US3545687A

US3545687A - Media mill

Info

Publication number: US3545687A
Application number: US740504A
Authority: US
Inventors: William R Mosby
Original assignee: Martin Marietta Corp
Current assignee: Martin Marietta Corp
Priority date: 1968-06-27
Filing date: 1968-06-27
Publication date: 1970-12-08
Anticipated expiration: 1987-12-08

Description

United States Patent Inventor William R. Moshy Savannah, Georgia Appl. No. 740,504 Filed June 27, 1968 Patented Dec. 8, 1970 Assignee Martin Marietta Corporation New York, New York a corporation of Maryland MEDIA MILL 3 Claims, 7 Drawing Figs.

11.5. C1. 241/66, 241/69,24l/i72 Int. Cl. ..B02c 17/04, B02c' 17/16 Field of Search 241/36, 69,

74,171,172, 179,180, 65-6, 46, 46.02, 46.17; 18/( inquired) [56] References Cited UNITED STATES PATENTS 2,699,294 1/1955 Johnson 241/36 3,243,128 3/1966 Tight 241/172X 3,352,501 11/1967 Krumholz 241/74 3,432,109 3/1969 Geissel 241/172 Primary Examiner--Donald G. Kelly Attorney-John A. Crowley, Jr. and Francis J. Mulligan, .Ir.

ABSTRACT: A media mill for dispersing particulate solids or liquids in a continuous liquid phase having a closed cylindrical body with entrance and exit ports. An agitator driven by a shaft passing through sealed bearings is provided along with an element to restrict flow of dispersion through the exit port so as to permit pressure buildup in the mill and avoid whipping of air or other ambient atmosphere into the dispersion being produced.

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PmEmEum 8mm 3545-687 sum 3 0r 3 WILLIAM R. MOSBY MEDIA MILL The present invention is concerned with dispersing apparatus and, more particularly, with apparatus for dispersing solid or liquid phases in a continuous liquid phase.

A number of apparatuses have been designed to efficiently disperse solids such as pigments, extenders and the like in liquids, such as natural drying oils, bodied oils, and similar substances used as vehicles in paints and printing inks. One of the more recent classes of apparatus for this purpose are represented by media'grinders such as disclosed in the duPont U.S. Pat. Nos. 2,581,414 and 2,855,156. In a media grinding apparatus, a crude pigment-oil dispersion is mixed with a media, such as sand or steel shot, and agitated under highshear conditions for a certain period of time. The product produced by the media grinder differs from the feed thereto (after the media has been separated from the product), not so much by a difference in ultimate particle size of the pigment dispersed in the vehicle, but" rather in the degree of dispersion obtained. Thus the media grinder. does not cause much attrition of the ultimate particles of the pigment or other solid being treated, but rather causes a very effective dispersion of fine particles to exist. In the product from the media grinder there is relatively little tendency for pigment particles to agglomerate.

While the media grinders such as disclosed in the aforementioned duPont patents possess considerable advantage, they do have some drawbacks. As conceived by the duPont workers, media grinders are rather high, bulky pieces of apparatus which are not readily made portable. Furthermore, being open to the atmosphere, these media grinders quite effectively disperse air into the liquids being treated.'ln order to achieve an air-free dispersion; it is often necessary to treat the product obtained from the media grinder by conventional three-roll milling. This milling-squeezes out the air dispersed in the product from the media grinder, but effectively does not change the degree of dispersion produced. From the foregoing it is clear that the art has sought a more portable type of media grinder which will produce essentially gas-free dispersions. By means of a special design, these advantageous results are obtained by means of the present invention.

It is an object of the present invention to provide a novel media grinder particularly adapted to be portable.

Another object of the present invention is to provide a novel media grinder which is capable of producing essentially gasfree dispersions of solids and/or liquids in a continuous liquid phase. A,

Another objectof the present invention is to provide a novel media grinder which can be readily dismantled for cleaning or routine maintenance. 1 1

Other objects and advantages of the present invention will become apparent from the following description taken in light of th the drawing in which: 7

FIG. I is a view in elevation of the media grinder of the present invention;

FIG. 2 is another view in elevation of the media grinder of the present invention;

FIG. 3 is a cross-sectional view in elevation of the essential portions of the media grinder of the present invention;

FIG. 4 depicts an agitator adapted'to be employed in the media grinder of thepresent invention;

FIG. 5 shows bearing and associated seals employed in a media grinder of the present invention;

FIG. 6 shows a liquid or paste withdrawal port employable in a media grinder of the present invention; and

FIG. 7 shows a combination bottom seal, drive shaft agitator-coupler employable in= th e media grinder of the present invention. I

Referring now to FIG. I'media grinder 11 comprises an elongated hollow cylindrical body 12 mounted in such fashion that its axis is at an angle of about 30 from the horizontal. Water jacket 13 having inlet port 14 and outlet port 15 extends around the periphery of the lower portion of cylindrical body 12. Cylindrical body I2 has flange 16 at the upper end thereof to which cover-l7 is bolted by means of bolts 18.

Gasket 19 lies intermediate flange l6 and cover 17. Cover 17 also includes upper bearing housing 20 depicted more particularly in FIG. 5 and pressure gage 21. The lower end of cylindrical body 12 terminates in the flange 22 to which bottom 23 is bolted. Bottom 23 also supports lower seal housing retainer 24 which lower seal housing and drive shaft coupling is depicted in detail in FIG. 7. Between bottom 23 and flange 22 lies gasket 25 held in compression by bolts 26 not shown in FIG. 1. Inlet 27 for crude liquid solid dispersions to be treated in media grinder 11 is positioned slightly above bottom flange 22. Withdrawal port 28, through which the final dispersion is removed, is positioned above water jacket 13 and below flange l6. Withdrawal port 28 is shown in detail in FIG. 6. Additionally at substantially the same level as inlet 27 on cylindrical body 12 is a media withdrawal means consisting in its simplest form of tapped pipe outlet 29. Agitator 30 depicted in detail in FIG. 4 is driven by drive shaft 31 which is coupled to agitator 30 within housing24. Drive shaft 31 is conveniently driven itself by shaft 32 acting through coupler 33. 33. Shaft 32 is caused to rotate within bearings 34 by the action of belt 35 on pulley 36.

The entire aforedescribed media grinder assembly is mounted on cart 37 by means of mounting frame 38 and bearing mounts 39. As shown in FIG. 2, belt 35 is actuated by motor 40 also mounted on cart 37 by means of motor mount 41. It is to be understood that inlet port 14 and outlet port 15 of water jacket 13 are connected in a convenient manner to a source of cooling water and a drain system, respectively, and that inlet port 27 is connected in at least a moderate, pressuretight manner to a source of crude dispersion having a continuous liquid phase. The discharge from withdrawal port 28 can be allowed to drop into any convenient container such as a bucket or holding tank.

One form of the media grinder l l of the present invention is shown in cross section in FIG. 3. It is to be noted that in this embodiment agitator 30 comprises central shaft 42 having four disks 43 welded thereon. Rods 44 extend between disks 43 and above and below the uppermost and lowermost of disks 43, respectively. Agitator 30 is driven by shaft 31 operating through lower seal coupling 45. Agitator shaft 30 is connected to lower seal coupling 45 by means of square drive insert 46. Lower seal coupling 45 is supported in rotary sealed fashion on bottom 23 and guided by bearing 47 comprising sleeves 48 with lubricant space 49 therebetween. Lubricant such as grease can be supplied through standard grease fitting 50. It is necessary that bearing 47 be sturdily constructed with rather close tolerances since, in operation, it is required to support, in sealed fashion, a shaft rotating at high speed under high torque. The upper end of shaft 42 is supported in sleeve bearings 51 having another lubricant space 49 fed by grease fitting 50 therebetween. Upper sleeve bearings 51 are enclosed by upper bearing housing 20. Disks 43 rotatable in unison with agitator shaft 42 have a diameter smaller than the inside diameter of cylindrical body 12 so as to leave free space between the wall of cylindrical body 12 and the rim of agitator disks 43. Mass transfer of material flowing through grinder 11 from inlet 27 to withdrawal port 28 takes place in this free space as well as through openings 52 in the disks themselves.

Media grinder 11 is powered such that the rim speed of I agitator disks 43 is about 1200 to about 3300 feet per minute (ft./min.), advantageously about 2000 ftjmin. At this speed a substantial amount of shear is imparted to the liquid-solid mass in the mill and, at the same time, the centrifugal force generated causes the liquid to cling to the climb the inner walls of cylindrical body 12. When the liquid-solid mass in media grinder reaches the height of withdrawal port 28, the liquid phase plus finely divided solids tends to pass through screen disk 53 positioned across withdrawal port 28. The coarser media is held back by screen disk 53. As processing proceeds, the resistance to flow created by screen disk 53 causes the liquid level to rise and effectively seal withdrawal port 28 against entrance of air or other ambient atmosphere. Thus media grinder II is capable of producing essentially gasfree dispersions once it is substantially completely full of liquid and media. As is common in the art of media grinding the media employed in media grinder 11 can be steel shot, sand, ceramedia, aluminum pellets and the like. As will be apparent from FIGS. 1 and 2, media grinder 11 is mounted such that the axis of central shaft 42 and all parts coaxial therewith are at an angle of about 30 to about 50 or even 65 to the horizontal. In order to facilitate moving the mill, setting up the mill in specific locations to feed holding tanks of various sizes and for other purposes, the platform of cart 37 can be segmented and hinged and provided with an elevating screw or similar device to vary the mounting angle of the mill.

FIG. 4 through 7 illustrate highly advantageous and preferred variations of specific areas of the embodiment depicted in cross section in FIG. 3. Agitator 30 is shown -in FIG. 4. In this embodiment the central shaft comprises three

pieces

54, 55 and 56. Three disks 42 are bored to fit on central shaft portion 55 and are spot welded thereon.

End pieces

54 and 56 are welded onto central portion 55. Square drive sockets 57 are machined into the ends of

end pieces

54 and 56. Square drive inserts 46 on top bearing spindle 58, as shown in FIG. and lower seal coupling, as shown in FIGS. 3 and 7, cooperate with square drive sockets 57 to insure positive rotation of central shaft 42 of agitator 30. Openings 52 in disks 43 are clearly shown in FIG. 4 as are connecting rods 44. Connecting rods 44 assist in agitation by substantially completely eliminating any dead spots in the material being milled.

FIG. 5 shows an alternative and advantageous form of top seal bearing in which spindle 58 floats. Spindle 58 is held in upper bearing housing by means of threaded cap nut 59 held in place on a threaded portion of spindle 58 by means of set screw 60. The lower end of cap nut 59 rests upon and rotates against outer Teflon gasket 61 which in turn is seated against housing 20. Inside housing 20 is packed bearing 62 held in position by setscrew 63. Below packed bearing 62 and separated therefrom by lubricant space 49 is sleeve bearing 51. Lubricant is supplied to lubricant space 49 by grease fitting 50. As shown in FIG. 5 upper bearing housing 20 is made integral with cover 17 provided with bolt holes 64. An additional lower seal is provided by shoulder 73 bearing against Teflon ring 74.

FIG. 6 shows details of withdrawal port 28 and screen 53. Withdrawal port nipple 65 is welded to cylindrical body 12 at the point where port 28 passes therethrough. The outer portion of nipple 65 is threaded externally to coact with internal threads on extension 66; Flanged screen retainer 67 fits snugly within nipple 65 and holds screen disk 53 between the inner end of the retainer and the flangelike internal surface 68 on nipple 65. When extension 66 is screwed tightly on nipple 65 with retainer 67 in place, screen disk 53 is held securely in position across withdrawal port 28. Screen disk 53 and its supporting structure are particularly advantageous in that the screen is merely a die-cut circle of commercial screening which can be readily replaced from the outside of the mill if damage occurs or clogging becomes severe.

FIG. 7 shows details of an advantageous and preferred lower seal-bearing coupler unit 45 having square drive insert positioned at the top thereof. Square drive insert is affixed to or integral with rotating spindle 69 which is coupled to drive shaft 31 by means of left-hand threads 70. The reduced diameter end 70 of drive shaft 31 rotates within sleeve bearing 48 separated from each other by lubricant space 49. Lubricant is supplied to lubricant space 49 by means of grease fitting 50. Sleeve bearings 48 are held in position by pressure exerted on seal and bearing housing 71 by threaded retainer 24 acting against bottom 23. A seal is provided between rotating spindle 69 and seal and bearing housing 71 by means ofTeflon ring 72 atop bronze sleeve bearings 48 and by either a Teflon O-ring seal or by a shoulder-ring seal 75 positioned at or near the lower periphery of rotating spindle 69. Shoulder 76 on rotating spindle 69 assists in providing media agitation in the lowermost portion of media grinder 11 to eliminate any possibility of a dead spot in this area.

Not particularly illustrated in the drawings but nevertheless important to the safe operation of the aforedescribed mill are temperature and pressure sensing elements. It will be evident to those skilled in the art that operation of the media mill of the present invention involves production of much waste heat. Such heat, especially in the lower body of the substrate being dispersed can cause excessive pressures to form and even explosion of the mill, in severe cases, such as in dispersal of pigments in lacquer-type vehicles containing volatile solvents. Those skilled in the art will appreciate that ordinary safety precautions will dictate the use of cutoff circuits connected to the power source actuated by temperature and pressure sensing devices, and pressure relief valves, bursting disks and the like on strategic locations of the mill. Especially important is a temperature sensing device positioned an inch or two above substrate inlet 27.

While the present invention has been described in conjunction with advantageous embodiments, those skilled in the art will recognize that modifications and variations may be resorted to without departing from the spirit and scope of the invention. Such modifications and variations are considered to be within the purview and scope of the invention.

I claim:

1. A media mill comprising:

A. An elongated cylindrical enclosure mounted with its longitudinal axis positioned at an angle of about 30 to about 65 to the horizontal for containing and separating from I the ambient atmosphere a media charge and a substrate to be acted upon by said media, said substrate comprising a continuous liquid phase carrying a particulate solid or liquid material, and said enclosure having a bottom and a top, and an entrance port and an exit port for said substrate spaced longitudinally apart thereon;

B. Means to agitate said media in said enclosure comprising an agitator shaft having agitator disks thereon; said agitator shaft being mounted insaid enclosure between a driving center and a dead center, said driving center and said dead center being mechanically sealed against media contamination and said driving center being mounted in, passing through and sealed against the bottom of said cylindrical enclosure and being coupled to a means for rotating positioned outside said enclosure;

C. A cooling means surrounding at least a portion of said enclosure; and

D. A screen disk associated with said exit port and held in place at said exit port from the outside of said enclosure, said screen disk having interstices of size to prevent the passage of media therethrough and to permit restricted flow of substrate therethrough to inhibit entry of said ambient atmosphere into said enclosure while said apparatus is in operation.

2. An apparatus as in claim 1 wherein said driving center comprises a drive shaft passing through an opening in said one end of said cylindrical enclosure, a spindle mounted on the interior end of said drive shaft, a drive insert fixedly mounted on said spindle coaxially with said spindle and said drive shaft, a bearing mounted within a housing surrounding said drive shaft and means to attach said bearing to the bottom of said enclosure.

3. An apparatus as in claim 1 wherein the exit port is positioned on said cylinder near the top extending downwardly and the entrance port is positioned near the bottom extending upwardly.