Patent Description:
<CIT> discloses a refiner and a method for refining fibrous material. The refiner disclosed in <CIT> comprises at least one first refining surface and at least one second refining surface which are arranged at least partly substantially opposite to one another in such a manner that a refiner chamber receiving the material to be refined is formed between them. The first refining surface comprises openings arranged through the first refining surface, through which fibrous material to be refined is arranged to be fed into the refiner chamber, and/or the second refining surface comprises openings arranged through the second refining surface, through which fibrous material refined in the refiner chamber is arranged to be discharged from the refiner chamber, or vice versa. The document <CIT> discloses a blade element pair for a refiner according to the preamble of claim <NUM>.

By feeding the fibrous material to be refined through the first refining surface into the refiner chamber and/or by removing the already refined fibrous material from the refiner chamber through the second refining surface, or vice versa, it is possible to feed fibrous material into the refiner chamber so that the distribution of the material in the refiner chamber is substantially even, which effects on the efficiency of the refining and the capacity of the refiner. The degree of grinding, i.e. the degree of refining, provided by the disclosed refiner is not, however, high enough for providing exceptionally far-refined, typically wood-based, fibrous material to be utilized for example as an additive in manufacturing of new biobased products.

An object of the present invention is to provide a novel blade element pair for a refiner intended for refining fibrous material.

The invention is characterized by the features of the independent claim.

In the blade element pair disclosed at least one of the blade elements is rotatable and the openings in one of the blade elements are at different axial or radial positions from the openings in the other blade element when the blade elements of the blade element pair are set substantially opposite to each other.

Because in the solution disclosed the openings in the rotor refining surface do not coincide or overlap with the openings in the stator refining surface and therefore do not allow the material to be refined to go straight from the opening in the rotor refining surface to the opening in the stator refining surface, all the fibrous material is forced, at least to some extent, under influence of the refining effect because there is no fibrous material portion which could go through the refiner without ending up under the refining effect. This increases the degree of grinding of the fibrous material when compared to prior art solutions comprising openings extending through stator and rotor blade elements. The invention also discloses a refiner according to claim <NUM>.

Some embodiments of the invention are disclosed in the dependent claims.

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.

<FIG> shows a very schematic side view of a conical refiner <NUM> partly in cross-section. The refiner <NUM> comprises a stationary refining element <NUM>, i.e. a stator <NUM>, comprising a number of stator blade elements <NUM> having a refining surface <NUM>. The stator <NUM> may be supported to a frame structure of the refiner <NUM>, the frame structure being not shown in <FIG> for the sake of clarity. According to an embodiment of the stator <NUM> it may comprise only one blade element <NUM> of a conical shape and extending over a whole periphery of the stator <NUM> so that this single blade element provides a complete uniform refining surface <NUM> of the stator <NUM>. According to another embodiment of the stator <NUM> it may comprise at least two segment-like blade elements , i.e. blade segments <NUM>' as shown later in <FIG>, that are arranged adjacent to one another whereby the refining surfaces <NUM> of the originally separate segment-like blade elements together provide the complete uniform refining surface <NUM> of the stator <NUM>. The term blade element, when referring to the stator <NUM> of the refiner, may thus refer to a blade element providing the complete refining surface <NUM> of the stator <NUM> or to a blade segment providing only a part of the complete refining surface <NUM> of the stator <NUM>. The refining surface <NUM> is typically provided with blade bars and blade grooves therebetween, an embodiment of the blade bars and the blade grooves shown later in <FIG> and <FIG>.

The refiner <NUM> further comprises a rotary refining element <NUM>, i.e. a rotor <NUM>, comprising a number of rotor blade elements <NUM> having a refining surface <NUM>. According to an embodiment of the rotor <NUM> it may comprise only one blade element <NUM> of a conical shape and extending over a whole periphery of the rotor <NUM> so that this single blade element provides a complete uniform refining surface <NUM> of the rotor <NUM>. According to another embodiment of the rotor <NUM> it may comprise at least two segment-like blade elements, i.e. blade segments <NUM>' as shown later in <FIG>, that are arranged adjacent to one another whereby the refining surfaces <NUM> of originally separate segment-like blade elements together provide the complete uniform refining surface <NUM> of the rotor <NUM>. The term blade element, when referring to the rotor <NUM> of the refiner, may thus refer to a blade element providing the complete refining surface <NUM> of the rotor <NUM> or to a blade segment providing only a part of the complete refining surface <NUM> of the rotor <NUM>. The refining surface <NUM> is typically provided with blade bars and blade grooves therebetween, an embodiment of the blade bars and the blade grooves shown later in <FIG> and <FIG>.

The rotor <NUM> comprises a hub <NUM> which is shown in <FIG> highly simplified and against which the at least one rotor blade element <NUM> is supported to. The hub <NUM> of the rotor <NUM> is connected to a shaft <NUM> and the shaft <NUM> is connected to a highly schematically depicted motor <NUM> arranged to rotate the shaft <NUM> and, by the shaft <NUM>, the rotor <NUM> for example in a rotation direction indicated with an arrow RD. The refiner <NUM> may also comprise a loading device not shown in <FIG> for the sake of clarity, which loading device may be connected to the shaft <NUM> for moving the rotor <NUM> back and forth, as indicated schematically with an arrow AD, in order to adjust a distance between the opposite blade elements <NUM>, <NUM>, i.e. in order to adjust a size of a refiner chamber <NUM> or a blade gap <NUM>, forming between the stator <NUM> and the rotor <NUM>. The size of the refiner chamber <NUM> relative to the other components of the refiner is exaggerated in <FIG>.

The stator blade element <NUM> further comprises openings <NUM> extending through the blade element <NUM> and the rotor blade element <NUM> comprises openings <NUM> extending through the blade element <NUM>, the openings <NUM>, <NUM> thus extending through the whole thickness of the stator and rotor blade elements <NUM>, <NUM>. In an axial direction of the stator blade element <NUM> and in the axial direction of the rotor blade element <NUM>, the axial direction indicated schematically by an arrow A in <FIG>, the openings <NUM> in the stator blade element <NUM> are at different axial positions from the openings <NUM> in the rotor blade element <NUM> when the blade elements <NUM>, <NUM> are opposite to each other. In other words, in the blade element pair comprising the stator blade element <NUM> and the rotor blade element <NUM> to be set substantially opposite to each other the openings <NUM>, <NUM> in one of the blade elements <NUM>, <NUM> are positioned not to coincide or overlap in the axial direction A with the openings <NUM>, <NUM> in the other blade element <NUM>, <NUM> when the blade elements <NUM>, <NUM> are set substantially opposite to each other. The setting of the blade elements <NUM>, <NUM> substantially opposite to each other thus refers to the positioning of the blade elements <NUM>, <NUM> such that the refining surfaces of the blade elements <NUM>, <NUM> are substantially directed towards each other, in other words, the refining surface of one blade element is set towards the refining surface of the other blade element of the blade element pair and end edges of the blades are aligned to match their operation position in the refiner.

The operation of the refiner <NUM> of <FIG> is as follows. The fibrous material to be refined is fed into an inner volume of the rotor <NUM> both through a first end of the refiner <NUM> having a larger diameter and through a second end of the refiner <NUM> having a smaller diameter, as schematically indicated by arrows indicated with reference sign F. Alternatively, the fibrous material to be refined may be fed into the inner volume of the rotor <NUM> only through the first end of the refiner <NUM> having the larger diameter or through the second end of the refiner <NUM> having the smaller diameter if there are openings extending through the hub <NUM> of the rotor <NUM>, thus allowing the fibrous material flow from one end of the rotor <NUM> up to the other end of the rotor <NUM>. It is to be noted that position of the cone can be contrary to that of <FIG> so that the smaller diameter end of the cone is located on the shaft side, the operation is still as described. The fibrous material is typically wood-based lignocellulose containing fibre material but could also be some other plant-based fibrous material. The consistency of the fibrous material to be fed into the refiner <NUM> is low, in the range of <NUM> - <NUM>%, for example <NUM> - <NUM>%, preferably <NUM> - <NUM>%.

From the inner volume of the rotor <NUM> the fibrous material flows through the openings <NUM> in the rotor blade element <NUM> into the refining chamber <NUM>, as shown schematically with arrows indicated with reference sign F15. In the refining chamber <NUM> the fibrous material is refined in response to the interaction of the stator refining surface <NUM> and the rotor refining surface <NUM>. The fibrous material refined in the refining chamber <NUM> is discharged out of the refining chamber <NUM> through the openings <NUM> in the stator blade element <NUM>, as shown schematically with arrows indicated with reference sign F14.

Because in the axial direction A of the stator blade element <NUM> and the rotor blade element <NUM> the openings <NUM> in the stator blade element <NUM> are at different positions relative to the positions of the openings <NUM> in the rotor blade element <NUM>, i.e. because the openings <NUM> in the stator blade element <NUM> are aligned not to coincide or overlap with the openings <NUM> in the rotor blade element <NUM>, there is no direct passage through the both elements <NUM>, <NUM>, thus all the fibrous material is forced, at least to some extent, under influence of the refining effect and there is no fibrous material portion which could go through the refiner <NUM> without ending up under the refining effect. This takes place because the openings <NUM> in the rotor refining surface <NUM> do not coincide with the openings <NUM> in the stator refining surface <NUM> and allow the material to be refined to go straight from the opening <NUM> in the rotor refining surface <NUM> to the opening <NUM> in the stator refining surface <NUM>. This increases the degree of grinding of the fibrous material when compared to prior art solutions where a direct passage through stator and rotor blade elements is formed. Still, however, the capacity of the refining may be maintained.

<FIG> shows a very schematic side view of a cylindrical refiner <NUM> partly in cross-section. The basic structure and operation of the cylindrical refiner <NUM> is substantially similar to that of the conical refiner <NUM> of <FIG> above, the main difference being the cylindrical form or shape of the stator and rotor instead of the conical shape. Because of this difference between the form or shape of the stator and rotor the size of the refining chamber is adjusted in the cylindrical refiner <NUM> by adjusting the stator diameter, as indicated schematically with the arrow AD in <FIG>. The positioning of the openings <NUM>, <NUM> in the stator and rotor blade elements <NUM>, <NUM> of the cylindrical refiner <NUM> is, however, similar to that shown and explained above in view of <FIG>.

<FIG> shows a very schematic side view of a disc refiner <NUM> partly in cross-section. The basic structure and operation of the disc refiner <NUM> is substantially similar to that of the conical refiner <NUM> or the cylindrical refiner <NUM>, the main difference being the disc-like form or shape of the stator <NUM> and the rotor <NUM> that are arranged at a substantially perpendicular angle relative to the shaft <NUM>. For the sake of clarity, the hub <NUM> of the rotor <NUM> has been omitted in <FIG>. Equally to the conical refiner <NUM> and the cylindrical refiner <NUM>, the stator <NUM> and the rotor <NUM> may comprise only one blade element <NUM>, <NUM> with a shape of a ring and extending over a whole periphery of the stator <NUM> or the rotor <NUM> so that this single blade element provides a complete uniform refining surface <NUM>, <NUM> of the stator <NUM> or the rotor <NUM>, or alternatively, the stator <NUM> and/or the rotor <NUM> may comprise at least two segment-like blade elements arranged adjacent to one another whereby the refining surfaces <NUM>, <NUM> of the originally separate segment-like blade elements together provide the complete uniform refining surface <NUM>, <NUM> of the stator <NUM> and/or the rotor <NUM>. As explained above, the refining surface <NUM>, <NUM> is typically provided with blade bars and blade grooves therebetween.

Furthermore, referring to the disc refiner of <FIG>, the at least one stator blade element <NUM> comprises openings <NUM> extending through the blade element <NUM> and the at least one rotor blade element <NUM> comprises openings <NUM> extending through the blade element <NUM>, the openings <NUM>, <NUM> thus extending through the whole thickness of the stator and rotor blade elements <NUM>, <NUM>. In a radial direction of the one stator blade element <NUM> and in a radial direction of the rotor blade element <NUM>, the radial direction indicated schematically by an arrow indicated with reference sign R in <FIG>, the openings <NUM> in the stator blade element <NUM> are at different radial positions from the openings <NUM> in the rotor blade element <NUM> when the blade elements <NUM>, <NUM> are opposite to each other. In other words, in the blade element pair comprising the stator blade element <NUM> and the rotor blade element <NUM> to be set substantially opposite to each other, the openings <NUM>, <NUM> in one of the blade elements <NUM>, <NUM> are positioned not to coincide or not to overlap in the radial direction R with the openings <NUM>, <NUM> in the other blade element <NUM>, <NUM> when the blade elements <NUM>, <NUM> are set substantially opposite to each other.

The fibrous material to be refined is fed into the refiner <NUM> on the rotor <NUM> side of the inner volume of the refiner <NUM> as shown schematically with arrows indicated with the reference sign F. The fibrous material to be refined flows through the openings <NUM> in the rotor blade element <NUM> into the refining chamber <NUM>, as shown schematically with arrows indicated with reference sign F15, and the fibrous material refined in the refining chamber <NUM> is discharged out of the refining chamber <NUM> through the openings <NUM> in the stator blade element <NUM>, as shown schematically with arrows indicated with reference sign F14.

Because in the radial direction R of the stator blade element <NUM> and the rotor blade element <NUM> the openings <NUM> in the stator blade element <NUM> are at different positions relative to the positions of the openings <NUM> in the rotor blade element <NUM>, i.e. because the openings <NUM> in the stator blade element are aligned not to coincide or overlap with the openings <NUM> in the rotor blade element <NUM>, all the fibrous material is forced, at least to some extent, under influence of the refining effect, i.e. there is no fibrous material portion which could go through the refiner <NUM> without ending up under the refining effect, thus increasing the degree of grinding of the fibrous material when compared to prior art solutions.

<FIG> shows schematically a side view of another disc refiner <NUM>. The disc refiner <NUM> of <FIG> comprises a first stator 4a and a second stator 4b and therebetween a rotor <NUM>, whereby there are provided two refining chambers, i.e. a first refining chamber 13a between the first stator 4a and the rotor <NUM> as well as a second refining chamber 13b between the second stator 4b and the rotor <NUM>. The rotor <NUM> is arranged in a slidably manner at the end of the shaft <NUM> and the loading device (not shown for the sake of clarity) are allowed to load the second stator 4b so as to adjust the size of the refining chambers 13a, 13b as indicated schematically with the arrow AD.

The stators 4a, 4b each comprises at least one blade element <NUM>. The refining surfaces <NUM> of the blade elements <NUM> at different stators 4a, 4b may have similar or different characteristics. The rotor <NUM> comprises at least one blade element <NUM> which is two-sided, i.e. blade element having refining surfaces <NUM> on both sides of the blade element <NUM>. Alternative the rotor <NUM> could comprise at least two one-sided refining elements connected to each other. The refining surfaces <NUM> at opposite sides of the rotor <NUM> may have similar or different characteristics.

When the refiner <NUM> of <FIG> is operated, the fibrous material to be refined is fed into the refiner <NUM> on the first stator 4a side of the inner volume of the refiner <NUM> as shown schematically with arrows indicated with the reference sign F. The fibrous material to be refined flows into the first refining chamber 13a through the openings <NUM> in the stator blade element <NUM> of the first stator 4a, as shown schematically with arrows F14 on the left side of the rotor <NUM>. The fibrous material refined in the first refining chamber 13a is discharged out of the first refining chamber 13a into the second refining chamber 13b through the openings <NUM> in the rotor blade element <NUM> of the rotor <NUM>, as shown schematically with arrows F15. Furthermore, the fibrous material refined in the second refining chamber 13b is discharged out of the second refining chamber 13b through the openings <NUM> in the stator blade element <NUM> of the second stator 4b, as shown schematically with arrows F14 on the right side of the rotor <NUM>.

The disc refiner <NUM> of <FIG> is an example of a refiner comprising two blade element pairs, i.e. a first blade element pair comprising the stator blade element <NUM> of the first stator 4a and the rotor blade element <NUM> of the rotor <NUM> as well as a second blade element pair comprising the stator blade element <NUM> of the second stator 4b and the rotor blade element <NUM> of the rotor <NUM>, the rotor blade element <NUM> of the rotor <NUM> thus being common to the both blade element pairs. Other solutions for providing a refiner with more than one blade element pair is also possible, for example by increasing a number of the rotors in the refiner.

<FIG> shows schematically, partly in cross-section, a side view of a blade element pair <NUM> for a conical refiner <NUM>. The blade element pair <NUM> comprises a stator blade element <NUM> comprising a number of adjacently positioned stator blade segments <NUM>'. Each stator blade segment <NUM>', and thereby the complete stator blade element <NUM>, comprises a first edge 5a, i.e. a first end edge 5a or an inner edge 5a intended to be directed towards the refiner end having the smaller diameter. Similarly, the stator blade element <NUM>, and thus each stator blade segment <NUM>', comprises a second edge 5b, i.e. a second end edge 5b or an outer edge 5b intended to be directed towards the refiner end having the larger diameter. The axial direction A of the stator blade element <NUM>, and thereby the axial direction A of each stator blade segment <NUM>', extends between the first edge 5a and the second edge 5b. Each individual stator blade segment <NUM>' further comprises side edges 5c, 5d extending between the first 5a and the second 5b edges. Inner surfaces of the stator blade segments <NUM>' are provided with stator blade bars <NUM> and stator blade grooves <NUM> therebetween forming the refining surface <NUM> of each individual stator blade segment <NUM>' and thereby the refining surface <NUM> of the complete stator blade element <NUM>.

The blade element pair of <FIG> further comprises a rotor blade element <NUM> comprising a number of adjacently positioned rotor blade segments <NUM>'. Each rotor blade segment <NUM>', and thus the complete rotor blade element <NUM>, comprises a first edge 8a, i.e. a first end edge 8a or an inner edge 8a intended to be directed towards the refiner end having the smaller diameter. Similarly, the rotor blade element <NUM>, and thus each rotor blade segment <NUM>', comprises a second edge 8b, i.e. a second end edge 8b or an outer edge 8b intended to be directed towards the refiner end having the larger diameter. The axial direction A of the rotor blade element <NUM>, and thereby the axial direction A of each rotor blade segment <NUM>', extends between the first edge 8a and the second edge 8b. Each individual rotor blade segment <NUM>' further comprises side edges 8c, 8d extending between the first 8a and the second 8b edges. Outer surfaces of the rotor blade segments <NUM>' are provided with rotor blade bars <NUM> and rotor blade grooves <NUM> therebetween forming the refining surface <NUM> of each individual rotor blade segment <NUM>' and thereby the refining surface <NUM> of the complete rotor blade element <NUM>. Fastening holes in the blade segments <NUM>', <NUM>', intended to receive fastening means for fastening the blade segments <NUM>', <NUM>' in the refiner, are denoted with reference number <NUM> in <FIG>.

Each stator blade segment <NUM>', and thereby the complete stator blade element <NUM> comprises in the axial direction A thereof successive refining surface zones 6a, 6b, 6c, 6d, 6e, 6f, <NUM>, <NUM>, 6i, wherein the refining surface zones 6b, 6d, 6f, <NUM> are refining surface zones comprising the openings <NUM> extending through the whole thickness of the stator blade segment <NUM>' and the refining surface zones 6a, 6c, 6e, <NUM> and 6i are refining surface zones of solid structure, i.e. not comprising such openings. Mutually, each rotor blade segment <NUM>', and thereby the complete rotor blade element <NUM> comprises in the axial direction A thereof successive refining surface zones 9a, 9b, 9c, 9d, 9e, 9f, <NUM>, <NUM>, 9i, wherein the refining surface zones 9a, 9c, 9e, <NUM> and 9i are refining surface zones provided with the openings <NUM> extending through the whole thickness of the rotor blade segment <NUM>' and the refining surface zones 9b, 9d, 9f, <NUM> are refining surface zones of solid structure, i.e. not comprising such openings. Thus there is at least one zone which is solid and at least one zone which has openings in both the rotor element and the stator element. More preferably, at least one of the elements has more than one solid zone in addition to a zone with openings whereas in the other element the amount and order of solid zones and zones with openings is reversed.

When the conical refiner <NUM> is assembled and the stator blade element <NUM> and the rotor blade element <NUM> are set substantially opposite to each other for the use, the refining surface zones 9a, 9c, 9e, <NUM> and 9i of the rotor blade segments <NUM> comprising the openings <NUM> are set in the axial direction A of the blade segments, i.e. in the axial direction of the refiner, towards the refining surface zones 6a, 6c, 6e, <NUM> and 6i of solid structure in the stator blade segment <NUM>, and correspondingly, the refining surface zones 6b, 6d, 6f, <NUM> of the stator blade segments <NUM>' comprising the openings <NUM> are set in the axial direction A of the blade segments <NUM>', <NUM>' towards the refining surface zones 9b, 9d, 9f, <NUM> of solid structure in the rotor blade segments <NUM>'. In other words, the zones with the openings <NUM>, <NUM> as well as the solid zones of the opposite elements go in shifted phases, i.e. in reversed order. Thereby the refining surface zones provided with openings in one blade segment <NUM>', <NUM>' are set opposite to the refining surface zones without openings in the other blade segment <NUM>', <NUM>'. This means that in the blade element pair <NUM> the refining surface zones of the blade segments <NUM>', <NUM>' comprising openings <NUM>, <NUM> are aligned not to coincide or overlap with each other in the axial direction A of the blade segments <NUM>', <NUM>' when the refining surfaces <NUM>, <NUM> of the blade segments <NUM>', <NUM>' are substantially opposite to each other. In other words, the openings <NUM>, <NUM> of the opposite elements <NUM>, <NUM> do not overlap and thus no rectilinear passage through the both elements is formed. This, in turn, means that no fibrous material portion can go from the opening <NUM> in the rotor blade element <NUM> straight to the opening <NUM> in the stator blade element <NUM> without getting under influence of the refining because there will be no straight see through connection between the openings <NUM> in the stator blade element <NUM> and the openings <NUM> in the rotor blade element <NUM>.

The refining surface zones disclosed above may be utilized in the blade elements for the cylindrical and disc refiners too.

In the blade element pair of <FIG> the openings <NUM> in the rotor blade segments <NUM>' are arranged at a central portion of the rotor blade segments <NUM>' whereas the openings <NUM> in the stator blade segments <NUM>' are arranged at the side edges 8c, 8d of the stator blade segments <NUM>'. The openings <NUM> in the stator blade segments <NUM>' are thus indents arranged at the side edge 8c, 8d of the blade segments <NUM>', the indents extending through the whole thickness of the blade segment <NUM>' and from the side edge 8c, 8d of the blade segment <NUM>' towards the opposite side edge 8c, 8d. The advantage of the openings being indents at the side edge of the blade segment is that a rigidity of the blade segment is higher than the rigidity of the blade segment having openings at the central portion of the blade segment. This, in turn, provides a possibility to reduce the thickness of the blade segment, thus reducing weight of the blade segment and energy needed to rotate the rotor if applied at the rotor blade segments too.

In the blade element pair of <FIG> the openings <NUM> in the rotor blade segments <NUM>' are round whereas the openings <NUM> in the stator blade segments <NUM>' are elongated. Alternatively the openings <NUM>, <NUM> could also be for example oval or triangle or have different polygonal shapes. The size of the openings may vary largely from a minimum of a fibre length to a maximum of even half of the element length and the size of the openings may vary between different refining surface zones. A total open area of the openings <NUM>, <NUM> in the blade element <NUM>, <NUM>', <NUM>, <NUM>' is from <NUM>% to <NUM>% of the surface area of the refining surface, <NUM>, <NUM> of the blade element <NUM>, <NUM>', <NUM>, <NUM>', typically about <NUM> - <NUM>%, but values less than <NUM>% are sometimes preferred, depending on refiner capacity and raw material used. A low total open area of the openings <NUM>, <NUM> relative to the surface area of the refining surface, <NUM>, <NUM> of the blade element <NUM>, <NUM>', <NUM>, <NUM>' increases a total length of cutting edges of the blade bars, thus increasing the degree of grinding of the refined fibrous material. As explained, the open area consists of one or more openings <NUM>, <NUM> the shape of which can be round, oval, triangle or any polygonal shape and may be similar or may vary within a refining element and/or within a refining element pair, for example the shape of the openings may differ zonewise, like dissimilar openings on the first end area to the second end area of the element, or the shape or shapes of the openings <NUM>, <NUM> may be different in the stator element compared to those of the rotor element as in <FIG>. Further, the size of the openings <NUM>, <NUM> may vary within a refining element and/or within a refining element pair, for example the size of the openings may vary zonewise, like smaller openings on the first end area and larger openings on the second end area of the element or vice versa, or the openings <NUM> of the rotor element may be of different size from the openings <NUM> of the stator element as in <FIG>. The openings <NUM>, <NUM> within an element may be like holes or perforations lying in the middle part between the side edges of the element but they may also be like indents or cutouts at the side edges.

<FIG> shows schematically an upper view of a rotor blade segment <NUM>' of <FIG> and a refining surface <NUM> thereof. The refining surface <NUM> comprises blade bars <NUM> and blade grooves <NUM>. The blade bars <NUM> provide the refining effect to the fibrous material and the blade grooves <NUM> convey the material to be refined on the refining surface <NUM>. In <FIG> it is shown also, as superimposed by broken lines, some blade bars <NUM> and blade grooves <NUM> of a stator blade segment <NUM>' to be set opposite to the rotor blade segment <NUM>'. In the following properties of the refining surface <NUM> for the rotor blade element or segment are considered but properties of the refining surface <NUM> for the stator blade element or segment are similar unless otherwise specifically mentioned.

According to an embodiment a pitch P of the refining surface <NUM>, i.e. a common width of a single blade bar <NUM> and of a single blade groove <NUM> next to the blade bar <NUM> is at most <NUM>. The pitch P of at most <NUM> provides a very dense blade bar - blade groove -configuration, whereby a cutting edge length provided by the blade bars <NUM>, <NUM> of the stator and rotor blade elements <NUM>, <NUM> in the refiner is very high. This, in common with the opening configuration in the stator and rotor blade elements <NUM>, <NUM> as disclosed above, has an effect that the degree of grinding of the fibrous material to be refined will be very high, even as high as that at least part of the refined material has particle size properties of nanofibrillar cellulose. The term "nanofibrillar cellulose" refers herein to a collection of separate cellulose microfibrils or microfibril bundles derived from plant-based, and especially wood-based fibrous material. Synonyms for the nanofibrillar cellulose (NFC) are for example nanofibrillated cellulose, nanocellulose, microfibrillar cellulose, cellulose nanofiber, nano-scale cellulose, microfibrillated cellulose (MFC) or cellulose microfibcrils. Depending on the degree of grinding a particle size of the separate cellulose microfibrils or microfibril bundles is of some nanometres (nm) or micrometres (µm). A mean length of the separate cellulose microfibrils or microfibril bundles may for example be <NUM> - <NUM> and a mean diameter may for example be <NUM> - <NUM>.

According to an embodiment a width W<NUM>, W<NUM> of the respective blade bar <NUM>, <NUM> is at most half of the pitch P of the blade element. According to this embodiment, and referring back to <FIG> it thus means that the width W<NUM>, W<NUM> of the respective blade bar <NUM>, <NUM> is at most equal to a width W<NUM>, W<NUM> of the blade groove <NUM>, <NUM>. The effect of this embodiment is that volume of the blade grooves <NUM>, <NUM> in the blade elements <NUM>, <NUM>', <NUM>, <NUM>' will be high enough to prevent a clogging of the refining surfaces <NUM>, <NUM> of the blade elements <NUM>, <NUM>', <NUM>, <NUM>'.

According to an embodiment a height of the blade bar <NUM>, <NUM> is typically at most <NUM> but heights lower than <NUM>, for example less than <NUM>, even less than <NUM> may be preferred in case of very dense groove-bar-pattern. Typically bar height is reduced during operation, but in the refiner of the solution even low heights are possible without sacrificing hydraulic capacity because pulp is fed through the holes and groove volume is not limiting the hydraulic capacity.

The pitch of the blade elements and the total open area of the openings in the blade elements may be selected in combination such that the common cutting edge length of the blade bars in the refiner is preferably at least <NUM> per one revolution of the rotor <NUM>.

According to an embodiment of the blade element pair <NUM> the blade bars <NUM>, <NUM> in the blade elements <NUM>, <NUM>', <NUM>, <NUM>' forming the blade element pair <NUM> are crosswise to each other. Referring again to <FIG> showing the refining surface <NUM> of the rotor blade segment <NUM>' and the blade bars <NUM> and the blade grooves <NUM> therein it can be seen that the blade bars <NUM> and the blade grooves <NUM> are arranged at a blade bar angle α<NUM> of about <NUM>° relative to the axial direction A, depicted by the dot-and-dash line in <FIG>. Generally the blade bar angle α<NUM> in the rotor blade element is <NUM>° - <NUM>°, for example <NUM>° - <NUM>°. The blade bars <NUM>, and thereby the blade grooves <NUM>, in the stator blade segment <NUM>' are, in turn, arranged at a blade bar angle α<NUM> of about <NUM>° - <NUM>° relative to the axial direction A to the opposite direction relative to the blade bars <NUM> and the blade grooves <NUM> in the rotor blade segment <NUM>'. The orientation of the blade bars <NUM> and blade grooves <NUM> in the stator blade segment <NUM>' relative to the orientation of the blade bars <NUM> and the blade grooves <NUM> in the rotor blade segment <NUM>' are indicated schematically in <FIG> by broken lines. Generally the blade bar angle α<NUM> in the stator blade element may for example be <NUM>° to <NUM>°.

The crosswise orientation of the blade bars <NUM>, <NUM> in the opposite blade elements <NUM>, <NUM>', <NUM>, <NUM>' in the blade element pair ensures that sufficiently high shear forces are to be focused to the fibrous material to be refined by the opposite blade bars <NUM>, <NUM>. For that effect to be achieved an angle between the blade bars <NUM>, <NUM> in the refining surfaces <NUM>, <NUM> of the oppositely set blade elements <NUM>, <NUM>', <NUM>, <NUM>', i.e. the intersecting angle α<NUM>+ α<NUM> may vary between <NUM>° - <NUM>°.

Claim 1:
A blade element pair (<NUM>) for a refiner (<NUM>, <NUM>, <NUM>) intended for refining fibrous material, the blade element pair (<NUM>) comprising a stator blade element (<NUM>, <NUM>') and a rotor blade element (<NUM>, <NUM>') to be set substantially opposite to each other and each blade element (<NUM>, <NUM>', <NUM>, <NUM>') of the blade element pair (<NUM>) comprising a refining surface (<NUM>, <NUM>) comprising blade bars (<NUM>, <NUM>) and blade grooves (<NUM>, <NUM>) extending along the blade element (<NUM>, <NUM>', <NUM>, <NUM>') and openings (<NUM>, <NUM>) extending through the blade element (<NUM>, <NUM>', <NUM>, <NUM>'), the openings (<NUM>, <NUM>) in one of the blade elements (<NUM>, <NUM>', <NUM>, <NUM>') being at different axial (A) positions in an axial (A) direction of the blade element (<NUM>, <NUM>') from the openings (<NUM>, <NUM>) in the other blade element (<NUM>, <NUM>', <NUM>, <NUM>') when the blade elements (<NUM>, <NUM>', <NUM>, <NUM>') of the blade element pair (<NUM>) for a conical or cylindrical refiner (<NUM>, <NUM>) are set substantially opposite to each other, or the openings (<NUM>, <NUM>) in one of the blade elements (<NUM>, <NUM>', <NUM>, <NUM>') being at different radial (R) positions in a radial (R) direction of the blade element (<NUM>, <NUM>') from the openings (<NUM>, <NUM>) in the other blade element (<NUM>, <NUM>', <NUM>, <NUM>') when the blade elements (<NUM>, <NUM>', <NUM>, <NUM>') of the blade element pair (<NUM>) for a disc refiner (<NUM>) are set substantially opposite to each other,
characterized in that the refining surface (<NUM>, <NUM>) of the blade element (<NUM>, <NUM>', <NUM>, <NUM>') comprises at least one solid refining surface zone (6a, 6c, 6e, <NUM>, 6i, 9b, 9d, 9f, <NUM>) without openings and at least one refining surface zone (6b, 6d, 6f, <NUM>, 9a, 9c, 9e, <NUM>, 9i) with openings (<NUM>, <NUM>) and the refining surface zone provided with openings (<NUM>, <NUM>) in one blade element (<NUM>', <NUM>') is set opposite to the refining surface zone without openings in the other blade element (<NUM>', <NUM>'), and that the openings (<NUM>, <NUM>) in the stator blade element (<NUM>') are arranged at a side edge (5c, 5d, 8c, 8d) of the stator blade element (<NUM>').