US3270563A

US3270563A - Apparatus for analyzing for particle size distribution

Info

Publication number: US3270563A
Application number: US313365A
Authority: US
Inventors: Thomas D Sharples
Original assignee: Pennsalt Chemical Corp
Current assignee: Pennwalt Corp
Priority date: 1963-10-02
Filing date: 1963-10-02
Publication date: 1966-09-06
Anticipated expiration: 1983-09-06

Description

Sept. 6, 1966 D{ SHARPLES 3,270,563

' APPARATUS FOR ANALYZING FOR PARTICLE SIZE DISTRIBUTION Filed Oct. 2. 1963 4 Sheets-Sheet 1 INVENTOR. THOMAS D. SHARPLES,

NEW Am ATTORNEY Sept. 6, 1966 T. D. SHARPLES 3,270,553

APPARATUS FOR ANALYZING FOR PARTICLE SIZE DISTRIBUTION Filed 001:. 2, 1963 4 Sheets-Sheet 2 m INVENTOR.

ATTORNEY THOMAS D. SHARPLES e G b (7 b i v 5 Sept. 6, 1966 'r. n. SHARPLES 3, 5

APPARATUS FOR ANALYZING FOR PARTICLE SIZE DISTRIBUTION Filed Oct. 2, 1963 4 Sheets-Sheet s 7 INVENTOR.

THOMAS D SHARPLES mbaflwl wa ATTORNEY Sept. 6, 1966 T. D. SHARPLES 3,270,553

APPARATUS FOR ANALYZING FOR PARTICLE SIZE DISTRIBUTION Filed Oct. 2, 1963 4 Sheets-Sheet 4 I5 I NVENTOR.

THOMAS D. SHARPLES WWW ATTORNEY United States Patent 3,270 563 APPARATUS FUR ANAIJYZING FOR PARTICLE SIZE DISTRIBUTIUN Thomas D. Sharples, Lansdale, Pa., assignor to Pennsalit Chemicals Corporation, a corporation of Pennsylvania Filed Oct. 2, 1963, Ser. No. 313,365

. 12 Claims. (Cl. 73432) This invention relates to analyzing powders and the like for particle size distribution. More specifically this invention relates to analyzing solids for particle size distribution by settling them in liquid in a centrifugal field and continuously or periodically measuring the weight of the settled sol-ids.

In the manufacture of certain products containing small size solid particles, it is of the utmost importance to have the particles meet certain size distribution specifications. For instance, in the manufacture of explosives or rocket fuel, it is essential that the powder concerned be of the desired size. Should, for instance, the oxidizer particles in a rocket propellant mixture be too small the rocket may explode at or near its launching site: should the particles be too large the desired thrust will not be developed. In the manufacture of paints, it is also essential that the particle size be Within a desired range. Large particles may hang on the brush and create streaks on the painted surface. In the manufacture of insecticide powders, care is taken that the particles be not too coarse lest they clog spray nozzles. On the other hand, insecticide powder must be of sufiicient dimension that it will not readily blow away in the wind.

Analyzing for particle size distribution by measuring the settling rate of a suspension of the particles is old and well known in the art. For instance, in the Patent 2,597,899 to Payne there is thoroughly disclosed a procedure and apparatus for determining particle size by forming a suspension of the particles in a gas and then continuously measuring the weight of settlement. Such procedures have been found effective, especially in instances in which a uniform gaseous suspension of the solids is readily achieved.

The present invention may be regarded as an improvement over the prior art methods and it is especially useful with solids of small size (less than ten microns) with which it is difiicult to form a stable gaseous suspension. The present invention involves formation of a suspension of the solids in the liquid and has the distinct advantage that a uniform liquid suspension can oftentimes be formed where uniform gaseous suspensions cannot. This may be explained at least partly by the tendency of small solids in a gaseous suspension to agglomerate. Such agglomeration in a liquid suspension may be avoided by the use of liquids having dielectric constants much greater than air. Dispersing agents also can of course be used in liquid suspensions.

An obvious drawback of using liquid suspension settlin g procedure is the time required under the mere force of gravity to settle the solids. For instance, the settlement of some solids in a liquid medium of density similar to the solids may take weeks or even months of undisturbed quiescence.

While attempts have been made in the prior art to analyze particle size by measuring the rate of settlement of solids in a liquid suspension in a centrifugal field, such attempts have not been accurate since readings have been made by stopping the machine, removing the con- "ice tainer, and measuring the specific gravity (for example) of the liquid. Methods based on volumetric estimates of deposited solids have likewise been inaccurate.

In the present invention I continuously or periodically measure the weight of the centrifugally settled solids. I have found that it is possible to determine particle size distribution by forming a suspension of the solids in a liquid, placing the suspension in a centrifugal system at one side of the axis of the system and without stopping rotation recording the unbalance of the system against elapsed time as the solids settle. By this means I am able to determine the weight of the settled solids vs. time and to derive the distribution of size. Thus I achieve greater accuracy in working with a uniform liquid suspension and at the same time I am not required to wait for virtually intolerable lengths of time to obtain results. Under my invention it is entirely practical to run a size analysis over a range from for instance microns to 1 micron, a range so great as to be of impractical character with gravity devices of the prior art.

It is, therefore, an object of the present invention to provide an apparatus, as well as a process, for analyzing particle size distribution in a way which gives unusually accurate results.

It is a further object of the invention to provide an apparatus and a process to enable particle size distribution analysis of unusual accuracy in a relatively short time.

Further objects of my invention will be apparent to those skilled in the art, upon reading the following specification and examining the accompanying drawings, both of which describe preferred embodiments of the invention.

Referring generally to the drawings:

FIGURE 1 is a front elevation, partly in section, showing an apparatus embodying the invention;

FIGURE 2 is an enlarged fragmentary sectional view showing a portion of an apparatus embodying the invention;

FIGURE 3 is a reduced fragmentary side elevation partly in section of a portion of FIGURE 2 and thereabove;

FIGURE 4 is a reduced fragmentary sectional view taken on the line 4-4 of FIGURE 2;

FIGURE 5A is a view of the index or target of the apparatus. FIGURES 5B through 5F are views of the target while the device is operating;

FIGURE 6 is a sectional view taken on the line 6-6 of FIGURE 7 and showing an element of a modified apparatus embodying the invention with its cover broken away;

FIGURE 7 is a diametrical half section of the element of FIGURE 6;

FIGURE 8 is an enlarged fragmentary sectional view showing a modified form of indicating arrangement for an apparatus embodying the invention;

FIGURE 9 is a sectional view taken on the line 9-9 of FIGURE 8; and

FIGURE 10 is a schematic diagram of a circuit and display means suitable for use with the indicating arrangement in FIGURES 8 and 9.

An apparatus embodying the invention is shown in FIG- URE 1 and generally designated 10. It comprises a base element 12 to which is secured a motor 14- having its drive shaft extending downwardly into the base and terminating in a drive pulley 16. Preferably the motor is of the DO precision drive type with an attached tachometer which is connected to a feed back control power supply (not shown). A mount 18 is secured to the underside of the base element 12 and is formed with an arm 20 to which is secured an upstanding bearing shaft 22. The shaft comprises a tubular element receiving a mounting bolt 24 with an enlarged head 24a and a nut with spring washers for constant pressure. The shaft is provided with an annular shoulder 28 and between the bolt head 24a and the shoulders 28 are clamped a bearing assembly comprising bearing units 30 held apart by a spacing sleeve 32.

As shown a pulley 34 telescopes over the bearing units and the spacer sleeve 32 and is held in clamping relation thereover by a threaded plug 36. A woven drive belt 38 is trained over the drive pulley 16 and the rotor pulley 34 and operatively connects the two.

At its upper end the rotor pulley 34 is enlarged and presents a cup-shaped end 40. Secured to the rim of the cup-shaped end by a bolted holding ring 42 is a diaphragm 44. Preferably the diaphragm is of flexible metal and provides torque transmission from the rotor pulley to a spindle 46 comprising another part of the rotor When the embodiment of FIGURE 1 is operating the diaphragm offers the only lateral support for the rotating elements above it.

The spindle is secured to the diaphragm 44 by a clamping bolt 48 provided with an enlarged head 50 (FIG- URE 2) at its upper end and being threaded at its lower end to receive Washers and a clamping nut 52. Held between the spindle 46 and the head 50 are the inner races of a pair of bearing units 54. The outer races of the bearing units are secured in a clamping cup 56 by a screw ring 58.

Extending upward from the base element 12 above the spindle is the rotor housing 60. In a preferred embodiment the spindle bearing is secured to the upper end of the housing by a pair of flexible supports in the form of rolling diaphragms 62 of the type known commercially as Belloframs. The inner margins of the diaphragms are clamped to the bearing cup by a guide ring 64 bolted thereto, while the outer margins are secured at the upper end of the rotor housing by securing ring 66. The outer margins are spaced from each other by a spacing ring 68, and the clamping ring 66 and the spacing ring 68 are secured to the spindle housing by a series of bolts. As shown a passage 60a extends from the outside of the rotor housing along the housing wall, through the spacing ring 68 and into the space between the diaphragms.

Above its head 50 the clamping bolt is formed with a reduced neck which receives a yoke assembly 70. The yoke assembly, also a part of the rotor, has pairs of diametrically opposed arms 72 and is surmounted by a feed assembly 74. The fed assembly 74 includes a base washer 76 which is engaged about its periphery by an annular outer compartment wall 78. Secured about the inward flange at the lower end of the outer wall 78 is the annular inner compartment wall 80. The outer and inner compartment walls are formed on their inner surfaces with inwardly extending radial vanes as shown, and passages terminating in

spouts

82 and 84 communicate respectively with the two compartments. The

spouts

82 and 84 are oriented in the same direction as the pairs of yoke arms 72, respectively. As shown, the upper end of the clamping bolt 48 is reduced and threaded and receives a hold-down cap 86 which securely holds the base washer 76 against the yoke assembly. Centrally the upper end of the clamping bolt mounts the index plug 88 or target.

As shown in FIGURES 1 and 2. the yoke arms 72 are apertured in alignment adjacent their distal ends, respectively, and pivotally mount, as by trunnion-like pins 90, a pair of tube shields 92 which are free to swing thereabout. The tube shields may be of light metal or glassfiber-reinforced plastic. Tubes 94 are received into the shields 92, respectively, and engage rubber cushions 96 at the outer ends of the tubes (FIGURE 1). The tubes which may be of glass are provided with pouring spouts and the volumes contained by the tubes are adjusted for equality by the careful cutting of a slot in the pouring spout over which excess filling liquid flows when the apparatus is operated. It is essential to the accurate operation of the apparatus that the tubes be adjusted to Weigh and hold as near as possible the same amount of liquid (within 0.1 ml. or better).

Secured to the rotor housing is a cover 98 provided with a drain tube 100 and having a central opening at its upper end covered by a closure plate 102.

Fluid fittings

104 and 106 are mounted in the plate 102 and connected with tubes 108 and 110, respectively, which extend along the underside of the plate and which have spouts aligned with the inner and outer compartments, respectively, of the filling assembly 74 at the top of the rotor.

Mounted on the cover plate 102 between the

fittings

104 and 106 is an upstanding optical assembly that comprises a housing 112 supporting an eye piece 114 and a camera 116. At its lower end the housing supports an adjustable microscope objective lens 117 adapted to be moved up or down into focus by the rotation of the sleeve 117a. The housing also includes a lighting assembly (FIGURE 3) which may comprise a lamp 120. This may be of the xenon-filled capacitor-discharge type. In an enlarged portion 122 the optical assembly housing includes a partial mirror 124 angled to project light from the lighting assembly down toward the target or plug 88. The mirror also passes the reflected light back from the plug so that it may be viewed from the eye piece 114 and recorded in the camera 116. Adjusting means 126 are provided to move the mirror. A unit of appropriate lenses 127 is provided for necessary focusing of the light images onto the objective.

Attention is now directed to the plug 88 or target, as shown in the FIGURE 5A enlargement. The upper surface of the plug is provided with two marks, one of which a is placed as close as possible to the mechanical rotational center of the spindle. The second mark b is displaced from the first by a small distance of, for instance, .010" to .015" on a radial line in the same plane as the axis of the tubes 94 when the device is in operation. The index or target may be formed on the upper end of the plug 38 by giving the end a mirror finish and etching away all but the two marks by masking techniques in a conventional etching process. Thus the marks are preferably tiny mirrors.

In a preferred form of the invention the light-source tube is powered by a current supply that provides two modes of operation. In one mode the driving frequency is quite high, While the power pulse is relatively 'low so that visually it provides continuous illumination that is suitable for focusing through the microscope on the target 80. The second mode of operation is that of a single short durationfl'ash of very high instantaneous power.

In operation, the motor 14 is actuated to drive the rotor. As the rotor is advanced through slow speeds to running speed, pressure is applied through the passage in the rotor housing 60 to the area between the diaphragms 62 (FIGURE 2) by means not shown. The diaphragms thus urge the rotor into central position and support it through its critical speeds and filling. With the rotor at an operating speed the tubes 92 will have swung out to the position as shown in FIGURE 1 and the device is ready for filling.

A suitably prepared suspension having, for instance, on the order of 1 to 2 grams per hundred milliliters of solids to be tested is introduced into one of the two centrifuge tubes 94 by Way of the fitting 104, spout 108, the chamber defined by Wall '80 and tube 84. The liquid introduced into the second tube through fitting 106, spout 110, the chamber defined by wall 78 and tube 82, may be the same liquid as that of the suspension. This liquid may be doctored as by the solution of a salt therein to make the rotor better balanced at the outset. By means.

such as air pressure displacement, pumps or gravity feed, the two liquids are run into their respective tubes as rapidly and as simultaneously as possible and sufficiently in excess of the exact volume of the sedimentation tubes to insure that they overflow into the cover 9-8. Thus, exact adjustment of volumes is assured. Once the spindle is up to running speed and tilled, the pressure may be vented from the area within the diaphragms 62 since the spindle is in a condition of equilibrium and needs no lateral support at this level.

As quickly as possible after filling, a photomicrograph of the index 88 or target is made by camera 116 with both the continuous mode of illumination and the periodic flash. At regular time intervals similar exposures are made on successive frames of the camera film. Short intervals give virtual continuity.

Reference to the drawings will indicate how the analysis is made by the photomicrographic record taken by camera 116. As shown in FIGURE 5B in the instance of exact balance the axial mark on the index or target 88 will appear as a single dot a The off-axis mark will appear as a circle due to the continuous low level illumination. Superimposed on this circle 0 will be a single highly exposed spot b which shows the exact location of the rotor at the instant of the high intensity flash. When the rotor is laterally unbalanced with respect to the plane of the tubes as by disparity of we-ght distribution in a direction normal to the plane of the tubes, the on-axis mark (FIGURE C) will be highlighted as a bright spot a on a light circle 11, the center of which is the true axis of rotation e. Outside this first circle d will be the one 0 made by the oihaxis mark b As the run progresses the diameter of both circles will change. If, for instance, at the commencement of the run the record appears as shown in FIGURE 5]) indicating unbalance in the plane of the tubes and in the normal direction as well, an intermediate record may appear as FIGURE 5E and the final record (taken when stability is reached due to the settling of all solids at the outer end of the tube) may appear as in FIGURE SF. The growing unbalance reflected in the change in the position of the marks is, of course, due to the change in position of the center of gravity of the suspension contained by the tube. This change in position for each exposure can be calculated from the position of the marks after correcting with respect to the initial unbalance @as indicated by the position of the marks in FIGURE 5D, \for instance.

The calculations necessary to reach the individual determinations will not be dwelt on in this specification. They will be readily developed by one skilled in the art. From the change in center of gravity one skilled in the art will be able to compute the weight of the settled solids for each reading. This in turn may be converted into percent solids settled at each reading. Then with regard to the influence of centrifugal force successive computations based on settling formulae well known in the art as discussed in the Payne patent will give the particle size distribution in the sample.

Depending on the particle size distribution of the material, viscosity of the liquid and precision required, the analysis may be programmed for sedimentation at a single speed or a number of speeds of the rotor. In addition to the photographic records at known time intervals, it also may be necessary to record the speeds and the temperature. For work of the utmost precision thermometer elements inside the tubes 94 may be preferred.

Another use of the structure as disclosed in FIGURES 1 through 5 may be in simple comparision. In this operation a standard suspension is introduced into the tube opposite the unknown suspension. Assuming ball-ance at the commencement of the operation any unbalance during the run will indicate in the unknown suspension an excess or deficiency of solids in a certain determinable size range. Depending on the tolerances permitted, the sample and the product it represents may be accepted or rejected. Even for comparison work of utmost precision temperature records will not be required provided both liquids are at the same temperature and are otherwise of the same character.

The apparatus disclosed may also be used to derive complete sedimentation curves without concern tor absolute particle size.

A modification of .a portion oi the apparatus embodying the invention is shown in FIGURES 6 and 7. As shown the modified rotor indicated generally at 200 may comprise a shallow cup-shaped container 210. The cupshaped container is formed with a mounting sleve 212 which is adapted to be received on the reduced portion of the clamping bolt 48 above the head 50 in place of the yoke assembly '70. The container is provided with a drain opening 214 and is equipped with inner baffle structure as shown in FIGURE 6. The rightward half as shown in FIGURE 6 of the bafiie structure comprises a series of semi-circular baffies 216 of different radii arranged and supported in the rotor 200 on the container top 218. Extending radially inward from the innermost semi-circular bathe are vanes 220. On the leftward side the inner baffle structure comprises a plurality of radial v-anes 222 preferably thickening in width as the periphery of the structure is approached as shown. Thus the interior of one-half the container is divided into a plurality of equal pie-slice shapes. The entire cover is secured against a shoulder in the side wall of the container 210 by a clamping ring 224. The top is provided with a central opening 226. To facilitate filling the container 21 space 228 is left between the baffles and the bottom wall of the structure.

In operation of the modified structure the rotor 200 is mounted above the head 50 on the clamping bolt 48. Care is taken that the off-center dot on the index or target 88 is in the plane of the middle vane 222a. The filling assembly 74 (FIGURE 2) may be dispensed with, being replaced by a single washer under cap 86. When the structure is up to speed a quantity of the unknown suspension is delivered to the rotor 200 through the fitting 104 and the spout 108 directly into the opening 226 in cover 218. The filling is completed when excess liquid drains through the drain opening 214 and the suspension will be evenly distributed throughout the two sides of the container.

The first film record is immediately taken and further records are taken at predetermined intervals thereafter. It will be apparent that the solids on the right-hand side of the container as shown in FIGURE 6 will have to settle only to the inner surface of the next outer semicircular-bafile and this will be accomplished rapidly. The solids in the left-hand side of the container, however, must settle all the way to the periphery of the container. Hence, assuming the structure is balanced before it is filled with the unknown suspension, it will remain balanced at the beginning of the run. After the solids on the rightward side of the structure as shown in FIGURE 6 have settled against the semi-circular baffles, settling on the leftward side will continue and the center of gravity of the leftward side of the structure will move outward of the center of gravity of the rightward side of the structure. This will create an unbalance toward the leftward side manifest by the movement of the index or target 88 as shown on the record. The unbalance will grow and finally come to equilibrium when the solids on the left ward side finally settle against the periphery. Periodic reading of the unbalance as with the earlier described embodiment may be used to develop an analysis of particle size distribution.

A primary benefit of the structure of FIGURES 6 and 7 is that since the same suspension is used on both sides of the container, no corrections for differences in viscosity, temperature, etc. between the two sides need be made.

Referring'to FIGURE 8 a modified form of the recording means is shown. In this embodiment the bearing clamping ring 58'.

units 54 are clamped in a modified bearing cup 56 by a The bearing cup has a depending sleeve portion 300 which is disposed among and in contact with a plurality of uniformly spaced force transducers 302 mounted in the rotor housing 60' (FIGURE 9). The transducers are radially adjustable by means of respective set screws 304 and are electrically connected to a suitable outlet 306. Screws 308 provide additional support.

As suggested by FIGURE the transducers may be arranged in an electrical bridge through suitable connections and the output from the bridge may be fed to an oscilloscope 312 or other display or recording means to produce a sine wave 1 or other design.

As a means for orienting the signal with respect to the position of the off-balance, the drive pulley 46) may be provided with an outwardly extending steel pin 313 aligned with the plane of the sedimentation tubes in the first embodiment discussed or the plane of the vane 222a in the second embodiment shown in FIGURES 6 and 7. Positioned on the rotor housing 60 may be a suitable magnetic pickup 314 of the type comprising a coil surrounding a magnet, the leads of the coil being connected as suggested in FIGURE 10 to the oscilloscope input. Such a pick-up is of commercially available form and sold to a number of specifications under the trademark Electro by Electro Products Laboratories, Inc., Chicago 40, Illinois. By such indexing means the pin 313, upon cutting across the magnetic field of the magnet of the pickup 314, will produce an instantaneous current in the pickup causing a pip g to appear in the sine wave f on the oscilloscope screen.

It will be apparent to those skilled in the art that the extent of unbalance of the rotor Will be indicated by the amplitude of the design appearing on the oscilloscope. By means of the index pip g the position of the off-balance can be indicated and by recording the appearance of the face of the oscilloscope at regular intervals the progress of the sedimentation operation may be indicated. By calculations comparable to those for the FIGURES 1 through 4 and FIGURES 6 and 7 embodiments, the desired information can be developed.

In reviewing the foregoing disclosure of embodiments of the invention as Well as operation procedures, it should certainly be noted that the development is based on measurement in a centrifugal field of the actual weight of the settled solids as opposed to estimating their volume or to the specific gravity of the liquid above them. Thus in the analysis for particle size distribution of small solids I achieve an accuracy not heretofore possible.

It should be understood that variations are possible within the scope of the invention. Therefore, having particularly described my invention, it is to be understood that this is by way of illustration, and that changes, omissions, additions, substitutions and/or other modifications may be made without departing from the spirit thereof. Accordingly, it is intended that the patent shall cover, by suitable expression in the claims, the various features of patentable novelty which reside in the invention.

1 claim:

1. An apparatus for assisting in the analysis of particle size distribution comprising a spindle, means to drive said spindle, suspension-receiving chamber means mounted on the spindle, the chamber means having fixed walls and partitions of different configuration on opposite sides of the spindle and means to indicate the unbalance of the spindle.

2. The apparatus of claim 1 wherein the means to indicate the unbalance of the spindle comprises an indicator plug mounted on the spindle having indicia thereon at the axis of the spindle and spaced therefrom, means for illuminating said indicia with steady low power illumination and with periodic high power illumination of short duration, and photographic recording means.

3. The apparatus as described in claim ll wherein the means to indicate the unbalance of the spindle comprises at least one force transducer adapted to be actuated by the rotating spindle, means for displaying the signal from the transducer and means for indicating on the means for displaying the occurrence of a rotation of said spindle.

4. The apparatus of claim 1 wherein the spindle is supported at only one point, said point being remote from the chamber means so that the spindle is free to move laterally in all directions in the plane of the chamber means, whereby when the spindle operates at abovecritical speeds it has a self-balancing feature.

5. The apparatus of claim 1 wherein said suspensionreceiving chamber means is provided with partitions including radial vanes on one side of the spindle and a.

plurality of concentric semi-cylindrical bafiles of various radii on the other side of the spindle, and further comprises a pair of substantially radial end-walls to one of which the semi-cylindrical bafiles are attached, the distal edges of the semi-cylindrical bafiles being spaced from the other end wall, one of said end walls having a central suspension-receiving opening.

6. An apparatus for analyzing for size distribution of particles in a suspension comprising a rotor having suspension-containing means on opposite sides of its axis, the portion of the containing means on one side of the axis having at least one non-radial bafile means against which solids may settle not duplicated in the portion of the containing means on the opposite side of the axis, means to rotate the rotor, and means to indicate the unbalance of the rotor as it turns.

7. An apparatus as described in claim 6 wherein the means to indicate the unbalance of the rotor comprises an indicator plug mounted on an end of the spindle having indicia thereon at the axis of the rotor and spaced therefrom, means for illuminating said indicia with steady low power illumination and with periodic high power illumination of short duration, and photographic recording means.

8. The apparatus as described in claim 6 wherein the means to indicate the unbalance of the rotor comprises at least one force transducer adapted to be actuated by the rotating rotor, means for displaying the signal from the transducer and means for indicating on the means for displaying the occurrence of a rotation of said rotor.

9. An apparatus for assisting in the analysis of particle size distribution comprising a spindle, compartment means mounted on opposite sides of the spindle, the compartment means having rigid structure including fixed nonradial walls remote from the axis of the spindle for bearing the weight of the material in the compartment means respectively, the structure being of different configuration on opposite sides of the spindle respectively, means to drive the spindle, and means to indicate the unbalance of the spindle and compartment means as the particles settle under the influence of centrifugal force.

10. The apparatus of claim 9 wherein the spindle is supported at only one point, said point being remote from the compartment means so that the spindle is free to move late-rally in all directions in the plane of the compartment means, whereby when the spindle operates above critical speed it has a self-balancing feature.

11. The apparatus of claim 9 wherein the means to indicate the unbalance of the spindle comprises an indicator plug having indicia thereon at the axis of the spindle and spaced therefrom, means for illuminating said indicia with steady low power illumination and with periodic high power illumination of short duration, and photographic recording means.

12. The apparatus as described in claim 9 wherein the means for indicating the unbalance of the spindle comprises at least one force transducer adapted to be actuated by the rotating spindle, means for displaying the signal from the transducer and means for indicating on the spindle.

References Cited by the Examiner UNITED STATES PATENTS Petnofi 73465 X Grela et a1.

Whitby 73-432 Pickels et al. 73-61 X Thies'sen et a1. 7332 10 3,009,388 11/1961 Polanyi 73--61 X 3,076,342 2/ 1963 Hilgers 73-460 3,206,983 9/1965 Muschelkn awtz 73-61 X 5 FOREIGN PATENTS 1,232,877 4/1960 France.

338,847 7/1921 Germany.

DAVID SCHONBERG, Primary Examiner.

Claims

1. AN APPARATUS FOR ASSISTING IN THE ANALYSIS OF PARTICLE SIZE DISTRIBUTION COMPRISING A SPINDLE, MEANS TO DRIVE SAID SPINDLE, SUSPENSION-RECEIVING CHAMBER MEANS MOUNTED ON THE SPINDLE, THE CHAMBER MEANS HAVING FIXED WALLS AND PARTITIONS OF DIFFERENT CONFIGURATION ON OPPOSITE SIDES OF