Patent Publication Number: US-9427743-B2

Title: Spiral jet mill apparatus for micronisation of a powdered material or a material containing particles in general, with a novel system for feeding and dispensing the powdered material to be micronised, and corresponding process for micronisation of a powdered product

Description:
This application is a National Stage Application of PCT/EP2013/057881, filed 16 Apr. 2013, which claims benefit of Serial No. MI2012A000635, filed 17 Apr. 2012 in Italy, each of these applications being incorporated herein by reference. To the extent appropriate, a claim of priority is made to each of the above disclosed applications. 
     TECHNICAL FIELD OF INVENTION 
     The present invention relates in general to the sector of devices and apparatus for grinding and crushing materials and products containing and formed by particles, such as, typically, powders, products and similar compounds in powdered form, into smaller particles, and in particular relates to an apparatus for the micronisation of a powdered product or similar substance comprising a micronising mill operating with high-energy jets of a gaseous fluid such as air, which said mill uses a novel, innovative system of dispensing the powdered material and product to be micronised and feeding it to the jet mill. 
     The present invention also relates to a corresponding process for the micronisation of a powdered product. 
     BACKGROUND OF THE INVENTION AND PRIOR ART 
     Current technology for crushing powders, such as powdered compounds for use in the pharmaceutical industry and powdered material in general, offers numerous solutions, some of which are alternative to one another, including powder micronisation systems based on the use of a high-energy gaseous-fluid-jet mill, also called a jet mill. 
     Said jet mills have a relatively simple construction and structure, normally comprising: a circular grinding or micronisation chamber wherein a series of high-energy jets, generated by a compressed gaseous fluid such as air, cause continuous collisions between the powdered product particles, and consequently their micronisation; a system of feeding and loading the powdered material into the micronisation chamber based on the use of a Venturi tube, also simply called a Venturi, namely a narrowing or throat in a pipe into which a gaseous fluid is conveyed so as to cause a negative pressure that attracts the powdered material; and a selection or classification system, of the static or dynamic type, associated with a central zone of the micronisation chamber and designed to classify the crushed and micronised particles and separate them selectively according to particle size. 
     The high-energy jets of gaseous fluid are inclined in relation to the radius of the micronisation chamber, with the result that said jets cause a fluid dynamic flow of gaseous fluid in said chamber that draws the particles of powdered material with it and presents two components: a first tangential component that rapidly moves the particles of powdered material in a vortex around the axis of the micronisation chamber, and a second radial component that tends to move the particles from the peripheral zone to the central zone of the micronisation chamber. 
     In this way, the powdered material or product is subjected, in said fluid dynamic flow in the micronisation chamber, to continual mixing and collisions between its particles. 
     Moreover, in the flow generated by the high-energy jets of gaseous fluid, the particles are subject to a centrifugal force that also leads to classification, whereby the finer and already micronised particles tend to move towards the central inner part of the micronisation chamber, from which they are evacuated, while the larger ones, not yet micronised, tend to remain in the peripheral outer zone of the micronisation chamber and to rotate around the axis on the periphery, thus undergoing further collisions. 
     The micronisation process is normally but not solely performed on powdered materials and practically dry powders. 
     Improvements over the years have led to optimisation of the configuration and geometry of the holes or nozzles through which the high-pressure jets of gaseous fluid are activated and created, both in the micronisation chamber and in the micronised particle classification system, where a dynamic classifier has been introduced in particular, already used in other types of apparatus, which uses a rotary element with peripheral wings that only allows micronised particles of the required size to pass through. 
     Nevertheless, current micronisation technology, including that based on the use of jet mills, still presents problems and limitations that need to be overcome and solved with further improvements, especially as regards feeding of the powdered material to be micronised to the micronisation chamber of the jet mill. 
     In particular, the current system of feeding the powdered material to be micronised, typically comprising a Venturi tube, as already stated, presents the following problems and drawbacks.
         Noise level of Venturi tube. The presence of a Venturi tube means that the feed system is rather noisy. This noise can only be partly attenuated by suitably closing the feed section.   Abrasion of Venturi tube. The Venturi is subject to abrasion over time, due to the passage of the powder. This abrasion phenomenon is particularly accentuated in the throat area of the Venturi tube, causing a reduction in its efficiency with a variation in the operation of the jet mill.   Blockage of Venturi tube. This phenomenon, also called “blow-back”, is particularly accentuated with fatty, electrostatic or damp powders, and tends to project the powder back through the entrance cone of the Venturi tube, thus preventing correct operation of the jet mill.   Irregularity of the dispensed material to be micronised, i.e. an irregular, imprecise quantity of powdered material, which is fed through the Venturi tube to the jet mill. With the dispensing systems normally used at present, such as single- or double-screw or rotary-valve dispensers, the powder flows into the Venturi tube in an irregular, uncontrolled way, with the result that the quantity of powdered material dispensed by said dispensing systems and the corresponding particle size vary over time, in an uncontrolled way.   Limitation of the ratio obtainable between the quantity of powder dispensed and the operating pressure of the gaseous fluid in the jet mill. As the Venturi feed system communicates directly with the micronisation chamber of the jet mill, its operation is necessarily dependent on the conditions in said chamber, so in order to obtain the negative pressure involved in the Venturi effect, the pressure of the gaseous fluid in the Venturi tube must be at least equal to that of the gaseous fluid in the zone of the nozzles that dispense the high-energy jets for micronisation of the powder. Moreover, for each grinding or micronisation pressure value there is a minimum quantity of powder, dependent on the density, size and other characteristics of the powder which must be fed into the micronisation chamber to allow the operation of the mill and prevent blow-back.   Finally, a further drawback of the current technology which needs to be remedied, again associated with the use of a Venturi type feed system, is that with said Venturi system it is practically impossible to control and feed to the jet mill relatively low flow rates or quantities of the material to be micronised, and at the same time operate with high operating pressures in the jet mill to activate the high-energy fluid jets for micronisation of the powdered material.       

     Furthermore, it is remarked that screw feeders, as those adopted in the actual technique, for feeding and transporting powders, have relevant problems related to the metal abrasion during the feeding, that can contaminate the final product. 
     Moreover screw type feeders cannot inject powders directly into a jet mill. 
     Indeed, as before discussed, in order to inject the powders an additional tool for acceleration and injection of the powders is required, as for example a Venturi type pneumatic feeder that aspirates the powder leaving the screw and finally blow it with high gas consumption into the spiral mill. 
     Beneath all mentioned disadvantages and limitations the screw feeder and the Venturi system underlay and imply strong wear if abrasive powders have to be transported. 
     Still, screw type feeders cannot feed sticky powders or powders with low or no flowing behavior (e.g. flake like powders, short fibres or most of powders with average particle size below 10 microns down to nanometers) and cleaning is very difficult and time consuming. 
     It is also remarked that the nowadays increasing demand of powders with submicron and nanometre sized particles requires efficient production methods, and the actual state of the art of jet milling technologies appears as not being capable of completely fulfilling this task, as above outlined. 
     For instance, blocky shape abrasive diamond powders with a particle size below 10 microns cannot be efficiently transported by using a screw type feeder, as those adopted at present in the technique. 
     Moreover also the methods for producing powders, in particular with low impurities, to be used in application involving grinding or lapping, as diamond powders, SiC (Silicon Carbide), WC (Tungsten Carbide), CBN (Cubic Boron Nitride) and B4C (Boron Carbide) powders, appear to require further improvements. 
     PURPOSE AND SUMMARY OF THE INVENTION 
     A first purpose of the present invention is therefore to provide a novel apparatus for micronisation of powders, in particular of the type comprising a high-energy fluid-jet mill, which eliminates the above-mentioned drawbacks present in the prior art, and above all can control and precisely dispense the quantity of powdered material fed to the micronisation apparatus, i.e. to the corresponding jet mill, to be micronised. 
     A further more general purpose of the present invention is also to increase the overall efficiency of the micronisation process used for powders and similar materials, by means of precise control and dispensing of the quantity of powdered material fed to the zone in which said material will be micronised. 
     A third purpose of the present invention is to find a solution that allows the jet mill to be fed with low flow rates and quantities of material to be micronised, at the same time operating with high operating pressures to generate the fluid jets in the mill, as required to obtain optimum micronisation of superior quality with given types of powdered materials. 
     Finally, a fourth purpose of the present invention is to improve and make even more efficient and controllable the micronisation of powders and powdered compounds specifically designed for use and application in the pharmaceutical field, an industry in which said needs for increasing efficiency of the micronisation process and increasingly high quality of the micronised product are particularly felt. 
     Moreover another possible purpose of the invention can be directed to improve the actual technique for producing powders, in particular with low impurities, and thereby produce improved and more efficient powders, to be used in application involving grinding or lapping, as diamond powders, SiC (Silicon Carbide), WC (Tungsten Carbide), CBN (Cubic Boron Nitride) and B4C (Boron Carbide) powders, and other types of powder. 
     Said purposes can be deemed to be fully achieved by the powder micronisation apparatus having the characteristics defined in independent claim  1 . 
     Particular forms of embodiment of the present invention are defined by the dependent claims. 
     In the powdered material micronisation apparatus of the present invention the jet-mill is specifically of the spiral type, that means that the nozzles are forming a circle, and are not all directed towards one point, as in other micronization systems, like for instance the fluidized bed jet-mills with opposite nozzles, and thereby with jet trajectories incident in a common point. 
     Moreover an essential feature of this proposed powdered material micronisation apparatus, compared to the systems at present known, is the combination of a spiral jet-mill, instead of a opposite jet mill, with a new generation of powder feeders, of the type of a powder pump, implying better milling results at higher efficiencies and lower impurities level, as those caused by wear, without limitations of powders to be handled. 
     Even flakes or fibres can be precisely injected into the mill. 
     In particular the system or apparatus here proposed is composed by only one single feeding step, and the feeder is a so called powder pump without any mechanical moving parts in contact with the powder. 
     The feeding of the powder is made in a volumetric way and in a dense phase mode instead of the traditional mechanical and pneumatic transport of the powder. 
     Therefore the powder is flowing at low speed to the milling chamber (normally by the factor  3  to factor  10  lower particles speeds compared to pneumatic powder feeding). This reduce dramatically the wearing, and makes easy the control of final feed-rates. No limitations are indentified by the applicant regarding the powders to be handled. With multiple feeding parts in series the synchronization is fundamental to avoid clogging or emptying of the feeding line 
     Advantages of the Invention 
     There are numerous advantages, some of which have been implicitly stated above, associated with the novel powder micronisation apparatus according to the present invention, such as those listed in below by way of example:
         greater efficiency and yield of the micronisation process compared with conventional systems that use a Venturi tube to feed the material to be micronised;   more precise control over time of the quantity of powdered material subjected to the micronisation process;   the ability to obtain a micronised powder complying with the desired quality requirements with relatively low flow rates of the material to be micronised.       

    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       These and other purposes, characteristics and advantages of the present invention will clearly appear from the following description of a preferred embodiment thereof, given by way of example but not of limitation, by reference to the annexed drawings, wherein: 
         FIG. 1  is a scheme illustrating an apparatus according to the present invention for the micronisation of a powdered material or the like; 
         FIG. 2  is a further scheme which illustrates in a little more detail a system, included in the micronisation apparatus shown in  FIG. 1 , for feeding and dispensing the powdered material to be micronised; 
         FIG. 3  is a first test report and diagram, showing the results of a first series of experimental tests conducted with the apparatus according to the invention shown in  FIG. 1 ; 
         FIG. 4  is a second test report and diagram, showing the results of a second series of experimental tests conducted with the apparatus according to the invention shown in  FIG. 1  by feeding it with a relatively low flow rate of powdered material; and 
         FIGS. 5 and 6  are two photographic images of the actual apparatus used to conduct the experimental tests referred to in the reports shown in  FIGS. 3 and 4 . 
     
    
    
     DESCRIPTION OF A PREFERRED EMBODIMENT OF THE MICRONISATION APPARATUS ACCORDING TO THE INVENTION 
     With reference to the drawings, an apparatus or unit, conforming to the present invention, for grinding or micronisation of a material containing and formed by particles to be micronised, typically constituted by a product, compound, substance or powdered material P in general, is indicated as a whole as  10 , and comprises in particular:
         a container or receptacle  11 , containing a basic reserve of powdered material or product P, also called “the powder”, to be micronised;   a micronising mill  12 , of the spiral jet type, wherein the powdered material or product P is micronised; and   a feed system, indicated in general as  13 , designed to feed the powdered product or material P from container  11  to jet mill  12 , where it is micronised.       

     In detail, feed system  13  operates so as to aspirate and attract powdered product P from container  11 , along a first transport or entrance line  14 , and then feed it to jet mill  12 , along a second transport or exit line  16 . 
     In this way, powdered product P is conveyed along the first transport line  14  installed upstream of feed system  13 , and subsequently conveyed along the second transport line  16 , installed downstream of feed system  13 , from container  11  to jet mill  12 , where powdered product P is micronised. 
     As jet mill  12  possesses substantially known characteristics, it is only schematically illustrated in the drawings, and will not be described in detail. 
     It will merely be mentioned that jet mill  12  comprises an annular outer pressure chamber  12   a  and a circular inner micronisation chamber  12   b , separated from one another by an annular intermediate wall  12   c  in which are drilled a plurality of channels or through holes  12   e , suitably inclined relative to the radius of micronisation chamber  12   b , which place the two chambers  12   a  and  12   b  in communication. 
     In operation, jet mill  12  is supplied with a fluid F, in particular air, at high pressure, which is introduced into outer pressure chamber  12   a , and emerges, in jet form, in inner micronisation chamber  12   b  through channels  12   e , formed in annular separation wall  12   c  between the two chambers  12   a  and  12   b.    
     In this way a system of high-energy jets G is generated, which are inclined and tangential to an imaginary circle, and which cause a vortical motion and an air spiral around the axis of micronisation chamber  12   b , converging towards a central area  12   b ′ thereof. 
     Powdered material P in turn is fed by feed system  13  to inner micronisation chamber  12   b  of jet mill  12 , with the result that particles of powdered material P are drawn by the vortical motion generated by jets G in micronisation chamber  12   b , and are consequently liable to collide continually with each other and be crushed, so as to micronise powdered material P. 
     In particular, in the micronisation chamber, due to said vortical motion, the particles of powdered product P are subject to a centrifugal force that tends to move them towards annular wall  12   c , so that they remain in the micronisation zone until the particles exceed a given size or have not yet been sufficiently crushed. 
     When said particles have been completely crushed, they are subjected to a radial force that tends to move them towards central zone  12   b ′ of micronisation chamber  12   b , whence they are evacuated. 
     The vortical motion in the micronisation chamber therefore acts in such a way as to classify the particles and determine their evacuation, once micronised. 
     Micronisation apparatus  10  also contains an evacuation system, schematically illustrated with a pipe  18  and fitted at the outlet of jet mill  12 , which has the function of evacuating from micronisation chamber  12   b  the gaseous flow consisting of fluid F and the material, indicated as P′, containing the particles of micronised powder, and conveying them to a separation system with known characteristics not shown in the drawings, designed to separate and collect the micronised particles from gaseous fluid F. 
     Optionally, micronisation apparatus  10  can also be fitted with an auxiliary exit, schematically illustrated by arrow  19 , to recover the powder from jet mill  12 . 
     Optionally, micronisation apparatus  10  can also contain, along transport line  16  fitted downstream of microdispenser device  20 , a coaxial disperser  15  with known characteristics, schematically illustrated with an arrow in  FIG. 1 , which has the function of dispersing the particles of powder so as to optimise their distribution in the flow fed to micronisation chamber  12   b.    
     According to one characteristic of the present invention, feed system  13  of micronisation apparatus  10  comprises, alternatively to conventional feed systems usually based on a Venturi tube, a microdispenser device  20 , which dispenses powdered product P micrometrically, and feeds it or injects it directly into micronisation chamber  12   b  of jet mill  12 . 
     Due to said microdispenser device  20 , and unlike conventional Venturi type feed systems, which do not usually allow precise dispensing and control of the quantity of powdered material introduced into the jet mill to be micronised, in micronisation apparatus  10  according to the present invention the quantity or flow rate of powdered material P which is fed into jet mill  12  to be micronised is dispensed and determined precisely and kept constantly under control. 
     For this purpose, microdispenser device  20 , which is an essential part of micronisation apparatus  10  according to the invention, transfers and feeds powdered product P from container  11  into micronisation chamber  12   b  of jet mill  12  in a way totally different from and alternative to Venturi type feed systems based on the creation, in a narrow section of a boundary layer, of a negative pressure designed to attract and feed the powdered material from the outside to the micronisation area. 
     Conversely, microdispenser device  20 , as more particularly specified below, is designed to attract and feed powdered product P from container  11  to jet mill  12  via a series of high-frequency pulses imparted to the valves of said microdispenser device  20 , which generate pneumatic microtransport of powdered material P along transport lines  14  and  16 , and at the same time precisely dispense the quantity transported and fed. 
     In more detail, microdispenser device  20 , which is an integral part of micronisation apparatus  10  according to the invention, is as described in the international patent applications published as WO 03/029762 A1 and WO 2010/11881 A2. 
     For all further details and clarifications not expressly described herein regarding microdispenser device  20 , an essential part of micronisation apparatus  10 , reference should therefore be made to said applications, the content of which must be deemed to be incorporated in the description of the present invention. 
     However, for the sake of clarity and completeness information, microdispenser device  20  is schematically illustrated in  FIG. 2 , and its basic characteristics will be described briefly below. 
     As already stated, microdispenser device  20  is designed to receive powdered material P from container  11  along inlet line  14  and to feed it, in batched form, through outlet line  16  to micronisation chamber  12   b  of jet mill  12 , where powdered material P will be micronised by the effect of high-energy air jets G, acting in said micronisation chamber  12   b.    
     In particular, microdispenser device  20  comprises one or more dispensing units or sections, indicated as  21 , associated with a suction line  22 , wherein a vacuum or negative pressure is created, for example through a suction pump  23 , and a pressure line  24 , in which a pressure is generated, for example through a pressure pump  25 . 
     A plurality of control valves  26  and  27  are fitted to place each dispensing unit  21  selectively in communication with suction line  22  and pressure line  24  respectively. 
     The various dispensing units  21  are designed to receive powdered material P from container  11  via transport line  14  and to dispense it, after measuring, to outlet line  16 , so that it feeds jet mill  12 . 
     A plurality of control valves  28  and  29  are fitted to place each dispensing unit  21  selectively in communication with inlet line  14  and outlet line  16  respectively. 
     It is therefore clear that the dispensing process, which is performed with microdispenser device  20  and allows jet mill  12  to be fed with an exactly determined quantity and at an exactly determined flow rate of powdered material, is basically the volumetric/quantitative type. 
     This dispensing process, as first illustrated, is based on filling dispensing units  21 , which in turn define a given volume and consequently a given quantity of powdered material with which they are filled, and subsequent emptying of said dispensing units  21  so as to dispense the powdered material, after measuring, to jet mill  12 . 
     In the operation of micronisation apparatus  10 , the operator sets microdispenser  20 , via setting and control means and taking account of the characteristics of powdered material P to be micronised, to feed jet mill  12  in the time unit with the desired quantity of powdered material P. 
     Said setting and control means in turn control the various control valves  26 ,  27 ,  28  and  29 , namely their opening and closing, via suitable high-frequency pulses so as to cause each dispensing unit  21  to be filled, cyclically and alternately, with powdered material P originating from container  11 , and subsequently emptied, thus feeding jet mill  12  with the quantity of powdered material P set by the operator. 
     In this way powdered material P, which is fed to micronisation chamber  12   b  where it will be micronised, is precisely measured, and its quantity is precisely determined, and kept constantly under control over time. 
     Microdispenser device  20  presents a special configuration and comprises suitable control and dispensing means, fully and clearly described in the above-mentioned patent applications WO 03/029762 A1 and WO 2010/11881 A2, which have the effect that microdispenser device  20  micrometrically dispenses and measures, in response to suitable commands issued at high frequency to control valves  26 ,  27 ,  28  and  29  associated with the various lines  14 ,  16 ,  22  and  24  connected with dispensing units  21 , the quantity of powdered material P which is introduced into the pipe of outlet line  16  and consequently feeds micronisation chamber  12   b  of jet mill  12 . 
     Powder P, originating from container  11 , is therefore suitably micrometrically measured, while it passes through microdispenser device  20 , from which it is introduced into the pipe of outlet line  16 , so as to feed micronisation chamber  12   b  of jet mill  12 . 
     Powdered material P is also fed to micronisation chamber  12   b  by pneumatic micrometric transport, due to the effect of the high-frequency pulses that control the opening and closing of the various control valves  26 ,  27 ,  28  and  29 . 
     The pipes of lines  14  and  16  for the transport of powdered material P to and from microdispenser device  20  respectively are dimensioned on the basis of the maximum flow rates allowable to feed jet mill  12  via feed system  13 . 
     Starting material P, containing the particles to be micronised, which is fed and dispensed through microdispenser  20 , can consist of dry powders, a liquid solution or a paste, or a mixture often described by the English term “slurry”. 
     It will also be appreciated that the microdispencer device  20 , differently from the traditional pumps, performs the feeding step without any mechanical moving parts in contact with the powdered material. 
     Still the feeding is made in a dense phase mode, instead of the traditional mechanical and pneumatic transport of the powder. 
     In this way the powder is flowing at low speed to the milling chamber (normally by the factor  3  to factor  10  lower particles speeds compared to pneumatic powder feeding), with the effect of reducing considerably the wearing. 
     Experimental Tests 
     Micronisation apparatus  10  according to the invention, including microdispenser  20 , has been subjected to detailed experimental tests with the following purposes:
         to verify the overall operation of said apparatus  10  according to the invention;   to compare the results obtained with micronisation apparatus  10 , an essential part of which is microdispenser device  20 , with those obtained with micronisation apparatuses that use a conventional powder feed system, of the Venturi type.       

     In particular the experimental tests were performed on a micronisation unit or apparatus comprising the following components:
         5-litre powder container, with powder stirring system;   pneumatic microdispenser supplied by P&amp;S, of the type described in the above-mentioned patent application WO 03/029762 A1;   spiral jet mill type MC50, manufactured by Micro-Grinding, suitably modified to allow it to be coupled to the microdispenser, and with a system for recovering the product from a lower zone of the jet mill (version BD of the mill);   cyclone for separating the micronised powder, with type 50FC filter and incorporated cartridge, for recovery of ultrafine powder particles.       

     The plant was tested with a powdered product consisting of lactose. 
     A first series of experimental tests was performed under the following conditions in the test unit:
         relative pressure of gaseous grinding fluid, compared with atmospheric pressure: approx. 7 [barg];   dose of powdered product: approx. 300 [g/h].       

     In this first series of tests the spiral or jet mill, in combination with the pneumatic microdispenser, always operated correctly. 
     For the sake of completeness and to demonstrate said correct operation, the results of the particle-size analysis of the micronised powder output by the jet mill in this first series of tests are specified in the test report shown in  FIG. 3 . 
     A second series of tests was performed under the following operating conditions in the test unit:
         relative pressure of gaseous grinding fluid, compared with atmospheric pressure: approx. 9 [barg];   dose of powdered product: approx. 20 [g/h].   process gas flow in a range between 10 kg/h and 400 kg/h of compressed gas, or, by considering the ratio between mass of gas and mass of powder, with this ratio in a range between 25 g and 400 g of powder per each ton of compressed gas, or similarly between 25 mg and 400 mg of powder per each kg of compressed gas.       

     The above operating conditions used in said second series of tests, corresponding to a relatively low flow rate, namely 20 [g/h], of powdered material to the jet mill where it is to be micronised, and a relatively high operating pressure, namely 9 [barg], in the jet mill, designed to generate high-energy fluid jets, are not usually obtainable with conventional micronisation systems, wherein the jet mill is fed with Venturi type feed systems. 
     Also in this second series of tests the spiral mill or jet mill, in combination with the pneumatic microdispenser, always operated correctly, providing a micronised product complying with the desired quality requirements. 
     For the sake of completeness and to demonstrate said correct operation, the results of the particle-size analysis of the micronised powder output by the jet mill in this second series of tests are specified in the test report shown in  FIG. 4 . 
     Briefly, these tests clearly demonstrate that the spiral mill or jet mill, in combination with the pneumatic microdispenser, always operates correctly, under all the operating conditions tested, confirming the innovative characteristics of micronisation apparatus  10  according to the invention. 
     Also for the sake of completeness, the photographic images in  FIGS. 5 and 6  show the apparatus according to the invention, including jet mill  12  and microdispenser device  20 , which was constructed and used to perform the said experimental tests. 
     From the above description, it is therefore clear that the present invention fully achieves the intended purposes. 
     In particular it provides a novel micronisation apparatus or unit which presents significant improvements and better performance compared with the apparatus currently known and used to micronise powders, in particular apparatus designed for use in the pharmaceutical industry, and also allows the quantity of powdered material to be introduced into the micronisation chamber for micronising to be controlled and dispensed with great precision, leading to significant favourable effects on the micronisation process as a whole. 
     Variations 
     Variations on micronisation apparatus  10  described above are obviously possible, and also fall within the scope of the present invention. 
     For example, more than one microdispenser device can be fitted to feed jet mill  12  with different materials containing particles, or different products in powdered form.