EP2164633A2

EP2164633A2 - Industrial planetary mill for producing nanomaterials using mechanochemical processes

Info

Publication number: EP2164633A2
Application number: EP08790029A
Authority: EP
Inventors: Renato De Silva; Paolo Plescia; Andrea Bianco; Luigi De Notaris
Original assignee: Assing SpA
Current assignee: Assing SpA
Priority date: 2007-06-27
Filing date: 2008-06-27
Publication date: 2010-03-24
Also published as: WO2009001397A8; WO2009001397A3; ITRM20070364A1; WO2009001397A2

Abstract

An industrial mill for the production of materials having a nanometric and/or micrometric grain size using mechanochemical processes is characterized in that it comprises, in combination, a rotating assembly (G) with two or more jars (3) designed to rotate about a central vertical axis (A) of the rotating assembly itself and about their own axis of vertical symmetry (B) via a purposely designed kinematic chain of transmissions and gears (4, 5) that transmits to each jar (3) a motion of rotation equal and opposite to the rotation of the rotating assembly (G) to obtain triggering of the rotations of grinding masses purposely provided inside the jars (3). In this way, the jars (3) that contain the material to be ground move without ever loosing the orientation with respect to a reference system external to the rotating assembly (G), and grinding via said grinding masses inside the jars (3) takes place substantially by friction and not by impact. Said jars (3) are uniformly distributed about the central vertical axis of rotation (A) of the rotating assembly (G).

Description

INDUSTRIAL PIANET-ARY MILL FOR PRODUCING NANOMATERIALS USING MECHANOCHEMICAL PROCESSES

The subject of the present invention is a newmechanical friction mill for the production of nanomaterials using mechanochemical processes. Thanks to the special form of the movement that is generated in the innovative mill that is described, there is brought about a marked crushing of the material, which rapidly brings the grain size to miσrometric and nanometric dimensions, at the same time generating the chemico-physical conditions necessary for triggering chemical reactions, such as elimination of the structural water and of hydroxyls, reticular destruction of the crystalline materials, sintering of materials that cannot be mixed together, change of phase, etc.

In order to generate such effects, up to the present day ball mills have been used at an industrial level, which present the advantage of having a high productivity but with extremely long treatment times.

The mill according to the present invention, instead, enables for the first time the mechanochemical effects to be achieved in short times. According to a peculiar characteristic of the invention, the mill has been devised and designed for discharging the most part of the mechanical grinding energy not in crushing by impact as the majority of the existing mills, but by friction, as planetary mills . Currently existing planetary mills have never been produced at an industrial scale. Known in the world are some examples of friction mills of medium-to-low scale, such as the Russian vibration mills or the Australian nutation mills (Hicom) or the eccentric mills manufactured by the German firm ZoZ . All these systems work using an eccentric source of movement that accelerates grinding masses inside one or at most two grinding chambers. Said systems never exceed a few hundred kilograms of material treated per hour . Only the Hicom mill can reach higher levels of productivity, but only for mere grinding, whilst for the mechanochemical action said mill has an extremely limited productivity.

In the mill according to the invention, instead, the planetary movement is for the first time brought to an industrial dimensional scale and applied to mechanochemistry, through a peculiar technical solution that enables the productivity to be increased and the material to be kept indefinitely within the jars until conclusion of the process, as well as to be extracted easily through a purposely devised and built system for expulsion of the powder.

The main purpose of the invention is substantially to provide a mechanical apparatus for generating mechanochemical effects in addition to marked grinding (micronization) of the materials treated.

Another purpose of the invention is to provide an apparatus that enables pressures of friction to be reached suitable for triggering chemical reactions on the materials, such as oxidation, reduction, phase change, sintering, amorphization, etc., thus causing formation of micromaterials and nanomaterials . , '

This has been obtained, according to the invention, by providing an innovative mill comprising a rotating assembly with at least two jars that rotate about a central axis and about their own axis, through a complex system of transmissions and gears. This set of gears is designed to transmit to each jar a motion of rotation equal and opposite to the rotation of the rotating assembly so as to enable triggering of rotation of the masses inside the jars so that the jars will move without ever loosing the orientation with respect to an external reference system.

Abetter understanding of the invention will be obtained from the following detailed description with reference to the figures of the attached plates of drawings, which illustrate, purely by way of non-limiting example, a preferred embodiment thereof.

In the plates of drawings:

Figure 1 is a view in elevation that shows a cutaway illustration of the mill according to the invention; Figure 2 is a side view of the mill provided with fixed protection panellings, together with the system for loading the material to be treated from above;

Figure 3 is a front view of the mill of Figure 2, corresponding to that of Figure 1; and Figure 4 is a top view of the mill of Figure 2, in which also visible, in the top part of the figure, are the doors, half-open, for access to the jars.

With reference to Figure 1, the mill according to the present invention is basically constituted by a supporting frame T mounted on which is a rotating assembly, which substantially represents the core of the machine. The rotating assembly is constituted by a cage G made of tubular sectional elements, which is set in rotation by the control assembly or rotation assembly 4 of the mill. The rotation occurs with respect to the geometrical axis A of the cage G, which is set vertically. In the example illustrated, symmetrically arranged about said axis A of the cage G and inside the cage are four cylindrical jars 3, the respective axis of symmetry B of which is also vertical. When the cage G is set in rotation, a complex system of gear transmissions and reductions 4 transmits to each jar 3 the planetary movement of rotation. According to a peculiar characteristic of the invention, it is envisaged that the geometrical axis B of each jar 3 rotates (orbits) about the axis of symmetry A of the cage G, but at the same time each jar 3 rotates in an opposite direction also on itself in such awaythat -with respect to an external observer

- each jar 3 does not rotate about its own axis of symmetry.

In other words each jar 3, which rotates about its own axis B with a relative motion with respect to the cage G, performs a translatory motion with respect to a reference external to the cage itself, according to which each jar 3 translates about the axis A of the rotating assemblywithout changing its own orientation in space. According to the invention, each jar 3 contains inside it a given amount of grinding masses in the form of balls, or bars or full cylinders, which can be made of steel, zirconium, or other suitable material.

The particular type ofmovement to which each individual jar is subjected 3 is such as to generate a relative motion between the internal grinding masses and the jar itself: to be precise, it is a uniform circular motion. In fact, the grinding masses, which are maintained in radial position by the centrifugal force, have a relative motion with respect to the jar precisely on account of the dynamics of themovement of the individual jar 3 with respect to the geometrical axis of rotation A of the rotating assembly G. The centrifugal force to which the grinding masses are subjected enables generation of the necessarypressure of themasses themselves on the internal surface of the jar 3. The combined action of the aforesaid pressure and of the relative uniform circular motion enables generation of the rolling friction and transfer of the energy from the grinding mass to the product to be ground, which tends to penetrate between the grinding mass and the internal surface of the jar 3. The cage G, which, as has been described previously, contains the jars 3 inside it, is located in a fixed structure or frame T, with respect to which it rotates.

In the preferred embodiment described herein, a plurality of fixed external panels (orpanelling) isprovided having the dual function of:

- preventing access to the mobile parts of the machine during operation; and

- providing the tightness required to prevent exit of powder. In the example illustrated, the aforesaid tightness to prevent exit of powder is provided via sliding elements made of felt purposely pre-arranged between the top part of the cage G and the external panelling.

It should moreover be noted that the presence of the panels and of the seals enable also evacuation of the ground material, which is obtained as described in what follows.

Each jar 3 is provided with purposely designed plugs

6 perforated on their own external surface, designed to enable exit of the powder. The perforated plugs 6 can be easily removed and can advantageously be replaced with blind plugs in the case where it proved advantageous to increase the time of permanence of the material within the jars 3. The plugs are arranged at a constant distance from one another in order favour an outflow of the ground material that is regular and uniform. In order to facilitate exit of the ground material, a flow of air is provided generatedbymeans of a fan/aspirator set downstream of the suction line. For said purpose an appropriate connection is provided between the intake mouth of the fan 14 and the air-outlet mouth 15 of the mill (Figure 2) .

The external fixed panels are provided, in an opposite position with respect to the outlet mouth, with an opening for inlet of the environmental air. Said opening is provided with a register for partialization of the flow. The particular current of air, thus purposely created, has precisely the purpose of evacuating the powder, which in this way comes out spontaneously fromthe holes of the lateral plugs of the jars.

Collection of the powder and its separation from the process air is made downstream, by means of a purposely provided cyclone or bag filter with abatement pre-chamber.

The use of the system envisages control of the intake via the register on the intake of the air 14 into the mill.

In this connection, it should be noted that the presence of the register is particularly important for regulating the flow of air that conveys the ground materials towards the outside : an excessively limited opening leads to clogging of the jars, whilst an excessively wide opening determines an excessive intake,' with consequent possibility of drawing in particles that have not yet been ground and that could pass through the plugs of the jar before being micronized. Optimal adjustment depends upon the degree of opening chosen for the register, which must be consequently chosen in an intermediate position such as to prevent both of the drawbacks described above. In the design stage of the experimental prototype, particular attention has been paid to the problems that would derive from the mechanical vibrations consequent upon the considerable rotating masses and their possible dynamic unbalancing. For this reason, it has been deemed necessary to provide an apparatus presenting geometrical symmetry. It may be noted in fact that the geometrical axis B of each of the jars 3 is eccentric with respect to the main axis of movement, which is the geometrical axis A of the cage G. Said eccentricity would have caused a dynamic unbalancing that would have been problematical to neutralize and that above all would not have provided guarantees of reliability of the mill over time.

From what has been said up to now, it is evident that the mill can be made with a number of jars 3, which can range from two upwards, provided that they are arranged in symmetrical positions about the axis of rotation A of the cage G, thus enabling a balanced mechanical ensemble to be provided in which the moving masses mutually compensate for the unbalancing that they would otherwise generate individually.

In order to optimize the yield of the mill in the different operating conditions and as the type of the materials treated by the mill itself varies, it is possible to modify the speed of rotation of the motor M continuously. Said variation is preferably carried out with a square inverter. It should be noted that, unlike the other adjustments mentioned above (e.g., replacement of perforated plugs with blind plugs) the variation of the speed can be carried out whilst the mill is in operation. This type of adjustment can be carried out only by subtraction: the nominal r.p.m. is the maximum one, at the mains frequency of 50 Hz, equal to approximately 300 r.p.m. ; with the inverter, it is hence possible to reduce said speed.

In the course of normal use of the mill, the product that is subj ected to grinding could trigger a flame ignition, possibly favoured by the increase in temperature due to the transformation of the grinding friction into heat. For this reason purposely designed nozzles are provided, which are designed to introduce inert gases into the jars 3. Via the introduction of inert gases into the jars 3, it is possible to reduce drastically the presence of oxygen inside them and consequently prevent the danger of ignition referred to above.

In the example illustrated, the motion of rotation of the cage G is provided through a three-phase asynchronous electric motor M, and a transmission 5 with pulleys and V-belts.

A kinematic chain with appropriate gear reducer 4, preferably in oil bath, transfers the motion to each individual jar 3: the system consequently has one degree of freedom.

The rolling bearings are all lubricated with grease.

In the devising and design stage, particular attention has beenpaid to the means of supply of the j ars 3. The problems tackled derive from the fact that the eccentricity of the axis B of the jars 3 with respect to the axis A of the cage G means that the corresponding supply duct must have a motion of drawing. Purposely provided seal means have hence been studied between the static part 1 and the rotating part 2 of the supply pipes of the jars 3. Also a series of solutions have been devised in order to overcome the^" drawbacks deriving from the fact that the product being supplied, in addition to being subjected to the force of their own weight, is subjected also to the centrifugal force following upon the aforesaid driving motion. Said solutions comprise, for example, helical scrapers for preventing any stagnation of material and favouring conveyance thereof inside the jars.

The product to be ground, which is introduced from above by gravity through the fixed duct 1, distributes in a practically equivalent way in the jars 3, with which said duct communicates via purposely providedmobile ducts 2 that rotate along with them. In this way, it is advantageously possible to supply the jars 3 with the material to be treated without stopping the mill. There is in any case to be taken into account the possibility that minor differences of flow of product can occur between one jar and the other in order to prevent said possible differences from having consequences in terms of dynamic unbalancing of the entire apparatus. In order to facilitate maintenance operations (both ordinary and extraordinary maintenance operations) , there is envisaged the possibility of easy disassembly of the components .

Saidpossibility regards in the first place the external panels.

The elements of the cage G, in turn, have been made in sectors bolted together, which can be disassembled from one another.

Disassembly of each of the jars 3 from the respective pins ismoreover facilitatedbyprovidingpurposely designed gripping hooks on their outer surface.

Finally, the bottom of each j ar 3 has a slight crowning, directed towards the centre, in which a hole is made to enable discharge by gravity of the balls, first by unscrewing the bottom lid, and then by sliding out a purposely provided spring which normally occupies the space of the hole for discharge of the balls, keeping them inside the jar during normal operation of the system.

Examples of use of the mechanochemical micronization mill The mill described up to now advantageously enables micronization of both hard and soft substances , both brittle and ductile ones, to be obtained and for the latter materials without having to resort to the use of embrittlement substances, such as for example liquid nitrogen. The latter characteristic constitutes a marked innovation, above all in the sector of urban solid waste, where it is possible to micronize waste made up of biological materials (meat, fats and animal and vegetable residue) rich in water and flexible, which in mills of a normal type would tend to create pulp that cannot be minced. The extreme energy of the mill manages, instead, to eliminate water and renders the material sterile (given the high pressure of friction) and is hence suitable for treating all types of organic residue even where there is risk of infection. The mill is then suitable for micronization of raw materials for producing toners for printers, usingmoreover the particular capacity for mixing the product in addition to grinding it, and for treating raw materials for pigments, such as for example titanium dioxide, enabling an extreme fineness to be achieved in a very short time. In these applications, the jars can be provided with ceramic coatings, and zirconium grinding masses can be used.

In summary, from what has been said, it appears clearly that the mill according to the present invention is substantially a mechanical apparatus for generating mechanochemical effects in addition to a marked grinding (micronization) of the materials treated.

It moreover enables friction pressures to be reached suitable for triggering chemical reactions on the materials, such as oxidation, reduction, phase change, sintering, amorphization, etc., determining the formation of micromaterials and nanomaterials .

From the numeric simulations conducted, it has been found that, in order to trigger said chemical reactions, friction pressures are required in the region of thousands of atmospheres.

From what has been said, the invention substantially consists of an innovative planetary mill provided with a rotating assembly, preferably comprising four jars 3 that rotate about a central axis A and about their own axes B, through a complex system of transmissions and gears 4. This assembly of gears transmits to each j ar 3 a motion of rotation equal and opposite to the rotation of the rotating assembly G so as to enable triggering of rotation of the grinding masses inside the "jars 3. As has already been mentioned, the jars 3 thus move without ever losing their orientation with respect to an external reference system. Precisely thanks to the fact that each j ar 3 rotates about its own axis B in an opposite direction with respect to the rotation of the rotating assembly G to which it is constrained, the grinding masses inside the jars have a relative motion with respect to the jar that contains them.

The speed of rotation of the jars 3, and hence the force of friction generated by the masses inside the jars themselves, is adjustable. With respect to the scheme of a normal planetary mill, the mill according to the invention presents numerous innovative elements, such as the complete absence of hunting and the absence of components of compression due to falling, which are typical of planetary mills that do not present a ratio of rotation between the planet and the satellites equal to unity.

Finally, particularly advantageous is the innovative method of extraction of the material from the jars 3, guaranteed by the effect of expulsion by centrifugal force through the orifices or holes 6 that are uniformly distributed on the lateral surface of the jars 3.

The invention can be applied to the treatment of waste and raw materials, in various industrial sectors, such as for example the industry of cement, pigments, treatment of metals and nanoparticles .

In conclusion, it should be noted that the mill according to the present invention is designed to treat industrial amounts of materials, in the region of thousands of kilograms per hour. In addition, it enables application of very high pressures during grinding, which are able to change the structural configuration of the material treated.

Advantageously, and unlike what has been known up to now, the mill according to the invention is designed to micronize also elastic materials that would not be processable with classic grinding by impact.

The present invention has been described and illustrated in a preferred embodiment thereof, but it is clear that technically and functionally equivalent modifications and/or replacements may be made by any person skilled in the branch, without this implying any departure from the sphere of protection of the present industrial patent right.

Claims

1. An industrial planetary mill for the production of materials having a nanometric and/or micrometric grain size using mechanochemical processes, characterized in that it comprises, in combination, a rotating assembly (G) with two or more jars (3) designed to rotate about a central vertical axis (A) of the rotating assembly itself and about their own axis of vertical symmetry (B) via a purposely designed kinematic chain of transmissions and gears (4, 5), which transmits to each jar (3) a motion of rotation equal and opposite to the rotation of the rotating assembly (G) , in order to obtain triggering of the rotations of apposite grindingmasses purposely provided inside the jars (3) ; thus obtaining that the jars (3) that contain the material to be ground will move without ever loosing the orientation with respect to a reference system external to the rotating assembly (G) and that grinding via said grinding masses inside the jars (3) will occur substantially by friction and not by impact .

2. The industrial mill according to the preceding claim, characterized in that said jars (3) are uniformly distributed about the central vertical axis of rotation (A) of the rotating assembly (G) .

3. The industrial mill according to Claim 1, characterized in that it comprises a supporting frame (T) mounted on which is the rotating assembly (G) , constituted by a cage with tubular sectional elements.

4. The industrial mill according to Claim 1, characterized in that in order to cause rotation of said rotating assembly (G) and said jars (3) a purposely designed system of transmissions and gears is provided, designed to transmit to each jar a planetary movement of rotation, in which the geometrical axis (B) of each jar (3) orbits with circular motion about the central axis (A) of symmetry of the rotating assembly (G) itself, in which - with respect to an observer external to the rotating assembly (G) - each jar (3) translates about the central axis (A) without rotating about its own axis of symmetry (B) .

5. The industrial mill according to Claim 1, characterized in that said grinding masses contained in each jar (3) are in the form of balls or bars or full cylinders.

6. The industrial mill according to the preceding claim, characterized in that, said grinding masses are made of steel and/or zirconium and/or other suitable material.

7. The industrial mill according to Claim 4, characterized in that the movement to which each individual jar is subjected is such as to generate, between the grinding masses and the jar (3) that contains them, a uniform circular relative motion, whilst the centrifugal force to which the grinding masses mixed to the material to be ground are subjected is such as to generate the necessary pressure of the masses themselves on the internal surface of the jar.

8. The industrial mill according to Claim 1, characterized in that the walls of each grinding jar (3) envisage openings (6) through which the ground or micronized material is evacuated.

9. The industrial mill according to the preceding claim, characterized in that said openings (6) for exit of the ground or micronized material are designed to be opened or closed by purposely provided plugs that can be easily removed.

10. The industrial mill according to Claim 1, characterized in that it envisages a fixed top vertical channel (1) for introduction of the materials to be ground, which communicates continuously with the jars (3) through respective mobile ducts (2) that rotate together with the jars themselves.

11. The industrial mill according to the preceding claim, characterized in that the mobile ducts (2) that convey the materials to be ground to the jars (3) are provided with wormscrews similar to augers, appropriately moved by the rotation itself of the jars (3), which facilitate conveyance of the materials into the jars.

12. The industrial mill according to Claim 1, characterized in that it envisages means for providing a flow of intake air, comprising a delivery gate valve that regulates the rate of intake, designed to favour inlet of the materials to be ground and exit of the ground powder.

13. The industrial mill according to the preceding claim, characterized in that said flow of intake air comprises or else is replaced by inert gases to eliminate the dangers of flame ignition within the jars (3) .

14. The industrial mill according to Claim 1, characterized in that it comprises a plurality of fixed external panels having the dual function of: preventing access to the mobile parts of the machine during operation; and providing the seal designed to prevent exit of powder.

15. The industrial mill according to the preceding claim, characterized in that said seal to the powder is obtained via sliding elements made of felt purposely pre-arranged between the top part of the rotating assembly (G) and the external panels.

16. The industrial mill according to Claim 8, characterized in that said openings (6) are arranged at a constant distance from one another in order favour a regular and uniform outflow of the ground material.

17. The industrial mill according to Claim 12, characterized in that said means for providing a flow of air and/or of inert gas comprise a fan/aspirator (14) set downstream of the intake line; there being provided for said purpose an appropriate connection between the intake mouth (14) of the fan and the air-outlet mouth (15) of the mill.

18. The industrial mill according to Claims 14 and 17, characterized in that the external fixed panels are provided, in a position opposite to the outlet mouth, with an opening for inlet of the environmental air; said opening being provided with a register for partialization of the flow of inlet air.

19. The industrial mill according to the preceding claim, characterized in that the collection of the powder and its separation from the process air and/or gas is made downstream, via an appropriate cyclone or bag filter with abatement pre-chamber .

20. The industrial mill according to Claim 12, characterized in that the control of the intake via the register provided on the inlet of the air (14) into the mill is designed to regulate the flows of air that convey the ground materials towards the outside in such a way as to prevent :

- clogging of the jars (3) on account of an excessively reduced opening of the register; and - the possibility of taking in particles not yet ground that would pass through the openings (6) of the plugs of the respective jar (3) before being micronized on account of an excessively large opening of the register.

21. The industrial mill according to Claim 1, characterized in that, in order to optimize the yield of the mill in the various operating conditions and as the type of the materials treated in the mill itself varies, it is envisaged to modify continuously the speed of rotation of a motor (M) , which moves both the rotating assembly (G) and the jars (3) via said kinematic chain of transmissions and gears (4, 5) .

22. The industrial mill according to the preceding claim, characterized in that said modification of the speed of rotation of the motor (M) , which is of an electrical type, is made with a square inverter.

23. The industrial mill according to Claim 21 or Claim

22, characterized'in that the variation of the speed of the motor can be made whilst the mill is in operation and in that said variation is possible only for reducing the r .p .m.

24. The industrial mill according to Claim 1, characterized in that saidmaterials tobe ground, micronized and brought to micrometric or nanometric dimensions comprise :

- inorganic materials, such as quartz, graphite, calcium and magnesium carbonates, feldspars, titanium dioxide, metal oxides, simple andmixed sulphides, asbestos, amphiboles, acidandbasic rocks, glasses, cements and debris from demolition and buildings, stones and rubble from excavations;

- organic materials such as cellulose, hard and soft woods, paper, non-chlorinated plastics of any type, PVC; and - biological organic materials, such as meat, animal and vegetable fats, vegetables, animal residue, animal flours .

25. The industrial mill according to Claim 1, characterized in that the jars (3) are provided with ceramic coatings .

26. The industrial mill according to Claim 1, characterized in that it is substantially constituted by a mechanical apparatus for generating mechanochemical effects in addition to a marked grinding or micronization of the materials treated.

27. The industrial mill according to Claim 1, characterized in that the movement applied to the jars (3) and the presence of the grinding masses inside them are such as to reach pressures of friction such as to trigger chemical reactions on the materials treated, such as oxidation, reduction, phase change, sintering, amorphization, etc., thus causing the formation of micromaterials and nanomaterials .

28. The industrial mill according to Claim 1, characterized in that the jar moves substantially with a motion of nutation.

29. The industrial mill according to the preceding claim, characterized in that said pressures are by friction are in the region of thousands of atmospheres.

30. A industrial mill for the production of materials having a nanometric and/or micrometric grain size using mechanochemical processes, substantially as described and illustrated in the present description and in the attached drawings.