US1671283A - Perimetric feed for tumbling mills - Google Patents

Description

May 29, 1928.

N. L. HALL PERIMETRIC FEED FOR TUMBLING MILLS Filed Jan. 18, 1927 A TTORNE YS.

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Patented May 29, 1928.

Pa-TENT OFFICE.

yNnvv'IoN L. HALL, 0F La SALLE, `ILLINOIS. i

"'PERI'METRIG; FEED Fora TUMBLNG MILLS.

`- Application med January 18,1927. "serial No; 161,894.

This invention relates to means forfeeding and circulating a load to and vthrough a" ball, tube,'or other' cylindrical grinding mill, the grinding` medium being a' tumbling load of balls, pebbles, or ro'dsand the invention particularly relates to means whereby ythe feed to themill is caused to enter the `mill at or'near the axialline of the same and then is Vpassed outvvardtovvard the perimeter of the mill interior so'that the' feed canfbe delivered into the .grinding chamber 'in the Space above the load, thus eliminating the retardation ofthe feed by the obstruction due to load.

Tn presentfday practice in tumbling mills,

the feed is'delivered into the mill atk or near Vits aXial lineand if thepulp or ball load 'within the mill has a depth 'which' isabove the Center line or` axis, it is required that the feed of balls orpulp shall pass into the mill against its contained load. If this load is vsurcharged above this' axis, it becomes difficult to cause the feed to enter themill against this surcharged load; In 'order to lessen this.

retardation, liqu'efying the pulp has been resorted to tomalre it tlow'readily but thlsdetracts from the grinding efficiency of the load when this additiony is made above a certain consistency of pulp. Thisl consistency is that'attainedwhenV the particles of pulp will stick to'and maintainan unvvashed condition on the surface of the balls or rods.'

Good practice `uses a ball loadwhich is carried as high asoperating 'conditions Will permit and yet not detract from theflargest `amount of feed vvhichcan'enter the mill,y this being, of course, coupled With other factors Which give a maximum Aof grindinglefliciency underoperatingconditions.` A' small mill load Will'dev'elop a mill productwvhrch is very different fromthatproduced by a' large load and for some products, particularly those ywhich require uniformity inl the graded sizes ofthe 'liner particles, the desired effects can only be secured by operating with a's'urcharged load, that is, a loadvzhichv fills the mill to aboveth-e axis thereof.

There is 'another vand 'very-important `element Which has to be 'consideredin tumbling mills. It is apparent that With a mill chamber entirely filled With a load, the center of gravity of theload'vvill be lidentical with the axis of'the mill 'and 4under 'these' circum-y stances the powerrequired'for revolvingthe mill is only that necessary for overcoming? inertia; the'load being'evently balanced over y the center line'in allpositio'ns.` VbAsthe load is diminished, with the'millunder rotation, the center of gravity of the 'load Willfbe at al distance from thel center'of the mill Aand to the ascending side andthis'necessitates power being` used to 'lift the load "duringy rotation `Which is 'in addition tov theipovver required forovercoming the mill and load inertia. As the loadv is still further diminished,'the center of gravity extends further from the mill centerA and the proportionate'power requirement per unit 4of load' is increased. It is obvious, therefore, that for an economical power application per unit of load, itI is necessary or desirableto have the center of gravity'of'the load as close to the mill*y center as possible. Speed conditions are variable under different` Aconditions such as mill diameter, size land Weight of load, etc., but in general there is an ideal peripheral speed for `the mill load which is practically the-'same for mills'of any diameter. The Aperipheral to secure the developmentof the`proper cascade Jfor the load. v

Considering the' cross section' taken' by a ball load during rotation of the mill, it 'will be observed that thaty part of the load Which is on the ascending side is comparatively quet. During rotation that part or sector of the load lwhich is toward'the exposed surface is fallingas a cascade and lupon reaching` thebottom of its descent, the ballsiimmedia-tely enter theload yin aY comparatively fixed position but varyin position and' pressure as they rise 'towardthezenithof their movement. This constant cascade anticonstant readjustment of the load parts develops effects of both impact and attrition, the amount of thesefeffects' being governedby the speed of rotation, the',\ veight'and size of the load, and the impulse of migration developed in the load conditions. During rotation the load partsare'constantly underlicing a change of position inthe load 'section and this is particularly t-hel'case When rods are used as a' grinding medium as here a constant twisting of the rods is perceptible c moisture in the pulp; load of balls; size and character of balls; hydraulic gradient of the pulp; character and position of disf` charge opening, and nature of material to be ground. Practically all mills usea holllow trunnion at the feed end of the mill y through which the feed is delivered.` Other types `of 4mills have feed scoops placed around the shell'of the mill midway of its ends, thus causing` the pulp to migrate from the mid section towards either end trunnion.

In none of them known to me is there a true perimetric feed or a feed which is discharged into the interior of the mill above the load line or the surfacoof the cascade and which, therefore, enters the mill uninipeded or unretarded bythe load.

A One of the spccificobjects of my invention is to provide atumbling mill with a feed `i'nechanisni disposed entirely within the c grinding chan'iber proper.

A further object is to provide for a peii nietric feed into the grinding chamber and cause this feed to ent-er `the grinding cham- 1" f ber at a point always above the cascade load.

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Another object is to provide the mill with a perimetri@ feed including conduits, one

`deliveringinto the other, and the last named conduit into the grinding chamber. which deliversthe feed to the grinding chamber eitherfin `a direction with or counter to the direction of rotation of the mill.

l Still another object is to provide a perimetric feed of such character that two of the feeding elements may be disposed in balanced relation within the grinding chamber to thus overcome an tendeiic to un- TY y balance the mill with its consequent requireinent of increased power vto run the mill.

i Other objects will appear in the course of the following description. c My invention is illustrated in the accompanying drawings wherein of approximately Go from that shown in Figure 2 Fig. 6 is a longitudinal sectional view of a tumbling inill but showing a different discharge means than that shown in Figure 1 and also showing a modification in the conduits which constitute the feeding means, this section being taken on the line 6 6 of Figure 7;

Fig. 7` is a section on the line 7 7 of i the feed moves into the mill and the action of the cascade diagrammatically;

Fig.` 11 -is va like view to Figure 10 `but showing the position of the feed and load when vthe mill has turned through approximately a quarter of a revolution.

Referring to these drawings andparticiilarly to Figures 1 to 5, it will be seen that I have illustrated more or less diagrammatically a tumblingmill consisting of an outer shell 10 with the heads 11 and 12. Thehead 11 has the axially extending trunnions 13 and the head 12 has like trunnions 13. Disposed within the entrance trunnion is a trunnion liner 14 which i extends through and is connected with an end liner 15. This trunnion liner 1st is engaged in any suitable manner with a spiral feed screw 16 of any ordinary or suitable character which scoops into a massof pulp or materialto be ground, lifts it up and by rotation, discharges it into the duct formed by the liner 14. The interior, or a portion of the interior, of the barrel or shell 10 is provided with the liner 17 whichhas a length practically equal to that of the grinding chamber 18 and this grinding chamber at its outlet end is closed or partially so by a transversely extending plate or liner 19, shown in Figure 1 as havinga' central grat` ing or perforated portion through which the comminuted material is discharged into the longitudinal liner 21. The mill. may be operated in any suitable` manner as, for instance, by the gear `wheel 10a.

So far I have described the necessary elements of an ordinary tuniblingmill, it being understood that the grindingchamber 18 is tobe partially filled to any extent required with balls, rods, pebbles, orother grinding elements, and that the iinground material isV xiii llt

i' ileiifzss ymeans ywhereby the material fledfto Vthe mill shall be discharged into the grinding space 18 adjacent the perimeter or periphery of the'mill. To this end l dispose within the mill at theentrance end thereof, the feed conduitliner or plate 22 which extends entirely across the space defined by the shell and is provided with the peripheral flange or rim 23 which bears against the barrel or shell. Adjacent the periphery of this vliner 22 and for a portion of the circumference of the liner, the liner is extended laterally forward as at 24, and then outward as at` 25. l The inner face of the liner is formed with an outwardly projecting flange orv rib 26 which, as shown in Figures 2 and 5, extends in an approximate spiral from a point intermediate or between the peripheryof llthe liner and the center thereof more or less conclentrically around the center to a point adjacent the periphery and then extends outward, as at 27, to the periphery. A more or less spiral conduit 28 is thus formed which' extends approximately three-fourths of the circumference of the shell. Outward of this conduit 28 is a second conduit 29 formed in the opposite portion of the liner 22, which conduit begins at a. point in advance of the termination 27 of the conduit 28, and eX- tends concentrically to this conduit 28 or eX- tends Vcirc'umferentially a relatively short distance. This second conduit 29 is separated from thefirst conduit for the greater -portion of its length by a wall 30 but adjacent the closed end of the conduit 29 formed by the inclined wall 3l there is an opening 32 in the wall which permits the material collected in the conduit 28 at the blind orv closed end thereof, to. pass into the conduit 29 at or nearthe blind or closed end thereof.

It is to be particularly noted in this connection that this opening 32 is disposed iny ad- Vance of the end wall 27` of conduit 28 and that thev opening 32 is disposed inv advance of the wall 31 of conduit 29 so that pockets `282L and 29a are thus formed, one at the terafter, is always above the load line or the cascade-line shown in dotted lines in Figures 2 and 5 and designated a. In Figure 2, the shell or barrel 10 ofthe mill is shown in such position that the opening 32between vthe conduits is at its zenith, while in Figure 5, the mill is supposed to have rotated .i

through approximately 60, the mill rotating in a counter-clockwise direction as shown by the' arrows inFigures'2 andb. llhile'i in F iguie l the opening 32 is shown`at `its Zenith, in Figure 3 the opening is shownrv at its nadir.v n

The operation lof the construction illustrated in Figuresl to 5 is as follows: The material to be comminuted is scooped up by feed spout 1G and fedl into tube 14 from which it is discharged onto the concavely curved face of wall 2 6, as shown in Figurev 2. This conduit 28 is at all times free from load pressure and as the milll rotates this massr of material is carried along over the interior surfaceof wall and so intothe conduit 28until itze'ventually arrives in they rial, that contained within the pocket' ofthe conduit, will move down this conduit inuthe directionof movement of the mill and will be discharged through the opening 32 into the conduit 29 and eventually after successive revolutions, will be discharged into the grinding chamber above` the load linea therein or above the toe of theicascade.

Assuming that the mill ha'sreceived its load until the face of the load under rotation would be as shown by the dot and dash linea., it will'be noticedfrom' Figure 5 that the materials to be picked up by the conduit 28 would have advanced about half way along the length of the conduit or be yldisposed almost in'unediately below the tubular feeding trunnion and at this'point the conduit. 29 has its inner end entering thev mill load. Thus, if either-fof these conduits were empty, both'of the conduits wouldl fill. It is also apparent, however, that any column of load filling the conduit 28 will have a vertical depth or head which is greater 'than the depth or head of the load in the conduit 29 due to the greater length of the conduit 28 and its advanced position. Consequently any load in conduit 29 will always be over-balanced by the lload in conduit 28 and this will tend to cause a flow of the load from conduit 28 into conduit 29 through the opening 232.

During rotation and with the mill just beyond the position shown in Figures the loads of both conduits will fall forward in the direction of rotation, leaving the pockets of conduits 28 and 29 emptied or siiibstantially so. The conduit 28 and its pocket because ofV their larger size, have a greater capacity than the conduitV 29l with its pocket and, therefore, the excess materiall in the pocket of conduit 28 flows laterally freelyv into conduit 29 and thus tends to assist the free lateral movement of material through lill) theopening `32 into conduit 297 thereby displacing ,the advanced material and forcing it into a radial plane which isy within the scope of the grinding chamber. lf both conduits 28 and 29 were of the same size in rcross section and relative radial `position i and did not have, the pockets at the er;-

i 29. By having the conduit which is normal` to the mill airis.

vtremitics of the conduits hutl terminated with the opening 32, there would be a lateral passage from conduit 29 to conduit due to the vertical. head. being greater in than 28 of greater size and providing the conduits with the respective pockets, the lateral displacement of i the feed in its movement from the plane of conduit 28 to the plane of conduit 29is very greatly aided.` The mill is considered to be revolving about its longitudinal axis in a horizontal position. The tendency ofthe falling load is to pass in a gravity plane conduit 'such as described becomes filled, any particle of the load is held by adyoinmg y parts froniheing laterally diverted by an inclined wall the revolving structure. lf.

the mill were revolving at a speed greater than that of the tumbling load, it would do velop an impulse to the load when any diverting face of the mill passed the load as, for instance, occurs in a centrifugal pump, but in cylindrical grinding mills the speed of the mill is too low to malte any such effect appreciable and the load falls in cascade upon a gravity plane without lateral in- 28a will fall upon this surface and. freely` move into the conduit 29, thus placing the excess diverted material within the'conduit 29 rather than in the conduit 28. Figure 3 shows a cross section of the conduits taken on the same planeas Figure l but. with the conduits inverted and this :ligure shows that the conduit 28 has a greater vertical. depth than conduit 29 and that thus the excess weight of material in conduit 28 will cause its load to surcharge the conduit; 29 or any space formed above the normal load of conduit 29 as it freely settles to repose hy gravity. It is, therefore, most desirable.

though not absolutely necessary, that the a greater depth than conduit 28 shall have conduit 29 and have its end advanced over the end of conduit 29. lf the conduits 28 lNhen a and 29 `were of thesame cross section, had the same radial position, and were similarly filled, then vduring rotation their. loads would advancev atthe same rate but if the depth of conduit '28 in cross sectionfbe greater than the sectional depth of conduit' 29, it is found in actual practice that the advancing toe of the/load in conduit 28 will have an advanced position over the toe of the load in `conduit 29. Therefore, when this advanced load ofthe larger conduit reaches the communicating opening 32, this load will spill laterally and some of theload in conduit 28 will talte position in' the smaller conduit 29 ahead of the materialin conduit 29 which is of less depth.

The blind ending of the conduits 28 and 29 causes the .pockets thus formed atl the ends of these conduits to virtually act as buckets in liftingtheir contained loads over the center lline and toward the cascading side. After these conduits havepassed the vertical center line, the forward movement of the feed in conduit 29 dischargesit into the grinding chamber' at a point above the mill load. lVhile some of the load'enters the lower end of conduit 2 9, as this conduit enters the mill load, yet conduit 29 does not become excessively filled due to the fact that it is already filled by the advancing feed, the speed of the mill and the speed of the cascade not allowing sutlicient time for the entire unloading of conduit 29. This conduit 29 tends to deliver its load as soon as the opening of the conduit passes the vertical center line or approximatelyas soon as the opening of the conduit leaves the mill load and this discharge continues until conduit 29 has entered the mill load. Thus, this conduit29 delivers its discharge in the direction of its rotation and always into the space above the mill load. Accordingly the mill load can be enlarged until it entirely fills the mill. Vhen this occurs no further discharge of feed is possible until the mill has discharged some of its load and then as soon as the space is provided for the feed, the conduit 29 will again begin to discharge.

The very important feature? vof advantage in my construction is that byhaving the conduits 28 and 29' extending from opening `32 in the same direction, the contained loads ing 32, to the end of the ,conduit can be varied without ruining its effect but 'preferably and properly its length should be great enough so that as its contained load falls in cascade, the tiniefactor and speedof the mill' will not allow` the conduit to fully empty. rlfhe speed of the mill is only slightly di i'i'erent from the movement ofthe load and before the conduit `9 can empty entirely, it again enters the load and all of the conduit load eonsolidates. The respective sizes of enduits 28 and 29 can be varied to suit' conditions for developing the -desired yflow of feed and these conduits can be spiral in shape, that is,

noted in Figure 2 that conduit 29 has a greater radial position' than conduit 28, al

though 4 conduit 28is the largerconduit Reviewiiw the path or circuitfor the feed: The feed' enters scoop 16, is Vdelivered through the trunnion liner 14, to the central chamber ofconduit liner 22 where it enters the conduit 28 and passes counter to rota tion towards the pocket 28u. Here it passes laterally through opening 32 into the blind end of conduit Q9 where it changes .thedirection of its travel toflow with the direction of rotation until it is discharged through the end opening of vconduit 29 and is delivered into the vacant space above, the load line or fareof,y the load in the grinding chan'iber. Delivery is always ymade above the load and, therefore, it is possible to completelylfill the grinding chamber regardless of the level of feed in the central entry chamber of the conduit liner 9,2.

ln the. construction illustrated in Fig.. 1, the load within the mill can pass through .the

screen and be discharged through thel vspout 21 near the axial line. Thus, it is apparent that the conduit 29 can discharge the feed to a fulll section of the mill if need he and that thehydraulic gradientbetween the points of feed and discharge can be controlled or established by this improved periy i ric feed `and, by the nature andvposition n the discharge opening.. The desired product of pulp is secured by adjustinglthe different conditions to suit and this is particularly true with regard to the length of` the mill, the hydraulic gradient of the pulp, and the `amount of loading'.A It will also be noticed that in the construction shown/in Figure 1, the load may beenlarged within the `grinding` mill or chamber to closely fill the mill section and that thus only av low power is needed in orderpto drive the mill, as previously explained.f

ln the construction shown in Figures 6 and "i", the arrangement of the conduits 33 and Sel is similar' to the conduits 28 and 29,

with this exception, however, that 11o/pockets are provided as in the'describedconstructions and conduit 34. 4opens, reversely to conof various Vradialf positions for special purposes.' Slt 1s to be duit 29 so that the product of feed is delivered within the grinding chamber counter tothe rotation/of the mill `instead ofin the loader `cascade nearly meets the Zenith of the` mill 'interior'when the loadingv action will cease for the reason that after the load in conduit 34 passes the vertical centerline ofthe mill, the gravityelfectontheload in conduit 34 will lcause it to Vfall in the same direction as the rotationof theA mill and thus l.

it will 'remain witliinthe conduit.

The;k loading thus made 4will approximate of the mill section whereasthe arrangement of conduits 28 and 29 permits the mill to be loa'ded'to any proportion ofits section or loe entirely filled if'necessary. Otherwise than as described above, thefconstructionof theliner 522 and of the entrance end of the apparatus is practically the saine as beforev described andthe same reference numerals have been used. l

ln the construction illustrated in Figures 6 and 7 however, Ihaveillustrated the drum or barrel 10 as being mountedupon the gear wheel 10a and upon the trackl 35 which en,n

gages the rollers 36. This does away with discharging the feed through the hollow trunnion 21 and the discharge passes through a grate 37 which Vextends entirely across the drum and has a solidv centralporr tion 38. v The ldrum is provided at its discharge end with the drip flanges 39 `which discharge into a launderor .trough 40. A hopper 41 discharges into the hollow trunnion liner-14. The open end construction which I have provided inFigure '6 permits an extension of the' hydraulic gradient to the perimeter ofthe mill shell kif need be,l

thus effecting a. rapid migration of the pulp under eXtreme gravity fintluence. Mill 1nteriors are often provided with undulating inner surfacesor lifting lugs to assist in' liftingv the loadvduring rotation but it is apparent that the larger' .the load, the

greater will be its surface friction with the liner and the grinding chainberand thus the less requirement there will be` for, any lug arrangement for holding the load rotation to the speed of the mill rotation. l have not illustrated the liners in Figures 1 or 6 as being provided with lugsbut I, do Vnot Wish;

tolie limited to the grinding chamberhav ,ing a plaininner surface. t In Figures 8 and 9 l havey shown a modification ort duplication ,of the mechanism illustrated in. Figures 1 and 2. Cylindrical mills y'should be' as closely balancedon their axis as is possible.

Bywproviding rthe twin conduits 28 and 29' the mill is made bilaterally symmetrical. These twin conduits can be concentric to each other or if limited within the range of 180, they can be of duplicate design on each side of a central line. This condition not only gives a balanced mill but likewise duplicates and increases the conduit discharge.

lith my improved feed arrangemei'it, it is possible to charge feed into the mill as long as any space exists therein. The desired ball load can be installed and then the mill can be charged with pulp to any degree necessary to give proper control of feed conditions. The mill length should be designed vOne very important point of advantage of the perimeter feed is that the operator lills the mill to the desired ball load and then with my perimeter feed arrangement any desiredamount of pulp can be fed to this ball load inasmuch as the feed of pulp is entirely independent of the amount of the ball load in the mill. feed mill, a ball load just above the mill axis limits and determines the feeding of the pump and, therefore, the latitude of the mill operation is thereby limited.

It will be seen that in this mill, as illustrated, at the perimeter of the load the speed of the cascade is greater than the speed ofthe mill. Otherwise the perimeter speed of the load and the speed ofthe mill are closely similar and similar speeds and forces are acting on the mill as well as on the load. The predominating forces are those of gravity, centrifugal force, and the reacting centripetal force, the overcoming `of any one of which involves an element of so that the conduit loads can move entire ly freely to lateral slopes of repose. Thus, in Figure 11 it will be seen that the load in 29 shown at its nadir, does not even lill the conduit cross section because under the motlons and forces acting, an element of "With an aXi al The conduit load at the left in Figure 11 can spill from the conduit 28 into conduit 29 and be fully protected from any obstruction or action by the mill load. If the conduit 29 `were open at the left or rear,.the

mill load would enter and interrupt the load action of this conduit. Thus it will be noted that my arrangement of conduits permits the load to be transferred and move within the conduits independently of the mill load. The load, therefore, within the conduits moves regardless of the mill load but still has a power of progression into the grinding chamber when the open end of the conduit is lifted out of the mill load.- Thus the mill load may be at a maximum, yet the central entry chamber defined by the wall 22 may be substantially empty. At all times,

however, there vis an unobstructed and continuous opening between the two chambers. Another object and advantage secured by any construction is as follows :-'-In grinding feldspar in a ball'milhthe feldspar is fed manually through the manhole until the mill is entirely filled. Then the manhole is closed and the mill is rotated but without load circulation. Then the entire load is removed through a screen, the screen acting to restrain the mill balls. The mill is entirely filled manually and after rotation the load consolidates, leaving a small vacant space above the cascade. With my construction I can close the screen at the discharge end, then entirely fill the mill, rotate the mill until the proper crush has been made, then open the discharge screen and allow theground material to discharge under continued rotation, and then feed the next batch through the feed liner, `thus making a. batch load circulate in discharge after grinding `and filling the next batch load through a manhole.

'As regards actual operation; with a trunnion feed, the space above the trunnion is air trapped but` the perimeter feed can permit the air to escape back through the feed. lfurtherinore the cascade is open and any air pressure is permitted to escape through the discharge screen.

I claim r* l. A tumbling mill including a shell or drum, a hollow trunnion at the entrance end of the shell and constituting a andmeans disposed within the shell conveving the feed from the tube tothe perimeter ofthe shell and including an approximately splral conduit having one end disposed approinmately concentric to the hollow trunnion and having the other end disposed at feed tube,

without opening `the mill or inserting the iis ige'vigzsa the lperiphery of the shell, anda secondi conduitl into which 'the first conduit discharges and extending concentrically to the shell and discharging at the perimeter ofv the grinding chamber of the mill.

2. A tumbling mill including a shell or drum, aholloW trunnion at the entrance 'end' ofthe shell and constituting, a feed tube,

, and means disposed Within the shell conlil drum, a hollow trunnion at the entrance endv ofthe shell and constituting a feed-tube, and means disposedv Within the shell conveying the feed from the tube to the perimeter of the shell and including an approximately spiral conduit having one end disposed approximately concentric to the hollow trunnion and having the other end disposed at the periphery of the shell, and a second conduit. into lwhich the firstconduit discharges and extending concentrically to the shell and discharging at the perimeter of thek grinding chamber yof the mill, the second` conduit being of less length than the first named conduit and of less cross sectional area but disposed radially outward of the.

inner Wall of the first namedy conduit.

4. In a tumbling mill, a grinding chamber and means for discharging. feed. into the.

grinding chamber at a point adjacent the perimeter of the mill and above the load therein, said means acting automatically to stop the feed When the load fills the chamber and automatically start the feed When the load has decreasedsufiicient to leave a space above the load.

5. A tube mill havingv a plurality of conimunicating feed conduits conveying feed from the axial center of the mill to thel perimeter thereof, said conduits having different radial positions.

6. A tube mill having a pluralitj7 of communicating feed conduits conveying feed from the axial center of the mill to the perimeter thereof, said conduits having different radial positions and having different ,lengths therein of relatively different cross sectional area.

7 A tumbling mill including` a rotatable shell having a feedV conduit at its entrance end. and means disposed Within theshell conveying the feed from said feed conduit to the r) perimeter of theI shell including a conduit extending `around`= the shell'y vadjacent one y end thereof and receiving feed,v from the first named" conduit, the other'end ofthevsecond named' conduit"v being closed, ai thirdlconduit ,j

disposed' inuf'ard of' the secondi conduit and extending concentrically to` and adjacent the periineteii ofltlieshell, the third named conduit being closed at one endV and.` discharging into the shell at its other endg thel secondv` named conduit adjacent its closed end having an opening into the third namedV conduit adjacent itsl closedend;

8. A tumbling mill including a rotatable shell having a feed conduit at its entrance end, and means disposed `Within the shell conveying feed from said"v feedi conduit to` thev perimeter of the shell including a: conduitV extei'idingaround the shell adj acent oneend thereof and receiving feed froml the first.' namedl conduit, the other end.' ofthe second-f named conduit being closed;y aj third' conduit! p disposed inward of the second` named conduit and extending concentrically to .and adjacent the perimeter of the shell, the third named conduit being closed,` at'one endy and'.

discharging into the shell at its other end,

the secondnamed conduit adjacent its closed*y end having an opening into ythe thirdnamed conduit adjacent its closed end, the third; named conduit discharging in the same di-k rection as the direction of rotation of the shell.

9. A tumbling mill including av rotatable *shell formed to provide .ai grinding chamber and' having a feed trunnion at its1center at; the entrance end of the shell, and meansdisLA posed Within the shell conveying the feed. from said trunnion. to the perimeter'of the grinding chamber including al conduit extending around tlie shell adjacent the 2en` trance end thereofr and receivingfeed from` the trunnion, the outerk end of the conduit being closed, a ysecond conduit' extending,

parallel to the firstA named conduit but to-` ward the discharge end-of the shellv and extending concentrically to and adjacent the perimeter of the grinding chamber and discharging thereinto, the second named conduit being closed at one end and bothcon'- duits having a communicating opening adjacent the closed ends of the conduits but dis` posed in advanceof said' closed ends, Where-` by to cause material to travelin the first named conduit reveisely to the movement of` the shell', the second named conduit discharg ing in the same direction as the direction of rotation of the shell'.

10. A tumbling mill including arotatabl'e shell formed to'provide a grinding chamber and having a feed trunnion at itsv entrance end, and means disposed Within the shellfor conveying thev feed fromv said trunnion to they perimeter ofthe grinding chamber including,v

a conduit extending around the shellf inside thereof and adj acentl the entrance end# thereof, said conduit receiving feed from the trunnion, the opposite end` oi' the conduit being closed, a second conduit disposed parallel to but inwardoilf the first conduit and extend ing concentrically-to and adjacent the perimeter of the grinding chamber ,closed at one end and there being an opening between the conduits disposed inward of the closed ends ot' both conduits whereby to torni pockets inthe ends ot the conduits, the lirst named conduit having its open end disposed in advance of its closed end whereby to cause ma,- terial to travel in ythe lirst named conduit reversely to the movementof the shell, the second named conduit discharging in the same direction as the direction of rotation of the shell.

11. A tumbling mill4 including a shell have ing a head at its entrance end, there being a' hollowti'unnion discharging through said head, a linei` plate disposed inward ot the head and deiining the entrance end of a grinding chamber, the plate` being formed with a rib extending towards the head and deiningan approximately spiral 'feed conduit, the conduit being closed at its outer end, the liner plate being also formed to provide a conduit odset to one side of the first named conduit 'of less cross sectional area than the iirst named conduit closed at its end adjacent the closed end ot the first named conduit and terminating at its end shortk of the termination of said first named conduit,there `being an opening between the conduits `inward ofthe closed ends `ot `both conduits, the second named conduit extendingaround the perimeter of the grinding chamber and being oit' less length than the first named conduit. f I y l 12 In a tumbling mill having a grinding chamber, means for discharging material to be treatedinto the grinding chamber at a point above the load therein and including a 4feed conduit carried by and rotatable with and opening into the grinding chamber and 'extending around the sa1ne,ithe Vdischarge mouth ot the conduit passing on each revolul tion downward into the load whereby the feed is stopped and being then carried above the load whereby the feed is allowed to vlow by gravityinto the chamber. H

13. In a tumbling mill having a grinding chamber, means for discharging material to be treated into the grinding chamber above the load therein `and,including a plurality of conduits extending around the grinding chamber, carried thereby, and rotatable therewith,` the conduits opening into cach other, one of the conduits receiving material to be treated and acting by gravity to `transfer the materialto the `adjacent conduit andon'e oit' the conduits opening intolthe grinding chamber, the discharge mouth ot the last named conduit on cach revolution of the mill passing down into the load and being then 'carried above the load whereby to permit the `teed within the conduit to flow down intothe chamber toward the perimeter of the chamber onto the Atace ot the load.

141. 1n a tunibling mill having a Ygrinding chamber, means for discharging material to beitreated into the grinding chaniiberA above the load therein including" a plurality of pairs or conduits, the pairs oi conduits being arranged to balance each other, each pair including a conduit extending around the grinding chamber inlan approximate spiral andreceiving at one end the material to be treated `and acting by gravity to :cause the material to. be transferred to the opposite end,` oit' the conduit, and the second conduit being closed at one end and at its other end opening into the first named conduit and then extending concentrically around the griding chamber and discharging'thereinto.

15. In a tumbling .mill having a grinding chamber, a closed toed conduit havingits entrance end' con'nnunicating withA a feed opening'and its outlet end communicating with the interior 0i the grinding chamber, the conduit extending approximately con centric to the axis of rotation ot the' grinding chamber.

1G. In a tun'ibiiiip` mill havin@r afirindin0r c; D i b chamber, and a hollow trunnion constituting means for :feeding material into the mill, ot means :for carrying said material :from said trunnion into `the grindingV chamberincluding twoparallel conduits extending concentrically tothe periphery of the mill one of' said conduits being longer than the other and being disposed adjacent the `inlet end of the mill and having an inlet end and a closed end, the inlet end communicating with the hollow trunnion, the shorter of the two conduits having a closed end disposed adjacent to the closed end of thev longer conduit andhaving the open end discharging into the grinding chamber, there being an opening betweenl the two conduits adjacent to the closed ends. l

17. A tumbling mill including'a rotatable grinding chamber, and tubular conduits disposed witliin the grinding chamber tor directing the material to be ground from a point adjacent the axis of the grinding chamber to the perimeter thereof, said conl duits freely discharging at the perimeterot and into the grinding chamber and in the same direction as the direction of rotation of. the mill. Y

18. A tumbling mill including a rotatable grinding chamber, and a tubular spiral conduit disposed within the grinding chainber open to receive material at its inner end and discharging said material at the perimeter ot and into the grinding chamber in the same directionas Vthe direction of rota` tion of the mill.

19. In a tumbling mill, a grinding cham- @Tangas ber, and means freely discharging feed into the grinding chamber at a point adjacent the perimeter of the mill `and discharging the feed in av direction the same as the rotation of the mill and above the load therein.v

20. In a tumbling millv having" a. grinding grinding chamber and extending around the same, the material to be treated passingsu'ccesively through the yconnected conduits, ythe last conduit of ther series discharging yin the same direction as the direction ofrotation of the mill.

2l. In a tumbling mill having a grinding chamber, means for discharging material to be treated into the grinding chamber at a point above the load therein, said means including a plurality of connected parallel conduits, the first conduit of the series reeeiving a load at the axis of the millthel last conduit of the series dischargimT the load at the perimeter of the mill, the feed conduits extending approximately concentrically yto the axis of rotation of the mill and being rotatable with the grinding chamber. n

22. In a tumbling mill having a grinding chamber, a tubular conduit for conducting material from the exterior of the mill into the grinding chamber, said' conduitbeing so formed as to permit material Within the conduit to move along the conduit independently of the load in the grinding chamber and freely discharging into the grinding chamber Whenever the mouth of the conduit 'is lifted above the load therein, said discharge being in a direction that same as the direction of rotation of the mill.

Q3. In a t-i'lmbling mill. having` a grinding chamber, a tubular feed conduitvhaving its entrance end communicating with an axial feed opening for the passage ofincoming material and having an unobstructed outlet en d extending in a similar direction to the perimeter of thegrindiug chamber and communicating with the interior of the grinding chamber, said conduit extending approximately concentric to the axis of rotation of the grinding chamber.

24. A tumbling mill includinga grinding chamber, means for introducing material into the mill at the longitudinal 'axial center thereof, and a tubular feed conduit receiving said material at said axial center, the conduit extending approximately concentrically to the axis of rotation of the grinding chamber and advancing the material from the center toward the perimeter of the grinding chamber and simultaneously advancing the material longitudinallywof the grinding chamber, the conduit discharging at the perimeter of the grinding chamber andin a direction at an angle to the longitudinaljaxis ofthe mill and above the load therein. f

A tumbling millincluding a rotatable `erindiner chamber and means for takin@ man r; b

terial at a. point in line with the axis of the mill and ydirectinglsad material tothe-perimeterof the millA including circumferentially elongated tubular conduits rotatablev with the' grinding chamber, the conduits being connected to each other andl being disposed lat diiferent radial dist'ance-sfrom. the axialcenter of theinilhthe conduits freely discharging at the perimeter .of and 1 into thegrinding chamber.` n

26; A tumbling mill including a rotatable grinding chamber, and means for taking iialterialffrom a vpoint coincident with the axis of theniill and,l discharging theimaterial at the perimeter of the grinding chamber'including circumferentially elongated tubular connected conduits disposed Within the mill, the conduits being so formed' as to convey he material radially and axially and the last conduit of the series discharging at the perimeter of and into the grinding chamber.

27. A tiunbling` mill including a grinding` chamber, means for 'introducing material into the mill at the longitudinal axial cen` tery thereof, tubular means for conveying said material into the grinding chamber and' discharging the material adjacent the perimeter of the grinding chamber, said tubular means extending parallel to the direction of rotation of the grinding chamber and including an extension into which thetubular rmeans discharges in a direction parallel to the longitudinal axis of the grinding chamber, said extension discharging parallel to the plane of rotation of the grindingchamberand extending in opposite direc-,tions beyond the discharge opening the v.first named 'tubular member. j

28. In atumbling mill, a grinding` `chamber and means for discharging material to be treated into the grindingI chamber at a point above the load therein including a tubular "feedconduit' rotatable with and opening into the grinding chamber and 'cX- tending around the same, the .feed conduit" being approximately spiral and receiving material atk the axis of thegmill, the conduit extending outwardly and circumfcrentially to the perimeter of the milll and having. a longitudinally displaced portion open at one end and discharging at the perimeter of the grinding chamber and in the plane of movement of the grinding chamber.

' 29. In a tumbling mill having a.l grinding f chamber, means for discharging material "to be treated into the grinding chamber at a point above the load therein including two connected, parallel conduits, the `first coi:-l duit of the series being` disposed 'at the entrance end yof the mill and receiving a load from the axis ofthe mill, said conduit `extending spiially around the mill to the peli-` imetei' thereof,' andtlieksecond conduit extending` parallel to the iistnanied conduit nut revei'tedwvth iielation` theretoandnto i which the first named conduit opens, the second nainedlconduit `having a cross sectional area less than that of the hist named coni duitwhei'eby'thegzload in the first named conduit Willoveibalance the loadin. the Second 3 namedconduit and prevent ieti'oiogfifes` l* sion of the load" in` the second named conv-14 diiit. l i i, 80, ln a tumbling,r millhaving a` grinding chamber, an axial lieed opening, a conduit ture.

Leimee ijotation of theniill and adjacent to the perimeter o the grinding chamber. 31. `In a tumbling mill having a `grinding chamber, an axial feed opening. a conduit through Whicliniateiialis advanced by i'o! tation ofthe inill havingits entrance `f end in communication with the eedopening and `its discharge end disposed adjacent the per`v iineteil oi" the grinding chamber, and means atthe discharge end of the conduit preventingthei'etuininoveinentof the load into the conduit but peimittingthe discharge of load from the conduit vinto `the grinding chambei` when the mouth of the conduit.rises-,above the load in the grinding chamber. I i ,In testimony whereof I affix my `signa- NEWToN L1. HALL.

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