Blade segment of disc refiner

A blade segment of a disc refiner for refining fibrous material has an inner circumference and an outer circumference as well as a first side edge and a second side edge which connect the inner circumference and the outer circumference. The side edges are curved, with one convex and the other concave. The segment has a refining surface with blade bars and grooves which define a pumping direction. The side edges of the blade segment curve in the vicinity of the inner circumference in the pumping direction, and in the vicinity of the outer circumference in a non-pumping direction.

CROSS REFERENCES TO RELATED APPLICATIONS

This application claims priority on Finnish application FI 20144124, filed May 26, 2014, the disclosure of which is incorporated by reference herein.

Not applicable.

BACKGROUND OF THE INVENTION

The invention relates to a blade segment of a disc refiner intended for refining lignocellulose material used in the production of fibrous material such as paper and board, with the blade segment comprising an inner circumference and an outer circumference as well as a first side edge and a second side edge which combine the inner circumference and the outer circumference.

A disc refiner consists of two or more opposite refining elements, at least one of which refining elements is rotatable. The rotating refining element can be referred to as a rotor, and the non-rotating, or stationary, refining element can be referred to as a stator. Between the refining elements is a refining gap, where the material to be refined is ground against the refining surfaces. The refining surface of the refining elements comprises blade bars and blade grooves. The refining surface is constituted by attaching one or more blade elements to the frame structure of the refining element, with the blade element having a refining surface which comprises blade bars and blade grooves. In stationary refining elements, said blade element can also be attached directly to the frame structure of the refiner. The refining surface of the refining element can consist of one uniform blade element, in which case a single individual annular planar blade element can constitute an entire refining surface of a refining element. Conventionally, the refining surface of the refining element of a disc refiner is, however, constituted of several planar blade segments placed side by side, in which case each blade segment on its own constitutes only some portion of the complete annular refining surface of the refining element, and the blade segments placed side by side together constitute the complete annular refining surface of the refining element.

A typical blade segment comprises an inner circumference of the blade segment directed in the direction of the inner circumference of the refining element and an outer circumference of the blade segment directed in the direction of the outer circumference of the refining element, and a first side edge of the blade segment and a second side edge of the blade segment connecting the inner circumference and the outer circumference of the blade segment, where the first side edge and the second side edge are straight, i.e. in the radial direction of the blade segment so that the blade segment resembles the shape of a sector of a ring. It is typical for said blade segments that the side edges of the blade segments constitute a point of discontinuity at the interface or at the point of contact of adjacent blade segments, which can result for example in disturbances both in the actual refining and in the flow of the material that is to be refined and that has been refined at the interfaces of adjacent blade segments and in their vicinity. Moreover, in order to ensure the structural strength of the blade bars, there is a need to make reinforcements when moving from one blade segment to another. There are also prior art blade segments where the side edges are not straight, i.e. not in the radial direction of the blade segment, but instead in the vicinity of the inner circumference the side edge is in the radial direction and then turns at one point away from the radial direction against the intended direction of rotation of the blade segment. Such a construction requires precise tolerances at the interfaces of the blade segments so that unrefined pulp would not escape through the refiner.

SUMMARY OF THE INVENTION

The object of the invention is to provide a novel blade segment of a disc refiner.

The blade segment of a disc refiner according to the invention is characterized in that the first side edge and the second side edge of the blade segment are curved so that one side edge is concave and the other side edge is convex.

According to an embodiment, the first side edge and the second side edge of the blade segment are curved side edges which comprise a single radius of curvature.

According to an embodiment, the blade segment comprises a refining surface, which comprises first refining surface portions that refine the material to be refined and second refining surface portions that run between the first refining surface portions and that carry the material to be refined, and the center line of the first refining surface portions and of the second refining surface portions is curved.

According to an embodiment, the magnitude of the radius of curvature and the direction of curvature of the center line of the first side edge and second side edge of the blade segment and of the second refining surface portion are essentially the same.

According to an embodiment, the first refining surface portion comprises a first blade bar running from the direction of the inner circumference of the blade segment to the direction of the outer circumference and the second refining surface portion is a first blade groove running from the direction of the inner circumference of the blade segment to the direction of the outer circumference and the upper surface of the first blade bar comprises second blade bars and between them second blade grooves.

According to an embodiment, the first refining surface portion comprises blade bars and between them blade grooves, and the second refining surface portion is a blade groove running from the direction of the inner circumference of the blade segment to the direction of the outer circumference.

According to an embodiment, at least one side edge of the blade segment comprises an area free from blade bars to constitute at least some portion of the second refining surface portion that is constituted between two adjacent blade segments.

According to an embodiment, the volume of at least one blade groove included in the first refining surface portion is adapted to change in the run direction of the blade groove.

According to an embodiment, the width and/or depth of the blade groove included in the first refining surface portion is adapted to change in the run direction of the blade groove.

According to an embodiment, the width and/or depth of the first blade groove constituting the second refining surface portion is adapted to change in the run direction of the blade groove.

According to an embodiment, the first side edge and second side edge of the blade segment curve in the vicinity of the inner circumference to the pulp-carrying direction, i.e. to the pumping direction, and in the vicinity of the outer circumference to the pulp-holding direction, i.e. to the non-pumping direction.

According to an embodiment, in the area on the side of the outer circumference of the blade segment, the portion of the non-pumping curve is 0 to 50%, preferably approximately 20 to 40% and most preferably over approximately 30% of the radius of the blade segment.

According to an embodiment, the blade segment is a blade segment of a rotatable refining element.

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

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1schematically shows a blade segment1of a disc refiner, i.e. a planar blade segment1seen in the direction of the refining surface2of the blade segment1. The blade segment1shown inFIG. 1is thus a planar blade segment that can be adapted to be a part of the stationary refining element of the disc refiner, i.e. a part of the stator, whereby the refining surface2of the blade segment1constitutes a portion of the refining surface of the stationary refining element, or it can be adapted to be a part of the rotating refining element of the disc refiner, i.e. a part of the rotor, whereby the refining surface2of the blade segment1constitutes a portion of the refining surface of the rotatable refining element. The blade segment1can have securing openings13, through which securing bolts can be inserted in order to fasten the blade segment1to the refining element. The blade segment can also be secured to the refining element so that the securing points do not extend through the blade segment, but there is bolt securing only at the back part of the blade segment, whereby the refining surface of the blade segment, i.e. the blade surface, remains intact.

The blade segment1comprises an inner circumference3or inner edge3or feed edge3directed to the direction of the inner circumference of the refining element of the refiner, and from the direction of the inner circumference3or inner edge3or feed edge3the material to be refined is fed into the refining gap, i.e. blade gap, located between the opposite refining elements of the refiner. The blade segment1further comprises an outer circumference4or outer edge4or outlet edge4directed to the direction of the outer circumference of the refining element of the refiner, and the material to be refined travels in the blade gap of the refiner during refining to the direction of the outer circumference4or outer edge4or outlet edge4and the material that has been refined exits the blade gap of the refiner through it. The inner circumference3and outer circumference4of the blade segment1constitute a portion of the inner circumference and outer circumference of a complete refining surface of a refining element. The blade segment further comprises a first side edge5and a second side edge6connecting the inner circumference3and outer circumference4of the blade segment1.

The refining surface2of the blade segment1comprises first refining surface portions7and between them second refining surface portions8, with the first refining surface portions7constituting refining surface portions that refine the material to be refined and with the second refining surface portions constituting refining surface portions that run between the first refining surface portions and that carry the material to be refined.

In the embodiment ofFIG. 1, the first refining surface portion7of the blade segment1comprises a first blade bar9and second blade bars11constituted at its upper surface and between them second blade grooves12, with the second refining surface portions8being constituted by the first blade grooves10between the first blade bars9, and the first blade grooves10constitute the feed grooves10of the blade segment1, which feed grooves10carry the material to be refined from the direction of the inner circumference3of the blade segment1to the direction of the outer circumference4. The width of the second blade bars11can be for example approximately 1.2 to 1.4 millimeters and the width of the second blade grooves12can be for example approximately 1.8 to 2.0 millimeters. The depth of the second blade grooves12can be for example approximately 5.0 to 7.0 millimeters. The width of the first blade grooves10on the inner circumference3of the blade segment1can be for example approximately 15 mm and can become narrower towards the outer circumference4for example so that the width of the first blade grooves10on the outer circumference4of the blade segment1is for example approximately 5 mm. The depth of the first blade grooves10, i.e. the distance from the upper surface of the second blade bars11to the bottom of the first blade bars10is greater than the depth of the second blade grooves12. The depth of the first blade grooves10can become smaller, i.e. the first blade grooves10can become shallower towards the outer circumference4of the blade segment1, but in this case, too, the depth of the first blade grooves10on the outer circumference4of the blade segment1is greater than the depth of the second blade grooves12. The second blade bars11and between them the second blade grooves12constitute dense blading, i.e. so-called microblading, on the refining surface2of the blade segment1, whereby the shearing length of the refining surface2of the blade segment1becomes considerably large. Said second blade bars11and second blade grooves12can be straight or curved in their respective run direction. The width and height of the second blade bars11and correspondingly the width and depth of the second blade grooves12can be constant or they can vary in the run direction of said blade bars11and blade grooves12.

In the embodiment ofFIG. 1, the first blade bars9and the first blade grooves10are curved, i.e. they run from the direction of the inner circumference3of the blade segment1to the direction of the outer circumference4of the blade segment1in a curved pattern, or in other words the center lines of the first blade bars9and the first blade grooves10are curved, i.e. they run from the direction of the inner circumference3of the blade segment1to the direction of the outer circumference4of the blade segment1in a curved pattern. The center line referred to inFIG. 1is only illustrated at one first blade groove10on the side of the first side edge5and marked with reference marking CL.

The shape of the first blade groove10is curved so that in the vicinity of the inner circumference3of the blade segment1it is pumping, i.e. it enhances the travel of the pulp to be refined from the direction of the inner circumference3of the blade segment1towards the outer circumference4, when the blade segment1constitutes a portion of the refining surface of the rotatable refining element and when the direction of rotation corresponds to the direction indicated by the arrow denoted with reference marking RD inFIG. 1. When moving towards the outer circumference4of the blade segment1, the blade groove10curves back so that in the vicinity of the outer circumference4of the blade segment1the blade groove10is non-pumping, i.e. it slows down the travel of the pulp to be refined towards the outer circumference4of the blade segment1. The pumping and non-pumping effect caused in the material to be refined by the rotation of the rotating refining element and by the direction of the first blade bars10on the refining surface is further illustrated inFIG. 4, which schematically shows the outlines of the blade segment1and the first blade grooves10running in the blade segment1. On the side of the inner circumference3of the blade segment1, the rotation of the rotating refining element and the direction of the first blade grooves10induce that the material to be refined is subject to a force effect the resultant of which is described by the arrow denoted with the reference marking P and which is directed towards the outer circumference4of the blade segment1. This can be seen for example by comparing the direction of the arrow P to the direction of the radius R of the blade segment1. On the side of the inner circumference3of the blade segment1, the material to be refined is thus subject to a force effect which promotes the travel of the material to be refined, i.e. it pumps the material to be refined towards the outer circumference4of the blade segment1. On the side of the outer circumference4of the blade segment1, as a result of the direction of the first blade grooves10the material to be refined is subject to a force effect the resultant of which is described by the arrow denoted with the reference marking N and which is directed towards the inner circumference3of the blade segment1. This can again be seen for example by comparing the direction of the arrow N to the direction of the radius R of the blade segment1. On the side of the outer circumference4of the blade segment1, the material to be refined is thus subject to a force effect which slows down or holds the travel of the material to be refined towards the outer circumference4of the blade segment1, in other words it has a non-pumping effect on the material to be refined.

In other words, when the blade segment1according toFIG. 1is intended to constitute a portion of the refining surface of the rotatable refining element and the direction of rotation of said refining element corresponds to the direction of the arrow denoted with the reference marking RD inFIG. 1, the direction of the feed groove10on the side of the inner circumference3of the blade segment1intensifies the travel of the material to be refined towards the direction of the outer circumference4of the blade segment1, and correspondingly on the side of the outer circumference4of the blade segment1the direction of the feed groove10slows down the travel of the material to be refined towards the direction of the outer circumference4of the blade segment1.

FIG. 1shows and alsoFIGS. 2 and 3show the portion of the refining surface of the rotatable refining element, i.e. of the refining surface of the rotor, constituting the blade segment1, but a similar piece can also be used in the stationary refining element, i.e. in the stator.

When the direction of rotation of the rotatable refining element of the refiner corresponds to the direction of the arrow denoted with the reference marking RD inFIG. 1, the first side edge5of the blade segment1thus corresponds to the side edge of the blade segment adapted to the direction of rotation of the rotatable refining element and the second side edge6of the blade segment1thus corresponds to the side edge of the blade segment adapted to the direction opposite to the direction of rotation of the rotatable refining element. When seen in the direction of rotation RD, the first side edge5of the blade segment1thus constitutes the front edge of the blade segment1and the second side edge6of the blade segment1constitutes the back edge of the blade segment1.

In the blade segment1according toFIG. 1, the first side edge5and second side edge6of the blade segment1are curved, in other words the first or front side edge5and second or back side edge6of the blade segment1run in a curved pattern from the inner circumference3of the blade segment1to the outer circumference4so that the first side edge5of the blade segment1has the shape of a concave curve and the second side edge6has the shape of a convex curve, in other words the center point of the radius of curvature of the curves constituted by the side edges5and6is residing in the direction of rotation RD of the rotatable refining element, ie. when rotating counter clockwise as inFIGS. 1-4the center points of the radii of the side edge curves reside on the left side of the corresponding side edges, and, respectively, the bottom points of the side edge curves are thus residing opposite to the rotating direction. Since the center point of the radius of curvature of the curves constituted by both side edges5and6is located in the same direction with respect to the direction of rotation RD of the rotatable refining element, it can be said that the direction of curvature of the curved side edges5,6is the same. Moreover, in order to simplify the structure of the blade segment1, the magnitude or value of the radii of curvature of the side edges5,6is essentially the same. The first side edge5and second side edge6of the blade segment1are curved so that the first side edge5and second side edge6curve in the vicinity of the inner circumference3to the pulp-carrying direction, i.e. to the pumping direction, and in the vicinity of the outer circumference4to the pulp-holding direction, i.e. to the non-pumping direction.

Both the first curved side edge5and second curved side edge6of the blade segment1are composed of only one radius of curvature. The magnitude of the radius of curvature may vary on the basis of the size category of the blade segment1, i.e. on the basis of the distance between the inner circumference3and outer circumference4of the blade segment1, i.e. on the basis of the radius R of the blade segment1.FIG. 1schematically shows the radius R of the blade segment1beside the first side edge5of the blade segment1. The essential matter is that when the blade segment1constitutes a portion of the refining surface of the rotatable refining element, the side edges5and6of the blade segment1curve in the vicinity of the inner circumference3to the pulp-carrying direction, i.e. to the pumping direction, and in the vicinity of the outer circumference4to the non-pumping direction, i.e. to the pulp-holding direction. In the area on the side of the outer circumference4, the portion of the non-pumping curve is 0 to 50%, preferably approximately 20 to 40% and most preferably over approximately 30% of the radius R of the blade segment1. When the first side edge5and second side edge6of the blade segment1are curved in this manner, the blade segments1can be aligned easily with respect to each other upon the installation of the blade segments1to the refining elements of the refiner. Another advantage of the structure is that the blade segments can be manufactured with larger tolerances without the possibility that unrefined pulp escapes from between the blade segments.

The curved side edges5and6of the blade segment1are especially advantageous when the second refining surface portions8, i.e. the first blade grooves10, i.e. the feed grooves10included in the blade segment1are made to be curved, as presented inFIG. 1and in the related description above, so that the radius and direction of curvature of the side edges5and6of the blade segment1and the radius and direction of curvature of the first blade grooves10of the blade segment1are the same. In this case, the first refining surface portions7, i.e. the first blade bars9, and the second refining surface portions8, i.e. the first blade grooves10running from the direction of the inner circumference3of the blade segment1to the direction of the outer circumference4in a curved manner can be arranged easily in the blade segment1without a need for the first blade bar9or the first blade groove10to continue from the direction of the inner circumference3to the direction of the outer circumference4over the interface of adjacent blade segments1from one blade segment to another in order to accomplish a desired refining surface blade pattern which comprises curved refining surface portions. Said curved first refining surface portions7, i.e. the first blade bars9, and the second refining surface portions8, i.e. the first blade grooves10can hence run from the direction of the inner circumference3of the blade segment1to the direction of the outer circumference4essentially as intact uniform portions without any points of discontinuity that might cause disturbance both in the actual refining and in the flow of the material that is to be refined and that has been refined. Another advantage is that the microgrooving constituted by the second blade bars11and the second blade grooves12on the refining surface2is directed to the pumping direction, in other words to the same direction as the curvature of the first side edge5on the side of the inner circumference3of the blade segment1. When going to the outer circumference4, the first side edge5curves away from the direction of the second blade grooves12, i.e. to the holding direction.

FIG. 2schematically shows a second blade segment1of a disc refiner seen in the direction of the refining surface2of the blade segment1. The blade segment1comprises an inner circumference3and an outer circumference4of the blade segment1and a curved first side edge5and a curved second side edge6combining the inner circumference3and the outer circumference4. The refining surface2of the blade segment1comprises first refining surface portions7and between them second refining surface portions8, with the first refining surface portions7constituting refining surface portions that refine the material to be refined and with the second refining surface portions8constituting refining surface portions that run between the first refining surface portions and that carry the material to be refined. The center lines of the refining surface portions7,8are curved from the direction of the inner circumference3of the blade segment1to the direction of the outer circumference4of the blade segment1as shown inFIG. 1.

InFIG. 2, the first refining surface portion7comprises a first blade bar9and second blade bars11constituted at its upper surface and between them second blade grooves12, with the second refining surface portions8being constituted by the first blade grooves10between the first blade bars9, and the first blade grooves10constitute the feed grooves10of the blade segment1, which feed grooves10carry the material to be refined from the direction of the inner circumference3of the blade segment1to the direction of the outer circumference4. The width of the second blade bars11can be for example approximately 3.5 to 4.0 millimeters and the width of the second blade grooves12can be for example approximately 4.0 to 4.5 millimeters. The depth of the second blade grooves12can be for example approximately 5.0 to 11.0 millimeters. The second blade bars11and the second blade grooves12can be straight or curved in their respective run direction, as shown inFIG. 2. The width and height of the second blade bars11and correspondingly the width and depth of the second blade grooves12can be constant or they can vary in the run direction of said blade bars11and blade grooves12within the above-mentioned range of variation.

FIG. 3schematically shows a third blade segment1of a disc refiner seen in the direction of the refining surface2of the blade segment1. The blade segment1comprises an inner circumference3and an outer circumference4of the blade segment1and a curved first side edge5and a curved second side edge6combining the inner circumference3and the outer circumference4. The refining surface2of the blade segment1comprises first refining surface portions7and between them second refining surface portions8, with the first refining surface portions7constituting refining surface portions that refine the material to be refined and with the second refining surface portions8constituting refining surface portions that run between the first refining surface portions and that carry the material to be refined. The center lines of the refining surface portions7,8are curved from the direction of the inner circumference3of the blade segment1to the direction of the outer circumference4of the blade segment1as shown inFIG. 1.

InFIG. 3, the first refining surface portion7comprises a first blade bar9and second blade bars11constituted at its upper surface and between them second blade grooves12, with the second refining surface portions8being constituted by the first blade grooves10between the first blade bars9, and the first blade grooves10constitute the feed grooves10of the blade segment1, which feed grooves10carry the material to be refined from the direction of the inner circumference3of the blade segment1to the direction of the outer circumference4. On the side of the inner circumference3of the blade segment1or in its vicinity, the microblading constituted by the second blade bars11and the second blade grooves12has been arranged to be sparser than on the side of the outer circumference4of the blade segment1or in its vicinity. On the side of the inner circumference3of the blade segment1, the width of the second blade bars11can be for example approximately 2.3 millimeters, and the width of the second blade grooves12can be for example approximately 7.0 to 9.0 millimeters, and the depth of the second blade grooves12can be for example approximately 8.0 to 18.0 millimeters. On the side of the outer circumference4of the blade segment1, the width of the second blade bars11can be for example approximately 2.2 millimeters, and the width of the second blade grooves12can be for example approximately 2.8 to 3.6 millimeters, and the depth of the blade grooves10can be for example approximately 4.0 to 8.0 millimeters. The blade bars11and the blade grooves12can be straight or curved in their respective run direction, and the width and depth of the blade grooves12can be constant or they can vary in the run direction of said blade grooves12for example within the above-mentioned range of variation.

In the blade segments shown inFIGS. 1, 2 and 3, an area free from blade bars9,11has been arranged beside the first side edge5, whereby said area is intended to constitute at least a portion of the portion of the refining surface2of the blade segment1intended as a feed groove10. The portion arranged beside the first side edge5of the blade segment1free from blade bars9,11is preferably dimensioned so that said portion can constitute a whole feed groove10, whereby when placing the first side edge5of the blade segment1with a butt joint with the second side edge6of the blade segment1located adjacent to it, the formation of an interface between adjacent blade segments is avoided in the area of the feed groove10, since this might disturb the flow of the material to be refined in the feed groove10.

For a person having ordinary skill in the art, it is obvious that as technology makes further progress, the basic idea of the invention can be implemented in many different ways. The invention and its embodiments are therefore not restricted to the examples described above, but they may vary within the appended claims.