US3579720A

US3579720A - Apparatus for subdividing fluid mass into grains

Info

Publication number: US3579720A
Application number: US695757A
Authority: US
Inventors: Emile Plumat; Jean Duthoit
Original assignee: Glaverbel Belgium SA
Current assignee: AGC Glass Europe SA
Priority date: 1968-01-04
Filing date: 1968-01-04
Publication date: 1971-05-25
Anticipated expiration: 1988-05-25
Also published as: ES361878A1; CH505645A; NL6818571A; GB1255968A; FR1593596A; NO124637B; BE721907A; DE1900329A1; CA921218A; AT295771B

Abstract

AN APPARATUS FOR SUBDIVIDING A MASS OF MATERIAL, WHICH MAY BE EITHER IN LIQUID OR PASTY FORM, INTO SMALL GRAINS BY BRINGING THE MATERIAL INTO CONTACT WITH A ROTATING PIECE SO THAT THE MASS OF MATERIAL WILL BE IMPELLED FROM THE PERIPHERY OF THE PIECE AND DIVIDED INTO INDIVIDUAL PIECES, AND PERMITTING THESE PIECES TO SOLIDIFY INTO GRAINS AS THEY TRAVEL THROUGH A GASEOUS MEDIUM, THIS BEING ACCOMPLISHED BY SUBMITTING THE PARTICLES TO GASEOUS CURRENTS WHICH ARE NONUNIFORM ALONG THE TRAVEL PATHS FOLLOWED BY SUCH PARTICLES.

Description

M y 1971 E. PLUMAT ETAL I APPARATUS FOR SUBDIVIDING FLUID MASS INTO GRAINS Filed Jan. 4, 1968 4 Sheets-Sheet 1 20 ms g5 m 72 mvsmoas, Emile Plumclt dean Durhoir BY W Zfya ATTORNEYS.

y 25, 1971 E. PLUMAT ETAL 3,579,720

APPARATUS FOR -SUBDIVIDING FLUID MASS INTO GRAINS Filed Jan. 4, 1968 4 Sheets-Sheet z mvsmona Emile Plumor Jean Du'rhoir av W ATTORNEYS.

25, 1971 PLUMAT ETAL $579,720

APPARATUS FOR suamvmme FLUID MASS INTO GRAINS Filed Jan. 4, 1968 I {Sheets-Sheet 3 V M /I44 nwsmoxs. Emile Plumot Jean Duthoir ATTORNEYSX 25, 1971 E. PLUMAT arm. 3, ,7 0

APPARATUS Fd'R susowwme mum MASS 1M0 mums Filed Jan. 4, 1968 4 Sheets-Sheet A FIG. 7

INVENTORS,

Emile Plumut Jean Durhoit ATTORNEY3.

United States Patent O 3,579,720 APPARATUS FOR SUBDIVIDING FLUID MASS INTO GRAINS Emile Plumat, Gilly, and Jean Duthoit, Marcinelle, Belgium, assignors to Glaverhel, S.A., Watermael Boltsfort, Belgium Filed Jan. 4, 1968, Ser. No. 695,757 Int. Cl. B22d 23/08; B29c 23/00 US. Cl. 182.5 15 Claims ABSTRACT OF THE DISCLOSURE An apparatus for subdividing a mass of material, Which may be either in liquid or pasty form, into small grains by bringing the material into contact with a rotating piece so that the mass of material will be impelled from the periphery of the piece and divided into individual pieces, and permitting these pieces to solidify into grains as they travel through a gaseous medium, this being accomplished by submitting the particles to gaseous currents which are nonuniform along the travel paths followed by such particles.

BACKGROUND OF THE INVENTION The present invention relates to the division of a mass of material into particles, or grains, particularly by subjecting the material to the centrifugal action of a rotating piece and by causing the resulting particles to solidify while traveling through a gaseous medium after having been thrown from such rotating piece.

The invention is particularly concerned with a process and apparatus which first causes the material, which may be in liquid or pasty form, to be brought into contact with a rotating piece and to be thrown therefrom, by the rotation of the piece, and thus subdivided into individual particles which are then caused to solidify into grains while traveling through a gaseous medium.

Various processes for producing glass heads have already been proposed. Thus, for example, Belgian Pat. No. 661,293 describes a process wherein spherical glass beads are produced by subjecting a thread of molten glass to the centrifugal action of a rotary piece which causes the glass to be dispersed in the form of spherical particles into a hot Zone in which the centrifugal piece is disposed. After leaving the centrifugal piece, the particles solidify by cooling in the relatively cold surrounding atmosphere.

It has been observed, however, that the means thus far proposed for carrying out these processes have not proven fully capable of solving all of the problems which arise in such processes.

SUMMARY OF THE INVENTION It is a primary object of the present invention to eliminate many of these problems.

Another object of the present invention is to improve the production of small grains of substantially any type of material capable of being placed in a liquid or pasty state.

Still another object of the present invention is to substantially improve the treatment to which such material is subjected after having been thrown from a rotary piece and while traveling to a collecting region.

These and other objects according to the present invention are achieved, in a method for subdividing a material into grains, by bringing a fluid mass of the material into contact with a rotating piece so that the material is expelled from the periphery of such piece and divided into particles which follow trajectories through a gaseous medium and which solidify into grains while traveling along these trajectories and before reaching a collecting zone, by the improvements which involve subjecting such particles to gas currents which present a gas flow that is nonuniform along such trajectories.

The objects according to the present invention are also achieved by certain improvements in apparatus for subdividing a material into grains, which apparatus includes means for supplying a fiuid mass of the material, a rotating piece arranged for receiving such mass and for expelling the mass from its periphery so that the material forms particles which travel along trajectories away from the rotating piece, means defining at least one gaseous medium through which the trajectories pass and in which the particles solidify into grains, and at least one receptacle for collecting the resulting grains. According to the improvements of the present invention, there are also provided gas current producing means associated with such medium for producing gas currents which act on such particles as they traverse such medium and which present a gas flow that is nonuniform along such trajectories.

The term fluid as employed herein is sufficiently broad to cover both pasty and liquid states. Gas current are nonuniform according to the present invention whenever the gas flow to which the particles are subjected varies along the particle trajectories. As will become more readily apparent from the description presented below, these gas currents generally have at least a component transverse to the above-identified trajectories.

Applicants have discovered that in many cases, when the particles produced by the centrifugal action of the rotating piece are subjected to localized gas currents each extending over a well-defined portion of the particle trajectories, the resulting accurately localized actions carried out on the particles permit a more effective control over the grain producing process to be achieved and result in a substantial reduction in the cost of producing the necessary gas flow.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevational cross-sectional view showing in diagrammatic form a portion of a first embodiment of apparatus according to the present invention.

FIG. 2 is a view similar to that of FIG. 1 of another embodiment of such apparatus.

FIG. 3 is a diagrammatic plan view relating to another embodiment of the apparatus according to the present invention.

FIG. 4 is a diagram illustrating one type of gas flow pattern according to the present invention.

FIG. 5 is a view similar to that of FIG. 4 relating to another such pattern.

FIG. 6 is a detail plan view showing part of one of the elements of the apparatus of FIG. 1.

FIG. 7 is a view similar to that of FIG. 1 of yet another embodiment of apparatus according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In general, the particles expelled from the rotating piece in apparatus according to the present invention follow trajectories which extend outwardly from the rotating piece to at least one receptacle where the resulting solidified grains, or beads, are collected. The particles are preferably expelled in all radial directions and all of the trajectories can be considered as together defining a surface on which the average of the trajectories lie. The trajectories pass through a first zone containing a first gaseous medium and then through a particle-solidifying zone containing a solidifying gaseous medium which is different from the first gaseous medium. These gaseous media can differ from one another, for example,

with regard to one or more physical states, such as the temperatures, thereof.

According to one feature of the present invention, it is preferred that the particles, before reaching the solidifying gaseous medium, and at the output of the first zone, be subjected to gas currents which flow transversely to the above-defined average surface in such a manner as to carry ofl? as rapidly as possible that portion of the first gaseous medium which was drawn along with the particles out of the first zone. Thus, the particles are withdrawn from the influence of the first gaseous medium as soon as possible after leaving the first zone.

Since these transversal currents carry off any of the first gaseous medium which may have escaped from the first zone, the result is a substantial reduction in the degree of mixing which would otherwise take place between the first gaseous medium tnd the solidifying gaseous medium. Such a mixing generally constitutes a contamination of the solidifying medium and substantially reduces its effectiveness. Thus, when transversal currents are employed for carrying off any gas escaping from the first zone, it is possible to begin the solidification treatment more rapidly and thus to accomplish the solidification with greater ease.

It is also possible to employ localized currents according to the present invention to prolong the times during which the particles are in free flight, or fall, prior to contacting the walls of the receptacle or other nongaseous bodies. This permits either a substantial increase in the rate at which the material can be converted into particles by a given solidifying arrangement and/or a reduction in the size of the solidifying means required for a given particle production rate. This improvement has led to the elimination of the problems created by the excessively large and cumbersome solidification zones which were previously required for treating large quantities of material. This improvement also permits an increase in the maximum dimensions of the grains, or beads, which can be obtained by the process, particularly when the rate of solidification of the particles is slow because of the composition of the product.

These improvements can be obtained, according to the present invention, by employing localized, or nonuniform, gas currents to deflect the particles so as to lengthen their actual trajectories. As a result, the particles are afforded a longer period of time to undergo solidification.

In apparatus in which the particles are first projected in a substantially horizontal direction by the centrifugal action of the rotating piece and then fall in the space surrounding the rotating piece, it is possible to increase the length of the particle trajectories by applying lo calized gas currents which first cause the particles to follow a substantially horizontal trajectory segment and to then follow an upwardly extending trajectory segment prior to being permitted to fall into the collection receptacle. The particle travel time is increased not only by the time required for the particles to travel over the ascending portion of their trajectories and by the resulting increase in their subsequent descent times, but also by the relatively long time period required for the particles to travel through the highest point of their trajectory, where their velocity is substantially reduced.

FIG. 1 shows one embodiment of the apparatus of the present invention which is intended to perform the operations discussed above.

This apparatus includes a rotary disc 20 which is supported, and rotated, by means of a hollow vertical shaft 22 disposed above the disc. The shaft is itself driven by a suitable motor which is not shown in the figure. The material to be treated, which is a molten salt for example, is preliminarily raised to the necessary high temperature by means of a known device which is also not illustrated and which is connected to the hollow shaft 22. This material flows through the interior of the shaft to the lower surface of disc 20. As a result of the rotation of the disc 20, the molten material remains constantly in contact with the rotating pieces and moves across the lower surface of disc 20. Also under the influence of the rotation of disc 20, the material spreads out over this lower surface to form a film which becomes thinner as it moves towards the periphery of the disc. This reduction in the thickness of the film is due to the fact that a given portion of the molten material occupies a progressively larger area as it moves toward the disc periphery.

When reaching the periphery of disc 20, the material is dispersed into the chamber 24 defined by

horizontal walls

26 and 28 and the generally cylindrical lateral wall 30. Wall 30 is provided with an annular opening 32.

The division of the molten material into individual particles occurs substantially at the periphery 33 of the disc, or slightly therebeyond, depending on the flow rate of the material being treated. Chamber 24 is provided with heating means which could be of the radiant type (not shown) but which are most often constituted by devices, indicated at 34, for delivering hot gases. Such devices could either be constituted by burners or by blowers delivering gaseous combustion products or hot air. Under the effect of the high temperature produced by such heating means, the particles resulting from the division, or fragmentation, of the film of molten material sphere, or assume spherical shape, in the chamber 24 while traveling over the initial portion 36 of their trajectories.

After passing through the openings 32, the particles begin to cool in the chamber 38 which surrounds chamber 24. Chamber 38 contains air at ambient temperature and this air might be more or less heated due to various causes which may or may not be desired. The spherical, solidified particles finally arrive at an annular collection trough 40 from which they can be subsequently removed by any known means.

According to the invention, the particles are submitted, over different segments of their trajectories, to the action of nonuniform gas currents. The arrangements shown in FIGS. 1 and 2 represent several dilferent gas current producing arrangements which can be employed. However, it should be understood that parts of these arrangements could be eliminated or additional parts could be provided, according to the invention, depending on the conditions which it is desired to create.

In certain cases, it is also possible to provide apparatus having numerous gas current blowing devices and to arrange this apparatus so that only selected gas currents are produced according to the needs of individual particle-forming procedures which differ from one another in the nature of the material being treated, the flow rate of material, the treatment temperatures, the average diameter, the shape, or the size distribution of the desired grains, etc.

The arrangement further includes a fresh air delivery tube 42 supplied by a suitable device (not shown) such as a ventilator, the tube opening into a chamber 44 disposed underneath the chamber 24 and communicating with an annular canal 46 through which the fresh air from tube 42 passes and which deflects this air so as to cause it to flow vertically just past opening 32. The resulting ascending air current 48 is controlled in such a manner as to carry off the hot gases which accompany the particles when they pass through opening 32. On the other hand, the velocity of the air can be sufficiently small to not impart any substantial elevation to the particle trajectory 50 traversing the opening of canal 46. In any event, the cooling of the spherical particles is augmented by the current 48 not only due to the velocity of this current, but also due to the fact that the particles are no longer under the influence of the hot gases originating in chamber 24.

In addition, after traversing the outer wall 52 of canal 46, the spherical particles traveling along trajectory portion 54 are subjected to a high velocity, concentrated, ascending current 56 emanating from a conduit 58 which could, for example, be connected to a compressed air source (not shown). This trajectory portion 54 thus has a steep upward inclination and has the efiect of increasing the overall trajectory followed by the particles. By increasing the trajectory of the particles in this manner, it is possible to increase the degree of cooling to which they are subjected and/ or to limit the radial dimension of the cooling chamber 38.

At a sufficient distance from the zone of action of the current 56 there is preferably disposed a particle decelerating arrangement constituted, for example, by two annular conduits 59 disposed symmetrically with respect to the particle trajectories, fed equally with compressed air, and producing currents 60 which are oblique with respect to the associated trajectory portion 62 and which are symmetrical with respect to that trajectory portion.

In those cases where it is desired to not only slow down the particles, but also to deflect their trajectories, the symmetrical nature of the currents 60 can be eliminated and either a single conduit 59 can be employed or the two conduits can be arranged to receive air flowing at different rates. One of these flow rates could be equal to zero at given times.

In order to prevent any undesired drop in the particle trajectories, it is possible to provide suitable additional ascending gas currents. For example, if it is desired to prevent such a drop in the trajectory portion 36 disposed in chamber 24, an annular conduit 66 can be provided and the current 64 issuing therefrom can be regulated in a suitable manner to effect the desired trajectory compensation. Since the conduit 66 is disposed in chamber 24, it is preferably supplied with hot gases. However, for a similar purpose, other conduits could be provided outside of chamber 24 and these conduits could be supplied with fresh air.

After the particles have reached the apex 68 of their trajectory, they might, if they have a suitably high horizontal velocity, component, tend to reach the lateral wall 70 of the chamber 38 and they might adhere to this wall if they have not as yet become sufiiciently solidified. It is also possible that they would break or experience undesirable wear if they should strike the wall 70 after having been sufficiently solidified, particularly if they are made of a material which is very fragile or friable.

According to the present invention, this is prevented by the provision of an annular sheath 72 formed by a closed exterior wall 74 and an interior wall 76 provided with openings 78 having an extremely oblique orientation. When a properly adjusted supply of gas is introduced into sheath 72 via inlet 82, this gas flows through openings 78 to form a curtain 80 of descending gas currents. This curtain 80, if the component currents thereof have sufficient velocity, serves to prevent the particles from coming in contact with the wall 76.

In addition, the air constituting the curtain 80 is eventually deflected by the particle collecting trough 40 and is evacuated in the form of an ascending current 84 which, as is true for the

currents

56, 60 and 80, contributes to the cooling of the spherical particles. Moreover, the ascending current 84 produces the advantageous effect of decelerating the spherical particles as they travel along the portion 86 of their trajectories and of attenuating the shock experienced by the particles when they come within the zone of influence of the curtain 80. Because the ascending current 84 serves to decrease the velocity of the particles just before they come within the zone of influence of the curtain 80, the velocity of the air constituting the curtain 80 can be given a lower value than would be required if the ascending current 84 did not exist. This reduction in the velocity of the curtain 80 serves to reduce the shock to which the particles will be subjected upon encountering this curtain.

It may be noted that the provision of means, such as conduits 59, for example, for producing oblique currents which act to decelerate the particles represents a particularly satisfactory solution to the problem of disposing means for varying the velocities of the gas currents without placing any devices in the paths to be followed by the particles.

An arrangement similar to the structure illustrated for producing the curtain could be provided wherever it is desired to limit the particle trajectories within a selected envelope. As has been mentioned above, these curtains of gas currents will serve to prevent the breakage of the grains which would otherwise occur if they came in contact with solid surfaces, and also serve to prevent the grains from sticking to such solid surfaces if they have not yet completely solidified.

In those embodiments of the process according to the present invention wherein the particles traverse a first zone containing a gaseous medium which is different from the cooling, or solidification, medium before entering this latter medium, it has been found to be desirable to protect the first zone against the entry of any of the cooling medium. It has been determined, in effect, that the conditions under which the treatment is carried out in the first zone are substantially improved, stabilized and rendered uniform when the entry of such other medium into the first zone is completely prevented or at least reduced.

According to one embodiment of the invention, this protection is achieved by regulating the delivery of the first gaseous medium in such a manner that the boundary of the first zone will be traversed by a current which is directed toward the exterior of such zone and which has a suflicient velocity to prevent the entry into the first zone of gas currents from the cooling medium. In effect, the first gaseous medium is urged by the centrifiugal action of the rotary piece and by the resulting particles toward the output of the first zone in the direction of the cooling zone. If a significant supply of gas were not delivered to the first zone, the result would be a pressure drop within the zone which would provoke the entry of gas from the cooling zone or from elsewhere. However, it has been noted that by increasing the delivery of suitable gas to the first medium it was possible to detect a progressive decrease, and finally a complete halt, in the entry of undesired gases into the first zone. In those cases where the outlet from the first zone must be relatively narrow, it has been found that an increase in the flow rate of the first gaseous medium was the most economical means of preventing the entry into the first zone of undesirable gases.

According to another technique for preventing undesired gases from entering the first zone, it has been found to be advantageous to provide means at the outlet of the first zone for producing a curtain of gas which will be impenetrable to the cooling gas medium. In order to render this curtain impenetrable, it has been found to be desirable to distribute the flow of gas constituting this curtain around the entire periphery of the first zone. The velocity and flow rate of the gas constituting this current can be increased to a point at which suitably placed temperature detectors, velocity detectors, or current flow direction detectors, or possibly determinations of the composition of the gas, have indicated that the entry of undesired gases has been completely eliminated.

It has been found to be particularly advantageous to supply this curtain with gas having such a composition and maintained at such a temperature that it would not in any way diminish the effectiveness of the first gaseous medium if it should find its way into the first zone. This permits the avoidance of many difficulties which would otherwise arise if the curtain designed to protect the first zone against the entry of gas from other zones were at such a temperature or of such a composition that it itself would present difiiculties if present in the first zone.

These inconveniences have also been eliminated, in other arrangements, by directing the gas curtain in the direction and the sense of displacement of the particles as they travel through the first zone.

Several specific arrangements for producing such protective currents will be described below with reference to FIG. 1. These arrangements are preferably constructed to produce two curtains which flow obliquely, and symmetrically, with respect to the particle trajectories and which flow in a direction toward the exterior of the first zone in such a manner as to permit the gas current producing elements, or blowers, to be spaced from the trajectories in order to avoid being struck by the particles, while maintaining the desirable effect produced by the flow of the first gaseous medium toward the cooling zone, which flow further reduces the possibility of entry of gas from the cooling zone into the first zone.

Also to be described below are arrangements which direct gas currents toward the region which is immediately adjacent the periphery of the rotating piece. These currents have been found to be capable of modifying the product of the division process. These currents also serve the purpose of replacing the gas escaping from the first zone through the opening 32. Various effects can be produced on the resulting particles by subjecting some parameter of the gas currents produced near the periphery of the rotating piece to a time-dependent variation.

It has equally been found to be advantageous to modify the direction of flow of these currents so as to vary their influence on the liquid or pasty material and also so as to vary their influence on the trajectories of the particles immediately after their formation.

To prevent the entry of cold air, the incidental openings in the chamber 24 are closed and particluarly, if possible, the opening for the passage of shaft 22 through wall 28 is furnished With a packing 88 of a known type or is closed as much as possible preferably by means of battles which are known per se and which are not illustrated in the drawings.

In addition, the gas current exiting through opening 32 is controlled, if possible, in a manner which will be sufficient to prevent the entry of cold air. The pressure drop which tends to occur in the chamber 24 due to the centrifugal movement of the gas toward the opening 32 is compensated, if possible, by the provision of various supply sources, such as

sources

34 and 66, for example. Preferably, there is also provided a protective curtain for the opening 32. This can be formed by currents 90 flowing parallel to the particle trajectory and produced by conduits 92, disposed in or near the opening 32. The curtain can also be produced by annular conduits 94 disposed in chamber 24 and blowing gas currents in a direction oblique to the trajectories from the interior of the chamber toward the opening 32 and these conduits are preferably supplied with hot gas in order to prevent any difficulties from being created by the deflected currents 96 emanating from the conduits 94 and directed toward the interior of chamber 24.

In addition, or alternatively, as desired, one or two annular conduits 98 can be arranged to blow gas streams which constitute one or more curtains 100 just in front of the opening 32. If they have suflicient flow rate, these latter curtains are equally effective for preventing the flow of cold air into chamber 24 and, as is true for the curtains constituted by

currents

90 and 102, for inducing a gas flow in a direction from chamber 24 toward the region surrounding this chamber.

In addition, near the periphery 33 of piece 20 there are provided several annular conduits both above and below the plane of this periphery. The

conduits

104 and 106 are provided with orifices which are positioned to produce horizontal currents 108 and 110, respectively. The

conduits

112 and 114 are formed to produce

oblique currents

116 and 118, respectively. There are also provided annular conduits for producing vertical gas currents, these being the

conduits

120 and 122 for producing downwardly directed currents 128 and 130', re-

spectively, and

annular conduits

124 and 126 for producing upwardly directed

currents

132 and 134, respectively. Each of the

conduits

120, 122, 124 and 126 has a rectangular cross section and these conduits are grouped in pairs with the conduits of each pair being placed side by side.

It has been discovered that by properly adjusting one or more of the

currents

108, 110, 116, 118, 128, 130, 132 or 134 to give them proper velocities, it is possible to modify the weights of the individual particles resulting from the dispersion of the molten film. It is thus only necessary to select the proper current velocity to achieve the desired average particle weight, or size.

It has also been found that different results are produced when different combinations of conduits are used for producing the gas currents in the vicinity of the periphery of disc 20. For example, it is sometimes desired to obtain not only a desired average particle weight, but also a desired granulometry, i.e., a certain distribution of the total weight of the product between the different groups obtained by classifying the resultnig particles according to their dimensions or individual weight. In this case, the range of individual particle weights can be enlarged by creating different conditions for the same production operation. For example, in the region of the disc periphery 33, there can be created two different current velocities one of which could be equal to zero. This can be created simply by modifying the gas delivery system for the associated conduit in a chosen manner, for example, by closing a flap disposed in a bypass, neither the flap nor the bypass being illustrated.

Preferably, the current velocity from one or more conduits is varied in a step-wise manner between two selected values during a succession of fixed time periods. This is shown in the diagram of FIG. 4 wherein the abscissa t represents time, the ordinate V represents current velocity and, during the time periods 136 and 138, this velocity is varied between a relatively low velocity 146 and a relatively high velocity 144. In order to modify the granulometry of the particles produced, it is possible to vary either the duration of one of the two velocities, as shown for the time period 148 of FIG. 4, or to maintain the time period constant and to increase the duration of one of the velocities while correspondingly decreasing the duration of the other velocity as is shown for the time period 150 of FIG. 4. It is also possible to modify the durations of both velocities without maintaining the overall time period constant.

Instead of acting on the velocity of the gas current, it is possible to act on the direction of such current. For example, the direction could be varied in a manner similar to that represented in FIG. 4 wherein the ordinate of the diagram would represent the angular direction of the current rather than its velocity. In the apparatus, this change in direction can be effected simply by selecting different ones, or combinations, of the

conduits

104, 106, 112, 114, 120, 122, 124 and 126 being utilized at any given instant. Various resultant current directions can be obtained either by combining the currents of several conduits situated on the same side of the plane of disc 20 or by providing suitable current directing elements (not shown).

In certain cases it is preferable to effect a continuous, or progressive, variation in one of the parameters of the gas current, For example, it might be desired to effect such a progressive variation in the velocity of the current being employed, and this variation could have the form shown in FIG. 5 wherein the abcissa t again represents time and the ordinate V again represents velocity. As is shown in this figure, the velocity of a given current can be varied between a minimum value 146 and a maximum valve 144 in several different ways, one variation between the two limiting values occurring during each time period. Thus, as is shown for the first time period illustrated, this variation can be prefectly linear. If it is desirable to maintain each variation time period constant, the rate at which the variation occurs can be modified in the manner shown for the time periods 152 and 154 so as to have a non-linear slope. It is also preferred to sometimes effect a continuous decrease in the current velocity during each time period, rather than the continuous increases shown in FIG. 5. Alternatively, it is possible to divide each time period into a half period during which the velocity is increased and a half period during which the velocity is decreased, the variations during the two half periods being symmetrical.

According to another feature of the present invention, one or more of the gas current supply devices disposed near the periphery of the rotary piece can be constructed to produce gas currents which are nonuniform around the peripheryof such piece. For example, the flow of gas from such device, or devices, can be distributed nonuniformly around the periphery of the piece. It has been found that various arrangements of this type ofler great possibilities for controlling and intervening in the production process without requiring recourse to the abovedescribed techniques for varying the gas currents with respect to time, which time variations can, in certain cases, upset certain conditions in the process.

For example, by providing alternating large and small gas flow rates which succeed one another around the periphery of the rotating piece rather than with respect to time, it is possible to continuously obtain the varying particle production conditions which are sometimes desired and which were discussed above in connection with the time-varying flow rate described with reference to FIGS. 4 and 5.

This distribution in space can also be modified either before each distinct fabrication period or, occasionally, during the course of fabrication in order to correct any noted deviation from the desired granulometric result, or even systematically and, for example, periodically during the entire production process.

Such an arrangement is shown in FIG. 6 for a segment of the

annular conduits

124 and 126. The conduit 124 is provided, in the region 156, with a relatively long slot 158 and, in the alternate sector 160, with a plurality of circular, spaced perforations 162. If the conduit 124 alone were supplied with gas under pressure, a substantial variation in the division conditions to which the molten film on rotating piece 20' was subjected would exist between the zones 160 and the zones 156 and such variation would result in a granulometric distribution which would tend to present two more or less attenuated peaks if plotted as a curve of the total weight of each fraction obtained by grading the particles according to size, the curve being drawn as a function of the dimensions of the particles.

The conduit 126, on the other hand, is provided in each region 156 with a few widely spaced openings 164, and in each region 160 with a larger number of orifices 166. If the conduit 126 alone is supplied with compressed gas, it will have a less marked effect on the granulometric distribution of the resulting product because the difference between the total orifice cross-sectional areas in

sectors

160 and 156 is substantially less than for the conduit 124.

In addition, if compressed gas is being supplied to conduit 124, the influence of this conduit on the resulting product can be progressively attenuated by progressively increasing the gas pressure in conduit 126. This is so because the widely distributed orifices 164 of conduit 126 are found in the same sectors as the slots 158, while the more numerous orifices 166 of conduit 126 are found in the same sectors as the small number of orifices 162 of conduit 124.

Thus, the arrangement illustrated in FIG. 6 offers the possibility of passing alternately between two different gas current conditions. It should be appreciated that it would be equally possible to provide three or more different gas current conditions which could alternate either in time or in space.

In effect, the gas currents produced by the devices adjacent the rotor periphery can act to further divide the particles produced by the disc 20 if the velocity of the resultant of these currents exceeds a certain threshold value. This threshold value can, in certain cases, be approximately equal to double the tangential velocity of the disc periphery.

When gas currents having a sufiicient velocity are provided, they will produce a supplemental division of at least some of the particles produced by the action of disc 20 alone. This supplemental division will have the effect of dividing each such particle into two or more smaller particles of about equal weight, the total weight of these smaller particles being almost equal to the weight of the initial particle. The weight difference between the initial particle and the several smaller particles is due to the fact that the supplemental division of each initial particle also creates a small cloud of extremely small particles.

Thus, this supplemental division serves to reduce the average weight of the particles produced and to increase the granulometric range of the resulting particles. This latter result is due to the presence of the following types of particles: (a) those which do not undergo a supplemental division; (b) the two or more particles produced by the supplemental division of at least some initial particles; and (c) the substantially smaller particles constituting the cloud produced by each supplemental particle division.

In certain cases it might be advantageous to produce a quantity of these substantially smaller particles. However, even if they are not desired, their presence should not prove annoying particularly since they could easily be removed by the gas currents present in the cooling zone, which currents could carry off these extremely small particles without removing the larger particles from the treatment zone.

According to another feature of the present invention, it would be possible to deflect the particles several times in opposite directions transverse to the surface which would be defined .by the trajectories if these trajectories were not influenced by the nonuniform currents according to the present invention. Such multiple deflections of the particle trajectories can be produced by submitting the particles to several gas currents flowing in respectively opposite directions transverse to the above-defined surface. This procedure has the advantage of combining the desirable properties of a relatively long particle travel time with those of a continual, accurately defined movement of the particles which prevents the mixing of particles which have just been formed with those which have already undergone the cooling treatment for a certain period of time. This prevents the time of travel through the cooling zone from varying substantially from one particle to another and thus permits the average particle travel time in the cooling zone to be reduced to a value which need be only slightly more than the time necessary for complete solidification. It would otherwise be necessary to extend the minimum particle travel time in the cooling zone to the time required for complete solidification in order to assure proper solidification of all of the beads.

FIG. 2 shows one embodiment of an apparatus for subjecting the particles to such conditions. This figure shows a rotary disc 20 carried by a shaft 167 and driven by a suitable drive device 168. The upper surface of disc 20 is supplied with a liquid material 170 from a tube 172. A conduit 174 is connected to a source of supply of fresh air for providing the ascending

gas currents

175 and 176, while a conduit 178 is provided for producing a descending current 180.

The trajectory 182 of each particle dispersed from disc 20 has an apex 184 and a low point 186. In order to prevent these particles from striking the exterior wall 188, the latter is protected by a curtain formed by ascending gas currents 190. The totality of the blown air is ultimately evacuated toward the top in the form of a current 192 in the direction of an aspiration device which could be a chimney and/or an exhaust ventilator. The particles are drawn along by the current and extracted by known means such as abrupt cross-sectional enlargements in the passage and/or vortex devices or other apparatus known per se and not illustrated.

It should be noted that it is also possible to produce local currents by aspiration, or suction, devices in place of highpressure, or blower, devices.

In further accordance with the present invention, it is possible to deflect the particles so that their trajectories follow helical paths by subjecting these particles to gas currents whose direction at at least one point in the solidification zone is subtantially inclined to the vertical plane passing through this point and in which the particles passing this point are projected. This permits the trajectories to be lengthened and, in addition, the particles are caused to reach the exterior wall of the solidification zone more or less tangentially so as to substantially reduce the shocks to which the particles will be subjected when striking this wall or, at the least, to facilitate the employment of techniques which permit these shocks to be avoided.

One arrangement for subjecting the particles of this type of motion is illustrated schematically in the plan View of FIG. 3 which shows a circular outer wall 194 around which are provided a plurality of devices 196, which might be in the form of inclined ramps or orifices, for blowing fresh air currents tangentially with respect to the wall 194. The combined effect of the currents produced by all of the devices 196 is a circular current 193. Under the influence of this circular current, the particles dispersed from the disc are caused to follow a spiral trajectory 200 rather than the normal trajectory 202 which is disposed in a vertical plane and which is substantially tangential to the periphery of disc 20.

The region enclosed by wall 194 is preferably given a sufficient height to permit the spiral 200 to have several turns. Such a spiral trajectory substantially increases the travel time of the particles and thus facilitates their solidification and cooling. In addition, since the particles are travelling substantially tangentially to the wall 194 as they approach that wall, any collisions they have with the wall will be relatively light. Moreover, the currents produced by devices 196 can be adjusted to prevent the grains from having any contact whatsoever with the wall so that all of the grains will fall directly into a receptacle disposed around the bottom of the treatment region just within the wall.

The gases forming the current 198 can be evacuated either from the top or from the bottom of the apparatus.

Another embodiment of apparatus according to the present invention is shown in FIG. 7 to include a molten material feeding system 204, a shaft rotation power source 206, a disc 20, a shaft 167 driven by the source 206 and supporting, and rotating, the disc 20. The apparatus also includes a hot chamber 24', hot gas supply devices 34, a protective lid, or dome, 28', an annular conduit 208 for producing a curtain of cold air currents for protecting the chamber 24' from the entry of gases from the region surrounding the chamber, and a cold chamber 38'. Under the hot chamber 24 is disposed a blower 210 communicating with a passage 212. Blower 210 delivers an air stream which is channeled by passage 212 to form an annular current 214 which flows upwardly past the chamber 24'. This ascending current serves to evacuate hot gases flowing out of chamber 24 as well as to oppose the downward inclination of particle trajectory 215 and to increase the cooling of the particles.

In an annular zone 216 surrounding the annular current 214, there is provided an annular conduit 218 supplied with compressed air by means of the pipes 220 and carrying vanes 222 which are oriented to produce an air flow which is directed upwardly and away from the longitudinal axis of the apparatus. The velocity of the air currents produced by device 218 is substantially greater than that required to simply prevent further descent of the particles and is given a value suflicient to deflect the particles upwardly in an abrupt manner so that the particle trajectories will pass through an apex 224.

The current 225 produced by device 218 also preferably have a tangential component for imparting a circulating motion to the particles as well as to the gaseous medium present in the region 216. Finally, the particles are collected in an annular hopper which includes a cone 226, a portion of which is shown in the figure.

To cite one specific example of a practical embodiment of the present invention, a device of the type illustrated was employed for centrifuging and sphering trisodium phosphate at temperatures of between C. and C., where the viscosity of the material is approximately ten poises. Material was supplied at a rate of 50 kg. per hour to a disc rotating in a chamber having a diameter of 600 mm. With a disc having a diameter of 250 mm. and rotating at a rate of 1500 r.p.m., microbeads having an average diameter of 400 microns were produced. Similarly, with a higher material delivery rate and with a disc having a diameter of 600 mm. and rotating at a speed of 3500 rpm, microbeads having an average diameter of 600 microns were produced.

As another example, 550 kg. per hour of sulfur were treated at a temperature of 150 C. in apparatus including a disc having a diameter of 250 mm. and rotating at 3500 rpm. to produce particles averaging microns in diameter.

Glass microspheres of 300 microns average diameter were produced from a molten glass mass having a viscosity of 100 poises and maintained at a temperature of 1350 C., when the molten glass was supplied at a rate of 550 kg. per hour to a disc having a diameter of 250 mm. and rotating at 3500 rpm.

Using apparatus having substantially the form shown in FIG. 1, microspheres having an average diameter of 3 mm. were formed when a current 48 of ambient air was given a velocity of 8 meters per second, this being the velocity required for maintaining horizontal bead trajectories. This process was carried out employing a cold chamber having a diameter of 10 meters. In addition, the apparatus was provided with air current means similar to the device 218 of FIG. 7 and this device was arranged to provide an air current 225 having a velocity of 40 meters per second and effecting a brutal deflection of the particle trajectories.

In order to further illustrate the advantages of systems employing localized currents, it has been found, to cite one example, that a chamber having a diameter of 8 meters was necessary for sufficiently cooling microspheres having a diameter of 1 mm. If a blowing arrangement for producing only the gas current 48 of FIG. 1 were employed in such an arrangement and disposed so that the current 48 was concentrated adjacent the outlet of the hot chamber, the diameter of the cooling chamber can be reduced from 8 meters to 3 meters without producing any difficulties. At the same time, it was found that the difiiculties of cooling the beads were substantially increased when their diameter was raised to a value of 2 mm.

It may be seen from the above descriptions that the pres ent invention is particularly concerned with the division into particles of a substance which is first caused to rotate on a centrifugal piece having a substantially vertical axis. The substance is delivered to a centrifugal piece in the form of a thread of molten material in such a manner that the thread will spread out in the form of a thin film and be dispersed from the periphery of the piece in the form of liquid particles. These particles will travel, as a result of the velocity imparted thereto by the centrifugal piece, along trajectories which first traverse a zone containing a gas at a sufliciently high temperature to permit the particles 13 to sphere under the influence of surface tension. Thereafter, the particle trajectories will pass through a zone containing air at a sufficiently low temperature to solidify the particles before they come in contact with any solid surface.

In accordance with a particular novel feature of the present invention, the particles are subjected to air currents which vary from one point to another along the trajectories.

In various embodiments of the present invention, means are provided for influencing the particles by different types of currents.

Broadly stated, the apparatus for dividing such material according to the present invention includes a supply of such material, either in a liquid or a pasty state, and a rotary piece disposed in such a manner as to receive the material, to rotate it, to divide it into particles and to project the particles along trajectories. The apparatus also includes means defining at least one gaseous medium for solidifying the particles in the form of solid grains as the particles follow their trajectories, and at least one receptacle for collecting the resulting grains. According to the present invention, there are also provided means for producing gaseous currents which act on the particles as they travel along their trajectories and which vary from one point to another along such trajectories.

In particular, the present invention is intended to produce spherical beads of the molten material and such apparatus includes a supply of the molten material, apparatus for permitting this material to blow onto the surface of a centrifugal piece having a vertical axis, and a chamber surrounding the centrifugal piece and containing a gaseous medium, the chamber being provided with means for heating the medium to temperatures at which it is possible for the liquid particles to sphere, preferably under the influence of surface tension. The chamber is also provided with an outlet opening positioned to permit the passage of the particles dispersed from the centrifugal piece in the direction of a cold zone surrounding the hot chamber.

Finally, the present invention relates to the materials divided into grains by the process according to the present invention and particularly to spherical particles obtained by the melting and centrifugal division of a material, followed by the cooling of the resulting particles.

It has been found that the present invention can be applied to an extremely large variety of materials. Among the materials which can be treated according to the present invention, it is necessary to cite glass, to which the invention is particularly applicable, primarily because the division of such material is relatively difficult particularly when it is desired to obtain very small spherical particles such as those utilized in reflecting paints. In effect, the division of such material is rendered difficult by the high viscosity which glass presents when in its molten state.

Moreover, the present invention easily overcomes the cooling difiiculties associated with the low thermal conductivity of glass, above all when it is desired to employ high material flow rates to obtain beads having relatively large dimensions, in which case the quantity of heat to be evacuated is relatively large considering the limited time available for carrying out the cooling operation.

The present invention is also particularly suitable for treating glass in view of the existing strict requirements that the beads be highly spherical and that they not be in any way contaminated, for example, as a result of contact with any type of solid or liquid body prior to complete solidification. These requirements are particularly strict when it is intended to utilize the optical properties of the beads, such as for the reflecting paint mentioned above. It has also been noted that the sphericity of the beads is highly desirable when they are to be capable of flowing easily and when there is a danger that the beads might tend to stick together when stored in bulk after fabrication.

Finally, the fact that glass tends to be highly adhesive throughout a large temperature range created problems in the prior art since it created the requirement that the particles not come in contact with one another or with any part of the apparaus during the bead-forming operation until after the beads had been completely solidified. It will be appreciated that the present invention substantially simplifies compliance with this requirement.

While glass thus presents these multiple problems and requirements, it is necessary to appreciate that one or more of these requirements are also associated with many other materials. This is evidently true for materials which are themselves made of glass or which are more or less similar to glass but which are known as enamels, slag or scoria.

In addition, the present invention can be advantageously applied to the production of grains of a large number of various types of salts, among which can be cited, for example, sodium chloride, bicarbonate of soda, sulfates, nitrates and phosphates. The invention can also be applied to the treatment of a large number of types of fertilizers. The invention can also be applied to the granulation of detergents, waxes, sulfur and plastic materials, such as polystyrene and polyethylene for example.

However, the invention is not limited to materials which are placed in a liquid state by being melted under the effect of a high temperature. In effect, the invention can be applied to the fabrication of grains of a material which is in its solid state only when cooled to below atmospheric temperatures. For example, the invention can be utilized in combination with suitable cold air currents for freezing small drops of water obtained by centrifugation in order to obtain artificial snow.

There exists another group of materials which are placed in their solid state not by cooling, but by heating. Such is particularly the case for solutions, suspensions or pastes whose solidification requires the evaporation of the solvent or solvents contained therein. Among processes on materials of this type which can be carried out according to the present invention it is necessary to mention the drying of sludge and the fabrication of powdered milk and also of various types of salts, these processes being carried out not on molten material but on solutions which are preferably concentrated, saturated, or even supersaturated.

Among other materials which can be treated according to the present invention, it is necessary to mention substances having multiple phases. It is, however, necessary that these substances be initially in, or placed in, a state in which they can flow, i.e., a liquid or pasty state.

As the above enumeration demonstrates, depending on the material being treated and the result to be obtained, it may or may not be desired to produce grains having a more or less high degree of sphericity. If it is desired that the grains have a spherical shape, they can be made to sphere practically spontaneously if their viscosity is very low, as is the case for metals even when they are at a temperature very close to their melting point. In other cases it is often necessary to maintain a special spherin g zone presenting a temperature which is sufficiently high to maintain the material at a low viscosity for the required time. It should be mentioned that the supply of heat could come from the material itself, particularly if the sphering temperature is relatively low and/or if the material is delivered at a temperature clearly higher than its melting point and/or if the quantity of material treated per unit time is relatively large and/or if the thermal losses from the sphering zone are low. It has been found that, as a general rule, in order for particles to sphere in the time period currently provided by the process it is necessary for the material being treated to be maintained at a viscosity of less than 500 poises.

The first zone traversed before the solidification zone is also useful, or necessary, for certain other treatments of a chemical or other nature. In such case, it is possible to provide for the delivery of a gas which will facilitate or perform this treatment either due to the temperature of the gas, or to its composition, or to some other property of the gas. The solidification treatment could also be arranged to effect other than a thermal treatment, for example a chemical treatment.

By way of example, among the treatments which could be carried out either in the hot zone or in the solidification zone, could be mentioned, for example, the oxidation of metals in air to obtain oxide grains or metals having an oxidized surface, the depositing of various types of layers on the grains, the formation of hollow or spongy grains by the formation of internal gas pockets, etc.

Concerning the form, the position and the composition of the centrifugal piece and the manner of delivering a liquid or pasty material thereto, these can be in accordance with the possibilities set forth in Belgian Pat. No. 661,293. In particular, if the centrifugal piece is in the form of a disc having a more or less flat surface and rotatable about a vertical axis, it is possible to support this disc from the bottom or to suspend it from above, and the material to be treated can be delivered to the lower surface of the disc and/or to its upper surface by free flow, or via a conduit, or also through the hollow shaft supporting the disc from above. In addition, it is necessary to mention that the invention can be applied also to processes wherein the division is obtained with the aid of a centrifugal piece having a special configuration and where use is made of various phenomena of the extrusion type, such as in those cases where the centrifugal force causes the molten material to be forced through orifices carried by the rotating piece.

The present invention is also particularly advantageous for the production of grains of materials which can only be treated over a relatively limited temperature range. Such is the case for numerous types of glass, particularly window glass, with regard to which relatively low temperatures can not be employed cosity which glass would have at these temperatures, while relatively high temperatures are not acceptable under given industrial conditions, particularly because they require a great expenditure. However, it is particularly the case for many organic materials or bodies, such as hydrated salts, which decompose or are subject to various undesired reactions or lose molecules of water when maintained outside of a relatively narrow range of temperatures.

The present invention substantially reduces these difiiculties by accelerating the treatment of the material particularly during its solidification phase. Thus, the invention, for example, reduces the difiiculties associated with the treatment of materials which can not be overheated before or during their treatment.

The present invention thus permits a great variety of treatment conditions to be easily mastered and thus greatly expands the potential uses of the process of producing particles by centrifugal action. For example, the invention permits the production of grains, or beads, over an extremely wide range of diameters, which range extends at least from several microns to more than five millimeters, and permits the treatment of variable quantities at least as great as several tons per hour for a single centrifugal piece.

When the material permits, and above all for large quantities, it would be possible to terminate the solidification cooling by employing a liquid such as water or an oil which is selected for its non-toxicity with respect to the material being treated and which is preferably selected on the basis of its low cost.

In most cases, it is necessary to prevent the accumulation of solidified material on the centrifugal piece because such accumulation would render the treatment conditions uncertain and variable above all when the deposits leave the piece in a harmful manner, not to mention the fact that such deposits unbalance the rotating masses. This would exclude the possibility of any forced cooling of the rotary piece in a great many cases. However, this because of the high visdoes not mean that the liquid or pasty material being treated should not wet the piece, i.e., be temporarily adherent thereto and flow in the form of a thin film over the surface of the piece. In fact, such a temporary adherence and flow is useful, if not necessary, for facilitating the imparting of a rotary motion to the material by the piece, which is indispensable to a proper centrifugal action.

It will be understood that the above description of the present invention is susceptible to various modifications, changes, and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

We claim:

1. Apparatus for subdividing a material into grains, comprising, in combination:

material supply means for maintaining the material which is to be subdivided in a fluid state and for supplying a fluid mass of such material;

a centrifugal rotating piece disposed for receiving the mass supplied by said supply means and arranged to rotate for expelling the mass from its periphery by centrifugal action so that the material forms particles which travel along trajectories away from said rotating piece;

means defining a chamber enclosing at least one part of the peripheral portion of said rotating piece and the initial portion of the particle trajectories, said chamber having a particle outlet opening, the interior of said chamber being filled with a first gaseous medium at a temperature which is sufiiciently high to maintain the particles in their fluid state;

means defining a zone disposed outside of said chamber and containing a second gaseous medium through which passes a subsequent portion of the particle trajectories, said zone being at a temperature which permits the particles to solidify into grains;

localized gas current producing means disposed for acting on such particles as they travel along such trajectories to create a gas flow that is nonuniform along such trajectories; and

at least one receptacle for collecting the resulting grains.

2. An arrangement as defined in claim 1 further comprising means adjacent the particle outlet opening of said chamber for producing a curtain of gas currents which are impenetrable by the second gaseous medium, thereby preventing flow of the second gaseous medium into said chamber.

3. An arrangement as defined in claim 1 wherein said localized gas current producing means are disposed in said zone for deflecting thetrajectories of such particles.

4. An arrangement as defined in claim 1 wherein said localized gas current producing means are disposed in said chamber for producing localized currents which act on the particles during the initial portion of their trajectories for modifying the weight of the particles formed by the centrifugal action of said rotating piece.

5. Apparatus for subdividing a material into grains, comprising, in combination:

material supply means for maintaining the material which is to be subdived in a fluid state and for supplying a fluid mass of such material;

means defining a chamber enclosing at least part of the peripheral portion of said rotating piece and the initial portion of the particle trajectories, said chamber having a particle outlet opening and the interior of said chamber being filled with a first gaseous medium which causes the particles to be maintained in their fluid state;

means defining a zone disposed outside of said chamber and through which passes a subsequent portion of the particle trajectories, said zone being filled with a second medium which acts on the particles to cause them to solidify into grains;

at least one receptacle for collecting the resulting grains.

-6. An arrangement as defined in claim 1, wherein said gas current producing means comprise at least one element for producing a curtain of gas currents which is so oriented and which has such a velocity as to prevent the passage of particles through such curtain.

7. An arrangement as defined in claim 1, wherein said gas current producing means include at least one device for producing a plurality of localized gas currents located at progressively increasing distances from the rotating piece, each gas current flowing transversely to the particle trajectories and flowing in the opposite direction from its immediately adjacent gas current.

'8. An arrangement as defined in claim 1, wherein said gas current producing means includes elements producing at least two gas currents which are symmetrical, and which flow obliquely, with respect to the particle trajectories.

9. An arrangement as defined in claim 2, wherein said means for producing a curtain produces at least one pair of curtains of gas currents each flowing obliquely and symmetrically with respect to the particle trajectories and each flowing in a direction away from said chamber.

10. An arrangement as defined in claim '1, wherein said gas current producing means include: at least one unit disposed near the periphery of said rotating piece for producing at least one gas current flowing toward the region immediately adjacent such periphery where the material forms particles, the gas current produced by said unit being adjusted to modify the size of the particles formed by the centrifugal action of said rotating piece; and means for adjusting the current produced by said unit so as to increase the range of sizes of the resulting grains.

11. An arrangement as defined in claim wherein said means for adjusting the current are arranged for cyclically varying at least one parameter of the current produced by said unit between several selected values in order to distribute the sizes of the resulting grains between several specific ranges.

12. In apparatus for producing beads of a material and including a supply of the material in fluid form, means for delivering such fluid material, a centrifugal piece mounted for rotation about a substantially vertical axis and having at least one surface arranged to receive fluid material from such delivery means so that, as the piece rotates, the material will spread out in the form of a thin film which flows toward the periphery of the piece and is there initially divided into particles which are projected away from the piece along trajectories, a chamber surrounding the centrifugal piece and arranged to be traversed by the first portion of such trajectories, means associated with the chamber for producing temperatures therein which are sufficiently high to enable the particles to sphere, the chamber being provided with an outlet opening traversed by such trajectories, and means defining a solidification zone surrounding the chamber and arranged to be traversed by a subsequent portion of the trajectories, the improvement comprising means for producing gas currents directed to act on the particles, which currents are nonuniform along such trajectories.

13. An arrangement as defined in claim 12 wherein said means for producing gas currents include at least one device for blowing cold air currents past said chamber outlet for withdrawing the particles from the influence of any hot gases which may flow through said opening together with the particles.

14. An arrangement as defined in claim 13 wherein said means for producing gas currents are arranged for producing at least one localized air current flowing transversely to the trajectories of the particles and having a velocity sufficient to deflect the particles upwardly and for producing at least one air current acting on at least one substantially horizontal portion of the trajectories and having a velocity which is not greater than that required for just suspending the particles at their existing height.

15. An arrangement as defined in claim 12 wherein said means for producing gas currents are arranged for producing a curtain of air currents having a velocity suflicient to prevent the passage of the particles and flowing in the direction in which the particles move just prior to leaving said solidification zone.

References Cited UNITED STATES PATENTS 1,601,897 10/1926 Wiley et al 182.6X 2,062,093 11/1936 Kann 18-2.6 2,136,988 11/1938 White 182.6X 2,641,028 6/1953 Steele.

2,888,060 5/ 1959 Kjell-Berger 1'82.6X 2,973,550 3/1961 Russell.

3,266,085 8/ 1966 Nacke 182.6

J. SPENCER OVER'HOLSER, Primary Examiner J. E. ROETHEL, Assistant Examiner U.S.. Cl. X.R. 182.6