FIELD OF THE INVENTION

The present invention concerns the particle grinding field and, in particular, a fluid grinding mill.

KNOWN ART

Mills and, in particular, the fluid energy mills date back to the first years of the twentieth century and divide in two typologies: with fluid "spiral" or "oval" jets and with opposed fluid jets.

Current spiral or oval fluid jet mills have been improved in the last fifteen years and usually comprise a grinding chamber providing for a series of nozzles circumferentially arranged in the grinding chamber. The nozzles put a fluid in the gaseous form into the fluid chamber in order to generate a spiral vortex of the material introduced into the chamber. The material supported by the fluid and, in particular, the material particles grind themselves by colliding one with another, thereby reducing their own particle size.

However the Applicant observed that currently known fluid grinding mills do not allow obtaining particle sizes smaller than one micron.

There are other typologies of mechanical mills allowing to obtain measures smaller than one micron.

However the Applicant observed that such typologies of mechanical mills get warm, typically increasing of at least 30° the treated product and, for this reason, are not adapted to be used in pharmaceutical field, cosmetic field and food industry.

The Applicant further observed that this typology of mechanical mills can pollute the treated product, due to the lubrication fluids necessary for their operation.

Therefore the Applicant posed the problem of implementing a grinding mill allowing to obtain a particle size smaller than one micron and, at the same time, not having the drawbacks of the mechanical mills in terms of overheating and pollution of the treated products.

SUMMARY OF THE INVENTION

Therefore, a first aspect of the present invention concerns a fluid grinding mill comprising:

- at least one feeding device to feed the product to be ground;

at least one grinding chamber comprising an inner perimeter; said grinding chamber being connected to said feeding device to feed the product to be ground;

at least one cyclone separator downstream of said grinding chamber; characterized in that said grinding chamber comprises:

at least one first plurality of injecting nozzles to inject process fluid into the grinding chamber; the nozzles of said at least one first plurality are angularly spaced out along the inner perimeter of said grinding chamber; each nozzle having an angle (a) with respect to said inner perimeter of the grinding chamber;

at least one second plurality of injecting nozzles to inject process fluid into the grinding chamber, the nozzles of the second plurality being spaced out longitudinally in said grinding chamber with respect to the nozzles of said first plurality of nozzles; the nozzles of said at least one second plurality are angularly spaced out from one another along the inner perimeter of said grinding chamber;

selecting means adapted to selectively activate which of the plurality of nozzles has to be operated depending on the process and the grinding particle size to be obtained.

In the above said aspect, the present invention can have at least one of the preferred characteristics hereinafter described.

In the scope of the present invention with "longitudinal direction" or "longitudinally" is meant a general direction coincident or parallel with the extension axis of the grinding chamber, in the shown embodiment the extension axis of the grinding chamber corresponds to the symmetry axis of the grinding chamber. Preferably, the grinding chamber comprises angle adjusting means to angularly adjust the position of each nozzle of said at least one plurality of the first nozzles with respect to the inner perimeter of the grinding chamber.

Conveniently, the selecting means are adapted to change an inner height, measured in the longitudinal direction, of the grinding chamber so that to vary the inner volume of the mixing chamber and to selectively select whether all plurality of nozzles, or only one or more, are allowed to give onto the inside of the mixing chamber thereby putting pressurized fluid into the grinding chamber.

Preferably, the selecting means for selectively controlling the activation of the plurality of nozzles comprise at least two opposed lids of the grinding chamber, at least one lid being longitudinally movable in order to change its position and/or an inner height (H) of the grinding chamber thereby allowing all plurality of nozzles, or only one or more, to put pressurized fluid into the grinding chamber.

Advantageously, each lid is keyed on a threaded shaft rotated by convenient motor means, the rotation of said shaft by said motor means entailing the translation of at least one lid.

Preferably, there are sealing elements circumferentially arranged on the outside of each lid.

Preferably, each nozzle of said at least one second plurality of nozzles is angled with respect to the inner perimeter of the grinding chamber.

Conveniently, the grinding chamber comprises angle adjusting means to angularly adjust the position of each nozzle with respect to said perimeter.

Conveniently, the feeding device to feed the product to be ground into the grinding chamber comprises a Venturi tube able to accelerate the particles of the product entering the grinding chamber up to a speed comprised in the range 20 - 100 m/s.

Preferably, the mill comprises a classifier between the grinding chamber and the cyclone separator; the classifier comprising a head portion adapted to penetrate into said grinding chamber and adjusting means adapted to adjust the penetration value of said head portion into the grinding chamber.

Advantageously, the mill comprises at least one cyclonic separator comprising at least one first filter and at least one second filter.

Conveniently, the first filter comprises at least one cylindrical bag.

Preferably, said nozzles of said at least one first and at least one second plurality of nozzles are of convergent-divergent type.

Further characteristics and advantages of the invention will be more evident from the detailed description of some preferred embodiments, but not exclusive, of a fluid grinding mill according to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Such a description will be hereinafter explained referring to the attached drawings, provided for purposes of illustrations only, and thereby not limitative, wherein:

figure 1 shows a perspective schematic view of a fluid grinding mill according to the present invention;

figure 2 shows a sectional view of the grinding chamber and the Venturi tube according to the present invention, in a first shape of the grinding chamber;

figure 3 shows a sectional view of the grinding chamber and the Venturi tube according to the present invention, in a second shape of the grinding chamber;

figure 4 is a sectional view of a portion of the grinding chamber of figure 2 and 3;

figure 5 is a sectional view of the grinding chamber and the classifier according to the present invention; and

figure 6 is a schematic view of an alternative embodiment of a cyclonic separator according to the present invention.

DETAILED DESCRIPTION OF SOME EMBODIMENTS OF THE INVENTION

Referring to figures, a fluid grinding mill according to the present invention is denoted with the numeral reference 100.

The fluid grinding mill 100, as shown in figure 1 , comprises a feeding device 2 to feed the product to be ground, a grinding chamber 3 and at least one separating cyclone 4 downstream of the grinding chamber 3 and adapted to separate the ground product obtained in the desired particle size from the fluid carrier.

Referring to the embodiment shown in figures 2 and 3, it can be seen that the feeding device 2 to feed the air is a Venturi tube 13 having an inlet 13' for the product to be ground and a second inlet 13 " for the process fluid or fluid carrier.

The Venturi tube 13 is connected to the grinding chamber 3. The Venturi tube sucks the material to be ground from a first inlet 13 ', whereas the Venturi tube sucks the process fluid from the second inlet 13 " .

Inside the Venturi tube 13 the material to be ground is mixed with the process fluid, therefore the process fluid supports the material to be ground as dispersed powder.

The Venturi tube 13 is sized for giving to the material to be ground entering the mixing chamber 3 an acceleration in the range from 20 to 100 m/s, depending on the process fluid pressure and the mass of the product to be ground. Preferably, the Venturi tube 13 is sized for giving to the material to be ground entering the mixing chamber 3 an acceleration in the range from 30 to 60 m/s.

The grinding chamber 3 has a substantially cylindrical shape with a diameter D in the range from 18 to 160 mm and an inner height H in the range from 2 to 300 mm.

The inner height H of the grinding chamber 3 can vary during the grinding process, as better described in the following.

The grinding chamber 3 comprises at least one first plurality of injecting nozzles 5 to inject process fluid into the grinding chamber 3, the process fluid exiting from the nozzles 5 further accelerate the flow of gas and material to be ground that takes a spiral arrangement due to the circular shape of the grinding chamber 3 and to the arrangement and tilt of the nozzles 5.

The number of nozzles 5 of the first plurality of nozzles can vary from 2 to 15 depending on the diameter of the first mixing chamber 3.

By way of example, for a mixing chamber 3 with diameter D in the range from 20 to 60 mm, a number of 3 to 8 nozzles could be recommended, on the contrary for a grinding chamber 3 with diameter D in the range from 60 to 100 mm, a number of nozzles from 4 to 10 could be recommended and, lastly, for a grinding chamber 3 with diameter D in the range from 100 to 150 mm a number of nozzles from 4 to 12 could be recommended.

The nozzles 5 of the first plurality, as better shown in figure 4, are angularly spaced out along the inner perimeter of the grinding chamber 3, preferably the nozzles 5 of the first plurality are spaced out at equal angles along the inner perimeter of the grinding chamber 3. In other terms, substantially they are all at the same mutual circumferential distance.

Each nozzle 5 of the first plurality is angled or tilted with respect to the inner perimeter of the grinding chamber so that to form an angle a in the range from 3° to 70°, preferably from 5° to 60°.

The grinding mill 100 according to the present invention comprises angle adjusting means to angularly adjust the position of each nozzle 5 with respect to the inner perimeter of the grinding chamber 3.

The angle adjusting means are such to allow a variation of the angular a in the range from 0 to 45° with respect to the base angle. In other terms, if the base angle a previously fixed for a process is equal to 30°, such an angle will have to be varied during the process or between a process and the following one, for example by adding or subtracting 15° depending on the particle size to be obtained.

According to a first embodiment, the adjusting means comprise a toothed ring nut not shown in figure and circumferentially arranged outside of the nozzles 5. The ring nut is engaged with a toothed end of each nozzle 5. The toothed end is a portion of cogwheel. Each nozzle 5 is further pivoted to angularly rotate with respect to the perimeter of the chamber 3. By rotating the ring nut, the toothed end of each nozzle 5 is activated and, consequently, the angular rotation thereof with respect to the inner perimeter of the grinding chamber 3 is driven. The ring nut can be moved manually or by a mechanical or oleo-pneumatic system.

Different angle adjusting means can be provided without departing from the protection scope of the present invention.

The nozzles 5 of the first plurality of nozzles are nozzles of the convergent- divergent type or "de Laval" nozzles and are supersonic exhaust nozzles.

Referring to the embodiment shown in figure 3, it can be seen how the grinding chamber 3 comprises a second plurality of nozzles 6.

The nozzles 6 of the second plurality are angularly spaced out along the inner perimeter of the grinding chamber 3, preferably the nozzles 6 of the second plurality are spaced out at equal angles along the inner perimeter of the mixing chamber 3. In other terms, substantially they are all at the same mutual circumferential distance.

The second plurality of nozzles 6 is arranged in said grinding chamber as longitudinally spaced out with respect to the first plurality of nozzles 5.

Referring to figure 3, it can be seen that the nozzles 6 are arranged on the same plane being on the right and longitudinally spaced out with respect to the plane containing the nozzles 5 of the first plurality.

The second nozzles 6 of the second plurality of nozzles can be of the same amount of the first nozzles 5 of the first plurality of nozzles.

Alternatively, the second nozzles 6 can be of higher or lower amount, without departing from the protection scope of the present application.

Moreover, the second nozzles 6 may even not be arranged in a position corresponding to the first nozzles 5.

In a not shown embodiment, the grinding chamber 3 comprises a third plurality of nozzles.

The nozzles of the third plurality are angularly spaced out along the inner perimeter of the grinding chamber 3, preferably the nozzles 7 of the third plurality are spaced out at equal angles along the inner perimeter of the grinding chamber 3.

The third plurality of nozzles is arranged in the grinding chamber as longitudinally spaced out with respect to the first and second pluralities of nozzles.

According to this embodiment, the nozzles of the third plurality are all arranged on the same plane. Such a plane is longitudinally spaced out with respect to the plane containing the nozzles 5, 6 of the first and second pluralities.

The nozzles of the third plurality of nozzles can be of the same amount of the nozzles 5, 6 of the first and second pluralities of nozzles.

Alternatively, the third nozzles can be of higher or lower amount than the nozzles 5 or 6 of the first or second plurality, without departing from the protection scope of the present invention.

Moreover, the nozzles of the third plurality can even not be arranged in a position corresponding to the nozzles 5, 6 of the first or second plurality of nozzles. Additional pluralities of nozzles can be provided, each one spaced out in the longitudinal direction, without departing from the protection scope of the present invention.

The nozzles 5, 6 inside the grinding chamber 3 are such that the particles to be ground will reach a speed in the range from 10 m/s to 1800 m/s.

Advantageously, the mill 100 comprises selecting means adapted to selectively activate the plurality of nozzles depending on the process and the grinding particle size to be obtained.

In other terms, all the pluralities of nozzles can be in use during the grinding process (in the case shown in figure, both the pluralities of nozzles), or only one or more depending on the process and the grinding particle size to be obtained.

The selecting means 9 for selectively controlling the activation of the plurality of nozzles comprise the two opposed lids 14, 15 of the grinding chamber 3. Each lid 14, 15, being longitudinally movable in order to change the inner height H measured in the longitudinal direction of the grinding chamber 3 and then to selectively select whether all plurality of nozzles 5, 6, or only one or more, are allowed to put pressurized fluid into the grinding chamber 3.

Referring to the embodiment shown in figure 2, it is possible to move the lids 14, 15 so that only the first plurality of nozzles 5 can put pressurized fluid into the grinding chamber 3 or, as shown in figure 3, it is possible to move the lids 14, 15, or only one of them, so that, by increasing the height H, also the second plurality of nozzles 6 gives onto the inside of the mixing chamber 3 thereby being able to put pressurized fluid therein.

The lids 14, 15 can be in fact moved from a first configuration, in which their mutual distance and consequently the height H of the grinding chamber 3 are such that only the nozzles 5 can put process fluid into the grinding chamber 3 by having a second configuration in which the mutual distance between the two lids 14, 15, or the height H of the grinding chamber 3, is increased so that also the nozzles 6 of the second plurality of nozzles give onto the inside of the grinding chamber 3 thereby being able to put pressurized fluid therein.

In other terms, by varying the mutual distance of the lids 14, 15 it is possible to determine whether only one plurality of nozzles (for example the plurality of nozzles 5) or several pluralities of nozzles are present on the side wall of the grinding chamber 3.

Alternatively, still according to this embodiment, it is possible to change the position of the lids 14, 15 so that there will be only the second plurality of nozzles 6 giving onto the inside of the mixing chamber 3 and putting process fluid therein.

If more pluralities of nozzles are provided and longitudinally spaced out from one another, the movement of the lids 14, 15 would allow selecting a plurality of nozzles, for example a third plurality, with a given angle a of the nozzles or another plurality, for example the second one, with another given angle a or, again, increasing the height H of the inner chamber so that several plurality of nozzles can operate, for example the first and the second pluralities of nozzles or all together, each one with its own angle a.

In other terms, by varying the position of the lids 14, 15 it is possible to translate, increase or decrease the inner volume of the grinding chamber 3 by allowing only one plurality of nozzles, or all the pluralities of nozzles or part of them (for example the second and the third plurality of nozzles), giving onto the inside of the grinding chamber 3. To move the lids 15 and 14, each of them is keyed on a threaded shaft rotated by convenient motor means, the shaft rotation by the motor means causing the translation of at least one lid 14, 15, whereas the rotation in the other shaft way causes the translation of at least one lid 14, 15 in the other way.

Two O-rings 19 are provided as sealing elements and circumferentially arranged on the outside of each lid so that sealing is obtained.

Each O-ring 19 is therefore positioned between a lid 14, 15 and the side wall of the mixing chamber 3.

The grinding chamber 3 is connected via a duct 17 to a cyclone separator 4. The duct 17 leading the ground product supported by the carrier gas to the separating cyclone comprises a classifier 8.

Referring to the embodiment shown in figures 2, 3 and 5, the classifier 8 is a tubular element concentrically assembled inside the threaded shaft.

The classifier 8 is placed between the grinding chamber 3 and the cyclone separator 4 and has a head portion 8' adapted to penetrate into the grinding chamber 3, as shown in figure 5.

The head portion 8' of the classifier is usually circular or inscribable in a circumference.

Preferably, the circumference of the classifier head has a diameter from 5 to 50 mm.

By varying the penetration depth of the head of the classifier 8 into the grinding chamber 3, it is possible to further vary the particle size of the product.

In other terms, by increasing the penetration of the classifier head into the chamber, the particle residence time inside the grinding chamber 3 increases, thus obtaining further particle collisions that will lead to a further decrease of the particle size.

For this purpose, the mill according to the present invention has penetration adjusting means adapted to adjust the penetration value of the head of the classifier 8 into the grinding chamber 3.

The penetration adjusting means are adapted to allow varying the penetration depth from 5 to 50 mm and can be of mechanical, hydraulic or pneumatic type.

Downstream of the connecting duct 10 there is a cyclone separator 4.

In a known way, the separating cyclone 4 comprises on top a vent 21 for the carrier gas and, on the bottom, a tank 22 for the collection of the ground product.

The cyclone separator 4 comprises at least one first filter 23 and at least one second filter 24.

The first filter 23 is an antistatic bag filter and is preferable made of polyester, serving to prevent the ground product now with the desired particle size from dispersing in the environment, instead of falling in the collection tank 22.

In order to increase the fluid-solid separation efficiency, the first filter has a cylindrical base with a plurality of cylindrical bag 24, which are reciprocally placed side by side and substantially extend vertically from said base.

Each bag 24 has a diameter d in the range from 10 to 30 mm.

The number of bags can vary from 1 to 20.

The extent in the substantially vertical direction of each bag 24 is comprised in the range from 50 to 200 mm.

The second filter 25 is a filter of known type, for example an absolute cartridge filter usually named ULPA, and is for filtering the carrier gas before the dispersion thereof in the environment against possible material particles, with a size lower than 0.2 microns, still dispersed therein.

To the embodiments herein represented in detail various modifications can be made, anyway remaining in the protection scope of the invention, defined by the following claims.