US2970781A - Vibratory mill - Google Patents

Description

J. M. MORRIS VIBRATORY MILL Feb. 7, 1961 3 Sheets-Shea Filed Aug; 7, 1957 ATTORNEYS Feb. 7, 1961 J. M. MORRIS 2,970,781

VIBRATORY MILL Filed Aug. 7, 1957 3 Sheets-Sheet 2 INVENT OR.

JOHN M. MORRIS BY ATTORN EYS Feb. 7, 1961 J. M. MORRIS VIBRATORY MILL Filed Aug. '7, 1957 3 Sheets-Sheet 3 INVENTOR.

JOHN M MORRIS VIBRATGRY MILL John M. Morris, Louisville, Ky., assignor, by mesne assignments, to Chain Belt Company, Milwaukee, Wis., a corporation of Wisconsin Filed Aug. 7, 1957, Ser. No. 676,742

6 Claims. (Cl. 241-175) This invention relates to apparatus for doing work by vibration and in particular to a vibratory ball mill that may be operated at high amplitudes of vibration without imposing excessive stress on the various portions of the mill structure.

One of the commercial processes for comminuting material is ball milling, a process in which the material to be comminuted and a plurality of hardened steel balls are placed in a rotatable container and the comminuting operation is performed by crushing the material between the balls as the container is rotated, usually about a horizontal axis. Laboratory size ball mills have been constructed to operate by vibration instead of rotation of the container. The ordinary type of such a vibratory ball mill when built in larger sizes is unsatisfactory because of the excessive stresses that develop in certain portions of the apparatus. While an ordinary structure may be built heavier or reinforced at the point of stress concentration this is not practical in a ball mill or similar vibratory apparatus because the additional weight of the material used for reinforcing produces nearly as much additional stress as it strengthens the structural elements.

The principal object of this invention is to provide a vibratory ball mill that may be built in large sizes without overloading any of the portions of the mechanism.

Another object of the invention is to provide a vibratory ball mill that is operated at a resonant frequency of vibration so that the forces actually applied to the ball mill to produce vibration are small compared to the inertia forces developed in the mill.

A still further object of the invention is to provide a vibratory ball mill in which the supporting resilient members are distributed over a large portion of the base of the mill to minimize the concentration of force at any particular point in the frame of the vibratory mill.

A still further object of the invention is to distribute the supporting springs of a vibratory mill substantially in proportion to the mass distribution of the member to be vibrated so that bending forces in the member are minimized.

These and more specific objects and advantages are obtained in a vibratory ball mill constructed according to the invention.

According to the invention the improved vibratory ball mill comprises a round bottom container the walls of which may be reinforced with external ribs, supported on a plurality of springs arranged generally in rows of at least three springs each distributed over the lower portion of the container or its reinforcing framework in proportion to the distribution of the mass of the framework and container and means for applying vibratory force to the container at a frequency substantially equal to the natural period of vibration of the container on the supporting springs.

A preferred form of the invention is illustrated in the accompanying drawings.

In the drawings:

Fig. I is a perspective view of the improved vibratory Sttes Patent C) ce 2,970,781 Patented Feb. 7, 1961 2 ball mill showing the container, the driving motor, means for applying the vibratory force to the container, and the resilient means upon which it is supported.

Fig. II is a plan view of the vibratory mill container.

Fig. III is a vertical section taken substantially along the line III-III of Fig. II.

Fig. IV is a horizontal section taken substantially along the line lV-IV of Fig. III.

Fig. V is a front elevation of a vibratory mill showing an alternative location for the eccentric weight shaft.

Fig. VI is a front elevation of a vibratory mill in which the vibratory force is applied through an exciter member.

These specific figures and the accompanying description are intended merely to illustrate the invention and not to impose limitations on its scope.

A vibratory ball mill constructed according to the invention comprises a heavily reinforced U-shaped container 1 that is resiliently supported from a base 2 by a plurality of springs 3, preferably coil or helical although other types of springs may be used, interposed between an upper surface of the base 2 and the under surface of the subbase 4 of the container 1. Vibratory force from a pair of unbalanced weights 5 carried on disks 6 mounted on a shaft 7 is transmitted through shaft bearings 8 to the reinforced container 1. The shaft 7 carries a pulley 9 that is connected through belt 10 to a motor pulley 11 of a drive motor 12. The drive motor 12 is adjustably mounted on a motor stand 13 that is separate from the base 2 and that is preferably braced from the base 2 to maintain proper tension in the belt 10.

Referring now to Figs. I, II and III and in particular to Fig. III, the reinforced container 1 comprises a generally U-shaped inner liner or inner member 15 that is laterally braced by a plurality of generally horseshoe shaped ribs 16 which in turn are cross braced by a plurality of intermediate plates 17 extending from rib to rib. The end ones of the horseshoe shaped ribs-16 are made of heavier stock than the intermediate ribs and are flush with the ends of the U-shaped liner 15. The ends of the container, that is, the ends of the U-shaped liner 15, are closed by end plates 18 that are generally U-shaped in outline and that are secured to the end ones of the ribs 16. To provide the utmost rigidity the ribs 16, the intermediate plates 17, and the liner 15 are welded together along their contacting surfaces and, for accessibility, the end plates 18 are securely bolted to the end ribs 16. The subbase 4 fitting under the lower portions of the ribs 16 is securely welded thereto so as to make a complete box-like construction.

The base 2 is similarly fabricated'from steel plates cut to the appropriate sizes and welded together. This base comprises an upper deck or portion 20 that has a generally fiat upper surface and upwardly inclined wing portions 21 at each end to, match corresponding upwardly inclined portions of the subbase 4.

In this particular embodiment twenty-eight coil springs 3 are used to support the reinforced container 1 from the base 2. These springs are arranged in four rows as shown in Fig. IV with eight springs in each of the outer rows and six springs in each of the inner rows. The end springs in each row are interposed between the inclined wing portions 21 of the base 2 and the inclined end portions of the subbase 4. These inclined end springs serve as stabilizing means to prevent lateral shift of the container on the vertically arranged intermediate springs. Each of the springs is provided with a spring seat at each end that is rigidly attached both to the spring and to the upper portion 20 or the inclined wing portions 21 of the base and to the subbase 4 of the container 1. Thus the springs serve both in tension and compression during the vibration cycle and because of the rigidly connected end portions also act to prevent lateral displacement of the container 1.

Material to be comminuted is introduced into the container through an opening 25, Fig. II, and after comm'inuation is discharged through an opening located either in the end plate 18 or in the rounded bottom of the container and which is closed. by a grillwork 26 the spaces of which are narrow enough to prevent escape of the steel balls or other grinding medium used in the ball mill and which are wide enough to allow'the escape of the comminuted material. If the discharge opening is in the bottom the discharge passes the space left vacant by the omitted, ones of the coil springs and a suitable duct provided through the base 2. The large central opening appearing in Fig. II is normally closed by a thin steel cover plate that is bolted to the side flanges 27 ofangle irons forming the end braces across the open portion of the liner 15 and plates 28 that extend along the tops of the ribs 16 and are welded thereto. The cover plate may be removed when it is necessary to get into the container for cleaning purposes or for replacement of the grinding balls or other medium.

An essential feature of this construction is the distribution of the springs 3 throughout the juxtaposed areas of the subbase 4 and the upper surface and Wings 21 of the base 2. This distribution of springs is roughly proportional to the distribution of mass of the reinforced container 1. If the distribution were exact each increment of mass of the reinforced container 1 and its sup porting spring 3 would have the same natural period of vibration as any other increment of mass on its supporting spring. With the springs distributed in proportion to mass and with a number, at least three, generally in line in each direction, the frame of the container is substantially free of bending stresses. This follows because the force from each increment of mass of the container and frame is transmitted. directly to its supporting spring. The frame is thus equivalent to a continuous beam having a plurality of supports and having its load distributed over the several supports. Since the bending moments in such a beam are much lower than when the beam is supported only at its ends it follows that, for a fixed load, a much smaller beam can be used. In a vibratory apparatus this reduction in required size is very significant because of the reduction in the total mass that must be vibrated. If this distribution were maintained throughout the assembly small exciting forces applied to the reinforced container 1 at that resonant frequency would without the transmission of large forces produce relatively large amplitudes of vibration of each increment of mass without the transmission of substantial force from one increment of mass to another. Although such ideal distribution cannot be precisely realized nevertheless the distribution illustrat d approaches the optimum distribution and in that manner minimizes the forces transmitted from part to part through the frame and reinforcing members of the reinforced container 1. Further, by operating at the natural or resonant frequency, the forces transmitted from the eccentric weights through the bearings 8 need supply only the losses in the system and. not the inertia forces and therefore the bearings 8 may be relatively light compared to the mass of the equipment.

The four center springs were eliminated, fromthe array of springs for two reasons. First, there is a relatively small amount of mass concentrated at the center of the reinforced container 1 since most of the mass appears in the reinforcing ribs 16 and end plates 18 as well as the liner 15 itself. Since this mass appears primarily along the sides and ends of the structure rather than at the center it is desirable to, concentrate the springs along the marginal areas under this mass rather than at the center. The second reason for eliminating the central springs is the difficulty of providing access to the, bolts or; nuts; that-lock the spring seats inposition, Thus,

while the two center springs on each of the end rows may be reached through access openings 30 in the end ribs 16 it would be difiicult to tighten nuts on the center springs even though such access openings were provided in the intermediate ribs 16. Likewise it would be difficult to reach the lower ends of such springs because of the honey-comb nature of the reinforced base 2.

In some installations, depending upon the mass of the container 1 and its distribution, it may be desirable to eliminate more of the springs from the intermediate rows and thus leave the resilient support primarily around the marginal area of the subbase 4 and main base 2. This distribution may be determined by considering the relative mass of the end ribs 16 and end plates 1'8 in comparison with the side walls of the liner 15 and the intermediate ribs 16. Thus if these latter members are relatively light it may be desirable to reduce the amount of resilient force applied to the midportions of the ends of the subbase 4.

While the vibratory system has several possible modes of vibration the desired mode, with the container moving in an elliptical orbital path, may be obtained. by selecting an operating speed for the shaft 7 that corresponds to the natural frequency in vertical vibration of the container l on the springs 3.

When the exciter shaft '7 and the eccentric weights 5 are located at the top of the container as illustrated in Figs. I and III there is a considerable distance between the exciting shaft and the center of gravity of the con tainer assembly. As a result the motion of the container tends to approximate the motion of a connecting rod in that the upper portion of the container describes a circular or generally circular vibration while the bottom of the container adjacent the springs describes a substantially vertical vibration combined with a rocking motion. The amount of transverse vibration at the bottom of the container is dependent upon the lateral stiffness of the spring support and the condition of resonance between the spring support and the container tending to cause the container to rock about the horizontal axis through its center of gravity.

At times it may be desirable to cause the entire container assembly to execute a generally orbital vibration in which all parts of the container execute orbital paths of approximately the same shape and size. In order to do this it is desirable to locate the eccentric weight shaft as near to the center of gravity of the assembly as is reasonably possible and to arrange the spring rate of the supporting springs so as to secure a generally equal restoring moment or restoring force in both horizontal and vertical directions. The arrangement shown in Fig. V is an approximate approach to such a condition of pure translatory vibration. In this structure a container C having end plates 31, one of which is fitted with a grill G providing a discharge opening, is supported by U- shaped ribs 32 which with a subbase 33 forms a vibratory structure. The subbase 33 is supported from a main base 34 by a large plurality of springs 35 interposed between the adjacent faces of the bases and arranged to provide both vertical and lateral support for the vibratory structure. An eccentric weight shaft 36 carrying eccentric weights 37, which is driven from a motor 38 through a belt 39 and pulley 40, supplies a vibratory force to excite vibration of thecontaiuer 30 and its supporting subbase.

While not shown in the drawings the bearings for the shafts 36 are preferably located in the hub-like portion of the end plates 31 which are similar to the end plates 18 shown in Fig. I.

By locating the eccentric shafts 36 nearer to the center of the vibrating assembly a larger horizontal component of vibration is produced at the bottom portion of the container. This augments or enhances the circulating motion of the material being processed. Whereas the generally vertical vibration combined withrocking motion as produced by the eccentric shaft located at the top of the container agitates the material to provide grinding it does not provide a SUfi'lClCHlI horizontalcomponent in connection with the orbital motion to thoroughly mix the contents of the container and keep it cir culating. The orbital motion is necessary to secure adequate agitation of the material as well as a circulatory motion of the material to keep it mixed.

The arrangement shown in the preceding figures in which the vibratory assembly comprising the container and its supporting ribs is resiliently supported from a base mounted directly on the foundation transmits a substantial amount of force to the foundation, when the system is in operation. This follows because the foundation on which the base 2 or the base 34 of Fig. V is mounted must withstand the maximum force exerted by the springs 3 or 35. Very often this transmitted force excites vibration of adjacent structures and is very annoying to any occupants of the surrounding space. With heavier equipment the magnitude of the vibratory forces so transmitted to the foundation may be suflicient to endanger the adjacent structures. It is therefore desirable to isolate the vibration in the vibrating structure and minimize the transmission of vibration to adjacent structures or buildings. The arrangement of Fig. VI is designed to minimize such transmission of vibration to outside structures.

In the structure shown in Fig. VI a vibratory container 50 supported on generally horseshoe shaped ribs 51 and subbase 52 forms a vibrating container assembly that is resiliently supported on tie rods 53 from a resiliently mounted frame 54. The tie rods 53 are pivotally mounted at each end so that the container assembly may oscillate laterally like a pendulum. The frame 54 is resiliently supported by low rate springs 55 from a framework 56 erected from the floor or foundation.

Vibratory force developed by eccentric weights 57 carried on a rotating shaft 58 is transmitted through the shaft bearings to a vibration exciter mass 59 corresponding in appearance to the base 2 or the base 34. This exciter mass 59 is connected by springs 60 to the container assembly subbase 52. The shaft 58 is driven from a motor 61 through a belt 62.

In this arrangement the mass of the exciter member 59 is preferably from A to /2 the mass of the vibrating container assembly and the rate of the springs 60 is selected so that the combination of the springs 60 with the vibrating container assembly and the exciter member 59 forms a resonant system having a natural frequency at the desired speed of operation.

In this assembly the springs 60 must provide both vertical and horizontal resilient connections between the vibrating container assembly and exciter member 59 so that as the driving force of the eccentric weight 57 produces an orbital motion of the exciter member 59 a corresponding orbital motion of the container assembly results. The magnitude of the horizontal and vertical components of such orbital motion may be varied by adjustment or selection of the rate of the springs 60 in the horizontal and vertical directions.

In this arrangement the exciter member 59 may execute vibrations having from two to five times the amplitude of motion of the container assembly but the force of such vibration is not transmitted to the foundation or to the frame 56. This follows because the only force that can be transmitted to the frame 56 is that transmitted through the springs 55 and the small horizontal components that may be transmitted because of the instantaneous angularity of the supporting links 53.

This arrangement is suitable for large equipment since the large forces required to vibrate the container are well distributed and no portion of the system is subjected to high stress. I

Various modifications may be made in the structure, in the placement of the eccentric weight shaft 7 with respect to the container, and the distribution of springs Without losing the advantages of the invention as long as the springs are distributed roughly in proportion to the mass distribution of the container.

I claim:

1. In apparatus for doing work by vibration, in combination, a container, a subbase integral with the container, distributed means rigidly interconnecting and supporting the walls of the container from the subbase, a main base at least coextensive in area with the subbase and spaced in opposed relation to the subbase, a plurality of springs arranged substantially in rows of at least three springs each interposed between and interconnect ing the opposed marginal portions of the subbase and base, and other springs connecting those portions of the subbase and base bounded by the marginal portions,

each of said springs having a spring rate that is generally proportional to that portion of the total mass of the container and subbase that is supported by that spring, whereby vibratory bending stresses in said subbase are minimized, and means for applying vibratory force to the container at a frequency generally equal to the natural frequency of the container and subbase and said springs.

2. In apparatus for doing work by vibration, in com between and resiliently connecting the marginal areas of the base and subbase, and other springs acting in parallel with said plurality of springs interposed between and connecting those areas of the base and subbase bounded by said marginal areas, each of said springs having a spring rate that is generally proportional to that portion of the total mass of container and subbase that is supported by that spring, whereby vibratory bending stresses in said subbase are minimized.

3. In apparatus for doing work by vibration, in combination, a work member that comprises a container mounted on a rigid frame, said frame having a generally horizontal surface and a pair of inclined surfaces, a base member having surfaces spaced from and opposed to said horizontal and inclined surfaces, means for applying vibratory force to said work member at -a working frequency, a plurality of springs arranged substantially in rows of at least three springs each interposed between and connecting the marginal areas of said horizontal surfaces and said inclined surfaces, and other springs interposed between and connecting those portions of said opposing surfaces that are bounded by said marginal areas, each of said springs having a spring rate proportional to the mass of that portion of the work member supported thereby and cooperating with that portion to form a vibratory system having a natural frequency generally equal to said working frequency whereby all portions of the Work member tend to vibrate in synchronism and vibratory bending stress in the work member is minimized. 1

4. In apparatus for doing Work by vibration, in combination, a work member that comprises a container mounted on a rigid frame, said frame having a generally fiat portion at least coextensive with said container, a second member having a surface spaced from and opposed to the generally flat portion of the frame, a plurality of springs arranged substantially in rows having at least three springs each interposed between and connecting the marginal portions of the frame and second member, other springs connecting those portions of the frame and second member bounded by the marginal portions, each of said springs having a spring rate generally proportional to the mass of that portion of the container and frame connected thereto and cooperating with such mass to form a vibratory system having a natural frequency, and means for applying vibratory" force to one of said members. at a frequency generally equal tosaid natural frequency, whereby each of said springs and the associated portions of the members tends to vibrate at the same frequency and bending forces in the members are minimized.

5. In apparatus for doing work by vibration, in combination, a container, a subbase integral with the container, a plurality of rigid means along each side of the container interconnecting the walls of the container to the subbase to prevent deflections of said walls relative to said subbase, a main base generally coextensive with the subbase, a plurality of springs arranged in rows of at least three springs in each row interposed between and connected to opposing surfaces of the subbase and main base with the lines of action of the springs extending generally perpendicular to such surfaces, each of said springs having a spring rate that is generally proportional to the mass of the subbase and container supported thereby, and means for applying a vibratory force to the container at a frequency generally equal to the natural frequency of each spring and the mass supported thereby.

6. In apparatus for doing Work by vibration, in combination, a container, a subbase integral with the container, a plurality of rigid means supporting the side walls ofthe container from the subbase to prevent deflection of the walls relative to the base, a main base generally coextensive with the subbase, a plurality of springs arranged in rows of at least three springs to a row connected between marginal areas of the subbase and main base, and other springs connected between those areas of the subbase and main base bounded by saidrmarginal areas, each of said plurality and said other springs having a rate that is proportional to the mass of the container and subbase supported thereby, whereby said subbase is uniformly supported during vibration,

and means for applying vibratory force to the container I at a frequency generally equal to the natural frequency of each spring and the mass supported thereby.

References Cited in the file of this patent UNITED STATES PATENTS

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