CH710824B1 - Device and method of assay - Google Patents

Abstract

The present invention relates to a device (100) for dosing a main material (10) and a secondary material (20) comprising a main chamber (5), the chamber comprising: an inlet (1) arranged to receive the material main (10), an outlet (9) arranged to discharge the main material (10) and the secondary material (20), an opening (8) between the inlet (1) and the outlet (9), and arranged to receive in the main chamber the secondary material (20). The device also comprises a tongue (6) in the main chamber (5) in correspondence of the opening (8), so as to prevent the flow of the main material (10) in an area (7) located between the tongue (6), the outlet (9) and a side wall (3) of the main chamber (5), and so as to allow in this zone (7) only the gravity flow of the secondary material (20). The invention also relates to a metering and extrusion system comprising a metering device according to the invention and an extruder, as well as a metering method. The materials to be dosed are p. ex. different plastic granules.

Description

Description

TECHNICAL FIELD [0001] The present invention relates to a device and a method for assaying at least one secondary material in a main material.

STATE OF THE ART [0002] Dosing devices between a main material and at least one secondary material are known. The main material and the secondary material are generally solid, for example and without limitation granules, crushed material or powder particles.

Such metering devices allow for example dosing different plastic granules (main material, dye, catalyst, etc.) for extrusion or injection processes for example.

[0004] Most existing metering devices make use of mechanical drive devices for auxiliary materials and sometimes also for the main material. The training of these materials can be done with augers, treadmills or vibrating benches for example.

The assay is then carried out batchwise batchwise, which are then mixed and released into the supply duct of the machine.

The dosage can also be carried out continuously, the main material feed being generally left free (feeding by the effect of gravity). In the continuous dosing devices, the total flow rate consumed by the machine can be measured, to allow calculation of the flow rate required for the secondary materials.

BRIEF SUMMARY OF THE INVENTION [0007] An object of the present invention is to provide a metering device free from the limitations of known devices.

Another object of the invention is to provide a simpler dosing device than the known devices.

Another object of the invention is to provide a less expensive metering device than the known devices.

According to the invention, these objects are achieved in particular by means of a metering device of a main material and a secondary material comprising a main chamber, this chamber comprising an inlet arranged to receive the main material, a outlet arranged to discharge the main material and the secondary material, the main material flowing from the inlet to the outlet by the effect of gravity.

In addition, an opening between the inlet and the outlet is arranged to receive in the main chamber the secondary material.

The device according to the invention also comprises a tab arranged to enter at least partially into the main chamber in correspondence of the opening, so as to prevent the flow of the main material in an area below this tab between this tongue, a side wall of the main chamber and the outlet of the device, and so as to allow in this area only the gravity flow of the secondary material.

The dosing device according to the invention is a device that operates continuously, not in batches of material.

The metering device according to the invention is therefore a passive device, because it exploits the force of gravity for the flow of the main material and the (or) auxiliary material (s), called ( s) hereinafter, secondary subject (s). It also exploits a property of many granular materials: in a vertical flow channel whose cross section is essentially constant, the velocity of each particle or granule is substantially constant, at the edge and at the center of the flow channel. It is thus noted that the metering device according to the invention is devoid of moving elements such as augers, treadmills or vibrating benches and is therefore simpler and cheaper than known solutions.

In the context of the present invention, the word "tongue" (or deflector) designates an element in the main chamber which defines with a portion of the side wall of the main chamber of the metering device and with the output of the device an area in which the secondary material can flow by the effect of gravity. In this zone there is no flow of the main material.

Since the tongue is placed between the inlet and the outlet of the main chamber, and since the main material flows from the inlet to the outlet by the effect of gravity, this main material comes into contact with an upper surface of the tongue, that is to say its surface closer to the input of the device, and slides on this surface without being able to cross. The main material can not flow into the area directly below this surface.

By against the lower surface of the tongue, that is to say its surface closer to the output of the device, comes into contact with the secondary material.

The invention also relates to a method of metering a main material and at least one secondary material, comprising the following steps - receiving the main material in correspondence of an entrance of a main chamber of a dosing device, - flow of the main material in the main chamber, from the inlet to an outlet of the metering device by the effect of gravity, - reception of the secondary material in correspondence of an opening between the inlet and the outlet of the metering device, - flow of the secondary material by the effect of gravity only in an area between a tab arranged to enter the main chamber in correspondence of the opening, a side wall of the main chamber and the outlet, the tongue preventing flow of the main material in this area.

BRIEF DESCRIPTION OF THE FIGURES [0019] Examples of implementation of the invention are indicated in the description illustrated by the appended figures in which:

Fig. 1 illustrates a sectional view of an embodiment of a dosing device according to the invention, co operating with an extruder.

Fig. 2 illustrates a top view of the metering device of FIG. 1.

Figs. 3A and 3B illustrate a perspective view of two embodiments of the tongue of a metering device according to the invention.

Fig. 4 illustrates a sectional view of another embodiment of a metering device according to the invention.

Fig. 5 illustrates a top view of the metering device of FIG. 4.

Example (s) of embodiment (s) of the invention [0020] FIG. 1 illustrates a sectional view of an embodiment of a metering device 100 according to the invention, cooperating with a machine, for example and without limitation an extruder 4.

The metering device 100 according to the invention comprises an inlet 1, arranged to receive the main material 10 and an outlet 9 arranged to evacuate the main material 10 and one or more secondary materials 20, 20 '. In the illustrated example, there are two secondary materials 20, respectively 20 '. It should be understood, however, that the invention is not limited to this particular embodiment, and that it suffices to have only one secondary material 20 (or 20 ').

As indicated by the arrow B in FIG. 1, the main material 10 flows into the main chamber 5 of the device 100 according to the invention from the inlet 1 to the outlet 9 by the effect of gravity.

The metering device 100 according to the invention comprises at least one opening 8 disposed between the inlet 1 and the outlet 9, and which is arranged to receive the secondary material 20 in the main chamber 5. In the illustrated example the device 100 comprises two openings 8, respectively 8 '.

The openings 8, 8 'are arranged to allow the arrival in the main chamber 5 of the (the) secondary material (s) 20, 20'.

The upper part of the main chamber 5 of FIG. 1, that is to say the part closest to the inlet 1, has a substantially parallelepiped shape defined by at least one side wall 3. Of course, the parallelepiped shape is not limiting and any other shape ( for example hemispherical, cylindrical circular section, prismatic, etc.) can be considered. The lower part of the main chamber 5 of FIG. 1, that is to say the part closer to the outlet 9, has a substantially frustoconical shape, with the tip of the cone directed towards the outlet 9. In this case too, the cone shape is not limiting and any other form (eg pyramidal, etc.) may be considered.

The metering device 100 of FIG. 1 comprises two feeds of secondary materials 2, respectively 2 ', which allow the arrival of the secondary materials 20, 20' respectively in the main chamber 5 through the openings 8, respectively 8 '.

In a variant, the feeds of secondary materials 2, 2 'form a single piece with the metering device 100. In another variant, they are separate parts of the metering device 100 and are connected to the metering device. fixed or removable.

The main chamber 5 fills with primary material and / or secondary as this material is consumed by the device downstream, located under the metering device 100, such as an extruder 4.

The material that fills the main chamber 5 consists partly of the main material 10 and partly secondary materials 20, 20 '. Each material 10, 20, 20 'flows into the main chamber 5 by the effect of gravity.

The main material 10 flows from the inlet of the main chamber 1, while the secondary materials 20, 20 'are conducted inside the main chamber 5 by the secondary material feeds 2, 2' . It is noted that these secondary material feeds 2, 2 'comprise tabs or baffles 6' respectively 6 ', which prevent the flow of the main material 10 in the zone 7 respectively 7' below and in line with said deflectors 6 , 6 '. In this way, the baffles 6 'and 6' respectively allow the only secondary materials 20 'respectively 20' to fill this zone 7 respectively 7 '.

In other words, the device according to the invention comprises at least one tongue 6 which is arranged in the main chamber 5 in correspondence of the opening 8, through the side wall 3, so as to prevent the flow of the main material 10 in the zone 7 located under this tab 6, between this tongue 6, a side wall 3 of the chamber 5 and the outlet 9 of the device 100, and so as to allow, in this zone 7 only, the gravity flow of the secondary material 20. Preferably, this tongue 6 is inclined and oriented downwards from the side wall 3 towards the opposite portion of the side wall 3 of the main chamber 5.

In a preferred embodiment, illustrated for example in FIG. 1, only part of the tongue 6 enters the main chamber 5, the other part remaining outside this chamber 5.

The secondary material 20, when it leaves the confinement zone 7 defined by the tongue 6, the side wall 3 of the main chamber 5 and the outlet 9, moves substantially at the same speed as the portion of the main material 10 having bypassed the tongue 6.

In a variant, the tongue 6 comprises an upper surface 60 (visible for example in FIGS 3A and 3B), that is to say its surface closer to the inlet 1 of the device, on which slides the main material 10 without being able to pass through it, and a lower surface 62 (visible for example in FIGS 3A and 3B), that is to say its surface closer to the outlet 9 of the device, and opposed to the surface superior 60.

In the variant illustrated in FIGS. 3A and 3B, the tongue 6 has a substantially parallelepiped shape, of small thickness, and therefore the surfaces 60, 62 are substantially parallel. This form is however not limiting. For example in another variant, the surfaces 60, 62 may not necessarily be parallel or planar.

In the variant illustrated in FIG. 1, the portion of the tongue 6 which enters the main chamber 5 comprises an end 64, substantially parallel to the direction of flow of the main material and the secondary material and indicated with the arrow B. This end 64 of curved shape downwardly advantageously makes it possible to guide the secondary material 20 more effectively in the main chamber 5, delimiting the confinement zone 7. This is illustrated by the dashed vertical lines in FIG. 1 which are in the vertical extension of the ends of the tongues 6, respectively 6 ', and which indicate the virtual separation between the main material 10 and secondary materials 20, 20' during their flow. These lines do not therefore correspond to any concrete or physical element separating the two subjects.

With such an arrangement, we take advantage of the property relative to the substantially constant speed of each element of matter, main or secondary. Indeed, the limit of the flow zone of the main material 10 and the secondary material 20, which corresponds to the limit between the zones 5 and 7 vertically above the edges of the tongue 6, including its end 64, is approximately vertical, except when approaching the conical portion or in the conical portion which forms the lower portion of the side wall 3 of the main chamber 5.

Each tongue 6, 6 'may constitute a one-piece piece with the secondary material feeds 2, respectively 2'. In another variant, the tongues 6, 6 'are separate parts from the secondary material feeders 2, 2' and are connected to the respective supply of secondary material 2, 2 'in a fixed or removable manner.

In the variant illustrated in FIG. 1, the tongue 6 forms an angle a, visible in FIG. 1, with respect to the outer face of the vertical side wall 3 of the main chamber 5, and in particular the portion of this outer face which is above the tongue 6. The value of this angle a is chosen so as to ensure that on one side the main material 10 can slide on the upper surface 60 of the tongue 6, and that on the other side the secondary secondary material 20 can come into contact with its lower surface 62.

In a variant, this angle a is greater than 30 °, for example equal to 45 ° or 50 °. This angle must be less than 90 ° to allow gravity flow of the secondary material into the main chamber 5.

In a preferred embodiment, each tongue 6, 6 'is movable, that is to say it can change position in time, by a translational movement and / or rotation, to change the proportions of the dosage. This change of position of the tongue 6 (6 ') can relate to a change of inclination and / or a modification of the extent of the tongue 6 (6') disposed in the main chamber 5.

However, it should be understood that normally the movement of the tongue 6 is performed before the operation of the metering device 100, and not during this operation. Thus, during the operation of the metering device 100, as a rule there is no moving part (except of course the main and secondary materials 20 (20 ') flowing).

In this regard, in a variant the metering device 100 according to the invention comprises a motor (not shown) arranged to move the tongue 6 (6 ') with respect to the side wall 3 of the main chamber 5, to change the dosage proportions between the main material 10 and the secondary material 20.

In a variant, the tongue 6 can slide in the main chamber 5 with a translational movement as indicated by the arrow A in FIG. 1. In this way, if the tongue 6 enters even more into the main chamber 5, the section s, and therefore the volume, of the zone 7 will be even larger, if on the other hand it leaves more of the main chamber 5 the section s, and therefore the volume, of the zone 7 will be smaller, which allows to vary with precision the proportions of dosage of the secondary material 20 with respect to the main material 10.

In other words, in this variant, the tongue 6 has a variable size in the main chamber 5 because of its displacement, to allow to vary the dosage of different materials. In other words again, the upper surface 60 of the tongue 6 which comes into contact with the main material 10 and / or its lower surface 62 which comes into contact with the secondary material 20 (and therefore the volume of the zone 7) can be adjusted by sliding.

In this case, advantageously the tongue 6 can cooperate with one or more guides 30, as shown in FIGS. 3A and 3B. These guides not only allow to retain and limit the downward movement of the tongue 6 but also serve as secondary deflectors on either side of the tongue 6. Indeed, with the two lateral guides visible in FIGS. 3A and 3B, such as side walls, the tongue 6 forms as an upside down gutter or a flow channel in which the secondary material 20 flows, and around which flows the main material 10.

In the variant of FIG. 3A, these guides 30 are fixed relative to the side wall 3 of the device 100, and the tongue 6 slides relative to these guides 30.

In the variant of FIG. 3B, these guides 30 are movable relative to the side wall 3 of the device 100 in the direction indicated by the arrow D.

The presence of these guides 30 improves the dosing accuracy. In the case where one side of the tongue 6 is against one of the side walls 3 of the main chamber 5, it is not necessary to add a guide on this side. In the case where the tongue 6 has a width L (visible for example in FIG 3A) corresponding to the width of the main chamber 5, it is also not necessary to use the guides 30, the walls of the chamber main 5 realizing the function of these guides.

In another variant the tongue 6 is telescopic, so its dimensions, including its length, can change with the same sliding effect described above.

As previously stated, for the secondary material 20 to completely fill the zone 7, it must also remain in contact with the lower surface 62 of the tongue 6. To allow a good flow of particles of the secondary granular material 20, the width L of the tongue 6, therefore of the flow chimney, must be sufficient. Typically, the width L of the tongue 6 is greater than 5 to 10 times the average particle size (20 to 40 mm for 4 mm granules). The choice of the angle α and the width L of the tongue 6 will have to take into account the flow properties of the secondary material used.

In a variant, the tongue 6 can rotate in the main chamber 5 relative to the side wall 3 of the device 100 with a rotational movement as indicated by the arrow C in FIG. 1 for the tongue 6 '. In this way, if the free end of the tongue 6 'back to the input 1 during its flip-flop movement, the section s', and therefore the volume, of the zone 7' will be even larger, if on the other hand it goes down to the outlet 9, the section s', and therefore the volume, of the zone 7 'will be smaller, which also makes it possible to vary the dosage proportion of the secondary material 20' with respect to the main material 10 .

In other words, in this variant, the tongue 6 'has a variable size in the main chamber 5 because of its rotation, to allow, by this variation of inclination of the tongue 6', to vary the relative dosage of different materials. In other words again, the volume of the zone 7 'can be adjusted by rotation of the tongue 6'.

In another variant, the translational and rotational movements of the tongue 6 (and / or the tongue 6 ') can be combined.

In the variant of FIG. 1, the main chamber 5 comprises lateral walls 3 substantially vertical (that is to say substantially parallel to the direction of the force of gravity indicated with the arrow B) at least for a certain length downstream (below) of the tongues 6, 6 ', so that the main material 10 and the secondary materials 20, 20' move downstream of the tongues 6, 6 substantially at the same speed.

The height of the portion of the chamber 5 located below the tongues 6, 6 'is preferably greater than or equal to the largest width of the chamber 5. Moreover, this height, but also the angle of the part conical at the bottom of the chamber 5 (preferably but not exclusively less than 45 ° from the vertical), also contribute to the homogeneity of the falling speeds of each element of matter, main or secondary.

The ratio between the flow of main material 10 entering the main chamber 5 and the flow rates of the secondary components 20, 20 'is proportional to the ratio of the section S of the zone occupied by the main material 10 and the sections s, corresponding to the zones 7, 7 'occupied by the secondary material 20, 20', which correspond to the section s, s 'in vertical projection of the tongues 6, 6' (as visible in FIG 2).

This ratio also depends on the apparent densities of the materials under consideration. In the context of the present invention, the term "bulk density" p (or "bulk density") refers to the ratio of the mass of a material contained in a given volume, including the volume of interstitial air, and the given volume. If the material is constituted by a granule or a particle for example, the apparent density makes it possible to take into consideration the empty spaces between the different granules / particles.

The ratio R of mass flow rate between the flow rate of the secondary material 20 and the total flow rate is given by the following formula: (1) in which: - pi designates the bulk density of the main material 10 - p2 denotes the density apparent from the secondary material 20 - S the horizontal section (i.e., perpendicular to the flow direction of the materials 10, 20 as indicated by the arrow B in Fig. 1) of the main chamber 5 at the tongue 6 (visible for example in Fig. 2) - the horizontal section of the tongue 6 in the main chamber 5 (visible for example in Fig. 2).

If the bulk density of the main material 10 pi is substantially equal to that p2 of the secondary material 20, then (2) With (1) and (2) which are approximate, because they do not no differences in the density of other auxiliary components (20 ', ...) or slight variations in speed of the material elements in the different sections.

In other words, the ratio R of mass flow rate between the flow rate of the secondary material 20 and the total flow rate are related to the ratio of the section s occupied by the tongue 6 in the main chamber 5 and the section S of the metering chamber 7 at the level of the tongue 6.

As discussed, the section s occupied by the tongue 6 in the main chamber 5 can be adjusted by sliding and / or rotation, to change the dosage of the corresponding materials.

For proper operation of the system, the main chamber 5 preferably comprises the main material 10, at least at the level (at the height) of the tabs 6, in order to dose in the right proportions this main material 10 with the material secondary 20, by a simultaneous descent of the two materials, main and secondary. In this regard, the device 100 according to the invention may comprise a sensor (not shown), for example and without limitation a capacitive sensor, placed for example in correspondence of the inlet 1 of the main chamber 5, in order to verify the presence of the main material 10 in the main chamber 5. In the absence of main material 10, the arrival of the secondary materials 20, 20 'is immediately stopped. The optimal position of this sensor is calculated according to the section ratios s and S. In another variant the arrival of the secondary material 20 is stopped automatically when the main material 10 is missing.

To compensate for dosing inaccuracies due to the fact that the velocities of the materials are not perfectly equal in the exit zone of the deflectors 6, 6 ', the device 100 according to the invention may comprise an on-line measuring device of flow rate of different materials (not shown), for example a device for optical volume flow measurement ("Cinegran") and / or a gravimetric weight loss measurement device ("loss-in-weight").

In this case, the device according to the invention may also comprise an electronic module (not shown) for controlling the size and / or the position and / or the movement of the tongues 6, 6 'to obtain the desired dosage.

It should be noted that in case of failure of the measuring device and / or the electronic module, it is always possible to perform the dosing of different materials but passively, using only the force of gravity.

When the desired dosage for one of the materials is low, for example of the order of magnitude of a few percentage units or less, it may be that the device as described above is difficult to put in place in practice, because the tongue 6 would be very small. It must also be considered that particles and / or granular materials flow poorly in too confined spaces.

A solution to this problem is visible in FIG. 4: instead of being directly in the main chamber 5, the tongue 6 for the metering of the secondary material 20 is located in a secondary chamber 50, itself located in the main chamber 5. The device is made in such a way that the main material 10 flowing from the top of the main chamber 5 also fills the secondary chamber 50.

The material leaving the secondary chamber 50 will have a ratio R 'mass flow between the secondary material 20 and all the material passing through the secondary chamber 50, depending on the section S'de the secondary chamber 50 to the inlet of the deflector 6, which is given by the following formula:

(3) [0071] The granular material present in the secondary chamber 50 flows into the main chamber 5 through an outlet channel 90 of section S ", such that S" <S '.

Let So the section of the main chamber 5 at the outlet of the secondary chamber 50, and still considering a relatively constant flow of the granules in this horizontal section, the final ratio R "mass flow between the secondary material and the whole of the material (principal + secondary) follows as a first approximation the following relation: (4) [0073] In the case where the bulk density of the main material 10 ρΊ is substantially equal to that p2 of the secondary material 20, then (5) [0074] In another variant not illustrated, the material of the main chamber 5 can flow itself after reduction, in another chamber also filled with the main material.

The invention also relates to a metering and extrusion system of a main material 10 and at least one secondary material 20 comprising: - the metering device 100 as described above, - a machine, for example an extruder 4.

The invention also relates to a method for metering a main material 10 and at least one secondary material 20, comprising the following steps - receiving the main material 10 in correspondence with an inlet 1 of a chamber main part 5 of a metering device 100, - flow of the main material 10 in the main chamber 5, from the inlet 1 to an outlet 9 of the metering device 100 by the effect of gravity, - receiving the material secondary 20 in correspondence of an opening 8 between the inlet 1 and the outlet 9 of the metering device 100, - flow of the secondary material 20 by the effect of gravity only in an area 7 located between a tab 6 arranged for entering the main chamber 5 in correspondence of the opening 8, a side wall 3 of the main chamber 5 and the outlet 9, the tongue 6 preventing the flow of the main material 10 in this zone 7.

Reference numerals used in figures [0077] 100 Dosing device A Sliding direction of tongue B Direction of material flow C Tongue rotation arrow D Guide sliding direction L Tab width 1 Input

2, 2 'Supply of secondary material 3 Side wall 4 Extruder 5 Main chamber 6,6' Tab 7, 7 'Containment area 60 Top surface 62 Bottom surface 64 End 8,8' Aperture 9 Outlet 10 Main material 20, 20 ' Secondary Matter 30 Guide 50 Secondary Chamber 90 Exit Channel

Claims (14)

claims A device (100) for metering at least one secondary material (20) into a main material (10) comprising a main chamber (5), said chamber comprising: an inlet (1) arranged to receive the main material (10); ), an outlet (9) arranged to discharge the main material (10) and the secondary material (20), the main material (10) flowing from the inlet (1) to the outlet (9) by the effect gravity an opening (8) between the inlet (1) and the outlet (9), said opening (8) being arranged to receive in the main chamber (5) the secondary material (20), a tongue (6) in the main chamber (5) in correspondence of said opening (8), so as to prevent the flow of the main material (10) in an area (7) located between said tongue (6), said outlet (9) and a side wall (3) of said main chamber (5), and so as to allow in said zone (7) only gravity flow of the secondary material (20). 2. Device according to claim 1, comprising a motor arranged to move the tongue (6) relative to said side wall (3) of said main chamber (5). 3. Device according to claim 2, said motor being arranged to move the tongue (6) by sliding. 4. Device according to claim 3, comprising at least one lateral guide (30) cooperating with said tongue (6) during sliding. 5. Device according to claim 2, said motor being arranged to move the tongue by rotation relative to said side wall (3). 6. Device according to one of claims 1 to 5, said tongue forming an angle (a) relative to the side wall (3) of the main chamber (5). 7. Device according to the preceding claim, said angle (a) being between 30 ° and 90 °. 8. Device according to one of claims 1 to 7, wherein the mass flow ratio between a flow rate of the secondary material (20) and a total flow is related to the ratio between the section (s) occupied by the tongue (6). ) in the main chamber (5) and the section (S) of the metering chamber (7) at the tongue (6). 9. Device according to one of claims 1 to 8, comprising a device for measuring the flow of the main material (10) and / or secondary (20). 10. Device according to the preceding claim, comprising an electronic module for controlling the size and / or position and / or movement of the tongue (6) according to a flow measurement of the main material (10) and / or secondary (20) performed by said flow measuring device, to obtain the desired dosage. 11. Device according to one of claims 1 to 10, said tongue (6) comprising an end (64) substantially parallel to the flow direction of the main material (10) and secondary (20) in the main chamber (5). ), to better guide the secondary material (20) in the main chamber (5). 12. Device according to one of claims 1 to 11, comprising a secondary chamber (50) located in the main chamber (5) and arranged so that the main material (10) flowing in the main chamber (5) also fills the secondary chamber (50), the secondary chamber (50) comprising an inlet arranged to receive the main material (10), an outlet (90) arranged to discharge the main material (10) and the secondary material (20), an opening between the inlet and the outlet, said opening being arranged to receive in the main chamber (5) the secondary material (20), a tongue (6) in the secondary chamber (50) corresponding to said opening, so preventing flow of the main material (10) in an area (7) between said tongue (6), said outlet and a side wall (3) of said secondary chamber (50), and so as to allow in said zone (7) only the flow by gravity of the secondary material (20). 13. System for metering and extruding a main material (10) and at least one secondary material (20) comprising: - the metering device (100) according to one of the preceding claims; an extruder (4). 14. A method for determining a main material (10) and at least one secondary material (20), comprising the following steps - receiving the main material (10) in correspondence of an input (1) of a main chamber (5) of a metering device (100), - flow of the main material (10) in the main chamber (5), from the inlet (1) to an outlet (9) of said metering device ( 100) by the effect of gravity, - receiving the secondary material (20) in correspondence of an opening (8) between the inlet (1) and the outlet (9) of said metering device (100), - flow of the secondary material (20) by the effect of gravity only in an area (7) located between a tab (6) arranged to enter the main chamber (5) in correspondence of the opening (8), a side wall (3) of the main chamber (5) and said outlet (9), said tongue (6) preventing flow of the main material (10); ) in said zone (7).