FIELD OF THE INVENTION

[0001] The invention relates to refiners for refining fibrous material and especially to a blade element for a refiner for refining fibrous material. BACKGROUND OF THE INVENTION

[0002] Refiners used for refining fibrous material, such as refiners used for manufacturing mechanical pulp or in any low consistency refining, comprise typically two refining elements opposite to each other and turning relative to each other, i.e. one or both is/are rotating. The refining elements comprise refining sur- faces provided with blade bars and blade grooves therebetween, the blade bars be ing intended to defibre and refine the material to be refined and the blade grooves being intended to convey the material to be refined forward along the refining sur faces. The refining surface of the refining element is typically formed of several blade segments fastened to a body of the respective refining element. The complete refining surface of the refining element is thus formed of the refining surfaces of several blade segments fastened next to each other in the refining element.

[0003] All processes for manufacturing pulp from lignocellulosic mate rial produce shives as an undesired quality problem. A shive is a particle or fibre bundle or wood fragment that is produced by incomplete splitting of wood material into fibres during cooking or mechanical treatment. The shives not only contami nate the quality of the produced pulp but also deteriorate operation of some pro cessing devices such as refiners.

[0004] In manufacturing of chemi-thermomechanical pulp (CTMP) ap plication of low consistency refining, i.e. LC refining, is increasing. In low con- sistency refining the consistency of the material to be refined is less than 6%, typi cally between 1% and 4%. A problem of producing high-quality pulp when the par ticle size distribution of the pulp is very wide is pronounced in the low consistency refining, especially in terms of shive control. The shives have a tendency of blocking the refining surfaces, and thereby degrade quality of the refined material and a ca- parity of the refiner.

BRIEF DESCRIPTION OF THE INVENTION

[0005] An object of the present invention is to provide a novel blade element for a refiner for refining fibrous material, as well as a novel refiner for re fining fibrous material. [0006] The invention is characterized by the features of the independ ent claims.

[0007] The invention is based on the idea of at least one equalizing pocket that extends along the refining surface of the blade element and crosses a number of the blade bars and a number of the blade grooves for equalizing flow of the fibrous material along the refining surface.

[0008] At the equalizing pocket at least a portion of the flow of the fi brous material to be refined on the refining surface is interrupted and allowed to equalize or balance before proceeding further on the refining surface. [0009] Some embodiments of the invention are disclosed in the de pendent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In the following the invention will be described in greater detail by means of preferred embodiments with reference to the accompanying drawings, in which

[0011] Figure 1 is a schematic side view of a conical refiner in cross- section;

[0012] Figure 2 is a schematic planar upper view of a blade element applicable to be used in the refiner of Figure 1; and [0013] Figure 3 is a schematic planar upper view of a detail of the blade element of Figure 2.

[0014] For the sake of clarity, the figures show some embodiments of the invention in a simplified manner. Like reference numerals identify like ele ments in the figures. DETAILED DESCRIPTION OF THE INVENTION

[0015] Figure 1 shows schematically a side view of a conical refiner 1 in cross-section, which refiner may be used for refining a fibrous material, such as a wood material containing lignocellulose or another fibre material suitable to be used for manufacturing paper or paperboard, for example. The refiner 1 shown in Figure 1 is of conical type but disc refiners, conical-disc-refiners and cylindrical re finers could be used as well as an example here. Generally, a refiner comprises at least two substantially oppositely positioned refining elements at least one of which is rotating, and a refining chamber formed between each two substantially oppositely positioned refining elements. In the following a refiner with only one rotatable refining element is described. [0016] The refiner 1 of Figure 1 comprises a frame 2 and a stationary, fixed refining element 3, i.e. a stator 3, supported on the frame 2. The frame 2 pro vides a body for the stator 3 unless the stator 3 is provided with a separate body to be fastened to the frame 2 of the refiner 1. [0017] The stator 3 comprises one or more stator blade elements 4 comprising blade bars and blade grooves therebetween. The blade bars and the blade grooves in each one or more stator blade elements 4 form a refining surface 5 of the respective blade element 4. A complete refining surface of the stator 3 is formed either of the refining surface 5 of a single stator blade element 4 extending over the whole circumference of the stator 3 or of the refining surfaces 5 of two or more blade elements 4 having a form of a blade segment and fastened next to each other in the stator 3 so that the complete refining surface 5 extending over the whole circumference of the stator 3 is provided. In the latter case the refining sur face 5 of each stator blade segment 4 provides only a part of the refining surface of the stator 3. For the sake of clarity, both the refining surface of each one or more stator blade elements 4 as well as the complete refining surface of the stator 3 are herein denoted with the same reference sign 5. Additionally, same reference sign 4 may be used to denote a segment-like blade element for the stator 3 as well as a single blade element extending over the whole circumference of the stator 3. [0018] The refiner 1 further comprises a rotatable refining element 6, i.e. a rotor 6, of the refiner 1. The rotor 6 comprises a hub 7. The rotor 6 further comprises one or more rotor blade elements 8 supported to the hub 7, each one or more rotor blade elements 8 comprising blade bars and blade grooves there between. The blade bars and the blade grooves in each one or more rotor blade elements 8 form a refining surface 9 of the respective blade element 8. A complete refining surface of the rotor 6 is formed either of the refining surface 9 of a single rotor blade element 8 extending over the whole circumference of the rotor 6 or of the refining surfaces 9 of two or more blade elements 8 having a form of a blade segment and fastened next to each other in the rotor 6 so that the complete refining surface 9 extending over the whole circumference of the rotor 6 is provided. In the latter case the refining surface 9 of each rotor blade segment 8 provides only a part of the refining surface of the rotor 6. For the sake of clarity, both the refining surface of each one or more rotor blade elements 8 as well as the complete refining surface of the rotor 6 are herein denoted with the same reference sign 9. Additionally, same reference sign 8 may be used below to denote a segment-like blade element for the rotor 6 as well as a single blade element extending over the whole circumference of the rotor 6.

[0019] The hub 7 of the rotor 6 is connected to a driving motor 10 by a shaft 11 so that the rotor 6 can be rotated relative to the stator 3 in a direction of arrow RD, for instance, the arrow RD thus indicating an intended rotation direction 5 RD of the rotor 6.

[0020] The refiner 1 may also comprise a loading device which, for the sake of clarity, is not shown in Figure 1. The loading device can be used for moving back and forth the rotor 6 attached to the shaft 11, as schematically shown by ar row A, in order to adjust a size of a refining gap 12, i.e. a refining chamber 12, be lt) tween the stator 3 and the rotor 6, wherein the fibrous material is actually refined. A structure and operation of different applicable loading devices are generally known for a person skilled in the art of refining and are therefore not disclosed herein in more detail.

[0021] The fibrous material to be refined is fed into the refiner 1 via a 15 feed channel 13 in a manner shown by arrow F. The fibrous material fed into the refiner 1 passes into the refining chamber 12 through a first end 12’ or a feed end 12’ of the refining chamber 12 having the smaller diameter. In the refining chamber 12 the fibrous material is defibrated and refined while the water contained in the material vaporizes. The already refined fibrous material flows away from the refin- 20 ing chamber 12 through a second end 12" or a discharge end 12" of the refining chamber 12 having the larger diameter into a discharge chamber 14 wherefrom the refined material is removed via a discharge channel 15 from the refiner 1, as schematically shown by arrow D.

[0022] It is emphasized that in addition to the conical refiners the blade 25 element of the solution described herein is applicable to disc refiners and cylindri cal refiners and to refiners comprising both a conical portion and a disc portion, as well.

[0023] Figure 2 is a schematic planar upper view of a blade element 4, 8, having a form of a blade segment 4, 8, applicable to be used for forming a part of 30 the refining surface 5, 9 of the stator 3 or the rotor 6, whereby the complete refining surface 5, 9 is provided by arranging necessary number of the blade segments 4, 8 of Figure 2 next to each other around a circumference of the stator 3 or the rotor 6. The embodiments of the blade element disclosed below are to the appropriate ex tent applicable to the single blade elements extending over the whole circumfer- 35 ence of the stator 3 or of the rotor 6 as well. Figure 3 is a schematic planar upper view of a detail of the blade element of Figure 2. [0024] The blade segment 8 comprises, on a front surface 22 thereof, the refining surface 5, 9 provided with blade bars 16 and blade grooves 17 there between, the blade bars 16 and the blade grooves 17 extending along the front sur face 22 of the blade segment 4, 8. The blade bars 16 and the blade grooves 17 have a longitudinal direction and a width direction, or a lateral direction, substantially crosswise to the longitudinal direction thereof. The blade bars 16 are intended to defibre and refine the material to be refined and the blade grooves 17 are intended to convey the material forward along the refining surface 5, 9.

[0025] The blade segment 4, 8 comprises an inner end edge 18 or a first end edge 18 or a feed end edge 18 to be directed towards the first end 12’ of the refining chamber 12, i.e. towards an end of the refining element 3, 6 having the smaller diameter. The fibrous material to be refined is fed or supplied onto the re fining surface 5, 9 over the first end edge 18.

[0026] The blade segment 4, 8 further comprises an outer end edge 19 or a second end edge 19 or a discharge end edge 19 to be directed towards the second end 12" of the refining chamber 12, i.e. towards an end of the refining ele ment 3, 6 having the larger diameter. The refined fibrous material is discharged from the refining surface 5, 9 over the second end edge 19.

[0027] In conical and cylindrical refiners the inner end edge 18 of the blade segment 4, 8 provides an axially inner end 18 of the blade segment 4, 8 and the outer end edge 19 of the blade segment 4, 8 provides an axially outer end 19 of the blade segment 4, 8, the direction from the axially inner end 18 towards the ax ially outer end 19 providing the axial direction of the blade segment 4, 8. In disc refiners the inner end edge of the blade segment would be a radially inner end of the blade segment and the outer end edge of the blade segment would be a radially outer end of the blade segment, the direction from the radially inner end towards the radially outer end thus providing the radial direction of the blade segment. In other words, the blade segment 4, 8 has a longitudinal direction extending between the inner end edge 18 and the outer end edge 19, as denoted in Figure 2 with a schematically shown arrow LD extending from the inner end edge 18 up to the outer end edge 19 of the blade segment 4, 8. When the blade segment 4, 8 is mounted in a refiner, the longitudinal direction LD of the blade segment 4, 8 or a projection thereof is substantially parallel to an axial direction of the refiner in case of cylindrical and conical refiners and substantially parallel to a radial direction of the refiner in case of disc refiners. For the blade segments 4, 8 intended to the con ical and cylindrical refiners the longitudinal direction LD of the blade segment 4, 8 thus corresponds to the above-mentioned axial direction of the blade segment 4, 8 and for the blade segments 4, 8 intended to disc refiners the longitudinal direction LD of the blade segment 4, 8 thus corresponds to the above-mentioned radial di rection of the blade segment 4, 8. [0028] The blade segment 4, 8 further comprises a first side edge 20 or a leading side edge 20 extending from the inner end edge 18 of the blade segment 4, 8 up to the outer end edge 19 of the blade segment 4, 8. The first side edge 20 is the edge of the blade segment 4, 8 that first meets the edge of a counter blade seg ment during the rotation of the rotor 6. So in the rotor 6 it provides the side edge of the blade segment 8 to be directed towards the intended rotation direction RD of the rotor 6 and in the stator 3 it provides the side edge of the blade segment 4 to be directed to opposite direction relative to the intended rotation direction RD of the rotor 6.

[0029] The blade segment 4, 8 further comprises a second side edge 21 or a trailing side edge 21 opposite to the first side edge 20 and extending from the inner end edge 18 of the blade segment 4, 8 up to the outer end edge 19 of the blade segment 4, 8. The second side edge 21 is thus, in turn, the edge of the blade segment 4, 8 that last meets the edge of a counter blade segment during the rotation of the rotor 6. So, in the rotor 6 it provides the side edge of the blade segment 8 to be directed to the opposite direction relative to the intended rotation direction RD of the rotor 6 and in the stator 3 it provides to be directed towards the intended ro tation direction RD of the rotor 6. In the embodiment of Figure 2 the first 20 and second 21 side edges are straight, but they could also be curved as well. The direc tion of the blade segment 4, 8 extending between the first side edge 20 and the second side edge 21 perpendicularly to the longitudinal direction LD of the blade segment 4, 8 is a circumferential direction CD of the blade segment 4, 8. The cir cumferential direction CD of the blade segment 4, 8 thus forms a normal N to the longitudinal direction LD of the blade segment 4, 8.

[0030] The inner 18 and the outer 19 end edges together with the first 20 and second 21 side edges define a periphery of the blade segment 4, 8.

[0031] The refining surface 5, 9 of the blade segment 4, 8 further com prises a number of equalizing pockets 23, i.e. at least one equalizing pocket 23 or one or more equalizing pockets 23 that extend(s) along the refining surface 5, 9 of the blade segment 4, 8. The equalizing pockets 23 are portions of the refining sur- face 5, 9 at which the flow of the fibrous material along the refining surface 5, 9 is allowed to equalize or balance before proceeding again forward along the refining surface 5, 9. The equalizing pocket 23 has a first end 23’ and a second end 23", the equalizing pocket 23 thus having a longitudinal direction or a direction of exten sion in the direction between the first end 23’ and the second end 23", the longitu dinal direction of the equalizing pocket 23 being shown schematically in Figure 2 by a line denoted with the reference sign 231. The equalizing pocket 23 begins at the first end 23’ from a blade bar 16, extends over one or more blade bars 16 and its /their neighbouring blade grooves 17 crossing those all, and ends at the second end 23" to another blade bar 16. A start point or an end point of an equalizing pocket 23 may locate on a neighbouring blade segment 4, 8. [0032] The equalizing pocket 23 is arranged to cross, along its longitu dinal direction 231, a number of the blade bars 16 and a number of the blade grooves 17, i.e. at least one blade bar 16 or one or more blade bars 16 and the re spective blade grooves 17 surrounding and/or remaining between the number of the blade bars 16. Therefore, in its minimum, the equalizing pocket 23 may be ar- ranged to cross one blade bar 16, whereby the equalizing pocket 23 is arranged to extend over the single blade bar 16 and the blade grooves 17 on both sides of the blade bar 16. However, typically, the equalizing pocket 23 is arranged to cross at least two blade bars 16, whereby the equalizing pocket 23 is arranged to extend over the at least two blade bars 16 and the blade grooves 17 between the at least two blade bars 16 as well as the blade grooves 17 surrounding the outermost blade bars 16 in the direction of the extension 231 of the equalizing pocket 23. In the em bodiment of Figure 2, the equalizing pockets 23 are arranged to extend over four to seven blade bars 16 depending on a position of each equalizing pocket 23 in the refining surface 5, 9 of the blade segment 4, 8. The number of the blade bars 16 crossed by the pocket 23 can be from one blade bar 16 up to any number, however, in such a way that at least one pocket 23 is formed between the side edges 20, 21 of the blade segment 4, 8.

[0033] An effect of the at least one equalizing pocket 23 is to provide an intentional or a purposeful break in otherwise substantially continuous course or run of the at least one blade bar 16 and the respective blade grooves 17, whereby at least a portion of the flow of the fibrous material to be refined on the refining surface 5, 9 from a direction of the first end edge 18 of the blade segment 4, 8 to wards the second end edge 19 of the blade segment 4, 8 is interrupted and allowed to equalize or balance and re-mix at the equalizing pocket 23 before proceeding further towards the second end edge 19 of the blade segment 4, 8. An angle (X ₂₃ 1 between the longitudinal direction 231 of the equalizing pocket 23 and an axial direction A or a radial direction of the blade segment 4, 8 is over 0 degrees but less than 90 degrees, preferably 10 - 80 degrees, and more preferably 30 - 80 degrees. The longitudinal direction 231 of the equalizing pocket 23 is thus arranged to devi ate from an axial/radial direction A of the blade segment 4, 8 and from a direction of a normal N of the axial/radial direction A of the blade segment 4, 8. The axial/ra dial direction A of the blade segment 4, 8 and the direction of the normal N of the axial/radial direction A of the blade segment 4, 8 are shown schematically in Figure 2.

[0034] In the embodiment of Figure 2 each equalizing pocket 23 is ar- ranged to cross the respective blade bars 16 and the blade grooves 17 at an angle of about 90 degrees. Therefore, in the embodiment of Figure 2 a crossing angle be tween the longitudinal direction 231 of the equalizing pocket 23 and the blade bars 16 is about 90 degrees. Generally, the crossing angle between the longitudinal di rection of the equalizing pocket 23 and the blade bar 16 may be from 90 ± 50 de- grees. The effect of this angle range is that the direction of extension of the equal izing pocket 23 deviates from the direction of the blade bars 16 and the blade grooves 17 to such an extent that it is ensured that at least a portion of the flow of the fibrous material is interrupted and allowed to stabilize and then re-mix at the equalizing pocket 23 before proceeding further towards the second end edge 19 of the blade segment 4, 8, thus enabling better treatment of shives.

[0035] The longitudinal direction 231 of the equalizing pocket 23 is thus arranged to deviate from the direction of the blade bars 16 as well as from the ax ial/radial direction A of the blade segment 4, 8 and its normal line N.

[0036] The refining surface 5, 9 of the blade segment 4, 8 of Figure 2 comprises altogether three series 24 of consecutively and substantially corre spondingly oriented equalizing pockets 23, wherein the ends 23’, 23" of the con secutively arranged equalizing pockets 23 in the series 24 of the equalizing pockets 23 are separated from each other by a single blade bar 16. Each series 24 of the consecutively and substantially correspondingly oriented equalizing pockets 23 are arranged to extend over at least a portion of the refining surface 5, 9 from a direction of the second side edge 21 of the blade segment 4, 8 towards the first side edge 20 of the blade segment 4, 8.

[0037] Generally, the refining surface 5, 9 of the blade segment 4, 8 may comprise at least one series 24 of at least two consecutively and substantially cor- respondingly oriented equalizing pockets 23, wherein each series 24 of the equal izing pockets 23 is arranged to extend over at least a portion of the refining surface 5, 9 and wherein the ends 23’, 23 of the at least two consecutively arranged equal izing pockets 23 are separated from each other by at least one blade bar 16. With the pockets 23 closest to the side edges 20, 21, the first or last pocket 23 of a pocket series 24, the separating blade bar 16 may be and usually is located on a neighbour- ing blade segment 4, 8.

[0038] The at least one series 24 of the equalizing pockets 23 arranged to extend over at least a portion of the refining surface 5, 9 of the blade segment 4, 8 provides an equalizing or balancing effect of the flow of the fibrous material to take place effectively on a larger portion of the refining surface 5, 9 of the blade segment 4, 8 in a circumferential direction thereof when compared to possibly to tally separate equalizing pockets 23 decentralized at random locations in the refin ing surface 5, 9.

[0039] The number of the series of the pockets 23 can be several. In Figure 2 there are three series 24 in parallel orientation but mutual orientation of the series could ne non-parallel as well, for example such that the series 24 closer to the outer end edge 19 could be oriented in steeper crossing angle with respect to the series 24 locating more inner.

[0040] The effect of the feature that the ends 23’, 23" of the consecu tively arranged equalizing pockets 23 in the series 24 of the equalizing pockets 23 are separated from each other by at least one blade bar 16 is, in turn, that the flow of the fibrous material in at least partly circumferential direction of the blade seg ment 4, 8 along the equalizing pockets 23 is interrupted at some point, i.e. excessive flow of the fibrous material in at least partly circumferential direction of the blade segment 4, 8 is not allowed, and the fibrous material is thereby forced to flow again mainly towards the discharge end edge 19 of the blade segment 4, 8, thus also pre venting a clogging of the refining surface 5, 9 of the blade segment 4, 8. The at least one blade bar 16 between two consecutive equalizing pockets 23 thus provides an element that separates two consecutive equalizing pockets 23 from each other in a longitudinal direction of the series 24 of the equalizing pockets 23 or terminates the equalizing pocket 23 at the respective end 23’, 23" thereof.

[0041] Furthermore, referring to the embodiment of Figure 2, the se ries 24 of the equalizing pockets 23 are arranged at the refining surface 5, 9 at an angle that deviates from the direction of the normal N of the axial/radial direction A of the blade segment 4, 8. Thus, the pockets 23 are distributed more uniformly over the axial/radial length of the refining surface instead of being located on the same axial/radial position. Generally, according to an embodiment, at least one series of at least two equalizing pockets is arranged at the refining surface at an angle deviating from the direction of the normal N of the axial/radial direction A of the blade element. This has several benefits. Material flow towards the discharge end edge 19 is not hindered but is maintained or improved, also wear of the blade element is more uniform. Furthermore, pressure variations that possibly appear during operation of the refiner may be avoided.

[0042] The blade segment 4, 8 disclosed has a specific intended orien tation for installing it in the refiner 1, at which orientation the blade bars 16 and the blade grooves 17 are arranged relative to the intended rotation direction RD of the rotor 6 of the refiner 1 at such an angle that promotes the flow of the fibrous material towards the second end edge 19 of the blade segment 4, 8. At the same time the at least one equalizing pocket 23 is arranged relative to the intended ro tation direction RD of the rotor 6 of the refiner 1 at such an angle that resists the flow of the fibrous material towards the second end edge 19 of the blade segment 4, 8. In the implementation of the embodiment of Figure 2 this is performed by ar ranging the blade bars 16, and respectively the blade grooves 17, such that an angle oci ₆ between the normal N relative to the axial direction A or radial direction of the blade segment 4, 8 and the blade bar 16, or a tangent of the blade bar 16, on the side of the leading edge 20 is larger than 90 degrees. In other words, the bars/grooves 16, 17 and a pocket 23 or a series 24 of the pockets 23 are mutually tilted to opposite directions with respect to the direction A, which equals the axial direction in case of a conical/cylindrical refiner or the radial direction in case of a disc refiner.

[0043] By arranging the blade bars and respectively the blade grooves relative to the intended rotation direction RD of the rotor of the refiner at an angle promoting the flow of the fibrous material towards the second end edge of the blade element, it is ensured that the fibrous material to be refined has a general flow direction towards the discharge end edge of the blade element, thereby pre venting the blocking of the refining surface by the fibrous material to be refined. However, by arranging the at least one equalizing pocket relative to the intended rotation direction RD of the rotor of the refiner at an angle resisting the flow of the fibrous material towards the discharge end edge of the blade element, such an ef fect is, however, subjected to at least a portion of the flow of the fibrous material that shortly interrupts the flow of material towards the discharge end edge of the blade element and allows it to equalize or balance before proceeding further to wards the discharge end edge of the blade element. [0044] According to an embodiment of the equalizing pocket 23, a vol ume of the equalizing pocket 23 is arranged to decrease from the first end 23’ of the equalizing pocket 23 towards the second end 23” of the equalizing pocket 23. The decreasing volume of the equalizing pocket 23 from the first end 23’ towards the second end 23" forces the fibrous material entered into the equalizing pocket 23 to exit the equalizing pocket 23 towards the discharge end edge 19 of the blade segment 4, 8 after being equalized or balanced in the equalizing pocket 23.

[0045] The decreasing volume of the equalizing pocket 23 from the first end 23’ towards the second end 23" may be achieved by arranging at least one of a width and a depth of the equalizing pocket 23 to decrease from the first end 23’ of the equalizing pocket 23 towards the second end 23" of the equalizing pocket 23. In other words, the width and/or the depth of the equalizing pocket 23 may be ar ranged to decrease from the first end 23’ of the equalizing pocket 23 towards the second end 23" thereof. [0046] The width of the equalizing pocket 23 refers to a measure of the equalizing pocket 23 that is substantially crosswise to the direction between the first end 23’ and the second end 23" of the equalizing pocket 23 and may be deter mined as a distance between an end 16a’ of a blade bar 16a extending from a di rection of the first end edge 18 of the blade segment 4, 8 towards the equalizing pocket 23 in question and an end 16b’ of another blade bar 16b that extends from the equalizing pocket 23 in question at least partly towards the second end edge 19 of the blade segment 4, 8 and is substantially opposite to the herein first men tioned blade bar 16a (Figure 3).

[0047] The depth of the equalizing pocket 23 may be determined as a vertical distance between a bottom of the equalizing pocket 23 and a level of a top surface of the blade bar 16.

[0048] According to an embodiment of the equalizing pocket 23, at least one of the width and the depth of the equalizing pocket 23 is arranged to de crease dynamically from the first end 23’ of the equalizing pocket 23 towards the second end 23" of the equalizing pocket 23. In other words, the width and/or the depth of the equalizing pocket 23 is arranged to decrease dynamically, i.e. in a sub stantially continuous manner, from the first end 23’ of the equalizing pocket 23 to wards the second end 23" of the equalizing pocket 23, whereby the fibrous material entered into the equalizing pocket 23 is forced to flow away from the equalizing pocket 23 further towards the discharge end edge 19 of the blade segment 4, 8 in a substantially even manner, without causing undesirable turbulences in the flow of the fibrous material. Stepwise decrease of the width and/or the depth of the equal izing pocket 23 is of course possible but less preferable.

[0049] Referring again to the embodiment of Figure 2, the equalizing pockets 23 are arranged at the refining surface 5, 9 of the blade segment 4, 8 at an angle relative to the first end edge 18 and the second end edge 19 of the blade seg ment 4, 8 such that the first end 23’ of the equalizing pocket 23 is closer to the first end edge 18 of the blade segment 4, 8 than the second end 23" of the equalizing pocket 23. This embodiment, especially together with the decreasing volume of the equalizing pocket 23 towards the second 23" thereof, has an effect according to which the fibrous material entered into the equalizing pocket 23 is forced to con tinue the flow towards the outer end edge 19 of the blade segment 4, 8. This kind of alignment of the equalization pockets 23 leads also to the alignment of the series 24 of the equalization pockets 23, wherein one end of the series 24 of the equaliza tion pockets 23 is closer to the first end edge 18 of the blade segment 4, 8 and the other end of the series 24 of the equalization pockets 23 is closer to the second end edge 19 of the blade segment 4, 8. The series 24 of the equalization pockets 23 is thus aligned or directed at least partly towards the second end edge 19 of the blade segment 4, 8.

[0050] Furthermore, in the embodiment of Figure 2, a volume of the equalizing pockets 23 remaining closer to the second end edge 19 of the blade seg ment 4, 8 are arranged to be smaller than a volume of the equalizing pockets 23 remaining closer to the first end edge 18 of the blade segment 4, 8. Generally, ac cording to an embodiment of the blade element, a volume of at least one equalizing pocket remaining closer to the second end edge of the blade element is arranged to be smaller than a volume of at least one other equalizing pocket remaining closer to the first end edge of the blade element. This has the effect that a dwell time of the fibrous material entered into the equalizing pocket 23 decreases towards the discharge end 12" of the refining chamber 12, the flow of the fibrous material to wards the discharge end 12" of the refining chamber 12 thereby being more effec- tive close to the discharge end 12" of the refining chamber 12.

[0051] According to an embodiment of the blade segment 4, 8, referring especially to Figure 3, widths W ₁₇ of the blade grooves 17 extending from the equal izing pocket 23 at least partly towards the second end edge 19 of the blade segment 4, 8 are arranged to increase in the direction from the first end 23’ of the equalizing pocket 23 towards the second end 23" of the equalizing pocket 23. In general terms it may therefore be determined that the equalizing pocket 23 has a first end 23’ and a second end 23” and that widths W17 of the blade grooves 17 extending from the at least one equalizing pocket 23 at least partly towards the second end edge 19 of the blade element 4, 8, i.e. of those grooves 17 that are crossed by the pocket 23, are arranged to increase in a direction from the first end 23’ of the equalizing pocket 23 towards the second end 23” of the equalizing pocket 23. The widths W17 of the blade grooves 17 are arranged to increase substantially continuously at the equalizing pocket 23 such that the blade groove 17 at the first end 23’ of the equal izing pocket 23 is the narrowest one and the blade groove 17 at the second end 23” of the equalizing pocket 23 is the widest one and that each blade groove 17 closer to the second end 23" of the equalizing pocket 23 is at least little bit wider than the blade groove 17 closer to the first end 23’ of the equalizing pocket 23. The varying width of the grooves 17 enables fibres/shives/particles of different sizes to redis tribute to grooves 17 corresponding their sizes, when the material flow has stabi lized at the equalization pocket 23. Widening of the grooves 17 in this order, i.e. from the first end 23’ towards the second end 23” is beneficial to ensure smooth flow of particles. In case of reverse order, the widest groove could be filled with the smaller particles and the shives with bigger size could not find an exit that fits for them. The width W17 of the blade groove 17 at the first end 23’ of the equalizing pocket 23 may for example be 1 - 5 mm and the width W17 of the blade groove 17 at the second end 23" of the equalizing pocket 23 may for example be 5 - 10 mm.

[0052] The increasing width of the blade grooves 17 towards the sec ond end 23" of the equalizing pocket 23 ensures that also shives of bigger size en tered into the equalizing pocket 23 are able to exit the equalizing pocket 23 and thereby are able to be defibred and refined and not to block the refining surface 5, 9. This embodiment, especially together with the decreasing volume of the equal izing pocket 23 towards the second 23" thereof, effectively ensures that the pulp flow is forced to mix again, thus forcing the material including shives to exit the equalizing pocket 23 and flow towards the outer end edge 19 of the blade element 4, 8. [0053] It will be obvious to a person skilled in the art that, as the tech nology 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.