TECHNICAL FIELD OF THE INVENTION

The present invention relates to a refiner disc of a refiner for refining of lignocellulosic material. It also relates to a refiner segment for use in such a refiner disc.

BACKGROUND

A commonly used refiner of e.g., lignocellulosic material comprises two relatively rotating discs between which the material is refined or defibrated. The pair of relatively rotating discs may in particular comprise one rotating disc, referred to as a rotor, and one static disc, referred to as a stator. Alternatively, the pair of relatively rotating discs may comprise two rotating disc which are rotating in opposite directions. These refiner discs, or at least one of them, comprises an active surface which may comprise a set of bars and dams for providing an efficient refining of the material. The active surface of the refiner disc is at least a part of the surface over which the material flows and is treated. The active surface is often provided on a number of refiner segments which are separate parts which are supposed to be attached to the refiner disc whereby the active surface of the refiner disc is made up from a number of refiner segments. The bars may be substantially radially extending and protruding structures that are arranged on the active surface of the refiner disc and are mainly used to achieve an efficient refining of the lignocellulosic material. The dams are also protruding structures provided on the active surface, but they are not generally provided in a radial direction. The dams are instead provided on the active surface in such a way that a particular dam contacts, or connects, two neighbouring bars. That is, a dam is provided so that it spans over a direction that connects two adjacent bars. The direction may be approximately orthogonal to the bars, but it can also be provided at an angle with regard to the bars. A particular purpose with the dams is to lift the material that flows in the area between the bars (below called grooves) in an upward direction, towards a disc gap defined as the gap between two opposing refiner discs, e.g., the disc gap between a rotor and a stator or the disc gap that separates the two relatively rotating discs. It is in the disc gap between the discs that the material is refined or defibrated. In the common case where each bar connects to one or several dams, a natural consequence of the geometry is that a number of partially enclosed or bounded areas are created between adjacent bars. The main part of the refining material will flow in these areas. A particular problem associated with refiner discs equipped with bars and dams is that the bars and dams, being structures protruding from the surface of the refiner disc, will be worn down due to the abrasive contact they have with the material to be refined. The efficiency of the refiner disc will as a consequence decrease over time and there will be a need to replace refiner segments in order to achieve a satisfactory quality of the refined material, e.g., pulp.

SUMMARY

An object of the invention is to provide an improved refiner disc to be used in a refiner for refining of lignocellulosic material.

A further object of the invention is to provide a refiner disc and a refiner segment to be used in the refiner disc which when used in a refiner will provide an effective refining process giving refined material of high quality.

This is achieved in a refiner disc and in a refiner segment according to the independent claims.

According to one aspect of the invention a refiner disc of a refiner for refining of lignocellulosic material is provided. Said refiner disc having an active surface which will be facing another refiner disc when used in the refiner, wherein said active surface comprises a pattern of bars and grooves disposed in a number of pattern areas, wherein said pattern areas are positioned side by side with each other to cover at least a part of the active surface, wherein each of said pattern areas has a length, I, extending between a first end and a second end of the pattern area and a width, w, extending between two side edges, which two side edges both extend between the first and second ends of the pattern area, wherein said second end is provided at an outer circumference of the active surface and the first end is provided closer to a centre, C, of the refiner disc than the second end is and wherein a distance between the two side edges is smallest in the first end of the pattern area and is increasing towards the second end of the pattern area, and wherein each of said pattern areas is positioned on the active surface such that a centre line, c, of the pattern area, which is positioned in a centre of the pattern area and is extending from the first end to the second end of the pattern area, is provided at an angle, p, to a radius, R, of the refiner disc passing through a centre position, cp, of the pattern area 41; 41', said angle, p, being between 10°-60°, wherein at least some of the bars are extending along a direction between the two side edges of the pattern area in which the bars are provided, wherein at least 80 % of a total number of bars 10 which are provided within one pattern area 41; 41' extend only within said pattern area 41; 41'.

According to another aspect of the invention a refiner segment for use in a refiner disc according to the invention is provided, wherein said refiner segment comprises a part of the active surface of the refiner disc.

Hereby an active surface having a pattern of bars and grooves providing a more seamless volumetric decrease is achieved. The pattern areas are located side by side over the active surface in a tilted direction compared to the radial direction. The design of the active surface according to the invention provides for a uniform fiber quality with less dust and shives. Furthermore, a uniform wear and longer lifetime of the active surface pattern when the refiner disc is used in a refiner for refining lignocellulosic material is achieved according to the invention. By providing the bars and grooves in pattern areas according to the invention, where most of the bars are not extending outside the pattern area where it is provided, the sizes and extension directions of the bars within each pattern area can be freely varied within each pattern area. Hereby the design of the active surface can easily be optimised for example in order to achieve a volumetric decrease and hereby a uniform flow of material over the active surface. Thanks to the design of the active surface pattern according to the invention a more seamless volumetric decrease is provided which will provide the benefit of a more stable feed of wood chips, less micro-pulsation between the refiner discs, less point wear and hereby a lower energy consumption.

In one embodiment of the invention the pattern area is delimited in its second end by a part, s, of the outer circumference of the active surface, which part, s, is reaching between the two side edges of the pattern area, said part, s, having a length corresponding to an arc length of a circular sector having a central angle being between 1°-15° or between 4°-12° in a circle with the outer circumference of the active surface.

In one embodiment of the invention the centre line, c, of the pattern area is provided at an angle, p, to a radius, R, of the refiner disc, said angle, p, being between 20°-40°. In some embodiments of the invention the bars each has a length, a thickness and a height wherein the height is extending in a perpendicular direction from the active surface, whereby a thickness, bw, of the bars within each pattern area are the same or will decrease towards the outer circumference of the active surface.

In some embodiments of the invention a distance, gw, between adjacent bars in the same pattern area are the same or will decrease towards the outer circumference of the active surface. By adopting a thickness of bars and a distance between adjacent bars a more dense pattern can be provided towards the outer circumference of the active surface whereby a suitable volumetric decrease can be provided.

In some embodiments of the invention an angle, b, between a direction of length extension of each bar in a pattern area and a radius, R, of the refiner disc passing through a middle point of this bar, is the same or is decreasing towards the outer circumference of the active surface. A decreasing angle b for bars provided closer to the outer circumference can be provided for counteracting an increasing acceleration of the material caused by the centrifugal force closer to the outer circumference.

In some embodiments of the invention in a first part of the pattern area starting from the first end and extending towards the second end of the pattern area the bars are not extending all the way between the first and second side edges but are leaving an open wedge-shaped area without bars between adjacent pattern areas. Hereby the feeding of material will be improved and there is less risk that material is getting stuck between bars.

In some embodiments of the invention there are at least three end bars in each pattern area which are shorter than an adjacent bar in a direction towards the first end of the pattern area, which end bars are the bars positioned closest to the second end of the pattern area, whereby these end bars each extends towards the outer circumference of the active surface.

In some embodiments of the invention dams are provided to the active surface, whereby each dam extends between two adjacent bars, wherein at least four dams are positioned such that they together form a continuous dam provided along a smooth curve.

In some embodiments of the invention each pattern area comprises a continuous last dam comprising at least four dams which are connecting at least five end bars of this pattern area, which end bars are the bars positioned closest to the second end of the pattern area, whereby the continuous last dam of a number of pattern areas are connected, whereby a combined continuous last dam is provided substantially along the outer circumference of the active surface. Hereby a distribution of load is improved and the bars within each pattern area are strengthened. A production process of the active surface is also facilitated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a refiner wherein a refiner disc according to the invention may be used.

FIG. 2 is a schematic illustration of a cross-section of a refiner disc arrangement wherein the refiner disc according to the invention may be used.

FIG. 3 is a schematic top view of a refiner segment according to one embodiment of the invention.

FIG. 4 is a schematic illustration of a refiner segment attached to a refiner disc such as a rotor disc or a stator disc. Figure 5a is a schematic illustration of an active surface of a refiner disc according to one embodiment of the invention. Figures 5b and 5c show a part of the active surface in Figure 5a in more detail.

Figure 6 is a schematic illustration of an active surface of a refiner disc according to one embodiment of the invention. Figures 7a-7c are schematic illustrations of refiner segments according to different embodiments of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Throughout the drawings, the same reference designations are used for similar or corresponding elements. Generally, all terms used herein are to be interpreted according to their ordinary meaning in the relevant technical field, unless a different meaning is clearly given and/or is implied from the context in which it is used. Any feature of any of the embodiments disclosed herein may be applied to any other embodiment, wherever appropriate.

For a better understanding of the invention, it may be useful to begin with a brief description of a general refiner. To this end reference is made to FIG. 1 which schematically illustrates a refiner that can utilize the invention. Fig.l shows schematically an exemplary pulp refiner 100 in a cross-sectional view. The arrangement is housed in a housing 26 that represents the outer casing of the refiner device together with all components of the device that is not essential for understanding the present invention. Examples of components not shown are an electrical motor for driving e.g. the rotation shaft, the feeding mechanism for the lignocellulosic material etc. Inside a second housing 31 a rotor refiner disc 30 and a stator refiner disc 30* are linearly aligned along a shaft. The rotor refiner disc 30 is attached to a rotation shaft 15 arranged on bearings 16. The rotation shaft 15 is connected to a motor, not shown, that rotates the shaft 15, and thus the rotor refiner disc 30. The stator refiner disc 30* facing the rotor refiner disc 30 can be provided with a centrally located through hole 32 that extends between a feeding channel 14 for lignocellulosic material and a refining area 19. The feeding of material into the refining area 19 need not necessarily be provided via a centrally located through hole as shown in Figures 1 and 2 but can instead be distributed via through holes distributed in another way than exactly centrally. The rotor refiner disc 30 can in certain embodiments be provided with a center plate 17 having a surface facing the incoming flow of lignocellulosic material. The surface of the center plate 17 can be provided with structures that will direct the lignocellulosic material outwards. The rotor refiner disc 30* and/or the stator refiner disc 30 comprises an active surface to enable steering and grinding of the pulp. The active surface comprises often a pattern of bars and dams which will be described in more detail below. The refiner disc comprises normally a number of refiner segments, each comprising a part of the active surface. The refiner segments can be attached to and removed from the refiner disc and can hereby be exchanged when a pattern on the active surface has been worn out. In some refiners there may be two rotor refiner discs instead of a rotor and a stator refiner disc, where the two rotor refiner discs are rotated in opposite directions. The present invention can be applied also in such refiners. During use, lignocellulosic material such as wood chips or prepared wood, e.g., pulp, will be fed by means of a feeding mechanism, such as a screw feeder, not shown, through the feeding channel 14. The material will pass through the hole 32 in the stator refiner disc 30* and enter an area 19. The area 19 is essentially defined by the open area between the rotor 30 and the stator refiner disc 30* and this area can be quite small during operation. The lignocellulosic material flowing into the area 19 will be incident on the center plate 17 on the rotor refiner disc 30. The center plate 17 acts to steer the lignocellulosic material out towards the refiner segments on the rotor and/or stator refiner disc.

In order to provide a more detailed description of a rotor-stator arrangement in which the invention may be used reference is made to FIG.2. FIG. 2 illustrates a cross-sectional side view of a rotor - stator arrangement housed in a housing 31 in a refiner as e.g., described above. Shown is a rotor refiner disc 30, that is arranged to rotate around a rotation shaft and a stator refiner disc 30*. The rotor refiner disc 30 is provided, on the surface facing the stator refiner disc 30*, with an active surface 1. The stator refiner disc 30* may also be provided, on the surface facing the rotor refiner disc 30, with an active surface 1. The active surface 1 can be provided to one or more refiner segments 2 as described above. Such refiner segments 2 provided on the rotor refiner disc 30 and the stator refiner disc 30* respectively may or may not be equally designed. The refiner disc according to the invention may be either one or both of the rotor and stator refiner discs 30, 30* or one or both of two rotor refiner discs in the case of two rotating discs. The rotor and stator refiner discs may in certain versions of a refiner be referred to as segment holders since one of the purposes of the refiner discs are to carry refiner segments. Also illustrated in FIG. 2 is an inlet 32 for the lignocellulosic material subject to refining. The inlet 32 is arranged in a central area of the stator refiner disc 30*, however, a central location of the inlet 32 is not necessary as discussed above. Arranged in a center area of the rotor refiner disc 30, opposing the inlet 32, is a center plate 17. The purpose of the center plate 17, which was described above with reference to FIG. 1, is to distribute material that falls in from the inlet 32 towards the outer sections of the rotor refiner disc 30. That is, the center plate 17 acts to distribute the material towards the active surface 1 arranged on the rotor refiner disc 30. In examples comprising two rotor refiner discs which are rotating in opposite directions, inlets for feeding of material may be arranged differently as commonly known within this art. A general refiner that can utilize the invention has now been described above in relation to Figures 1 and 2. FIG.3 provides a schematic illustration of a refiner segment 2 according to one embodiment of the invention. The refiner segment 2 is to be provided to a refiner disc 30. This can be both a rotor refiner disc 30 and a stator refiner disc 30* but will only be referred to as refiner disc 30 hereafter. The refiner segment 2 consists in this particular example of a sector of a circle with a removed middle part. There are however other possible geometries of refiner segments, which will be discussed further below. The refiner segment 2 is to be attached to a refiner disc 30. A refiner segment 2 may be provided in the shape of a sector of a circle, optionally with a removed central area for leaving room for a center plate 17 or an inlet 32 as described above. A refiner segment 2 may also be provided in the shape of another part of a circle. A refiner disc 30 may thus be provided with a number of refiner segments 2 whereby it will either be completely covered by refiner segments 2 or partially covered. In case the refiner segment 2 form part of a rotor refiner disc 30, the center area of the rotor refiner disc may comprise a center plate 17 as described above.

FIG.3 illustrates a refiner segment 2 having an inner periphery 18a, an outer periphery 18b, a first side edge 21a and a second side edge 21b. The inner periphery 18a is the periphery of the refiner segment 2 that is intended to be closest to a center, C, of the refiner disc 30 when the refiner segment 2 has been attached thereto. The refiner segment 2 comprises on an upper surface la, i.e. a surface which will be facing a material flow, a pattern of bars 10 and grooves 20 which will be a part of the active surface 1 of the refiner disc 30 when the refiner segment 2 is attached to the refiner disc 30.

FIG. 4 is a simplified view of the refiner segment 2 in FIG.3 when attached to a refiner disc 30 of a stator ora rotor, having a center C. The radial direction is illustrated by means of an arrow denoted R. The radial direction extends from the center C of the refiner disc 30 toward the periphery of the refiner disc 30, passing on its way through the inner 18a and outer 18b peripheries of the refiner segment 2.

In a refiner in which a refiner disc according to the invention can be used wood chips is refined into fiber or pulp. Large particles are refined into small particles. The pattern of bars and grooves on the active surface 1 of the refiner disc 30 should suitably provide a volumetric decrease towards the outer circumference. A more coarse pattern can be provided in the center of the refiner disc and a more dense pattern in the periphery. The configuration, size, spacing and directions of bars in the pattern should be adapted for achieving this. As seamless design as possible is suitable both for fiber quality and uniformity and for wear of the refiner segments.

Figure 5a shows schematically an active surface 1 of a refiner disc 30 according to one embodiment of the invention. According to the invention a refiner disc 30 for use in a refiner 100 for refining of lignocellulosic material is provided. Refiner segments 2 for use in a refiner disc 30 are also provided. The active surface 1 as shown in Figure 5a can be provided on a number of refiner segments 2 as shown in Figure 3. The refiner segments 2 are provided on the refiner disc 30 such that a combined active surface 1 as shown in Figure 5a is provided to the refiner disc 30. The active surface 1 will be facing another refiner disc when used in the refiner and the material to be refined will hereby flow over the active surface 1 between the two refiner discs. The active surface 1 comprises a pattern of bars 10 and grooves 20 disposed in a number of pattern areas 41, wherein said pattern areas 41 are positioned side by side with each other to cover at least a part of the active surface 1. A groove 20 is formed between two adjacent bars 10. The active surface 1 is delimited by an inner circumference 118a and an outer circumference 118b. Inside the inner circumference 118a of the active pattern 1 there may be provided other structures on the refiner disc 30 for transporting and/or refining material. There may also be provided openings for receiving the material as described above in relation to Figures 1 and 2. The pattern areas 41 are in this embodiment of the invention only provided radially outside a circular pattern border 119 which is provided on the active surface 1 in between the inner circumference 118a and the outer circumference 118b. The circular pattern border 119 is an imaginary border and is only shown in part by a dotted line in Figure 5a. Another type of inlet bars 110 are provided in the area between the inner circumference 118a and the circular pattern border 119. The inlet bars 110 are provided mainly for transporting and distributing the material from a material inlet towards the pattern areas 41. In some refiner discs there may also be provided an outer blanked part outside the outer circumference 118b of the active surface 1. A section, A, of the active surface 1 is enlarged and shown in Figure 5b (corresponding to the refiner segment 2 as already shown in Figure 3). In Figure 5b only one pattern area 41 is shown completely. Each of said pattern areas 41 has a length, I, extending between a first end 43a and a second end 43b of the pattern area 41 and a width, w, extending between two side edges 45a, 45b of the pattern area 41. The two side edges 45a, 45b both extend between the first and second ends 43a, 43b of the pattern area 41. The second end 43b of each pattern area 41 is provided at the outer circumference 118b of the active surface 1 and the first end 43a of each pattern area 41 is provided closer to a centre, C, of the refiner disc 30 than the second end 43b is. A distance between the two side edges 45a, 45b is smallest in the first end 43a of the pattern area 41 and is increasing towards the second end 43b of the pattern area 41. The pattern area 41 is delimited in its second end 43b by a part, s, of the outer circumference 118b of the active surface 1, which part, s, is reaching between the two side edges 45a, 45b of the pattern area 41. In some embodiments of the invention this part, s, has a length corresponding to an arc length of a circular sector having a central angle being between 1°-15°, or between 4°-12°, in a circle with the outer circumference 118b. Accordingly, if the central angle of the circular sector is 1° there will be room for 360 pattern areas 41 in the active surface 1 and if the central angle of the circular sector is 15° there will be room for 24 pattern areas 41 in the active surface 1. Hereby, a width, w, of the pattern areas 41 in their second end 43b will be adapted such that between 24-360 pattern areas 41 can be provided side by side with their second ends 43b along the outer circumference 118b of the active surface 1.

Furthermore each of said pattern areas 41 is positioned on the active surface 1 such that a centre line, c, of the pattern area 41, which is positioned in a centre of the pattern area 41 and is extending from the first end 43a to the second end 43b of the pattern area 41, is provided at an angle, p, to a radius, R, of the refiner disc 30 passing through a centre position, cp, of the pattern area 41, said angle, p, being between 10°-60° or in some embodiments between 20°-40°. Hereby the pattern area 41 can be said to be tilted from an imaginary radial location where the centre line, c, would be provided along a radius of the refiner disc 30, to a tilted position where the first end 43a of the pattern area 41 has been rotated towards the outer circumference 118b while the second end 43b has been fixed to the outer circumference 118b. The direction of this tilt is coordinated to be opposite to a rotation direction of the refiner disc when used in a refiner for refining material.

At least some of the bars 10 are extending along a direction between the two side edges 45a, 45b of the pattern area 41 in which the bars 10 are provided. Most of the bars do not extend outside the pattern area 41 in which they are provided, i.e. the bars both start and end within the pattern area 41. For example, at least 80 % or at least 90 % of a total number of bars 10 which are provided within one pattern area 41 extend only within said pattern area 41. Hereby each pattern area 41 comprises its own set of bars 10. Hereby, sizes and direction of extensions of bars within the pattern areas 41 can be freely varied within each of the pattern areas 41. Possibly, there could be for example one or two bars 10b which are extending over a pattern area side edge 45a, 45b into a neighbouring pattern area which will be further discussed below.

In the embodiment as illustrated in Figures 5a and 5b all the bars 10 except from the bars which are closest to the second end 43b in the pattern area 41, called end bars 10a, are extending along a direction between the two side edges 45a, 45b of the pattern area 41. The end bars 10a in each pattern area 41 are each shorter than an adjacent bar 10 or end bar 10a in a direction towards the first end 43a of the pattern area 41, whereby these end bars 10a each extends towards the outer circumference 118b of the active surface 1. In the specific embodiment shown in Figures 5a and 5b it can also be seen that one of the bars 10b, which bar 10b is the last bar 10 before the end bars 10a, is reaching over a side edge 45b and into the adjacent pattern area 41 and will there act as the last and shortest end bar 10a. This is not necessary but may be suitable for example for production reasons.

The bars 10 each has a length, a thickness (bw) and a height, wherein the height is extending in a perpendicular direction from the active surface 1. The lengths of those bars 10 which are extending along a direction between the two side edges 45a, 45b of the pattern area 41, i.e. all the bars except the end bars 10a, can in some embodiments be such that they are reaching almost all the way between the two side edges 45a, 45b of the pattern area 41. The direction of extension of the bars 10 may not be along the shortest way between the two side edges 45a, 45b, however the length of at least 75% of the bars 10 in a pattern area 41 can in some embodiments be at least 75% of the width, w, of the pattern area 41 where each respective bar is positioned. In some embodiments of the invention at least 90% of the bars 10 which are extending along a direction between the two side edges 45a, 45b of the pattern area 41 have a length which is at least 75% of the width, w, of the pattern area 41 where each respective bar is positioned. In the embodiment of the invention as shown in Figures 5a-5c, but not necessarily, a thickness, bw, of the bars 10 within each pattern area 41 will decrease towards the outer circumference 118b of the active surface 1. This can be seen in Figure 5c. Hereby, in some embodiments the bars 10 will be thinner and thinner the closer they are to the outer circumference 118b. A decreasing thickness of the bars may be suitable because a more dense pattern can then be provided closer to the outer circumference 118b where the material has been refined into smaller parts. However, in another embodiment of the invention all the bars 10 or at least some of the bars 10 may have the same thickness.

Furthermore, in the embodiment as shown in Figures 5a-5c, but not necessarily, a distance, gw, between adjacent bars 10 in the same pattern area 41 is decreasing towards the outer circumference 118b of the active surface 1. This is illustrated in Figure 5c where the distance gw has been marked. This may also be suitable for providing a more dense pattern of bars and grooves towards the outer circumference 118b. However, the distance between adjacent bars 10 may also be the same throughout the pattern area. By adopting a thickness of bars and a distance between adjacent bars a more dense pattern can be provided towards the outer circumference of the active surface whereby a suitable volumetric decrease can be provided.

Furthermore, in the embodiment as shown in Figures 5a-5c, but not necessarily an angle, b, between a direction of length extension of each bar 10 in a pattern area 41 and a radius, R, of the refiner disc 30 passing through a middle point of this bar, is decreasing towards the outer circumference 118b of the active surface 1. Decreasing towards the outer circumference 118b can mean that the angle, b, is decreasing in average towards the outer circumference 118b, whereby it is not necessary that the angle, b, is changed between each of the bars 10. This is illustrated in Figures 5a and 5c and can be suitable in order to counteract an increasing acceleration of the material caused by the centrifugal force closer to the outer circumference. This may be suitable for a uniform distribution of material though the refiner However, the direction of length extension of the bars 10 may also be the same for all bars.

Furthermore, in the embodiment as shown in Figures 5a-5c, but not necessarily, in a first part of the pattern area 41 starting from the first end 43a and extending towards the second end 43b of the pattern area 41 the bars 10 are not extending all the way between the first and second side edges 45a, 45b but are leaving an open wedge-shaped area 47 without bars between adjacent pattern areas 41. This is illustrated in Figure 5c. Hereby the feeding of material will be improved and there is less risk that material is getting stuck between bars. This may be suitable for a uniform distribution of material though the refiner.

In Figure 3 (and in Figures 5b and 5c) one embodiment of a refiner segment 2 corresponding to the active surface 1 as shown in Figure 5a is shown. This refiner segment 2 is in the form of a sector from a circle with an opening in the middle as described above. A number of such refiner segments 2 are combined onto the refiner disc 30 to form the active surface 1 as shown in Figure 5a. However, the refiner segments can also have other shapes such as for example shapes shown in Figures 7b and 7c where each refiner segment is a part of a circle with an open centre where the pattern areas 41 are kept intact such that a refiner segment comprises only complete pattern areas 41 and no parts of pattern areas as for the refiner segment 2 shown in Figure 3.

Figure 6 shows schematically an active surface 1' according to another embodiment of the invention. Most of the details are however the same as for the embodiment shown in Figures 5a-5c and will not be described in detail again. A difference is that in this embodiment dams 11 are provided to the active surface 1', whereby each dam 11 extends between two adjacent bars 10. Dams 11 may be provided substantially orthogonally directed with regard to the bars 10 but may also be provided with an inclination to the bars 10. Each dam 11 connects two adjacent bars 10. Dams are provided for lifting the material up from the grooves 20 at regular intervals for improving the refining process. In Figures 7a-7c three different shapes of refiner segments 102; 102'; 102” are shown corresponding to the active surface 1' of Figure 6. Details of the dams 11 are marked in Figure 7a.

In some embodiments of the invention a number of dams 11, such as at least four dams 11 are positioned such that they together form a continuous dam provided along an imaginary smooth curve. In the embodiment as shown in Figure 6 and Figures 7a-7c each pattern area 41' comprises one continuous dam 11a which is provided along one of the side edges 45b. In this embodiment eighth adjacent bars 10 are linked by a continuous dam 11a, however the number of connected bars 10 can of course vary. Such a continuous dam 11a is suitable compared to separate dams for example in production of the refiner segments. Furthermore, a continuous dam can strengthen the bars and a distribution of load over the refiner may be improved. in some embodiments of the invention and as shown in Figures 6 and 7a-7c, each pattern area 41' can also comprise a continuous last dam lib comprising for example at least four dams 11 which are connecting at least five end bars 10a of this pattern area 41'. The end bars 10a are the bars positioned closest to the second end 43b of the pattern area 41a as described above. The continuous last dam lib of a number of pattern areas 41' can be connected by a connecting dam lib' as shown in Figure 7a, whereby a combined continuous last dam 11c is provided substantially along the outer circumference 118b of the active surface 1; 1'. Substantially can mean that a distance for the dams 11 from the outer circumference 118b can differ somewhat as shown in for example Figure 7a. The combined continuous last dam 11c can be seen in Figure 6 to be provided all the way around the outer circumference 118b of the active surface 1'. A combined continuous last dam 11c may be suitable in some embodiments of the invention, for example because it may provide a more robust and durable construction, and a production of the active surface can be facilitated.

Different types of refiner segments 102; 102'; 102'' corresponding to the active surface 1' of Figure 6 are shown in Figures 7a-c. A number of such refiner segments 102; 102'; 102'' are combined onto a refiner disc to provide an active surface 1' as shown in Figure 6. The refiner segment 102 of Figure 7a is in the form of a sector of a circle with a central opening. In such a form of a refiner segment 102 there may only be room for one or a few complete pattern areas 41' together with parts of pattern areas 41'. If the pattern areas 41' instead are kept intact the refiner segments 102'; 102'' can instead be of another form as shown in Figures 7b and 7c. In the refiner segment 102' of Figure 7b four complete pattern areas 41' are provided in each refiner segment 102' and in the refiner segment 102'' of Figure 7c twelve complete pattern areas 41' are provided.

Other arrangements of dams 11 can be provided to the active surface 1; 1' than the one shown in relation to Figures 6 and 7.