[0001] The invention relates to a method according to the preamble of claim 1 as known from
EP 0 756 615 B1.
[0002] A device and a method for producing an asphalt mix are known from
DE 576 958 C. The device includes a mixer with a single shaft having paddles to force the mix.
The mix is solely consisting of a bituminous liquid and a dust-like filler. For producing
the mix, first, the bituminous liquid is filled into the mixer. For avoiding clumping,
the dust-like filler is then spread slowly over the liquid in a region that extends
along the length of the mixer on a side where the paddles are moving downwards. A
special hopper with a controllable flap is provided to discharge the filler into said
region so that the filler is slow discharged into a downwardly directed flow of liquid.
[0003] Reference is now made to
WO 83/00700 which describes a method and apparatus for the production of asphalt concrete. According
to this previous method, the mix is made from aggregate and bituminous liquid wherein
the aggregate is divided into a coarse fraction, a fine fraction and a filler portion.
First, the coarse fraction and the bituminous liquid are mixed, then the filler fraction
is added, and last, the fine fraction is added. The apparatus for carrying out such
production method is described in detail. The mixing method of
WO 83/00700 has been commonly known as "KGO II" mixing method. The known mixing method is characterized
by force mixing. The filler is discharged at once, and then the mixing is conducted
by the force of mixing paddles.
[0004] Next, reference is made to the above mentioned
EP 0 756 615 B1. In such patent, there is shown and described a test equipment and method for testing
of asphalt specimens, called TOD test. The specimens are heated and the deformation
in the specimens is determined. The deformation over temperature is plotted in a graphic.
The curve of a specimen produced by the KGO II mixing method still shows sharp buckles
and cracks. This shows the tendency of an asphalt to crack. In
EP 0 756 615 B1, a new mixing method is given reducing such tendency to crack. The mixing method
of
EP 0 756 615 B1 - known as KGO III mixing method - is characterized by controlling the flow rate
and time intervals for discharging the filler and the fine fraction. The filler discharge
is such controlled that the filler is powdered over the liquid distributed over the
surface of the coarse fraction. To understand this, one can compare the mixing methods
with a preparation of a pancake dough. If the flour is discharged at once into the
milk, a forced mixing is necessary. Nevertheless, the dough becomes lumpy. If, however,
the flour is powdered over the milk when mixing the dough, lumps are avoided. The
same technique is used in the KGO III mixing method. By such mixing, the bituminous
liquid, the filler and the fine fraction material becomes enclosed in a combined suspension
where the filler, the fine fraction and the coarse fraction are parts of a closed
liquid volume. This condition is testable by the TOD-test. The flow rate and the time
intervals for discharging the filler and the fine fraction are controlled in such
a way that the closed liquid volume is established.
[0005] With the mixing method of
EP 0 756 615 B1, one has changed from a force mixing to a flow mixing. Further details of the theory
and the praxis of such flow mixing are given in "Method and means used in production
of asphalt mix. Theory of suspension, mixing method, method of testing, method of
analyses", dissertation at Lund University by Ohlson, Karl Gunnar, Institutionen för
Trafikteknik, LTH, bulletin 132, available at the Lund University, Box 118, SE-22100
Lund (Sweden) under the code "CODEN LUTVDG/(TVTT-3110)/1-113/(1995)", Lund 1995.
[0006] When trying to conduct the KGO III mixing method in practice, namely in some asphalt
plants, especially such one as given in
WO 83/00700, some problems have been raised. It was particularly difficult to find the optimised
time intervals and flow rates for developing the closed liquid volume.
[0007] Starting from the state of art as given in
EP 0 756 615 B1, the object of the invention is to improve an mixing method according to the preamble
of claim 1 in such way that the time intervals and flow rates can be easier optimised
to develop the closed liquid volume and that the production of an asphalt mix with
still further reduced tendency to crack is producible.
[0008] Such object is achieved by the mixing method having the steps of enclosed claim 1.
[0009] According to the invention, the fine fraction is discharged into a downwardly directed
material flow in the mixer comprising at least two shafts rotating in opposite directions.
[0010] Advantageous embodiments of the invention are given in the dependent claims. A device
for carrying out the invention is given in the further independent claim.
[0011] The invention shall be used in all production by mixing methods where the mix of
coarse fraction and the bitumen are added to the mixer before the filler and the fine
fraction are admixed. In fact the method refers to the Swedish patent no.
506 581 from 1994-04-19, and the corresponding
EP 0 756 615 B1, respectively.
[0012] The invention shows the exact position for discharge of the filler and the fine fraction
to the mixer of the asphalt plant that produces suspension asphalt mixes for road
paving. In suspension asphalt mixes, the bitumen, the filler, and the fine fraction
particles are permanently bound to the surface area of the coarse fraction particles.
Asphalt plants that lack the invention produces sedimentary asphalt mixes which segregate
shown by that the fine fraction material in the paving is more or less diverted from
the coarse fraction. This can be verified, for example, by the TOD test.
[0013] Suspension in asphalt mix is formed from the filler material where the main portion
is smaller than, for example, 0.074 mm. The suspension also includes the fine fraction
of the aggregate that normally is smaller than size, for example, 4 mm. The coarse
fraction consists of particles larger than the particles of the fine fraction. The
suspension is developed on the surface of the coarse fraction aggregates.
[0014] In accordance with
SE patent 506 581 and
EP 0 756 615 B1, respectively, the filler material is spread in the bituminous liquid by the flow
in the mixer, in penetrable thickness over the films of liquid already developed on
the surface area of the coarse fraction. the distribution is obtained through choice
of time intervals between adding the components and through control of the flow rates
when spreading the material over the flow of the coarse fraction in the mixer. The
production by the KGO III (as known from
EP 0 756 615 B1) is called "Flow Mixing".
[0015] When spreading the fine fraction in the bituminous liquid, this shall also be made
by calibration of the intervals and flow rates in the same manner as when spreading
the filler material.
[0016] One reason for the present invention is the discovery of that the filler material
and the fine fraction have different requirements for being mixed by the flow. The
reason for this is that the quantity of fine fraction material is a number of times
larger than the quantity of the filler.
[0017] The invention is to be used in production of asphalt mix where the coarse fraction
and the bitumen liquid are mixed before the addition of the filler and the fine fraction
material as in the
SE patent no. 506 581.
[0018] According to an advantageous embodiment using a mixer with essentially horizontal
rotating mixing shafts having radially extending paddles or the like mixing tools,
the fine fraction material is discharged along the mixers wall that is parallel to
the shaft of the mixer in order to create an excessive pressure in the material in
the mixer, and gravitation force that increases the rate of flow relative to the rate
of rotation of the paddles, which lessens the work of the paddles in the materials
whereby the coatings of the suspension develop the mix into a structure that remains
permanent until the mix is paved.
[0019] According to the invention, the asphalt mixers downwards directed material flow is
loaded with the fine fraction material in order to increase the rate of flow of the
material in the mixer in relation to the rate of rotation of the paddles by the gravitation
force of the fine fraction material.
[0020] Advantageously, the load on the material stream increases the rate of flow in the
mixer by the equalization of high pressure in the loaded zone and the low pressure
in the unloaded zone. This is possible, since the mixed materials in the mixer behave
like a liquid during the flow mixing method.
[0021] A further advantage is the increase in the flow rate in the mixer in relation to
the rate of rotation of the paddles and that this lessens the paddle work and shear
in the mix.
[0022] According to a further advantageous embodiment, the method for production suspension
asphalt mix by change from force mixing to flow mixing is characterized by admixing
the bituminous liquid and the coarse fraction of mix to make the mix flow like a liquid
to which flow the filler, normally particles smaller than about 0.074 mm, is flow
mixed by adding at a slow flow rate whereafter the fine fraction material with particles
normally smaller than about 4 mm (and greater as the filler particles) is flow mixed
by spreading of the material over paddles or the like mixing tools in a zone where
the flow is downwards, this creating an excessive pressure in the material by gravitation
force and position energy. This increases the rate of flow relative to the speed of
rotation of the paddles, and by this, lessens the shear force of the mixing tools
in the mixer whereby the coatings of the suspension on the surface of the coarse fraction
develops the mix into suspension.
[0023] In a still further advantageous embodiment, the downwards stream in the mixer is
loaded, especially with the fine fraction material, as to produce a levelling out
of the fluid mix, by this increasing the flow rate of the stream in the mixer in relation
to the speed of rotation of the paddles.
[0024] It is preferred that the paddle work in the mix is reduced by spreading the fine
fraction material over the mixer's paddles of the downwards flow.
[0025] An advantageous embodiment of a device for carrying out the method in accordance
with the invention has a plate or a drum that guide the inflow of material to the
mixers wall, parallel to the shafts of the mixer, in order to connect and to load
the downwards flowing material stream for spreading to the other parts of the mixer
not loaded with the fine fraction. Preferably, the paddles in the downwardly flowing
stream are loaded with the inflow of material for spreading the fluid mix to the lower
part of the mixer.
[0026] A preferred embodiment of the invention is described in further detail below with
reference to the enclosed drawings in which
- Fig. 1
- is a plan view of an asphalt mixer for producing asphalt mix; and
- Fig. 2
- is a sectional view through the mixer of Fig. 1.
[0027] In a preferred embodiment of the invention, an asphalt mix is produced as described
in
EP 0 756 615 B1. Reference is also made to
WO 83/00700 with further details in view of the separation of an aggregate into a coarse grained
portion, a fine grained portion and a filler portion. Still further, reference is
made to the dissertation of the inventor Ohlson, Karl Gunnar: "Method and means used
in production of asphalt mix", Lund University, bulletin 132, 1995 (details see above).
[0028] The figures show a mixer used in the preferred embodiment. The mixer 10 has a mixer
body 11, having vertical side walls 12, 13 and end walls 14, 15. There is a bottom
17, comprising two portions 18 which are arcuate in cross section and which are connected
together adjacent the longitudinal centre of the mixer body 11. Means for mixing materials
within the mixer body 11 comprises a pair of shafts 21 and 24 which are supported
adjacent the ends by suitable gearings 25. The shafts 21, 24 are simultaneously rotated
by means of an electric motor 20 and suitable gearing 26. The direction of rotation
is shown by arrows 27, 28.
[0029] The shafts 21, 24 are on axes from which the radii of the bottom portions 18 extend
as best shown in fig. 2, and each shaft 21, 24 is provided with a plurality of mixing
tools. Here, paddles 30 are used which are connected with the shafts 21, 24 by means
of arms 31.
[0030] As shown in fig. 2, the paddles 30 are moving upwards in a center portion of the
mixing body 11, as shown by arrow B. Near the side walls 12, 13, which extend parallel
to the shafts 21, 24, the paddles 30 are moving downwards.
[0031] The coarse fraction, the filler fraction and the fine fraction are discharged by
a discharging means, generally indicated by D. Said discharging means D has an opening
42 closable by a closing means, indicated E. Further details for providing the aggregate
are not shown, but known in the art, see for example
WO 83/00700. The discharging means D has a guiding means C which leads the discharged materials
away from the upwards directed zone B to a zone A2 or A1, alternatively, where the
flow in the mixer is directed downwards. In the embodiment shown, the fine fraction
guiding means C for guiding the fine fraction into zone A2 has a plate 44 which directs
the inflow of material 50 to the sidewall 12.
[0032] By the
SE patent 506 581 and
EP 0 756 615 B1, it is made known that the flow of the filler is to be connected to the flow of the
coarse fraction in the mixer through a slow discharge of these materials, whereas
by the shown embodiment of the invention, the spreading of the fine fraction in the
bituminous liquid is made by fast discharge to the area marked by zone A1, alternative
A2 shown in figure 2.
[0033] At a fast discharge, the flow of the fine fraction material will produce an overload
of the material by which the gravity of the material and the nature of the fluid to
flow from high to low areas increases the flow rate of the fine fraction in to other
parts of the mixer that are less loaded.
[0034] With this technique, producing of a batch of asphalt mix last only about 1 minute.
To put in the coarse fraction needs about 3 sec. Thereafter, the bitumen is sprayed
in within 7 - 8 sec. Then the coarse fraction and the bitumen are mixed for about
7 -10 sec. Then the filler flow is started with the optimised flow rate and time,
this is typically about 17 sec. After the optimised time interval, the fine fraction
is added. Although the fine fraction is typically about 25 % by weight of the total
aggregate and the filler is only about 7 to 9 %, the adding of the fine fraction takes
only up to 10 sec., depending on the circumstances at and above the discharge gate.
Thus, the time for adding the fine fraction is, compared to the masses involved, much
less as the time for adding of the filler. Thus, by choosing the optimal location
for discharging the fine fraction, it is possible to reduce essentially the total
time for flow mixing a batch of asphalt. The mentioned time intervals are adjustable
to meet the requirements for flow mixing.
[0035] As visible from Fig. 2, the mixer 10 has three zones, one (B) in which the flow of
materials is directed upwards, and two (A1 and A2) in which the flow is directed downwards.
Fig. 2 shows an example of a mechanical solution by said plate 44, mounted to steer
the flow of the fine fraction to the place of discharge in accordance with the invention.
The plate 44 can be installed permanently. Preferably, however, the guiding means
can be made movable for only directing the fine fraction (or the filler and the fine
fraction) into the downwardly directed material flow.
[0036] The previously known asphalt plants were discharging filler and fine fraction material
in the zone B where the material flow is upwards, between the two shafts 24. This
caused the flow of the coarse fraction in the mixer to stop. When the flow of the
coarse fraction has been stopped as described, the flow mixing ended; and to start
the flow required force mixing by the paddles, this resulting in that only part of
the coarse fraction particles become coated by suspension. Fine fraction particles
not suspended in the liquid, rode on top of the mix being the result of the upwards
pressure created by the paddles work. The invention overcomes that problem by directing
the fine fraction, and, if wished, the filler into a downwardly directed stream.
[0037] This reduces the shear force of paddles 30 on the filler bitumen films of the coarse
fraction when mixing in the fine fraction material whereby the mix develops into a
suspension. The paddle work is reduced through that the fine fraction is spread, when
added to the mixer, over the paddles 30 in the zone A1 or A2 where the force of gravitation
and the nature of flowing mix to level out, both work in the same direction as the
paddles 30 in the mixer 10.
[0038] The force of gravitation is the result of the position energy of the material in
zone A1 (alternative zone A2). The levelling energy is a result of over loading, this
caused by the inlet of the fine fraction in zone A1 or A2. Example of such force is
a container divided in half by a wall. If filled with water on the one side of the
wall and a valve is opened at the bottom of the defining wall, the water from the
filled side will flow to the other side until the water is levelled in the two parts.
[0039] The invention exposes a combination of three forces for reducing the shear of the
paddles, 1) the energy of the flow, 2) the force of gravitation, and 3) the position
energy. As long as the mix is fluid, the materials are mixed by the flow. If the admixing
of the fine fraction divert from the invention, the mixing process will change from
flow mixing to force mixing and the mix consistency from fluid to clogged.
[0040] At the place of adding the fine fraction in the method of the invention, all paddles
of the mixes drive the flow in the same direction. This lessens the paddle work compared
to conventional asphalt mixers. The turning paddles as well as the rest of the paddles
on the shaft of the invention, drive the fluid mix in a flow parallel with the mixers
sides 12, 13 at the end of the shaft. No accumulation is found at the turning paddles
when driving the liquid mix.
EP 0 756 615 B only describes time intervals and control of flow rate as the means for mixing. The
manner and place for adding the fine fraction in the mixer is not accounted for.
[0041] The invention is used on different types of asphalt plants for production of suspension
asphalt. Without the invention, many plants fail to produce suspension asphalt paving.
[0042] The invention develops a liquid mixing process. There is no shear in liquids. This
is one reason for that the suspension develops on the surface of the coarse fraction
and remains there until the mix is paved.
1. Method for producing an asphalt mix that includes a coarse fraction, a fine fraction,
filler and bituminous binder with the following steps in the mentioned order:
a) mixing the coarse fraction and the liquid binder in a mixer (10) and
b) discharging the filler with a controlled flow rate to powder the binder liquid
which is distributed over the surface of the coarse fraction with the filler and
c) spreading the fine fraction over the layer of filler,
wherein the discharge of the filler and the fine fraction is controlled in such a
way that the filler and the fine fraction becomes enclosed in a combined suspension
where the filler, the fine fraction and the coarse fraction are parts of a closed
liquid volume,
characterized by using a mixer (10) with at least two mixing shafts (21, 24) having mixing paddles
(30) wherein the shafts (21, 24) and their paddles (30) are rotating in opposite directions
so that the paddles (30) on the side near to the other shaft are moving upwards and
the paddles (30) located near to a wall (12, 13) of the mixer (10) which wall (12,
13) extends essentially parallel to the shafts (21, 24) are moving downwards
and by discharging the fine fraction into a downwardly directed material flow in the
mixer (10).
2. Method according to claim 1,
characterized by discharging the fine fraction material along a mixer wall (12, 13) extending essentially
parallel to the shaft (21, 24) where the paddles (30) are rotated in a downward direction.
3. Method according to any of the preceding claims,
characterized in that the flow rate for discharge the fine fraction is bigger than the flow rate for discharging
the filler and/or that the fine fraction is discharged in a shorter time as the filler.
4. Method according to any of the preceding claims,
characterized in that the fine fraction is discharged, so that fine fraction material is aggregated above
the fluid level of the downwardly directed flow in the mix.
5. Method according to any of the preceding claims,
characterized in that the fine fraction is discharged into the downwardly directed mix flow with a velocity
of the mix flow.
6. Device for producing asphalt mix and for carrying out the method of any preceding
claim, with a mixer (10) and discharge means (D) for discharging materials to be mixed
into the mixer (10), wherein the discharging means (D) has a fine fraction separating
means for separating a fine fraction from a coarse fraction and a filler;
characterized in that the mixer (10) comprises at least two mixing shafts (21, 24) having mixing paddles
(30) wherein the shafts (21, 24) and their paddles (30) are rotatable in opposite
directions so that the paddles (30) on the side near to the other shaft are moving
upwards and the paddles (30) located near to a wall (12, 13) of the mixer (10) which
wall (12, 13) extends essentially parallel to the shafts (21, 24) are moving downwards
and in that the discharging means (D) leads the fine fraction via a fine fraction guiding means
(C) to a location (A2) of the mixer (10) where the materials to be mixed are moved
downwards.
1. Verfahren zur Herstellung einer Asphaltmischung, die eine Grobfraktion, eine Feinfraktion,
Füller und Bitumenbinder aufweist, mit den nachfolgenden Schritten in der angegebenen
Reihenfolge:
a) Mischen der Grobfraktion und des flüssigen Binders in einem Mischer (10) und
b) Zuleiten des Füllers mit einer gesteuerten Flussrate zum Einstäuben der Binderflüssigkeit,
die über die Oberfläche der Grobfraktion verteilt ist, mit dem Füller und
c) Verbreiten der Feinfraktion über die Füllerschicht,
wobei das Zuleiten des Füllers und der Feinfraktion derart gesteuert wird, dass der
Füller und die Feinfraktion in einer vereinigten Suspension eingeschlossen werden,
wobei der Füller, die Feinfraktion und die Grobfraktion Teile eines geschlossenen
Flüssigkeitsvolumens sind,
gekennzeichnet durch Verwendung eines Mischers (10) mit wenigstens zwei Mischpaddel (30) aufweisenden
Mischwellen (21, 24), wobei die Wellen (21, 24) und ihre Paddel (30) sich in entgegen
gesetzter Richtung drehen, so dass sich die Paddel (30) auf der Seite, die neben der
anderen Welle liegt, aufwärts bewegen und sich die Paddel (30), die neben einer sich
im Wesentlichen parallel zu den Wellen (21, 24) erstreckenden Wand (12, 13) des Mischers
(10) liegen, abwärts bewegen, und
durch Zuleiten der Feinfraktion in einen abwärts gerichteten Materialfluss in dem Mischer
(10).
2. Verfahren nach Anspruch 1,
gekennzeichnet durch Zuleiten des Feinfraktionsmaterials entlang einer Mischerwand (12, 13), die sich
im Wesentlichen parallel zu der Welle (21, 14) erstreckt, wo die Paddel (30) in einer
abwärtigen Richtung gedreht werden.
3. Verfahren nach einem der voranstehenden Ansprüche,
dadurch gekennzeichnet, dass die Flussrate zum Zuleiten der Feinfraktion größer ist als die Flussrate zum Zuleiten
des Füllers und/oder dass die Feinfraktion in einer kürzeren Zeit als der Füller zugeleitet
wird.
4. Verfahren nach einem der voranstehenden Ansprüche,
dadurch gekennzeichnet, dass die Feinfraktion derart zugeleitet wird, dass das Feinfraktionsmaterial über dem
Flüssigkeitsfüllstand des abwärts gerichteten Flusses in der Mischung angesammelt
wird.
5. Verfahren nach einem der voranstehenden Ansprüche,
dadurch gekennzeichnet, dass die Feinfraktion in den abwärts gerichteten Mischungsfluss mit einer Geschwindigkeit
des Mischungsflusses zugeleitet wird.
6. Vorrichtung zum Herstellen einer Asphaltmischung und zum Ausführen des Verfahrens
eines der voranstehenden Ansprüche, mit einem Mischer (10) und einer Zuleitvorrichtung
(D) zum Zuleiten von Materialien, die in den Mischer (10) eingemischt werden, wobei
die Zuleitvorrichtung (D) eine Feinfraktionstrennungsvorrichtung zum Trennen einer
Feinfraktion von einer Grobfraktion und einem Füller aufweist,
dadurch gekennzeichnet, dass der Mischer (10) wenigstens zwei Mischwellen (21, 24) aufweist, die Mischpaddel (30)
aufweisen, wobei die Wellen (21, 24) und ihre Paddel (30) in entgegen gesetzter Richtung
drehbar sind, so dass sich die Paddel (30) auf der Seite benachbart zu der anderen
Welle aufwärts bewegen und sich die Paddel (30) neben einer sich im Wesentlichen parallel
zu den Wellen (21, 24) erstreckenden Wand (12, 13) des Mischers (10) abwärts bewegen,
und dadurch, dass die Zuleitvorrichtung (D) die Feinfraktion über eine Feinfraktionsführungsvorrichtung
(C) zu einer Stelle (A2) des Mischers (10) führt, wo die zu vermischenden Materialien
abwärts bewegt werden.
1. Procédé pour fabriquer un mélange d'asphalte contenant une fraction grossière, une
fraction fine, une charge et un liant bitumineux, procédé comprenant les étapes suivantes
dans l'ordre ci-après :
a) on mélange la fraction grossière et le liant liquide dans un mélangeur (10), et
b) on décharge la charge suivant un débit contrôlé pour poudrer le liant liquide distribué
à la surface de la fraction grossière avec la charge, et
c) on étale la fraction fine sur la couche de charge,
procédé selon lequel
la sortie de la charge et de la fraction fine est contrôlée pour que la charge et
la fraction fine soient enrobées dans la suspension combinée dans laquelle la charge,
la fraction fine et la fraction grossière font partie d'un volume de liquide fermé,
procédé
caractérisé en ce que
on utilise un mélangeur (10) ayant au moins deux axes (21, 24) portant des pales de
mélangeur (30),
les axes (21, 24) et les pales (30) tournant en sens opposé de façon que les pales
(30), sur le côté proche de l'autre axe, remontent et que les pales (30) proches de
la paroi (12, 13) du mélangeur (10) descendent, la paroi (12, 13) s'étendant pratiquement
parallèlement aux axes (21, 24), et
on évacue la fraction fine dans la direction descendante du flux de matière dans le
mélangeur (10).
2. Procédé selon la revendication 1,
caractérisé en ce qu'
on évacue la matière de la fraction fine suivant une paroi (12, 13) du mélangeur,
cette paroi s'étendant sensiblement parallèlement à l'axe (21, 24), les pales (30)
tournant dans le sens descendant.
3. Procédé selon l'une quelconque des revendications précédentes,
caractérisé en ce que
le débit de sortie de la fraction fine est supérieur au débit de sortie de la charge
et/ou la fraction fine est sortie en un temps plus court que la sortie de la charge.
4. Procédé selon l'une quelconque des revendications précédentes,
caractérisé en ce qu'
on décharge la fraction fine de façon que la matière de la fraction fine soit agrégée
au dessus du niveau de liquide du flux de mélange descendant.
5. Procédé selon l'une quelconque des revendications précédentes,
caractérisé en ce que
la fraction fine est évacuée dans le flux de mélange descendant à la vitesse du flux
de mélange.
6. Dispositif pour fabriquer un mélange d'asphalte et pour effectuer le procédé selon
l'une quelconque des revendications précédentes comportant un mélangeur (10) et un
moyen de sortie (D) pour décharger la matière à mélanger dans le mélangeur (10),
le moyen de sortie (D) ayant un moyen de séparation de la fraction fine pour séparer
la fraction fine de la fraction grossière et de la charge, caractérisé en ce que
le mélangeur (10) a au moins deux axes (21, 24) portant des pales (30), des axes (21,
24) et des pales (30) tournant en sens opposé de sorte que les pales (30) du côté
proche de l'autre axe remontent et que les pales (30) proches de la paroi (12, 13)
du mélangeur (10) descendent, la paroi (12, 13) s'étendant pratiquement parallèlement
aux axes (21, 24), et
le moyen de sortie (D) conduit la fraction fine par un moyen de guidage (C) vers l'emplacement
(A2) du mélangeur (10) là où descendent les matières à mélanger.