US3602439A - Pneumatic mill for extra-fine powder - Google Patents

Abstract

A supersonic jet mill for producing extra fine and uniform powder from pregranulated material continuously, having a chamber to pulverize material by mutual collision and friction of granular material in a swirl of supersonic pneumatic fluid introduced through jet nozzles, another chamber to separate the pulverized fine powder from coarse powder in a swirl of pneumatic fluid, a cylinder to take out the fine powder without including material in process, and conduits to return the coarse powder to the pulverization chamber by way of the jet nozzles with auxiliary pulverizing effects.

Description

2,958,472 11/1960 Erickson...................... 241/39 Primary ExaminerDonald G. Kelly Altorizey-Wenderoth, Lind & Ponack ABSTRACT: A supersonic jet mill for producing extra fine and uniform powder from pregranulated material continuously, having a chamber to pulverize material by mutual collision and friction of granular material in a swirl of supersonic 241/39 pneumatic fluid introduced through jet nozzles, another 3302c 19/06 chamber to separate the pulverized fine powder from coarse 241/5 39 powder in a swirl of pneumatic fluid, a cylinder to take out the fine powder without including material in process, and conduits to return the coarse powder to the pulverization chamber by way of the jet nozzles with auxiliary pulverizing 241/39X 7 effects.

ll t i te t Inventor Niro Nakayama Osaka, Japan Appl. No. 844,986 Filed July 25, 1969 Patented Aug. 31, 1971 Assignee Nippon Pneumatic Mfg. Co., Ltd.

Osaka, Japan 8 Claims, 3 Drawing Figs.

References Cited UNITED STATES PATENTS Hate fies [54] PNEUMATIC MILL FOR EXTRA-FIN E POWDER [51] Int. [50] Field of PATENIED M1631 IBH 3602.439

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INVENTOR NIRO NAKAYAMA BY WWW, 55114192 71444 ATTORNEYS PATENTED M1831 l97| 3 02 439 SHEET 2 or 2 2| INVENTOR F|G.3 NIRO NAKAYAMA BY 574 x444 ATTORNEYS PNEUMATIC MILL FOR EXTRA-FINE POWDER The present invention relates to a pulverizer, and more particularly to a continuous pneumatic mill of the kind to reduce pregranulated material to fine powder in such a hydrodynamic way as to pulverize material by mutual collision and friction of particles thereof in a pneumatic swirling fluid with high speed and separate the produced fine powder from coarse granules by the centrifugal force of the swirling fluid.

Conventional continuous pneumatic mills of, the abovedescribed kind drive the pneumatic swirling fluid with'a speed less than the speed of sound propagation, and therefore fail to provide a sufficiently great degree of mutual collision and friction between granules in the pneumatic swirl, and therefore material cannot be pulverized to extra fine mesh. Conventional mills of the above-described kind carry out both pulverization and separation in the same chamber where the pneumatic fluid is swirled, and therefore fail to separate the produced fine powder substantially from coarse powder due to disturbances attributed to the pulverization, and therefore the produced fine powder is not substantiallyuniform in size. Moreover, conventional mills take out the produced fine powder without sufficiently isolating it from the material in process, and therefore the product cannot help but contain some of material in process. Furthermore, conventional mills do not carry out auxiliary pulverization to any extent as the separated coarse powder is returned to the main pulverization process for repulverization, and therefore efficiency cannot be improved at all during the repulverization.

An important object of the invention is to provide a continuous pneumatic mill which pulverizes pregranulated material to extra fine mesh size.

Another important object of the invention is to provide a continuous pneumatic mill which separates fine powder of substantially uniform mesh from coarse powder following the pulverization.

A further object of the invention is to provide a continuous pneumatic mill which takes out the separated fine powder without allowing material in process to be included in the fine powder.

A still further object of the invention is to provide a continuous pneumatic mill which improves efficiency during repulverization of the coarse powder separated from fine one.

A more specific object of the invention is to provide a continuous pneumatic mill which pulverizes pregranulated material in a chamber where supersonic pneumatic fluid is swirled, separates the resultant fine powder from coarse powder in another chamber where the same pneumatic fluid is swirled but with a reduced speed, and takes out the separated fine powder in a sufficiently isolated relation to material in process, and returns the separated coarse powder to the pulverization chamber after some auxiliary pulverization on the way.

Other objects and various features of the invention will be more apparent from the following description of a preferred form of the invention shown by way of example in the accompanying drawings, in which:

FIG. 1 is a vertical section of a pneumatic mill in accordance with the invention;

FIG. 2 is a top end view of the pneumatic mill shown in FIG. 1; and

FIG. 3 is an enlarged vertical section ofajet nozzle shown in FIGS. 1 and 2.

As wholly illustrated in FIGS. 1 and 2, the embodiment of the invention comprises an annular pulverization chamber 1. an annular separation chamber 2 mounted on the pulverization chamber 1, a delivery cylinder extending downward from the center of separation chamber 2 through the pulverization chamber 1, a conical guide drum connected to the delivery cylinder 10. a cylindrical stack 16 connected to the guide drum 15, a plurality ofjet nozzles 3 arranged around the pulverization chamber 1, an annular manifold 13 connected to the jet nozzles 3, a plurality of return pipes 11 arranged around the separation chamber 2, and a feed nozzle 6 connected to the pulverization chamber 1.

A pneumatic source (not shown) is connected both to the manifold 13 at an inlet flange l9 and to the feed nozzle 6 at an inlet nozzle 17 for supply of high pressure driving fluid.

The pulverization chamber 1 has a plurality of apertures 4 through the annular sidewall thereof. The apertures 4 are equally spaced from each other around the circumference of chamber 1 and are directed in an eccentric relation to the center of chamber 1, and the jet nozzles 3 are opened to the apertures 4 at one end, respectively. The pulverization chamber 1 has at least one radial aperture 5 through the annular sidewall thereof, and the feed nozzle 6 is connected to the aperture 5 at one end. The ceiling of pulverization chamber 1 is common with the floor of separation chamber 2, and the common member is provided with an annular aperture 7 in the center thereof for communication between chambers 1 and 2.

The separation chamber 2 has a plurality of apertures 8 through the annular sidewall thereof. The apertures 8 are equally spaced from each other around the circumference of chamber 2 in an eccentric relation to the center of chamber 2 and are directed, and the return pipes 11 are connected to the apertures 8 at one end, respectively.

The upper end of delivery cylinder 10 opens into the center of separation chamber 2, while the lower end thereof is opened into the upper port of guide drum 15. The lower port of drum 15 opens toward a suitable container (not shown) to receive the product. The upper end of delivery cylinder 10 is provided with an annular flange 9 which extends into the separation chamber 2 just like an umbrella sufficiently to shelter the annular aperture 7 thereunder. The middle portion intermediate both ends of delivery cylinder 10 is surrounded with the annular aperture 7 provided in the ceiling of pulverization chamber 1.

The'cylindrical stack 16 extends upward from the center of guide drum 15 through the delivery cylinder 10 and separation chamber 2. The lower end of stack 16 opens into the guide drum l5 and the upper end thereof opens to the atmosphere.

Each of the jet nozzles 3 which is connected to the corresponding aperture 4 of pulverization chamber 1 at one end 22 is connected to the annular manifold 13 at the other end 20 by a pipe 14. As particularly shown in FIG. 3, the jet nozzle 3 is divided into two sections one on each side of a throat 21 where the inner diameter of nozzle is a minimum; one section extends from manifold end 20 to the throat 21 with a gradually decreasing inner diameter, and the other section extends from the throat 21 to the chamber end 22 with a gradually increasing inner diameter. I

The graduation of inner diameter of jet nozzle 3 is determined such that the speed of the high pressure driving fluid is changed from subsonic to supersonic immediately after it passes the throat 21 as it runs through the nozzle 3 from the manifold end 20 to the chamber end 22. When the pneumatic fluid exceeds the speed of sound propagation, there may occur a shock wave increasing pressure abruptly, say, at a critical point 24 in FIG. 3. The pressure within nozzle 3 will be a minimum intermediate the throat 21 and the critical point 24 where the shock wave occurs.

Each jet nozzle 3 is provided with a radial aperture 23 through the sidewall thereof. The aperture 23 is located at a place between the throat 21 and the critical point 24, that is, at a place where the pressure within nozzle 3 is a minimum. Each return pipe 11 which is connected to the corresponding aperture 8 of separation chamber 2 at one end is connected to the aperture 23 of the corresponding jet nozzle 3 at the other end.

The feed nozzle 6 which is connected to the aperture 5 of pulverization chamber 1 at one end is connected to a hopper 18 at the other end for supply of pregranulated material. The hopper end of nozzle 6 is also connected to the inlet nozzle 17 in a manner such that material will be driven into the pulverization chamber 1 through the feed nozzle 6 by high-pressure pneumatic fluid.

In the operation of the pneumatic mill, subsonic high-pressure driving fluid is initially supplied from the pneumatic source both to the inlet nozzle 17 and to the inlet flange 19 while pregranulated material is supplied into the hopper 18.

On one hand, the driving fluid entering the inlet flange 19 is fed into the pulverization chamber 1 by way of the manifold 13, connecting pipes 14, jet nozzles 3 and eccentric apertures 4. The fluid reaches supersonic speed as it passes the throats 21 of nozzles 3, and the supersonic fluid is swirled in the pulverization chamber 1.

On the other hand, the driving fluid entering the inlet nozzle 17 is also fed into the pulverization chamber 1 but by way of the feed nozzle 6 and radial aperture 5. The fluid carries pregranulated material from the hopper 18 into the pulverization chamber 1. The materials grains are then swirled in the supersonic fluid flowing through the jet nozzles 3 into the pulverization chamber 1.

While being swirled, the material grains are pulverized by acute mutual collision and friction. During this time, centrifugal force tends to move relatively large particles toward the periphery of chamber ll while relatively small particles are moved toward the center of chamber 1. Therefore, the finer they are pulverized, the nearer the particles move to the center of chamber 1.

The pulverized particles coming nearer to the center of pulverization chamber 1 are driven into the separation chamber 2 by way of the annular passage 7. They are then guided to the relatively peripheral area of separation chamber 2 along the lower edge of annular flange 9.

The driving fluid is still swirling in the separation chamber 2 but with a reduced speed which is less than the speed of sound propagation. In the chamber 2, the swirling speed of the fluid is sufficient to carry out to a substantial extend centrifugal separation. Thus relatively fine powder tends to move toward the center of separation chamber 2, while relatively coarse powder tends to move toward the periphery of chamber 2.

The fine powder is then guided to the upper end of delivery cylinder 10 along the upper edge of annular flange 9. The fine powder is taken out by way of the delivery cylinder 10 and down the guide drum 15. And gas is exhausted to atmosphere by way of the guide drum and cylindrical stack 16,

The coarse powder which is moved toward the periphery of separation chamber 2 is returned to the pulverization chamber 1 by way of the eccentric apertures 8, return pipes 11, jet nozzles 3 and eccentric apertures 4.

The returning fluid flows with sufficient case because each return pipe 11 is connected to the corresponding jet nozzle 3 through the radial aperture 23 which is located at a place where pressure is almost a minimum in the nozzle 3, that is, between the throat 21 and the critical point 24. Then the coarse powder is pulverized to some extent by mutual collision and friction in the shock wave occuring around the critical point 24 in the jet nozzle 3, before it is fed into the pulverization chamber 1. The coarse powder which is already pulverized to some extent in the jet nozzle 3 is further repulverized in the pulverization chamber 1 together with material newly fed through the feed nozzle 6.

The above-described operation is continued automatically. Fine powder is continuously taken out by way of the delivery cylinder 10 and guide drum 15 into a suitable container as long as subsonic high-pressure driving fluid is supplied through the inlet nozzle 17 and the inlet flange 19 while material is supplied through the hopper 18.

Since the pneumatic swirling fluid is supersonic in the pulverization chamber 1, the number of intergranular collisions the amount of friction is great in the swirl and therefore pregranulated material is pulverized to substantially extra fine mesh size.

Since the separation process is carried out in the chamber 2 that is different from the pulverization chamber 1, the separation is substantially free from disturbances attributed to the pulverization and therefore fine powder of substantially uniform mesh is separated from coarse powder following the pulverization.

Since the annular flange 9 shelters theannular aperture 7 thereunder sufficiently, the produced fine powder is isolated from material in process and therefore the produced fine powder is taken out without material in process being contained in the fine powder.

Since the return pipes 11 are connected to the respective radial apertures 23 located in the manifold side of critical point 24, some auxiliary pulverization is carried out as the separated coarse powder is returned to the pulverization chamber 1 for repulverization and therefore efficiency is improved during repulverization of the coarse powder separated from the fine powder.

It will thus be seen that the continuous pneumatic mill in accordance with the invention obtains powder of extra fine and uniform mesh from pregranulated material without allowing material in process to be contained in the product taken out while improving efficiency during repulverization of the separated coarse powder.

While a preferred embodiment of the invention has been illustrated by way of example in the drawings and particularly described, it will be understood that modification may be made in the shown embodiment. Moreover, the features of the embodiment shown in the drawings are mutually interchangeable so far as they are compatible.

What is claimed is: i

1. A pneumaticpulverizer to reduce pregranulated material into substantially fine and uniform powder continuously, comprising an annular chamber to swirl supersonic pneumatic fluid therein to pulverize pregranulated material, another annular chamber mounted on said annular pulverization chamber to swirl pneumatic fluid therein to separate pulverized fine powder from coarse powder, a cylinder extending downward from the center of said annular separation chamber through said annular pulverization chamber to deliver separated fine powder, nozzle means arranged around said annular pulverization chamber to jet supersonic pneumatic fluid into said pulverization chamber, conduit means arranged around said annular separation chamber to return coarse powder from said separation chamber to said pulverization chamber, means connected to said jet nozzle means to distribute pneumatic fluid to said jet nozzle means, means arranged around said pulverization chamber to feed pregranulated material into said pulverization chamber, means connected to said delivery cylinder to guide delivered fine powder out of said delivery cylinder, and means connected to said guide means to exhaust a gas from said guide means; said annular pulverization chamber being provided with an annular passage in the center thereof communicating with said annular separation chamber, said annular passage surrounding a portion intermediate the upper and lower ends of said delivery cylinder, said annular pulverization chamber being provided with a plurality of ports through an annular sidewall thereof to introduce supersonic pneumatic fluid therethrough, said ports in said pulverization chamber being spaced equally around the circumference of said annular pulverization chamber and directed in an eccentric relation to the center of said pulverization chamber to swirl supersonic pneumatic fluid satisfactorily therein, said separation chamber being provided with a plurality of ports through an annular sidewall thereof to withdraw pneumatic fluid therethrough, said ports in said separation chamber being spaced equally around the circumference of said separation chamber and directed in an eccentric relation to the center of said separation chamber to withdraw swirling fluid, said pulverization chamber provided with at least one radial port through an annular sidewall thereof to introduce pneumatic fluid therethrough, said delivery cylinder being provided with an annular flange extending from the upper end thereof into said separation chamber to shelter said annular passage sufficiently to keep separated fine powder from being mixed with material in process entering said separation chamber through said annular passage, said jet nozzle means being connected to said eccentric ports in said pulverization chamber, said return conduit means connected to said eccentric ports in said separation chamber, and said feed means being connected to said radial port in said pulverization chamber.

2. A pnuematic pulverizer in accordance with claim 1 wherein said jet nozzle means comprises a plurality of nozzles, each of which has a throat intermediate both ends thereof, the inner diameter of said jet nozzle being a minimum at said throat and gradually increasing toward both ends thereof, the graduation of the inner diameter of said jet noule being such that pneumatic fluid is changed from subsonic to supersonic speed, causing a shock wave immediately after it passes said throat as it flows through said jet nozzle from one to the other end thereof, the pressure within said jet nozzle being a minimum intermediate said throat and a critical point where the shock wave occurs.

3. A pneumatic pulverizer in accordance with claim 2 wherein said return conduit means comprises a plurality of pipes connected respectively to said jet nozzles to return coarse powder from said separation chamber to said pulverization chamber by way of said jet nozzles.

4. A pneumatic pulverizer in accordance with claim 3 wherein each of said jet nozzles is provided with a radial port intermediate said throat and said criticalpoint where the shock wave occurs, said radial port being connected to said return pipe to facilitate the return flow and to pulverize coarse powder in the shock wave before returning in to said pulverization chamber.

5. A pneumatic pulverizer in accordance with claim 4 wherein said distribution means comprises an annular manifold connected to an outside pneumatic source.

6. A pneumatic pulverizer in accordance with claim 5 wherein said feed means comprises inlet means connected to an outside material source, another inlet means connected to an outside pneumatic source, and nozzle means connected to both of said inlet means to feed material by pneumatic fluid.

7. A pneumatic pulverizer in accordance with claim 6 wherein said guide means comprises a conical drum.

8. A pneumatic pulverizer in accordance with claim 7 wherein said exhaust means comprises a cylindrical stack extending upward from the center of said conical drum through said delivery cylinder and said separation chamber.

Claims (8)

1. A pneumatic pulverizer to reduce pregranulated material into substantially fine and uniform powder continuously, comprising an annular chamber to swirl supersonic pneumatic fluid therein to pulverize pregranulated material, another annular chamber mounted on said annular pulverization chamber to swirl pneumatic fluid therein to separate pulverized fine powder from coarse powder, a cylinder extending downward from the center of said annular separation chamber through said annular pulverization chamber to deliver separated fine powder, nozzle means arranged around said annular pulverization chamber to jet supersonic pneumatic fluid into said pulverization chamber, conduit means arranged around said annular separation chamber to return coarse powder from said separation chamber to said pulverization chamber, means connected to said jet nozzle means to distribute pneumatic fluid to said jet nozzle means, means arranged around said pulverization chamber to feed pregranulated material into said pulverization chamber, means connected to said delivery cylinder to guide delivered fine powder out of said delivery cylinder, and means connected to said guide means to exhaust a gas from said guide means; said annular pulverization chamber being provided with an annular passage in the center thereof communicating with said annular separation chamber, said annular passage surrounding a portion intermediate the upper and lower ends of said delivery cylinder, said annular pulverization chamber being provided with a plurality of ports through an annular sidewall thereof to introduce supersonic pneumatic fluid therethrough, said ports in said pulverization chamber being spaced equally around the circumference of said annular pulverization chamber and directed in an eccentric relation to the center of said pulverization chamber to swirl supersonic pneumatic fluid satisfactorily therein, said separation chamber being provided with a plurality of ports through an annular sidewall thereof to withdraw pneumatic fluid therethrough, said ports in said separation chamber being spaced equally around the circumference of said separation chamber and directed in an eccentric relation to the center of said separation chamber to withdraw swirling fluid, said pulverization chamber provided with at least one radial port through an annular sidewall thereof to introduce pneumatic fluid therethrough, said delivery cylinder being provided with an annular flange extending from the upper end thereof into said separation chamber to shelter said annular passage sufficiently to keep separated fine powder from being mixed with material in process entering said separation chamber through said annular passage, said jet nozzle means being connected to said eccentric ports in said pulverization chamber, said return conduit means connected to said eccentric ports in said separation chamber, and said feed means being connected to said radial port in said pulverization chamber.

2. A pnuematic pulverizer in accordance with claim 1 wherein said jet nozzle means comprises a plurality of nozzles, each of which has a throat intermediate both ends thereof, the inner diameter of said jet nozzle being a minimum at said throat and gradually increasing toward both ends thereof, the graduation of the inner diameter of said jet nozzle being such that pneumatic fluid is changed from subsonic to supersonic speed, causing a shock wave immediately after it passes said throat as it flows through said jet nozzle from one to the other end thereof, the pressure within said jet nozzle being a minimum intermediate said throat and a critical point where the shock wave occurs.

3. A pneumatic pulverizer in accordance with claim 2 wherein said return conduit means comprises a plurality of pipes connected respectively to said jet nozzles to return coarse powder from said separation chamber to said pulverization chamber by way of said jet nozzles.

4. A pneumatic pulverizer in accordance with claim 3 wherein each of said jet nozzles is provided with a radial port intermediate said throat and said critical point where the shock wave occurs, said radial port being connected to said return pipe to facilitate the return flow and to pulverize coarse powder in the shock wave before returning in to said pulverization chamber.

5. A pneumatic pulverizer in accordance with claim 4 wherein said distribution means comprises an annular manifold connected to an outside pneumatic source.

6. A pneumatic pulverizer in accordance with claim 5 wherein said feed means comprises inlet means connected to an outside material source, another inlet means connected to an outside pneumatic source, and nozzle means connected to both of said inlet means to feed material by pneumatic fluid.

7. A pneumatic pulverizer in accordance with claim 6 wherein said guide means comprises a conical drum.

8. A pneumatic pulverizer in accordance with claim 7 wherein said exhaust means comprises a cylindrical stack extending upward from the center of said conical drum through said delivery cylinder and said separation chamber.

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