FI126475B

FI126475B - Blade element

Info

Publication number: FI126475B
Application number: FI20155449A
Authority: FI
Inventors: Christer Hedlund
Original assignee: Valmet Technologies Oy
Priority date: 2015-06-11
Filing date: 2015-06-11
Publication date: 2016-12-30
Also published as: FI20155449A

Description

Blade element

FIELD OF THE INVENTION

[0001] The invention relates to a blade element for a refiner for refining fibrous material, the blade element comprising a refining surface provided with blade bars and blade grooves therebetween, the blade bars having side walls facing away from one another.

BACKGROUND OF THE INVENTION

[0002] Refiners used for manufacturing mechanical pulp are typically formed of two refining elements opposite to each other and turning relative to each other, i.e. one or both of them is/are rotating. The refining elements comprise refining surfaces provided with blade bars and blade grooves therebetween, the blade bars being intended to defiber and refine the material to be refined and the blade grooves being intended to convey the material to be refined forward along the refining surfaces.

[0003] The refining surfaces of the refining elements are typically formed by blade elements comprising the blade bars and the blade grooves, whereby the refining surface of the refining element is implemented by a single blade element intended to provide a complete refining surface of the refining element or by several blade elements, also called blade segments, which together provide the complete refining surface when the individual blade elements are fastened to the refining element next to each other.

[0004] WO-publication 2004/110628 discloses a refining surface provided with blade bars and blade groves therebetween. The blade bars are formed of at least two different blade bar parts connected to each other such that one of the blade bar parts is farther ahead in the intended rotation direction of the refining surface than the other blade bar part, and the wall of the side of the intended rotation direction of the refining surface is at least in some blade bar parts over at least part of its length substantially inclined. The inclined side wall of the blade bar causes the material to be refined to move more efficiently out of the blade grooves up to a blade gap between the opposite refining surfaces. The inclined side wall has thus an effect similar to that of a dam remaining at a bottom of a blade groove between neighbouring blade bars but without a tendency of causing the blade groove becoming clogged of the material to be refined. Other examples of prior art refining surfaces are disclosed in publications US 6616078 B1, FI 79868 C, EP 0899375 A2, US 5836525 A, US 1744226 A and GB 2031299 A.

BRIEF DESCRIPTION OF THE INVENTION

[0005] An object of the present invention is to provide a novel blade bar construction for a refiner.

[0006] The blade element according to the invention is characterized in that the side walls of the at least one blade bar comprise on both of its side walls steps which are abrupt enlargements extending to at least partly transversal direction relative to the side walls of the blade bar and away from one another, the blade bar comprising in the longitudinal direction thereof at least two successive blade bar parts connected to each other, the steps being at a connecting point of the two successive blade bar parts and mirror images relative to an imaginary centre line of the blade bar, and that the blade element comprises at least one defibration zone and at least one refining zone successive to the at least one defibration zone and that at least a portion of the blade bar comprising the steps remains in the at least one defibration zone.

[0007] An advantage of the blade element being provided with blade bars having steps on both of its side walls is that a rotatable refining element of the refiner provided with the blade element comprising blade bars as disclosed may be rotated into both directions.

[0008] Some embodiments of the invention are disclosed in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] In the following the invention will be described in greater detail by means of preferred embodiments with reference to the accompanying drawings, in which [0010] Figure 1 is a general upper view of a blade element; [0011] Figure 2 is a schematic view of an embodiment of some blade bars; [0012] Figure 3 is a schematic front view of the blade bar of Figure 2; and [0013] Figure 4 is a schematic view of an embodiment of some other blade bars.

[0014] For the sake of clarity, the figures show some embodiments of the invention in a simplified manner. Like reference numerals identify like elements in the figures.

DETAILED DESCRIPTION OF THE INVENTION

[0015] Figure 1 is a schematic general upper view of a blade element 1. The blade element 1 of Figure 1 is a disc-like blade segment intended to provide a part of a refining surface of a refining element in a disc refiner intended for refining fibrous material, such as wood material. The blade element 1 of Figure 1 comprises a blade element body 2 and a refining surface 3 on an upper surface thereof. The blade element 1 comprises an inner edge 4 or a feed edge 4 or an inner periphery 4 which is directed towards a centre of the disc refiner and through which the material to be refined may be fed into a blade gap between opposing refining elements. The blade element 1 further comprises an outer edge 5 or a discharge edge 5 or an outer periphery 5 through which the material already refined in the blade gap between the opposing refining elements may be discharged out of the blade gap, as well as a first side edge 6 and a second side edge 7 providing the side edges of the blade element 1 of Figure 1.

[0016] Next to the inner periphery 4 of the blade element 1 the refining surface 3 is provided with blade bars 8 and blade grooves 9 therebetween. Next to the outer periphery 5 of the blade element 1 the refining surface 3 is provided with other blade bars 10 and other blade grooves 11 therebetween. The blade bars 8 and the blade grooves 9 next to the inner periphery 4 of the blade element 1 provide a defibration zone 12 intended to disintegrate woods chips fed into the refiner to individual fibres. The blade bars 10 and the blade grooves 11 next to the outer periphery 5 of the blade element 1 provide a refining zone 13 that is successive to the defibration zone 12 in an intended flow direction of the material to be processed, or in a direction of a radius R of the blade element 1, the radius R extending from the inner periphery 4 up to the outer periphery 4 and disclosed schematically with an arrow R. The refining zone 13 is intended to refine the material to be processed, i.e. fibrillation and fibre shortening of the material to be processed is intended to take place at this zone of the blade element 1.

[0017] Differing from the embodiment of Figure 1 at least some of the blade bars 8 remaining in the defibration zone 12 may also extend to the refining zone 13.

[0018] Alternatively to the embodiment of the blade element of Figure 1, a blade element may be intended to provide a part of only a single zone in a refining element having multiple zones, whereby the refining element may comprise several neighbouring blade elements both in a direction of the radius of the refining element and in a peripheral direction of the refining element. In that case the defibration zone 12 and the refining zone 13 could lie on separate blade elements so that the defibration zone 12 alone could provide a radially inner element and, respectively, the refining zone 13 could form a radially outer element.

[0019] Figure 2 is a schematic view of an embodiment of some blade bars 8, showing only some portions of the blade bars 8 in the radial direction of the blade element 1. Figure 3 is a schematic front view of the blade bar 8 of Figure 2. The blade bars 8 are elongated, extending in a direction away from the inner edge 4 of the blade element 1 and they have generally a top 8’, a first side wall 8” or a first flank surface 8” and a second side wall 8”’ or a second flank surface 8”’. If an intended rotation direction of the blade element 1 of Figure 1 is to the right, the first side wall 8” provides a leading side of the blade bar 8 and the second side wall 8”’ provides a trailing side 8”’ of the blade bar 8, whereby the blade bars 10 remaining in the refining zone 13, as being curved forward, provide an effect that restrains the flow of the material to be refined towards the outer edge 5 of the blade element 1. Flowever, if the intended rotation direction of the blade element 1 of Figure 1 is to the left, the first side wall 8” provides the trailing side of the blade bar 8 and the second side wall 8”’ provides the leading side 8”’ of the blade bar 8, whereby the blade bars 10 remaining in the refining zone 13, as being curved backward, provide an effect that enhances the flow of the material to be refined towards the outer edge 5 of the blade element 1.

[0020] The blade bars 8 are formed of successive, interconnected blade bar parts 8a, 8b, 8c, each blade bar part 8a, 8b, 8c providing a portion of the complete blade bar 8. At an interconnecting point 15 of the successive blade bar parts 8a, 8b; 8b, 8c there are abrupt enlargements on both of the side walls 8”, 8”’ of the blade bar 8, that is a first step 14” on the first side wall 8” of the blade bar 8 and a second step 14”’ on the second side wall 8”’ of the blade bar 8. The steps 14”, 14”’ are in a substantially same position in a longitudinal direction of the blade bar 8, i.e. they lie in the blade bar 8 substantially on the same radial level or radial position from the inner edge 4 of the blade element 1 towards the outer edge 5 of the blade element 1. With that definition it is meant that there may be a difference of maximum 20% of a length of the blade bar part 8a, 8b, 8c between mutual positions of the steps 14”, 14’” in the longitudinal direction of the blade bar 8. The steps 14”, 14”’ extend to a direction, that is at least partly transversal to a longitudinal direction of the blade bar 8 such that the steps 14”, 14”’ extend or are directed away from one another, or in other words, the steps 14”, 14’” are directed outwards from both of the side walls 8”, 8’” of the blade bar 8. In the embodiment of Figure 2 the steps 14”, 14’” form a right angle with an imaginary centre line CL of the blade bar 8 and the steps 14”, 14’” are arranged to extend to at least partly transversal direction relative to the longitudinal direction of the side walls 14”, 14’” of the blade bar 8. However, a value of the angle between the imaginary centre line CL of the blade bar 8 and the steps 14”, 14’” may vary to the extent that the steps 14”, 14’” are at least partly transversal to the longitudinal direction of the side walls 8”, 8’” of the blade bar 8. In the height direction of the blade bar 8 the steps 14”, 14’” extend from the bottom of the blade groove 9 preferably up to the top 8’ of the blade bar 8.

[0021] An advantage of the blade element 1 being provided with blade bars 8 having the steps 14”, 14’” on both side walls 8”, 8”’ of the blade bars 8 is that the rotatable refining element of the refiner provided with the blade element 1 comprising blade bars 8 as disclosed may be rotated into both directions, whereas in prior art solutions, such as in the embodiments disclosed in WO-publication 2004/110628, the blade bar configuration predetermines the intended rotation direction of the rotatable refining element.

[0022] In the embodiment of Figure 2 the successive interconnected blade bar parts 8a, 8b; 8b, 8c are straight so that the imaginary centre line CL of the blade bar 8 provides an imaginary centre line for each blade bar part 8a, 8b, 8c, the imaginary centre lines of the successive blade bar parts 8a, 8b; 8b, 8c thus being congruent. Furthermore, in the embodiment of Figure 2 the steps 14”, 14”’ are mirror images relative to the imaginary centre line CL of the blade bar 8. This provides an advantage that the effect of the blade bars 8 to the fibrous material to be processed is the same irrespective of the intended rotation direction. In other words, in this case performance or working of the blade element is independent of the intended rotation direction of the rotatable refining element relative to the blade element 1 provided with the blade bars 8 disclosed above.

[0023] In the embodiment of Figure 2 the steps 14”, 14’” are provided by arranging a width of the successive blade bar parts 8a, 8b; 8b, 8c to decrease in the longitudinal direction of the blade bar 8, i.e. in a direction from the inner edge 4 of the blade element 1 towards the outer edge 5, i.e in a direction of the radius R of the blade element 1. Thereby, as seen in the direction from the inner edge 4 of the blade element 1 towards the outer edge 5, the width of a preceding blade bar part 8a at a back end thereof, i.e. at the end of the blade bar part 8a facing towards the outer edge 5 and referred to with a reference sign 16’, is smaller than the width of a following blade bar part 8b at a front end thereof, i.e. at the end of the successive blade bar part 8b facing towards the inner edge 4 and referred to with a reference sign 16”. Decreasing width of the blade bar parts 8a, 8b, 8c has the benefit of providing guiding surfaces 8”, 8’” which force the material towards the step 14”, 14”’ which in turn forces the material to proceed to the blade gab between the blade bars 8 of the opposing refining elements.

[0024] The length of the individual blade bar part 8a, 8b, 8c in the blade bar 8, i.e. the density of the stepping or the steps 14a”, 14a’”, in the direction from the inner edge 4 of the blade element 1 towards the outer edge 5, may for example be 5 - 65 mm, preferably 20 - 40 mm.

[0025] According to an embodiment of the blade bar 8 of Figure 2, the steps 14”, 14’” are tilted towards the outer edge 5 of the blade element 1 such that the steps 14”, 14’” provide bevels or inclined surfaces, that enhance the rise of the fibrous material to be defibrated and refined from the bottom of the blade grooves 9 towards the tops 8’ of the blade bars 8. The angle of the steps 14”, 14’” in respect of the bottom of the blade groove 9, or in respect of the blade element body 2, may for example be 20 - 70 degrees, preferably 30 - 45 degrees. With the bevelled steps 14”, 14’” it is possible to replace dams that are traditionally located at bottoms of the blade grooves between neighbouring blade bars. The removal of the dams reduces a tendency of the blade grooves becoming clogged of the material to be refined.

[0026] Furthermore, in the embodiment of the blade bar 8 of Figures 2 and 3 tops of the blade bar parts 8a, 8b, 8c are rounded, whereby the top 8’ of the complete blade bar 8 is rounded so that there are no sharp edges at a top part of the blade bar 8.

[0027] According to an embodiment of a blade bar or a part thereof, a cross sectional profile of a top of the blade bar or the part thereof in a direction perpendicular to the longitudinal direction of the blade bar or the part thereof comprises only a number of curved portions each having a radius of curvature. In this embodiment, the top of the blade bar or the part thereof may thus comprise in the direction perpendicular to the longitudinal direction of the blade bar or the part thereof only one curved portion or several curved portions with possibly different radius of curvatures. In this embodiment the top of the blade bar or the part thereof thus comprises no sharp side edges but the blade bar or the part thereof may comprise some sharp side edges lower in the side walls of the blade bar, i.e. closer to the bottoms of the blade grooves, whereby the side walls of the blade bar of the part thereof may comprise flat surfaces, which may be bevelled or inclined.

[0028] According to an embodiment of a blade bar or a part thereof, a cross sectional profile of the top of the blade bar or the part thereof in a direction perpendicular to the longitudinal direction of the blade bar comprises only a single curved portion having a single radius of curvature. In this embodiment, the top of the blade bar or the part thereof thus comprises in the direction perpendicular to the longitudinal direction of the blade bar or the part thereof only one curved portion. In this embodiment the top of the blade bar of the part thereof thus comprises no sharp side edges but the blade bar or the part thereof may comprise some sharp side edges lower in the side walls of the blade bar or the part thereof, i.e. closer to the bottoms of the blade grooves, whereby the sides of the blade bar or the part thereof may comprise flat surfaces, which may be bevelled or inclined.

[0029] According to an embodiment, a blade bar or a part thereof is rounded such that a cross sectional profile of the blade bar or the part thereof in a direction perpendicular to the longitudinal direction of the blade bar or the part thereof comprises only a single or multiple curved portions each having a radius of curvature. In this embodiment, the cross sectional profile of the whole blade bar or the part thereof comprises either one curved portion or several curved portions with possibly different radius of curvatures in the direction perpendicular to the longitudinal direction of the blade bar or the part thereof but does not at all comprise any sharp side edges, whereby the side walls of the blade bar does not comprise any flat surfaces. The embodiment of the blade bar 8 and the parts 8a, 8b, 8c thereof shown in Figures 2 and 3 is a blade bar comprising several curved portions in the direction perpendicular to the longitudinal direction of the blade bar 8. In Figure 3 there are shown arrows denoted by reference signs R1, R2, R3, R4 and R5 that indicate very schematically the curved portions and the radius of curvatures of the curved portions in the blade bar 8 in the direction perpendicular to the longitudinal direction thereof, R1 indicating the curved portion in the top 8’ of the blade bar 8 and R2, R3, R4, R5 indicating the curves portions in the side walls of the blade bar 8.

[0030] The blade bars 8 or the parts 8a, 8b, 8c thereof having the rounded tops 8’ lie preferably only in the defibration zone 12 of the blade element 1 but may in some blade bar configurations extend also into the refining zone 13 of the blade element 1.

[0031] Because of the rounded top 8’ of the blade bar 8 or the part 8a, 8b, 8c thereof in the defibration zone 12 a risk of fibrillation and fibre shortening effect on the refined material is reduced in the defibration zone 12 of the blade gap. In other words, the rounded tops 8’ or top surfaces of the blade bars 8 or the parts 8a, 8b, 8c thereof in the defibration zone 12 provide on the material, i.e. wood chips, an effect which crushes the wood chips into smaller pieces and individual fibres but does not substantially increase fibrillation degree of the fibres or decrease fibre length, which takes place in traditional blade elements comprising traditional blade bars with sharp edges in the top of the blade bars. In the embodiment of Figure 1, the fibrillation and fibre shortening then takes place substantially only in the refining zone 13 comprising the blade bars 10 if tops of them are provided with sharp edges.

[0032] Figure 4 is a schematic view of second blade bars 8, showing only some portions of the blade bars 8 in the radial direction of the blade element 1. The blade bars 8 of Figure 4 are otherwise similar to those of Figure 2 but the blade bars 8 of Figures 4 have planar top surfaces 8’, whereby the blade bars 8 of Figure 4 comprise sharp side edges 17”, 17”’ between the planar top surface 8’ and the side walls 8”, 8”’.

[0033] The blade bars 8 of Figure 4 may be utilized in the defibration zone 12 if it is intended to provide fibrillation and fibre shortening effect on the material to be refined already in the defibration zone 12. Alternatively the blade bars 8 of Figure 4 comprising the sharp side edges 17”, 17”’ may be utilized in the refining zone 13 wherein the fibrillation and the fibre shortening effect is intended to take place.

[0034] Although the benefits of the invention could be partly achieved if only a few of the blade bars 8 of the blade element 1 have the shape of the invention, it is preferable that at least 20%, and more preferably at least 50% of the blade bars 8 are equipped with steps 14”, 14’” on their both side walls according to the invention. It is preferable also that substantially all the blade bars 8 of the blade element 1 have the shape of the invention. More preferably substantially all the blade bars 8 at least in the defibration zone 12 have the shape of the invention.

[0035] The steps 14”, 14”’ of two neighbouring blade bars 8 can lie on the same radial level but preferably there is a radial shift between neighbouring steps 14”, 14’” in a blade groove 9 so that the first step 14” of one blade bar 8 lies radially on a higher or lower level than the second step 14’” in its neighbouring blade bar 8, i.e. in the blade bar 8 on the opposite side of the same blade groove 9. Then the shape of the blade groove 9 is even more irregular with multiple edges and multifaceted walls which may further improve chip guidance to the blade gab. The radial shift could be for example of 20 -50% of the length of a blade bar part 8a, 8b, 8c.

[0036] In addition to blade elements intended for the disc refiner, the features of the blade bars as disclosed herein may be utilized as well in blade elements intended to cone refiners and cylindrical refiners. The features of the blade bars as disclosed herein may also be used both in low consistency refiners and in high consistency refiners.

[0037] It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

Claims

1. Teräelementti (1) jauhimeen kuitumateriaalin jauhamiseksi, terä-elementin (1) käsittäessä teräharjoilla (8, 10) ja niiden välissä olevilla teräurilla (9, 11) varustetun jauhinpinnan (3), teräharjojen (8, 10) ulottuessa suunnassa teräelementin (1) sisäreunasta (4) kohti teräelementin (1) ulkoreunaa (5) ja omaten toisistaan poispäin olevat kyljet, tunnettu siitä, että ainakin yhden teräharjan (8) kyljet (8”, 8”’) käsittävät sen molemmilla kyljillä (8”, 8”’) kynnykset (14”, 14”’), jotka ovat äkillisiä laajentumisia ulottuen ainakin osittain poikittaiseen suuntaan suhteessa teräharjan (8) kylkiin (8”, 8”’) ja poispäin toisistaan, teräharjan (8) käsittäessä pituussuunnassaan ainakin kaksi peräkkäistä toisiinsa kytkettyä teräharjaosaa (8a, 8b, 8c), kynnyksien (14”, 14”’) ollessa kahden peräkkäisen teräharjaosan (8a, 8b, 8c) liittymiskoh-dassa (15) ja peilikuvia teräharjan (8) kuvitteellisen keskilinjan suhteen, ja että teräelementti (1) käsittää ainakin yhden kuidutusvyöhykkeen (12) ja ainakin yhtä kuidutusvyöhykettä (12) seuraavan ainakin yhden jauhatus-vyöhykkeen (13) ja että ainakin osuus kynnyksiä (14”, 14”’) käsittävästä terä-harjasta (8) on ainakin yhdellä kuidutusvyöhykkeellä (12).A blade element (1) for refining a fibrous material, the blade element (1) comprising a refining surface (3) having blade brushes (8, 10) and intermediate blade grooves (9, 11), the blade brushes (8, 10) extending in the direction of the blade element (1). ) from the inner edge (4) towards the outer edge (5) of the cutting element (1) and having flanks spaced apart, characterized in that the flanks (8 ", 8" ') of at least one blade brush (8) comprise it on both sides (8 ", 8") ') thresholds (14 ", 14"') which are sudden expansions extending at least partially transverse to the sides (8 ", 8" ') of the blade brush (8) and away from one another, the blade brush (8) comprising at least two successive interconnections the blade brush portion (8a, 8b, 8c), the thresholds (14 ", 14" ') at the junction (15) of two successive blade brush portions (8a, 8b, 8c) and mirror images of the blade brush (8), and the blade element (1) comprising at least one defibration zone (12) and at least one refining zone (13) following at least one defibration zone (12) and that at least a portion of the blade brush (8) having thresholds (14 ", 14" ') in the defibration zone (12).

2. Patenttivaatimuksen 1 mukainen teräelementti, tunnettu siitä, että teräharjan (8) kynnykset (14”, 14”’) sijaitsevat olennaisesti teräelementin (8) samalla säteittäisellä tasolla.Blade element according to Claim 1, characterized in that the thresholds (14 ", 14" ') of the blade brush (8) are located substantially on the same radial plane of the blade element (8).

3. Patenttivaatimuksen 1 mukainen teräelementti, tunnettu siitä, että teräharjaosat (8a, 8b, 8c) ovat suoria ja peräkkäisten teräharjaosien (8a, 8b, 8c) kuvitteelliset keskilinjat (CL) ovat yhteneviä.Blade element according to claim 1, characterized in that the blade brush parts (8a, 8b, 8c) are straight and the imaginary center lines (CL) of the successive blade brush parts (8a, 8b, 8c) are congruent.

4. Patenttivaatimuksen 1 tai 3 mukainen teräelementti, tunnettu siitä, että kynnykset (14”, 14’”) peräkkäisten teräharjaosien (8a, 8b, 8c) liitty-miskohdassa (15) on aikaansaatu järjestämällä edeltävän teräharjaosan (8a) leveys pienentymään kohti seuraavaa teräharjaosaa (8b).Blade element according to Claim 1 or 3, characterized in that the thresholds (14 ", 14 '") at the junction (15) of the successive blade brush parts (8a, 8b, 8c) are achieved by providing a width of the preceding blade brush part (8a) (8b).

5. Jonkin edellisen patenttivaatimuksen mukainen teräelementti, tunnettu siitä, että kynnys (14”, 14’”) on kallistettu kohti teräelementin (1) ulkokehää (5).Blade element according to one of the preceding claims, characterized in that the threshold (14 ", 14 '") is inclined towards the outer periphery (5) of the blade element (1).

6. Jonkin edellisen patenttivaatimuksen mukainen teräelementti, tunnettu siitä, että kynnykset (14”, 14”’) ulottuvat teräharjan (8) tai sen osan (8a, 8b, 8c) yläosaan (8’) asti.Blade element according to one of the preceding claims, characterized in that the thresholds (14 ", 14" ') extend to the upper part (8') of the blade brush (8) or part thereof (8a, 8b, 8c).

7. Jonkin edellisen patenttivaatimuksen mukainen teräelementti, tunnettu siitä, että ainakin teräharjan (8) tai sen osan (8a, 8b, 8c) yläosa (8’) on pyöristetty.Blade element according to one of the preceding claims, characterized in that at least the upper part (8 ') of the blade brush (8) or part thereof (8a, 8b, 8c) is rounded.

8. Jonkin edellisen patenttivaatimuksen mukainen teräelementti, tunnettu siitä, että teräharjan (8) tai sen osan (8a, 8b, 8c) yläosan (8’) poikkileikkauksen profiili teräharjan (8) tai sen osan (8a, 8b, 8c) pituussuuntaan nähden kohtisuorassa suunnassa käsittää lukumäärän kaarevia osuuksia, joista jokaisella on kaarevuussäde.Blade element according to one of the preceding claims, characterized in that the cross-sectional profile of the upper part (8 ') of the blade brush (8) or its part (8a, 8b, 8c) is perpendicular to the longitudinal direction of the blade brush (8) or its part (8a, 8b, 8c). in the direction comprises a number of curved portions, each having a radius of curvature.

9. Jonkin edellisen patenttivaatimuksen mukainen teräelementti, tunnettu siitä, että 20 - 100 % teräharjoista (8) ainakin teräelementin (1) kuidutusvyöhykkeellä (12) on varustettu kynnyksillä (14”, 14”’).Blade element according to one of the preceding claims, characterized in that 20 - 100% of the blade brushes (8) are provided with thresholds (14 ", 14" ') at least in the defibration zone (12) of the blade element (1).

10. Jonkin edellisen patenttivaatimuksen mukainen teräelementti, tunnettu siitä, että kynnykset (14”, 14’”) kahdessa vierekkäisessä terähar-jassa (8), joiden välissä on teräura (9), on järjestetty sijaitsemaan teräelementin (1) samalla säteittäisellä tasolla.Blade element according to one of the preceding claims, characterized in that the thresholds (14 ", 14 '") in two adjacent blade brushes (8) between which the blade groove (9) are arranged are arranged to be on the same radial plane of the blade element (1).

11. Jonkin patenttivaatimuksen 1-8 mukainen teräelementti, tunnettu siitä, että kynnykset (14”, 14’”) kahdessa vierekkäisessä terähar-jassa (8), joiden välissä on teräura (9), on järjestetty sijaitsemaan teräelementin (1) eri säteittäisillä tasoilla sillä tavalla, että ensimmäinen kynnys (14”) terä-harjassa (8) sijaitsee suuremmalla tai pienemmällä säteittäisellä tasolla kuin toinen kynnys (14’”) toisessa teräharjassa (8) teräuran (8) vastakkaisella puolella.Blade element according to one of Claims 1 to 8, characterized in that the thresholds (14 ", 14 '") in two adjacent blade brushes (8) between which the blade groove (9) are arranged are arranged at different radial planes of the blade element (1). such that the first threshold (14 ") in the blade brush (8) is located at a greater or lesser radial plane than the second threshold (14 '") in the second blade brush (8) on the opposite side of the blade groove (8).