a significant influence on the hydraulic capacity, although other factors such as circumferential speed, groove width 32, and surface roughness also affect the resulting hydraulic capacity. Increasing the radially inward open area increases the absorption capacity while keeping other factors constant.

[0039] Reference symbol list

[0040] 1 Grinding arrangement

[0041] 2 grinding element

[0042] 3 grinding gap

[0043] 4 grinding surfaces

[0044] 5 Inlet

[0045] 6 Procedure

[0046] 8 grinding segment

[0047] 9 Axial extension of grinding element

[0048] 10 Rotation axis

[0049] 16 Rotor

[0050] 17 Stator

[0051] 18 Base plate

[0052] 19 Axially reduced thickness of the base plate

[0053] 20 treatment elements

[0054] 21 grinding bars

[0055] 22 Nut

[0056] 23 Dam

[0057] 24 Height of the grinding bar

[0058] 25 m elevation difference

[0059] 26 Predetermined partial height

[0060] 27 Predetermined amount

[0061] 28 Inner radius (grinding elements)

[0062] 29 Radial inner area

[0063] 30 Outer radius (grinding elements)

[0064] 31 Axial extended extent of grinding bars

[0065] 32 groove width

[0066] 35 penetrations (screw connections)

[0067] S Suspension

Claims

Patent claims 1. Grinding element (2) for a grinding arrangement with grinding bars (21) arranged on a base plate (18), wherein grooves (22) extending between the grinding bars (21) are formed by adjacent grinding bars (21) and a hydraulic capacity is determined by the open area of ​​the grooves in the circumferential direction, characterized in that the height (24) of the grinding bars (21) above the base plate (18) decreases from radially inside to radially outside, wherein the height difference (25) of the grinding bars (21) from radially inside to radially outside is provided for an increase in the open area to increase the hydraulic capacity radially inside.

2. Grinding element according to claim 1, characterized in that, at a predetermined part height (26), the open area of ​​the grooves (22) at the part height (26) at the inner radius (28) corresponds to the open area of ​​the grooves (22) at the part height (26) at the outer radius (30) + / - 10%, wherein the part height (26) is obtained by shortening all grinding bars (21) by a predetermined amount (27).

3. Grinding element (2) according to claim 2, characterized in that at the predetermined partial height (26) of the grinding bars (21) the open area at the inner radius (28) corresponds to the open area at the outer radius (30).

4. Grinding element (2) according to one of the preceding claims, characterized in that the predetermined part height (26) is assumed to be a maximum height of 3mm of the grinding bars (21) at the outer radius (30), preferably 2mm.

5. Grinding element (2) according to one of the preceding claims, characterized in that the grinding bars (21 ) at the inner radius (28) are formed with a height difference (25) of at least 1 mm, preferably at least 1.5 mm, to the grinding bars at the outer radius (30).

6. Grinding element (2) according to one of the preceding claims, characterized in that a greater height of the grinding bars (21) is compensated for by a reduced thickness (19) of the base plate (18) and / or by the shaping of the base plate (18).

7. Grinding element (2) according to one of the preceding claims, characterized in that the height of the grinding bars at the inner radius in the new state of the grinding element (2) is up to 50% greater, preferably up to 25% greater, compared to the height (24) of grinding bars (21) at the outer radius (30).

8. Grinding element (2) according to one of the preceding claims, characterized in that the height (24) of the grinding bars (21 ) at the inner radius (28) is at least 10% greater, preferably 15% greater, than the height (24) of grinding bars (21 ) at the outer radius (30).

9. Grinding element (2) according to one of the preceding claims, characterized in that the base plate (18) has a thickness reduced by at least 1.0 mm, preferably by at least 1.5 mm, at the inner radius (28) of the grinding bars (21).

10. Grinding element (2) according to one of the preceding claims, characterized in that the base plate (18) is inclined in a radially inner area (29) to compensate for the greater height of the grinding bars.

11. Grinding element (2) according to one of the preceding claims, characterized in that the thickness of the base plate (18) increases in the radial direction until the maximum thickness is reached, wherein the thickness of the base plate (18) preferably increases linearly at least section by section until the maximum thickness is reached.

12. Grinding element (2) according to one of the preceding claims, characterized in that the thickness of the base plate (18) and / or the shape of the base plate is formed radially inward in a radially inner sub-area (29), preferably in a sub-area of ​​20% to 50% of the area of ​​the grinding element equipped with grinding bars, to compensate for the grinding bars with greater height.

13. Grinding assembly with grinding elements (2) according to one of the preceding claims, characterized in that the grinding assembly is provided for equipping a rotor (16) and / or stator (17) of a refiner for providing a grinding surface (4).

14. Grinding arrangement (1) for grinding aqueous suspended cellulose fibers between two grinding surfaces (4) forming a grinding gap (3) and rotating relative to each other, wherein at least one, preferably at least the grinding surface of the rotor and particularly preferably both of the grinding surfaces (4) have grinding elements (2) according to one of the preceding claims 1 to 12, wherein the grinding elements form a grinding gap with constant width.

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