US3756400A

US3756400A - Method and apparatus for sifting out fine particles by utilizing supersonic vibration

Info

Publication number: US3756400A
Application number: US00170242A
Authority: US
Inventors: O Kammori; I Taguchi
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 1968-04-15
Filing date: 1971-08-09
Publication date: 1973-09-04
Anticipated expiration: 1990-09-04

Abstract

Method and apparatus for sifting out fine particles according to their original sizes, into which apparently larger-sized particles formed by the cohesion of such fine particles have been split by applying supersonic vibration in the solution, such sifting-out being carried out by applying supersonic vibration also to a set of the sieves of one or more mesh sizes.

Description

United States Patent [1 1 Kammori et al.

[ METHOD AND APPARATUS FOR SIFTING OUT FINE PARTICLES BY UTILIZING SUPERSONIC VIBRATION [75] Inventors: Ohiko Kammori; Isamu Taguchi,

Kawasaki City, Kanagawa Prefecture, Japan [73] Assignee: Nippon Steel Corporation, Tokyo,

Japan 22 Filed: Aug. 9, 1971 21 Appl.No.: 170,242

Related US. Application Data [63] Continuation-in-part of Ser. No. 815,983, April 14,

1969, abandoned.

[30] Foreign Application Priority Data 209/233, 3, 5, 1, 269, 317, 319, 379, 380, 364, 365; 210/19; 73/432 PS; 259/DIG. 43

1451 Sept. 4, 1973 [56] References Cited UNITED STATES PATENTS 3,490,584 l/l970 Balamuth 209/1 2,785,768 3/1957 Ganchard 55/103 X 3,305,481 2/1967 Peterson 209/233 UX 3,366,234 1/1968 Suhm et a1.... 209/21 3,463,321 8/1969 Vanlngen 209/233 X 3,472,202 10/1969 Webb 209/1 X OTHER PUBLICATIONS Allen-Bradley Sonic Sifter, l 1-4-65, pp. 2-8. 1 l465,

The Profitable Use of Testing Sieves, W. S. Tyler C0., Cleveland, Ohio; 9-24-1940; pp. 20-21 Primary ExaminerTim R. Miles Assistant ExaminerWilliam Cuchlinski, Jr. Att0rney-E. F. Wenderoth et a1.

[57] ABSTRACT Method and apparatus for sifting out fine particles according to their original sizes, into which apparently larger-sized particles formed by the cohesion of such fine particles have been split by applying supersonic vibration in the solution, such sifting-out being carried out by applying supersonic vibration also to a set of the sieves of one or more mesh sizes.

6 Claims, 12 Drawing Figures PATENTEDSEP 4191a SHEH 1 OF 2 FIG. 3

FIG. 2

FIG.

Attorneys FIG. 5 25 26*Y* METHOD AND APPARATUS FOR SIFTING OUT FINE PARTICLES BY UTILIZING SUPERSONIC VIBRATION This application is a continuation-in-part of Ser. No. 815,983 filed Apr. 14, 1969 now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates in general to a method and apparatus for sifting out fine particles, and more particularly to a method and apparatus for sifting out fine particles by utilizing supersonic vibration.

2. Description of the Prior Art A conventional and widely used method for sifting out fine particles such as powder of metal oxides, is the method using a sieve having a comparatively rough mesh size of more than about 0.04 mm, while applying mechanical vibration to the sieve. This method, however, is inefficient because as the mesh of the sieve becomes finer, it gets choked up, and such choing can not be avoided even by applying mechanical vibration, making it difficult to achieve good sifting-out. In order to overcome this difficulty, when sifting out fine particles in a solution by using a sieve having a fine mesh, there is used such a step as pressing from the top of the solution or, reversely, applying suction from the bottom of the sieve to reduce pressure, so as to raise efficiency. Even with such steps, the above method is not successful in achieving efficient sifting-out, because fine particles tend to cohere to form what appear to be larger-sized particles, which willnot be completely separated into fine particles even when such a dispersing agent as a surface activating agent is added and which larger-sized masses of particles tend to choke up the sieve and thereis thus great difficulty in sifting out particles according to various granular sizes.

In carrying out the conventional methods as described above metal filters of fine mesh in the form of metal or a net made of fine steel wire are generally used. However, it is difficult to obtain such a net having a mesh size less than about 0.04 mm.

Regarding the production of the metal filter, there is known a method for producing it by sintering metal powder. By this method it is possible to obtain sufficient mechanical strength and as fine a mesh size as about 0.01 mm, but the method is not successful in obtaining a uniform size of mesh. Therefore, it is difficult to produce metal filters having a uniform mesh and a mesh size less than 0.04 mm by the conventional metal filter production methods.

The above-mentioned difficulties in producing metal filters having a mesh size less than 0.04 mm and in sifting out fine particles accurately according to the actual size even when using a sieve having a comparatively rough-mesh size of about 0.04 mm by the conventional sifting-out methods, make accurate and efficient sifting-out of such fine particles as powder of metal oxides extremely difficult.

SUMMARY OF THE INVENTION On the basis of studies to eliminate the above drawbacks from the conventional sifting-out methods, the inventors of the present invention have achieved a method for sifting out fine particles accurately according to granular sizes after having separated particles which have cohered into larger-sized particles by utilizing supersonic vibration, and also by applying such vibration to the sieve so as to prevent its choking and to obtain good sifting-out of fine particles.

Supersonic vibration, has been used for the cohesion of such fine particles as coal dust in water into largersized particles so as to facilitate their precipitation to separation, for metal electrolysis to make fine powder of metals, for the overcoming of the cohesion of organic matters contained in a solution to make extremely fine particles of such matters, and for cleaning the mechanism of a watch.

However, such uses of supersonic vibration have nothing to do with its utilization according to the present invention for sifting-out of fine particles according to their actual sizes and increasing the sifting-out speed.

The principal object of the present invention is to provide a method of wet-type sifting-out of fine particles and an apparatus therefor, according to which method, supersonic vibration is applied to fine particles, so as to prevent cohesion of such particles, maintain them in the well dispersed state, and also to prevent choking of the sieve, thereby making possible rapid and efficient sifting-out of particles of a mesh size less than 0.04 mm.

Another object of the present invention is to provide a method of wet-type sifting-out of fine particles and an apparatus therefor, by which are made possible an increase of the sifting-out speed of fine particles and rapid and accurate sifting-out of various kinds of powder according to actual granular sizes.

In order to attain the above objects, the present invention is characterized by sifting out fine particles rapidly in a solution, applying supersonic vibration to one or more kinds of sieves of fine mesh and also to apparently larger-sized particles formed by the cohesion of fine particles, so as to separate them into original sizes. That is to say, the present invention comprises a method according to which supersonic vibration is applied to a solution made by placing the to-be-siftedout fine particles into water, alcohol or other liquids in which such particles are insoluble, to divide apparently larger-sized particles formed by the cohesion of such fine particles into original sizes of the fine particles; sieves of one or several different mesh sizes are used in a number of stages to sift out the fine particles according to granular sizes; supersonic vibration is applied to the separation zone to vibrate the sieve, so as to prevent chocking of the sieve and accelerate siftingout; and if necessary, sifting-out is accelerated by suction; all these features being for achieving an efficient sifting-out of fine particles.

Furthermore, the above described object of the present invention can be attained by providing an apparatus comprising a continer adapted to receive a liquid in which fine particles are suspended, a fine sieve means fitted to the container to assume an adequate position and a supersonic transmitter inserted in the container, said apparatus being characterized in that the said fine sieve means comprises preferably a plurality of metal filters each having multiple mesh openings of a fixed size in a fixed plane and superposed in closely spaced steps, the tip portion of said supersonic transmitter being in the form of a truncated cone having an end surface larger than the effective plane of said metal filters and positioned near the uppermost filter surface. The apparatus is further characterized in that the said container is divided into an upper and a lower portion,

the filter is interposed between both container portions, and the lower end of the upper container portion has an inner diameter smaller than the effective diameter of the filter while the upper and of the lower container portion has an inner diameter larger than the effective diameter of the filter.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-section of one embodiment of the apparatus according to the present invention for sifting-out fine particles by applying Supersonic vibration.

FIG. 2 is a cross section of another embodiment of the apparatus according to the present invention.

FIG. 3 is a cross-section of the main part of the structure of the apparatus shown in FIG. 2.

FIG. 4 is a cross-section of one embodiment of the sieve of fine mesh used in the apparatus according to the present invention.

FIG. 5 is a enlarged cross-section of part of the metal filter base used as starting material for the metal filter for the apparatus according to the present invention.

FIG. 6 is a enlarged cross-section of part of the metal filter produced from the base shown in FIG. 5.

FIG. 7 is a cross-section of one embodiment of the holder of the sieve used for the apparatus according to the present invention.

FIG. 8 (A), (B), (C), (D) and (E) are microphotographs of powdery vanadium carbide subjected to sizing by the apparatus of the present invention and shown fine particles of more than 20 u, 20-l 5 1., -10 u, 10-5 1., and not more than 5 g, respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENT One embodiment of the apparatus according to the present invention shown in FIG. 1, comprises mainly a horn-type supersonic oscillator I connected at its upper part with a supersonic wave generator, several cylindrical sieve supporting frames 2 placed one on another (for example, having dimentions of 35 mm inside dia., 44 mm outside dia. and mm height), the

sieves

3, 4 and 5 having different mesh sizes getting finer from the top down and being positioned between the frames 2. A line 6 leads from the supersonic wave generator to the oscillator l, and the vibration transmitter 7 is mounted on the tip of the supersonic oscillator l. A funnel 8 is provided beneath the lowermost sieve 5 and a suction pipe 9 connected with a suction pump opens into the space around the funnel 8. A transmitting medium 10 is provided around the oscillator 1.

According to the present invention, the application, as shown in FIG. 1, of supersonic vibrations directly to the sieve 3 from the vibration transmitter 7 for transmitting supersonic vibrations which is placed close (about 0.5 cm) to the sieve 3 in the transmitting medium in the liquid state, together with the reflection of supersonic vibrations from the

sieve

3, 4, etc., is effective in dispersing supersonic waves.

The present invention is characterized by using metal filters having a large number of mesh openings of a definite size in a fixed plane, as the aforesaid

fine sieves

3, 4, etc. in the sieving apparatus constructed as described above. In order to prepare such a metal filter as used in the present invention to sift out fine particles, a thin metal or organic filter having a fixed mesh size is used as a starting material. The material is plated with nickel or platinum so as to have a predetermined fine mesh size. The metal filter thus produced serves to partly reflect the supersonic energy transmitted thereto, by virtue of its metallic character, and the reflected supersonic energy is again reflected by the lower end surface of the supersonic transmitter. Such ultrasonic propagation is effective for perfect dispersion of fine particles between the transmitter and the filter. An experiment conducted by the present inventors for comparison between such a metal filter as described above and a typical marketed organic filter of the same mesh size proved that the metal filter is markedly higher in the speed and accuracy of sieving. It is possible to subject fine particles to a grain size distribution test or sizing, by superposing a number of metal filters having different mesh sizes one above another as illustrated.

One of the sieves 30 composing the said sifting-out device is shown in FIG. 4 (in contrast to the sieves 3 to 5 shown in FIG. 1). This sieve 30 is formed by securing a metal filter 32 having a mesh size as fine as l-50 p. in a ring 31 made of an elastic and corrosion resistant material such as ethylene tetrafluoride. In addition to ethylene tetrafluoride, there can be used as the material of the ring, acrylic resin, polyvinyl chloride, polyethylene and other synthetic resins and rubber; which are corrosion resistant and which can be substituted one for another depending on the kind of suspension. It is preferred that these rings have the same shape so that they can be interchanged and also have a shape such as to be water-tight where they abut one another.

The metal filter 32 having a mesh size as fine as l-50 p. is generally made by plating a metal film having many fine holes of uniform size with nickel and then with platinum to uniformly reduce the size of the holes. This filter is attached to the back of the ring 31 as described above or to an appropriate part of the ring 31 by an appropriate method, to form the sieve 30.

A description will now be given of the metal filter having a fine mesh used for the apparatuses according to the present invention. The metal filter is made from a metal film having many holes of a certain constant size. The film is subjected to electroplating, so as to reduce the size of the holes and to improve the mechanical strength and corrosion resistance. However, when using a metal film having too large a hole size to begin with, there can be produced only a metal filter having a poor quality having a small hole opening ratio and a low sifting-out efiiciency. When electro-plating conditions are not proper, the hole size of the metal filter becomes non-uniform and it is impossible to produce filters of uniform hole size. It is, therefore, recommended to use, as a starting material, a metal film having many holes of a constant size less than 50 u.

The following is an explanation of the filter production method according to the present invention, using examples:

A nickel film (IO-2O u thick: about 30 p. in mesh size) and having dimentions of 55 X 55 mm having many holes of constant, fine size made by photographic and electrolytic etching, was immersed in dilute hydrochloric acid for about 10 minutes to remove the surface layer, was rinsed with water, and immersed in and rinsed with methanol while applying supersonic vibrations at a frequency of about 40 KC. After being taken out of the solution and dried, it was placed between two brass plates 60 X 60 mm and 2.5 mm thick having, at their center, a hole of 45 mm dia. This combination was painted with an insulator except for the said metal film,

and dried. Being held hold in this way, the combination was immersed in an electro-plating bath, to be subjected to nickel plating using the film as a cathode and a nickel plate as an anode, under the following conditions:

The progress of plating was observed through an optical microscope from time to time; the operation was stopped when the holes were reduced to 2 larger than the desired hole size. After being completely rinsed with water, the nickel-plated metal film was subjected to platinum plating using itself as a cathode and a platinum plate as an anode, under the following conditions:

Electrolytic current density: l-5 mA/cm Volume of plating bath: 1000 ml Temperature of plating bath: about 70"C pH of plating bath: about 6.5 Composition of plating bath:

Platinic chloride (hexahydrate); l3 gll Monoammonium phosphate: 45 gll Diammonium phosphate: 240 gll The progress of plating was observed through an optical microscope from time to time; the operation was stopped when the desired hole size was obtained. After being rinsed with water, the platinum-plated metal film was rinsed with methanol and dried.

By using this method, it is made possible to produce metal filters having holes of any uniform size between 1 and t. Such metal filters have high mechanical strength and excellent corrosion resistance and therefore, they can to be used in filtration and other treatments of fine particles.

- For use in the sifting-out of particles for which high corrosion resistance is not required, the single layer of nickel is enough, and additional platinum plating can be omitted. The use of nickel and platinum for metal electro-plating makes it possible to reduce the hole size uniformly, but, for the metal electro-plating method according to the present invention there can be used copper or such other metals as are used for electro-plating of the normal type, as well as nickel and platinum used in the Example above.

FIGS. 5 and 6 illustrate the metal filter produced by the method of the present invention.

In the figures, the metal film 25, should be less than 20 ;1., preferably about 5-10 p, in thickness (T). The material of the metal film 25 is selected from among nickel, copper, iron, zinc, aluminum, chromium, silver, platinum, molybdenum, tungsten, silicon, germanium, etc. and their alloys, preferably nickel and copper. This metal film is so processed that many holes 26 of constant, fine size are made by a chemical or electrochemical method, with a predetermined distance from the edge of a hole to that of another (hereinafter referred to as the distance between holes) (Y) of less than 20 pi. The shape of the hole 26 made in the metal film 25 is generally square, or round, if required. The size (W) of the hole 26 (meaning the diameter if the hole is round) is required to be less than about t, such size being convenient for the reduction of the size by the deposit of a metal layer. The reason therefor is as shown in FIG. 6 that the specifications of the metal film 25 are determined according to the desired distance between holes 27 of the finished metal filter 34. If one half of the difference between the size of hole (W) in the metal film and the size of the reduced hole (W') in the metal filter 34, on which the metal layer has been despoited, that is, the thickness (X) of the metal layer deposited on the metal film, becomes too great, the size (W') of the reduced hole of the metal filter varies widely. The thickness of the metal layer deposited on the metal film is preferably less than 15 ,u. As described below, when the size of the reduced hole of the metal filter is desired to be 35-] u, the size of hole (W) on said metal film should be less than about 50 u.

The material of the metal layer 28 is a metal selected from among nickel, copper, tin, chromium, zinc, cadmium, gold, silver, platinum, etc. and their alloys according to uses of the metal filter, taking into consideration their mechanical strength and resistance to corrosion by solvents required for such uses.

Depending on the use, either a single layer or multilayer deposit of metal can be used. For depositing the metal layer on the metal film electroplating, chemical plating or other suitable methods can be used. Among these electro-plating is most-preferred, because it ensures overall coverage of the metal film with a metal layer, uniformity of the thickness of the layer and control to the desired thickness.

In anticipation of the application of supersonic vibrations the size of the hole (W') and the distance between holes (Y') of the metal filter 34 should be maintained respectively between about 35 and l p. and between about 20 and 50 u respectively while retaining the required hole opening ratio of 0.22O percent.

Referring to the method of producing a metal filter of finer hole size than the above described, that is, less than I ;1., such a metal filter can also be made by plating an organic filter base, thereby reducing the size of holes uniformly and making the filter rigid and corrosion resistant.

For plating said organic filter base with metal there can be used any known method, but in order to obtain good uniform hole size, the use of supersonic vibration during plating is recommended. Among various known methods for plating, one of those which is suited for the above purpose and by which good results can be obtained, is the three-staged plating method according to which are carried out firstly, a non-electrolytic (chemical) plating of an organic base with nickel, secondly, electro-plating with nickel, and thirdly, electro-plating with paltinum. Particularly, the plating with platinum is necessary to improve mechanical strength and corrosion resistance.

The application of supersonic vibration is useful in plating the metal film as well as in plating the organic filter base, as mentioned above. It is recommended that while being held in an appropriate state, a metal film having many holes of constant, fine size be immersed in a threatment bath, and the electro-plating carried out, using the film as thccathode, with the application of supersonic vibrations, so as to reduce uniformly the holes. By this method good results can be obtained, and

a three-stage metal layer is deposited on the film.

In using a metal filter having holes of fine size for the sifting-out according to the present invention, there are shown in FIG. 4. As shown in the figure, the holder 33 is made of a rigid, flexible, chemical corrosion resistant synthetic resin such as ethylene tetrafluoride, having a groove 37 on the inside surface between a concave part 35 on the top surface and a convex part 36 on the bottom surface, such groove 37 being so constructed as to receive the metal filter 34. A cut 38 is provided in the holder 33 for enabling it to be spread to receive the metal filter. The use of such a holder facilitates the fixing of the metal filter and accelerates the sifting-out speed, further raising the accuracy of measurement.

Briefly the sifting-out method according to the present invention, using the apparatus shown in FIG. 1 comprises placing a liquid such as methanol in the cylindrical supporting frames 2, moving the vibration transmitter 7 in the tip of the horn-type supersonic oscillator 1 to about 0.5 cm above the sieve 3 having an appropriate mesh size and applying supersonic vibration to the sieve. There is fed into the cylindrical supporting frame 2 a sample in the form of a methanol solution in which the to-be-sifted-out powder has been dispersed by supersonic vibration, and supersonic vibration is applied to sift the powder out in the frame 2. In this case, if necessary, suction is applied through the suction pipe 9. When using a number of sieves in multistages, uppermost sieve 3 is removed and rinsed with methanol after the above operation is finished, and then the vibration transmitter 7 is moved to about 0.5 cm above the next sieve 4 and the same operation as described above is repeated. Thus, particles are sifted out by successive use of the

sieves

3, 4 and 5 according to different granular sizes.

FIG. 2 shows another embodiment of the apparatus according to the present invention.

The apparatus shown in FIG. 2 includes a supersonic vibrator 11 and a supersonic transmitter 17 fitted thereto. The vibrator 11 is connected to a supersonic generator (not shown) through a cord 16. A container in the form of a funnel is divided into an upper portion 12 and a lower one 18. The upper funnel portion 12 receives the transmitter 17 and a liquid containing fine particles to be sifted out. Fine sieves 13 are interposed between these two

funnel portions

12 and 18. The sieves 13 are superposed and fastened by clamp means 20. A suction bottle 21 is connected with the lower funnel portion 18 and has a port 19 connected through a pipe to a pump for pressure reduction. A tube 22 is placed in the bottle 21 to collect the liquid flowing down from the lower funnel portion 18.

Referring now to FIG. 3, the tip portion of the supersonic transmitter 11 is in the shape ofa truncated cone. The plane end surface of the transmitter l 1 has a diameter 1 larger than the diameterfof the effective circular area of the filter 13 opposed to the transmitter end surface, which is adjacent to the surface of the filter 13 and in parallel therewith. This arrangement constitutes a feature of the present invention. It should be noted here that the effective circular area of the filter 13 refers to the part of the surface of the filter 13 which part remians uncovered by a filter holder receiving the circumferential annular portion of the filter 13. When it is placed between the two funnel poritons, the said part practically comes into contact with the suspension, that is, the liquid in which fine particles are suspended.

When the transmitter 11 having the truncatedconical tip portion is placed in the suspension existing in the upper funnel portion 12, with the tip surface located near the upper surface of the top filter 13, the

suspension surrounded by the plane end surface of the transmitter 11, the upper surface of the said filter 13 and the said wall of the upper funnel portion 12 is in a nearly closed condition (which is not a perfectly closed condition so that the liquid and the fine particles suspended therein flow through the narrow clearance between the transmitter and the side wall of the upper funnel portion). Therefore, the fine particles suspended in the liquid thus narrowly enclosed can be completely dispersed by supersonic vibration. Moreover, since the diameter 1 of the tip surface of the transmitter 11 is larger than the diameterfof the effective circular surface of the filter 13 opposed to the transmitter end surface, and also since both of the abovementioned surfaces are in spaced parallel relationship with each other, sufficient and uniform supersonic transmission to the surface of said filter 13 is possible. This also contributes to perfect dispersion of fine particles. The reason for such concentrated supersonic transmission to the fine particles just above the filter 13 is as follows: Even if the fine particles are once uniformly dispersed in a much larger amount of liquid, the fine particles existing at such places in the container where no sufficiently effective supersonic vibration is applied agglomerate immediately because of their cohesive property. Thus, perfect particle dispersion is difficult, and much supersonic energy is wasted. With this fact in mind it is contemplated in the present invention to apply supersonic vibration only to the fine particles just above the filter 13, whereby the fine particles just about to be sifted out by the filter are perfectly dispersed. Also, no more dispersion than necessary takes place. This is extremely advantageous in terms of operating efficiency. In addition, according to the present invention, fine particles suspended in a liquid are sieved while supersonic transmission is performed; therefore, the sieves (filters) will not get clogged.

When superposing different metal filters 13 according to our invention, it is effective to place them in such a way that the higher the filter position the larger the mesh size, and also to space the filters 13 closely, the preferable spacing being less than 2 mm. This is due to the fact that there occurs effective supersonic transmission even to the lowermost filter and that, because of the close spacing of the filters, the suspension fills the space between the filters continuously by capillarity. The suspension is the supersonic transmitting medium. Therefore, if the space between the filters is continuously filled with the suspension, there occurs desirable ultrasonic transmission even to the fine particles over the lowermost filter, so that the sizing or grading accuracy is improved. It is not preferable for the filter spacing to exceed 2 mm because the suspension becomes discontinuous.

Furthermore, in the present invention it is convenient in respect of grading to make the sizes of the upper and

lower funnel portions

12 and 18 and the filters 13 as required, in such a way that, as shown in FIG. 3, the inner diameter s of the lower end of the upper funnel portion 12 is smaller than the diameterfof the effective circular area of the filters 13 while the inside diameter s of the upper end of the lower funnel portion 18 is larger than the said diameter f of the filters 13. By doing this, it is possible to prevent fine particles from entering between the bottom surface of the upper funnel portion 12 and the filter holder and between the top surface of the lower funnel portion 18 and the filter holder during a sizing operation.

As illustrated and aforementioned, the liquid collecting tube 22 is located below the lower funnel portion 18. This serves to collect fine particles which are smaller than the mesh size of the lowermost filter 13. The fine particles received by this tube are, as required, separated from the liquid by means of a common organic filter and subjected to weight measurement and analysis. The tube 22 should be spaced from a rubber plug fitted to the top of the suction bottle so that the pressure reduction through the port 19 is effective.

An adequate supersonic frequency employed in the apparatus of the present invention is on the order of -100 KC. The supersonic transmmiter is made preferably of a material which has excellent corrosion resistance such as stainless steel. The vertical shift of the transmitter to a predetermined position is conducted by a handle operation.

As mentioned above, the method of the present invention makes possible not only separating the particles cohered into apparently larger-sized particles into original sizes of fine particles but also sifting-out of fine particles according to granular sizes and aquisition of particles of desired granular size. Such sifting-out is rapid and efficient, and can be carried out without choking of the sieves, making possible operation for a long time without replacement or cleaning of the sieves.

The method of the present invention is devised for universality in use, so that it can be applied to wet-type sifting-out of and granular tests on fine powder, foreshadowing the possibility of manufacture of apparatuses for these purposes. Moreover, it is anticipated that the filtration speed for removing fine particles from solution could be greatly raised by use of the method of the present invention, as compared with those obtained when using various filters in the conventional manner. Therefore, it is expected that the application of the method of the present invention will be highly effective, for instance, in the removal of yeast from draught beer, the separation of slime from pyrite containing precious metal and the recovery of rare metal during smelting.

Examples of the present invention will be described hereinafter.

Here follow examples, in which fine particles of vanadium carbide, an oxide inclusion residue extracted from steel, and a sulfide residue extracted from steel were subjected to sizing by using the apparatus shown in FIG. 2.

EXAMPLE 1 Under the following conditions, 100 mg of marketed synthetic vanadium carbide powder was submitted to sizing.

In this example, the apparatus shown in FIG. 2 was as follows:

Metal filters: four in number Size of mesh opening: 20 p, .4., 10 11., 5 ,1.

Space between filters: 1.5 mm

Diameter of the tip of the supersonic transmitter, 6

: 19 mm Diameter of the effective filter area,f 16 mm Diameter of the lower end of the upper funnel portion s 15.5 mm

Diameter of the upper end of the lower funnel portion 5' 16.5 mm

Distance between transmitter tip and topmost filter Supersonic frequency 20 KC Liquid Methyl alcohol The sieving operation was as follows: First, methyl alcohol (5 ml) was supplied into the upper funnel portion, and supersonic transmission was started. After methyl alcohol got into the lower funnel portion, the fine particles previously dispersed in methyl alcohol (about 5 ml) by supersonic vibration were fed gradually into the upper funnel portion with a squirt. Sifting was continued while methyl alcohol was replenished little by little. After the completion of sieving, cleaning was done well with methyl alcohol. Then supersonic transmission was stopped, the transmitter was drawn out, and the pressure reducting pump was operated for suction for 2 or 3 minutes. Thereafter, the clamping means was removed and the filters were taken out together with the holders. The assembly of the filters and holders were placed in a dryer, where the fine particles of vanadium carbide were dried. The particles were then allowed to stand for cooling in a dessicator and directly weighed. The weight of the fine particles on each of the filters was ascertained from the weight of the metal filter and holder which had previously been weighed.

FIG. 8 (A), (B), (C), (D) and (E) are microphotographs showing the particles of vanadium carbide on each of the filters, and correspond to the grain sizes of more than 20 IL, 20-15 l5p.-l0 ;L, 10-5 1.1., and not more than 5 ;1., respectively. As will be clear from the photographs, the grading result was very successful. In addition, Table 1 shows the weight ratio obtained for each grain size range. The operation was repeated five times to examine the reproducibility. As a result, it was made clear that the reproducibility was sufficiently excellent to stand good in actual practice. Besides, the average time required for the sizing was 15 minutes. This means that the grading operation was high in efficiency.

With the use of the aforesaid apparatus of the present invention, mg of oxide inclusion residue extracted from steel was subjected to sizing under the same conditions as in Example 1. While, in Example 1, the weight ratio for each of the particle size ranges was determined. Example 2 was directed to analysis of the composition of the particles in each of the different grain size ranges. Based on the result of the analysis, the content ratio of the components, that is, silicon oxide (Slo aluminum oxide (A1 0 ferrous oxide (FeO), manganese oxide (MnO), and chromium oxide (Cr O in each particle size range was obtained as seen in Table 2. The particle analysis was carried out in the following manner. The particles left on the metal filters taken out with the holders were put in a beaker containing methyl alcohol, and supersonic vibration was applied from below, with water used as its transmitting medium, thereby separating the particles from the filters. Thereafter, the particles were submitted to filtration with the use ofa usual organic filter (such as a German filter and a New clupore filter) and then subjected to the intended analysis. In this example, the particles The aforesaid apparatus was used under the same operating conditions as in Example 1 to grade 50 mg of particles of a residue including sulfides which had been extracted from steel. Three different metal filters of 10 l, 5 u and 3 across mesh openings were employed in this example. After completing the sizing, detection of compounds was carried out by the method of X-ray diffraction analysis. The result is shown in Table 3.

Table 3 makes it clear that ferrous sulfide (FeS) and cementite (Fe C) coexisted in the extracted residue.

TABLE 3 Grain size t) Detected compound More than FeS 10-5 FeS 5-2 FegC Not more than 2 Fe,C (Not subjected to sizing, left intact) Fe,C

The method of the present invention for sifting out fine particles by using supersonic vebration can also be applied to research on inclusions and precipitates in metal samples. Supersonic vibration can also make it possible to isolate the inclusions and precipitates from the samples, retaining the same forms as they are present in the samples and accelerating the dissolution of the sample matrix with a dissolving solution such as iodine-method. Measurement of size distribution and determination after size classification of the inclusions and precipitates can be carried out, using the inclusions and precipitates residues which have been isolated by the above-mentioned supersonic dissolution method and classified according to the name sizes as they are present in the samples by the method of the present in- LII vention of sifting out. The results are of much use in tests and research on metal samples.

What we claim is:

1. An apparatus for sifting out fine particles by utilizing supersonic vibration, comprising:

a container adapted to receive a suspension containing fine particles to be sifted out,

a sieve means fitted in the container, said sieve means comprising a metal filter having a multiplicity of mesh openings of a definite size in a fixed plane, and

a supersonic transmitter having the shape of a truncated cone and placed in said container, the transmitter having a plane tip surface which is larger than the effective area of said metal filter and located near the upper surface of the filter in parallel therewith.

2. An apparatus as claimed in claim 1 wherein said sieve means comprises a plurality of metal filters superposed in steps spaced sufficiently close for said suspension to fill the space between the filters continuously by capillarity.

3. An apparatus as claimed in claim 2 wherein the metal filter spacing does not exceed 2 mm.

4. An apparatus as claimed in claim 1 wherein said container is divided into an upper and a lower portion, the filter is interposed between said container portions, and the lower end of the upper container portion has an inner diameter smaller than the effective diameter of the filter while the upper end of the lower container portion has an inner diameter larger than the effective diameter of the filter.

5. A method of sifting out fine particles by utilizing supersonic vibration, which comprises;

preparing a suspension by mixing a powdery substance with a liquid in which the substance is insoluble,

placing the thus prepared suspension in a container having a sifting device therein with at least two filters superposed and spaced sufficiently closely to one another that said suspension fills the space between said two filters spontaneously due to capillary action, and

placing a supersonic transmitter in said container near the upper surface of the uppermost filter and operating said transmitter for imparting a supersonic vibration having a frequency of 10 to KC to the filters through the suspension between the transmitter and the uppermost filter and the suspension between the filters, whereby fine particles are sifted from said suspension as it passes through the filters.

6. A method as claimed in claim 5 wherein said supersonic transmitter is positioned about 0.5 cm above the upper surface of the sieve.

Claims

1. An apparatus for sifting out fine particles by utilizing supersonic vibration, comprising: a container adapted to receive a suspension containing fine particles to be sifted out, a sieve means fitted in the container, said sieve means comprising a metal filter having a multiplicity of mesh openings of a definite size in a fixed plane, and a supersonic transmitter having the shape of a truncated cone and placEd in said container, the transmitter having a plane tip surface which is larger than the effective area of said metal filter and located near the upper surface of the filter in parallel therewith.

5. A method of sifting out fine particles by utilizing supersonic vibration, which comprises; preparing a suspension by mixing a powdery substance with a liquid in which the substance is insoluble, placing the thus prepared suspension in a container having a sifting device therein with at least two filters superposed and spaced sufficiently closely to one another that said suspension fills the space between said two filters spontaneously due to capillary action, and placing a supersonic transmitter in said container near the upper surface of the uppermost filter and operating said transmitter for imparting a supersonic vibration having a frequency of 10 to 100 KC to the filters through the suspension between the transmitter and the uppermost filter and the suspension between the filters, whereby fine particles are sifted from said suspension as it passes through the filters.