Mechanical pulping refiner plate having curved refining bars with jagged leading sidewalls and method for designing plates

A refiner plate for a mechanical refiner of lignocellulosic material including: a refining surface on a substrate, wherein the refining surface is adapted to face a refining surface of an opposing refiner plate; wherein the refining surface includes bars and grooves between the bars and the bars have at least a radially outer section in which the bars include a leading sidewall having an irregular surface in the outer section.

BACKGROUND OF THE INVENTION

This invention relates to disc refiners for lignocellulosic materials (referred to as “fibrous material”), and more specifically to disc refiners used for producing mechanical pulp, thermomechanical pulp and a variety of chemi-thermomechanical pulps (collectively referred to as mechanical pulps and mechanical pulping process).

In the mechanical pulping process, raw fibrous material, typically wood or other lignocellulosic material, is fed through the middle of one of a refiners discs and propelled outwards by a strong centrifugal force created by the rotation of one or both discs. The disc(s) typically operate at rotational speeds of 1200 to 2300 revolutions per minute (RPM). While the fibrous material is retained between the discs, energy is transferred to the fibrous material from refiner plates attached to the discs. The energy transferred to the fibrous material separates individual fibers in the fibrous material from a network of fibers in the material. The separation of individual fibers constitutes refining of the fibrous material into a pulp product that may be used to form paper, fiberboard and other fiber based products.

The refiner plates each have surfaces with patterns of bars and grooves. The surfaces are opposite to each other when a pair of refiner plates are mounted in a refiner. The bars and grooves on the opposing refiner plate surfaces generate repeated compression forces that act on the fibrous material flowing between the plates. The compression action against the fibrous material results in the separation of lignocellulosic fibers from the feed material and provides a certain amount of development or fibrillation of the fibrous material. The fiber separation and development is necessary to transform the raw fibrous material to a suitable pulp for fiber board, paper or other fiber based products. The refining action imparted by the bars and grooves may also generate some cutting of the fibers, which is usually a less desirable result of the mechanical pulping process.

In the mechanical pulping refining process, a large amount of friction occurs that reduces the energy efficiency of the refining process. It has been calculated that the refining efficiency of the energy applied in mechanical pulping is in the order of 5 percent (%) to 15%.

Efforts to develop refiner plates which work at higher energy efficiencies typically involve reducing the operating gap between opposing discs. Conventional techniques for lowering energy consumption in mechanical refiners typically rely on design features of refining patterns on the front face of refiner plate that speed up the feed of material across the refining zone. These techniques often result in reducing the thickness of the fibrous pad in the gap between the opposing plates. When energy is applied to a thinner fiber pad, the compression rate becomes greater for a given energy input and results in a more efficient energy input.

A drawback to reducing the thickness of the fiber pad are that the operating gaps between the refiner plate bars is reduced. Reducing the gap between the opposing refiner plate bars often results in an increase in fiber cutting, a loss in pulp strength properties due to the cut fibers, and a reduction in the operating life of the refiner plates due to the excessive wear of plates. A narrow gap, e.g., clearance between bars on opposing plates, may achieve a higher compression ratio and higher efficiency but suffers a reduced operational life. There is a link between operating refining gap and refiner plate lifetime, the latter being exponentially reduced with reducing gap. Reducing the operating refining gaps results in an increase in the wear rate of the refiner plates and shorter plate life.

There is a long felt need for refiner plates that provide high energy efficiencies in transferring the mechanical energy from the rotation of the plates into the fibrous feed material, having relatively long operational plate lives and that minimize the cutting of fibers in the feed material.

BRIEF DESCRIPTION OF THE INVENTION

A novel refiner plate has been developed to improve energy efficiency, while maintaining a large operating gap between refiner plates on opposing discs. Advantages of the refiner include high energy efficiency, maintaining high fiber quality, and long operating life of the plates.

In one embodiment, the refiner plate is an assembly of rotor plate segments having an outer refining zone with refining bars that have at least a radially outward refining section with a curved longitudinal shape to form large holdback angle at the outer plate periphery of at least thirty (30) degrees and preferably angles of 45, 60 and 70 degrees. The leading sidewalls of the refining bars have surfaces that are serrated, jagged or otherwise irregular. The bars with irregular surfaces on the sidewalls and large holdback angles increase the retention time of feed material in the outer refining zone and thereby increase the refining of the fibrous material by the outer zone.

A refining plate has been developed with a refining surface to face the refining surface of an opposing plate in a mechanical refiner. The refining surface includes a plurality of bars upstanding from the substrate of the plate. The bars extend radially outwardly towards an outer periphery of the plate, and have a serrated, jagged or other irregular surfaces on the leading sidewall (face) of the bars. The bars may be straight or curved, such as with an exponential or in an involute arc. The bars form an aggressive holdback angle at the outer radial regions of the bars. The refining plate may be a rotor plate and arranged in a refiner opposite to a stator plate or another rotor plate.

A refiner plate has been developed for a mechanical refiner of lignocellulosic material comprising: a refining surface on a substrate, wherein the refining surface is adapted to face a refining surface of an opposing refiner plate, and the refining surface includes bars and grooves between the bars, wherein the bars have at least a radially outer section and the bars each include a leading sidewall having an irregular surface in the outer section.

A refiner plate has been developed for a mechanical refiner of lignocellulosic materials, the plate having a refining surface comprising: a plurality of bars upstanding from a substrate of the surface, wherein the bars extend outwardly towards an outer periphery of the plate, and the bars include an irregular leading sidewall on at least a portion of the bars.

A method has been developed for mechanically refining lignocellulosic material in a refiner having opposing refiner plates, the method comprising: introducing the material to an inlet in one of the opposing refiner plates or array of plate segments; rotating at least one of the plates with respect to the other plate, wherein the material moves radially outward through a gap between the plates due to centrifugal forces created by the rotation; as the material moves through the gap, passing the material over bars in a refining section of a first one the plates and through grooves between the bars, wherein the bars have at least a radially outer section in which the bars include a leading sidewall having an irregular surface in the outer sections; inhibiting the movement of the fibrous material through the a groove by the interaction of the fibrous material and the irregular surface on the leading sidewall of the bar adjacent the groove, and discharging the material from the gap at a periphery of the refiner plates.

DETAILED DESCRIPTION OF THE INVENTION

The mechanical refining process applies cyclical compressions to a fibrous pad of fibrous material moving between opposing refining plates. The compressions result from the rotation of one plate relative to the other and, particularly, to the crossing of bars in the opposing plates. The compressions cause fibers in the material to separate from a network fibers in the material. The plates are typically mounted on discs in a refiner, wherein at least one of the discs rotates one of the refiner plates. The energy efficiency of the refining process may be improved by increasing the compression ratio of the fibrous pad and increasing the period during which fibers in the pad are subjected to the compressions. The increased compression ratios are achieved with the refiner plate designs disclosed herein without necessarily reducing the gap between the plates or reducing the gap only to the extent now done in conventional high energy efficiency refiners.

A relatively wide gap, e.g., 1.0 mm (millimeters) to 2.0 mm, between the rotor and stator plates in a refiner (as compared to the gap in high energy efficiency refiner e.g., 0.3 mm to 0.7 mm) must be achieved through a thicker pulp pad formed between the plates. A high compression ratio is achieved with a thick pulp pad using a significantly coarser bar and groove pattern on a refiner plate as compared to the bar and groove patterns on conventional rotor plates used in similar high energy efficiency applications.

A coarse bar and groove pattern for a refining zone of a refiner plate has been developed having a lower density of bars as compared to the typical bar and groove patterns used in conventional high energy refiner plates. The fewer bars in a coarse pattern have fewer the compression cycles applied by the bars of the rotor as they pass across the bars on the stator, as compared to the compression cycles that occur with conventional plates having a higher density of bars. With respect to the coarse density of bars, the energy being transferred by the fewer compression cycles tends to increase the intensity of each compression cycle and increase the energy efficiency of each cycle to transfer energy from the plate to the fibrous material.

Refiner plates have been developed that have a relatively short, in a radial direction, effective refining surface, a coarse bar and groove pattern, aggressive holdback angles and other features to provide for a long retention of fibrous material in the effective refining zone of the plate. These features, which can be applied singularly or collectively, yield a higher energy concentration in the refining zone by reducing the cycle rate of bar crossings (resulting in fewer compression events during a plate rotation), and extending the retention time for the raw fibrous material in the refining zone. These features allow a larger operating gap between the plates and, thus, provide for high compression rates applied to a thick fiber mat between plates having a generous gap between them. In one embodiment, the high intensity of compression events may be achieved by lowering the number of bar crossing events and maximizing the amount of fiber present at each crossing.

The rotor refiner plate designs disclosed herein achieve high fiber retention and high compression to provide high energy efficiencies, while preserving fiber length and improving wear life of the refiner plates. Various stator plate designs used with the rotor plates disclosed herein may achieve the desired results of high compression ratio, enhanced energy efficiency, extended fiber retention between the plates, long fiber lengths.

FIGS. 1 and 2shown a side view and a front view, respectively, of a rotor plate segment10having an inlet section12and an outer section14. An array of plate segments is arranged in a annulus on a refiner disc to form a circular refining plate. The rotor plate is mounted on a rotatable disc and the stator plate is mounted on a stationary disc. The rotor plate faces the stationary stator plate with a refining gap between the plates. The rotor and stator plate may each be formed of plate segments. The segments of the stator plate may have similar bar and groove features as the rotor plate segment, or may have other bar and groove features. The rotational direction (see arrow15) for the rotor plate is counter-clockwise. Alternatively, the rotor plate may face an opposing rotor plate (rotating in a clockwise direction) with a refining gap between the plates.

The inlet section12feeds the incoming fibrous material to the outer refining section14, with minimal frictional energy and minimal work of the feed material. The inlet may have bars that form a coarse and open pattern, such as shown in U.S. Pat. No. 6,402,071, entitled “Refiner Plates With Injector Inlet” and issued to Luc Gingras.

A slippage area16is between the inlet12and outer refining areas14and may include triangular posts. The slippage area is an annular area that allows feed material discharged from the inlet section12to be properly distributed, e.g., uniformly distributed, before entering the outer refining section14. The triangular posts in the slippage area promote uniform distribution of feed material entering the annular refining section14.

The refining section14of the refiner plate segment is where most of the energy is applied to the feed material and most of the refining action occurs. The refining section14may extend over a radial distance of between 100 millimeters (mm) to 200 mm, or four to eight inches. The outer section may be comprised of curved bars20which have an increasing holding angle as they move radially outward to the outer edge of the plate. The holding angle may change gradually as shown inFIG. 2or may be increased by providing a stepped change in the bar angle by forming each bar as a series of straight bars sections having different angles.

Grooves21are between the bars and are defined by the trailing sidewall30and leading sidewall28of adjacent bars20. The leading sidewall faces the rotational direction (arrow15) of the rotor plate. InFIG. 2, the leading sidewall28is on the left-hand side of each bar. The grooves provide passages through which feed material, steam and other materials move radially in the gap between the plates.

The height of the bars, e.g., the distance from the substrate surface22of the plate to the upper ridge of the bars20may be initially tapered and transition24to a uniform height for most of the length of the bars. The initial taper of the bars facilitates the feeding of material to the outer section14.

The angle of the bars20at the inlet of the refining section14may vary from a 20 degree feeding angle to a 20 degree holding angle. These angles are the angle of the bars with respect to a radial line. The feeding and holdback inlet angles are angles that a bar20forms at the inlet to the bar. A feeding angle is a positive angle from a radial line in the same direction as the rotation as the rotor plate, e.g., counterclockwise15. A holdback angle is a positive angle from a radial line in the opposite direction of rotation of the rotor plate. In the plate segment10shown inFIG. 2, the inlet angle is neutral, i.e., approximately zero degrees with respect to a radial line.

At the outer periphery25of the plate, the outlet angle of the bars20is preferably a holding angle of between 45 degrees and 80 degrees, and more preferably between 50 and 70 degrees. A holding angle is an angle with respect to a radial in the direction of the rotor plate rotation15. The holding angle of the outlet to the bars inhibits the flow of fibrous material between the plates and thereby increases the retention time of the material in the refining section14.

The angle of the bars gradually increases from the inlet to the outlet in an angular direction aligned with the rotation of the rotor plate. In the rotor plate embodiment shown inFIG. 1, the angle is neutral (zero) at the inlet and gradually increases along the bar in a direction towards the outer periphery25of the plate. The rate of change of the bar angle may be small at radially inward portions of the bar and gradually increase at radially outward portions of the bar. The bar angles from the radially inward edge of the refining section14to the radially outer edge may increase continuously in an curved arc, exponential arc or involute arc, or discontinuously such as in staggered rows of short bars. Further, the bars may be curved, a series of short straight sections (where each section has a greater angle that the prior inner section) or other lateral bar shape that achieves the desired increase in the angle of the bars. By increasing the angle of the bars to very wide bar angles at the outlet, the bars contribute to high retention of the feed material in the plate and increased retention time of the feed material in the refining section14.

Retention of fibrous feed material in the refining section14is aided by the jagged leading sidewalls28of bars. The trailing sidewalls30of the bars may be smooth, jagged or have some other irregular surface pattern. Optionally, the width of the bars may vary due to the variable gap between the jagged surface on the leading sidewalls28and the smooth surface of the trailing sidewall30.

The jagged pattern applied on the leading sidewalls28of the outlet bars may have irregular surface patterns along the length of the wall such as: zig-zag, sawtooth, a series of semi-circular bumps, sinusoidal, sideways Z-pattern, and other irregular surface shape features. The width of the bar may vary approximately by one fifth to one half, and preferably by one third, due to the irregular surface on the leading sidewall. The irregular surface shape features of the leading sidewalls provides increased longitudinal friction to the feed material moving through the grooves, particularly along the leading sidewall of the bars. The friction caused by the leading sidewall increases the retention period of the fibrous feed material in the refining section and promotes the movement of the feed material over the bars rather than through the grooves.

The smooth surface trailing sidewalls allow for relatively free passage of steam and other liquids through the grooves21which tend to be displaced by the feed material in the grooves and, thus, move along the trailing sidewalls. In some cases, the trailing sidewalls may include surface profiles shaped to cause additional turbulence in the fiber material flowing through the grooves to ensure an increased amount of turbulence in the flow, which can help push fibers towards the leading edges on the opposite side of the grooves. Further, the grooves may include may include surface dams, subsurface dams or steam management system dams, see, e.g.,64inFIG. 10 and 74inFIG. 12, to increase turbulence of the flow through the grooves, retain the fiber flow in the refining zone and reduce the flow of fibers in the lower region of the grooves. Due to centrifugal forces from the rotor disc, fiber and other solid materials tend to move along the leading sidewalls of the grooves. The jagged leading sidewalls slow the flow of fibrous material through the grooves in the refining section.

FIGS. 3 and 4shown a side view and front view, respectively, of a plate segment34having bars20with a jagged leading sidewall36that appears from a top down view of the bar as a series of number sevens (“7”) arranged end-to-end. The corners formed by the series of sevens may be rounded to ease manufacture and molding of the plate segments. The leading sidewall36surface features may extend the entire length of the bar wall surface, or may extend along just a radially outer portion of the bar (as shown inFIG. 2). In addition, the jagged leading sidewall may be may be tapered from the ridge26towards the root (at the plate substrate surface22) of the bars, so that the jagged feature is most prominent at the upper corner edge of the bar where most refining is accomplished and becomes less significant along the depth of the bar, particularly deep in the groove. The grooves provide hydraulic capacity to moving feed material, steam and water through the refining section of the refiner plates.

The jagged features on the leading sidewall28can vary in size and shape. Preferably, the outer protrusions of the jagged corners, e.g., points on a saw-tooth shape and corners in a series of “7” shape, are spaced apart from each other by between 2 mm to 8 mm along the length of the bar sidewall. The protrusions of the jagged sidewall surface features have a depth of preferably between 1.0 mm to 2.5 mm, where the depth extends in to the bar width. The depth of the protrusions may be limited by the width of the bars. A bar20typically has an average width of between 2.0 mm and 6.5 mm. The bar width varies due to the jagged sidewall surface features, particularly the protrusions, on the leading sidewall.

FIGS. 5 and 6show a side view and front view, respectively, of a rotor refiner plate segment40. The outer zone42includes a radially inward section44having a fine inlet for breaking down feed material to produce high quality pulp. The inward section44forms the inlet to the outer zone42of the bars. The inward section of each bar20has a fine groove pattern46in the ridge26of the bar. The fine groove is in addition to the grooves21between adjacent bars.

The inward section44of the outer zone42may be formed by bars having a tapered ridge that gradually increase in height to a transition24and continues radially outward in the outer zone, as shown inFIGS. 2 and 4. Alternatively, the bars in the inward section may each include a fine groove46that effectively doubles the number of bars in the inward section44as compared to the bars radially outward of the inward section. A finer bar pattern in the inward zone22provides lower intensity separation of the raw feed material to better preserve the fiber length and strength properties from the raw material.

The rotor plate40has a refining zone42in which the initial refining work on the feed material is achieved with a finer bar pattern on inward section44, in contrast to the coarse bar pattern in remaining portion45of the refining zone. One use of having an initial fine refining pattern in the inward section is where there is a requirement for high pulp quality. In the inward refining section44, the fine bar pattern results in lower intensity compressions to the fibrous material that the stronger compressions that would occur with the coarse bar pattern in the inward refining section pattern shown inFIG. 2and with the coarse bar pattern of the outer refining section45ofFIG. 6. The lower intensity compressions of the fine bar pattern of section44preserves the properties of the fiber to a greater extent than if high intensity compressions are applied over the entire primary refining zone42.

An alternative exemplary bar and groove pattern for the inward section44is shown in U.S. Pat. No. 5,893,525 (incorporated fully by reference) which shows a series of fine bars which are narrow and greater in number than the bars in a radially outer portion42. Other bar and groove patterns with fine, narrow bars may also be appropriate, depending on the plate design, the material to be refined, and the intended purpose of the plate. Alternatively, the number of bars in the inward refining section44may be coarser and less dense, such as shown in section60ofFIG. 8, than the density of bars in the outer refining zone45.

The transition zone47between the inward refining zone44and outer refining zone45may include cutting bars, a narrow annular gap between separate bar sections in zones44and45, or connecting bars between the zones44,45. The transition zone may include cross-over grooves48in the narrow bars46of the inner refining section. The cross-over grooves allow material flowing through shallow grooves51in the inner refining section44to deeper grooves21in both the inner and outer refining sections44,45. The cross-over grooves also allow the number of bars to be reduced, such as in one-half, in the transition zone47. The cross-over grooves may extend radially outward to a leading or trailing sidewall of an adjacent bar. The cross-over grooves48open through a leading sidewall28in the bars radially inward of the jagged section of the leading sidewall of the bars20. The cross-over grooves48may be arranged on the plate segment in a Z-pattern, such as shown in U.S. Pat. No. 5,383,617, to promote feeding of material into the main grooves21between the bars. As an alternative to cross-over grooves, a downwardly sloping ramp at a radially outer bar end may terminate bars that do not continue into the next refining zone.

In the Z-pattern, the cross-over grooves48are aligned along a line that is not tangent to the refiner plate. This line of alignment for the cross-over grooves shifts48at least once on the plate segment40. While the cross-over grooves form a Z-shape, other arrangements of the cross-over grooves may be used such as aligning the cross-over grooves at a common radial distance, along straight lines in each plate segment and in a “W” shape.

The refiner plate may include a feed material inlet zone49that is radially inward of the refining zone42. The inlet zone49may include straight breaker bars53or curved breaker bars as shown inFIG. 2. Preferably, the inlet zone49(FIG. 6) or12(FIG. 2) forwards the feed material into the refining zone42,14with minimum energy input. There are numerous known variations of bar patterns for the inlet zones12,49. It is a matter of design choice as to which inlet zone variation is most appropriate for a particular plate design. The inlet zone affects the ability of the refiner to break down the feed material, handle steam and distribute feed. The inlet zone directs the fibrous feed material to the refining zones14,44where most of the refining of the feed material is performed.

FIGS. 7 and 8are side and front views, respectively, of a refiner rotor plate segment50having an extended outer zone58with serpentine bars54. The inward feeding56of the bars20feed the fibrous material to the outer refining section58, so that the feed material can be broken down gradually without excessive energy being applied. The inlet to the feeding section56may have bars with feed angles of between 10 and 45 degrees. These feeding angles may remain constant through the feeding section. Alternatively, the angles of the bars may change gradually from a feed forward angle at the inlet to a reverse angle at the outlet edge of the feeding section56. By providing a positive feeding effect on the feed material, the feeding section there is less accumulation of fibrous material in the feeding section56and thus less energy is applied this section. The main energy application should be in zone58. Feeding section56should be a feeding zone with some effect on particle size reduction, but not a large energy input. The selection of the angles and geometry of bars and grooves in the feeding section56is a design choice and can be varied to achieve good feeding of fibrous material to the outer refining section58or other desired refining effects. Preferably, the bars20in the feeding section56continue to the radially outward refining section58. Alternatively, the bars20in the feeding section56may end before the inlet edge of the outer refining section58. To provide a transition from the inward annular section56to the outward annular section58, an annular transition zone may separate the bars from the feeding section56from those of the outward refining section58. The transition zone between the annular sections56,58may include a Z-pattern or chevron (W) pattern, such as is shown inFIGS. 6,12,25and27

The bars of the inner zone60are coarser and less dense than the bars of the sections56,58, which has double the density of bars than in the inner zone60. A coarse bar pattern may assist in feeding material to the bars in the radially outward section(s). However, a coarse inlet may result in a coarse breaking down of the raw material (such as wood chips) and in fiber cutting, which is desirable for certain refining applications.

The bars in the outer refining sections or zone58,42and14of the refiner plate segment may have a variety of geometries to provide various desirable performance features, such as extended feed material retention. Curving the bars along their length in a radial direction increases the hold angle and thereby increases retention time. Applying a jagged or otherwise irregular surface on the leading sidewall of the bars further promotes retention time of feed material, e.g., fibers, in the outer zone and thereby increases the amount of refining performed on the feed material. The jagged leading sidewall surface on the bars may extend the length of the bars in the outer zone or may be limited to a radially outward section, e.g., the outer half of the outer zone.

The inlet zone60of the refiner plate segment50has a large feeding angle to minimize the retention time of feed material in the inlet zone. In addition, the staggered bar inlets62form large operating gaps at the entrance of the inlet zone. The combination of large operating gaps and short retention in the inlet zone, result in a small amount of energy being consumed in the inlet zone and thereby increases the energy efficiency of the plate. The energy savings from the inlet zone may be applied to concentrate the energy applied to the refining area at the radially outer58sections of the plate segment50. While the bars in the inlet zone60need not be curved, they preferably have a significant feed angle to minimize retention in the inlet. However, other bar shapes and angles may be used in the inlet zone60depending on the feed material and the need to break down feed material in the inlet zone.

The inlet zone60of rotor plate segment50has a smaller operating gap as compared to the inlet zones in the other rotor plate segments10,34and40, disclosed herein. The operating gap is the radial distance occupied by the inlet. A narrow gap indicates that the refining zone (outer zone58) begins at a relatively small radius of the plate segment. A narrow gap may achieve material pre-separation and fiber shortening.

The jagged leading sidewall surfaces28of the bars20are applied only in the outer few inches of the plate segment in refining section58. In addition, this outer section58has the bars20with substantial holdback angles, such as greater than an average angle of 20 degrees. The jagged bar surfaces and holdback angles in the outer few inches of the refining zone concentrate fiber pad formation and energy input in the outer section58of the plate segment50.

Most of the refining energy applied by rotor plate50will be applied in the refining section58. The large holdback angle of the bars in section58and the jagged leading sidewall surfaces of the bars retain the fibrous material in section58. The increased retention time allows a greater portion of the refining energy to be applied in section58. In contrast to section58, the strong feeding angles of the bars and smooth sidewall surfaces in section56result in a reduced amount of energy transfer in this section of the plate50. Accordingly, a large portion of the refining work done by plate50is concentrated in the refining section58, even though this section has same number of bars as does section56.

FIGS. 9 and 10show a side view and front view, respectively, of a refiner plate segment60having steam evacuation channels62. These channels tend to be at least as wide as the combined width of a groove and bar. The channels are between and parallel to two bars and may extend the length of the portion of the bars having an irregular leading sidewall. The steam evacuation channels allow steam to vent through the wide channels62and radially outward from the outer periphery25of the plate. The channels may include dams64, e.g., split dams in which a leading region of the dam is lower than a trailing portion of the dam to allow trap fibers in the channel but allow steam to pass through the channel. Examples of split dams are shown in U.S. Pat. No. 6,607,153.

The grooves21separating the bars20may have a combination of surface dams, subsurface dams, or even no dams at all, depending on the overall plate design combination and operational conditions for the refiner plate.

FIGS. 11 and 12show a side view and front view, respectively, of a refiner plate segment70having steam evacuation channels72. The steam evacuation channels allow steam to vent through the wide channels72and radially outward from the outer periphery25of the plate. The channels may include dams74, e.g., split dams. The channels72and grooves21separating the bars20may have a combination of surface dams, subsurface dams, or even no dams at all, depending on the overall plate design combination and operational conditions for the refiner plate.

The outer refining zone76includes the steam channels72, aggressive holdback angles, e.g., 45 degrees, on the bars, and serrated surfaces on the leading sidewalls28of the bars. Arranging the serrated surfaces and aggressive holdback angles towards the outer refining portions of the rotor plate segment70increases retention time of the feed material in the refining zone(s) of the plates and concentrates the energy applied by the plates to the refining process occurring in the outer regions of the refining zone.

The inner refining zone78has a fine refining pattern, similar to the pattern shown in zone44for the rotor plate segment40. The various refining and inlet patterns and features shown on the plate segments disclosed herein may be rearranged and combined to form additional rotor plate designs that incorporate the substance of the plate patterns and features disclosed herein but differ in some respects from the plate segments70,60,50,40,34and10. In other words, the plate segments disclosed herein are exemplary and provide a person of ordinary skill in the art of designing refiner plate segments with sufficient information to design plate segments that incorporate the refining features disclosed herein, such as refining bars with serrated leading sidewalls and aggressive holdback angles, e.g., greater than 45 degrees, in the outer radial sections of the refining zone(s).

By increasing the retention time in the refining zone and concentrating energy to refining, the rotor plates disclosed herein, e.g.,70,60,50,40,34and10, provide high energy efficiency refining without necessarily having to reduce the refining gap between the plates, e.g., rotor and stator plates, to the same extent, e.g., 0.5 millimeters (mm) to 0.7 mm, conventional used in high energy efficiency plates. Using the rotor plate segments disclosed herein, the refining gap, for example, may be between 0.7 mm and 1.0 mm, which is similar to the refining gap used with conventional plates, or may be increased to 1.2 mm to 2.0 mm. Increasing the refining gap tends to increase the operational life of the refiner and stator plates and reduce the occurrences of breakage of the refining patterns on the plates.

FIGS. 13 to 16are each a top down view of the ridge26and particularly the profile of the irregular surface on a leading sidewall of a bar in the outer refining zone of a refiner plate segment. The upper ridge26of each bar20includes a profile of the upper corner of the leading sidewall28and the trailing sidewall30. The leading sidewall has an irregular surface, e.g., serrated feature, that may be most pronounced at the upper corner of the sidewall. The irregular surface features of the leading sidewalls28may be confined to the outer radial portions of the bar, but may extend the entire length of the outermost refining zone or the entire refining zone.

The irregular surface features may have a variety of shapes, including the series of “7”s shown inFIG. 13, the saw tooth feature shown inFIG. 14, the series of concave grooves in the leading sidewall as shown inFIG. 15, a series of teeth, e.g., rectangular teeth, as shown inFIG. 16and any such shape that will increase friction in the fiber flow along the leading edge of the bars. The shape of the irregular features is intended to increase friction applied to fibers moving along the leading sidewall. The shape of the irregular sidewall may depend on the feed material, and plate segment composition, manufacturing and molding considerations.

FIG. 17shows in cross section a bar20having a irregular trailing sidewall300, e.g., a series of “7”s, and an irregular surface, e.g., a series of “7”s, on the leading sidewall28. The irregular surface300of the trailing sidewall is optional and may have a surface shape of any of the irregular surfaces shown herein for the leading sidewall. An irregular surface on the trailing sidewall may assist in pushing fibers moving along in the trailing wall towards the leading sidewall.

FIG. 18shows in front view the same irregular surface feature on the bar leading sidewall as shown inFIG. 18. The irregular surface feature may be more pronounced on the bar sidewall near the bar ridge26where most refining occurs. The irregular surface feature may become progressively less pronounced on bar sidewall in the direction of the plate substrate22. The protrusions76of the irregular surface tend to retard the movement of feed material through the grooves and thereby increase the retention time of feed material in the refining zone(s) of the plates. The protrusions76may be tapered from ridge26to substrate22. Near the substrate22of the plate the protrusions may blend into a smooth lower surface78of the leading sidewall28.

FIG. 19is a schematic diagram of an enlarged view of a bar110on a rotor plate with a groove114between adjacent bars110. The upper portion, e.g., upper one third, of each bar110includes a row of teeth116each having a side face118slanted to push fibers moving over the bars into the next groove114. The side face118of each tooth has a leading edge120that is aligned with the sidewall122of the bar. A trailing edge124of the side face118may be recessed into the bar by, for example, a third of the width of the bar. A rear surface126of each tooth may be substantially perpendicular to the plate. A sloped front surface128may meet the rear surface of the next tooth and assist in pushing fibers up into the gap between the stator and rotor plate.

FIGS. 20 and 21are side views and front views, respectively, of another exemplary rotor plate segment130having an inner fine refining zone132, a middle refining zone134and an outer refining zone136. The fine refining zone includes bars138separated by deep grooves140. Each bar has a shallow groove142that effectively divides each bar into a pair of bars and thereby doubling the number of bars in the fine refining zone. Cross-over channels144at the outer edge of the fine refining zone directs fiber and liquor in the shallow grooves142out through the trailing edge of the bar and into a groove at the inlet to the middle refining zone134. The leading sidewalls146have an irregular surface, such as a series of half-cylinders that are most pronounced at the upper edge of the bars. The bars terminate at the outer edge of the middle zone. The bars148of the outer refining zone136are substantially the same in number as the bars in the middle zone134. The leading sidewall surface of the bars148have a shape of a series of “7” arranged end to end. The irregular surfaces of the sidewalls of the bars in the middle and outer refining zones increases the friction applied to the fibers flowing in the grooves and thereby increases the retention time of the fibers in those zones.

Further, the bars in the inner, middle and outer zones132,134and136are relatively straight on the rotor plate segment130. The angle of the bars increases from zone to zone. For example, the angle of the bars in the inner zone is relatively shallow, e.g., zero degrees to 10 degree holdback angle. The angle of the bars in the middle zone is more aggressive, such as 20 degrees to 40 degrees, and the angle of the bars in the outer zone is most aggressive, such as greater than 45 degrees and may be 60 degrees or 70 degrees.

FIGS. 22 and 23are side views and front views, respectively, of an exemplary stator plate segment80. The refining bar and groove patterns disclosed herein are most applicable to rotor plates but may be applied to stator plates. The stator plate80may have an outer zone82with bars84that are curved, e.g., exponentially or in an involute arc, to increase retention time of feed material in the refining outer zones of the rotor and stator plates. The leading and trailing sidewalls of the stator bars84may have smooth wall surfaces. Jagged sidewalls may not be needed on the bars of the stator plate, because the centrifugal forces acting on the feed material in the grooves86in the stator plate are reduced as compared to those forces on material in the rotor plate. Further, the bars of the stator plate segment may have various patters of feed and holding angles and bar shapes depending on the application of the refiner and the selected rotor plate pattern.

The stator plate segments are arranged in an annular array on a stationary disc of a refiner machine. Similarly, rotor plate segments are arranged in an annular array on a rotating disc of the refiner machine. The arrays of stator plate segments and rotor plate segments are opposite to each and separated by a narrow gap through which fibrous material passes during the refining process. The fibrous material may be fed into the gap by passing through a center inlet in the stator disc and the array of stator plate segments.

FIGS. 24 and 25are side views and front views, respectively, of a second exemplary stator plate segment90. The stator plate segment90may be used in conjunction with the rotor plates40and70. The bars92at an inner refining zone93are split to form a fine refining pattern that is complementary to the fine refining bar patterns44,78shown on the rotor plates40and70. The stator bars92are substantially straight. The grooves between the coarse section96of bars include a series of dams94to increase retention time of the feed material in the refining zone.

FIGS. 26 and 27are side views and front views, respectively, of a third exemplary stator plate segment100. The stator plate segment100may be used in conjunction with the rotor plates40and70. The bars102at an inner refining zone104are split to form a fine refining pattern that is complementary to the fine refining bar patterns44,78shown on the rotor plates40and70. The stator bars102are curved to provide a large holdback angle in the radially outward regions of the stator plate segment. The grooves between the bars102in a section108of coarse bars include a series of dams106to increase the retention time of the feed material in the refining zone. The stator and rotor plate design may operate in holdback or in feeding mode, depending on the required operating gap, fiber retention and refining results. The stator plate100, due to its large feeding (or holding) angle can cause great influence in operation with the rotor plates shown herein with features, such as aggressive holdback angles and jagged leading sidewalls. Accordingly, the stator plate may complement the desired longer retention time in the refining zones in the outer sections of the plates, which is achieved with the rotor plates disclosed herein.