US2499347A - Electrical circuits for grinding mills - Google Patents

Description

5 Sheets-Sheet l J. A. ADAMS ELECTRICAL CIRCUITS FOR GRINDING MILLS GRM/UNG M/LL CO/Vf/@O 10H/V61,

BAY/C W/YTER JY/PPLY INVEN TOR.

ATTORNEY JAMES A. ADAMS March 7, 1950 .1. A. ADAMS ELECTRICAL CIRCUITS FOR GRINDING MILLS 5 Sheets-Sheet 2 Filed April V16, 1945 BY d.

ATTORNEY March 7, 195@ J. A. ADAMS ELECTRICAL CIRCUITS FCR CRINDING MILLS 3 Sheets-Sheet 5 Filed April 16. 1945 INVENTOR.

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ATTORNEY JAMES A. ADAMS NON `N um atentec Mar. 7, 1.9750

UNITED STATES Ars-NT oF-F1 James A. Adams, @leuven-1Com., assigner to The Mine :an-cl Smelter Supply Company, Denver, 0.010., a 'corporation of Colorado Application Apxgfill, 194'5., .Se1'ial N0. 588,479

This invei-ition relates to a method 'of and apparatus for controlling `the grinding vand'er separation of solid material particles ormixtures of Vsolids and liquids, `and more particularlyto Ythe control of one or more elementsofnagrinding circuit, such as-a mill and a elassier in series. The princi-ples ci" this invention are particularly applicable to the grinding and separation of ore lfor treatment in a ini-11 or the like Vto recover valuable mineral constituents, but are alsoap-i plicable to the grinding -a^nd/o1separation of other `solid material, as vfor use yin chemical processes or `for other purposes.

Previously, attempts have heendmacle to control grinding yand separationof ores-hy suspending a solid bodyuin the -pulp -at the overflow of -a classifier and. :attempt control-ot the size 4of particles in the overow by measuring ther-varying buoyancyof the suspended body HoWe-ven-such attempts `have 1iotbeen particularly ysuccessful Ibecause .solids tenditoadheretolthe body Iand change its buoyancy, lwhich leads to considerable `inaceuracy inconsistencybecause achange of only 1% crf2%solids-`in:annota-puln-for `txample, "be the -equivalent .of only t2 for '13 LA of a` diaphragm or against twohalancinjg diaphragms. `A changeintheipulp density .causes a corresponding change in the dierence intre- .sistance `to flow -of air `.at the diferer-it 1,1eyels,

` so that the-,dlaph1sagm er diaphragrnsfreect .ing such-differences-.rnay he used to-.iauate a Acontrol mechanism A.Whicl'i may controlgiagcornponent of the-ipu1p :so :asv to maintainthe.- density constant. Such sa )pulp density regulator has been used with ,marked .CESSIfn mining eclistrcts. all over the itworld, sinner .ita y,seilsitiyeto less than 1% Solids. ,E Eciyyeyenfthe1 areinumerous instances intwhichga idensity'contro'ller, noumatter howiaecurate, is -.inef.ective to main- .tain a -desredparticle sin y .as in Lthe .'iouerow of a classifier. Particularly when the @otegor salidsf-oftheenulpwisenut itselff-.lwmogeeeous 1n reflect `accurately changes or 'differences v-in particle size. Consequently, the particle Size- Which is oitenithe desideratum ofthe next step, sucht-as otatonis not-maintained uniformly.

Anotliei solutionof theprcblem, adequate and effective i-nnunierous- 'instances' is that disclosed :and -claimed in my'U. S. vPatent No. 2,246,822, granted May f6, 1941, and in rny-pendingappllcation Serial No. 595,894, filed Getober Vl2, :1943. As vdisclosed therein,y the sou-nd of the grinding mill is utilized `in controlling thefteed to the mill, as it has beenftoundthat the sound ofthe mill dtersforfvarious conditionsiof .operation, and that the `:sound `Var-ies in yolurnein accordance with the loaden 4the mill `and the grinding results. The foregoing v in'iproyement 4thus includes the useof ancise meter. Aor rsound -vdetectorfto control Aa mill feed cincuit-by .changfing an element `or elements of the mill ffeed. While highly successful pin. certain installations, such improvement is limite-d to mills in'whch :there Vare very tew extraneous noises to;interfiere with the-:accurate reflection vof the :millfcondition,'andalsofwhere therese is sufficiently iuni- .iferm that ,the nuisance'of continualfresettingfis avoided. Suc-h :difference in-feed may'. bezdueto Lyariations in the Aore/,and sucient diierence in vfeed .sometimes to .he objectionable fmay mbe `:caused fby v, the tendency fororefrom `a; Crusher Vto.'segregate inea storage hin. Thus, -as aster- .age bin .is abeinglled, material collects in a coneshapedpile, the largerA lumps rollingfitog the fed-ges pf-r theiipile, against the- -Wall of, the bin. As the hin isV lled, the `'material ttherein vis somewhat segregated, Withanginner cylindenor thelile of fines or ,small lumps'jbeing, :in ;the .center and langer Ymateria-l -andlurnps surrounding ethe cylinder. When preis-withdrawn gir-om the itin, the small lumpsandinesfinthe eenterfltendg-:to `he remouediirst, the -ore inthe-loin formngffan inverted cone-:With f itsfapeX-iat- `the outlet. r: Ghus, lthe pre withdrawn ',-iromthe bin tends utoube smaller inv size at; mst, ...with the averageA Asize of the lumps gradually snowing langer, sos thatgthe 'feed tothemill will Yaili! inffsizeanclfproportionate ease of grinding. A suicient disparity in. the average'zsizenat different times may; re- V.quire `,frequent adjustment r1of r,a ngjill .eontnolled inaccordancefwith sound.

@Among the Qbiects fof -f the :present .inventief-'1 ,are to proyideafcontrolfdeyice whiohtaecuigately reects thev actual-size;- ,on particles, such as` separated inf@rpredetermnedeee effiaiclessitsr! :Among Otten-Objects@ teatri-Sent intention specic gravity, the density fcontrol-lerucanngtit .arteproyiclaavnoyel method.fork automatically maintaining a desired particle size or density condition in a predetermined zone of a separator, classifier, or the like; to provide such a method which will regulate the feed of liquid to a classifier or separator and/or grinding mill in accordance with conditions in the classifier or separator; to provide such a method which will regulate the feed of solids and/or liquid to a grinding mill; to provide such a method which will utilize conditions, such as the particle size, the power requirements of the classifier, and the mill load, in controlling the operation of a grinding mill and classifler in series; to provide such a method which will prevent an overload in a grate type mill from adversely affecting the classifier operation; to provide such a method which will be effective in operation; to provide apparatus for carrying out the above method; to provide a novel control device responsive to the actual size of particles; to provide such apparatus which may include the above novel particle size responsive device; to provide such apparatus which may include a device responsive to the specific gravity of the pulp discharged from or in a predetermined zone of the classifier; to provide electrical circuits for effecting control of the mill and classifier and thereby automatically regulating the grinding operation; and to provide such apparatus which will be efficient and effective in operation.

Additional objects and the novel features of this invention will become apparent from the description which follows.

In accordance with this invention, the operation of a separator, such as a classifier, is controlled by varying the liquid or water feed thereto in accordance with the actual size of particles of a predetermined zone of the classifier. Normally, such zone will be the overflow which comprises finished product of the grinding circuit, and the water added to the classifier feed is increased in case the particle size increases and is decreased in case the particle size decreases. Thus, the classifier feed water is varied in accordance with the actual size of particles in the overflow. Such direct regulation will operate to maintain the discharged particles of a predetermined size or 'range of sizes, because if there is an increase in the amount of smaller particles, without a corresponding increase in the classifier feed water, the 'density of the pulp in the classifier will increase, so that the larger particles will not settle as quickly and will begin to come over in the overflow. As soon as these larger particles are detected, if the classifier feed water is increased, the pulp is diluted and the larger particles will again settle, so that the overflow will again contain particles of the desired size range. On the other hand, if the number of smaller particles decreases, the pulp will become more dilute, with the result that some vof the particles in the overflow range will settle, and the average of the overow particles Vwill'be smaller. As soon as this difference is detected, if the classifier feed water is reduced, then the density of the pulp will increase and the overflow particles will again fall within the desired range.

It will be observed that control of the classifier feed water in accordance with the particle size in effect controls the density of the pulp in the classifier, but more effectively provides the desired result-a desired overflow particle size range. Also, the foregoing method may be applied individually, but may also be a valuable step of the following further method of this invention.

In further accordance with this invention, the

operation of a circuit which includes a grinding mill operating in series with a classifier is controlled by varying the feed to the mill in accordance with the power requirements of the classifier, preferably with accurate control of the classier feed water, in accordance with changes in the density or in the actual size of particles of a predetermined zone of the classier. The feed to the mill so controlled may comprise the feed of solids, such as ore, or also the feed of liquid, such as water. By controlling the feed to the grinding mill in accordance with the power requirements of the classifier, variations such as in the hardness of the ore will be compensated for. Thus, if the ore becomes harder, the smaller particle output of the mill will decrease and the average size of the particles will become greater, and a larger proportion of the classifier output will be returned for regrinding. Also, the increase in recirculated particles will increase the amount of material necessary to be moved by the classifier, so that the power requirements of the classifier, or sand load, will increase. Unless corrected by decreasing the feed to the mill, to cause the particles t0 be ground fine, the load on the classifier, and also on the mill, will increase until either oi' both become overloaded. Thus, when the power requirements of the classifier increase, the feed to the mill is decreased, in accordance with this invention.

Similarly, if the ore becomes softer and softer, the mill products become finer, so that there is less return of oversize particles to the mill, So that the load on the classier becomes less. To correct this condition, the feed to the mill is increased when the power requirements of the classifier, or sand load, decrease, also in accordance with this invention.

In further accordance with this invention, in the case of a grate type will-whose output and the corresponding sand load decrease on the occurrence of an overloadthe mill feed is stopped when the power requirements of the mill reach a predetermined minimum. At the same time, the normal control based upon the power requirements of the classifier is reversed so that the setting of the feed to the mill will have decreased by the time the feed belt is started up again. Thus, the mill feed will decrease until the overload is cleared, whereupon the power requirements of the mill will increase until a predetermined minimum is reached; at this time, the control of mill feed is varied normally, i. e., directly in accordance with the power requirements of the classifier. With respect to grate type grinding mills, the foregoing is a valuable feature of this invention, since the steps thereof not only provide overload protection, but also eliminate the factor which caused the overload, i. e., too high a feed rate.

Apparatus for carrying out the above methods may be constructed in any suitable manner, but la preferred form of apparatus, constructed in accordance with this invention, is illustrated in the accompanying drawings, in which:

Fig. l is a simplified diagram of a mill and classifier circuit provided with control apparatus constructed in accordance with this invention;

Fig. 2 is a simplified diagram of an ore and water feed control for the grinding mill;

Fig. 3 is a diagram of a device responsive to the density of pulp, such as disclosed in my U. S. Patent No. 2,205,678;

Fig. 4 is a diagram of an electrical circuit for a control panel of Fig. 2;

Fig, issa diagram' of an alternativa electrical circuit-for the control panel of Fig..2;;

Figs. 6 and 7 are plan views of discs formedas cams and utilized in the circuit, of Fig. 5;

Fig, Si is a top plan view of av particle size responsive device and a connected diagram of an electrical circuit associated therewith;

Fig. 9 is a side elevation of the particle size responsive device of Fig. 6; and

Fig. 101is an end elevation` thereof.

Apparatus constructed in accordance with this invention, as illustrated in Fig. 1., maybe utilized in controlling the oper-ation of a grinding mill M anda classiiier C in seriesv therewith, the ground product of the mill passing to Athe classier through a conduit Il). Material fed to the 'mill may include solids, such as ore, passing to themill through an ore feed line II, the new' through which is regulated by a feed control device I2; a basic liquid supply, such as water, supplied throughV a pipe i3; automatically supplied liquid, such aswater, which may comprise about 25% of themill water requirements and the flow of which through a pipe Il is regulated by a valve I5; and pulp containing oversize particles returned from theclassier through a conduit i6.

In addition to the feed from the mill through conduit Ill, the feed to the classifier may include basic liquid, such as water, supplied through a pipey Il, and automatically controlled liquid, such as water, supplied through a pipe I8, and the flow thereof regulated by aV valve I9. The feed' control device l2 and the regulating valves I5 and I9 are preferably actuated or controlled electrically,

although other types of control may be utilized, if

desired. The overilow or discharge or"v pulp containing a desired size range of particles, through a'f conduit 20, is normally supplied to the next step in the process, such as to a conditioner or'flotation apparatus in an ore separation treatment. The motive power for the mill M is preferably supplied by an electric motor 2l having power leads 22`, and motive power for the classier is preferably supplied in a similar manner by an electric motor 23 having power leads 2li. It will be understood', of course, that the parts as shown in Fig. 1 are diagrammatic only and that no attempt is made therein to show the exact relationship of' parts or to show the exact position of pipes or conduits leading to or from the mill orclassifier, but su'ch relationship and position will be apparent to those skilled in theart, including the'position of'a device D which is responsive to a condition of the pulp, such as the density or actual size ofY particles, in a predetermined zone of the classiensuch as the overflow.

In one embodiment of this invention, the' ore feed control device I2 and automatic mill water supply valve I5 are regulated in accordance with the power requirements of the classifier, and for this purpose a control panel P may be connected by leads 25' and 25 with the ore feed' control dee vice I2 and' water valve I5', respectively, theelectrical parts installed within the control panel P, which will be described in detail later, being connected with a` classifier current transformer 21 by leads 2B, and with a classifier voltage transformer 29 by leads 3U.

In case the mill M is a gratetype` mill' or similar mill in which the power requirement drops upon an overload, in further accordance with this invention control means are provided* in panelP'which will operate to reverse the" ordinary control. procedure in the case of. an.overloaded m1l..andf at thesametimestopthe ore conveycn:- l

belt...v For this: purpose, the; control; devices in panel P- may be, connected. with; amill; motor cur'- rent transformerl 3l by leads 32; A mill motor voltageA transformer. maylv also be: utilized or', as Will appear' subsequently, a voltagel source such as; 110 volts may be utilized. in measuring themill power requirements;v

'The classifier power requirement elements'and the grinding mill. power. requirement; elements arerinterconnectedand integrated in such-a man'- neri that: when the power requirements of mill motor 2fI. drop; due to the overload, the feed mechanism isv stopped and the feed' ratei is' re'- duced to= prevent the overloadI from occurring again: when thefeeding mechanism isV started up. Thus; the manner of control is reversed; sov that ai low power requirement of' the classier motor '23g caused: by the decreaseVv of'disicharge from the mill to the. classi'er and'y a consequent decrease inthe classifier load", will cause'fa decrease in' the feed to the mill' instead of an increase in` the same.. Also; as soon as the overload is cleared and thev power requirements of the mill motor 2l rise, the normal control is reinstated.

As indicated previously, the water feed to the classi-lier is Apreferably regulated in accordance with the size of particles or the density of the pulp discharged from the classifier and measured by device D which is responsive to such conditions in the pulp. For controlling valve' |91, device D may' be connected byT leads 33` tol av control panel 34, which may contain electrical ap paratus to be described in detail laten and which is connected by leads 33 with valvev I9.

The variations in particle size in the discharge from the classifier maybe dueto one or more of a number of different causes. Normally, the density of the pulp will vary in' accordance with the size ofv particles therein, but there' are some ores which are not 'homogeneous' in specic gravity, so that measurement ofthe pulp density of the classiiier discharge is' not sufficiently exact to determine the particle size. Thus, with respect to' those ores which produce a' pulp which is homogeneous in density, the' device D may be responsive to the pulp density, butV for'those ores with respect to which the pulps produced are not homogeneous'in density, the deviceD preferably'is responsive to the actual size of the' par t'icles'. Also, even' forV ores which produce pulps homogeneous in density, a device which is re sponsive' to the actual size of" the' particles is equally operative, so that such a devicel can be used on' all ores, and is, therefore, more universally applicablek than a device responsive only to density.

The apparatus'of Fig. 1 operates'to' control the particle size or discharge of the grinding circuit, in which the mill and classier arelin series and the oversize orv classifier reject is returned to the mill` but it will be understood that the principles of this inventionl are equally applicable to a circuit in' which thereis4 no return from'the classifier to themill. The apparatus'of Fig; 1 isparticularly adapted to' carry out the method previsously outlined, as follows.V

Variation in. particle size' may be affected byl water tends to' have the: opposite` effect; so that; normal. variations; in. particlesize: will. be'. auto-4 matcally' -wmpensateld for. through device. 1g,

However, an increase or decrease in the larger particles passing to the classifier from the grinding mill tends to change the volume of material handled by the classifier rakes and thereby tends to increase or decrease the load on the classifier, reflected in the power requirements of motor 23. Such change in the larger particles requires further control in addition to a change in the amount of dilution water added to the classifier, since the mill will now be working at less or greater than desired capacity. This control may be effected, as through panel P, by increasing or decreasing the amount of orefed to the mill, and at the same time increasing or decreasing the amount of Water fed to the mill, upon an increase or decrease in larger particles. Also, a compensating control upon a decrease in larger particles tending to decrease the load on the classifier is effected, as through panel P, by decreasing the amount of ore and water fed to the mill, since the mill is now attempting to produce at a rate greater than its capacity and is overloaded. As soon as the mill produces the required amount of finer and larger particles, such as predetermined for efficiency of operation of the circuit, the mill feed is maintained at the new level. At the same time, the particle size or density of the classifier overflow is maintained substantially constant, throughout changes in the mill feed, which may be occasioned by changes in the size or hardness of the ore feed.

The mill power requirement transformers may also be utilized to stop the conveyor belt upon a heavy overload on the mill, and to start the conveyor belt again when such overload is removed, as by control effected in a manner to be described subsequently.

When the feed to the mill is increased to increase the size of particles fed to the classifier, such increase also compensates for the reduction in oversize particles returned by the classifier to the mill through conduit IS. The oversize sands returned decrease when the amount of larger particles to the classifier decreases upon an increase in the amount of finer particles, and vice versa. Thus, when the feed to the mill is increased, the amount of oversize particles tends to increase, and vice versa, so that the grinding mill may be relatively quickly brought back to the desired production rate, in accordance with the hardness of the ore and the size of the feed.

From the foregoing, it is apparent that the method and. apparatus of this invention, as described so far, provide automatic maintenance of the particle size overow of the classifier and automatic regulation of the grinding mill operation to increase feed when the mill is operating below capacity and to decrease feed when the mill is overloaded. This holds true for all ball and rod mills, because the classifier sand load is indicative of the mill load at all times in the overfiow type mill, and control by the combination of the mill power requirements and the classier sand load satisfies conditions when a grate type mill is used.

The feed to the grinding mill may be controlled in the above manner by apparatus constructed as illustrated in Fig. 2, and including electrical elements of panel P which may be constructed in any suitable manner, as including the elements of panel 34 'of Fig. 1 and further including elements connected as in the manner of the circuit of Figpll, or, alternatively, the circuit of Fig.` 5. In the apparatus of Fig..2,

power leads 22 to the mill motor and power leads 24 to the classier motor correspond to the same elements of Fig. l, as Well as the classifier current transformer 21 and leads 28 therefrom to panel P, classifier voltage transformer 29 and leads 3D therefrom to panel P, and mill motor current transformer 3| and leads 32 therefrom to panel P.

For controlling the feed of ore 36 to the grinding mill, a storage bin 31 may be provided at its lower end with any suitable type of discharge control, such as a gate operated by a lever 38. One end of lever 33 is attached to the gate and the opposite end of the lever may be attached to an endless V-belt 39, or the like, which circumscribes pulleys 40 and 4|. Pulley 40 is rotated in either direction by a reversible motor 42, connected by wires 43 with panel P. From bin 31, the ore may be moved to the grinding mill by a suitable conveyor, such as including an endless belt 44 which at one end passes around a pulley 45 driven by a motor 46. Leads 41 to motor 46 pass through a starting switch 48, to which control wires 49 lead from panel P. As will be evident, reversible motor 42 is adapted to vary the amount of ore passing from bin 31 to belt 44 in small increments, whereas the belt motor 46 is stopped to terminate the feed to the grinding mill, such as upon the occurrence of an overload on a grate type mill. In lieu of the gate operated by lever 38, belt 44 may be driven at different speeds to vary the amount of ore fed to bin 31 by small increments.

For controlling the fiow of Water to the classifier through pipe |8 in which a suitable valve I9 is installed, as also indicated in Fig. l, an endless V-belt 50 may be utilized to open and close the valve by engagement with a valve wheel 5|, the opposite end of belt 50 engaging a pulley 52 turned by a reversible motor 53, similar to reversible motor 42 and connected with panel P by wires 54. The fiow through pipe I4 controlled by valve I5 of Fig. l, may be regulated in a similar manner, as by a reversible motor 55 similar to motor 42 and connected to panel P by a set of wires 56 tributary to leads 43. Or, the flow of Water to the grinding mill may be controlled by motor 42, connected with the valve therefor in the same manner as motor 53 and valve controlled thereby.

A control device D responsive to the size of particles of a predetermined zone of the classifier may be constructed generally as in Fig. 2. Such device may include a pair of rollers 51 mounted on and rotated in opposite directions by shafts 58. One shaft 58 ls relatively fixed as to bodily movement, and the other movable with respect thereto, so that a change in the size of particles passing between the rollers will cause the shafts to move closer together or further apart as the case may be to operate a suitable switch. Shafts 58 extend from a housing 59, in which is installed bearings, shaft rotating means, and other control apparatus, including a switch for transmitting the effect of Ychanges in the size of particles through wires .65 to panel P.

A control device responsive to changes in the density of the pulp of a predetermined zone of the classifier may, as in Fig. 3, include a housing 62 to which an air pipe 63 leads, for supplying air to a shorter tube 64 and a longer tube B5. The difference in back pressure caused by air escaping from the tubes is measured by sensitive diaphragms in housing 82 and transmitted elecf trically by wires 66, ywhich may be connected, rito control panel P in lieu of wires 60 oi the control device of Fig. 2. Further details of the construction oi` preferred devices operating in the above manner are to be found .in my U. S. Patents No. 2,204,644, granted Junel, 1940, and No. 2,205,678, granted June 25, 1940.

As in Fig. 2, vthe apparatus of this invention may be constructed so that at least some of the regulation may be made manual or automatic at the operators option, by including on panel P' switches 67, 68 and 69, respectively, for changing the ore feed and water control, the ore conveyor belt, and classifier water from hand control to automatic control, and vice versa. Control panel Pl may further include push button switches 'I0 for starting and stopping motors 42 and 53, and motor 55, or one of the positions of switches 6l and 69 may be an oir position. Also, a record of the various steps carried outby the apparatus, may be provided by a chart 'l'l ,and cooperating pens for recording various factors, such as the particle size or density of the classier overiiow,

the classifier motor load or power requirements, the mill motor load, the amount of ore fed to the mill, the amount of water fed to the mill, and the amount of water fed to the classifier, any of which may be omitted, if desired. The panel P' may include direct reading meters l2 and 13 for indicating the classier motor load and the mill motor load. Also, a suitable meter, such as indicating the particle size of the classifier overflow, or density thereof, may be added or substituted for one of the other meters.

The elements installed in panel P may include those necessary to form the circuit shown in Fig. 4, which is adapted to regulate the reversible motors 42 and 55. respectively adapted to control the feed oi ore to the grinding mill, and the water to the grinding mill. The circuit of Fig. 4 is also adapted to stop the conveyor motor it of Fig. 2 when the grinding mill is overloaded, and is particularly applicable to a grinding mill, such as a grate type mill, whose power requirements decrease upon an overload. Aside from the forward windings l5 and reverse windings 'It of motors 42 and 55, leads 43 and 55 for these motors, and also control wires @leading to the starting box of the conveyor belt drive motor, the remainder of the wiring and elements of Fig. 4 are preferably installed in panel P. As will be evident, motors 42 and 55 may be controlled in parallel, the central wires of the leads connecting a wire 'il or one side of a suitable supply of elec tricity. such as 110 volts A.-C., with. a common terminal of the forward and reverse windings of the motors. lOne set of outside wires of leads 43 and 56 lead from the forward windings, and connect at a common terminal with a wire T8, in turn adapted to connect the forward windings of the motors, through a relay switch '19. with a wire 80 forming the opposite side of the 110 volt A.C. supply. Similarly, the other set of outside wires lead from the reverse windings ofthe motors and connect at a common terminal with a wire 8l, which in turn connects through a relay switch B2 with wire 80. As will be evident, when switch F9 is closed, motors 42 and 55 will run in the forward direction, and when switch 32 is closed, the I motors l2 'and 55 tend to vturnfirstfin one direcm y' tion, then the other, such `alterna'ition insuring that slack :in thevalve or the gate-will he .taken up "if van Tadded :impetus `in either direction lis given to eiecta change in the ieedand also 'to eiect changes .in 'slight increments .to .prevent overruning of the control. For the above purpose, .and to veffect necessary changes `in the feed due to'variations ,in the power requirements Loi the classier, 'coils -83 Vand Ble', connected by leads 28 and 30with'the classifier curreutzand voltage transformers, respectively, .are operatively disposed with .respect tola disc 85, similar toa r:watt meterdisc. vvWhenever the .currentrdrawn by the classifier rmotor increases, 'and `.the :voltage remains :substantially .constant sor decreases insufficiently to counteract the increase in current. disc L:B5 will be rotated against the force exerted by a :torsion spring Athrough an .angle correspending to 'ithe increase in 'the .power .requirement oi .theclassilen Such'rotation nf thedis'c 85 will cause ia fiagor tab .81 attached tto disc 85 to intercept a greater .proportion .of :the light directed ifrom a bulb 88 toward. a fphotoelectric cell 89. 'Bulb 88 may be rconnected across :wires S0 and 9i leading from source wires fll and 4lill, respectively, in series 4with a normally closed switch i210. Photoelectric cell 89 :controls a relay 92 which in turn controls the position of a double throw switch :93, the central contact larm of which ,is connected with wire 80. Preferably, disc 85 is oscillated by interrupting current :to coil 84 by asv/itch 94 in one :of leads llili, :alternately opened and-closedby a `cam' rotating at a Asuitable speed, such as yabout 30 R. P. M. This causes a proportional amount of light :to .reach the. photoelectric cell, and causes the control change to be based on cumulative effect, rather than temporary variations.

When switch 93 is in one .closed position, ia relay arrangement is actuated -fto close switch t9 and ycause motors 42 and -55 ftorun in the forward direction, and when switch 93 is inthe opposite closed position, 'another relay arrangement is actuated to close switch 02 and cause `motors 142 and '55 to run in the reverse direction. vSuch re,- lay varrangement for causing :the motors to `run in the forward direction may include :afswitch :96 in series with a solenoid 97! for yclosing 'forward motor .control yswitch 19, :one `contact of rswitch Abeing mounted on a loi-metallic vstrip 598 `:and connected'with power wire `Sii by a tributary wire 99. l.The other fcontact olswitch et is mounted on a. pivoted or viiexible arm |00 and lconnec'ted by la wire till with solenoid 9i, a tributary wire .I 02 completing the circuit to the other `power Wire '11. 'Bi-metallic strip 9B may :be `heated by a resistance coil .i933 in accordance with :the 1cur-- rentpassingthereto through'a wire its from ,one contactfof 'switch '93. To insure :positive "action ofI switch 96, a cam |05 is provided `to periodically move pivoted arm toward strip V313 :and cause thecontacts rof switch 98 'to close in case strip "B8 is bent suiiiciently in the required direction. Ca-m lilis preferably rotated at 'a relatively slow Arate, such as about 3 R. P. M., so ythat the motorsnormally will not run continuously in either direction, but only periodically.

similar relay Varrangen'ient for causing the motors vto :run in the reverse direction may be provided by aswitch H36 in series with a solenoid Iiifl for closing .reverse motor control switch 82.,

of itch .tilt .is mounted 'on a vbinnetallc switch 'lie being similar to switch 95. Thus, one

dto ,be heated :by fa resista'i'ice-cnilj,y i ance. with current passingv tlfieretc.` I` fire 1.09. :from itherreversinscontact of switch '1:06' .being :connected to solenoid |01 by a wire ||0 and the solenoid being con- -nected to wire |02. The other contact of switch |06 is mounted on a pivoted arm and connected to wire 99, thus completing the circuit to the other power wire 80. The action of cam in tending to close switch |08 is periodic and alternates with the action on switch 99, so that during normal operation switch 90 is closed for a short period, then switch |06, and so on.

Heating coils |03 and |06 are connected in parallel through a rheostat ||2 and a wire ||3 to the other power wire 11. The heating coils l2 trolled by a photoelectric cell |22 responsive to the amount of light from a bulb |23 and intercepted by a tab or flag |24 mounted on a disc |25. Disc.. |25 is rotated against the force of a torsion spring |26 in accordance with the amount of current passing through a coil |21 connected to leads 32 from the mill motor current transformer 3| of Fig. 2, so that the angle through which the disc is rotated will correspond to the load on the mill motor. A Voltage coil |28 may be provided, to complete a set-up similar to that of a watt meter,

. and may be connected by leads |29 with a mill may be connected to the same end of the rheostat winding, so that heating of the coils will be identical, or the coils may be connected to opposite ends of the rheostat, as shown, to obtain a greater range of adjustment and a differential in adjustment. Thus, if the rheostat arm is set at the center of the winding, as shown, the resistance of each portion of the winding will be the same, so that the same current difference will be necessary to cause switch 96 to be closed for a longer period than switch |06, or vice versa. However, if the rheostat arm is set to one side of the center to place a greater resistance in series with coil |03, for instance, a greater current difference will be necessary to cause switch 96 to be closed for a longer period than switch |06, and vice versa.

If the amount of light intercepted by tab 81 is less than that for which the photoelectric cell 89 is set, the forward contact will close, sending current through heating coil |08, to bend the bimetallic strip toward the pivoted strip and cause switch |06 to remain closed for a longer period than switch 96. The ultimate effect will be that the motors will turn in the reverse direction a suciently greater amount to reduce the feed of ore and water to the grinding mill. Similarly, if the amount of light intercepted should be greater than that for which the photoeleotric cell 99 is set, the reverse contact will close, sending current through coil |03 and causing switch 96 to remain closed for a longer period of time. thereby increasing the feed of ore and water to the grinding mill.

For recording the classifier load on chart 1|, a heating coil ||5 may be connected in series with one of the contacts of switch 93, such as by a wire ||6 from coil ||5 to wire |04 connected with the forward contact, the circuit being completed by a wire I I1 from coil I|5 to wire |02 and thence to power wire 11. Heating coil ||5 is adapted to cause a bi-metallic strip I I8 to bend in accordance with the current passing through the coil, and strip ||8 carries a pen which marks a line on the chart corresponding to the classifier power requirements.

For shutting off the conveyor belt motor and reducing the setting of the mill ore and water feed upon an overload on the grinding mill motor, contact wires 49, which lead to starting box 48 of Fig. 2, may be connected across a suitable power source, one wire 49 being connected to wire 90, and the other wire 49 being connected at a common terminal with bulb 88 through normally closed switch |20 with wire 9|. Switch |20 is thereby adapted to be opened to stop the conveyor motor and also to shut off bulb 88, which automatically causes motors 42 and 55 to run only in the reverse direction and thereby reduce the setting of the ore and water feed to .the grinding mill. f

To open` switch |20 upon an overload on the grinding mill motor, ai relay solenoid |2| is conits upper contact.

motor voltage transformer or with power wires 11 and 80, as desired, the latter being preferred as simpler.

It will be evident that switch I 20 may be omitted, along with the remainder of the mill motor power requirement circuit, sc that bulb 88 may be connected directly to the power leads. This provides a circuit adapted to control the usual type of grinding mill, wherein the mill ore and water feed is at all times regulated directly in accordance with the classifier motor power requirements.

An alternative circuit, as illustrated in Fig. 5, is particularly useful in contro-lling the operation ofa grate type grinding mill and a classifier in series and includes a pair of discs |3| and |32, respectively rotated in accordance with the power requirements of the classifier and the grinding mill. The circuit is operated from power leads |33 and |34, connected to a suitable source of electricity, such as 110 volts A.C. The disc |3| is adapted to be rotated, similarly to disc of Fig. 4, against the force of a torsion spring 88 and in accordance with a load on the classifier as determined by current and voltage coils 83 and 84, respectively connected to the classifier current and Voltage transformers by leads 28 and 30. Similarly, discv |32 is rotated against the force of a torsion spring |26 and in accordance with the load on the mill motor as determined by a current coil |21 connected with the mill motor transformer by leads 32, and also by a voltage coil |28 connected by leads |29 with power leads |33 and |34, as shown, or alternatively with a mill motor voltage transformer.

Disc |3| may be made in the form of a cam, as in Fig. 6, having an outline similar to an involute curve or spiral. Disc |3| is connected by a wire |35 to a solenoid or relay coil |38, the opposite end of the solenoid 'being connected by a wire |31 with power lead |34. The angular position of the disc determines engagement thereof with a contact |38 mounted on a pivoted arm |39 connected to power lead |33, as shown. Pivoted arm |39 is periodically moved toward disc |3| by a rotating cam |40, so that whenever the disc is in an angular position to cause engagement with contact |38, current will flow through coil |35 to close a double throw switch |4I, also connected by wire |31 with power lead |34, against This causes current to pass from switch |4| through a wire |42 and one of the outside leads 43 and 56 to the reverse windings 15 of motors 42 and 55. The circuit is completed through a wire |43 connecting the central leads 43 and 50 with a time delay switch |44, which is connected by a wire |45 with the power lead |33 and is periodically opened and closed by a rotating cam |46. Cam |46 breaks the motor circuit a Sucient number of times, such as 8 per minute, to cause the control motors to stop a predetermined period of time. The relative period during lwhich the control motors are ananas? stoppedmay he izegnlatedran :screw l'llf'l whichfmoyes one contaetcof :theswitchtowamd and away-from fthe other contact.. :Suena-regulation prevents the motors :from :running continuously and also :causes .changessinz-the.oreandwater feed to the mill totake place by lincrements..

In order -to ,stop Kthe ore conveyor .and lreverse the direction, .of control .upon .a Ipredetermined overload on the grinding mill motor, disc |3i2 may be provided, .as in Eig. "l, -with :an extending portion Suso ,positioned that as .cam- |40 rotates tto move a pivoted ar-m. |5.|. periodicallyl toward disc |32, a Contact |52 will normally fail Ato..en gage disc |32. However... whenianroverload prede.- termined amount is imposed. .upon .the grinding mill motor, disc .|32 will he moved angularly sui cient1y.so that 4contact 15.2 will engage ex tending portion |59. This will causev current to pass from contact '1| 52 .and .arm 151|., .connected with power lead. 133, as..shown, throughfthe disc and 'awire A53 to a relay ,coil |54. Yllheoppositeend of coil |54 is .connected by :a wire |55 withpower .lead |34,v .and @coil |54 .is .adapted to move a .double throw switch L56 from closure against a lower -contact, .1in :the position shown, sto closure against ,the .upper contact, .in .the .opposite yposiion.

.In the.v normal position 4as show-n, current .flows through :a wire |511 .from power .lead |33 and. through .the lower .contact .of .switch |55, and .also through a wire .158.. vconnected with power .lead |34, .to wires 4.9 leading to starting box 4.8 of 2, `for controlling .the conveyor .drive motor.. Thus, with switch |555v closed against. ,the lower contact, current will be supplied through wiresll to the starting .boxand theconveyor ,drive ,motor will I zeepv running.

However, whencoil |5|lis energized hyengagement of Contact .15| and disc. |32 when an overload in the ,grinding mill motor rotates disc |32 T.

to a .predetermined position, .switch |56 'is `moved. to the upper Icontact, thereby opening the .lower Contact and shutting off the supply of current through wire 4S to the starting 'box of the, con veyor motor, and thus stopping `vthe motor and conveyor. At the same time, switch ,energizes coil |36 `through a Wire 1.5.9, so that switch |"4| will move to the .upper contact', even 'though disc |`3| 'is not inengagement with .contact |38.. When switch |l| moves to the upper contact, current passes through vwire |48 tothe reverse windings 16 ,of the .control motors, thereby continuously reducing the. ore and water feed to 'the Ygrin-ding mill as long vas Ythe overload continues, thereby reversing the. direction of control or the mill feed. 'The delay switch ,HM may, .oi course, delay the time at which .such decrease in -feed will begin, so that. a .momentary overload may `not cause such decrease but a sustained overload will' have such eect. Thus, when `the overload disappears and contact |52 and disc 4|32 are `no longer in engagement, switch |56 will dropback to the lower contact `to start'the conveyor motor, and normal regulation ofthe feed to -Athe grinding mill in accordance with the -powerrequirements of the classier` `motor will `beginagain- `It-will be evident that' the foregoing control not only stops the conveyor belt' to protect thev grinding mill upon overload, but also removes the. cause of 'the overload by reducing the Afeed until :the time the conveyor :belt islagain started.

.It will again 'beca/ident that :the-.circuit .Eig-z. 5 4 mas/*be adapted. to eontrolfan :ovendow tuna mill, as distinguished from a `gnate.:type millilly' eliminating the action .of .switch 4.55,.,as. by leav 14 ing leads 132 `and i129 disconnected. .as fas leads. |53. mill .ore and water .feed directly in accordance with the classier power requirements lat :all times.

It will .be understood that .the grinding mill, and particularly a grate :type mill, is started iup through hand control, and ,then Aswitched over to automatic control after the mfnl and -classier are operating properly at the ldesired load. This is preferable because the classifier :operation should. `be stabilized before automatic :control effected, and also in the case of a -grate `.type mill, because the mill :overload circuit is respon` sive to a .decrease in the mill power requirements andrwhen a .mill is started, especially ii there is no ore in the `mill initially, the powerl requirements will be less than required to stop the conveyor belt, etc. Thus, .any tendency .for the overload relay to operate at .low initial load. is

obviated.

.The novel particle size `responsive device D .of this invention may includa-,as illustratediin Figs. 8 to l0, inclusive, a base |63 on which is :mounted afmotor Itl provided with speed reduction gearing H52 adapted to drive vdirectly one of shafts 58 on which rollers 5l are mounted. 'Ill-ie other shaft 58 is rotated in the opposite :direction by interengaging herringbone gears |53. vmounted on shafts 58, as in Fig. .10. The gears L63 permit slight movement of the rollers .51 toward .and away from each other .in accordance with the sizeof particles passing therethrough, lthe .rollers preferably being immersed in the pulp in .the overflow ,orY any other desired .zone of the classi- Pderer separator. The driven shaft 5S 4is journalled in a block itt, pivotally mounted by Ya pin or .stud |55 on a standard 235 attached to base |60, as in Figs. 9 and 10. As in Figs. .8 and -9, a relatively long arm itl is attached at one end to block |64 and vcarries on its opposite lend a Contact 1&8. The length of arm i'l `in com-parison with the 'distance between `the axes -of pin and driven shaft 53, provides a ratio ofv movement of contact |58 of three or more times the movement of the rollers 51 when diierent sized particles pass therethrough. `Contact |68, upon sufficient movement of the rollers toward each other, willengage a relatively xed lcontact |69, such contact being mounted upon an arm I'm pivoted at one end .for adjustment hy a Screw acting against the pressure of .a compression spring |72. As Willbeevident from Fig. 8., in case `the size. oi the particles passing be.- tween rollers. 5l increases, arm 61 will tend to he moved from the full toward. the dotted position of Fig. 8, thereby causing .contacts |63 and |69 toseparate. However, as soon-as the size oipar. ticles decreases suiCiently, the contacts |i8 and |69 will again engage upon pivotal movement of arm |161 .from `the dotted to the full position.

The control device D, as illustrated in Figs. 8 to .10., inclusive, may he placed so that the Ashafts 58 lr-nrtend vertically or horizontally er .at anyother desired angle into the pulp, either in a zone of the classifier or outside the classifier. in a receptacle or pipe connected with the .classilier overflow. Also, such device may, as in. Fig. 8, be connected with a control circuit, the elements which may be mounted in panel .allot 1, or Apanel P .oi'l'ig .Such circuit may include power leads i i5.. and. .ilnonnec' ed. tacoma. monv terminals ll'i and llt, respectively', and.. supplying `current to .motor 8.5i through.- wiresV f Maand it. Contact |Eilisco11nected-h5! a-wire 'Ihis will cause the regulation :of the l |8| with-wire |80, while contact |69 is Aconnected with the remainder of the circuit by a wire |82.

Elements of such circuit include an operating transformer |83, an indicating transformer |84 connected in parallel with transformer |83, and adapted to show on a gage |85 the size of particles passing through the rollers 51, a heating element |86 operated by transformer |83 and controlling a thermal switch |81, and a relay coil |88 in series with switch |81 for controlling a double throw switch |89 and thereby controlling the passage of current through forward and reverse windings and 16 of classiiier dilution water control motor 53. Transformers |83 and |84 are utilized to convert the voltage of power leads |15 and |16, which is suiciently high to operate motor |6|, to a lower voltage, such as 10 volts, to provide greater sensitivity in heating element |86 and in the indicating parts. One side of the primary winding of each transformer |83 and |84 is connected by wires |90 with wire |82 leading from relatively fixed contact |69 of the particle responsive device D. The opposite side of the primary winding of each transformer is connected with common terminal |11 by wires |9I, so that when contacts |98 and |69 are in engagement, current will flow through the primary winding of each transformer.

The secondary of operating transformer |83 is connected by wires |92 to heating element |86, so that the amount of current passing through the heating element and the cumulative effect thereof will correspond to the relative amount of time that contacts |68 and |69 are closed. Thermal switch |81 is provided with a relatively flexible, pivoted, or otherwise movable arm |93 and an opposite arm |94 comprising a loi-metallic strip adapted to bend in accordance with the heating thereof by element |86. Movable arm |93 of switch |81 is connected .by a wire |95 with common terminal |18 and the bi-metallic strip |94 of switch |81 is connected by a wire |96 with relay coil |88, the circuit through switch |81 and relay coil |88 being completed by a wire |91 connecting coil |88 with the other common terminal |11. Thus, coil |88 will be energized whenever switch |81 is closed.

Relatively fine particles passing between rollers 51 will not cause contacts |68 and |69 to open, While relatively coarse particles will hold the contacts open continuously, and intermediate particles will cause the contacts to open and close in accordance with the variation in size of particles, so that the transformers |8| and |82 will be energized continuously, intermittently, or not at all depending upon the size of particles. When the desired size range is passing between the rollers, the transformers will be energized intermittently, so that the cumulative effect of heating element |86 will be to maintain bi-metallic strip |94 in such a position that switch |81 will be opened and closed periodically by a timing cam |98 which is rotated at a relatively slow speed, such as 3 R. P. M. Thus, relay coil |88 will be energized for longer or shorter periods,

ordinary dial thermometer.

leads 54 and to forward winding 15 of motor 53, while with the upper Contact closed, current tends to pass through a wire 203 to the other outside lead 54 and to reverse winding 1S. The circuit through the windings of motor 53 is completed from lead 54 common to windings 15 and 16 through a wire 204 to a micro-switch 295, and thence through a wire 206 to common terminal |18.

Micro-switch 205 is utilized to interrupt periodically the flow of current to the windings of motor 53, an operating lever 291 thereof being intermittently contacted by the teeth of a cam 208, to open the switch for a short time interval, cam 208 being attached to or driven at the same rate as cam |98. The plurality of teeth of cam 208 cause the micro-switch to be opened a considerably greater number of times per minute than the switch |81 tends to be closed. Due t0 the intermittent opening and closing of the micro-switch, the motor 53 will not run continuously in either direction, but will open or close the valve controlling the classifier water supply by increments. Since the lower Contact of switch |89 is normally closed, a further advantage of the interruption of current to the motor windings by micro-switch 205 lies in the fact that in case switch |89 is being shifted from the lower to the upper contact, the circuit will normally be open if switch |89 is only momentarily closed, or when switch 89 closes, so that when microswitch 205 again closes, switch |89 will have been moved into engagement with the upper contact by energization of relay |80.

The foregoing also produces a slight time delay in activation of the control motor, which delay may be adjusted by a set screw 2 0 acting against a block 2| attached to a lever 2|2, in turn attached to the micro-switch, the micro-switch being mounted on a plate 2|3 pivotal about a pin 2| 4. By adjusting the angular position of the micro-switch by set screw 2|0, the length of time during which one of the teeth of cam 201 will depress leverl 206 sufficiently to close the micro-switch may be varied.

An additional adjustment may be obtained through a set screw 2|5 adapted to engage one end of a lever ZIB attached at the opposite end to a block 2|1 on which switch |81 and heating element |86 are mounted, and which is pivotal about a pin 2|8. Set screw 2|5 is adapted to move the end of lever 2|6 against a leaf spring 2|9, to adjust the relative position between switch 81 and cam |98 and thereby determine the amount of time the switch |81 will tend to be closed during operation.

For indicating the relative fineness of the particles passing between the rollers, the secondary of indicating transformer |84 is connected by wires 220 with a heating coil 22|, the coil surrounding one end of a closed tube 222 containing an expansible fluid adapted to actuate a pointer mounted in gage |85, as by a Bourdon tube, in-substantially the same manner as an Gage |85 may be calibrated in terms of particle size fineness, so that the average size of the particles will be indicated thereby, since the measurement indicated by gage |85 will correspond to the cumulative heating effect of current passing through coil 22| ,lwhich 'in turn, correepondsto :the relative portion of time during which the contacts |68 and-469 vare closed. i

The operation of the control device and cramaai? cuit of Fig. 8' may be described briefly as follows: Assuming that the lever 461 remains in the full position of Fig. 8, the particle size will be smaller than that desired, so that the contacts i553 and Hit will remain closed, thus causing current to ow through transformers 183 and 84. Through transformer itt, heating coil i136 will cause bimetallic strip l-Qil to bend toward flexible strip ld, thus causing switch 81 to be closed sooner than normal by cam itil and thereby energizing relay itlil and causing current `to be supplied through the reverse winding 'I6 the next time and each time micro-switch Zlivcloses. This will move the valve controlling the liow of Water to the classifier toward its closed position and thereby reduce the amount of water (the result desired when the particle size is less than nor-k mal).

When a suliicient number of larger particles being to pass between the rollers to cause contacts and iet to separate a sufficient portion of the time, the result will be that switch i8@ will alternate between the upper and lower contacts equally, thereby resulting in motor 53 remaining at a standstill in case the micro-switch 2635- is open at the times that switch 89 closes either contact, or will cause the motor 53 to run in the forward and then in the reverse direction an equal amount, intermittently, in accordance with the setting."4 of time delay adjusting screw 2li?.

If the average. size ofr particles passing between rollers 5l should become larger than de sired, contacts Hi8 and 69 will remain open all or a greater part of the time. This will reduce the amount of heat produced by. element |86, thus causing bi-metallic strip 94 to bend away from flexible strip E93, so that switch 87 will be open a greater` amount of the time during each revolution of cam Hi8. Consequently, relay itil will be energized during a smaller proportion of the time, so that switch 489 will remain in engagement with the lower contact a greater proportion of the time. As a result, current will be supplied the forward windings l5 of motor 5t a greaterA proportion of the time, and the dilution water control valve will be opened by increments, thus increasing the amount of dilution water supplied to the classier- (the result desired when the particles are larger than desired).

From the foregoing, it will be'apparent that the method and apparatus of this invention, including the various modifications described, are effective in controlling operations of the character described which may vary. widely. The principles of this invention find profitable application in wet grinding of ore, i. e., in which water is introduced into the grinding mill and a slurry or pulp consisting of water carrying more or less nely divided solid ore particles, as in suspension, is supplied to a. classifier in which additional, water may be added and larger particles are separated from thesmall'er particles by settlingv of the larger particles. Thek circuit may be so arranged that oversize particles are returned to the mill for regrinding and so that only particles of a predetermined size range are supplied to the next treatment step, such as a notation machine. However, the principles of this invention are applicable generally to grinding wherein a liquid. is added to the solid, either at the` grinding mill, or at the classifier or other type of separator, or at both ;,y and certain aspects of this invention `18 are applicable to other types of grinding, such as dry, and tol material other than ores.

It will be apparent that various changes and additional modifications may be made. For instance, the photoelectric cell control of the circuit of Fig; 4 may be utilized in place of either the cam disc control responsiveV to the mill load or the classifier load, in a circuit similar to that of Fig. 5, and also the cam control of the circuit oi'Fig. 5 may be substituted for the photo-electric controlresponsive to the mill load or the classier load in a circuit similar to that of Fig. 4.

In addition, a circuit including a condenser and' a varyingV capacitance for regulation, may be utilized for time delay in any of the circuits described; Also, the discs I3! and 32 of Fig. 5 may be connected in series in such a manner that when the load on the grinding mill reaches a predetermined value, disc 132 will regulate the water to, the classifier and decrease the same until the mill load is reduced.

It will further beY apparent that various other changesmay be made, all without departing from the. spirit and scope of this invention.

Whatis .claimed is:

l. Separation apparatus comprisinga classi'- er; means responsive to the sizeof particles of a predetermined zone of said classifier including a pairof rollers submergedlin said zone rotatable in opposite directions and movable toward andi away.l from each other in accordance with the size of particles passing between said rollersyand means actuated by said responsive means. for controlling the operation of said classilier.

2; In apparatus for controlling a grinding cire cuit which includes, a millv and a classifier, and responsive tothe size of particles in a predeterminedf-zone of'said classilier, a pair of rollers submerged in said zone` movable toward and `away from each otherin accordance with the size of particles passing between said rollers; means for rotating said rollers in opposite directions; and an electrical switch constructed and arrangedto 'be opened and closed in accordance with the distance between said rollers.

3. Apparatus for controlling a grinding mill and a classier in series, comprising electrically operated means for regulating the feed oi solids and liquid to said mill; electrically operated. means for controlling the dilution liquid supplied to said classier; a conveyor for carrying solids to saidmill; an electricmotor for furnishing motive power to said classifier; an electric motor for furnishing motive power to said mill ;v a transformer responsive to' the current drawn by said mill motor; a. transformer responsive to the current drawn .by'said classifier motor; a transformer responsive to the, voltage in the line to said classier motor; an angularly: movable disc in a ield produced by said mill motorv current transformer; asource of radiant energy and an electronic cell normally intercepting` such radiant. energy; an

interrupterattached to said. disc for regulating the amount of radiant energy intercepted by said cell upon angular movementV of said disc due to a. change inV the current passing to said mill motor; a relay operable by said electronic cell; a switch adapted to be opened and closed by said relay to stop and start said conveyor; a second source. of radiant energy and an electronic cell normally intercepting such radiant energy; an angularlymovable disc in a field created by said classiervmotor current and voltage transformers; an interruptor attached to said second mentioned disc for regulating the amount of energy intercepted by said second mentioned cell; a relay controlled by said second mentioned cell; a double throw switch controlled by said relay; a heating coil connected in series with each side of said switch; a thermal switch in operative proximity to each heating coil; a rheostat in series with said heating coils; a reversible motor for controlling said means for regulating the feed of solids and liquid to said mill; a cam for periodically closing said thermal switch; and electrical relays in series with said thermal switches for causing current to pass to the forward and reverse winding of said control motor upon closing of the respective switch.

4. Apparatus for controlling a grinding mill and a classifier in series, comprising electrically operated means for regulating the feed of solids and liquid to said mill; a conveyor for moving solids to said mill; electrically operated means for regulating dilution liquid supplied to said classifier; an electric motor for furnishing motive power to said classifier; an electric motor for furnishing motive power to said mill; a transformer responsive to the current drawn by said classifier motor; a transformer responsive to the current drawn by said mill motor; a voltage transformer responsive to the voltage in the line to said classifier motor; an angularly movable disc in a field produced by said classifier motor current and voltage transformers, said disc being in the form of a cam; a movable arm carrying a contact adapted to engage said disc; means for periodically moving said arm toward said disc; a relay coil adapted to be energized normally upon engagement of said disc and contact; a double throw switch normally closed in one position but adapted to be closed in the opposite position upon energization of said relay coil; a reversible motor for controlling said means for regulating the feed of solids and liquid to said mill and having forward and reverse windings connected respectively in series with the opposite sides of said double throw switch; a time delay switch in series with each said motor winding; a cam for periodically opening and closing said switch; a second disc in a field produced by said mill motor current transformer, said disc having an extending portion and being movable angularly in accordance with the power requirements of said classifier; a movable arm having acontact adapted to engage said disc and periodically moved toward said disc; a second relay coil in series with said disc and arm; a double throw switch normally in a first position and movable to the opposite position upon energization of said second relay coil; electrically operated means for driving said conveyor and controlled by said switch, so that when said switch is moved from said first position said conveyor will be stopped; and a connection between said switch and said first disc for energizing said first relay coil to reverse the control of solid and liquid feed to said mill when said second relay coil is energized.

5. Apparatus for controlling the operation of a classifier in accordance with the size of particles of a predetermined zone of said classifier, comprising a pair of rollers movable toward and away from each other in accordance with the size of particles passing between said rollers; means for rotating said rollers in opposite directions; an electrical switch constructed and arranged to be opened and closed in accordance with the distance between said rollers; means for regulating the supply of dilution water to Said classier; a reversible motor for controlling said regulating means; a pair of transformers having primary windings in series with said switch; a heating element in series with the secondary of each transformer; a heat responsive indicator actuated by one heating element; a thermal switch having a heat responsive contact carrying arm and a flexible contact carrying arm, said heat responsive arm being adapted to be moved toward and away from the flexible arm in accordance with heat produced by the other heating element a cam for periodically moving said flexible arm toward said heat responsive arm to close said contacts; means for adjusting the relative position of said thermal switch with respect to said cam; a relay coil in series with said thermal switch; a double throw switch normally closed in a first position and movable to the opposite closed position upon energization of said coil, said switch being in series with the forward winding of said reversible motor when in said rst closed position and in series with the reverse winding of said motor when in the opposite closed position; a quick-acting switch in series with a common lead of said motor windings; cam actuated means for periodically opening and closing said quick-acting switch; and means for adjusting the relative periods during which said quick-acting switch is open and closed.

6. Control apparatus responsive to the size of particles carried by a liquid, comprising a pail' of rollers immersed in said liquid and movable toward and away from each other in accordance with the size of particles passing between said rollers; parallel shafts for rotating said rollers in opposite directions; means for rotating one of said shafts; a pivotal mounting for the other of said shafts; a pair of engaging gears on said shafts; an arm attached to said pivotal mounting; an electrical switch constructed and arranged to be opened and closed in accordance with the distance between said rollers, one contact of said switch being mounted on said arm; and means for adjusting the position of the opposite contact of said switch to regulate the amount of separation of said rollers required to open said switch.

7. Apparatus for controlling a grinding circuit which includes a mill and a classifier, said mill being of a type in which the load and output each decrease upon an overload, comprising means for regulating the feed to said mill; means for regulating the feed of dilution liquid to said classifier; electrically operated means responsive to the power requirements of said classifier for controlling said mill feed regulating means; electrically operated means responsive to the power demands of said mill and associated with said electrically operated means responsive to the power requirements of said classifier for stopping said mill feeding means a predetermined period and reversing the regulation of Said mill feed upon an overload on said mill; and means responsive to the size of particles in a predetermined zone of said classifier inclusive of a pair of rollers submerged in said liquid and movable toward and away from each other in accordance with the size of particles passing between said rollers for controlling the flow of liquid into said classifier.

8. Apparatus for controlling a grinding mill and a classifier in series, comprising electrically operated means including a reversible motor for regulating the feed of solids and liquid to said mill; an electric motor for furnishing motive power to said classifier; a transformer responsive to the current drawn by said classier motor; means for causing successive reversals in small substantially equal increments of said reversible motor during normal operation of said mill and classifier; and electrical means operable by current produced by said transformer for increasing the increments in one direction to effect an increase in the feed to said mill upon a decrease in current required by said classifier motor, and for increasing the increments in the opposite direction to effect a decrease in the feed to said mill upon an increase in the currentl required by said classiiier motor.

9. Apparatus for controlling a grinding mill and a classier in series, comprising means for supplying basic water requirements to said classifier; means for supplying additional water to said classifier; electrically operated means, including a reversible motor, for regulating the feed of solids and liquid to said mill; an electric motor for furnishing motive power to said classifier; a transformer responsive to the current drawn by said classifier motor; means for causing successive reversals in small substantially equal increments of said reversible motor during normal operation of said mill and classifier; electrical means operable by current produced by said transformer for increasing the increments in one direction to effect an increase in the feed to said mill upon a decrease in current required by said classiiier motor and for increasing the increments in the opposite direction to effect a de crease in the feed to said mill upon an increase in the current required by said classier motor; means responsive to a condition of the pulp in said classifier; and means actuated by said responsive means for controlling said additional classifier water supply means.

10. Apparatus for controlling a grinding mill and a classifier in series, said mill being of a type decreasing in capacity upon overload, comprising electrically operated means including a reversible motor for regulating the feed of solids and liquid to said mill; a conveyor for carrying solids to said mill; an electric motor for furnishing motive power to said classifier; an electric motor for furnishing motive power to said mill; a transformer responsive to the current drawn by said 22 classifier motor; means responsive to the current drawn by said mill motor; means for causingr successive reversals in small substantially equal increments of said reversible motor during normal operation of said mill and classier; electrical means operable by current produced by said transformer for increasing the increments in one direction to effect an increase in the feed to said mill upon a decrease in current required by said classifier motor and for increasing the increments in the opposite direction to effect a decrease in the feed to said mill upon an increase in the current required by said classier motor; and means controlled by said mill motor current responsive to means for stopping the feed of solids to said mill for a predetermined interval upon an overload on said mill.

11. Apparatus for controlling a grinding mill as defined in claim 9 wherein said responsive means is inclusive of a pair of rollers submerged in said liquid and movable toward and away from each other according to the size of particles passing between said rollers and wherein the means actuated by said responsive means is actuated according to the amount of separation between said rollers.

JAMES A. ADAMS.

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

UNITED STATES PATENTS Great Britain ---2.--- Apr, 6, 1943

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