US2621859A - Fluid swept ball mill with ball moving rotor and stationary drum - Google Patents

Description

Dec. 16, 1952 E. D. PHILLIPS 2,621,359

FLUID swam" BALL MILL WITH BALL MOVING ROTOR AND STATIONARY DRUM Filed Oct. 24, 1949 4 Sheets-Sheet 1 F'Czcaf.

W mull;

SOUND PRO OF/NG MA TE/P/A L INVENTOR 5 1/5/2577 .0. pH/L u ATTORNEY Dec. 16, 1952 E. D. PHILLIPS 2,621,859

FLUID SWEPT BALL MILL WITH BALL MOVING ROTOR AND STATIONARY DRUM Filed Oct. 24, 1949 4 Sheets-Sheet 2 50 (/ND PROOF/NO MA TEP/AL INVENTOR 51/5/9577 0 pH/LL/PS ATTORNEY Dec. 16, 1952 E. D. PHILLIPS 2,621,859

FLUID SWEPT BALL MILL WITH BALL MOVING ROTOR AND STATIONARY DRUM Filed Oct. 24, 1949 4 Sheets-Sheet 5 SOUND PROOF/NC? MA 7' E R/A L.

INVENTOR 5 1/5/9577 0. pH/LL/PS RNA ATTORN EY Dec. 16, 1952 E. D. PHILLIPS- FLUID SWEIPT BALL. MILL. WITH BALL MOVING ROTOR AND STATIONARY DRUM Filed 001:. 24, 1949 4 Sheets-Sheet 4 INVENTOR SOUND PROOF/N6 MA TER/A L fVf/QETT Y E N m T T A Patented Dec. 16, 1952 FLUID SVVEPT BALL MILL WITH BALL MOV- ENG ROTOR AND STATIONARY DRUM Everett D. Phillips, Saginaw, Mich.

Application October 24, 1949, Serial No. 123,245

11 Claims.

My present invention broadly relates to means, primarily mechanical, for reducing, even to superfine form, certain fragmentary materials such as coals (including extremely diflicult to reduce anthracite), cement clinkers, iron pyrites, coke breezes, petroleum cokes, pigments, grains and many other vegetable matters. This application is a continuation-in-part of my co-pending application entitled Ball Mill, Serial No. 531,951, filed April 20, 19%, now abandoned; and this application contains subject matter relating to Figures 8 and 4.- not claimed herein but claimed in my continuation-in-part application No. 269,820, filed February 4, 1952.

An important object of my invention is to so design the particular arrangement of mechanical means that it is readily adaptable to having associated therewith an active fluid medium by which the reduced material can be most efiectively collected and continuously removed from the region of the reducing means.

I am fully aware of the fact that numerous efiorts have been made to create and design means having the-same objectives as my invention. These designs have produced only moderate degrees of success. The general objective of my invention is to materially expand the success obtainable over anything heretofore accomplished in the particular field. In this connection, I cite in particular a number of fairly wellknown so-called drum and ball or ball mill commercial products, also commonly termed pulverizer. Each of these products, I know from first hand experience, have been criticized by commercial users and condemned by competition because of their relatively large power and space requirements. There are several major deficiencies contributing to the present inefliciency of the drum and ball type pulverizers.

First, and perhaps the greatest deficiency is the inability of these mills to separate the finely round materials from the almost solid mass of material and balls rotating in the revolving drum before the reduction of these materials to a superfine product. This lack of separating capacity partially explains the relatively large power requirements of such mills. This excessive power requirement makes it diilicult for this type of mill to successfully compete against high speed impact or hammer mill pulverizers, ball race type pulverizers, roller bearing mill type pulverizers and others whose power requirements are rela tively lower but producing a coarsely ground product.

Second, an excessive amount of energy is expended in rotating the drum or its equivalent inefiiciency are being displaced commercially by spreader stokers, particularly in the small and medium size. installations. Until my invention,

nothing was being done to eliminate these deficiencies of the drum and ball type mill, despite both the possibility and necessity for such improvement.

In the conventional drum and ball mill pulverizer, movement of the balls is dependent solely upon the balls being dragged into and maintained in action by the slight frictional and point contact existing between the balls and the wall of the rotating drum. This frictional contact is limited to those few of the balls that manage to make individual respective contact with the inner surface of the rotating drums. The total area of frictional contact is but a minute fraction of either the balls or the inner surface area of the drum. Thus, these conventional ball mills must be operated over a longer period of time to effect the same amount of reduction as will occur in a mill in which the movement of the balls is effected by positive engagement between the balls and their agitating means. Such increased operating time reduces efiiciency and increases wear. This major handicap to effective reduction is one of the objectionable aspects of the said prior practices overcome by the instant invention. The greater quantity of power required to turn the rotor of my ball mill, due to the positive engagement with the balls, is ofiset by the elimination of the necessity for moving the mass and weight of the drum or grinding chamber shell. Thus, although the power consumption, per revolution, of my invention and of ball mills of conventional design are approximately equal, appreciable emciency is obtained by my invention since the total reducing action obtained by each revolution of my invention is several times that of conventional ball mills. Further, since the balls in my invention are positively pushed and lifted into cascading position rather than raised into cascading position by a combination of frictional and centrifugal forces, my mill may be efiiciently operated at less revolutions per minute. This speed reduction permits a power source of lesser horsepower to apply the same torque to the shaft driving the mill. These are but two of the ways in which my mill obtains a substantial increase in efficieney over ball mills of conventional design.

Another excessively expensive, operational handicap in these prior products arises out of the weight distribution opposing rotation. The weight is normally concentrated at an unnecessarily excessive radial distance from the center of rotation without provision of any counterbalance means, thereby creating an excessive, counter to rotation, torque plus a decidedly lopsided wear and tear on the supporting journals and bearings. These objectionable factors are also overcome by the instant invention. By rotating only the rotor within the drum rather than the drum itself, the moment arm of the operating load is reduced, thus, reducing the torque necessary to operate the mill.

Another object of the instant invention is that of materially facilitating the making of repairs and the replacement of parts.

A further object of my invention is the elimination of certain of the operational hazards common to ball mills of conventional design. These hazards and their elimination are specifically brought out in connection with the description of the structure relating to them.

Other important objects of the instant invention will become readily apparent to those skilled in the particular art as its description in connection with the figures of the accompanying drawings is hereinafter carried out, which figures may be briefly identified as follows:

Figure 1 is a mid portion, cross-sectional side view elevation of one embodiment of the instant invention.

Figure 2 is a cross-sectional on line AA, right end view in elevation of Figure 1.

Figure 3 is a mid portion, cross-sectional side view elevation of a limited modified form of the instant invention.

Figure 4 is a cross-sectional on line 44, right end view elevation of Figure 3.

Like reference symbols in the same figure and in the various figures of the drawings represent like elements and parts in the same. Referring first to Figure 1, numeral I indicates a horizontally mounted, preferably metallic, cylinder, partially closed at each end by preferably metallic, ellipsoidal heads 2, bolted, as indicated, or welded to cylinder I. The heads 2 are illustrated as ellipsoidal but may vary somewhat in shape without departing from the principle of my invention. The numerals 5 indicate suitable stationary mounting supports for the cylinder I and the elements associated therewith. The cylinder I, as mounted on the supports 5, is stationary and cannot rotate.

The numeral 1 indicates a second cylinder or liner internally of, and more or less uniformly spaced from, cylinder I by spacing elements 6 and I and bolting elements 9. The linear I is partially closed at each end by ellipsoidal heads 8 bolted or welded to cylindrical liner 1. Like the heads 2, the heads 3 may vary in shape some- What from that of an ellipsoid without departing from the principle of my invention. The second cylinder I together with the heads 8 define the grinding chamber which is also stationary and cannot rotate. The elements I and I5 indicate cylindrical stub shafts extending from outside internally of the said cylinders through close fitting openings centrally located in the respective heads 2 and 8. Each of the stub shafts I5 and. I5 is supported in and by one of the roller bearing elements I! mounted upon the brackets 4 and 4. The brackets 4 and 4 are fixedly attached to the head elements 2. On the inner end of each of the stub shafts I5 and I5 a spider leg element I3 is securely mounted to rotate with its associated stub shaft. In some installations it may be preferable to make elements I3 and I5 and I3 and I5 in one piece. The spider leg elements are spaced apart the length of thesecond cylinder I. The use of the stub shafts I5 and I5 leaves the major part of the internal, horizontal housing space unobstructed. The purpose of leaving the area between the spider leg elements I3 unobstructed will appear more fully hereinafter.

To each of the spider legs I3 (six being shown in Figure 2) is af'fixed, by bolts I4, a radially extending plate element I2. As shown in Figure 2, each of the plate elements l2 has, at its right hand side, a radially extending straight edge. The spider legs of the right and left elements I3 are so arranged that the straight edges of the corresponding right and left plate elements I2 are aligned in the same plane, which plane is parallel to the axis of the stub shafts I5 and I5. Thus, the elongated pusher bars or rectangular plate elements II in Figure 1, and II, H1, H2, H3, H4 and H5 in Figure 2, can have their end portions aflixed, as by welding, to the respective straight edges of the plates I2. The plate elements, spider leg elements I3, and pusher bars II together form a six paddle cage or rotor occupying a major portion of the internal area of the second cylinder 1. The ends of the rotor may each be made as a single part, but such part should have openings or apertures to permit material to pass into the rotor. The rotor operates as an agitator for actuating the grinding balls.

A body of grinding balls I!) are placed in the grinding chamber. The diameter of the balls I9 is such that the layer of balls in contact with the inner surface of the second cylinder I will not be contacted by the pushers II of the rotor. The proportion of the total area of the inner surface of the second cylinder I which will be covered by the outer layer of balls will vary according to the size of the ball charge put in the mill. The protective layer of balls is neither stationary nor is it always made up of the same balls. The halls being positively moved by the pusher bars II frictionally engage those of the balls forming the protective layer. This frictional engagement causes the balls in the protective layer to be constantly agitated and moved in the same direction of the rotor, although at a slower speed. It is by this means that the protective layer is enabled to accomplish an appreciable amount of grinding. The movement of the protective layer in the direction of movement of the rotor causes some of the balls in the layer to be dislodged and removed where the pusher bars I I emerge from the body of balls. These balls are replaced in the area where the pusher bars I I enter the body of balls.

The minimum number of balls necessary to operate the mill is that quantity of balls which will form the outer protective layer plus additional balls for cascading action. The precise number of balls used will depend upon the type of material being reduced. The mill has been found to operate satisfactorily. with certain materials, with a ball charge occupying approxiher from thepass'agezil; Although the passages 20'- am??? are" shown-"and" described as at the ex-- treme ends of the g rindin'gn'chamber preferred arrangement; it-is possible torelo'ca te them closer: together without departing from theiprinciple of my invention.

As ares'ult of the description of themechanism" up to this point; I the reducing? operation may" be stated by way of illustrationas followszas'is mechani'cally' apparent, any suitablesource of driv me" power, sucha'sanelectric'motoli may be used to drive the rotor. Power may be delivered tothe" rotor by'either or bbth-of the stub shafts 1'5" and i.

Rotation of the stub'shafte causes similar motion" i'n'the' rotor forcing the pusher barsthrough the body or grindingballs i9; The'iririer shell E and outer shell'z; comprisingtlie c'ylindiical'drum remain stationary at all times,- thus; all of the motion for generating thegrinding or" reducing action of my invention is? imparted to the grindrin -bails Hl'by'the rotor, Thisfidesign limitsthe' ener'gy requirements ofinvention to' that which is: necessary toniov'e'the rotor against the resistance of the'giincling balls ahd tliecharge of material'being reduced. Theenergy require ments-of previous 'de'vices of this-type for moving the mass of the *drumare eliminated.

is readily apparent; the movemelit'of' the agitators or pusher bars H3 etc; the' preferred direction of which is'cloclcw'is'e as: viewed 'iriFig ure 2, will forcibly maintain" all of the-balls in action with respect to-each'cther ahe all other surfaces contacted by these balls.- The rotor is operatecl'at a relatively low angular-velocity The exact revolutions: per minute will vary: according to that which will produce the most efficient results with the particular material-and-thesize of the charge of grin ding/balls involyed.--

Those-o1 the-balls it in the pathsof-th erotatpusher bars H" which do not escape fromrthe pusher bars will be carried thereby into the upper region of the grinding chamber, free'of the group of grinding. balls in the lower portion of the grinding" ch'anib'ei" from which point theraised grinding" balls 23 will" cascade" oownwer" v'ith considerable impact momentum The he which thes'e ba'lls l Syraised bythe'pushefb l i, winteelevated "will depend,- in part; upon'trle'an gula-r velocity oi the rotor; Byelirnina 11g. the central shaft through the" rotor; the cascading. balls are enabled to fell upon the materialwithout interference. Thus; all of the velocity obtained by the falling balls is available'for reducing the material. This fcatuie a'lone'a'ddsrnaterially to the eificiency of my invention Those ofthe balls 19 adjacent to the p'ath'of' the'rbtating pusher bars El Willa o'be carried" atleast partially into the upper" region of" the grinding chamber.

All of the principles of reducing or pulverizing utilized in isolated cases; namely, crushing, irn-- pact andattrition, not heretofore combined ina' single unit,"are simultaneously and most citric-'- 6 constructed:

tiy'ely brdughtto bear inme iistantiriyritiori; B way of explanation? reduction by crushing-'00 curs between'those of the balls adjacent the walls-of the grinding chamber'be'ing forced toiroll on snrfaceswitn the niate'rial'beirig crushedbe tween the moving ballsand the stationary yirall surface; reduction by impact is eifecteld by" the cascading balls rename Withappreciab e impact on fragmentsof the materian and reductionby' attrition occurs through theactio'n' of any two or more rh'ovingba-ll's competingwi-thieacn other in forcefully rubbing the same'materialr Rotation of' the pusher Bars: H not only el e va'te's the balls" [9 but also'b'oth theheavies a'n'd fines of the material being reduced: Astream'of sweeping or transpoi t fluidis passed" through the grinding c am er by means or thepassag s z! and 2 2; The lines of the material eleyatec'l by the rotor' will be entrained by this" fluid and re moved'rfomme grinding chamber through passage 221 The size'ofthe'fines which'will be thusremo'ved may be conti'olled by regulating the volume of fiuid'b'eing passed through the grinding chamber. through or sucked through the grinding chamber. Bypla'cing the input passage2l andoiitp'ut'pas; sage 22 at the extreme opposite-ends of the'g'rinding' chamber, sweeping of the entire grinding chamber by thefi'uid is assured;

As to-refihementsand special features; reference -is made to Figures l 'an'd 2*joi'ntly.

Elementl6 indicates employing keys in key- Ways to lock each" of thespid er' lei; elements l3 to'their respectiveshaftsil Sand I5".-

To facilitate assembl making'repairs madeplacing parts, the lower halves of 'cylinder s I; and 7, together with their corre'spondiri'g heads 2" and 8, are indicated to be separate in construction from their respective upper haflyes. A'smore fully shown in Figure 2, the upper halves of thesejs'aine cylinders and their respective'heads are indicated to each be constructed 'in'two equal quarter'se'ction'si The flanges 3' 3 a nd 3 together'with the bolts'and n'uts' 3& Sa 'and 35. respectively are then'ians necessary for properly'assembled external and internalcontainersand for securing them m-piaoedurmg-operations; p

In "Figure 2 itis-indicate'd that-there are super imposed on' the pusher bars ll, et'cl, facin'es' H1, H1, H'2',- H3! H4 and 5*, held in place by in set head bolts and' Hilts ll", Hi", 2", 3'', I I4" and I I5", respectively. Sinceiit is elementary that the 1 Wear and tearon the parts of the mill involvedin" the act'iilal reduction operation is bo'und to be" severe even though" these parts are made of materials selected for u'nusuaildiimbility, replacement of parts is acon'stant prob lem. My design makes it possible to minimize the cost of this replace'rnentby "simplyrenewing the fa'cing H, et'c'. Since" and labor;

Since it is' 'also'"elementaryithatthewear a'noli lower; ha f" of the*cylinder1 win likewise be setfeie'feiien' throug tear on the inner surface" ofthe its niaterial may be the ni'o'st -durable' available and it is protected in' art' by'thela'y'er of "Hans" should also be made ofthe rnost durable mate The fluid may be either forced" I this replacement can be accomplished by 'remoying just one ofthe quartef'sections" of the cylinders or drum, there automatically results-asubstantial saving 'in time rial obtainable. The'additional expense of such material will be more than recovered by the savings effected in replacement of time and. labor.

By eliminating the necessity for rotating the entire cylinder portion or drum of the mechanism, it is possible to utilize insulation plus the inner and. outer cylinder construction without increasing the power requirements of the mill. Such a construction, applied to conventional ball mill designs, would appreciably increase their power requirements. Thus, by my design, without increasing the cost of operation, the user can have the benefit of quieter operation by filling of the space intervening between the inner and outer cylinders, as indicated by the hatchings of this particular space in the drawings, with any one of the many sound proofing materials now available. Because of the high temperature prolonged reducing can create, which may be further increased by using a preheated gaseous medium for sweeping the grinding chamber, a sound proofing material composed primarily of asbestos would be among those preferable in such a case.

Where the matter of rotating a heavy cylinder and its contents is involved, as it is in all of the drum and ball reducing mills with which I am acquainted, the matter of wear of the journals and bearings becomes a very series problem due to the excessive weight supported by these elements. The problem of rapid wear is aggravated by the unbalanced torque loads generated by the mill, plus the exposure of the journals and bearings to the material being reduced and the frequently preheated, material saturated, pressurized, fluid for sweeping the grinding chamber. The arrangement of Figure 1 indicates that no such aggravated journal and bearing problem exists in the case of the instant invention. In my invention the cylinder or drum is stationary, thus, relieving the journals and bearings of this weight. The torque radius is reduced, and the design offsets, at least partially, the load attendant lifting the cascading balls by the weight of the balls acting downwardly on those of the pusher bars moving downwardly through the body of grinding balls in the lower portion of the grinding chamber. Furthermore, my design permits the journals and hearings to be completely isolated from the operating area of my mill. Since the drum or cylinder is stationary, the stub shafts l5 and I5 may pass through the drum or cylinders without contact with any parts other than a dust and pressure seal. The bearings may be mounted outside the drum and sealed from the wear and corrosion promoting materials within the drum.

All of the drum and ball mechanisms, with which I am acquainted, introduce the collection and removal fluid into the grinding chamber through an opening in the center of one end head and remove the fluid through a similar opening in the center of the other head. To avoid having balls enter these openings, the total number of grinding balls is chosen with a margin of safety to have a top level somewhat lower than the lowest points of these openings. Because of the circular nature of the conventional grinding chamber this necessarily limits the number of grinding balls to somewhat less than one-fourth of the number of balls the grinding chamber could hold if completely filled. The design of my invention makes feasible using enough balls to fill at least one-half of the available cylinder volume. Although such a quantity of grinding balls is frequently neither necessary nor desirable, the capacity is available when needed. Conventional ball mills are incapable of accomplishing this.

When it comes to reducing the harder materials that offer greater resistance thereto, as in the case of anthracite coals as compared to bituminous coals, it is elementary that more can be accomplished with such materials if greater reducing forces are employed. When mere frictional engagement between the grinding balls and the driving force is employed, as is the case in conventional drum and ball mechanisms, an ineflicient reducing action results as compared to the position engagement between the grinding balls and the driving force characteristic of the instant invention. The positive engagement between the pusher bars II and the grinding balls I 9 insures thorough and constant agitation of all of the grinding balls in the grinding chamber. It is clear that such a solution with respect to reducing the harder materials will automatically serve to accelerate reduction of the softer ma-- terials.

From the foregoing, in addition to it being readily apparent that the instant invention permits substantial power savings and a substantial increase in operating efliciency over conventional drum and ball mechanisms, it is equally apparent that substantial savings in weight of materials and mounting spaces are effected.

When it comes to efliciency in the matter of collection and removal of the reduced portion of the material involved, it is clear that the action of the pusher bars ll, of the instant invention serves to expose all of the material charge to the grinding chamber sweeping fluid. In conventional ball mills much of the material charge remains submerged in the ball charge. Thus, efiiciency, in this respect, is necessarily greatly in favor of the instant invention.

In conventionad drum and ball products, as well as in the instant invention, simplification of design calls for introducing the material to be reduced at one end of the cylinder or grinding chamber. Since operating speed or efficiency also depend, in part, upon having the material undergoing reduction equally distributed over the length of the reducing region. which region becomes quite large in some industrial requirements, the even distribution resulting from the extensive thorough agitation of the material by the pusher bars H in the instant invention, increases the efficiency of my invention.

The hazard arising from the operation of an exposed rotating cylinder or drum, common to conventional drum and ball practices is eliminated by the design of my invention. The danger of explosion attendant too small a. charge, when the material charge is a combustible material, such as coal, is reduced by my invention since it permits, as a normal operating condition, a larger charge.

Example I A ball mill substantially as shown in Figures 1 and 2 was operated to reduce coal. The condition of this coal as it was fed to the mill was:

Size, 1% to 2 inches with no fines. Grindability index, 6% Hardgrove.

The analysis of the coal as used was:

ass-1,959

The specifications of the mill used were:

Inside length of grindingchamber inches 48 Inside diameter of grinding chamber do 30 Diameter of grinding balls" do 1% Total Weight of grinding balls punds 1600 Total weight of grinding balls in protective layer p0l1nds 500 Power was supplied by a 40 horsepower D. C. motor through a gear reducer having approximately 80% eificiency. The mill was operated at 16 revolutions per minute.

Mild steel grinding balls were used and the charge of grinding balls occupied approximately one-third of the lower one-half of the grinding chamber. A charge of 300-400 pounds of coal was first placed in the mill, which charge 'became the circulating load of the mill. Then during a period of one hour 1040 pounds of coal were fed into the mill together with 1650 pounds of air at a pressure of 5.1 inches of water. The air supplied to the mill represented approximately of the total air necessary for combustion. Total power consumption during the one hour operation was 13.5 kilowatts. The approximate power received by themill was 10.44 kilowatts. This is a power requirement of 20.1 kilowatts per ton for pulverizing.

Quantities of pulverized coal were obtained by bleeding 01f a small part of the air passing through the mill together with the entrained fines and passing same through a 7 inch standard American Society of Mechanical Engineers cyclone which separated and collected the coal from the air. Samples of grams each were taken from the cyclone, weighted and screened for 20 minutes. The efficiency of this cyclone was unknown but is not believed to be greater than 85 per cent. The analysis of these samples was not corrected for the cyclone efficiency. Analysis of these samples showed:

Percent Percent Screen Retained through on Screen Screen 100 mesh i 2. 97. 150 mesh 6. 53 91.02 200 mesh 12. 78. 37 325 mesh 23. 7 54.67

EmampZcII A ball mill substantially as shown in Figures 1 and 2 was operated to reduce coal. The condition of this coal as it was fed into the mill was:

Size, 1 to 2 inches with no fines. Grindability index, 64 Hardgrove.

The specification of the mill, power supply and ball charged used were the same as those for the mill used in Example I. A charge of 300-400 pounds of coal was first placed in the mill, which charge became the circulating load of the mill. Then during a period of two hours 2314 pounds of coal at the rate 1157 pounds per hour was fed into the mill together with 1650 pounds of air per hour at a pressure of 5.1 inches of water.

The m l was al n ted at 5.0 revolu pns e m utet l owe ensumpt pn dur n th two hour operation wasflfisgs -;ki-low atts. The approximate power received by the mill was 22.8 kilowatts during the two hours. Ifhis is a power requirement of approximately 19:71 kilowatts per ton for pulverizing.

S ples of th m teria t eate by t m e t en in t sam manner a t at fo E am Anal i o thes s m les s w Percen t through Screen Percent I Retained Screen H on Screen The coal was burned in the same furnace and flile ed Q Exam e .A tota o 2 pounds of water was evaporated. The percentageof CO2 in the flue gases was 14.1, giving it an cie o .z n oxim te 0 As to the modified form of the instant invention mentioned in connection with Figures 3 and 4, the modification is limited to the ball charge and the meansformamtaining the same in act on- H vin ull de cr b d t e in an i e tion in all otherrespects, f o r the sake of brevity, this part of thespcc ficfil ion is limited tothe paricula modi yin a ects Refer n to Fi u 3, th i n wa l of the inner cylinder 1 isshown to be .so constructed as to have a longitudinal series r closely spaced channels or grooves 23 therein each oflwhich completely circles the said inner wall. The grooves are so shaped as to substantially fit that part of the arc of veachof those ones of the larger balls l9 shownto be positioned therein. Referring to Figure .4, thelarger balls l9 are also shown to be positioned in whatmay be termed ock ts rmed by th a a po oned u h bars or partitions H, H1, H2, H3, H H5, U6, U7, 'I a l l9 and H10, which pockets so taper, radia lyi w rd mmm h balls J 9 cannot e a e ther from b way o the n e n n n ach pocket. The balls in each pocket are as closely spaceds t ei s z w l p rmit- Referring to Figure 3, the said pusher bars .or partitions H, etc., are shown to extend between the two plates [2. Each'plate I2 is affixed to its corresponding spider l g of the respective elements 13, ,as by being bolted thereto by the indicated multiplicity of bolts M. The end of each of the partitions II are bent at a right angle to the main body of the partition by which affixation to the respective plates 12 may be accomplished by installation of the bolts 24. Although Figure 3 indicates bolted construction, they may be welded. Thus, when shafts I5 and IE, or either, are rotated, the elements l3, affixed thereto, transmit the rotary motion to the balls l9 through the plates 12 and partitions II. The movement of the partitions H urges the balls l9 along their respective grooves until cascading of ,the balls l9 takes place due to gravity overcoming their centrifugal force. The cascading action of the balls I9 is limited by the partitions ll since the inward taper of the pockets between the partitions prevents inward escape of the balls [9. The taper of the pockets also acts to increase the pressure applied by the balls to the material lodged in the grooves. This accelerates the reduction of the material.

In order to take advantage of the full reduction potential of my modified ball mill, a charge of smaller size balls indicated in part by the symbol I9, is used to fill what would otherwise be an idle, potential reduction area within the rotor. The larger balls, being exposed as they are to the activities of the smaller balls, receive from them supplementary power to act as crushers. The pockets between the partitions. H act as channels for introducing the material to the grooves 23 after it has been subjected to preliminary reduction by the action of the smaller balls IS. The material, once having entered the grooves 23 may be ground to a fine powder by the action of the larger balls [9. The pockets also serve effectively as elevators for raising the reduced material into the upper portion of the grinding chamber where the fines will be en-- trained by the sweeping fluid for removal.

Thinking in terms of long lives for the parts directly involved in the various reducing activities, it is important to use the most durable, suitable materials obtainable for these parts. Thus, the fact that the hatching used in the drawings with respect to these parts is that of the standard indication for steel (without qualification) is not to be taken as an intended limitation to steel per se.

In both of the described forms of my invention the life of the grinding chamber liner or inner cylinder is appreciably extended by the use of the layer of balls constantly in contact with the walls of the lower portion of the grinding chamher. This layer of balls absorbs the impact of the cascading balls, protecting the walls of the grinding chamber against the wear incident to the constant blows occurring in ball mills of conventional design. The convex shape of the heads used on my grinding chamber contribute to both the safety and efiiciency of my invention. These heads are so shaped that the charge of free or cascading balls, balls l9 and IS in Figures 2 and 4, respectively, cannot become jammed between the heads and the rotor. The heads, as they extend outwardly from the straight portion of the grinding chamber, are designed to curve on a radius at least equal to the radius of the balls with which the mill is charged. Preferably, this radius is greater than that of the balls. The curvature of the heads is designed to become tangent to the straight portion of the inner cylinder at a point sufliciently outwardly from the ends of the rotor to permit the griding balls free travel between the rotor and the heads. By elimnating all sharp corners and permitting the grinding balls freedom of travel throughout the entire area of the grinding chamber the formation of pockets of material is avoided. These pockets, when the material is combustible, create a serious explosion hazard and their elimination is an appreciable improvement in safety.

My invention has heretofore been described as primarily used for grinding dry, solid fuel. Because of its positive and continuous agitation of both the material being processed and the balls and its adaptability to operation with a pressurized sweeping fluid, it is capable of handling fuels containing high percentages of total moisture. The construction of existing mills of this type has prevented their use with high moisture content materials. For fuels containing inherent moisture only, preheated sweeping fluids are not required for satisfactory operation of my pulverizer. Since a high percentage of surface moisture is acquired in the transportation of solid fuels between the mines and their ultimate point of use, it is necessary to preheat the sweeping fluid to a high enough temperature to vaporize the moisture and dry the fuel as it is pulverized. The design of my invention, permitting the grinding chamber to be insulated and the bearings to be isolated from the grinding chamber, ideally adapts my invention to the use of a heated sweeping medium.

The pulverizer mill described as used in Examples I and II has successfully pulverized and delivered to a burner coals having total moisture contents between '7 and 12 percent without employing a preheated sweeping fluid. Although this type of operation is not desirable from the standpoint of furnace efficiency, it illustrates the capacity of my mill.

My invention will operate with either the dry or Wet process and for that reason is readily adaptable and suitable for eflicienctly grinding and dispersing other materials requiring the wet process such as pigments, for example.

Since my invention, by its design and construction, is suitable to fabrication from steel plate rather than the conventional cast iron castings, an expensive type of fabrication at best, it is structurally suitable for safe operation under pressures of pounds per square inch or more.

The recent development of gas turbines, at present in the experimental stage, requires pulverizers capable of operation under pressures as high as '75 pounds per square inch. Gas turbines require pulverizers capable of continuous and consistent superfine pulverization at low cost. The circumstances of installation of many gas turbines, such as locomotives, make a compact pulverizer an absolute essential. Conventional pulverizer designs, whether or not they are the drum and ball type, are incapable of meeting the specifications of gas turbines. My invention fulfills and meets these requirements.

Numerous modifications of my invention may be made Without departing from the principle of my invention. Each of these modifications are to be considered as included in the hereinafter appended claims unless the claims by their language expressly provide otherwise.

I claim:

1. A ball mill comprising a stationary horizontal drum provided with a smooth inner cylindrical surface and with heads closing the ends of said drum, said drum having therein a body of grinding balls for cascading movement therein, said drum having an inlet at one end for a carrying fluid and having an outlet at the other end thereof for said fluid whereby to carry ground material out of said mill, a drum-shaped cage within and extending substantially the full length of said drum, said cage having supporting ends and having elongated pusher bars supported thereby, said cage having a stud shaft at each end thereof and extending from said ends axially of said cylindrical surface and rotatably carried by the heads of said drum, said pusher bars being positioned radially of said surface with their edges which are adjacent to said surface parallel thereto and spaced therefrom a distance more than the diameter of said balls and less than twice the diameter of said balls, whereby rotation of said cage cascades said balls with a layer of balls in contact with said surface.

2. A ball mill as defined in claim 1, in which the inner surface of the drum is curved at the ends of the cylindrical surface on a radius of curvature greater than the radius of said balls,

13 whereby to avoid lodging of material to be crushed at that point.

3. A ball mill comprising a stationary horizontal drum provided with a smooth inner cylindrical surface, a drum head closing each end of said drum, whereby, said drum and said drum heads provide a shell, said shell having an inlet and an outlet into and out of said shell located at the ends of said drum whereby to provide for the flow of fluid through said drum, a body of grinding balls within said drum, a pair of plates within said shell positioned perpendicularly to the axis of said cylindrical surface, said plates defining a plurality of openings therethrough of substantial size, a plurality of pusher bars interconnecting said plates and positioned radially of said cylindrical surface, said plates and said pusher bars constituting a rotatable agitator, a stud shaft extending from each of said plates and journalled in said drum heads axially of said cylindrical surface, and extending through at least one of said drum heads to provide power receiving means for rotating said agitator with the edges of said pusher bars adjacent to said cylindrical surface parallel to said axis, said edges being spaced from said surface a distance greater than the diameter of said balls and a distance less than twice the diameter of said balls, whereby the agitator moves the plurality of balls upon rotation of said agitator together with any occluded material being ground, the layer of balls in contact with said cylindrical surface rolling thereon, and whereby said balls and occluded material are elevated and dropped, with finely ground material being removed by a stream of fiuid flowing through said drum during the dropping of said ground material.

4. A ball mill comprising: a stationary, horizontal drum provided with a smooth inner cylindrical surface and with heads closing the ends of said drum, said drum having therein a body of grinding balls; conduits communicating with the interior of said drum whereby a carrying fluid may flow through said drum for removing ground material from said drum; a cylindrical cage within and extending substantially the full length of said drum, said cage having supporting ends and pusher bars supported thereby; said cage having a stud shaft at each end thereof and extending from said ends axially of said cylindrical surface and rotatably carried by the heads of said drum, said pusher bars being positioned radially of said surface with their edges which are adjacent to said surface parallel thereto and spaced therefrom a distance more than the diameter of said balls and less than twice the diameter of said balls, whereby rotation of said cage cascades said balls with a layer of balls in contact with said surface and between said surface and said cascading balls.

5. A ball mill, the improvement therein comprising: a stationary, horizontal drum closed on each of its ends; a rotatable drum-shaped cage within and extending substantially the full length of said drum having supporting ends and elongated pusher bars supported thereby, said cage having a stud shaft at each end thereof and extending from said ends axially of said drum and rotatably carried by the closed ends of said drum; said drum having a smooth inner surface in the direction of rotation of said cage; said drum having therein a body of grinding balls; a layer of balls between said cage and the lower portion of said drum, said layer of balls being between said drum and the cascading balls of said body of balls; said drum having a carrying fluid inlet at one end and a carrying fluid outlet at the other end whereby a fluid may flow through said drum for removing ground material.

6. A ball mill as described in claim 5 wherein said closed ends of said drum are convex and said cage is co-extensive with the straight ,portion of said drum.

'2', A ball mill as described in claim 5 wherein said closed ends of said drum are convex and said cage is ,co-extensive with the straight portion of said drum; the inner surface of the drum being curved at the ends of the cylindrical surface on a radius of curvature greater than the radius of said balls, whereby lodging, adjacent said ends, of material to be crushed may .be avoided.

8. A ball mill, the improvement thereincomprising: a stationary, horizontal, cylindrical drum having convex ellipsoidal closing means on each of its ends; a pair of spiders having pusher bars therebetween for forming a rotatable, hollow, cylindrical cage within and extending substantially the full length of the cylindrical drum; a stud shaft mounted to each of said spiders and rotatably carried by said closing means; said drum having a smooth inner surface in the direction of rotation of said cage; a body of grindin balls within said drum; a layer of balls between said cage and the lower portion of said drum said layer of balls being between said drum and the cascading balls of said body of balls; said drum having a carrying fluid inlet at one end and a carrying fluid outlet at the other end whereby a fluid may flow through said drum for removing ground material.

9. A ball mill comprising: a stationary, horizontal drum having a smooth inner surface; heads for closing the ends of said drum; said drum and said heads defining a grinding chamber; a body of grindin balls within said grinding chamber; a pair of stud shafts, one rotatably mounted in each of said heads concentrically of said grinding chamber; a journal exterior of said drum for supporting each of said stud shafts; a rotor, includin a plurality of pusher bars, mounted within said grinding chamber, the periphery of said rotor spaced from the inner surface of said grinding chamber a distance greater than the diameter of one of said balls of said body of grinding balls and less than twice the diameter of one of said balls of said body of grinding balls; power means for driving said rotor; conduits communicating with said grinding chamber whereby a carrying fluid may flow through said grinding chamber for removing ground material from said grinding chamber.

10. A ball mill comprising: a stationary, horizontal drum closed on each of its ends, said drum having therein a body of grinding balls for cascading movement, said drum having means for passing a ground material entraining fluid therethrough, a drum shaped cage within and extending substantially the full length of said drum, said cage having supportin ends and having elongated pusher bars supported thereby, said cage having a stud shaft at each end thereof and extending from said supporting ends axially of said cylindrical surface and rotatably carried by the heads of said drum, said pusher bars being positioned radially of said surface with their edges which are adjacent to said surface parallel thereto and spaced therefrom a distance more 15 than the diameter of said balls and less than twice the diameter of said balls, whereby the rotation of said cage cascades said balls with a layer of balls in contact with said surface, said drum provided with a smooth inner cylindrical surface in the direction of rotation of said cage.

11. A ball mill, the improvement therein comprising: a stationary, horizontal drum closed on each of its ends; a rotatable drum shaped cage within and extending substantially the full length of said drum having supportin ends and elongated pusher bars supported thereby, said cage having a stud shaft at each end thereof and extending from said ends axially of said drum and rotatably supported by the closed ends of said drum; said drum having a smooth, inner surface in the direction of rotation of said cage; said drum having therein a body of grinding balls; a layer of balls between said cage and the lower portion of said drum, said layer of balls being between said drum and the cascading balls of said body of balls; means for passing a ground material entraining fluid through said drum.

EVERETT D. PHILLIPS.

REFERENCES CITED The following references are of record in the file of this patent:

Number Number UNITED STATES PATENTS Name Date Bolthoff June 18, 1878 Due June 10,1890 Kreiss Dec. 19, 1899 Holman Feb. 5, 1901 Commichau Mar. 13, 1906 Thuneman Oct. 28, 1919 Canda May 19, 1925 Hildebrandt Nov, 2, 1926 Duncan Feb. 4, 1930 Corbishley Feb. 28, 1933 Schmidt Dec. 5, 1933 Larsen Oct. 29, 1935 Kiesskalt Aug. 4, 1942 FOREIGN PATENTS Country Date Great Britain of 1876 Germany Aug. 10, 1886 France Oct. 10, 1902 France Sept. 3, 1909 Germany Mar. 7, 1923 Great Britain Apr. 7, 1927

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