[0002] The invention further relates to a blade segment for a refiner intended for defibrating lignocellulose-containing material, the refiner compris- ing at least two refining surfaces arranged coaxially relative to each other, at least one of which refining surfaces is arranged to rotate around a shaft, and between which refining surfaces the material to be defibrated is fed, and which blade segment can be arranged to form at least a part of at least one refining surface, and which blade segment comprises first bars extending from the in- ner circumference of the refining surface to the outer circumference of the re- fining surface and between them first grooves, and the upper surfaces of which first bars further comprise second grooves connecting said first grooves, and between which second grooves there are second bars.

[0003] Disc and cone refiners used for treatment of fibrous material are typically formed of two or possibly more refiner discs opposite to each other which are arranged to turn relative to each other so that at least one of said refiner discs is arranged to rotate around a shaft. In disc refiners the re- finer disc is disc-like and in cone refiners it is conical. In a refiner comprising two refiner discs, one of the refiner discs further comprises an opening through which the material to be refined is fed into the refiner. The part of the refiner disc where said feed opening is located can be called a feed end. The refiner discs are positioned in such a way that they form a refiner gap between them, where lignocellulose-containing material is defibrated. The distance between the refiner discs is longest on the feed side or at the feed point of the lignocel- lulose-containing material, i. e. , in a disc refiner, in the middle of the discs, and

in a cone refiner, at the cone end having a smaller diameter, said gap being reduced towards the discharge point or discharge side of the material to be refined in order to gradually grind the material to be refined.

[0004] The refining surfaces of refiner discs are typically formed of protrusions, i. e. blade bars, extending from the inner circumference of the re- fining surface to the outer circumference of the refining surface, and of grooves between the blade bars. Hereafter, blade bars are also called bars. The shape of these grooves and bars per se may vary in different ways. Thus, for exam- ple, in the radial direction of the refiner disc the refining surface may be divided into two or more circular parts, each circumference having bars and grooves whose number and density as well as their shape and direction may deviate from each other. Thus, the bars may be either continuous over the whole length of the refining surface radius or there may be a plurality of separate, successive bars in the radial direction. At the refiner rotor, the bars and the direction thereof have a greater effect than at the stator because of the rotation of the rotor, whereby the fibrous material to be refined is subjected especially by the rotor bars to a refining force resultant which affects with a velocity de- termined on the basis of the radius and rotational speed of the refining surface.

The bars of the stator form counter pairs or a counter surface for the rotor, re- quired in refining, the blade bars crossing each other during refining like scis- sor blades. However, there is a small clearance between the rotor bars and stator bars of the refiner, and the fibrous material is mainly ground or refined between them.

[0005] Refining surfaces of refiner discs can be formed directly onto the surface of the refining discs for example by casting or by separate machin- ing but usually a refining surface is formed of blade segments which are ar- ranged next to each other on the refiner disc both in the radial and in the circu- lar direction of the refiner disc so that the refiner disc is provided with a uniform refining surface. Thus, each blade segment forms a part of the refining surface of the refiner disc.

[0006] In the case of a disc refiner, the inner circumference of the refining surface refers to the middle part of the refining surface and, in the case of a cone refiner, to the end of said cone with the smaller diameter. The outer circumference of the refining surface naturally refers, in the case of a disc re- finer, to the outer part of the refining surface, i. e. the part where the circumfer-

ence of the refining surface is largest, and, in the case of a cone refiner, to the end of said cone with the larger end.

[0007] Attempts have been made earlier to improve the load capac- ity or refining capacity of refiners by increasing the combined length of the re- fining surface bars. As a result, such blade or refining surface solutions have been designed and used, where blade bars are located closer and closer to each other. In such"dense blades", it is the volume or capacity of the grooves that determines the production capacity of the refiner blade. Due to the manufacture, blade bars typically have a clearance angle of 1 to 5°, which means that doser to the bottom of the groove the bar is thicker. This limits the groove volume even more. In addition, in cast blades the groove surfaces are rough, which causes flow resistance to the fibrous material to be refined. The narrower a groove is, the stronger becomes the flow resistance. A problem of these"dense blades"is, therefore, that they tend to be blocked. On the other hand, even the above mentioned blade solutions have not been successful in increasing the refiner capacity in a desired way.

[0008] US publication 4 676 440 discloses a typical refiner blade for a high-consistency refiner. The blade formation of the publication consisting of blade segments is formed of three refining surface zones in the radial direction of the refiner disc, whereby in the outer zones of the refining surface the blade bars are positioned very close to each other in order to achieve a high refining capacity. Because of this, the volume of the grooves between the bars has become smaller. Therefore, on the refining surface of at least one of the refiner discs there is also one or more discharge channels having a substantially lar- ger cross-section than said grooves in order to discharge steam generated during refining from between the refining surfaces. With these discharge chan- nels, it has been possible to diminish the problems caused by steam generated during refining in the refining process, but the discharge channels may, how- ever, make the refining more uneven and, in practice, the steam discharge channels described in the publication are arranged too sparsely with respect to each other.

[0009] US publication 5 467 931 discloses a refining surface, wherein the efficiency of a refiner with densely arranged bars has increased due to a higher flow capacity of the refiner blades. Flow capacity has increased primarily because material has been chamfered away from the background edges of the blade bars. The publication also discloses a blade bar, the upper

surface of which is provided with small grooves at sparse intervals, which can slightly increase the flow capacity of the grooves between the bars and facili- tate the discharge of steam produced during refining from between the refining surfaces. Said grooves on the upper surface of the blade bar also add to the combined cutting length of the bars of the refining surface to some extent, but, in practice, the oblique structure of the upper surface of the blade bar hinders these small grooves from participating in the refining of the material before the blade bar has worn significantly, which means that one has not, nevertheless, succeeded in substantially increasing the refining capacity of the refiner.

BRIEF DESCRIPTION OF THE INVENTION [0010] It is an object of the present invention to provide a new refin- ing surface or blade solution for a refiner, enabling a higher refining capacity than previously.

[0011] The refining surface of the invention is characterized in that the second bars are narrower than the first bars.

[0012] Furthermore, the blade segment of the invention is charac- terized in that the second bars are narrower than the first bars.

[0013] According to the essential idea of the invention, at least one refining surface of a refiner intended for defibrating lignocellulose-containing material comprises first bars extending from the inner circumference of the re- fining surface to the outer circumference of the refining surface and between them first grooves, and the upper surfaces of the first bars further comprise second grooves connecting said first grooves, between which second grooves there are second bars, which are narrower than the first bars. According to an embodiment of the invention, the average width of the first bar is 2. 5- to 40-fold in respect of the average, combined width of the second bar and the second groove. According to another embodiment of the invention, the total area of the refining zones of the refining surface formed of the second bars and the sec- ond grooves is 60 to 90%, preferably 70 to 80%, of the total area of the refining surface.

[0014] With the solution of the invention, a high cutting length can be achieved on the refining surface. Since the first grooves have a volume that is clearly larger than previously, an optimal, steady feed of the. fibrous material to be refined can be achieved over the entire area of the refining surface. The refining surface of the solution can thus provide both the desired capacity and

a good quality of the refined pulp. Unlike before, the same refining surface so- lution can also be applied to the refining of both long and short fibre.

BRIEF DESCRIPTION OF THE FIGURES [0015] The invention will now be described in more detail in the at- tached drawings, in which Figure 1 schematically shows a side view of a typical disc refiner in cross-section, Figure 2 schematically shows a side view of a typical cone refiner in cross-section, Figure 3 schematically shows a part of a refining surface of a disc refiner, seen in the direction of the refining surface, Figure 4 schematically shows a top view of a first bar of the refining surface according to Figure 3, Figure 5 schematically shows a cross-section of the bar according to Figure 4 along line V-V of Figure 4, Figure 6 schematically shows a second refining surface of the disc refiner, seen in the direction of the refining surface, Figure 7 schematically shows a third refining surface of the disc re- finer, seen in the direction of the refining surface, Figure 8 schematically shows a part of a refining surface of the rotor of a cone refiner, seen in the direction of the refining surface, Figure 9 schematically shows a part of a refining surface of the sta- tor of a cone refiner, seen in the direction of the refining surface, Figure 10 schematically shows a cross-section of the refining sur- face according to Figure 8 along line C-C of Figure 8, Figure 11 schematically shows a cross-section of the refining sur- face according to Figure 9 along line C-C of Figure 9, Figure 12 schematically shows a detail of the refining surface in cross-section, Figure 13 schematically shows a part of a refining surface of a re- finer, seen in the direction of the refining surface, Figure 14 schematically shows a cross-section of the refining sur- face according to Figure 13, Figures 15a and 15b schematically show two embodiments of the refining surfaces, seen in the direction of the refining surfaces, and

Figures 16a and 16b schematically show the refining surfaces ac- cording to Figures 15a and 15b in detail in cross-section, Figure 17 schematically shows a refining surface of a cone refiner, Figure 18 schematically shows a refining surface according to the solution being used in a double disc refiner, Figures 19 to 22 schematically show test run results achieved with both a conventional refining surface and the refining surface according to the solution and Figure 23 schematically shows a blade segment of a refiner.

[0016] For the sake of clarity, the invention is shown simplified in the figures. Like parts are denoted with like reference numerals in the figures.

DETAILED DESCRIPTION OF THE INVENTION [0017] Figure 1 shows schematically a side view of a typical disc re- finer in cross-section. The disc refiner comprises two disc-like refining surfaces 1 and 2, which are positioned coaxially relative to each other. In this embodi- ment, the first refining surface 1 is in a rotating refiner disc 3, i. e. a rotor, which is rotated by a shaft 4. The second refining surface 2 is in this case in a fixed refiner disc 5, i. e. a stator. The refining surfaces 1 and 2 of the refiner discs 3 and 5 may be either formed directly onto the discs or formed of separate blade segments in a manner known per se. Figure 1 shows further a loader 6 con- nected to affect the refiner disc 3 via the shaft 4 in such a way that it can be pushed towards the refiner disc 5 to adjust the gap between them. The refiner disc 3 is rotated via the shaft 4 in a manner known per se by means of a motor not shown for the sake of clarity.

[0018] The lignocellulose-containing material to be defibrated is fed through an opening 7 in the middle of the second refining surface 2 to the gap between the refining surfaces 1 and 2, i. e. the refiner gap, where it is defi- brated and refined. The material to be defibrated can be fed into the refiner gap also through other openings on the refining surface 2, which are not shown in the figure for the sake of clarity. The lignocellulose-containing mate- rial that has been defibrated is discharged through the gap between the refiner discs 3 and 5 from the outer edge of the refiner gap, i. e. the outer circumfer- ence of the refiner discs 3 and 5, into a refiner chamber 8, from where it is fur- ther discharged along a discharge channel 9. Thus, at the opening 7 in the middle of the refining surface 2 there is the feed point or feed side for the fi-

brous material to be refined and at the outer circumference of the refiner discs 3 and 5 there is the discharge side or discharge point for the refined fibrous material.

[0019] Figure 2 shows schematically a side view of a typical cone refiner in cross-section. The cone refiner comprises two conical refining sur- faces 1 and 2, which are positioned within each other coaxially. In this em- bodiment, the first refining surface 1 is in a rotating conical refiner disc 3, i. e. a rotor, which is rotated by means of the shaft 4. The second refining surface 2 is in a fixed conical refiner disc 5, i. e. a stator. The refining surfaces 1 and 2 of the refiner discs 3 and 5 may be either formed directly onto the discs or formed of separate blade segments in a manner known per se. Further, Figure 2 shows a loader 6 connected to affect the refiner disc 3 via the shaft 4 so that it can be pushed towards the refiner disc 5 to adjust the gap between them. The refiner disc 3 is rotated via the shaft 4 in a manner known per se by means of a motor not shown for the sake of clarity.

[0020] The lignocellulose-containing material to be defibrated is fed through an opening 7 in the middle of the second refining surface 2, i. e. from the end of the cone structure having the smaller diameter, into a conical gap between the refining surfaces 1 and 2, i. e. a conical refiner gap, where it is de- fibrated and refined. The material that has been defibrated is discharged through a gap between the refiner discs 3 and 5 from the outer edge of the refiner gap, i. e. from the end of the cone structure with the larger diameter, into the refiner chamber 8, from which refiner chamber 8 it is further discharged along the discharge channel 9. At the opening 7 in the middle of the refining surface 2 there is the feed point or feed side for the fibrous material to be re- fined and at the end of the refiner discs 3 and 5 having the larger diameter there is the discharge side or discharge point for the refined fibrous material.

[0021] Figure 3 shows a part of a refining surface of a disc re- finer intended for refining fibrous material with a high concentration. The refin- ing surface is provided with a pattern of first bars 12 and first grooves 13 be- tween them. Figure 4 shows an embodiment of the bars 12 of the refining sur- face in Figure 3, and Figure 5 shows a section along line V-V of Figure 4.

The first bars 12 have upper surfaces 18 and side surfaces 19 with edges 20.

The pattern of bars 12 is divided into two refining surface zones 16, the inner zone 16 and the outer zone 16', whereby the bars 12 and the grooves 13 in the inner zone 16 are more sparsely distributed than in the outer zone 16'. The

bars 12 in the inner zone 16 are intended for bringing about a first disintegra- tion of the material and for advancing the material outward to the outer zone 16'. The bars 12 in the outer zone 16'are placed more closely to each other, which means that there are more bar edges for effecting the substantial work- ing and refining of the material. The pattern of bars 12 can also comprise more zones, whereby the pattern is usually made denser from zone to zone in the radially outward direction.

[0022] Figure 4 shows an embodiment where a plurality of smaller grooves or second grooves 15 are placed along the bars 12, which grooves are arranged slightly angular in relation to the longitudinal direction of the bars 12 and are open to both side surfaces of the bars 12. Due to the bars 12 provided with oblique, smaller second grooves 15 on the upper surfaces 18, the first bars 12 as well as the first grooves 13 between them can be made wider without that the working upper surface of the bars 12 loses its effective- ness. By means of the wider first grooves 13, the steam and, respectively, liq- uid flow in the grooves 13 is facilitated and the disturbance of the working of the fibrous material is minimised.

[0023] Figure 6 shows another embodiment of the bars 12.

Unlike in Figure 4, the bars 12 are arc-shaped. The smaller second grooves 15 on the upper surface 18 of the bars 12, however, are always oblique in relation to the longitudinal direction of the bars 12. The second grooves 15 therein should be suitably in the substantially radial direction.

[0024] According to Figure 7, the smaller grooves 15 are an- gular in different directions, preferably in such a way that they cross each other on the upper surface of the bars 12. Alternatively, they can be offset in the lon- gitudinal direction of the bars 12 so that they do not cross each other. These embodiments allow that the rotation direction of the refiner discs can be changed.

[0025] Figure 8 shows schematically a blade segment 10 forming a part of a refining surface 1 of the rotor of a cone refiner, seen in the direction of the refining surface 1. Figure 9 shows schematically a blade segment 11 form- ing a part of a refining surface 2 of the stator, seen in the direction of the refin- ing surface 2. The refining surfaces 1 and 2 comprise blade bars 12, i. e. bars 12. The bars 12 form first bars of the refining surfaces 1 and 2. Between the bars 12 there are grooves 13 forming first grooves of the refining surfaces 1 and 2. The upper surface of the bars 12 is provided with a dense structure of

grooves, comprising grooves 15 and bars 14 between them. The bars 14 form second bars of the refining surfaces 1 and 2. The grooves 15 form second grooves of the refining surfaces 1 and 2. The bars 14 and grooves 15 of the refining surface 1 of the rotor are schematically shown in Figure 10, which illus- trates a cross-section of the refining surface 1 along line C-C of Figure 8. The bars 14 and grooves 15 of the refining surface 2 of the stator are schematically shown in Figure 11 illustrating a cross-section of the refining surface 2 along line C-C of Figure 9.

[0026] The refining surfaces according to Figures 3 to 11 are char- acterized in that the refining surfaces comprise first bars 12 and first grooves 13 between the first bars 12. Further, the upper surface 18 of the first bars 12 comprises second bars 14, between which there are second grooves 15. In their direction of travel, the second bars 14 are narrower than the first bars 12, and the second grooves 15 are also in their direction of travel narrower than the first grooves 13. The upper surface of the first bars 12 is thus provided with a dense structure of grooves, i. e. a structure of microgrooves, for refining the lignocellulose-containing material. The refining surfaces are formed in such a manner that the total area of the microgrooved refining zones formed of the upper surfaces of the bars 12 equals 60 to 90% of the total area of the refining surfaces. The refining surfaces are preferably formed in such a manner that the total area of said microgrooved refining zones is 70 to 80% of the total area of the refining surfaces.

[0027] The purpose of the microgrooved refining zones on the up- per surface of the bars 12 is to refine said lignocellulose-containing fibrous ma- terial. Between the refining surfaces 1 and 2 of the refiner there is a small clearance, due to which the refining of said fibrous material takes place be- tween the refining surfaces 1 and 2. The purpose of the first grooves 13 is to transport fibrous material to be refined to the refining zones formed of the mi- crogrooved upper surfaces of the bars 12 and to transport the refined material away from between the refining surfaces 1 and 2. In addition, the purpose of the first grooves 13 in high-consistency refining is to transport water vapour produced during refining away from between the refining surfaces 1 and 2.

[0028] The refining surfaces 1 and 2 can be implemented in various ways. For instance, the first bars 12 and the first grooves 13 between them on the refining surfaces can be formed in a variety of ways in respect of their size and shape. The bars 12 can be, for instance, 15 to 80 mm, preferably 20 to 40

mm, wide. The width of the grooves 13 between the bars 12 can be, for in- stance, 5 to 40 mm, preferably 10 to 30 mm, for example. Both the bars 12 and the grooves 13 can be formed in such a way that their width remains the same or changes according to the direction of travel of the bars or grooves. The depth of the grooves 13 can be 10 to 40 mm, for example. The grooves 13 can be formed in such a way that the depth thereof remains the same or changes in the direction of travel of the grooves. It can be said that as the width and/or depth of the groove 13 changes, the cross-sectional area of the groove 13 or the volume of the groove 13 changes. Thus, the cross-sectional flow area of the grooves 13 can vary between 0.5 and 16 cm2.

[0029] As to the shape of the bars 12, they can either extend di- rectly in the radial direction of the refining surface from the shaft of the refining surface to the outer circumference of the refining surface or the bars 12 can be curved at a standard or a varying angle from the shaft of the refining surface to the outer circumference of the refining surface, whereby the edges of the bars 12 can be curved uniformly or they may have steps. The shape of the bars 12 naturally determines the shape of the grooves 13 between the bars 12. Fur- ther, the bars 12 can be formed in such a way that they are pumping at the feed end of the fibrous material to be refined and retentive or non-pumping at the discharge end of the refined fibrous material, which is why it is possible to compensate for a low pumping centrifugal force on the feed side and a high pumping centrifugal force on the discharge side. An example of this is shown in Figure 23 wherein the first bars 12 are pumping at the feed end and non- pumping at the discharge end. In this example the second bars 12 are pump- ing throughout the blade segment according to Figure 23. The attachment points of the blade segment are denoted with reference numeral 21.

[0030] A pumping blade bar means that when the refiner rotor ro- tates in the pumping direction, the blade bar produces for the mass particle both a circular velocity component and a radial velocity component directed away from the centre, whereby the mass particle tends to move away from between the refiner discs. A retentive blade bar, for its part, means that when the refiner rotor rotates in the retentive direction, the blade bar produces for the mass particle both a circular velocity component and a radial velocity compo- nent directed towards the centre, whereby the mass particle tends to remain between the refiner discs.

[0031] The width of the second grooves formed on the upper sur- face of the first bars 12 can be 1 to 3 mm, for instance. Also the width of the second bars 14 which remain between the second grooves 15 can be 1 to 3 mm, for example. The average width of the first bars 12 is thus about 2. 5- to 40-fold in respect of the combined average width of the second bars 14 and the second grooves 15. The bars 14 and the grooves 15 may have a constant width in their direction of travel but said width of the bars 14 and the grooves 15 can also change in their direction of travel. Said second bars 14 and sec- ond grooves 15 are thus positioned as densely as possible on the upper sur- face of the first bars 12 so that the cutting length of the refining zones of the refining surfaces 1 and 2 becomes as great as possible.

[0032] The bars 14 and the grooves 15 can be formed on the upper surface of the bars 12 in such a manner that they form an angle of about 5 to 30° to the radius of the refining surface in one direction or another. The bars 14 can be formed such that with a specific radius, the angle of attack of the bars 14 on the opposing refining surfaces is constant over the entire area of the refining surface. The grooves 15 can be formed such that they can be ei- ther pumping or retentive. When the grooves 15 are pumping, the pulp is taken more effectively towards the discharge, thus achieving a uniform refining re- sult. If the grooves 15 are retentive, the refining result is not so uniform but, on the other hand, the residence time distribution of the fibrous material is greater.

Thus, to achieve a uniform refining result, refining surfaces are used, the sec- ond grooves 15 of which are pumping. If it is more important to achieve a long refining treatment of fibrous material than a uniform refining result, refining sur- faces are used, the grooves 15 of which are retentive. The grooves 15 can also be implemented in such a manner that the purpose thereof is not to affect the time the material to be refined remains between the refining surfaces.

[0033] The second grooves 15 on the upper surface of the bars 12 can be, for instance, 3 to 5 mm deep. Thus, the first grooves 13 are at least twice as deep as the second grooves 15. In practice, the greatest groove depth of the grooves 15 is determined by the thickness of the wear surface of the refining surfaces. The depth of the groove 15 can either be constant or vary in the direction of travel of the groove 15. The depth of the groove 15 can also vary in the width direction of the groove 15 so that, for instance, the groove 15 is deeper on the front side than on the back side, which produces a lifting force and the blade does not cut through the fibre matting nor break the fibres. The

front side refers to the front edge of the groove 15 and the back side to the back edge of the groove 15, when seen in the rotation direction of the refiner disc. This solution is shown schematically in Figure 12, which illustrates a first bar 12 in cross-section. Such a solution can be advantageous when the aim is to achieve a high load capacity for the postrefining of mechanical pulp or for short-fibred pulp. In the refining of long-fibred pulp, the grooves 15 can have an equal depth or they can even be deeper on the back side of the groove than on its front side.

[0034] The refining surface according to the solution makes it pos- sible that in the refining, a very small load on the bar can be used without im- pairing the hydraulic capacity of the refiner. Usually when long-fibred pulp is refined with short-fibre blades intended for refining short fibres, a sufficient hy- draulic capacity is not achieved and the blades of the refiner are blocked. On the refining surface according to the solution, grooves 13 with a clearly larger volume than previously enable an optimal, constant feed of the fibrous material to be refined in the entire area of the refining surface. Due to the bars 14 and grooves 15 on the upper surface of the bars 12 and forming the refining zones of the refining surfaces 1 and 2 and providing a clearly denser structure of bars and grooves than the previously known solutions, a high cutting length can be achieved on the refining surface. The refining surface of the solution can thus provide a desired capacity and a good quality of the refined pulp. In addition, unlike previously, the same refining surface solution can be applied to the re- fining of both long and short fibre. Further, with a specific energy consumption which is 10 to 20% lower than before, the refining surface of the solution pro- vides the same quality or strength change as previously. Furthermore, by using the same cutting length as before, the refiner can be used with a load that is 20% greater without any blade contact. Also, a greater power can be used without decreasing the fibre length of short fibre, which means that short-fibre refining can be carried out by using fewer refiners.

[0035] Figures 19 to 22 show test run results achieved with both a conventional refining surface and the refining surface according to the solution.

Figure 19 shows a situation in which long fibre is refined with the conventional refining surface (broken line) and with the refining surface according to the so- lution (continuous line). The purpose was to increase the refining degree, i. e. freeness of pulp from the value of CSF 700 ml to the value of CSF 300 ml. It appears from Figure 19 that, in the case of the conventional refining surface,

185 kWh/ton of energy was needed to increase said refining degree, whereas the energy demand in the case of the refining surface of the solution was only 140 kWh/ton, which corresponds to an energy saving of 25%. Figure 20, in turn, shows that the bonding strength (Scott Bond) of pulp developed clearly faster when the refining surface of the solution was used. In the case of the refining surface of the solution (continuous line), 120 kWh/ton of energy was needed to achieve the bonding strength of 400 J/m2, whereas the energy de- mand of the conventional refining surface was 150 kWh/ton. Thus, particularly when long fibre is refined, the refining surface of the solution provides consid- erable energy savings in comparison with the conventional refining surface.

[0036] Figure 21 shows a situation where short fibre is refined with the conventional refining surface (broken line) and with the refining surface according to the solution (continuous line). The purpose was to increase the tensile index of the fibre from the starting value of 41 kNm/g. On the basis of the test run, it was not reasonable to load the conventional refining surface more than 80 kWh/ton, because, after this, the tensile index started to become lower. In this case, the tensile index of a specimen made of the test run pulp was 67 kNm/g. At the same time as the tensile index started to become lower, the distance between the refining surfaces of the refiner became shorter, which caused a risk of a harmful contact between the opposing refining surfaces. The refining surface of the solution did not have this problem, wherefore higher tensile indexes were achieved and the load capacity of the refiner was main- tained until the end and the test produced a tensile index of 73 kNm/g with a refining energy of 120 kWh/ton.

[0037] Figure 22 shows how the fibre length changes in the case of the refining surface of the solution (continuous line) and in the case of the con- ventional refining surface (broken line). Although there was no essential differ- ence between the cutting lengths of the conventional refining surface and the refining surface of the solution, the conventional refining surface cut fibre, whereas the fibre length did not essentially decrease by using the refining sur- face of the solution. With an energy consumption of 120 kWh/ton in the refin- ing, the fibre length decreased from 0,87 mm to 0,78 mm when the refining surface of the solution was used, whereas in the case of the conventional refin- ing surface, the fibre length decreased to 0,66 mm and a contact occurred be- tween the refining surfaces. Particularly in the refining of short fibre, the refin- ing surface of the solution provides, above all, the advantage of a higher load

capacity of the refiner since, conventionally, if the refiner is loaded too much, the refining surfaces will have a harmful contact. Thus, more energy can be consumed per each mass ton, without decreasing the fibre length substantially or having a contact between the refiner surfaces. The refining surface of the solution is thus particularly suitable for fibres which are sensitive to overload and to a refiner surface contact. Examples of such situations include postrefin- ing of mechanical pulp and short-fibred mechanical pulp and refining of chemi- cal pulp and recycled fibre pulp.

[0038] Bars with a design presented above can be placed in any zone on the refining surface, but preferably at least in the outer zone where the working and refining are most intensive and the distance between the oppos- ing refining surfaces is the shortest, i. e. the refining gap is the smallest and possible steam development the greatest. During the working of fibrous mate- rial with the refining surfaces presented above, the upper surfaces of the bars 12 and the edges of the smaller second grooves will work on the material. The steam the development of which arises in the case of a high concentration re- fining and the liquid flow that passes through the refining gap in the case of a low concentration refining are led away from the upper surfaces of the bars 12 and can pass out through the grooves 13 between the bars 12 so that the working of the fibrous material is not disturbed. In this way, a high capacity can be achieved and the pulp quality maintained. By providing the refining surfaces with arc-shaped first bars 12 with substantially radial, smaller second grooves 15 on the upper surface, an increased capacity can be obtained and, at the same time, a high pulp quality achieved so that the smaller second grooves 15 bring about an effective fibrillation of the fibrous material.

[0039] Figure 13 shows schematically a part of a refining surface, seen in the direction of the refining surface, and Figure 14 shows schematically the refining surface according to Figure 13 in cross-section in the longitudinal direction of the groove 13. In the refining surface according to Figures 13 and 14, the number of the second bars 14 increases from zone to zone from the feed side of the refining surface to the discharge side of the refining surface.

Thus, seen from the feed end of the refiner, the first refining surface zone comprises the lowest number of second bars 14 and the last refining surface zone the highest number of second bars 14. This can be implemented, for in- stance, so that in the first refining surface zone seen from the feed end, the width of the second grooves 15 between the second bars 14 corresponds to

the maximum value of the variation range of the groove width presented above, and in the last refining surface zone, the width of said grooves 15 cor- responds to the minimum value of the variation range of said groove width.

The refining surface zones are denoted in Figure 13 with reference numeral 16. Of course, as seen from Figure 13, the second grooves 15 between the second bars 14 can also be essentially wider at the feed end than at the dis- charge end.

[0040] Figure 14 also shows how the depth of the second groove 15 changes so that the depth of the groove 15 at the end of each refining surface zone is smaller than at the beginning of the next refining surface zone. Hence, the grooves 15 become lower step by step towards the discharge side. This leads to a half-dam, which physically hinders return flows of the refined mate- rial. The grooves 15 could also be implemented in such a way that they be- come steadily lower towards the discharge side. The depth of the second grooves 15 on the upper surface of the first bars 12 and the depth of the first grooves 13 are dimensioned, for instance, so that the maximum values of the variation ranges of the groove depths mentioned above are used on the feed side and the minimum values of the variation range of said groove depths are used on the discharge side.

[0041] The embodiment according to Figures 13 and 14 is charac- terized in that the cross-sectional flow area of the refining surface remains the same or becomes smaller towards the discharge of the material to be refined, whereby the flow rate of the fibrous material to be refined remains the same or becomes higher towards the discharge. A stepwise denser structure of the re- fining surface decreases the cross-sectional flow area, whereby the smaller cross-sectional flow area is compensated for by making the grooves deeper.

On the other hand, as the number of grooves increases in the direction of the outer circumference of the refining surface, the bigger cross-sectional flow area is compensated for by lower grooves. This provides even flow of the re- fined material and fibre treatment in which the return flows of the refined mate- rial can be minimised and the residence time distribution decreased so that all fibres are provided with as uniform treatment as possible. A uniform fibre treatment is advantageous in applications where a high strength and density of paper is required without decreasing the paper porosity. Also the smoothness and quality of the paper surface improve as the number of unrefined fibres de- creases. In addition, it is easier to control the pressure rise between the refiner

discs, as a result of which the refiner runs more smoothly and does not have so much vibrations and has a no-load operation power that is about 20 to 30% smaller than before.

[0042] Figures 15a and 15b show a part of a refining surface, seen in the direction of the refining surface, and Figures 16a and 16b show the refin- ing surface according to Figures 15a and 15b in cross-section. For the sake of clarity, In the embodiment according to Figures 15a, 15b, 16a and 16b, one or more foils 17 are provided on the refining surface 1 of the rotor plate 3 of the refiner, for example, by casting. The foil 17 is placed onto the bottom of the first groove 13.

[0043] The foils 17 are placed onto the refining surface of the rotor plate 3 such that when the rotor rotates in the pumping direction, the foils 17 produce a lifting force. At the same time, a power is produced in the stator, restricting the pumping effect of the bars 12 and simultaneously causing an effective mixing of the fibres and water, which prevents the refining surfaces from being blocked. In addition, due to the suction effect caused by the foils 17, the grooves of the refining surface of the stator are cleaned. When such a rotor provided with foils 17 rotates in the non-pumping direction, the foil 17 acts as a pumping part causing a push force, which intensifies the pumping effect and improves the passing through of the fibre materials. The push force of the foil 17 causes a pressure pulse, which pushes the pulp through the refiner.

Due to the solution, the refiner throughput difference between the pumping and non-pumping directions of the rotor becomes smaller.

[0044] The foil can be continuous and be located on the blade sur- face either radially or in a curved manner. A radial foil provides a stronger pulse than a curved one. The foil can also consist of bits. The foil bits can also be randomly placed on the refining surface. Typically, the foil has a length of 30 to 80 mm, preferably 50 to 60 mm, the length being defined in the trans- verse direction to the first groove. The depth of the foil can be, for instance, about 20 mm, and the shortest distance of the foil from the counter surface is, for instance, 3 mm in the beginning. As the refining surfaces wear, the distance becomes shorter and the power of the suction pulse becomes higher. The fre- quency of the desired suction pulses can be controlled by changing the num- ber of foils on the refining surface.

[0045] Foils and a gradually denser structure of bars and grooves as well as either a stepwise or a regular change in the groove depth can natu-

rally also be utilised as such in other refining surface solutions than in the refin- ing surfaces provided with both the first bars 12 and first grooves 13 and the second bars 14 and second grooves 15. Thus, these features can be utilized, for example, in the refining surfaces according to Figures 1 and 3 of the US- publication 4676440 or in the refining surface according to Figure 17. Figure 17 shows schematically a refining surface, which only comprises second grooves 15 and second bars 14 arranged densely with respect to each other and which are known as microgrooves and micro bars. The refining surface of Figure 17 is a highly preferred solution as a refining surface of the stator, the refining surface of the rotor being in accordance with the above description.

The refining surface of Figure 17 can especially be used as a counter surface for the refining surfaces shown in Figures 13 to 16. A counter surface can naturally also be any previously known refining surface solution.

[0046] Figure 18 shows schematically a refining surface according to the solution being used in a double disc (DD) refiner. In the middle of Figure 18 there are two rotor plates attached to each other on their backsides and one refiner stator plate on each side of the rotor plates. Refining surfaces of said rotor plates are normally mirror images of each other and so are the two stator plates, i. e. if one of the two slots of the refiner function pumping then so does the other one, too, by means of which the functioning of the two-slot re- finer of Figure 18 is ensured, i. e. the gaps between the plates of the slots can be kept under control. The two-slot refiner can be changed from pumping to non-pumping by changing both rotor plates and stator plates among each other. By doing so the refiner is changed from pumping to non-pumping with- out changing the rotation direction of the refiner. The two-slot refiner can be changed from pumping to non-pumping also by changing the rotation direction of the rotor. Further one possibility to change from pumping to non-pumping is to change only the rotor plates among each other. The case demands that sta- tor plate design differs adequately from rotor plates because also after the change there have to be certain difference between blade bar angles of oppo- site refiner plates to avoid clashing of the plates. All the technical features pre- sented also in Figures 13 to 17 can naturally be used with double disc refiners.

Similarly all the technical advantages of the refining surface according to the solution are naturally present also in double disc refiners.

[0047] The drawings and the related description are only intended for illustrating the idea of the invention. In its details, the invention may vary

within the scope of the claims. The examples of the figures describe different embodiments associated with refining surfaces of the stator and rotor of either a disc refiner or a cone refiner, but it is naturally obvious that what is explained about the structure of the refining surfaces of the rotor and stator of a cone refiner, can also be applied, to the appropriate extent, to the structures of the refining surfaces of the stator and rotor of a disc refiner, and vice versa.