US3286939A

US3286939A - Vibratory ball mill

Info

Publication number: US3286939A
Application number: US327581A
Authority: US
Inventors: Karpenko Igor; Iii William H Engel; Richard W Dye
Original assignee: Glidden Co
Current assignee: Akzo Nobel Paints LLC
Priority date: 1963-11-26
Filing date: 1963-11-26
Publication date: 1966-11-22
Anticipated expiration: 1983-11-22

Description

5 1966 l. KARPENKO ETAL 3,

VIBRATORY BALL MILL Original Filed July 25. 1961 United States Patent 3,286,939 VIBRATORY BALL MILL Igor Karpenko, William H. Engel III, and Richard W.

Dye, Baltimore, Md., assignors to The Glidden Company, Cleveland, Ohio, a corporation of Ohio Continuation of application Ser. No. 128,303, July 25, 1961. This application Nov. 26, 1963, Ser. No. 327,581 2 Claims. (Cl. 241-175) This application is a continuation of our patent application S.N. 128,303, filed July 25, 1961.

This invention relates to a ball milling apparatus and process employing compound movement. It has exceptional ability to subdivide powered materials to extreme fineness very rapidly.

One use that it has been particularly effectively adapted for is in the preparing of highly dispersed pigment specimens for electron microscope examinations. Additionally, it has been used successfully for preparing powdered specimens for X-ray diffraction and emission spectrograph examinations. In laboratory size it can be made from conventional materials and assemblies very economically.

In essence, the ball mill of our invention comprises a base, a grinding chamber support connected to said base by a plurality of resilient props, an eccentrically-loaded rotating shaft passing from said base to said grinding chamber support and extending to a flexible bearing on said support, and at least one grinding chamber partially filled with solid particulate grinding media, each grinding chamber projected from said support at a position displaced from axis of rotation of said shaft. In the preferred embodiment the resilient props are positioned to describe the corners of a polygon around the axis of rotation of the shaft, and the grinding chambers are projected from at least some of the corner areas of the resulting polygon.

The improved grinding ability of the apparatus employing such grinding zone partially filled with loose particulate grinding media appears to stem from subjecting such zone, loaded with solids to be ground, to a high frequency, periodic, three-dimensional ellipsoidal oscillation of amplitude between about 10% and about 50% of the zone width while imposing an essentially rocking motion thereon with respect to at least one axis of the zone.

FIGURE 1 shows our preferred grinding apparatus in perspective. Case 11 is shown in dotted outline to illustrate the working parts of the equipment. Base 13 is recessed into the top of case 11. Motor housing 16 projects downwardly therefrom and conceals an electric motor, not shown. Power supply is brought to the electric motor by cord 19. Projecting from the corner areas of the base are four rubber props connecting the base to the corner areas of the grinding chamber support 15. Clamps 17 project from thecorner areas of grinding chamber support 15, each clamp holding firmly a grinding chamber 18. The grinding chambers are polyethylene bottles about cm. long and 3 cm. in diameter. Each grinding chamber contains 12 cc. (bulk volume) of 4 mm. glass beads as grinding media. The motor indirectly drives a rotating shaft which extends up into a flexible bearing connection, not shown, at the bottom center of grinding chamber support 15. The bottom of case 11 is weighted with 60 pounds of lead to prevent its'movement and is lined with sponge rubber to absorb noise. Case 11 customarily is fitted with a hinged lid, not shown.

Preferably the apparatus is mounted base-down for grinding, but it will grind effectively in any position, e.g., with base vertical. Similarly, one or a plurality of grinding chambers can be mounted at one time for simultaneous, comparative grinding. Alternatively and effectively,

the grinding chambers can be turned or pitched in virtually any direction. Also, a longer chamber can be held across either end or either side of the support using two clamps, to hold it in the place of two smaller chambers, and effective grinding has been done this way in our apparatus.

FIGURE 2 is a vertical cross section, 2-2, through the length of the grinding chamber support and base of FIG- URE l to show in more detail the driven rotating shaft arrangement between the base and the support. Motor shaft 22 projects through base 13 through hole 23 and is terminated by spur gear 24. Spur gear 24 meshes and drives larger spur gear 25 affixed rigidly to shaft 26. The bottom of shaft 26 rests in lower shaft bearing 27, a socket integral with and projecting from base 13. The upper end of shaft 26 is terminated with an eccentric metal journal 29, also afiixed to the shaft. Projecting from shaft 26, intermediate to the. ends thereof, is shaft weight 28, aflixed rigidly to the shaft so that its eccentricity is broadly opposite to that of journal 29. Journal 29 fits into deformable rubber retaining ring 30. The rubber retaining ring, in turn, is held in place by circular retainer 32, which is disposed about the center of grinding chamber support 15 and is integral therewith.

The lower ends of rubber props 14 button firmly into recesses 34 of the base comers. The upper ends of props 14 are loosely pinned to lugs 35 projecting from the four corners of grinding chamber support 15. For further ease of reference, a pair of grinding chambers are shown mounted from the upper lefthand corner of support 15. The mounting consists of bracket 36 welded to chamber support 15, a two-arm metal clamp 17 rigidly fastened to and projecting upward from bracket 36 and terminating in a screw-nut fastening at its upper extremity. In the bulged portion polyethylene bottle grinding chamber 18 is gripped securely. The base of the bottle is shown forward with the bottle closure depicted at the opposite end.

The embodiment shown in the drawings was constructed by modifying a conventional electric .sander,

namely the Shop-Mate brand oscillating sander, Model 280B, rated at 4000 oscillations per minute, drawing 2.0

amperes at 115 volts A.C. Such sander is manufactured by Portable Electric Tools, Inc., Chicago 2 0, lllinois.

This sander was converted into the milling apparatus illustrated by making the following modifications: removing the sponge pad and sandpaper grips from chamber support 15; removing the pressure knob from base 13 and the handle grip from motor housing 16; .weldingbrackets 36 near the four corners of grinding chamber support 15; attaching a conduit clamp 17 to each of the brackets; clamping on polyethylene bottles, one in each conduit clamp, each polyethylene bottle being partially full of grinding media; recessing base 13 and motor housing 16 into a wooden case which was ventilated with holes to provide for air-cooling of the motor. Other conventional oscillating or orbital sanders of this type can also be modified in essentially the same way for our service.

The preferred grinding media are balls having a diameter of A1" to A" for the size of chamber shown. Smaller or larger chambers can be used as well as smaller or larger diameter balls. The balls experimented with have been made of glass steel, and tungsten carbide. Alternatively such ba-l'ls can be made of stone, such as flint, alumina, or other hard material, preferably harder than the material being ground. Optionally, the balls can be replaced by small cylindrical pellets, rods, or irregular non-uniform particles. The grinding chamber optionally can be made of metal or other conventional r'haterial tough enough to withstand the impact of the balls, and it can be broadly tubular, i.e., prismatic, instead of simply cylindrical. Generally the chambers are longer than they are wide, and lengthening them even as much as lent results. The machine appears tobe most etficient,

when thefeed solids to be ground pass 50 mesh (U.S.S.) or are smaller. The size of the charge for grinding can be as little .as 0.2 gram per chamber although we have found the same machine capable of grinding times this much about as effectively. Similarly, the grinding media loading can be varied in the chamber, providing some room is leftfor their substantial movement, e.g., 80-90% (bulk volume) full. While most of our exploratory work with the machine has been for makingv small batches of extremely finely ground material, the machine can be made larger. Additionally, it is conceivable that the machine can be operated continuously or semicontinuously be feeding in and withdrawing charge from a grinding chamber through screens of mesh small enough'to. pass powdered feed in gas or liquid suspension while retaining the grinding media in the particular grinding cahmber.

While the particular machine illustrated is rated at 4000 V oscillations per minute, under our customary loadings we have frozen the periodidmotion of these grinding chambers at 1800-2200 oscillations per minute with a stroboscopic lamp and motion pictures. Under such conditions, the grinding 'media are not stopped, but show themselves to be in violent motion of a random nature within the confines ofa particular grinding chamber. Any point on-the outer surface of a grinding chamber appears to be generating by small amplitude, periodic gyrations,

'a generally ellipsoidal solid. When mounted in the position shown in FIGURE 1, each grinding chamber itself also appears to rock at the same speed, broadly pivoting about the center of its longitudinal axis in essentially the.

vertical plane as much as about .45 degrees from the horizontal, although as little as about 20 degree or smaller rockings have been observed in cases where elfective grinding was being done. In the position of the apparatus in FIGURE 1, the amplitude of gyration of a point on the cham'berwa'll in the horizontal plane is broadly between about 10% and about 40% of the width of the chamber and generally about 25%; in a vertical plane this amplitude is somewhat greaterbetween about 20% and about 50% and generally about 33% of the width of the chamber. All these motions are superimposed one on another at the speed of shaft rotation by rotation of the eccentrically-loaded and mounted shaft and by the resilient props. Under excellent performance conditions the frequency of gyration usually is about 2100 oscillations per minute.

While the drawing shows a particular embodiment of our device, obvious mechanical equivalents can be employed for the various members. Thus, springs such as coil springs can be used in place of the resilient rubber props, and the spring-loaded sleeve bearings or the like in place of the rubber ring. The clamps can be replaced by other suitable conventional devices to attach the grinding chamber to the grinding chamber support, e.g., projecting lugs welded to a grinding chamber, bolted fasteners, etc. Rotating shaft .26 need not be offset from the driving motor but, of course, can be projected straight through the base into motor housing. All fasteners and connections can be replaced by their obvious mechanical equivalents where rigidity or pivoting is required- Illustrative of the effectiveness of our machine for grinding and dispersing is its use in the study of titania crystallites, that is, the smallest discrete unit into which titanium dioxide pigments can subdivided other than by the crystal fracture. In the calcination very tenacrouslv; forming material crystallites aggregate very tenaciously.

Ordinarily, the crystallites have an approximate size range of 0.01 to 0.6 micron. In the aggregated form,they can be classified conveniently as tertiary (40-1000 microns,

usually large enough to be seen with the naked eye); secondary (broadly 1-40 microns, discernible with'low resolution optics); primaryv (approximately 013 to 1 micron, discernible by means of high resolution optics). These aggregates can be subdivided without crystal frac-. ture. However, subdivision becomes increasingly difficult descending from the tertiary. The crystallites themselves must be resolved by means. of the electron microscope and their measurement is conveniently .done 1 with' a Zerss Particle Size Analyzer, model TGZ.3. Distribution of the particle diameters can be recorded arithmetically, ex-

ponentially, or cumulatively.

To prepare titania pigment samples for such study a 20ml. grinding chamber of the embodiment illustrated is charged with 12 ml. of 4 mm. diameter glass beads. and 200 mg. of pigment. The loaded chamberis clamped 2 Suitable pigonto the mill and agitated for 15 seconds. ment usually is calciner discharge ground superficially in a ring roller mill, but it also can be straight out of the 1 calciner or lightly ground by other conventional methods. Four samples can be milled simultaneously. In this very short time of milling the preponderance of the pigment (rutile or anatase) is deaggregated'down to the crystallites. It is then necessary to'inconporate the ground pigment into aplastic medium'w-hich will sustain the .dis-

persed state of the pigment -and which also willsupport. the crystallites rigidly for examination in the electron microscope. .The supporting medium must be extremely thin .to minimize absorption of [the electron beam. The specimen film is made broadly by the technique described by Shuster et al., Ind. Eng. Chem., Anal. Ed. 1 18, pp.

653-657(1946). To accomplish thiswe add 2ml. of a 10% solution of-a cellulose nitrate. manufactured by the Mallinckrodt Chemical Works) dissolved in Z-ethdxy-ethanol acetate (Cellosolve acetate), I

mill this mixture for one minute to disperse it,remov'e the mixture from the milling chamber by successive wash- 1 ings with amyl acetate (generallyabout three washings),

transfer the washings to a ml. wide-mouth'bottle and dilute to a final volume to 50 ml. with additionalamyl acetate; dip a 1" x -3-' microscope slide into the pigment suspension at an angle of about 60 withdraw it immediately, and allow it to dry; strip the film from. the

upper side of the glass slide by easing the slide into a water'bath at a low angle; pick the film up from the water surface so that it covers the electron microscope grid supports; dry, and set up for examinationin the,

microscope.

The grinding. effectiveness of our milling using the,

same kind of pigment (titania discharged from at ca]- ciner) is highlighted by our experience. using other related milling devices with compound 'motion. We have found 3 that they take 4 to 8 hours or even longer to even approximate the fineness of grind we get with our inventive mill in 15 seconds. Furthermore, the results cannot even be remotely approached using a conventional lab-,

oratory ball mill of the porcelain jar type or using conventional hand mulling with a Hoover Muller or the like.

'either wet or drymilling to approach our fineness of grind and had relatively little effect on the reduction of primary aggregates.

In another experimental grinding of the rutile pigment,

a Sweco Vibro-Energy. mill, the trademark for a compound-motion mill made by the Southwestern Engineer (Parlodiom brand ing Co., was used. The titania here was ground in water slurry with essentially cylindrical alumina pellets, the mill providing superimposed horizontal and vertical gyration resulting in a three-dimensional, high frequency gyration of about 1150 cycles per minute. Samples of the ground pigment were taken at 2, 5, 7, 8, and 9 hours, and the bulk of the pigment was ground for about 14 hours. Electron microscope examination of the samples and production showed that the mill had little or no effect on the TiO below the one micron range for size reduction, and that its principal effect was to reduce the number of larger aggregates to smaller ones.

Further comparative testing was done on titania pigment by attempting to grind it in conventional pendular motion mills (Wig-L-Bug, made by the Crescent Dental Mfg. Co. of Chicago, Ill.) and the Spex Mixer mill made by Spex Industries of Scotch Plains, New Jersey. The motion of these milling chambers is essentially that of the end of a pendulum describing an elongated figure- 8 path very rapidly. The Wig-L-Bug is used in dental oflices to make amalgams. These milling chambers were partially filled with bead grinding media and gave very little deaggregation of the pigment in comparatively long milling periods.

In a further test in our machine, 4;" tungsten carbide beads were used to grind ilmenite ore. With a few seconds grinding, particles were reduced to an extremely fine state, and, upon examination, crystal fracture was evident.

We claim: 1. A vibratory ball mill comprising: a base; a grinding chamber support connected to said base by a plurality of resilient props;

a driven rotating shaft, loaded with an eccentric Weight, said shaft passing from said base to said grinding chamber support in a direction substantially normal to said support at rest, and extending into an eccentric journal flexibly engaged by said support;

said weight describing in rotation a path substantially normal to said shaft;

and a grinding chamber partially filled with solid par ticulate grinding media, said grinding chamber projected from said support at a position displaced from the axis of rotation of said shaft.

2. A vibratory ball mill comprising:

a base;

a grinding chamber support connected to said base by a plurality of resilient props;

said weight describing in rotation a path substantially normal to said shaft;

and a plurality of grinding chambers, each partially filled with solid particulate grinding media, each grinding chamber projected from said support at a position displaced from the axis of rotation of said shaft.

References Cited by the Examiner UNITED STATES PATENTS 2,247,978 7/1941 Van Arkel 259-72 2,286,599 6/1942 Chott 241- 2,286,600 6/ 1942 Chott 241-175 2,760,729 8/1956 Mittag 241-175 X 2,882,024 4/1959 Behrens 259-1 2,982,485 5/ 1961 Fahrenwald 241-175 2,983,454 5/1961 Podmore 241-175 X ROBERT C. RIORDON, Primary Examiner.

H. F. PEPPER, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,286,939 November 22, 1966 Igor Karpenko et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 14, for "powered" read powdered column 2, line 62, after "glass" insert a comma; column 3, line 25, for "be" read by line 28, for "cahmber" read chamber column 4, line 2, for "very tenaciously" read of the pigment- Signed and sealed this 12th day of September 1967.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Arresting Officer 1 Commissioner of Patents

Claims

1. A VIBRATORY BALL MILL COMPRISING: A BASE; A GRINDING CHAMBER SUPPORT CONNECTED TO SAID BASE BY A PLURALITY OF RESILIENT PROPS; A DRIVEN ROTATING SHAFT, LOADED WIH AN ECCENTRIC WEIGHT, SAID SHAFT PASSING FROM SAID BASE TO SAID GRINDING CHAMBER SUPPORT IN A DIRECTION SUBSTANTIALLY NORMAL TO SAID SUPPORT AT REST, AND EXTENDING INTO AN ECCENTRIC JOURNAL FLEXIBLY ENGAGED BY SAID SUPPORT; SAID WEIGHT DESCRIBING IN ROTATION A PATH SUBSTANTIALLY NORMAL TO SAID SHAFT; AND A GRINDING CHAMBER PARTIALLY FILLED WITH SOLID PARTICULATE GRINDING MEDIA, SAID GRINGING CHAMBER PROJECTED FROM SAID SUPPORT AT A POSITION DISPLACED FROM THE AXIS OF ROTATION OF SAID SHAFT.