EP0681895A1

EP0681895A1 - Device to mix liquid substances with particles having different granule sizes and relative mixing method

Info

Publication number: EP0681895A1
Application number: EP95105226A
Authority: EP
Inventors: Romeo Paladin
Original assignee: PAL Srl
Current assignee: PAL Srl
Priority date: 1994-05-13
Filing date: 1995-04-07
Publication date: 1995-11-15

Abstract

Device to mix liquids with particles having different granule sizes, which comprises a mixing chamber (13) and includes a feeder inlet (11), a main outlet (14), injectors (15) to inject an adhesive mixture and possible agitation elements (18), the mixing chamber (13) cooperating with rotary feeder thrust means (12-112) and including also at least one screening extractor outlet (20) associated with riddle means (30) to screen the granule size of particles, the at least one screening extractor outlet (20) covering a zone which runs from the beginning of the feeder inlet (11) of the mixing chamber (13) to the vicinity of the first upstream injector (15) injecting the adhesive mixture, the screening extractor outlet (20) affecting the perimetric periphery of the mixing chamber (13) about at least 5% of the perimeter of the mixing chamber (13), the screening extractor outlet (20) cooperating with at least one channel (24) to convey the fine particles thus separated, and a relative method to mix in the mixing chamber (13) liquids with particles having different granule sizes, these particles introduced into the mixing chamber (13) by the feeder inlet (11) being centrifuged while they are fed forwards in the form of a rotary ring, this rotary ring cooperating with at least riddle or sieve means (30) which select the fine particles and are positioned on the periphery of the mixing chamber (13) upstream of the injection of the adhesive mixture, the particles which do not pass through the riddle or sieve means (30) being fed forwards in cooperation with the adhesive mixture, whereas the fine particles which pass through the riddle or sieve means (30) are fed into a conveyor channel (24).

Description

This invention concerns a device to mix liquid substances with particles having different granule sizes, as set forth in the main claim.
This invention concerns also the mixing method carried out with the device according to the invention.
The device is applied to mixing machines, namely machines which mix liquid substances, such as adhesive mixtures for instance, with materials that do not combine with each other, whether those materials be fine, granular, fibrous, chips or other materials.
To be more exact, this device is correctly applied to the preparation of pastes of particles, which are in particular but not only based on wood, with adhesive mixtures preferably with an aqueous base of a thermosetting type, for instance.
The device has the further purpose of separating, possibly rejecting and delivering particles having a fine granule size to a different subsequent mixing step.
Mixing machines of the state of the art include a mixing chamber with a substantially cylindrical configuration, which comprises at one end a main feeder inlet to feed solid material.
The solid material is fed by suitable rotary feeder means in the first segment of the mixing chamber towards the opposite end of the mixing chamber, where the main downstream outlet for the mixture produced is provided.
The action of these rotary feeder means causes the solid material to tend to be arranged in the form of a rotary ring against the inner sidewall of the mixing chamber.
Within the mixing chamber a shaft rotates that bears a plurality of mixing implements, which provide the rotary ring with the suitable centrifugal mixing force and which contribute to the feed of the material at the same time.
The axis of the rotary shaft coincides generally with the axis of the mixing chamber, but embodiments can be employed equally well with the axis of the rotary shaft inclined or askew in relation to the axis of the mixing chamber, or else with the rotary shaft parallel to the axis of the mixing chamber but offset laterally or upwards or downwards therefrom.
Likewise, mixing chambers can be employed of which the cross-section perpendicular to the lengthwise axis of the mixing chamber has an oval, elliptic, ovoidal, etc. form.
Injectors to inject the liquid adhesive products to be mixed with the solid material are included at least along the first segment of the mixing chamber.
Agitation elements are advantageously comprised downstream of the injectors or interposed therebetween and are positioned suitably in the interspaces between the mixing implements solidly fixed to the shaft.
In such a structure the finest particles of the uncombined solid material, in relation to the rotary feeder means, have a tendency to be arranged on the periphery of the rotary ring, and this tendency is enhanced as soon as these particles are affected by the introduction of the liquid substances by the injectors.
This fact entails the result that the distribution of the liquid substances does not takes place evenly in the whole thickness of the ring but takes place in a differentiated manner depending on the granule sizes of the solid material introduced.
In particular, the lighter particles having a smaller thickness and greater specific surfaces, owing to physical reasons and to their outer arrangement in the rotary ring, are often affected too much by the action of the liquid adhesive substances as compared to the particles having greater dimensions.
It is obvious that an uneven distribution of the liquid adhesive substances on all the particles of solid materials leads to a decrease in the efficiency of the mixer.
In particular, such a distribution leads to a non-homogeneous product and a high and excessive consumption of adhesive substances.
A disclosure has been made for extracting a part of the material to be mixed at a position immediately upstream of the injectors of adhesive material and of reintroducing this material downstream of the injectors, but this disclosure has been found to be not advantageous and does not overcome the problem; moreover, the problem of the incorrect distribution of the adhesive remains substantially unsolved.
DE-A-1.528.238 discloses the introduction of products of a given size at the initial part of the mixer and the introduction of the fine particles at the end part.
In this disclosure the products of a given size and the fine particles have to be separated upstream of the mixer.
According to this document of the prior art the fine particles are introduced through a lengthwise aperture the length of which can be adjusted from the end towards the beginning.
Moreover, these fine particles are delivered by a distributor which does not introduce them all at one very exact point.
It is obvious that the more the fine particles are introduced towards the end of the mixing chamber, the less those fine particles can be amalgamated.
The present applicants have designed, tested and embodied this invention to overcome this problem and to achieve further advantages.
This invention is set forth and characterised in the respective main claims, while the dependent claims describe variants of the idea of the main embodiment.
The invention discloses a device which can be employed advantageously, but not only, with solid materials of a particulate type based on wood, and which is suitable to make uniform the distribution of liquid substances, such as a water-based adhesive mixture or the like, on the whole range of the granule sizes of the solid material introduced into the mixing chamber.
The device according to the invention also enables an appreciable saving to be achieved in the adhesive mixture introduced into the mixing chamber to produce finished products such as, in particular, panels composed of particles which are advantageously, but not only, based on wood.
The invention is applied to mixers of a known type, so that existing mixers too can be converted according to the invention without requiring that these mixers should have special structures. In other words the invention is applied to all the mixing machines which, owing to the centrifugal action determined by the feeder means and rotary implements, are characterised by the formation of a ring of rotating particles within the mixing chamber with a peripheral distribution of the finest particles.
This device, taking advantage also of cooperation with suitable thrust implements included in the first segment of the mixing chamber, provides for the extraction by centrifuging of the finest particles which are positioned in the most peripheral layer of the rotating ring.
The finest particles are directed by centrifuging, and also by the action of the thrust implements, at least towards a screening extractor outlet provided in the periphery of the outer wall of the mixing chamber in a position that is not affected by the point of the beginning of the introduction of the adhesive mixture.
In this way it is ensured that the extraction involves a great quantity of fine particles which have not been wetted by the liquid adhesive substances.
The circumferential position of the screening extractor outlet can be at any perimetric point of the mixing chamber and can cover any perimetric area of that chamber in that zone, and in the description that follows we shall refer, for convenience of illustration alone, to a screening extractor outlet positioned below the mixing chamber.
According to the invention a sieve or riddle containing perforations of the desired size is included in cooperation with the screening extractor outlet for the fine particles so as to ensure a precise and efficient control of the granule size of the fine particles there extracted.
The perforations of the sieve or riddle may be circular, oval, square, rectangular, or lozenge-shaped or may have another desired geometric shape.
According to a variant the perforations have a deformation obtained by raising one edge towards the inside of the mixing chamber and possibly by lowering the diametrically opposite edge.
According to the invention one embodiment thereof arranges that the part raised towards the inside of the mixing chamber is upstream of the perforation in the direction of feed of the rotating ring.
The perforation, where it is circular, preferably has a nominal diameter within the range from 0.2 to 20 mm.
According to a preferred embodiment this diameter is between 1 and 4 mm.
Where the perforation has an oval, triangular or square form or another polygonal form, the nominal diameter is that relating to the circumference which is formed in the hole.
According to one embodiment of the invention the screening extractor outlet for the fine particles has a fixed width and a fixed length.
According to a variant the screening extractor outlet has a width can be adjusted as desired.
According to another variant the screening extractor outlet has a length which can be adjusted as desired.
The width and/or length of the screening extractor outlet can be adjusted by means of a gate valve that can restrict its span, the gate valve being capable of linear sliding or perimetric sliding along the perpendicular section of the mixing chamber.
According to one embodiment of the invention the lengthwise extent of the screening extractor outlet has a great size at least equal to the length of the feeder inlet through which the unseparated granular material is introduced.
According to a variant the length and/or width of the screening extractor outlet has a value required for the entry of the desired quantity of fine particles from the mixing chamber.
The screening extractor outlet covers always and only the dry zone located upstream of the injectors and begins advantageously in correlation with the beginning of the feeder inlet.
According to a variant an extractor element is comprised in cooperation with the screening extractor outlet and downstream thereof and is suitably inclined in relation to the direction of feed of the solid material and extends within the mixing chamber by a length which can be adjusted as desired. This extractor element cooperates with thrust implements in extraction of the outermost particles of the rotary ring and has the purpose of facilitating the extraction of fine particles which have still not reached the outer part of the rotary ring.
According to a variant the inclination of the extractor element in relation to the direction of feed can be adjusted.
According to a further variant the extractor element can also be oriented in relation to a plane perpendicular to the axis of the mixing chamber.
The extractor element can be flat or can have a shape like a spoon.
According to one embodiment of the invention the screening extractor outlet is connected to a receiving duct, the end part of which communicates with at least one conveyor channel.
In one embodiment of the invention the conveyor channel is connected at its downstream end to a delivery conduit, which communicates with the inside of the mixing chamber through at least one delivery inlet for re-introduction of the fine particles into the mixing chamber.
According to a variant the conveyor channel cooperates directly with the delivery inlet in re-introducing the fine particles into the mixing chamber .
According to a further variant the conveyor channel cooperates directly with the screening extractor outlet in receiving the fine particles from the mixing chamber; in this case the conveyor channel will have a conformation suitable for the receipt and conveying by means of a suitable lead-in for the flow of particles from the inside of the mixing chamber.
The conveyor channel is equipped with conveyor means to re-introduce the extracted fine particles into the mixing chamber; this re-introduction of the fine particles takes place at any point between the end of the screening extractor outlet and the downstream end of the mixing chamber.
The conveyor means can be of a mechanical type, with a piston or worm for instance, or of a pneumatic type employing aspiration or else of a type employing injectors of liquid substances or injectors of air.
The delivery conduit is equipped with suitable conveyor means which re-introduce into the mixing chamber the extracted fine particles.
This delivery conduit can be positioned in any circumferential position in relation to the mixing chamber.
Where the conveyor means operate with aspiration, according to the invention the conveyor channel cooperates either with slide valve means or with a cyclone means.
Where the circumferential position of the delivery conduit and its inclination make it possible, the delivery conduit can lack conveyor means to re-introduce the fine particles if this re-introduction can take place by gravity.
According to another embodiment of the invention the fine particles are not re-introduced into the mixing chamber but are delivered separately, together with the main flow of material leaving the outlet of the mixing chamber, to a post-mixer or to another different mixing process.
The mixing device according to the invention in this case will behave as a means that separates fine materials by centrifuging without requiring any additional equipment.
The fine particles engaged by the appropriate means, at the moment of their re-introduction into the mixing chamber through the delivery inlet, are removed by friction by the rotating mixture. In this way these fine particles are brought to cooperate with the surplus of liquid substance in the mixture, this surplus being generated by the smaller quantity of solid material affected by the liquid along the whole segment in which the fine particles are not within the mixing chamber.
According to the invention means to introduce steam, water or another suitable liquid are included in cooperation with and downstream, or only downstream, of the delivery conduit re-introducing the fine particles.
Where the fine particles are re-introduced upstream of the last injector of adhesive mixture, these fine particles interact directly with at least a percentage of the mixture introduced by the downstream injectors.
According to the invention the point of re-introduction of the fine particles , however, should not be too near the discharge zone so as to provide for the fine particles a sufficient segment of cooperation with the mixture produced up to that point.
The attached figures are given as a non-restrictive example and show some preferred embodiments of the invention as follows:-

Fig.1: shows diagrammatically a partly cutaway lengthwise view of a first form of embodiment of the mixer according to the invention;
Fig.2: shows a cross-section along the line A-A of Fig.1;
Fig.3: shows a partly cutaway lengthwise view of a variant of Fig.1:
Fig.4: shows a cross-section along the line B-B of Fig.3;
Fig.5: shows a cross-section of the mixer along the line C-C of Fig.3;
Fig.6: shows a variant of the mixer of Fig.1;
Fig.7: shows partly a variant of Fig.2;
Fig.8: shows diagrammatically a device to screen particles in association with the mixer according to the invention;
Figs. 9a and 9b: show two possible conformations of the riddle or sieve means.

A mixer 10 shown in Fig.1 includes a feeder inlet 11 to introduce solid material and rotary feeder means 12 formed as a worm to feed the solid material into a mixing chamber 13 and towards an outlet 14 for the mixture produced.
According to the variant of Fig.3 the rotary feeder means 12 consist of feeder thrust implements 112 fitted at least on the initial portion of a rotary shaft 16.
According to the invention the rotary feeder means 12-112 perform also the task of elements to extract the fine particles by centrifuging them towards the sidewall of the mixer 10.
According to the invention the feeder thrust implements 112 can be adjusted for inclination and for distance in relation to the sidewall of the mixing chamber 13.
The mixer 10 includes a plurality of injectors 15 to introduce an adhesive mixture, which are positioned in cooperation with at least the first segment of the mixing chamber 13; these injectors 15 can be of a type using a conduit, a nozzle or pressure or can be of another known type suitable for the purpose.
The rotary shaft 16 is equipped with a plurality of mixing implements 17 suitable to set in rotation the solid material and the liquid substances gradually introduced. The mixing implements 17 can have various forms of the state of the art.
The mixer 10 also includes in this case a plurality of agitation elements 18 positioned downstream of the last of the injectors 15 of the adhesive mixture.
According to the invention the agitation elements 18 are also equipped to introduce into the mixing chamber 13 steam, water or another suitable liquid or gaseous substance at least in the zone of re-introduction of the fine particles or downstream of that zone; this will take place when the water content in the adhesive mixture introduced upstream is, for processing reasons, less than the required quantity of water in the adhesive mixture.
The agitation elements 18 are positioned in the interspaces between the mixing implements 17 so as not to create contacts with those implements 17.
Upstream of the injectors 15 introducing the adhesive mixture, the mixer 10 is equipped with suitable thrust implements 19 borne and set in rotation by the rotary shaft 16; these thrust implements 19 cooperate with the rotary feeder thrust means 12-112 acting also as an extractor element and with at least one screening extractor outlet 20 provided in the wall of the mixing chamber 13 so as to extract the fine particles of the uncombined mixture of solid material introduced into the mixing chamber 13.
In this case the screening extractor outlet 20 is located in the lower part of the mixer 10, but its position could be at any circumferential point in the wall of the mixer 10 at the angle "β" of Fig.7 which can vary from 0° to 360°.
The screening extractor outlet 20 is located in the zone which is defined, along the axis of the mixing chamber 12, by the beginning of the feeder inlet 11 and by the first injector 15 of the adhesive mixture.
The screening extractor outlet 20 cooperates with a riddle or sieve 30 and begins advantageously in the vicinity of the beginning of the feeder inlet 11.
According to the invention the screening extractor outlet 20 takes up at least 5% of the periphery of the mixing chamber 13.
In the example shown in Figs.2 and 4 the periphery of the mixing chamber 13 taken up by the screening extractor outlet 20 is 50% of the whole perimeter of the mixing chamber 13; this perimetric zone can extend about the whole perimeter of the mixing chamber 13.
The fine particles are positioned by centrifuging in the outermost peripheral layer of the ring of solid material which becomes formed by the thrust action of the rotary feeder thrust means 12-112, mixing implements 17 and thrust implements 19.
In this connection at least the rotary feeder thrust means 12-112 have at their lower end an elongate conformation suitable for enhancing the centrifugal action (Fig.7).
The most downstream position of the screening extractor outlet 20 has as its limit the first of the injectors 15 injecting the adhesive mixture, care being taken to include a necessary safety segment between the screening extractor outlet 20 and the first injector 15.
In this way the fine particles extracted from the mixing chamber 13 have still not been lapped by the adhesive mixture.
A riddle or sieve 30 containing perforations 39 of a desired size and characteristics is included in cooperation with the screening extractor outlet 20; this riddle or sieve 30 has the purpose of selecting the particles passing through and of controlling precisely and accurately their granule size
In the embodiment of Figs.1 and 3, in which the screening extractor outlet 20 is positioned below the mixer 10, the riddle 30 takes up the lower half-casing of the mixer 10;
According to a first embodiment the screening extractor outlet 20 can have a fixed width and length, or else the width or length or both can be adjusted to pre-set the span of the screening extractor outlet 20 before processing begins or during processing.
The width and length of the screening extractor outlet 20 can be determined so as to vary the quantity of particles extracted from the mixing chamber 13.
The particles extracted pass from the screening extractor outlet 20 into a receiving duct 23 and thence into a conveyor channel 24.
The lengthwise axis of the receiving duct 23 coincides advantageously with the axis of positioning of the screening extractor outlet 20.
According to a variant the axis of the receiving duct 23 forms together with the axis of positioning of the screening extractor outlet 20 an angle which may vary between 0° and ± 90°, namely the angle "α" in Fig.7, in which the extreme positions represent the case of a receiving duct 23 perpendicular and tangential respectively to the mixing chamber 13
The conveyor channel 24 is equipped with means 25 to thrust the extracted particles; these thrust means 25 are of a known type and can be mechanical actuation means of a piston or worm type, for instance.
According to a variant these thrust means 25 are of a pneumatic type using a negative pressure or air injectors, water or steam injectors or injectors of another liquid or gaseous substance of a low density in order to fluidify the mass of particles and to assist their flow along the conveyor channel 24.
These injectors can be placed in only the initial portion of the conveyor channel 24 or can be distributed along the whole length of the conveyor channel 24.
These feeder thrust means 25 take the extracted particles to the vicinity of a delivery conduit 26 which comprises a delivery inlet 27 communicating with the inside of the mixing chamber 13 and located downstream of the screening extractor outlet 20.
The delivery conduit 26 too is equipped with thrust means 28 of a known type to re-introduce the particles into the mixing chamber 13.
Agitation elements 18 which act also as injectors to inject liquid or gaseous substances required to humidify the fine particles and/or the mixture are included in cooperation with the delivery inlet 27 or immediately upstream or downstream of the same 27.
The delivery inlet 27 too can take up any circumferential position in relation to the mixer 10, with the angle "γ" in Fig.5, which can vary between 0° and 360°.
In this case too the lengthwise axis of the delivery conduit 26 forms together with the axis of positioning of the delivery inlet 27 an angle, the angle "δ" of Fig.5, which can vary between 0° and ± 90°, so as to make possible, depending on the case in question, a re-introduction of the fine particles in a direction perpendicular or tangential to the mixing chamber 13 or in a direction between the perpendicular and the tangential directions.
When the fine particles are re-introduced in a perpendicular or substantially perpendicular direction and from above into the mixing chamber 13, the delivery conduit 26 can lack its thrust means 28 inasmuch as the reintroduction will take place by gravity.
According to the variant shown in Fig.6, the fine particles are not re-introduced into the mixing chamber 13 but, after being separated therefrom, are sent through an outlet 34 to a separate post-mixer (not shown) together with the product leaving the main downstream outlet 14 or else are sent to another separate mixing process.
According to another variant the invention includes two or more screening extractor outlets 20, each of which is associated with a separate receiving duct 23 and a separate conveyor channel 24 and possibly with different riddles or sieves 30 to select different granules sizes.
The fine particles thrust by the thrust means 28 through the delivery inlet 27 towards the inside of the mixing chamber 13 are drawn by friction by the rotating mixture formed up to that point. This mixture is supersaturated since the liquid substances are introduced in quantities sufficient for the whole volume of solid material introduced through the main upstream feeder inlet 11.
As far as the point of re-introduction of the fine particles there is therefore in the mixture a surplus of liquid, which affects the fine particles only in the segment downstream of their re-introduction into the mixing chamber 13.
This point of re-introduction of the fine particles, which is the position of the delivery inlet 27, can be at any point between the zone lapped by the injectors 15 of the adhesive mixture and the zone of the main downstream outlet 14 of the mixed product.
This point of re-introduction, however, should not be too near to the main downstream outlet 14 of the mixed product but should leave a sufficient segment of cooperation between the surplus of liquid substances and the fine particles reintroduced into the mixing chamber 13.
According to another variant shown in Fig.8 the mixer 10 according to the invention can be integrated into a system of separation of the fine particles, this system being located upstream of the mixer 10 itself.
This system comprises a silo 31 to store the separated material; this silo 31 feeds by means of a suitable dosing machine 32 the coarser particles directly to the main feeder inlet 11 of the mixer 10, whereas the finer particles are introduced separately by means of a relative dosing machine 33 into the mixer 10 downstream of the zone of introduction of the adhesive mixture, which is defined by the injectors 15.
This system of separation of the fine particles can be an alternative to the system according to the invention or can be complementary thereto, as is shown in Fig.8, in which there are also included the screening extractor outlet 20 and the conveyor channel 24 to obtain the separation of the fine particles too within the mixer 10.
Figs.9a and 9b show two types of deformations 35-36 of the perforations 39 with a nominal diameter 38.
Deformations 35 positioned upstream of the perforations 39 according to the direction of rotation (shown by the arrow 37) of the rotary feeder thrust means 12-112 face towards the inside of the mixing chamber 13, whereas deformations 36 positioned downstream of the perforations 39 face outwards.

Claims

Device to mix liquids with particles having different granule sizes, which comprises a mixing chamber (13) and includes a feeder inlet (11), a main outlet (14), injectors (15) to inject an adhesive mixture and possible agitation elements (18), the mixing chamber (13) cooperating with rotary feeder thrust means (12-112), the device being characterised in that the mixing chamber (13) includes at least one screening extractor outlet (20) associated with riddle means (30) to screen the granule size of particles, the at least one screening extractor outlet (20) covering a zone which runs from the beginning of the feeder inlet (11) of the mixing chamber (13) to the vicinity of the first upstream injector (15) injecting the adhesive mixture, the screening extractor outlet (20) affecting the perimetric periphery of the mixing chamber (13) about at least 5% of the perimeter of the mixing chamber (13), the screening extractor outlet (20) cooperating with at least one channel (24) to convey the fine particles thus separated.
Device as in Claim 1, in which the conveyor channel (24) cooperates with at least one delivery inlet (27) located in the periphery of the mixing chamber (13) at a position downstream of the screening extractor outlet (20).
Device as in Claim 1, in which the conveyor channel (24) cooperates with an outlet (34) for the differentiated feeding of the fine particles to downstream means.
Device as in Claim 2, in which at least one delivery conduit (26) is included between the delivery inlet (27) and the conveyor channel (24).
Device as in any claim hereinbefore, in which the screening extractor outlet (20) is associated with at least one receiving duct (23).
Device as in any claim hereinbefore, in which the conveyor channel (24) is associated with thrust means (25).
Device as in any claim hereinbefore, in which the screening extractor outlet (20) is positioned at a desired point of the periphery of the mixing chamber (13).
Device as in any claim hereinbefore, in which the delivery inlet (27) is positioned at a desired point of the periphery of the mixing chamber (13).
Device as in any claim hereinbefore, in which the screening extractor outlet (20) cooperates with means which can at least restrict its width.
Device as in any claim hereinbefore, in which the screening extractor outlet (20) cooperates with means which can at least restrict its length.
Device as in any claim hereinbefore, in which the rotary feeder thrust means (12-112) act also as an extractor element in the segment where they cooperate with the screening extractor outlet (20)
Device as in any claim hereinbefore, in which the screening extractor outlet (20) cooperates with at least one auxiliary extractor element extending within the mixing chamber (13).
Device as in any claim hereinbefore, in which the riddle or sieve means (30) include perforations (39) having a nominal diameter (38) between 0.2 and 20 mm.
Device as in any claim hereinbefore, in which the riddle or sieve means (30) include perforations (39) having a nominal diameter (38) between 1 and 4 mm.
Device as in any claim hereinbefore, in which the perforations (39) include at least one deformation (35) facing towards the inside of the mixing chamber (13) and positioned upstream of the perforation (39).
Device as in any claim hereinbefore, in which agitation means (18) having also the function of injectors of liquid or gaseous substances are included in cooperation with the delivery inlet (27).
Device as in any claim hereinbefore, in which agitation means (18) having also the function of injectors of liquid or gaseous substances are included in cooperation with the segment of the mixing chamber (13) running from the delivery inlet (27) to the main downstream outlet (14).
Method to mix liquids with particles having different granule sizes in a mixing chamber (13), which includes a feeder inlet (11), a main outlet (14), means (15) to inject an adhesive mixture and possible agitation elements (18), the mixing chamber (13) cooperating with rotary feeder thrust means (12-112), the method being characterised in that the particles introduced into the mixing chamber (13) by the feeder inlet (11) are centrifuged while they are fed forwards in the form of a rotary ring, this rotary ring cooperating with at least riddle or sieve means (30) which screen the fine particles and are positioned on the periphery of the mixing chamber (13) upstream of the injection of the adhesive mixture, whereby the particles which do not pass through the riddle or sieve means (30) are fed forwards in cooperation with the adhesive mixture, whereas the fine particles which pass through the riddle or sieve means (30) are fed into a conveyor channel (24).
Method as in Claim 18, in which the fine particles in the conveyor channel (24) are reintroduced into the mixing chamber (13) at a position downstream of the injector means (15) injecting the adhesive mixture.
Method as in Claim 18, in which the fine particles in the conveyor channel (24) are reintroduced into the mixing chamber (13) at a position in cooperation with the last downstream injector means (15) injecting the adhesive mixture.
Method as in any of Claims 18 to 20 inclusive, in which the fine particles are reintroduced into the mixing chamber (13) in the peripheral band covered by the agitation elements (18).
Method as in any of Claims 18 to 21 inclusive, in which the rotary ring, immediately upstream of the perforations (39) of the riddle or sieve means (30), encounters a deformation (35) facing towards the inside of the mixing chamber (13).