TECHNICAL FIELD
[0001] The present invention refers to a spare part for disc refiners used in the production
of paper.
[0002] In particular, the present invention refers to a spare part consisting of, respectively,
a stator and/or a rotor used in a low consistency disc refiner for the preparation
of pulp and paper stock, meaning that it has a dry fibre residue between 2% and 6%.
The pulp enters them from one end and exits from other side, passing through a rotating
body equipped with blades or an alternation of solids and voids (blades, holes, etc.,
derived from mechanical processing and made on one face or both) and a shell which
has fixed counter-acting blades. Such alternation of solids and voids (bars and grooves)
alternation is conventionally defined as "pattern".
[0003] The present invention has applications in applied mechanics in the field of paper
making and more specifically in the low consistency refining.
BACKGROUND ART
[0004] The refining process represents the only phase of the entire paper making process
in which the fibres are physically modified. It consists of a mechanical action in
which the fibres are processed through two or more consumable bladed fillings (rotors
or stators).
[0005] The fibrous pulp, which arrives at the refiner in the form of a low consistency aqueous
blend (meaning that it generally has a dry fibre residue between 2% and 6%), must
pass through the existing spaces between two (or more) opposing spare parts, respectively
comprising a rotor and a stator. In this context, the stator is defined as the specific
spare part with a fixed, static position inside the refiner, while the rotor is defined
as the specific spare part with a mobile position, which when rotating generates a
centrifugal effect for the refining the fibrous pulp.
[0006] The stator and the rotor in a low consistency disc refiner both comprise substantially
discoid metallic elements which each have a blade refining surface with an alternation
of blades (bars) and grooves, all of which have the same height (blades) and depth
(grooves).
[0007] The rotor, being the part which generates the motion, is normally driven around its
own axis of rotation in such a way that the blades of the rotor perform a rotary movement
in front of the blades of the stator with the interposition of an appropriate air
gap of constant height on all of the opposing surfaces of the discs.
[0008] In this passage between the blades of the rotor and the stator, the fibres are subject
to high levels of compression, friction and cutting, which determine major (and unique)
modifications to their physical structure.
[0009] The refining action causes modifications to the fibres of a physical nature which
can appear more or less intense in measure depending on the conditions adopted for
the treatment. Such modifications may be briefly summarized as:
- a) Swelling and hydration;
- b) Increases in plasticity and flexibility;
- c) External fibrillation;
- d) Internal fibrillation;
- e) Cutting and shortening of the fibres;
- f) Formation of fine particles.
[0010] Modern refiners for processing low consistency fibrous pulp (meaning that it generally
has a dry fibre residue between 2% and 6%) may be classified in 2 principle classes:
conical and disc.
[0011] The rotor and the stator have on one side a "pattern", alternately consisting of
blades (or bars) and crevices (or grooves).
[0012] The width, the length and the inclination of the bars (or blades) and the width and
depth of the empty spaces (or grooves) constitute the configuration of the spare parts
upon which the performance of the refiner depends.
[0013] On conical refiners, the principal characteristic is the angle of the cone.
[0014] The first conical refiners had a narrow angle: they are in fact assembled with a
cone which forms an approximately 10° angle with respect to the axis of rotation,
with spare parts which have quite large bars and for this reason they are considered
strong action cutting refiners.
[0015] Despite this, if used with spare parts with thinner bars, they give optimal results
with all types of fibres.
[0016] The difficulty of the substitution of spare parts has resulted in the substitution
of these refiners with those which are more functional having a medium angle, described
below.
[0017] Another type of conical refiner is the so called large angle refiner, the structure
of which is similar to that with a narrow angle but is assembled with spare parts
with an approximate 30° angle with respect to the axis of rotation.
[0018] The most recent versions and those which are more widely used for low consistency
pulps (meaning a pulp with a dry residue between 2% and 6%) are medium angle refiners
which are characterized by cones which form an approximate 20° angle with the axis
of rotation and, above all, mechanics which permit easy access to the zone of the
fillings therefore reducing maintenance times.
[0019] The principal parts which constitute a conical refiner are:
- 1. a shell with a pulp entry and exit;
- 2. a conical rotor;
- 3. a conical stator;
- 4. a regulation mechanism of the rotor.
[0020] The conical spare parts are used to limit axial forces.
[0021] In fact, the effective forces in play during this type of refining action are divided
into one which is axial (parallel) and one which is perpendicular to the refining
surface.
[0022] In terms of disc refiners, the principle of the latter is similar to that which governs
the conical refiners.
[0023] The pulp which has to be refined in this case is fed centrally to the area between
the discs and, due to the centrifugal force produced by the rotation of the rotor
disc, the pulp tends to move toward the periphery, undergoing the rubbing action between
the bars of the stator discs (fixed) and the bars of the rotor discs (mobile).
[0024] Given their high peripheral speed these machines usually guarantee optimal production.
[0025] Taking into account the disc fillings, this type of refiner is distinguished for
its very compact structure.
[0026] However, the loss of energy for pumping power (no load) is higher in comparison with
other machines.
[0027] Normally, it seeks to limit this loss by using shallow grooves.
[0028] Disc refiners have three basic layouts depending on the type of spare part used:
- refiners with a fixed disc and a rotating disc;
- refiners with two rotating discs and two fixed discs;
- multi-disc refiners (with more than two rotor-stator pairs).
[0029] Disc refiners can be further divided depending on the direction of the flow of pulp
inside the refiners themselves.
[0030] In terms of the quality of the refining, it is recognized that a substantial difference
exists between a refining action with discoid spare parts and refining with conical
ones.
[0031] In fact, due to the type of flow found between the rotor and the stator, and also
due to the vortices and the centrifugal forces generated, not all of the fibres treated
in the disc refiner can be refined; some can, in fact, follow the cavities of the
plate from the entry to the exit.
[0032] In fact, it has been demonstrated that, in some cases, a considerable number of fibres
are not refined in the first passage through the disc refiner.
[0033] As a consequence, the refining efficiency and the energy efficiency are relatively
low.
[0034] In a disc refiner, therefore, it is probable that the fibres which come into contact
with the blades tend to be over-refined to compensate for those which have not been
refined in a way which achieves the desired pulp freeness (°SR
- Shopper Riegler).
[0035] This causes an excessive formation of fines, a weakening of the refined fibres and
energy inefficiency applied to the fibre.
[0036] This all happens on a much smaller scale in the conical spare part, because the hydrodynamic
forces in play tend to push the fibres from the rotor towards the stator, creating
a sort of thrust and successive slippage of the pulp which avoids the immediate outflow
from the spare parts of the latter, therefore retaining the majority of the pulp.
[0037] In fact, the centrifugal force and the flows of the vortices on the inside of the
conical refiner create and facilitate the passage of the fibres from the grooves toward
the bars.
[0038] This creates, therefore, a type of spiral movement around the piece, as opposed to
what happens with the discs, given that the pulp is rapidly pumped toward the exterior.
[0039] The conical refiner, therefore, permits an improvement in processing, a more complete
and uniform treatment of the fibres and an improvement in energy efficiency which
is also due to the fact that the fibres are in contact with the bar for a longer time.
[0040] In the refining process itself the fibres are not refined individually but in flakes.
[0041] In the range of fibrous pulp with a consistency between 2% and 6%, where the low
consistency refining is located, the fibres are not free to move independently.
[0042] Inside the fibrous suspension, a non-homogenous structure composed of fibres is created
which, being close to one another, interact between themselves and generate flakes;
such flakes form and break up continually under the effect of the different intensities
of the cutting forces which exist in the grooves and in the refining zone.
[0043] The size and the thickness of the flakes (1-5 mm) are much larger compared to the
distance which is found between the bars of the stator and the rotor in the refining
phase (usually even less than a few tenths of a millimetre.)
[0044] For this reason, the probability that the flakes in this form can be driven between
the edges of the blades of the rotor and the stator is not very high. To promote the
effects of the refining (external fibrillation, delamination of the internal structure
of the wall, cutting of the fibres, etc.) the operative energy is transferred from
the refiner to the pulp in the following three modes:
- in the moment in which the flake is caught between the edges of the two bars, of the
stator and of the rotor, and the fibres are subject to cutting actions;
- when the bars are overlapped and part of the flake is found between the edge of the
tooth of the rotor and the surface of the stator and then between the two surfaces;
in this phase the elastic flakes of the fibre are compressed between the blades with
a dynamic filtration of the water from the fibres;
- with the continuous fibre-fibre friction action, inside the flakes, in the flow of
the pulp which passes through the cavities.
[0045] During the design stage of the rotors and stators of the refiners, the dimensions
of the bars and grooves (pattern) and the angle of the same pattern itself determine
the "cutting edge length" [L].
[0046] This length is measured in metres or kilometres.
[0047] The cutting edge length L represents, therefore, the total length of the "contact"
between the rotor and stator blades at each turn of the rotor and is expressed as
follows:

where:
DR = radial increment of the teeth (m);
nB = number of blades for each radial increment (number of teeth/sector x number of
sectors);
ni = number of interfaces (for 4 discs, ni = 2);
a = average angle between teeth and the radius of the tip of the same tooth.
[0048] Refining processes involve the use of considerable amounts of energy. In effect,
refining accounts for 25-30% of the total requirement of electric energy in paper
making and is therefore an important factor.
[0049] The energy consumed during the refining process is therefore a major factor influencing
the results of the refining.
[0050] With the machines in use today, it is not possible to transmit all of the energy
which is produced to the refining of the pulp, and a part of the energy is dissipated
in the form of friction and heating of the fibrous suspension.
[0051] In order to determine the efficiency of the refining process with sufficient precision,
it is important to know the real no-load power of the refiner used.
[0052] The power required to rotate freely, which is subtracted from the current consumption
in the refining phase, is the sum of the electric losses of the motor, of the mechanical
losses, due to friction in the motor and in the refiner, and of the hydraulic or circulating
power, which is the quantity of energy absorbed by the hydraulic action due to the
effect of turbulence or pumping.
[0053] The no-load power depends mainly on the diameter and rotary speed of the rotor part,
but it can also be significantly affected by the configuration of the bars and grooves
(i.e. by the pattern).
[0054] Factors like flow, consistency of the pulp and air gap (meaning the existing distance
between the stator disc and rotor disc) have a relatively minor importance.
[0055] The effective power applied, therefore, which determines the changes of the properties
of the pulp, is constituted by the power consumption in the refining phase from which
the no-load power must be subtracted.
[0056] For these reasons it is important to know the no-load power consumed by a refiner
with its spare parts, and, moreover, it is important to take into account the effective
wear of the spare parts.
[0057] No-load power can be determined through empirical measurements or calculated according
to theoretical formulas.
[0058] The factor to be noted, however, is that for each piece of machinery with a spare
part, the no-load power NL (no-load) can vary considerably in time, which means that
it has a high value when the spare parts are new and a lower value when they are worn
down.
[0059] Given that it is quite complex to obtain accurate measurements, it is often easier
to trust in calculations of values through universally recognized formulas, such as
the following:
- the no-load power NL is expressed in kW;
- K is a constant which varies between conical and discoid refiners;
- D is the diameter of the part expressed in meters;
- N is the number of repetitions per second.
[0060] This formula shows how the diameter of the disc is a decisive variable in the determination
of the no-load power consumption.
[0061] In practice, however, the experimental formula generally used for the determination
of the dissipated no-load power is the following:

where:
- NL is expressed in HP;
- the constant K is indicated as 3.083 x 10-13;
- D is the diameter of the part expressed in inches;
- N is the number of repetitions per minute.
[0062] Document
WO 2007/085703 describes a refiner comprising a stator and a rotor that comprise a planar portion
and a conical portion after the planar portion, which in turn comprise refining surfaces
provided with blade bars and blade grooves there between, and the planar portions
of the refining surfaces of the stator and the rotor comprising at least two refining
zones in the direction of the radius of the planar portion.
[0063] The refiner described in this document represents a typical example of an high consistency
pulp refiner, meaning that the pulp has a dry residue which is not lower than 22%,
in which the pulp is fed through a worm screw feeder. The discs of the high density
pulp refiners typically have blades and grooves which consist of an inclination (taper)
which forms a funnel entry between the stator and the rotor in order to direct the
high consistency pulp between the blades and the grooves of the stator and rotor.
[0064] On the other hand, the patterns of the stator and rotor disc in low consistency refiners
(dry residue between 2% and 6%) are always parallel to each other in order to improve
the refining of the cellulose and the distance between the rotor and the stator is
therefore constant on all the surfaces of the opposing discs.
[0065] The patent documents
DE 10203752 C1,
EP 1749922 A1,
DE 2535979 A1 and
WO 2007/048321 also describe high consistency refiners, as shown by the typical worm screw feeder
illustrated in the respective drawings attached to those documents. Consequently,
in these cases the patterns of the rotor and stator are also not parallel on all the
surfaces of the disc and present infeeds to improve the high consistency pulp feed.
[0066] None of these documents addresses the problem of supplying a spare part which increases
the cutting edge length and enhances the efficiency of the refining procedure, or
to supply a spare part, which, for the same cutting edge length, enables the use of
discs with smaller diameters with respect to those traditionally used, which would
allow one to achieve consistent economies in terms of the energy consumed by the refiner.
DESCRIPTION OF THE INVENTION
[0067] The present invention provides new spare parts for disc refiners for the refining
of low consistency fibre pulp, meaning that it has a dry residue between 2% and 6%,
composed of at least one rotor and at least one stator which, thanks to the special
configuration of the blade surface, and without any modification to the existing structure
of the refiner, simultaneously permits the following:
- improved refining;
- substantial energy savings
[0068] This is achieved through a spare part (stator/rotor) for disc refiners for the refining
of low consistency fibre pulp, meaning that it has a dry residue between 2% and 6%,
having the characteristics described in the main claim.
[0069] The dependent claims outline particularly advantageous embodiments of the spare parts
described above.
[0070] According to a particularly advantageous embodiment of the invention, and in strong
contrast with the configurations present in spare parts for disc refiners of the known
type - in which the respective blade surfaces of the rotor and of the stator are situated
on planes perpendicular to the axis of rotation of the rotor - the spare parts for
disc refiners according to the present invention have blade surfaces which have a
preset angle with respect to the planes which are perpendicular to the axis of rotation
of the rotor.
[0071] In a further particularly advantageous embodiment of the invention, and also in stark
contrast with the present configurations of the spare parts for disc refiners of the
known type, the spare parts for disc refiners according to the present invention have
blade surfaces with a generally curvilinear or irregular profile, though always parallel
to each other.
[0072] The embodiments described above allow one to obtain, alternatively or synergistically:
- a considerable increase in the cutting edge length L, that increases the efficiency
of the refining action of the disc refiner and, at the same time, allows one to increase
the production of a given refiner as though it were equipped with discs with larger
diameters - yet without requiring the substitution of the entire refiner with one
of a larger size; or
- the possibility to use, at the same cutting edge length, discs with smaller diameters
for the same refiner, which implies considerable energy savings; or
- to improve the refining action of any disc refiner for the refinement of low consistency
fibre pulp, meaning that it has a dry residue between 2% and 6%, given that the configuration
according to the invention makes it more difficult for the pulp to exit and, holding
it inside the fillings (rotor/stator) for a longer time, the latter is treated in
an improved and more uniform way.
[0073] In any case, as previously mentioned, it is necessary to emphasise how the spare
parts are configured to be inserted into existing disc refiners for the refining of
low consistency fibre pulp (meaning that it has a dry residue between 2% and 6%) according
to the present invention, without any further conversion or special maintenance of
the refiner other than the substitution of the worn discs. This is because the coupling
of spare parts according to the present invention have the same thickness as the fillings
they are designed to substitute.
DESCRIPTION OF THE DRAWINGS
[0074] Further features and advantages of the invention will become apparent from the following
description of some embodiments of the invention with reference to the annexed drawings,
given purely by way of a non-limiting example, in which:
- Figure 1 shows a Cartesian diagram which shows the advantages of using a refining
disc equipped with inclined pattern surfaces according to the present invention;
- Figures 2a, 2b, 2c, 2d and 2e show side view cross sections of five embodiments of
the spare parts, in particular the refining discs, having inclined, rectilinear profiles
(Figure 2e) and curves or mixtilinear profiles (Figure 2a, 2b, 2c, 2d) according to
the present invention;
- Figure 2f shows a side cross section of a known refining disc, therefore at a perpendicular
profile to the axis of the disc itself; and
- Figures 3a and 3b are perspective drawings showing a disc in the form of a rotor and
one in the form of a stator according to the present invention, with inclined rectilinear
profiles, which are usable as spare parts for a disc refiner for the refining of paper;
- Figure 4 is a cross section of a stator and a rotor according to the invention facing
each other, where it is clear that the respective blades (or patterns) are parallel
to each other.
DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0075] In figure 1, a Cartesian diagram with nonessential errors shows how, at an equivalent
cutting edge length, it would be possible to obtain a smaller disc diameter acting
on the angle of inclination (x) of the pattern with respect to a pattern which is
flat and perpendicular to the axis of the disc itself.
[0076] Using the known mathematical formula,

and keeping as a constant the cutting edge length, it is possible to derive the angle
x of inclination of the

pattern corresponding to a given cutting edge length, which corresponds to a predetermined
diameter.
[0077] By decreasing the diameter of the disc, at the same cutting edge length, it is possible
to determine a consistent conservation in terms of dissipated electric energy in no-load
conditions. Clearly, a greater inclination of the pattern corresponds to a smaller
disc diameter, but one must take into account a constraint in terms of the machine
stroke, which obviously cannot exceed the dimensions provided in the refiner.
[0078] It should be noted that by using the same formula, and keeping the diameter of the
disc constant in this case, it is also possible to understand how it would be possible
to obtain greater cutting edge lengths, with respect to traditional disc types, with
a spare part with an inclined pattern according to this invention.
[0079] This opens up very interesting opportunities from both a manufacturing and commercial
point of view. In fact, with the same disc diameters, a given refiner equipped with
spare parts according to the present invention could supply better performance in
terms of both the quantity of and the quality of refined product, thereby obviating
the need to substitute the refiner with one of a larger size when it is necessary
to increase production.
[0080] The Figures 2a to 2e show some examples of practical embodiments of the spare parts
for disc refiners which are obtainable according to the present invention.
[0081] It is worth comparing these figures with Figure 2f, which shows in a traditional
disc type, with a 26-inch (66.04cm) diameter for example. In particular:
- the disc illustrated in Figure 2a has, for example, a 24-inch (60.96 cm) diameter
and a rectilinear pattern with a uniform inclination angle (as do the discs shown
in figures 3a and 3b);
- the disc shown in figure 2d has, for example, a 22-inch (55.88 cm) diameter and a
uniformly curved pattern profile;
- the disc illustrated in figure 2c has, for example, a 22-inch (55.88 cm) diameter
and a pattern profile composed of differentially inclined rectilinear segments;
- the disc shown in figure 2b has, for example, a 20-inch (50.80 cm) diameter and a
pattern profile comprising both curved and rectilinear elements; and
- the disc shown in figure 2a has, for example, a 20-inch (50.80 cm) diameter and a
substantially saw-toothed pattern profile.
[0082] Clearly, the profile shapes and the diameters of the discs indicated above are example
embodiments of the invention which can be applied to any typology of refining discs
for the low consistency fibre pulp, meaning that it has a dry residue between 2% and
6%; the diameter and shape of the discs can be freely adapted to particular design
needs to take into account the quantity and quality of the product to be refined.
[0083] The spare parts according to the present invention can be manufactured using various
methods and technologies in accordance with design requirements.
[0084] The invention as described above refers to its preferred embodiments.
[0085] Naturally, while the principle of the invention remains the same, the details of
construction and the embodiments may widely vary with respect to what has been described
and illustrated purely by way of the example, without departing from the scope of
the present invention.
1. A spare part for disc refiners provided with either two, or four or a plurality of
refining discs, in particular a stator and/or rotor used in a disc refiner for refining
a low consistency paper pulp, i.e. a paper pulp with a dry fibre residue between 2%
and 6% and more specifically for the preparation of stock, where the stator and/or
rotor each comprise a disc-shaped metallic element with a refining blade surface having
alternating bars or blades and grooves, where the rotor is designed to be driven and
rotated around its own axis of rotation which passes through the centre of the disc-shaped
element so that the rotor bars or blades perform a rotary movement in front of the
stator bars or blades with a suitable gap in between, said gap having a constant height
over the whole surface of the opposed discs, wherein said blade surfaces or pattern
have regular or irregular inclined profiles, though always parallel to each other,
with a pre-set inclination angle greater than 0° in respect of a plane perpendicular
to the rotor axis of rotation.
2. The spare part according to claim 1, in which the blade surfaces or pattern seen in
a side cross section have a rectilinear and/or curvilinear profile.
3. The spare part according to claim 2, in which the side cross section profile is uniformly
rectilinear and has a constant angle.
4. The spare part according to claim 2, in which the side cross section profile comprises
a curved line.
5. The spare part according to claim 2, in which the side cross section profile comprises
rectilinear segments angled differently.
6. The spare part according to claim 2, in which the side cross section profile comprises
an assembly of rectilinear and curved elements.
7. The spare part according to claim 2, in which the side cross section profile substantially
has a saw-tooth shape.
8. The spare part according to claim 1, characterised in that it is designed to be mounted inside a disc refiner for low consistency pulp paper
refining, i.e. with a dry fibre residue between 2% and 6%, and more specifically for
the preparation of stock preparation, in the same space as that occupied by the traditional
disc that the spare part substitutes and without requiring any further modification
to the refiner.