AN AIR-JET MILL FOR FINE AND/OR CRYOGENIC MILLING AND SURFACE TREATMENT OF PREFERABLY HARD, ELASTIC AND/OR THERMOPLASTIC MATERIALS

Abstract: Air-jet mill provided with pregrinding chamber and inner sizer suitable for fine grinding (below 10 mu ) furthermore for cryogenic grinding and in a given case for surface treatment during grinding of preferably hard, elastic and/or thermoplastic materials. The facility representing the invention is an energy-saving unit, it does not comprise any moving components being exposed to heavy wear, has an inner sizer forming an integral part of the grinding space the former making use of the energy left after grinding in the system thus enabling a sharp sizing of fine fractions.

Description: AN AIR-JET MILL FOR FINE AND/OR CRYOGENIC MILLING AND SURFACE TREATMENT OF PREFERABLY HARD , ELASTIC AND /OR THERMOPLASTIC MATERIALS -j The object of the invention is an energy-saving in side sizing air-jet mill having a pregrinding chamber for fine ' grind ing of pe ferably various carbides , sili¬ cate s , oxides , ore s , pigment s or clastic mate rials , as well as for surface treatment and /or cryogenic grinding of the same . The air-jet mills known according to the present state of technics, could be traced back to five basic types. The first type is characteristic of the condi¬ tion that grinding takes place by making the material accelerated to high speed by the nozzle to impact against a so-called anvil. This facility provides adequate grinding effect, however, due to high speci¬ fic energy consumption its operation is not economic and the lining exhibits much wear highly contaminat- ing the ground product hereby. In order to eliminate this contaminating effect it is often practised to use linings with the same basic material than the material to be ground has. The best known version of this type now in use is the air- -jet mill of the Vortex system provided with outer sizer, ceramic lining and anvil. The other type of the air-jet mill widely used is the so-called Majec mill. He e, comminution takes place by the autogenous grind¬ ing effect of grains impacting against each other by the acceleration generated by two nozzles facing one another. This operation, however, exhibits energy- losses and thus very poor comminution efficiency. The nozzles can carry comparatively small amounts of grains and vortices occur also on the effect of the opposite air jets thus fairly reducing the number of :3 ' S iTUTg SHE T collision of grains. Known examples of this type are: DE 254369102 and DE 252347102. The third air-jet mill, the so-called Micronizer type is the one which has been used mostly. The essence of its operation is that grinding takes place in the discus-shaped grinding chamber on the effect of gas outflowing from the peripheral jet pipes. The gas jets first contact a circle in the outer third part or half of the grinding area. Material to be ground enters the grinding space in a vertical plane crossing the tangent of this circle, however, at angles of 60 to the ver¬ tical passing through the top of the grinding space. According to the theory of the designers, the grains exceeding in size a predetermined measure are circulating along this tangential circle , the smaller ones that is the ground end product discharges from the facility through an obstructing dam and the coarser grains, on the effect of the outflowing gas from the peripheral nozzles, are colliding with each other and are circulating as long as their measure re¬ duces below the required level. Under actual working conditions the operation of the facility does not meet the conditions of the above theoretical operation, yet the type is widely used as a unit presenting the best efficiency. Several patented inventions are there re¬ lative to the development of the former, e.g. US 18586, SF-33960, DE 32017781 Cl. These technical solutions represent the combination of the double-jet mill, the anvil type and the micronizer , where the coarse pro- duct is refed to the grinding space, or on applying an anvil-type pregrinder it is being attempted, with little success, to improve the fineness of grinding. Therefore, up to now, the unchanged basic type pro¬ vided with some kind of liner is most frequently used in the industry. SUBSTITUTE SHEET With the fourth type of the air-jet mills the increase of mill output was aimed at by a method which did not cause the shortening of the path of free movement of particles. In favour of this, the volume of grinding space and the number of nozzles has been increased, increas¬ ing hereby the output of mill relative to its unit volume, however, the efficiency of energy utilization has been worsened and the extent of wear increased, too. This type of mill had been called Jet-0-Mizer or Re- ductionizer. Aiming at the reduction of wear effect the design of the Double-Impact-Mill appeared on the market. In the return branch of the upper part of the mill a so-called directional-change-sizer and further grinding nozzles have been applied in some cases. It did not succeed to achieve the grain size of 1 ,um by the use of these types of mills. The fluid bed air-jet-mills could be included in the fifth type /e.g. DE 3140294 C2/ where frequency of collision of particles and thus the efficiency of grinding is increased by the use of four nozzles of larger diameter compared to the previous ones operated opposite to each other and being located in the bottom part of a large container. The nozzles operate to fluidize the entire amount of material in the container causing the finer grains already ready ground to be lead off having been passed previously through a ro¬ tating sizer in the top section of the container. Mean¬ while, the coarser fraction sued back down the wall of the container for repeated grinding. The facility exhibits good grinding and sizing efficiency, however, it is not suitable for fine /below 10 ,u/ grinding, partly because due to short path length of particles /high density/ the impact energy of the latter is little, partly because even the speed of SUBSTITUTE _£» S _ H _ rotation of the revolving part of the sizer, that is the fineness of the end product, cannot be increased beyond a certain limit. Another disadvantage of this design lies in the condition that the revolving part of the sizer is exposed to high wear and due to the high overpressure of the grinding space charging of material can only be carried out be the use of an in¬ volved sluice system. With the knowledge of types adopted so far, it can be established that the effi- ciency of air-jet facilities is favourable if par¬ ticles possess heavy energied and there is high pro- balitiy of impacting. On increasing the number of solid particles the probability of impacting may though be increased, however, the free path length required for particles to become accelerated shortens, consequent¬ ly, the impact energy diminishes, too, therefore there is a compromise forming the basic problem of air-jet facilities aiming at their running at all: either to increase the. free path length and make the ground product finer along with diminishing performance of the mill, or to increase the number of impacts which results in coarser product, however, improves the grinding ef¬ ficiency and performance of the mill. The invention aims at developing an air-jet mill structure capable of fine grinding very hard, or elastic and/or thermoplastic materials to below 10 ,um, which is energy-saving, it does not contain any movable parts, thus exhibits high resistance to abrasion. It features an inner sizer as an integrated part of the mill. Its sizing performance is sharp and the unit does not swallow major portion of the comminution energy. The invention based on the perception of the following: - grinding efficiency can considerably be ' improved by the adoption of pregrinding, adequately increasing SUBSTITUTE SHEET the number and arranging of nozzles, recirculation of coarser fraction into the pregrinding chamber, - on selecting adequate number of peripheral nozzles the same grinding work can " be made performed by all the nozzles, on eliminating movable parts, if material charged in a horizontal plane in tangential direction, a minimum abrasion wear can be achieved and even this can be confined to the easily replaceable elements of the pregrinding chamber, considerable diminution of wear of the pregrinding chamber can be attained at by the use of as many auxiliary nozzles as the confluently jetting main nozzles aiming at diverting the material from the wall are, by the development of a new profile lining element, and the adoption of curb of blades of adjustable blade angle a very sharp inner sizing can be obtain¬ ed /within the grain limits of 0.1-100 ,u/ without any input of outer energy by the utilization of energy left after grinding, by adequate axial adjustment of nozzles vacuum is generated in the charging orifice enabling the charg¬ ing and refeeding of materials to be ground as well as -surface treating materials and/or coolants into the system. This way the facility is suitable for surface treatment of grinding heat-sensitive and elastic materials too, setting of the angle of the peripheral nozzles in the grinding space /diverting the material from the wall /reduces the number of impacts on the wall thus enabling an optimum adjustment of the movement of the material. With construction of the air-jet mill, as per invention, material feed takes place in the horizontal SUBSTITU ≤ S H plane of the grinding space intangential direction, thus besides good grinding efficiency, wear of grind¬ ing space - occurring with the micronizer types - can be reduced. The use of pregrinding chamber, the smaller size of feed material considerably improves the efficiency of grinding. The number and positioning of peripheral nozzles should be selected such as to operate every nozzle performing the same grinding work: it is expedient to charge material into the grinding space after every second nozzle. /For instance, if six peripheral nozzles are applied and three tangentially set jet pipes are used, the grinding performance can be increased to the three-fold according to tests made./ In order to further improve grinding efficien¬ cy, the coarser fraction from the grinding space is refed to the pregrinding space through a channel by the effect of vacuum generated in the charging channel. The material charging nozzles /injecting channels/ are connected with the pregrinding chamoer, the latter being provided with wear resistant lining, where two or more nozzles set at 90 -180 angles to each other and/or shifted in the plane are injecting the material confluently. In the case of running more than two confluent nozzles, two are performing material feed, the remaining ones, however, are decreasing wear by reducing the probability of particles impact¬ ing against the wall of the chamber. The arrangement of nozzles, according to tne invention, just by giving rise to generation of vor¬ tices, i.e. by increasing the number of impacts of particles, results in very good grinding effect in the pregrinding chamber. The injecting nozzles are suitable also for introducing fresh material to be ground of surface treating materials and/or a coolant ->HEI-_ into the system corresponding to the particular grinding technology required, namely, having them properly adjusted, vacuum would be generated in the feed orifice causing the coolant or any reagent to get sucked in. Access of preground material into the grinding space is made possible by an injecting nozzle coaxial with the injecting pipe which exhibits the highest pressure in the system and is suitable for accelerating the preground material to an adequate velocity /the multiple of sound velocity/ in spite of the vortices generated by the confluent nozzles thus enabling them reaching the grinding space. On investigating the relation between commi¬ nution efficiency and pressure, it has been estab- lished that efficiency improves slightly up to 9 bar pressure, then rapid increase was experienced in the range 9-15 bar pressure and finally severe agglo¬ meration takes place in the range 15-25 bar pressure depending on the material, deteriorating the effi- ciency of comminution. With one potential alternative of design of the air-jet mill under the invention, there are four nozzles connected to the pregrinding chamber in tan¬ gential direction, the flow proceeds perpendicular to the main grinding space and the gas jets are gene¬ rating the vortex by contacting a circle of compara¬ tively small radius. With this solution, two nearly horizontal nozzles are shooting together the material to be ground, the other two nearly vertical nozzles, however, are conducting gas or air to the system. The latter may be linked to the containers of reagents or ' coolant. The injecting tubes are connected tangenti- ally at three ' points to the grinding space where the six peripheral nozzles rotatable around their vertical axes are lcoated symmetrically. The grinding chamber ' SUBSTITUTE SHEET by means of material recirculating pipes each in order to return the coarse fraction herewith. The inner sizer ' is designated to be symmetrical with the axis of the grinding space the former consist- ing of a surface area of a hyperboloid of revolu¬ tion and an adjustable curb of blades having the same axis as the discharge stub for the ground product. The other potential alternative of design of the air-jet mill under the invention differs from the one outlined before in the mode of development of the pregrinding chamber. With this solution, in the vertical cylindrical pregrinding chamber, there are two confluent shooting nozzles set an- angle within the range 150 -180 and another injecting nozzle placed in the axis of the blow-pipe and all three may be connected with a charging funnel each. " With either kind of developed design of the air-jet mill, the material to be ground flows in the required quantity by gravity from the storage container onto the charging dish /disc feeder, the latter being eccentrically shaken. An uniform stream of material from the disc feeder into the material charging funnels located along the edge of the dish. The invention will be visualized in connection with a realized example on basis of drawings attached, according to the following: . Fig. 1 shows the cross section of potential construction mode of the air-jet mill of the invention. Fig. 2 shows a section drawn along the line I-I indicated in Fig. 1. Fig. 3 shows section of another potential construction. Fig. 4 shows a longitudinal section of the material charging system -of the air-jet sϋBSTiτy?E SHEET . mill of the invention. With one of the potential constructions shown as an example, as it can be seen in Figs 1 and 2, three pregrinding chambers /l/ are connected to the grinding space /2/. The confluent nozzles /7/ located in the nozzle casing /6/ and the injecting nozzles /8/ are linked to the pregrinding space /5/ which is equipped with a wear resistant lining by means of charging ducts /9/ the latter being realized by Laval-profiles. The pregrinder is connected with the grinding space with a blowing duct /3/ and a material return duct /4/. The peripheral grinding nozzles /10/ are located symmetrical¬ ly in the grinding space which can be swivelled in the horizontal plane by turning the angle setter /ll/. In the grinding space /2/ there is a wear resistant lining /12/ and an adjustable curb of blades /13-/ concerning the angle. For carrying out the same a gear rim /15/ and a stub /14/ for setting the angle of blades are provid¬ ed. As it can be seen from the drawings, the discharge stub /17/ is located in the axis of the casing /16/ of the air-jet mill. Material charging stubs /18/ and air inlet stubs /19/ are also provided on the facility. _ Fig. 3 shows another potential mode of construc¬ tion. In this case, the pregrinding chamber is of a simpler design; the axes of confluent nozzles /!/ lo¬ cated in the nozzle casings /6/ are set at 150-180 , preferably 150 angles to each other and the three blow pipes, respectively. The angles to be set of the confluent nozzles should be selected in function of the radius of the pregrinding space in a way that it is the component of the velocity of preground material pointing to the grinding space. The development of the grinding casing /2/, the peripheral grinding nozzles /10/ and the ad¬ justable curb of blades /13/ as well as charging of ma- terial is identic with those outlined above. Material ■ in. i E SHEET charging system is given on basis of Fig. 4. The material storing hopper /20/ is equipped with adjust¬ able louvres /21/. The material flows from the hopper onto disc feeder /23/ being shaken by an eccentrically operating unit /22/ spreading the material uniformly and distributing the same into charging funnels /24/ the latter being connected to the material supply stub /18/. Main advantage of the air-jet mill of the in- vention lies in the condition that, in contrast to the facilities known so far, it is capable of producing grain fractions less than 10 ,um in size, moreover cryogenic grinding of thermoplastic materials and in a given case for applying surface treating materials con- temporarily with grinding. Further advantage of the facility lies in the excellent utilization of energy being fairly the consequence of the novel shaping of the inner sizer. The utilization efficiency of the grinding energy as compared to the conventional si- milar facility increases to one and a half-fold that of. Particular advantage lies in the condition that the unit does not comprise any movable parts which could be exposed to severe wear and the only one construc¬ tional part /the lining of the pregrinder/ which is exposed to the greatest wear can easily and at little expense be replaced. SUBSTITUTE SHEET

Claims: CLAIMS 1. Air-jet mill for fine grinding, surface treatment and/or cooled grinding, the facility being equipped with pregrinding chambers, circular-shape grinding space connected by blow pipes to the pre¬ grinding chambers, peripheral grinding nozzles in the grinding space and discharge stub for the ground product in its axis, as well as inner sizer, c h a ¬ r a c t e r i z e d by the condition that the pre¬ grinding chambers /l/ are connected with the grinding space /2/ preferably with three or more tangential blow channels /3/ and material return channel /4/, peripheral nozzles /10/ in the grinding space /2/ are arranged symmetrically along a circle and their number is preferably the two-fold of the injecting nozzles /8/. 2. Construction of the air-jet mill according to claim 1, c h a r a c t e r i z e d by the con¬ dition that there is a curb of blades /13/ in the grinding space /2/, the latter being replaceable and/ or the angle of blades adjustable during operation. The surface of the grinding space is shaped such that it rises along a circular arc on the bottom and exhibits a hyperboloid on the top. 3. Construction of the air-jet mill according to claim 1 or 2, c h a r a c t e r i z e d by the condition that three or more confluent nozzles /7/ set preferably at 90°-180° angles to each other being located in a nαzzle casing /6/ and an injecting nozzle /8/ located in the axis of the blow pipe /3/ are connected to the pregrinding chamber /l/ and all nozzles can be adjusted in axial direction. BUI Η __ SHE •5 " " 4. Construction of the air-jet mill according to any of claims 1 to 3, c h a r a c t e r i z e d by the condition that peripheral grinding nozzles /10/ are provided the latter being replaceable and rotatable in the horizontal plane. 5. Construction of the air-jet mill according to any of claims 1 to 4, c h a r a c t e r i z e d by the condition that in the grinding space and in the pregrinding space there is a very hard repleceable lining /5,12/ made preferably of sintered corundum or various carbides or glass-hard hardened steel. 6. Construction of the air-jet mill according to any of claims 1 to 5, c h a r a ' c t e r i z e d by the condition that the connection with the material stroring hopper /20/ is accomplished by adjustable louvres /21/, a disc feeder /23/ divided preferably into nine segments and is shaken by an eccentrically operated unit /22/, and by charging funnels /24/. 7. Contruction of the air-jet mill according to any of claims l to β, c h a r a c t e r i ze d by the condition that the horizontal nozzles /7,8/ of the pregrinding chamber are connected with the material supply ,gtub /18/, the vertical nozzles /8a/, however, to the storage tanks of the coolant and/or surface treating material. SUBSTITUTE SHEET

Inventors: CSILLAG ZSOLT, CZAFIT SANDOR, KALMAN TIBOR, LAJTAI BELA, LEGAT TIBOR, MOLNAR GABOR, MORZAL JANOS, ROSENMANN FERENC, SITKEI FERENC, SOLYMAR KAROLY, STEINER JANOS, SZABO BALINT, SZENTGYOERGYI GEZA, TOTH PAL, VALLO FERENC, ZSEMBERI LASZLO, CSILLAG, ZSOLT, CZAFIT, SANDOR, KALMAN, TIBOR, LAJTAI, BELA, LEGAT, TIBOR, MOLNAR, GABOR, MORZAL, JANOS, ROSENMANN, FERENC, SITKEI, FERENC, SOLYMAR, KAROLY, STEINER, JANOS, SZABO, BALINT, SZENTGYOERGYI, GEZA, TOTH, PAL, VALLO, FERENC, ZSEMBERI, LASZLO
Applicants: MAGYAR ALUMINIUM, MAGYAR ALUMINIUMIPARI TROESZT
Application year: 1986
Main classification: B02C19
IPC codes: B02C19