US2789773A - Vibrating ball mill having baffle plate for preventing short circuiting of material through the mill - Google Patents

Description

April 23,

Filed Dec.

1957 R B. STAUBER 2,789,773

VI BRATING BALL MILL HATIING BAFFLE PLATE FOR PREVENTING 9 SHORT CIRCUITING OF MATERIAL THROUGH THE MILL.

2 Sheets-Sheet l Aprnl 23, 1957 R; B. STAUBER 2,789,773

VIBRATING BALL MILL HAVING BAFFLE PLATE FOR PREVENTING SHORT CIRCUITING OF MATERIAL THROUGH THE MILL Filed Dec. 9, 1954 2 Sheets-Sheet 2 VIBRATING BALL MILL HAVING RAFFLE PLATE F OR PREVENTING SHORT CIRCUITING F MA- TERIAL THROUGH THE MELL Robert B. Stauber, Ottawa, Ill., assignor to Allis-Chalmers Manufacturing Company, Milwaukee, Wis.

Application December 9, 1954, Serial No. 474,153

Claims. (Cl. 241-47) The present invention relates to material comminuting mills of the type known as vibrating ball mills in which materials are comminuted in a vibrating container by the action of loose grinding bodies to which motion is imparted by the vibratory movement of the container.

A vibrating ball mill commonly has a cylindrically shaped container which is adapted to be resiliently mounted for vibratory movement, the longitudinal axis thereof being horizontally disposed. Actuating means are provided for imparting a gyratory motion to the container transversely of the longitudinal axis to effect grinding of material in the container by virtue of the grinding action of loose grinding bodies.

The gyrating movement of the container is transmitted from the wall of the container to the adjacent layer of grinding bodies. This movement is transmitted by friction to the next inner layer of grinding bodies and so on.

In addition to the individual movements of the grinding bodies, the grinding bodies and the material being ground in the container revolves as a whole in a direction opposite from the direction of gyration of the container. During operation of the mill the grinding bodies are more or less sparsely distributed in the upper portion of the container while the distribution of grinding bodies is quite concentrated in the lower portion of the container.

In dry grinding operations, material which has been ground may be continuously removed from the container by directing a stream of air through the container which picks up ground material and carries it out of the mill. This is referred to as air sweeping and may be accomplished by applying a suction to the discharge outlet of the mill or by introducing air under pressure through the inlet of the mill. When the material withdrawn from the mill by an air stream is delivered directly to a storage hopper, this is referred to. as open circuit grinding. When the material withdrawn from the mill is passed through a separating device, such as a centrifugal air separator, with the finer particles being delivered to a storage hopper and the larger particles being returned to the mill for further reduction, this is referred to as closed circuit grinding. In both open and closed circuit dry grinding operations it is desirable that the sizes of the particles removed from the mill should not exceed a predetermined size. One difficulty in preventing oversized particles from being discharged from prior art mills is that in such mills there is an opportunity for portions of unground material to be short circuited directly from the inlet to the discharge of the mill without being subjected to any grinding action by the grinding bodies.

This short circuiting of unground material also tends to occur in continuous wet grinding operations with prior art vibrating mills in which a slurry of material to be ground is continuously fed to the mill and a slurry of ground material is continuously discharged from the mill.

During a wet grinding operation with a prior art mill of the type referred to there is an opportunity for portions of unground material fed to the mill to float across the upper portion of the mill, where there is lesser grinding of Fig 3.

activity, and be discharged from the mill without being subjected to any appreciable grinding action by the grinding bodies.

It is stated above that there is only a sparse distribution of grinding bodies in the upper portion of the mill but the distribution of grinding bodies in the lower portion of the mill is quite concentrated. Thus, when material to be ground is circuited across the upper portion of the mill, in both wet and dry grinding operations, the material is subjected to little or no grinding action and oversized particles are discharged from the mill.

In accordance with the present invention a vibrating ball mill is provided in which the short circuiting of portions of unground material from the feed inlet to the discharge outlet of the mill is avoided. The invention is ap plicable for such mills for both wet and dry grinding operations.

A main object of the invention is to provide a new and improved vibrating type ball mill in which the short circuiting of the material to be ground from the feed inlet to the discharge outlet of the mill is prevented for both wet and dry grinding operations.

Another object is to provide a new and improved mill of the type referred to in which all the material to be ground is caused to pass through the lower portion of the mill where the grinding bodies or balls are most concentrated so as to subject all of the material passing through the mill to a substantial grinding action.

Another object is to provide a mill of the type referred to in which the efiiciency and the effective capacity of the mill in terms of the amount of material ground to the desired size per hour is increased.

Other objects will become apparent from the following detailed description of the invention and the accompanying drawings which show two embodiments of the invention.

In the drawings:

Fig. 1 is a vertical sectional view through the longitudinal axis of a vibrating ball mill embodying the present invention;

Fig. 2 is a cross sectional view taken on line IIII of Fig. 1;

Fig. 3 is a vertical sectional view through the longitudinal axis of a modified vibrating ball mill embodying the invention; and

Fig. 4 is a cross sectional view taken on line IV-IV Referring to Figs. 1 and 2, a suitably shaped container 10 having end walls 11 and 12 is shown suspended by cables 13 from a stationary overhead supporting structure 14. Container Iii is illustrated as having an arcuate bottom portion and as being cylindrical in shape. Container 10 is supported with the longitudinal axis thereof in a horizontal plane and resilient means such as springs 15 are provided between cables 13 and supporting structure 14 to allow container it to have a vibrational movement in vided, respectively, between shaft 25 and bearing hous ings 20 and 21.

Weight means 32 and 33 are rigidly attached, preferably in phase with each other, at opposite ends ofshaft 25','and each of the weight means has a center of gravity disposed eccentrically of the axis of shaft 25. Uponrotating shaft 25 the centrifugal forces imparted to shaft 2- Patented Apr. 23, 1957 by weight means 32 and 33 are transmitted through bearings 22 and 23 so as to cause container 10 to gyrate in a direction transversely of its axis.

A- motor 34 mounted on a stationary support 35 is provided for driving shaft 25. of the vibratng: ball mill.

As the container 10 of the mill is vibratable relative to motor-34, a flexible coupling 36. is:provided bctweenshaft 40 of the motor and shaft 25 of the mill.

A feed inlet 41 is provided -at'the top at one end of container 163 and a discharge outlet 42 is provided at the bottom at the opposite end of container Means for feeding a slurry of the material to beground to the mill such as a hopper 43 is also provided an aslurry of material to be ground iscontiuuously fed'to-the mill through inlet 41 and a slurry of ground-material is continuously withdrawn from the mill through dischargeopening 42..

A perforated discharge diaphragm or head 45 is positioned near discharge outlet 42, the perforations therein being large enough to allow the slurry of material to pass freely therothrough but small enough to prevent the escape of the grinding bodies or balls 45.

An imperforate baffle plate is provided for causing all the material to be ground to pass through the lower portion of the mill where the grinding bodies 46 are most concentrated so as to subject all the material passing through the mill to a substantial grinding action. Baffle plate 50 extends transversely of the axis of the mill, intermediate the feed and discharge openings 41 and 42, and is mounted in the upper portion of the mill with the lower edge-thereof being in the general vicinity of the horizontal center line of the mill and is shown slightly above the center line of the mill. A preferable longitudinal position for bafile plate 50 is approximately one-third the length of the mill from wall 11 at the feed end thereof. Material to be ground or otherwise acted upon by grinding bodies 46 enters feed inlet 41 in the form of a slurry and flows beneath battle plate till through the concentrated ball charge, through the perforated discharge diaphragm 45, and out discharge opening 42.

During operation of the mill the container lillnormally is about four-fifths full of grinding balls 46 and the slurry of material being ground. The greatest concentration of grinding balls is in the lower half of the mill. Portions of the material fed to the mill have a. tendency to float across the top of the material in the mill and, if battle plate 58 were not present, such portions of material would be short circuited or shunted across the top of the mill from inlet 41 through diaphragm 45. As there is only a sparse concentration of grinding balls in the upper half of the mill, portions of material would therefore escape fire-m the mill without being ubjected to any appreciable grinding action. The plate Sit has its edge so located that the plate intercepts the material tending to float. across the top of the mill; The presence of bafile plate so thus causes all material passing through the mill to pass through the lower portion of the millwhere the material is sure of being subjected to a substantial grinding action.

In the wet grinding operation, apparatus not shown may be provided for conveying back to the mill a portion of the material discharged through outlet 4-2. An overall advantage obtained with the use of the present invention is that a considerably lesser portion of the discharged material may be recirculated without sacrificing the degree of fineness to which the end product of the mill is ground or reduced because the baffle plate arrangement increase. the efficiency as well as the eifeotive capacity of the mill.

Referring to Figs. 3 and 4 of the drawings, a-vibrating ball mill embodying the invention is illustratedjwhichiis suitable,.-for, adry grinding operation. The construction oil-the millshowninhig. Sis similar-tolthe mill shown in Fig, 1 "and corresponding elements in Fig. 3 are desig-v nated bythesamereference numerals increased by 100. Two-structuralidifierences are thatithe mill; of Fig; 3 is A not provided with a perforated discharge diaphragm and the discharge outlet 142 is positioned at the top of the mill instead of at the bottom. In all other respects the mills of Figs. 1 and 3 are identical.

A fan 152 is provided for continuously removing from the mill, by suction, material which has been ground.

Thisis referred to as air sweeping. Air sweeping may also be effected-by introducing air under pressure through the feed inlet 141 of the mill. Fan 152 is preferably mounted on a stationary support (not shown) and a flexible conduit 153 is provided-to allow the mill to have a vibratory duction, that would be referred to as closed circuit grind-- ing. in both open and closed circuit dry grinding operations, it is desirable that the sizes of the particles removed from the mill should not exceed a predetermined size.

In dry. grinding operations, as in wet grinding operations, the grinding bodies 146 are more or less sparsely distributed in the upper portion of the container while the distribution of grinding bodies isquite concentrated in the lower portion of the container. B'afiie plate 150 is eitective to cause all the material to pass through the lower portion of the mill where the grinding balls 146 are most concentrated so that all the material passing through the mill is subjected to a substantial grinding action. If

baflle plate150 were not present, portions 'of'the material to be ground would follow the path of least'resistance and would be short c-ircuited or shun-tedthrough the upper portion of the mill where there is only a sparse concentration of grinding balls 146 and such portions of material would be subjectedtolittle or no grinding action. In such case, a considerable portion of the material discharged from the mill would consist of oversized particles.

Referring to the operation of'the mill generally, the ball'chargeand the material being ground revolves as a whole-in'adirection opposite the direction of gyration of the container. Referring Ito-Figs. 2 and 4, the gyratory movement of the'container" 10 is' indicated as counterclockwise and the revolving movement of the ball charge and material is indicated as counterclockwise.

It will beunderstood that the scope of the present inventionis not limited to the precise details of either of the two vibrating ball mills embodying the invention illustrated but that, within the scope of the appended claims, other embodiments of the invention'may readily occur to personsskilled in the art towhich'the invention pertains.

Itis claimed'and desired'to'secure by Letters Patent:

1. A vibrating type mill for grinding operations comprising a container with a substantially horizontally disposed longitudinal axis passing through the approximate center of said container and said container having an arcuately formed bottom portion, a plurality of grinding media partially filling said container, power driven means for imparting a-gyratorymovement to said container transversely of its axis, an inlet opening disposed at one end of said containerand a discharge openingdisposed at the other end of said container, and an imperforate baffle plate extending transversely of said axis in theupper portion of said container intermediate said inlet and 'dis charge openings-and having'a lower edgeterminating at an elevation in the general vicinity ofsaid'horizontal axis.

2. A vibrating type mill for wet-grinding operations comprisinga container with a substantially horizontally disposed longitudinal axis passing through the approximate center of'said container and said container having an arcuately formed bottom-portion, a plurality of grind ing media partially'filling'said container; power driven means for imparting a gyratory movement to said container transversely of its axis, an inlet opening disposed at one end of said container at the top thereof and a discharge opening disposed at the other end of said container at the bottom thereof, and an imperforate baifie plate extending transversely of said axis in the upper portion of said container intermediate said inlet and discharge openings and having a lower edge terminating at an elevation in the general vicinity of said horizontal axis.

3. A vibrating type mill for wet grinding operations comprising a container with a substantially horizontally disposed longitudinal axis passing through the approximate center of said container and said container having an arcuately formed bottom portion, a plurality of grinding media partially filling said container, power driven means for imparting a gyratory movement to said container transversely of its axis, an inlet opening at one end of said container at the top thereof and a discharge opening disposed at the other end of said container at the bottom thereof, an imperforate baffle plate extending transversely of said axis in the upper portion of said container and positioned intermediate said inlet and discharge openings approximately one-third the length of said container from the inlet end thereof, said bafile plate having a lower edge terminating at an elevation in the general vicinity of said horizontal axis, and a perforated discharge diaphragm mounted in said container extending transversely of said axis between said bafiie plate and said discharge opening to prevent grinding bodies from being discharged from said container.

4. A vibrating type mill for dry grinding operations comprising a container with a substantially horizontally disposed longitudinal axis passing through the approximate center of said container and said container having an arcuately formed bottom portion, a plurality of grinding media partially filling said container, power driven means for imparting a gyratory movement to said container transversely of its axis, an inlet opening disposed at one end of said container at the top thereof and a discharge opening disposed at the other end of said container at the top thereof, and an imperforate bafiie plate extending transversely of said axis in the upper portion of said container intermediate said inlet and discharge openings and having a lower edge terminating at an elevation in the general vicinity of said horizontal axis.

5. A vibrating type mill for dry grinding operations comprising a container with a substantially horizontally disposed longitudinal axis passing through the approximate center of said container and said container having an arcuately formed bottom portion, a plurality of grinding media partially filling said container, power driven means for imparting a gyratory movement to said container transversely of its axis, an inlet opening disposed at one end of said container at the top thereof and a discharge opening disposed at the other end of said container at the top thereof, an irnperforate bafile plate extending transversely of said axis in the upper portion of said container and positioned intermediate said inlet and discharge openings approximately one-third the length of said container from the inlet end thereof, said baflle plate having a lower edge terminating at an elevation in the general vicinity of said horizontal axis, and air sweeping means for effecting the withdrawal of ground material from said container through said discharge opening.

References Cited in the file of this patent UNITED STATES PATENTS 511,871 Atterbury Ian. 2, 1894 2,117,965 Kiesskalt et al May 17, 1938 2,507,917 Lonngren May 16, 1950 FOREIGN PATENTS 94,462 Germany Oct. 9, 1897 518,981 Great Britain Mar. 13, 1940 633,699 Germany Aug. 4, 1936 655,779 Germany Jan. 22, 1938

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