Fine media mill with improved disc

Information

  • Patent Grant
  • 6808136
  • Patent Number
    6,808,136
  • Date Filed
    Thursday, October 3, 2002
    22 years ago
  • Date Issued
    Tuesday, October 26, 2004
    20 years ago
Abstract
An agitator (10) with a rotatable axial shaft (24) with a plurality of grinding discs (22) connected generally perpendicular to the shaft (24) is provided having at least one grinding disc (22) with an axially extending pin (32) spaced radially outwardly from the shaft (24) and radially inwardly from a peripheral edge of the disc (22). The pin (32) is aligned with a smooth surface on a next adjacent disc (22).
Description




BACKGROUND




The present invention is directed to an agitator or media mill used to grind or deagglomerate a product in a carrier medium using a grinding media and, in particular, to an improved agitator mill having an improved disc arrangement which provides an enhanced level of grinding or deagglomerating capability.




Agitator mills are used generally to disperse solids, such as pigments, in a liquid carrier medium. The dispersion is carried out by grinding and mixing in the chamber of the agitator mill, which includes an agitator shaft that is used to rotate discs or radially extending pegs in order to de-aggregate or de-agglomerate the solids to be dispersed in the liquid. The shaft is generally driven by a mechanical device such as a motor. A grinding media, such as silica or the like, is placed in the agitator mill chamber and is used in connection with the discs or radially extending pegs to disperse the solid material in the liquid. After the grinding and mixing of the solids and liquid is complete, it is necessary to separate the mixture from the grinding media, and then to discharge the mixture from the milling chamber.




One such separator arrangement is described in U.S. Pat. No. 5,333,804, which is assigned to the assignee of the present invention, and is incorporated by reference as if fully set forth. This patent describes a prior known type of disc mill over which the present invention provides improved performance. An example of a known agitator mill utilizing axially extending pins located on the rotor which travel in spaces between fixed pins extending inwardly into the milling chamber is shown in U.S. Pat. No. 4,620,673 which is also incorporated herein by reference as if fully set forth. The two different types of mills (the disc mill and the axially extending pin mill) perform similarly in use.




In prior known disc mills, generally circular mixing discs are mounted on the drive shaft. The discs may be provided with arcuate slots in order to increase the pumping action of the liquid slurry and the grinding media. It has also been known to utilize a solid disc with radially extending bumps that extend from the inner periphery of the disc to the outer periphery in order to increase pumping and the impact force of the grinding media in a mill. Prior mills have also utilized axially and radially spaced apart arms or blades that extend radially from the agitator shaft, with pin-shaped activator elements extending from one or both sides of the arms.




It would be desirable to provide an agitator mill with an improved disc arrangement to improve mill performance in mixing or dispersing solids into a liquid carrier medium, for example by reducing the time required to reduce the particle size of the solid to a desired range and/or by providing the ability to produce a reduced particle size in comparison to the known prior art mills.




SUMMARY




The present invention provides an agitator with a rotatable axial shaft with a plurality of grinding discs connected generally perpendicular to the shaft. At least one grinding disc has an axially extending pin spaced radially outwardly from the shaft and radially inwardly from a peripheral edge of the disc, which is aligned with a smooth surface on a next adjacent disc.




In another aspect, the present invention provides an improved disc for use in connection with an agitator or fine media mill which includes at least one axially extending pin located in proximity to the disc periphery.











BRIEF DESCRIPTION OF THE DRAWINGS




The foregoing summary as well as the following detailed description of the preferred embodiments of the invention will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings an embodiment which is presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.




In the drawings:





FIG. 1

is a perspective view of an agitator mill constructed in accordance with a preferred embodiment of the present invention, in which the casing has been partially broken away to show the improved disc arrangement in accordance the invention;





FIG. 2

is a plan view of an improved disc in accordance with the present invention;





FIG. 3

is a side view taken along line


3


-


3


in

FIG. 2

;





FIG. 4

is a side view taken along line


4


-


4


in

FIG. 2

;





FIG. 5

is a top perspective view of a disc in accordance with a preferred embodiment of the present invention;





FIG. 6

is a side perspective view of a disc in accordance with a preferred embodiment of the present invention;





FIG. 7

is a side elevational view of the disc in accordance with a preferred embodiment of the present invention;





FIG. 8

is a top perspective view showing the arrangement of two discs in accordance with a preferred embodiment of the present invention;





FIG. 9

is a side perspective view showing the arrangement of the two discs in accordance with a preferred embodiment of the present invention shown in

FIG. 8

;





FIG. 10

is a side elevational view of the two discs shown in

FIG. 9

;





FIG. 11

is a side elevational view showing a velocity profile in a fine media mill with the known prior art discs;





FIG. 12

is a side elevational view showing a velocity profile illustrating the flow disruption created by the discs in accordance with the present invention; and





FIG. 13

is a milling disc comparison chart illustrating the increase in particle size reduction provided by the discs in accordance with the present invention in comparison to the known prior art discs.











DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS




Certain terminology is used in the following description for convenience only and is not limiting. The words “right”, “left”, “lower” and “upper” designate directions in the drawings to which reference is made. The words “inwardly” and “outwardly” refer to directions toward and away from respectively, the geometric center of the media mill and/or the improved disc in accordance with the present invention, and designated parts thereof. The terminology includes the words specifically noted above, derivatives thereof, and words of similar import. In the present application, the terms “a” or “one” are intended to mean at least one unless specifically noted. Additionally, the terms “grinding,” “mixing,” “deagglomerating” and “dispersing” have been used both singly and in combination to describe the processing of a medium in the mill, and any use of one or more of these terms is intended to include the other terms as well as other descriptions of such processing. The terms “agitator mill” and “fine media mill” are also used to indicate the type of mill that the present invention is directed to, and the use of either term is intended to include both.




Referring now to

FIG. 1

, there is shown an agitator mill


10


in accordance with a preferred embodiment of the present invention. The agitator mill


10


includes a housing


12


defining an internal milling chamber


14


. The housing


12


includes a first end


16


and a second end


18


. The housing


12


has been broken away in

FIG. 1

to show a plurality of agitator discs


22


in accordance with the present invention which are spaced apart by spacers


20


. The discs


22


and spacers


20


are located on an agitator shaft


24


which is rotatably supported at the first end


16


of the housing


12


. The agitator shaft


24


is driven to rotate at the desired speed by a motor drive system which is not shown in detail in the present application. The remaining components of a preferred embodiment of the agitator mill


10


are as shown and described in U.S. Pat. No. 5,333,804, which is incorporated herein by reference as if fully set forth. However, it will be recognized by those skilled in the art from the present disclosure that the discs


22


in accordance the present invention can be used in connection with other types of agitator mills and are not limited to use with the preferred agitator mill


10


shown and described. The agitator mill includes a product inlet


17


and a product outlet


19


. A separator screen arrangement


40


is located at the second end


18


of the housing


12


in order to prevent the grinding media from exiting the agitator mill


10


along with the product flow.




The number and spacing of the discs


22


and spacers


20


on the agitator shaft


24


can be varied for particular applications, depending upon the solids being de-agglomerated or dispersed and the viscosity of the liquid in which the dispersed solids are entrained.




The discs


22


in accordance with a preferred embodiment of the present invention are shown in detail in

FIGS. 2-10

. Referring to

FIGS. 2-4

, preferably each disc


22


includes a central opening


26


which is keyed to fit on the agitator shaft


24


such that each disc


22


rotates with the agitator shaft


24


. This can be done by providing flats on the agitator shaft


24


and corresponding flats in the central opening


26


. However, those skilled in the art will recognize from the present disclosure that other means may be utilized to connect the discs


22


to the agitator shaft


24


, such as a separate notch and key arrangement, if desired. Additionally, the outer periphery


28


of the disc may have various different configurations depending upon the application. For example, one or more flats may be provided on the outer periphery


28


of the disc


22


, or the outer periphery


28


of the disc


22


could be provided with other forms, such as teeth, undulations, or other shapes depending upon the mixing characteristics desired.




Preferably, the disc


22


also includes a plurality of arcuate openings or slots


30


to increase the mixing action. In the preferred embodiment, four kidney shaped slots


30


are provided on each disc


22


. Preferably, the circumferential ends of each slot


30


are angled as shown in detail in

FIGS. 2-4

in order to enhance the pumping action of the discs


22


. However, it will be recognized by those skilled in the art from the present disclosure that the shape, size and configuration of the openings


30


may be varied depending the particular application.




As shown in detail in

FIGS. 2-7

, at least one disc


22


, and preferably each disc


22


, includes at least one axially extending pin


32


located in proximity to the periphery


28


of the disc


22


. In a preferred embodiment, two pins


32


are located on each side of the disc


22


, with the two pins on the first side


34


of the disc


22


being spaced approximately 180° apart and the two pins


32


on the second side


36


of the disc


22


also being spaced approximately 180° apart and being offset 90° from the pins


32


on the first side


34


. Preferably, the pins


32


are positioned in a disc segment located between the slots


30


, and are preferably offset radially outwardly from the outside diameter defined by the slots.




In a preferred embodiment, the pins


32


are approximately cylindrical in shape and are attached in correspondingly located threaded openings in the disc


22


. Flats


33


may be provided on opposing sides of the pins


32


for engagement with an installation tool. However, it will be recognized by those skilled in the art from the present disclosure that the shape of the pins


32


can be varied depending upon the particular application. For example, oval-shaped, square or other cross-sectional profiles could be utilized. Additionally, the spacing and number of pins


32


can be varied depending upon the aggressiveness of the mixing action desired. Preferably, the pins


32


are made from tool steel. Those skilled in the art will also recognize from the present disclosure that the pins


32


can be attached to the disc


22


in any suitable manner, such as welding, interference fit, swaging or any other suitable method or may be formed integrally with the disc


22


by machining, casting or any other suitable forming process. The pins


32


are mounted axially such that they are generally parallel to the agitator shaft


24


.




In order to achieve optimum de-agglomerating, mixing and/or dispersion during milling, preferably the size and spacing of the pins


32


meet certain criteria based on the size of the mill


10


and discs


22


being utilized. The disc


22


has a predetermined outside diameter based on the size of the mill. The arcuate slots


30


also include an inner slot diameter K


DIA


, shown in FIG.


2


. Preferably, the pins


32


have a protrusion height h, shown in

FIG. 3

, that is in a range of 8% to 15% of a difference between the outside diameter of the disc


22


and K


DIA


. More preferably, the protrusion height h is between 11% and 12% of the difference between the outside diameter of the disc


22


and K


DIA


. The pins


32


also have a diameter that is in a range of approximately 90% to 110% of the protrusion height h, and more preferably is in the range of 105% to 107% of the protrusion height.




The pins


32


are preferably located on a pin circle having a diameter PC


DIA


that is in a range of 75% to 90% of the outside diameter of the disc


22


, and more preferably PC


DIA


is in the range of 85% to 87% of the disc o.d. in order to achieve optimum performance. Additionally, the distance S between adjacent discs


22


, as shown in

FIG. 10

, is in a range of approximately 210% to 530% of the pin protrusion height h.




In one preferred embodiment for a disc


22


having an outside diameter of approximately 9.54 inches and K


DIA


of 4.44 in., the pins


32


have a protrusion height of approximately 0.59 in. and are approximately ⅝ in. in diameter. PC


DIA


is approximately 8.2 inches and the spacing between adjacent discs


22


is in the range of 1.5 to 2 inches. Those skilled in the art will recognize that the above-noted dimensions are intended to be merely exemplary, and that other dimensions could be utilized. Preferably, other selected dimensions will meet the criteria set forth above in order to achieve optimum performance.




As shown in detail in FIGS.


1


and


8


-


10


, the location of the pins


32


on the neighboring discs


22


are also shown. In accordance with the present invention, the at least one pin


32


on the disc


22


is located in a complementary position to a smooth surface on the neighboring or next adjacent disc


22


. While in the preferred embodiment pins


32


extend from both surfaces


34


,


36


of each disc


22


, it will be recognized by those skilled in the art from the present disclosure that a pin


32


may extend only from one surface


34


,


36


, of a given disc


22


and that the position of the pin


32


is aligned with a smooth area on a neighboring or next adjacent disc


22


. It is also possible that the neighboring disc may be designed such that it does not include any pins


32


such that only every other disc


22


in the agitator mill


10


includes any pins


32


. However, in the preferred embodiment, the pins


32


on each disc


22


are aligned such that the pins


32


on the first face


34


of each disc


22


are generally aligned with one another, and the pins


32


on the second face


36


of each disc are also aligned, as shown.




The unique positioning of the pins


32


results in a greatly enhanced level of de-agglomerating, mixing and/or dispersion capability by forcing the pins


32


through the normal accelerating flow of the media/product mixture in the agitator mill


10


. The forcing action results in a diverting of the product flow around the parallel pins


32


as illustrated diagrammatically in FIG.


12


. The prior art arrangement of discs


2


without the pins


32


is shown in

FIG. 11

in which the velocity profile is generally highest at the surfaces of the discs (as represented by the longer arrows


41


) and lowest in an area midway between the discs (as indicated by the shortest arrow


42


). In comparison, the velocity profile shown in

FIG. 12

illustrates how the pins


32


divert the product flow around the pins


32


which eliminates the low velocity segment of the flow profile and causes a higher velocity as represented by arrows


43


. This forcing action creates a disruption in the flow across the first and second disc surfaces


34


,


36


which are generally flat, and results in a pulsating flow pattern towards and away from the disc surface. This combined action increases the velocity of the media/product mixture as it flows around each pin


32


, increasing the velocity beyond that normally obtained at the disc periphery


28


. The result is believed to be an increase in the maximum shear level attainable at a given agitator tip speed beyond that attainable with the conventional disc arrangement or the prior known axial pin agitation systems operated under the same conditions.




The higher media/product shear level obtained with this unique pin disc


22


utilized in the agitator mill


10


results in a significant and substantial increase in the rate of product dispersion when compared with the existing convention discs systems. Test data shown in

FIG. 13

, which compares a prior art disc with two separate tests of discs


22


with pins


32


in accordance with the present invention (designated


22


-


1


and


22


-


2


) shows an increase in de-agglomeration, mixing and/or dispersion capacities of 150-300% from those achieved in an agitator mill


10


having conventional discs operated under identical process conditions. As shown in

FIG. 13

, after 10 minutes of operation with a standard disc, the average particle was approximately 4.7 μm. In comparison, with the disc


22


having the pins


32


in accordance with the preferred embodiment of the present invention as described above, after 10 minutes the particle size was approximately 1.8 μm in Test 1 and approximately 1.5 μm in Test 2.




In the known agitator mill using discs without the axial pins


32


, the agitator mill is limited to a maximum Q


max


value which indicates a best achievable product dispersion as indicated by a minimum particle size after mixing to a point where further reduction in particle size is non-attainable. This would be represented by a horizontal line in

FIG. 13

which would be generally asymptotic to the performance curve to indicate the minimum particle size. By utilizing the improved disc


22


with the pins


32


in accordance with the present invention, the Q


max


value for a given agitator mill has changed and is a significant improvement over the prior known mills. This means that an agitator mill


10


equipped with the discs


22


with pins


32


in accordance with the present invention can obtain a higher operating efficiency with no other change to the equipment aside from the configuration of the discs


22


in order to produce the same particle size, and can also be used to generate an even smaller particle size than was previously attainable.




While the preferred embodiment of the present invention has been described in detail, those skilled in the part will recognize that other arrangements and instrumentalities can be used within the scope and spirit of the present invention. It is believed that the unique positioning of an axially extending pin located in proximity to the periphery of the disc and facing a smooth surface on the next adjacent or neighboring disc has provided this improvement over the prior known system. The discs


22


in accordance with the present invention having pins


32


can also be retrofitted onto existing equipment by replacement of one or more of the existing discs with discs


22


in accordance with the present invention. Accordingly, this invention is not limited to the precise arrangement shown but rather to the general concept of utilizing an axially extending pin on one disc


22


which extends toward a smooth surface of the neighboring or next adjacent disc.



Claims
  • 1. An agitator mill comprising a rotatable axial shaft with a plurality of grinding discs connected generally perpendicular to the shaft, at least one grinding disc having an axially extending pin spaced radially outwardly from the shaft and radially inwardly from a peripheral edge of the disc, which is aligned with a smooth surface on a next adjacent disc, andwherein first, second, third, and fourth axially extending pins are located on the at least one disc, the first and second axially extending pins extend from a first side of the at least one disc, and the third and fourth axially extending pins extend from a second side of the at least one disc, and wherein the first and second axially extending pins are spaced apart radially approximately 180°, and the third and fourth axially extending pins are spaced apart radially approximately 180°, and are offset from the first and second axially extending pins by approximately 90°, and further comprising four elongate arcuate slots, the axially extending pins being located in a radial position between the slots.
  • 2. The agitator mill of claim 1, wherein the at least one grinding disc includes a plurality of elongated arcuate slots, and the axially extending pin is located in a disc segment between the slots.
  • 3. The agitator mill of claim 1,wherein the pins have a protrusion height that is in a range of 8% to 15% of a difference between an outside diameter of the disc and an inside diameter of the arcuate slots.
  • 4. The agitator mill of claim 3, wherein the pins have a diameter that in a range of approximately 90% to 110% of the protrusion height.
  • 5. The agitator mill of claim 1, wherein the pins are located on a pin circle having a diameter that is in a range of 75% to 90% of a diameter of the disc.
  • 6. The agitator mill of claim 1, wherein a distance between the at least one disc and the next adjacent disc is in a range of approximately 210% to 530% of the pin protrusion height.
  • 7. The agitator mill of claim 1, wherein the at least on axially extending pin has a protrusion height of between 125% and 300% of a thickness of the at least one disc.
  • 8. A disc assembly for use with an agitator mill having a rotatable shaft accommodating a plurality of discs, each disc located along the rotatable shaft at a spaced-apart distance from another disc, comprising:a disc configured to mount on the agitator shaft; a plurality of slots positioned on a first face of said disc, wherein said disc has a center and said plurality of slots are positioned equidistant from said center to form a slot circle having an inner diameter and an outer diameter; and at least one pin protruding from a second face of said disc and having a protrusion height less than the spaced-apart distance, wherein said plurality of slots are kidney shaped and wherein said plurality of kidney-shaped slots are four kidney-shaped slots.
  • 9. A disc assembly according to claim 8, wherein the first face and the second face are the same face.
  • 10. The disc assembly according to claim 8, wherein said at least one pin is cylindrical in shape.
  • 11. The disc assembly according to claim 8, wherein said disc has a thickness and said at least one slot extends the thickness of said disc.
  • 12. The disc assembly according to claim 8, wherein said disc has an outer periphery and a center and said at least one pin is located closer to the outer periphery than the center.
  • 13. A disc assembly according to claim 8, wherein said disc has a center and said at least one pin is at least two pins, and said pins are positioned equidistant from the center and define a circular path along the first face of said disc.
  • 14. The disc assembly according to claim 13, wherein said disc has an outer diameter, and said circular path has a diameter ranging from approximately 75% to approximately 90% of the outside diameter of the disc.
  • 15. The disc assembly according to claim 14, wherein said circular path diameter ranges from approximately 85% to approximately 87% of the outside diameter of the disc.
  • 16. The disc assembly according to claim 8, wherein said disc has an outside diameter and the protrusion height ranges from approximately 8% to approximately 15% of a difference between the outside diameter of the disc and the inner diameter of the slot circle.
  • 17. The disc assembly according to claim 16, wherein the protrusion height ranges from approximately 11% to approximately 12% of the difference between the outer diameter of the disc and inner diameter of the slot circle.
  • 18. The disc assembly according to claim 8, wherein said at least one pin has a diameter ranging from approximately 90% to approximately 110% of the protrusion height.
  • 19. The disc assembly according to claim 18, wherein said at least one pin has a diameter that that ranges from approximately 105% to approximately 107% of the protrusion height.
  • 20. A method for mixing or grinding a product in a mill having a rotatable shaft, comprising:passing the product through the mill; rotating a plurality of grinding discs connected to the rotatable shaft, wherein at least one of the grinding discs has first, second, third and fourth axially extending pins located on the at least one grinding disc, wherein the first and second axially extending pins extend form a first side of the at least one disc, and wherein the third and fourth axially extending pins extend from a second side of the at least one disc, wherein the first and second axially extending pins are spaced apart radially approximately 180°, and the third and fourth axially extending pins are spaced apart radially approximately 180°, and are offset from the first and second axially extending pins by approximately 90°, and wherein the axially extending pins being located in a radial position between four elongate arcuate slots; and discharging the product from the mill.
  • 21. A method according to claim 20, wherein the disc further comprises a central opening keyed to fit on the agitator shaft.
  • 22. A disc assembly for use with an agitator mill having a rotatable shaft accommodating a plurality of discs, each disc located along the rotatable shaft at a spaced-apart distance from another disc, comprising:a disc configured to mount on the agitator shaft; at least one slot positioned on a first face of said disc; and at least one pin protruding from a second face of said disc and having a protrusion height less than the spaced-apart distance, wherein said at least one pin is at least a first pin, a second pin, a third pin, and a fourth pin; the first and second pin are located on the first face of said disc and are spaced about 180 degrees apart; the third and fourth pin are located on the second face of said disc and are spaced about 180 degrees apart; the third pin is offset about 90 degrees from said first pin and the fourth pin is offset about 90 degrees from said second pin; and, the second face opposes the first face, and wherein said disc has a center and said at least one slot is at least a first, second, third, and fourth slot positioned equidistant from the center and along a circular path on the second face of said disc, and each of said at least first, second, third, and fourth pins is positioned on a disc segment located between one of the at least first, second, third, and fourth slots, and each of said pins is offset radially outwardly from an outside diameter defined by said slots.
Parent Case Info

This application claims the benefit of Provisional Application No. 60/175,276, filed Jan. 10, 2000.

PCT Information
Filing Document Filing Date Country Kind
PCT/US01/00716 WO 00
Publishing Document Publishing Date Country Kind
WO01/51212 7/19/2001 WO A
US Referenced Citations (11)
Number Name Date Kind
1673927 Turner Jun 1928 A
2639901 Teale May 1953 A
3706314 Smith, Jr. Dec 1972 A
4066215 Pujol Jan 1978 A
4082231 Gould Apr 1978 A
4269363 Entzmann May 1981 A
4580736 Takahashi et al. Apr 1986 A
4811909 Inoki Mar 1989 A
4983046 Murata et al. Jan 1991 A
5333804 Liebert Aug 1994 A
5947599 Funk Sep 1999 A
Foreign Referenced Citations (2)
Number Date Country
2154059 May 1973 DE
1084731 Sep 1967 GB
Non-Patent Literature Citations (1)
Entry
International Search Report for International Application No. PCT/US01/00716, dated Feb. 21, 2001, published on Jul. 19, 2001 under No. WO 01/51212.
Provisional Applications (1)
Number Date Country
60/175276 Jan 2000 US