Crushing Practice and Theory

8/4/2019 Crushing Practice and Theory

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C R U S H I N G P R A C T I C Ea n d T H E O R Y

MILWAUKEE, "'.tISCONSIN 53201

07 RS()73.01


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C R U S H I N G P R A C T I C E. . a n d T H E O R Y... ~,~. ~

B y B ROWNE ll McGREWReprinted from ROCK PRODUCTS

ALLIS-CHALMERS

. Copyright 1950, 1951, 1952, 19B by Maclean-Hunter Publishing Co,UL . -~


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I N D E X IPage

Part I Historical summary . 3Part II Definitions used in crusher operation . 7

Part III Operating chorocteristics of various types of crushers . 8

Part IV Gyratory crusher concaves 11

Part V Gyratory reduction crushers - types and characteristics. . . . . . . . . . . . . . . . . . 13

Part VI Some factors which influence crusher performonce. . . . . . . . . . . . . . . . . . . . . . . 15..Part VII Jaw crushers, types and special uses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 18

Part VIII Crushing rolls and their use. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 22

Part IX Special types of roll crushers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 26

Part X Characteristics and performance of hammermills. . . . . . . . . . . . . . . . . . . . . . . .. 30

Part XI Crusher product curves and tables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Part XII Selecting the primary crusher. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 38

Part XIII Selection of quarry equipment for efficient crushing practice. . . . . . . . . . . . . . .. 41

Part XIV Comparison of gyratory and jaw crushers as primaries. . . . . . . . . . . . . . . . . . . .. 44

Part XV Selection of secondary and reduction crushers. . . . . . . . . . . . . . . . . . . . . . . . . .. 46

Part XVI Crusher operation in open and closed circuit compared.Advantages of surge bins and storage bins. . . . . . . . . . . . . . . . . . . . . . . . .. 49 I.:


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Crushing Practice and TheoryTHE EARLIEST U. S. patent on acrushing machine was issued in1830. It covered a device which, ina crude way, incorporated the drop-hammer principle later used in thefamous stamp mill, whose history isso intimately linked with that of thegolden age of American mining. Tenyears later another patent was issued,which comprised a wooden box,--con-taining a cylindrical drum-appar-ently of wood also--on which a num-ber of iron knobs, or hammers, werefastened; the expectation was thatthis drum, when revolved at about350 r.p.m., would shatter the rockfed into the top of the box. This de-vice, although it was conceived as animpact crusher and thus would rateas a forerunner of the hammermill,bore a somewhat closer resemblance tothe single sledging-roll crusher. Thereis no evidence that-either of theseearly inventors carried their workthrough to fruition.Eli Whitney Blake invented the firstsuccessful "mechanical rock breaker-the Blake jaw crusher patented in

1858. Blake adopted a mechanicalprinciple familiar to all students ofmechanics, the powerful toggle link-age. That his idea was good is at-tested to by the fact that the Blake-type jaw crusher is today the stand-ard by which all jaw crushers arejudged, and the leading machine ofthe class for heavy-duty primarycrushing service.

Early DesignsThe gyratory principle was thebasis of several rudimentary designs,

patented between 1860 and 1878, none

< tGofer 9yrotary breaker of 18aO.

Allis-Chalmers Manufacrurlmr Co., Los An-geles, Calif., district office.

By BROW NELL M cGREW '"Part I. Historical summaryof which embodie-d practical mechan-ical details-at least, not in the lightof our present-day knowledge of theart. ,!,he!l, in~!8_I~Jl...Ph!le~us.IN ,Gateswas granted a patent on a machinewhich included in its design all of theessential features of the modern gy-ratory crusher. The first sale of rec-ord antedates the patent by severalmonths, a No. 2 crusher, sold to theBuffalo Cement Co. in 1880. That wasthe first of several thousand gyratorycrushers which carried the name ofGates to the far corners of the earth.An interesting sidelight of theseearly days occurred in 1883 at Meri-den, Conn., where a coTii'esr~~'~~~tage(lbetween a Blake jaw crusher and aGates gyratory crusher. Each ma-chine was required to crush 9 cu, _y~.of stone, the feed-size and


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Power-Shovel LoadingThe steam shovel began to changethe entire picture of open-pit work-ing. With the stearn shovel came thereally "huge" No.8 crusher, with its18-in. receiving opening. Up to thistime the jaw crusher had kept pace

with the gyratory, both from thestandpoint of receiving opening andcapacity, but now the gyr~tory st~p-ped into the leading poaition, whichit held for some 15 years. Once the icewas broken, larger and larger sizesof the gyratory type were developedrapidly, relegating the once huge No.8 machine to the status of a second-ary crusher. This turn toward reallylarge primary crushers started justa few years before the turn of thecentury, and in_UIlO crushers with48~in.. receiving openings were being-built.

48-inch All is-ChalmoF$ gyratory dovelopedin 1910.Along about this time the jawcrusher suddenly came back to lifeand stepped out in front with a greatcontribution to the line of mammoth-size primary crushers: the 84- x 60-in.

machine built by the Power & Min-

ing Machinery Co. for a trap rockquarry in eastern Pennsylvania. Thisbig crusher was followed by a No, 10(24-il1. opening) gyratory crusher forthe secondary break. Interest createdby this installation reawakened theindustry to the possibilities of thejaw crusher as a primary breaker,and lines were brought up-to-date toparallel the already developed gyra-tory lines.

Tom Edison's ContributionAlthough his machines never came

into general use in the industry,Thomas A. Edison ranks as a pio-neer in the development of the largeprimary breaker j in fact, Edison iscredited with the promulgation of avery interesting and constructive bitof reasoning, which was the basis ofhis development. Concerned at thetime with the development of a de-posit of lean magnetic iron ore atEdison, N. J., he was using a numberof the small jaw crushers then avail-able for his initial reduction. Realiz-ing that to concentrate this ore at a. cost to permit marketing it competi-tively meant cutting every possiblecorner, he studied the problem of min-ing and crushing the ore as one of thesteps susceptible of improvement.In approaching the problem, Edi-son reasoned that the recoverableenergy in a pound of coal was approxi-

mately equal to the available energyin one pound of 50 percent dynamite;but the cost per pound of the dynamitewas about 100 times that of the coal.Furthermore, a large part of the dy-namite used in his mining operationwas consumed in secondary breakingto reduce the ore to sizes that thesmall primary crushers would han-dle. The obvious conclusion was thatit would be much cheaper to break thelarge pieces of ore by mechanicalrather than by explosive energy.With that thesis as a starting point,he set out to develop a large primary

breaker, a development which cul-minated several years later in thehuge and spectacular 8- x 7-ft. Edi-son rolls. A description of the actionof this machine will be found in alater section of this series. Duringthe early years of the present centurythese giant machines created consid-erable interest, and several were in-stalled in this country. However,they never became popular, and inter-est swung back to the more versatilegyratory and jaw types, Edison rollswere also developed in smaller sizesfor use as secondary and reductioncrushers. In his own cement plantEdison used four sets of rolls operat-ing in series to reduce the quarry-runrock to a size suitable for grinding.

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Other Types of PrimariesDuring the same years wherein the

industry was concerned with develop-ment of larger and still larger pri-mary crushers, another member of thefamily was born: the single, sledging-roll crusher. The Allis-Chalmers Co.entered this field in 1911, building twosets of 36-in. dia, x 60-in. face single-roll crushers for the Fairmount, 111. ,flux limestone plant of the Caspar-isStone Co; .Taking' the. name of itsproving ground, this machine waschristened the "Fairmount crusher."The machine quickly achieved a highdegree of popularity, and although itsfield of application is relatively lim-ited. quite a number of them were in-stalled for primary crushing service.The line was expanded to includesmaller sizes, as well as the big 60-x 84-in. machine.Development of concentration andcyanidation in the mining industrycalled for finer crushing than wasfeasible in the gyratory or jaw crush-ers then available. This requirementwas met for a number of years by the

double smooth-face crushing rolls,originally known as "Cornish" rolls.'As the mining industry during the

(60 in. " 84 in. FainnDunt lingle roll crusher.

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Superior McCully


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A gyrotory of recent design is this 42inchSuperior primary crusher being readied forshipment to Africa.at the time by the various crusherbuilders. One of our own early ex-periments along these lines was theinstallation of special concaves in sev-eral of the No. 4 crushers in theThornton plant mentioned above toreduce the crushing angle. The re-sults were encouraging enough tostart a more thorough investigationinto the design of crushing chambers.The disc crusher was one of the

first special machines brought out forfine crushing, and for several yearsthis new type enjoyed a wide popu-larity. The single toggle jaw crusherwas developed in larger sizes, and be-cause it could be operated at closersettings than similar sizes of theBlake type, found quite a field of serv-ice in small plants as a reductioncrusher.

Fine CrushingThe first .impcrtant development in

the move to adapt the gyratory crush-er to fine crushing was the debut ofthe Superior McCully fine-reductioncrusher, which was brought out bythe Power & Mining Machinery divi-sion of the Worthington Co. a fewyears before the Allis-Chalmers Co.took over tltese crushers. This ma-chine was designed along lines iden-tical to those of the standard SuperiorMcCully crusher with one importantexception; instead of the orthodox ta-pered top shell of the standard ma-chine, the new crusher was fitted witha cylindrically bored shell, the con-caves being vertical and reversible.The crushing head was flared cor-respondingly, this additional flare re-sulting, for a given size of receivingopening, in a head of much larger di-ameter. i'or example, whereas thestandard crusher with lO-in. receiv-ing opening has a head diameter ofabout 27 in. at the bottom, the cor-responding dimension for the lO-in.reduction crusher is about 40 in. Ec-

centric speeds were increased, andthrows were adjusted for operationat close settings. Originally these rna-chines were fitted with struight-faceconcaves; later the concaves were ta-pered at both ends to distribute thewear better; eventually non-chokingconcaves became standard equipment.It would be difficult for us, and te-dious for the reader, were we to at-tempt to chronicle all of the develop-ment work, some of it successful andsome not, which went on in the decadefo!1owing the end of the first WorldWar. One important contribution tothe art was the high-speed, direct-con-nected Newhouse crusher, which in-troduced a new principle of crushingfor cleanness and uniformity ofproduct.Some 20 years ago the principle of

the widely flared crushing head wascombined with some other new andradical departures from current prac-tice, and the Cone crusher entered thereduction crushing field. Two inter-esting innovations incorporated in thismachine were (1) an unusually largethrow and (2) "a spring loaded and ad-justable crushing bowl.

Special Gyratory ConcavesAbout the same time that the cone

crusher appeared, at least three dif-ferent builders applied the principleof curved-profile crushing chambers,certainly the most important and far-reaching improvement in crusher de-sign that had been made for manyyears-possibly the greatest since theinception of the gyratory type. In our

own case this development took theform of "non-choking" concaveswhich could be installed in any of th~existing models of gyratory crusherwithout any change in the shape ofthe crushing head. The type quicklybecame standard equipment in our re-duction crushers, the Newhouse andSuperior McCully fine reduction ma-chines. But of equal importance wasthe fact that the efficiency of manyhundreds of existing standard ma-chines, of an ages and styles, wasmarkedly improved at a very nominalcost by substituting these new curvedconcaves for the old straight-faceliners.All crushers developed up to thistime, except the very large machines

of the gyratory type, were providedwith some means of adjustment tocompensate for wear or to adjust forvariations in product size. The rangeof adjustment in most machines wassmall; adjustments in most cases re-quired shutting down the machine. Inthe gyratory types, after a certainamount of adjustment was made itwas necessary to reset the concavss.This did not constitute any seriousdrawback in primary and secondarycrushing service, because wear wasslow generally and the exact settingof discharge opening was not a criticalmatter. With the increase in demandfor fine crushing the situation alter-ed; it was necessary to set crusherscloser and to maintain the settingwithin closer limits. It-was imme-diately apparent that a crusher witha large range of adjustment, without

Two slx-Inch Superior McCully fine reduction crushers installed in the 1920's.

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the necessity of resetting the wearingparts, would be very desirable; as amatter of fact, the first cone crushersbrought out incorporated such a fea-ture, which proved to be very popular.

Special Setting AdjustmentOur own engineers studied this

problem along the lines of combiningwide range with speed of adjustment.The result of this study was the in-troduction of the idea of supportingthe mainshaft on an oil-operated hy-draulic jack. This idea was first in-corporuten in a special model of theNewhouse crusher, designated as the"Oil-Adjusted" crusher. A few ofthese machines were built and testedunder severe operating conditions,and the line would undoubtedly havebeen developed extensively had notthe "quiet" period through the early

1930's effectively checked the demandfor new crushers.We had not lost sight of the pos-

sibilities of this method of adjustment,however, and when -conditions showedsigns of improvement we were readyto incorporate the oil adjustment fea-ture into an entirely new machine, amachine which was to be designed inall its proportions specifically for re-duction crushing, with a scientifical-ly proportioned crushing chamber,"quick-set" adjustment, safety releasefor tramp-iron protection, and highspeed operation for maximum capacityat close settings. This machine, the"Type ~,:' was brought out early inHI3R . .Giant GyratoriesWeleft the big primary gyratories

back among the misty memories of thefirst World War. As a matter of fact,

there is not a great deal more to tellso far as these machines are concern-ed, except for one more big jump intop size. This machine, which hadreached a 48-in. receiving opening by1910 and 54-in. shortly thereafter,was developed a few years later intothe 60-in. size.Our own first 60-in. machines werebiiTIt in1926"-27;aiid-these crushers-two oCwhTcIl\Vere installed in aSouth American copper mine-set aworld record in weight and propor-

tions which still stands. These giantmachines, weighing about 500 tonseach, and rearing their steel frames tothe height of a two-story building, areindeed a long step forward from thefirst tiny No. 2 Gates crusher thatcame out of the little shop on Ran-dolph Street in Chicago some 60-oddyears ago.

Part II. Definitions Used in Crusher Operation

As IS THE CASE in every line of in-dustrial activity, a number of ex-pressions, peculiar to operation ofrock crushing plants, have come intocommon usage among crusher design-ers and operators. Inasmuch as theseterms are used rather loosely, andwith a considerable degree of freedomas to their exact meaning, it is desir-able to define a few of the more im-portant ones to make clear the sensein which they will be used in thiswork.

DefinitionsBlocking means the blockading ofthe crusher receiving opening by apiece of rock or ore that is too largeto enter the crushing chamber in any

position.Bridging means the blockading ofthe receiving opening by one or morepieces, any of which are small enoughto enter the crushing chamber, butwhich are prevented from doing so,either because they fall so as to spanthe opening, or so that they mutuallyblock each other from entrance.Choking means a complete, or prac-tically complete, stoppage of the down-ward flow of material in the crushingchamber. It may be the result of anexternal condition, such as a "back-up" of material occasioned by an ob-struction in the discharge chute, inwhich case choking is followed bypacking in the crushing chamber. Orchoking may be the result of a con-dition existing within the crushingchamber, such as too close a dischargesetting, too many fines in the feed, orsticky material. When so caused, pack-ing precedes-and brings about-thechokeup.The choke-point in a crushing cham-ber is that level in the chamber where

the capacity of the crusher is a mini-mum; that is, it is the bottle neck ofthe crushing chamber. It follows thatit is the point where choking is mostlikely to occur-particularly so if the.choke is promoted by a condition ex-isting within the crusher. Note thatthe existence of a choke-point doesnot imply that choking will necessarilyoccur; in fact. as will be explainedlater, all compression-type crushershave a choke-point at some level with-in the crushing chamber..' ~ Choke-feed implies a completelyfilled crushing chamber (or as full asthe design will permit), with a suffi-cient head of material above the receiv-ing opening to keep the crusher fullcontinuously. This contrasts with reg-ulated-feed, which implies that the flowof material to the crusher is throttledto a point somewhat below the capaci-ty of the machine. so that the crusheris never completely filled.-;Packing refers to a compacted orcompressed condition of the materialin the crusher, characterized by a com-plete or nearly complete absence ofvoids. Any condition which tends toretard the free movement of mate-rial downward through the crushingchamber tends likewise to promotepacking.Packing also is used to describe thebuilding up of fine, sticky material onthe diaphragm of a gyratcry crusher,or In the discharge chute below anytype of crusher.Ratio-or-reduction. Precisely, thisterm refers to the size of the largest

cube that the crusher will receive,divided by the size of the largest cubethat it will discharge. Actually, weare not dealing with exact cubes whenwe crush rock or ore; therefore it ismore convenient, at least when dis-

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cussing crushers of the compressionfamily, to base the ratio-of-reductionupon the dimensions of the crushingchamber.In crushers of the jaw and gyratorytypes the ratio-of-reduction is taken tomean the 'raiio- o - r the receiving open-ing (measured from the top of themovable member to the top of the sta-tionary member), to the dischargeopening, which may be "open side" or"close side," depending upon the typeof crusher, as will be explained later.For crushing rolls, either single Ordouble, the ratio-of-reduction is theratio of the greatest dimension thatthe machine will nip, to the dimensionof the discharge setting.The hammermiU is not quite soeasily gauged, because of the wide dis-parity in the size of product possiblewith anyone grate-bar spacing. The

only fair basis of comparison withother types, therefore, is to base theratio upon the size of the largest cubethat the mill will receive, divided bythe size of the product, this product tobe gauged by the same standards ofscreen analysis that are commonlyused to judge the products of the othertypes.

Crusher ClassificationsCrushers may be diVided into threegeneral classes, with. respect to themanner in which they'do their work:

(1) Pressure Crushers. This categoryembraces the several types of gyra-tory crushers and jaw crushers, aswell as the double crushing rolls, witheither smooth or corrugated shells.(2) Impact Crushers. This division isrepresented chiefly by the variousstyles of hammermill; also by the cagetype disintegrator. (3) CombinationImpact and Sledging Crushers. In this


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class we have the single or doublesledging roll crushers. An example ofthe former is the Fairmount crusher,of the latter, the Edison roll crusher.Some further subdividing and quali-fication might be applied to these gen-eral classifications, but these, for the

Imost part, are not of particular impor-tance. Pressure crushers, for example,may be divided into two sub-classes:the reciprocating, and the continuous-pressure, types. The gyratory and jawcrushers come under the first category,the crushing rolls under the second.Strictly speaking, the gyratory motionis not a reciprocating one, but it is so

with respect to any vertical radialplane through the crushing chamber;therefore it is convenient to view itin that light. Some roll crushers,notably the light coal crushing type,have more of a tearing action, as con-trasted to the heavy sledging per-formance of such machines as theFnirmount crusher.

,Part III. Operating characteristics of various types of crushers

IOIJR DlSCUSSIONS of the operatingcharacteristics of the various crush-er types we shall avoid, as far as pos-sible, burdening the reader with me-chanical details, which are coveredquite thoroughly in catalogues andbulletins printed for that purpose. Abrief general description of the es-sential features of each type WIllserve to clarify the action, for thosewho are not familiar with crushingequipment.Fig. 1 shows a sectional view of atypical gyratory crusher. This typE'of machine is, by virtue of chrono-logical priority, known as the "stand-ard" gyratory crusher. Although itincorporates many refinements in de-sign, . it. is fundamentally. the samecrusher that first bore the name of"gyratory"; its crushing chamber isvery much the same shape; the motionis identically the same, and the meth-od of transmitting power from belt tocrushing head is similar. Itis an in-teresting fact that the same similarityin essential features of design existsin the case of the "standard," orBlake type, jaw crusher, which issomething in the way of a tribute tothe inspiration and mechanical abilityof the men who originated these ma-chines.Essentially, the gyratory crusherconsists of a heavy cast-iron, or steel,frame which includes in its lower partan actuating mechanism (eccentricand driving gears), and in its upperpart a cone-shaped crushing chamber,lined with wear-resisting plates (con-caves) _ Spanning the crushing cham-ber across its top is a steady-rest(spider), containing a machined jour-nal which fixes the position of theupper end of the mainshaft. The ac-tive crushing member consists of themainshaft and its crushing head, orhead-center and mantle. This assem-bly is suspended in the spider journalby means of a heavy nut which, in allbut the very large machines, is ar-ranged for a certain amount of verti-cal adjustment of the shaft and head.At its lower end the mainshaft passesthrough the babbitted eccentric jour-nal, which offsets the lower end of theshaft with respect to the centerline ofthe crusher, Thus, when the eccentricis rotated by its gear train, the lower

end of the mainshaft is caused to gy-rate (oscillate in a small circularpath), and the crushing head, likewise,gyrates within the crushing chamber,progressively approaching, and reced-ing from, each element of the cone-shaped inner surface.The action of the gyratory crusher,and of the other member of the re-ciprocating pressure family, the jawcrusher, is fundamentally a simpleone, but as will be seen a great dealof thought and some very progressiveengineering has been expended uponthe design of crushing chambers toincrease capacities and to permit theuse of closer discharge settings forsecondary and fine-reduction crushing.'Referring to the table, alwaysavailable from the manufacturer,it will be noted that standard gy-ratory crushers are manufactured incommercial sizes ranging from 8 in. to60 in. receiving openings, Capacities

are listed, for minimum and maximumopen-side discharge settings, in shorttons per hour, and the horsepower re-quirements for soft and hard mate-rials are listed for each size. The ca-pacities, and the minimum settings,are based upon the use of standard(straight-face) concaves.

Rigidity P rime E ss en tia lTo stand up under the extremely

rugged work of reducing hard andtough rock and are, and in doing so tomaintain reasonably true alignmentof its running parts, the crushermust necessarily be of massive andrigid proportions, rigidity being ofequal importance to ultimate strength.Regardless of the tensile strength ofthe metal used in the main frame, topshell, and spider, these parts must bemade with walls and ribs thick enoughto provide this rigidity. Therefore itis practicable to use close-grained cast

Fig. 1: Sectional view of Superior McCully gyratory crusher.

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iron, and special high-test mixturesof cast iron, for these parts if themachine is intended for crushing softor medium materials. When very-hardand tough materials are to be crushedthe machine is usually strengthenedby substituting cast steel in one ormore of its parts.Wearing parts in the gyratory

crusher may be either chilled cast ironor manganese steel, depending on thecharacter of the material to be crushedand the particular class of service forwhich the machine is intended. Stand-ard crushers, in the small and mediumsizes, are customarily fitted with chill-ed-iron head and concaves for crush-ing soft and medium limestone andmaterials of similar hardness andabrasiveness, because its relativelvlow first cost and excellent wear-ingqualities make it the most economicalmaterial to usc when the service is nottoo ~evere. Manganese steel, whichcombines extreme toughness with un-surpassed wear-resistance, is the uni-versal choice for crushing hard, toughrock regardless of the class of serviceor type of crusher. Even though therock be quite soft and non-abrasive.it is general practice to use man-ganese steel concaves in the largersizes of primary crushers because ofthe shocks attendant upon handling-large and heavy pieces of rock.

Straight- Face ConcavesWhen used for primary or ccarse

secondary crushing service, the type?f crusher we have been describingIS usually fitted with the style of con.cave shown in Fig. 2. These are knownas "standard" or straight-face con-caves, which have been the standardtype of liner ever since the gyratorvcrusher came into popular use. Th~distinguishing features of this typeof concave are: ".(1) The receiving opening, for any

given size of crusher, is at amaximum.(2) The choke-point (point of mrm-mum capacity) is at the dischargeopening.(3) The ratio of reduction varies fordifferent sizes, ranging from

about 5.35 to 7.6, and averagingabout 6 V a for all sizes from 8 in.to 42 in. inclusive. These ratiosare based upon the use of stand-ard-throw eccentrics.

Usually the primary crusher is se-lected on the basis of (1) size of re-~ivi]1g_opetling and (2} capaCity:Mo:r::_e_9.ften-han __ot, .the gyratorycrusher with sufficiently Targe 'receiv-ing opening will have ample capacityfor the job. Furthermore, the per-missible minimum discharge settingfor the standard gyratory is usuallysmall enough to make an acceptablesecondary feed. For these reasons thestandard crusher is, as stated before,

usually supplied with straight-faceconcaves for primary crushing service.T~ere. are some secondary crushingapplications where maximum receiv-:

ing opening, for any given size ofmachine, is desirable. For such appli-cations straight-lace concaves are in-dicated, provided of course that thecrusher so fitted will have sufficientcapacity for the job in hand. On theother hand, most secondary-cand someprimary-crushing jobs require maxi-mum capacity and maximum ratio ofreduction, rather than maximum re-ceiving opening. The standard gv-ratory cr~she.r has been adapted f;rsuch applications by the introductionof an interesting and importantchanze in the shape of its crushingchamber, regarding which we shallhave more to say under the subject of"non-choking concaves." .There ar~ of course certain limitingfactors which govern the proportions

of the crushing chamber in thesestandard gyratory machines. One ofthese, the ratio of reduction whichcan safely be made in any given ma-chine, has already been mentioned. Asthe ratio of reduction is simply theratio of receiving opening to dis-charge opening, it follows that thislimitation is directly related to thesafe minimum discharge setting. Allcrusher manufacturers establish whatare considered to be safe""minimum-settings for the different sizes ofcrushers of their manufacture. Pub-lished capacity tables for gyratoryand jaw crushers generally list ca-pacities at settings .down to and in-cluding these minimum openings. Thepractice for gyratory crushers is topredicate these minimum settings uponthe use of standard-throw eccentrics'Le., throws which experience ha~proven to be right for each particu-lar size of crusher.

Crusher SettingsThe actual minimum safe scttirurwill vaiy somewhat, for any give~machine, depending upon the charac-

ter of the material. the amount of finesin the feed, and whether the crusher isbeing operated under choke-feed orregulated feed conditions. Itis possi-ble, when all conditions are favorableto operate gyratory crushers, withstandard throw eccentrics at smallerdischarge settings than a~e indicatedby the published tables. Generallyspeaking, however, it cannot be con-sidered good practice to do so; and

, any experimentation along these lines,,( should be accompanied by a close, check on the power consumption, tomake sure that the crusher is not beingoverloaded,

When it is necessary, or desirable,to operate a gyratory crusher at dis-charge settings below the minimumstandard, the safe procedure is to fitthe machine with a reduced throw ec-centric. The crusher manufacturer

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I'I C RU SH ER H EA DI .

' O PE N S ID EC LO SE S ID E,1 ,

i !, I I -!='w...~- CHOKE.m-~-~~=~d-,l POINT

Fig. 2; Section through a vertical plane in thecr ..shing chamb.r of a gy.olory .... sher

will be able to advise the operatorabout these special throws for rna-chines of his make.If a reduced throw eccentric is in-stalled, the capacity at any given set-ting will drop off approximately in di-rect proportion to the reduction inthrow. In some cases it is possible tocompensate, partially at least, for_thisdrop-off by speeding up the machine:Here, again, the manufacturer will beable to advise the operator as to themaximum safe speed for any particu-lar crusher of his line.Another factor which governs the

proportions of the crushing chamberis the maximum permissible angle be-tween the two crushing faces. Thisalso is subject to a certain amount ofvariation, depending upon the char-acter of the material, and upon thesize of the machine. Crushing anglesmay vary between the approximatelimits of 22 and 30 dez. in a line ofs!andard gyratory crushers. Itis pos-sible to use larger angles in the largersizes of crushers be-ause the greaterweight of the individual pieces of ma-terial tends to minimize slipping. Fur-thermore, in these large machines adifference of a few degrees in thecrushing angle makes a considerabledifference in the height, weight, andcost of the crusher.It is obvious that the coefficient-of-

friction of the material to be crushedhas a very direct. bearing upon themaximum permissible crushing angle.So~e slippery m~terials, even thoughquite soft, requtre special reduced-angle crushing chambers. In the stand-ard gyratory crusher this is accom-plished very simply by increasing thethickness of the coneaves at the tapand tapering them down toward th~discharge; in the jaw crusher thechange is generally made by insertinga wedge-shaped filler behind the liner


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~)latl~Son the movable jaw.For a given coefficient of friction.t he harder the material is, the smallerwill be the maximum permissibleerushinrr angle. Extremely hard, toughmaterials even thou qh their coefficient"i fri{'tiun be fa ir lv hig-h may requi rr-3pecial reduced crush ing angles top revent excassive slipping. Anyonewho hus seen hard granite bouldersshoot nut of a i';~,T3.tory or jaw crush-r. ')r has \\'atehcd a wide-arur!cr-rshcr at work on hard zranite ort ra n rock. has had a visual demon-.st rar ion of this physical fact.,\ ce rt a in amount of slippaee oc-(~\11'" in all pressure type crushers, re-ro;ardl,'ss of how small the crushinganro;k mnv be (that is. within prac-ticahle design Iimitsj, especially intilt) lower part o f the crushing cham-ber .dwrr the pi('cps are smaller and! i,-,hr'>I', T'nll"I' norma l ollerating' e-m-diti"I1:; thi~ t('nd('n'~y is c()\lntp.ra~~pdbv t:l" ,.\,,'i~ht , ) 1 ' material in the u nne rP~l't or the chamber. Another me'thodof corn nonsa tion is to "break" thean~l{' of the lower tier of concavcs ton rovide a rno rr- fa vorahle crush ingani.!:lp in this zone.

Crushing ActionFig. Z, showimr the "standard gyra,tory with strail.\'ht concavcs." is a sec-riou t h rou-r h an. vcrt ical, radial planein ~lll' t1'lIshing chamber of one of theint('!'))wdiate s izes of the crusher, IIIord(~r to u nde rata nd the crushing ac-' :011 i:l;~lCh a chamber it is helpfulto pnl1.,itie:' the process as though,~a('h ~ten took place in an orderly, and"id!'al" fashion, It is hardly neces-sa rv to add that the action never does

take piaee in just that fashion; never-tl1


12/53

t

F IG 2 in part I II illustrated the crosssoet ion of a typical gyratory crusher.Fig. :1 illustrates the same crushingch:lmber we huve been considering,

xcept that, ill place of the straight-face concave the non-choking type hasbeen substit utr-d, For the sake of di-rect compmisnn we have shown thesame discharge setting in both dia-grams, although a closer setting wouldbe perm issible [or the non-choking ar-rnng emunt.Inasmuch as the eccentric-throw is

the same, and the concaves in the up-per part of the chamber parallel thoseof the standard type, it follows thatthe successive drops of the materialin this zone would be similar. This istrue down to line 13. Then we note adifference in the new diagram; thedrop per stroke increases much morerapidly than in the former case until,at stroke 16, the line has arrived atthe discharge level.The choke-point has been raised to

point 13-14, instead of being at the dis-charge level. From the choke-point, ondown to the discharge level, each suc-cessive volume is greater than volumet3-14, and greater than the volumeimmediately preceding. Therefore, theshape of the crushing chamber in thezone below the choke-point is favorableto choke-free operation. Under certainconditions choking can occur in thiszone, however, as will be pointed outlater.The ratlo-of-volume-reduction be-

tween volumes 0-1 and 18-19 in the fig-ure previously discussed is obviouslygreater than the ratio between vol-umes 0-1 and 13-14 in the non-chokingdiagram; actually the ratio in the for-mer case is about 4 :1, and in the lat-ter about 1.75:1. Therefore, if weassume an equal percentage of voidsin the feed for both cases, it is ap-parent that the non-choking arrange-ment will not, when the choke-pointis reached, have compacted the mate-rial to as low a percentage of voidsas the straight-face chamber. Also,the actual volume of 18-19, in thestandard chamber, is substantiallysmaller than that of 13-14 in the non-choking chamber. Inasmuch as thesevolumes pass the choke-point in thesame time-period, the capacity throughthe 13-14 zone is obviously the greaterof the two.These two facts account for the su-

perior performance of the standardgyratory-s-and the standard jaw-crusher when fitted with non-chokingliners. As compared with the straight-face concaves, the salient features ofthe non-choking variety are:(1) They permit the use of smaller

Part IV. Gyratory crusher concaves

discllarge settings in any given sizeof crusher.(2) Capacities are considerablyhigher, particularly so in the rangeof finer settings.(3) Wear of crushing head and con-caves is more evenly distributed in

the lower part of the crushing cham-ber.(4) The receiving opening is re-duced, the amount of this reductiondepending upon the crusher setting,and upon the degree of curvature ofthe concave faces.(5) The ratio-of-reduction in the

different sizes of standard crushersvaries from about 6.75 to !l.5, aver-aging about 7.!l for the sizes men-tioned previously. This is also basedupon the use of standard-throw eccen-trics.(6) The crusher product is moreuniform, and will generally containless fine material.(7) Power requirements are very

definitely in favor of the non-chok-ing concaves.It is obvious that this type of con-cave has some very desirable features.

As a matter of fact, the developmentof scientifically designed, curved pro-file crushing surfaces is probably themost important single improvementever made in pressure-type crushers.The relative performance of non-chok-ing concaves in the standard gyratorycrushers is graphically illustrated inTable I. This table contains a com-plete list of capacity ratings for Suoperior McCully crushers, from 8 to42 in. inclusive, for straight-face, andnon-choking, concaves.This table also lists "Modified

Straight Concaves." These are con-caves having a lesser curve at the bot-

Fi9. 1: Standa rd gyratory ....Ith non -chokingconcave

11

- 1Prim,uy Hydro .. , gyratory tr~,her with

nGn-(hDKing 'QncaVe'li~tom partly approaching the non-chok-ing concaves but having the choke-point at the bottom of the chamber.They are used where the open-side set-ting is large enough to permit the useof straight concaves, but where someof the advantages of non-choking con-caves are desired. These include in-creased capacity, more uniform sizingand the distribution of wear to pre-vent "belling" of the head.Itshould be made clear at this pointthat these concaves, although theybear the title of "non-choking," do notafford absolute insurance againstchoking. In that respect the title isperhaps a trifle misleading. The veryfact that a choke-point exists at allwithin the crushing chamber makes itevident that choking can occur. Onthe other hand, they do minimize thedanger of choking, and their generalcharacteristics are such that their de-scriptive title is not too far afield.

Character of ProductAmong the salient features of the

non-choking concave, we mentionedthe character of the product. So farwe have been dealing with crusherswhose eccentric speeds are low enoughto permit the material to fall, witheach receding stroke of the activecrushing member, the full distance al-lowed by the close- and open-side phys-ical proportions of the crushing cham-ber, regardless of the shape of the con-caves. In such crushers, the maximumone-way dimension of product par-ticles is governed by the open-sidedischarge setting; therefore it is cus-


13/53

tomary to predicate both product andcapacity upon that setting. Actually,the sizing is done by the closing strokeof the crusher on the material in thezone just above the discharge opening;in other words, upon that materialwhich will be discharged during thenext opening stroke. It follows thatthe shape of the chamber immediatelyabove the discharge opening must havesome influence upon the product gra-dation, and we should expect thatnon-choking concaves, by virtue of thesmaller angle they afford betweenhead and concaves in , the dischargezone, would make a more uniform-and somewhat finer-product thanstraight concaves. This is true, and itis an important and favorable featureof these concaves, particularly so asapplied to the production of cornmer-cial crushed stone.One more word about the characterof product. As the percentage of voids

decreases in the crushing chamber,the amount of very fine material pro-duced at each stroke is apt to increase,due to the crushing of particlesagainst each other as they becomemore and more closely packed. There-fore the ratio-of-volume-reduction hasa definite influence upon the amountof fines in the crusher product. Thisis especially true of friable materials.On such materials the substitution ofnon-choking concaves for those of theconventional type will usually resultin marked decrease in the percentageof extremely fine material in thecrusher product.From the standpoint of power con-

sumption, the best machine is the onethat does the least amount of unnec-essary work. A certain amount of non-productive work is expended by anypressure-type crusher in "pushingaround" material which is alreadysmall enough to pass the dischargeopening but which is prevented fromdoing so because the particles aretrapped in the surrounding body ofmaterial.As the percentage of voids decreasesthe number of such trapped particlesincreases, the amount of non-produc-

tive work likewise increases, and thematerial becomes harder to move asit becomes more compacted. Actually,there is some work being accomplishedon this small material which mightproperly be classed as productivework; but, from the viewpoint of thecommercial crushed stone producer atleast, it is undesirable work: the at-tritional production of fines, men-tioned in the preceding paragraph.The clean-breaking crusher is the eco-nomical crusher, both from the stand-point of power consumption, and gen-eral wear and tear; And, because thenon-choking concaves make for clean-er breaking, they benefit the crusherin both of these respects. At com-parable discharge settings the powersaving may run as high as 20 percent,

Seclional vl.w of Sup.riot 9,ralory crusher,PRIMARY CRUIH

...,_.~)0.)Oj$--$ : 100 1 : Y . ' ":J.6!U lO G Y o "36$j 1040 I"36- JO O 1!4- 4 2 " ' " l., '".~ ))0 I!(" . o s M)(I 1 1 - \ '" I ' . . :1 00 ,"" ' - 7 " > O J ' I { "-41N . . . 'W"'17" 500 I v . -$ 4 . , , ,$4.7...

.US .510 610 610610 665 7m no15 0 1 93 , 1 , : 5 100 (1 -

0 9-11) 1 060 1110 tllO

To!tle I: Cr... her copocltl... !tol.d "n 'u n ,o"tlnllol.l. ieecl of quarry or ",I ..e-..." mot.rla 1weighing 100 Ib, per CII'. ft. _heel

12


14/53

P~ut V. Gyratory reduction crushers-types and characteristics

I THE PRECEDING pages we COycred briefly the development ofvarious types of reduction crushers ofthe gYl'atory family. Fig. 4 shows amodern gYl'utory reduction crusher,which introduced. the cylindrical topshell, flared head, lind reversible can-cans. Even with the older style ofstraight cnncavcs, with which this ma-chine was originally fitted, it repre-sented a distinct step forward in sec-ondary crusher design, and the laterintroduction of non-choking concavesincreased its efficiency and permittedthe usc of finer settings than wereoriginally allowablc. This type of rna-chine, although it hac; been supersededin the fine-reduction field by moreefficient types, still Iates as a veryexcellent crusher for secondary work.It has good capacity at moderate set-tings, is ruggedly constructed. andhas, for comparable sizes, relativelylarge receiving openings, as comparedto machines designed primarily forfine- red uction work.To show why this machine was adistinct step forward in secondary

crusher design, if is interesting tocompare the action of its. crushingchamber to the standard crusherchambers already described. And tomake clear the fact that the machinehad certain advanced features, evenbefore non-choking concaves were de-veloped, we first show a diagram of itscrushing chamber with the older typeof beveled, straight-face con caves(Fig. 5). Itshould be mentioned thatthese beveled cancaves were not thevery earliest type used in this crusher;they were preceded by plain, straightconcaves, which utilized the full ratedreceiving opening of the crusher, buthad the same disadvantage we notedin connection with this type, as usedin the standard gyratory-e-concentra-tion of wear at the discharge-point.The beveled type spread the wear outsomewhat, although at the cost ofsome reduction in the effective receiv-ing opening.The distinctive feature of the de-

sign shown in Fig. 5 is the decidedslope of the line-of-mean-diametersaway from the center-line of thecrusher, as this line runs downthrough the crushing chamber. Asthe volumes of the successive ringsof material are functions of theirdiameters, as well as their areas, itis apparent that these progressivelyincreasing diameters tend to offset thedecreasing areas; in other words, theflared head spreads the material as itmoves downward, thereby tending tominimize the ratio-of-volume-reduc-tron. The actual compression-ratio inthis chamber is about 1.5: 1, which islower than in either of the diagrams

previously discussed-and very muchlower than the case of the standardcrusher with straight concaves.That this departure from the older

conventional design was a decided im-provement for secondary crushing isapparent when we compare two ma-chines of approximately equal headdiameters, a logical comparison be-cause the diameter of the bottom ofthe crushing head directly affects thearea of discharge opening and, hence,the capacity of the crusher. The Su-per i 0 r McCully 10-in. reductioncrusher, with its 40-in. head, com-pares closely, in this respect, with the20-in. standard crusher, which has a3S-in. head. Using straight-face con-caves, the permissible minimum open-side settings are 1% in. for the for-mer, and 3% in. for the latter. Withnon-choking concaves these settingsare, respectively, 1% in. and 2% in.

Non-Choking ConcavesTo show the characteristics of thistype of crusher when fitted with non-

choking concaves we have prepared adiagram of the same size machine soequipped (Fig. 6). We now have thecumulative benefits of the flared headand curved-profile liners. There is amarked reduction in the number ofstrokes required to shift plane "0"down to the discharge level; the choke-point has been raised, and the ratioof volume reduction is lower (about1.2:1).

There is a decrease in the effectivereceiving opening. as compared withthe straight-face chamber, when using"full-curve," non-choking concaves,which is the type shown in our dia-gram. This effective opening is estab-lished by the maximum angle of nip;therefore it varies somewhat for dif-ferent materials, and in different sizesof crusher. For this crusher 26 deg.was chosen as the governing angle;about 28 deg. is the conservative maxi-mum for the largest machines of thistype.

High -Sp ee d Crus he rsSo far, all of the crushers we have

been discussing have been of the "low-speed" class; that is, with eccentl'i.cspeeds ranging between the approxi-mate limits of 100-200 r.p.m. It iscustomary, as before mentioned, torate such crushers at their open-sidedischarge settings, because there isa definite relationship between thesevalues. Most modern crushers, de-signed for what may properly beclassed as fine-rednction crushing, areof the high-speed type. The eccentricspeeds and shape of the crushingchamber in the machines of this typeare such that the maximum one-waydimension of the product particles isestablished by the close-side dischargesetting; consequently it has becomecustomary to rate these crushers atthis setting.

;

Fig. 4: Sectlanal ..iew af fine redllctian crllshe.

----------------,- ... ' .. _ .... ---~-"---- ..--13


15/53

Fig. 5' Roduction crusher-beveled straight-face cDncQves

Newhouse CrusherThe Newhouse crusher was one ofthe early developments in the high-speed class of fine-reduction crusher.This machine, a sectional view ofwhich is shown in Fig. 7, incorporatesseveral unusual features, at least oneof which is unique in crusher design.The eccentric is direct-driven by avertical motor mounted above thespider, the drive shaft running downthrough the hollow-bored mainshaft.Speeds range from 480 to 580 rpm,depending upon the size of the crush--er, and upon the frequency of theelectric current. Eccentric throws, ascompared with those of the crusherswe have been dealing with, are rela-tively low. This combination of smallthrow and high speed results in avery uniform product with a minimumamount of fines for any setting andratio of reduction. A unique featureis suspension by means of cables,eliminating the usual foundation, al-though the crusher can be set on afoundation where required.This crusher is usually furnishedwith full-curve, non-choking concaves,which are reversible in the top shell.

These concaves are of the same gen-eral contour as those shown in the dia-gram of the Superior McCully reduc-tion crusher chamber, (Fig. 6) andin general the crushing chamber issimilar, except that the chamber inthe Newhouse crusher is somewhatdeeper and, consequently, the headdoes not have as pronounced a flare.The important difference in the crush-ing action of these two machines liesin the difference in eccentric speed.That of the Newhouse crusher is sohigh that no material can dropthrough the almost parallel zone justabove the discharge point withoutbeing caught between head and con-caves and broken to a maximum one-way size closely approximating theclose-side setting.

:1

I I~I D IS C H , r . ,R G E P O IN T - - - ----.,-"'==~ i

l _ 1 . : _ 1 ~ Jfig. 6, Reduction crusher-non-choking can-

ceves

This crusher can be set somewhatcloser than comparable sizes of thereduction crusher previously de-scribed. Although it cannot be classedas a fine-crusher it does belong to thefine-reduction class. Furthermore, byvirtue of its large receiving openings,it rates as a machine for secondaryreduction work. Whell so used it isusually fitted with con caves of thenon-reversible, non-choking t y p e ,which arc designed to make use of thefull rated receiving opening of thecrusher, although they sacrifice thefeature of reversibility which permitswearing both ends of the concaves,"Hydrocone" Reduction CrusherThe "Hydrocone' crusher (Fig. 8),

was designed primarily with a view toachieving top performance in the fieldof fine-reduction crushing. Ithas alsobeen adapted to what is designatedsimply as "fine-crushing," which ex-tends into a range below that or-dinarily defined by the term "fine-re-duction."Although the eccentric speeds of thevarious sizes of this type are not quite

so high as the speeds used for theNewhouse crusher, the Hydroconecrusher definitely rates as a high-speedmachine, its product comparing quiteclosely to that of the former type, forequal close-side settings.Probably the outstanding feature of

the:Hydrocone crusher is the hydrau-lic 'support, from which its name is de-rived and which is clearly shown inthe sectional view. This device makesit possible to adjust the crusher toany desired setting within its range ina matter of seconds; adjustments maybe made while the crusher is running,although the feed must be shut off be-fore operating the adjusting pump. Anaccumulator in the hydraulic systemprovides protection against tramp ironor packing.

14

t

Fig. 7: Sectional- view- af a NewhoIH. c .... her

fFig. 9: Type R fine red .. ction cru.her

-~e-


16/53

Fig. 9 shows a diagram of the Hy-drocone crushing .chamber. A compari-son of this chamber with those pre-viously discussed is interesting. Itwillbe noted that the choke-point has beenraised far above the discharge level, infact, to a point not far below the nip-point for the recommended maximumone-way feed dimension. By virtue ofthe decided flare of the head, and thecorresponding flare of the top shellbore, the line-of-mean-diameters slopessharply away from the crusher cen-terline. For some. distance abo.... thedischarge point the angle betweenhead and concave is very acute; infact, at the open-side position of thehead th is zone is almost parallel.For recommended operating condi-tions, i.e., for safe combinations ofthrow and setting, and with screenedfeed, this type of crushing chamber

does not approach anything like achoke or near-choke condition. For thecombination shown in the diagram theratio of volume reduction is almost 1: 1from zone 0-1 to zone 2-3 at the choke-point; consequently, if the crusher isgiven a screened feed (as all fine-re-duction crushers should be) the re-duction in voids by the time the choke-point is reached cannot very wellreach serious proportions.The diagram shows the standardchamber. With screened feed thesecrushers will operate at close-side dis-charge settings equal to the throw ofthe head at the discharge point (usu-ally spoken of as "eccentric-throw.")

Medium nr Fine CrushingChamberThis crusher is a modification ofthe standard machine, developed for

fine-crushing duty. Mechanically. themachine is the same in every respectas the standard crusher of the sametype, but for each developed size ofmachine a special top shell and con-cave ring has been designed, with re-duced receiving opening, reduced an-gularity between head and concave,and, consequently, superior charac-teristics at the finer settings. Mediumcrushing chambers may be operatedat close-side settings of one-half theeccentric-throw, on screened feed;hence capacities at the finer settingsare better than those of the standardtype. Fine crushing chambers operateat one-fourth the eccentric throw. In-asmuch as the maximum feed-size issmaller in the case of the fine cham-ber, the ratios of reduction are ap-proximately the same for both ma-chines.

Part VI. Some factors which influence crusher performance

IIS ENTIRELY POSSIBLE for a crush-er to choke at some other point inthe crushing chamber than the theo-retical choke-point. When the settingof a fine-reduction crusher is too closefor its eccentric throw and ..for thegeneral proportions of its crushingchamber, there is a tendency towardbuilding up a choke in the zone imme-diately above the discharge opening,regardless of where the theoreticalchoke-point is located. The reason forthis is that the excessive movement ofthe head (in relation to the dischargesetting) mashes the material againstthe concave so tightly that the indi-vidual particles are shattered, or pul-verized.Such a crushing action builds up

fines very rapidly, and consequentlybrings about a rapid reduction in thepercentage of voids, even though thecrushing chamber may have a pro-gressive volume-expansion character-istic. Many materials, when mashedin the manner described, tend to cake,and to cling to the crushing surfaces;the movement becomes sluggish; morematerial crowds down from above,aggravating the packed condition, and,if the action progresses to the pointwhere all voids are eliminated, a chokeresults. .Characteristics or condition of the

material have a decided influence uponthe action just described. Soft, friablerock is more apt to pack than hard,clean-breaking rock; damp material ismore prone to cause trouble than dry,particularly so if the feed containsmany fines (e.g., unscreened feed).

High and Low Speed ProductsIt is important to note that the prod-

ucts of the two classes of crusher(low-speed and high-speed) cannot be

compared directly upon the basis oftheir respective open-side and close-side settings. Nor, indeed, can theproducts of any two types in the high-speed class be compared upon thisbasis, unless it is known that theirspeeds, throws, and general shape ofcrushing chamber are similar.As between crushers of the high-and low-speed types, the low-speedmachine at any given open-side set-

ting will make a finer product thanwill the high-speed machine at thesame clo:;e-side setting. For example,in one installation where the machinesare working on the same material, astandard type gyratory, fitted withnon-choking concaves, consistently de-

f-In the case of the high speed crusher, therewill naturallY be occasional pieces get throughtbat are a little larger than the close-side set-ting. but th ... e are 90 few that they are un-imncrtant,

FIIlIt redllctlDn crusher InltDUed In an Easternerushl"1 plant

15

livers a product 85 percent of whichpasses a square-opening test sieveequivalent to its open-side setting. Ahigh-speed, gyratory, fine-reductioncrusher in the same plant just asconsistently produces material 70 per-cent of which passes a square openingtest sieve, equivalent to its close-sidesetting. In both cases all material isreduced to a one-way dimension notexceeding these respective open- andclose-side settings.r This is a typicalcase which gives a pretty fair aver-age comparison of products from ma-chines rated on these two differentbases.These results might, at first glance,appear to be inconsistent in view of

the fact that the maximum one-waydimension is established in each caseby the respective open- and close-sidepositions, whereas the product analy-ses do not show similar percentagespassing these respective opening sizesin the test screens. The apparent in-consistency clears itself up, however,when we remember that the low-speedcrusher, as well as the high-speed ma-chine, does its sizing on the close-sideof its stroke. The governing point isthe distance (above the dischargepoint) that the material can fall (onceit has been broken to a one-way di-mension less than the open-side set-ting) before the head can catch itagain. In the high-speed crusher thispoint is quite close to the dischargeopening; in the low-speed machine itis some distance above the opening,the amount depending upon the shapeof the crusher chamber, as was madeclear in our discussion of the preced-ing diagrams.It is hardly practicable to rate theproduct of a high-speed, short-throwcrusher at its open-side setting. In thecase just noted, all of the product of


17/53

the second crusher mentioned, exceptfor an occasional fiat spall, passes asquare-opening test sieve equivalentto its open-side setting; in fact, atsome combinations of setting- andthrow, the 100 percent point will bebelow the open-side setting. It is im-possible to gauge a crusher pl"rJ'l~lctat, or near, the 100 percent passmgpoint beea use a few flat spalls, moreor less, in the sample will throw tho'analysis several points one way Ill"theother, giving results that are uncer-tain.There is a very wide variation inthe product delivered by ditTerent

types of high-speed crushers at sirni-lar close-side settings. Short-throwcrushers tend to give fu ir ly consistentresults, even on matcrial., of diver-rentphysical characteristics. The prod-uct of crushers with large throws. andlower eccentric speeds, will vary morewiduly, depc ndirnr to a much gn,aterextent upon the nature of the mate-rial. In judging the relative merits o fcrushers which are rated at theirclose-side sett ings, a check should bemade to determine just what kind ofproduct the crusher will deliver, withtefet'ence to any particular setting'.

Effect of Reduction Ratio\Ve have mentioned the fact that, as

the percentage of voids in the crush-ing chamber decreases, the productionof fines by attrition increases. This isequivalent to saying that, as the ratio-of-reduction in any given crusher isincreased, the percentage of fines inthe product will increase, even thoughthe discharjre setting remains un-chanced. Both of these statements aretrue, but the degree to which the prod-uct is affected depends to a muchgreater extent upon the ratio-of-vol-ume-reduction in the crusher cham-ber than it does upon the actual de-gree of reduction performed on thematerial. For a given ratio-of-reduc-tion, the type of crusher with a flaredcrushing chamber will usually delivera cleaner product than any of theolder types; conversely, more reduc-tion can be performed in the machinewithout creating excessive fines.The facts outlined in the foregoingparagraph have an important bearing

on crushing plant design. Commercialcrushing plant operators are usuallydesirous of making as few fines aspossible, and this is becoming in-creasinzly important as the demandfor small g-rades of screened materialincreases. To hold down the amount ofdust 01\ screenings in the combinedplant product, it is essential that theamount of reduction per crushingstage be held within conservative lim-its; moreover, it is important thatthe work in each stage be apportionedwith due regard to the characteristics

~-_..., ~'?";J: ,,~.:.:::-.---~ -"'T. " : 1I ~ - l

. L : . " i J " > ' . 4 -Fine red~ction type crusher installation In Midwest plant

of the crushers comprising thesestages.As an example, suppose that it is

required to make a reduction of 7:1in two stages of crushers, one astandard gyrutorv and the other afine-reduction crusher. We know fromour examination of the crushingcharacteristics of these types that, forequal reduction ratios, the volume-re-duction-ratio in the standard gyratoryis considerably higher than it is in thefine reduction crusher. Therefore, ifminimum production of fines is de-sirable, it is logical that the heavy endof the T : 1 reduction should be handledin the latter machine. Generally, forsuch a case, the split would be about3: 1 to the standard machine, and 4:1to the fine reduction crusher.

Kind of FeedWe have pointed out, directly and

by inference. that the feed to thecrusher should not contain an exces-sive amount of fine material; thiscould be stated a little more definitelyby saying that it should not contain

16

an excessive amount of material small-er than the crusher product size.Just what constitutes an "excessiveamount" depends of course upon sev-eral factors, chief among which arethe design of the crushing chamber,the setting, and the character of thematerial being crushed.Quarry operations do not usuallyrequire scalping ahead of the primarycrusher, although there are excep-tions to this. Gravel pit and miningoperations almost always requirescalping ahead of the primary ma-chine because of the large percentageof fine material in the pit-run, ormine-run, material. Generally, whenscalping is required at this point, thesplit is made at approximately theopen-side of the primary crusher.Screening between the primary andsecondary stages is always desirable,although it is by no means a universalpractice. Where very large primarycrushers are involved-with accom-panying large size product-it hasbeen common practice in the past topass the product of the primary rna-


18/53

J

chine directly into the secondary. Sofar as product gradation is concerned,this is equivalent to making the en-tire reduction in one machine, and itis inevitable that such a practice willincrease the amount of fines in theoverall plant product. This practice ofpast years can be attributed to thelack of proper screening equipmentto handle the coarse product of theselarge primary crushers. Now th~tscreens are available to clean thiscoarse material, there is no longerany excuse for such an arrangement.Screening ahead of fine-reduction

crushers is not only desirable, it isimperative from the standpoint ofboth safe and satisfactory operation.Preferably, a!1 material smaller thanthe crusher-product size should be re-moved from the feed. There is an oldsaying to the effect that, "It is cheap-er to screen than it is to crush," whichis trite but true. The fine-reductionworks on all material that entersits crushing chamber, regardless ofwhether or not the material is small-er than the discharge setting. Thiswork takes power, makes more fines,increases wear on the liners, and mayactually cut the capacity of the crush-er, due to sluggish movement of thefine material. When we add to thesethe greatly increased probability ofa choke occurring with the unscreenedfeed, the case for a clean, screenedfeed to the fine-reduction crusher isclear cut and incontrovertible.

Effect of Feed GradationIf the feed to any gyratory or jaw

crusher consisted entirely of cubes orspheres of a size that would just bare-ly enter the crushing chamber, thecrusher could not be expected to pro-duce anything like its normal ratedcapacity because the upper part of thecrusher could not shatter the largepieces enough to keep the rest of the

Hydrocone crusher arranged for regulatedfeed by belt co nveyo r.

Choke feeding two gyratory cru.he,.with limestone.crushing chamber busy. Such a condi-tion is o f course never met with inactual practice. We occasionally en-counter special applications where thecrusher is called upon to handle pieceswhich are all of the same size, out insuch a case the machine is chosenwith a large enough receiving open-ing to permit the pieces to fall atleast a short distance into the crush-ing chamber before they are nipped.Even so, the crusher is not apt toperform up to its rated capacity onsuch a feed-c-unless the receivingopening is quite large with respect tothe feed size.By far the greater number of crush-

er applications involve feeds whichare either graded (a mixture of large,medium, and small particles), orsized to a top dimension well withinthe effective receiving-opening dimen-sion of the crusher. Primary crusherfeeds usually fall under the "graded"category, and reduction crusher feedsunder the "sized." Graded feeds mayor may not have the undersize re-moved, depending upon the nature ofthe operation and of the material.Sized feed for reduction crushers isgenerally a screened feed which hasdefinite maximum and minimumlimits.The effect of the undersize in thefeed upon the capacity of the crusher

depends upon several factors. If thecrusher is a primary breaker, and thedischarge opening is large, undersizewill usually sift readily through thevoids between the large pieces of ma-terial, and discharge quickly. Thematerial must, of course, be free-flow-ing to behave in this manner. For sucha condition, large quantities of under-size may materially add to the ratedcapacity of the crusher, but it mustbe admitted that such a condition isthe exception rather than the rule.More often than not the dischargesetting even in primary crushers, issuch that the crushed material in thelower part of the crushing chamber

17

effectually throttles the flow of finematerial to the pace of the largerpieces; hence, any increase in capacitywould be due entirely to whateverincrease in density of the body of ma-terial might result from the presenceof the fines in the voids between thelarger pieces. This is usually notlarge, and as has been pointed out,the presence of fine material may evenbe detrimental under certain condi-tions.If a clean, sized feed to a reductioncrusher includes a preponderance ofparticles smaller than the dimensionbetween crushing surfaces at thechoke point, the effect upon capacitywill be beneficial. On the other hand,if there are enough larger particlesto trap these smaller pieces, we getthe same throttling effect mentionedin the preceding paragraph-unlessthe choke-point is well up in thecrushing chamber, where the smallpieces have a better opportunity tosift through. If capacity alone were tobe considered in selecting the feedsize for a reduction crusher, the idealwould be a feed having a one-way di-mension not exceeding the choke-pointdimension, and not smaller than theclose-side discharge setting.Choke-Feed vs. Regulated FeedThe product from crushers of thestandard gyratory type, or the older

reduction types, as well as all typesof jaw crushers, will be affected tosome extent by the method of feeding;that is, whether the machine is choke-fed or not. The choke-fed crusher pro-duces more fines, due to attritionalgrinding between particles in thecrowded crushing chamber. The differ-ence will not be as marked if themachine is fitted with non-chokingconcaves, but it will still be measur-able. Likewise, the choke-fed crusherwill usually show somewhat higherpower consumption, because it takes

42-inch Superior McCully crusher Qrrongedfor feeding by .ruck.


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power to produce these fines. Whenthese types of crushers are used forsecondary or reduction work, and op-erated under choke-feed conditions,the feed should preferably be intro-duced from one side, allowing it toflow around one of the spider arms tofill the bowl on the opposite side to apoint just above the choke-point.This method of feed will show amarked improvement over the full-choke method, both from the stand-point of clean product and lowerpower consumption.

A crusher with a high choke-pointincorporated in its design is not ap-preciably affected by choke feed.When these crushers are fully buried,the choke-point throttles back the ma-terial so as to prevent overloadingthe lower part of the crushing cham-ber, and there is so little active crush-ing surface above the choke-point thatvery few fines are produced in thiszone.The facts outlined in the preceding

paragraph apply to the action of the

crusher on screened feed. We havestressed the desirability of screenedfeed for all reduction and fine-reduc-tion crushers. If it should be neces-sary to feed un screened material tosuch machines, they should never bechoke-fed. The feed should be" regu-lated by mechanical means to a pointsafely within the rated capacity of thecrusher, so -that the chamber willnever be more than partially filledwith material. It goes without sayingthat even this expedient will not workon damp, sticky material.

Part VII. Jaw crushers, types and special uses

THAT POPULAR AND RELIABLE work-horse of the crusher family, thejaw crusher, has been developed in avariety of forms that probably out-rivals the variations of the gyratorycrushing principle. Several differenttypes of motion have been devised, anda great deal of mechanical ingenuityhas been displayed in the design ofmechanisms to generate these motions.Despite the infinite variety of details,however, most of the jaw crushers inpopular usage today have actionswhich closely approximate or exactlyduplicate one of the three types to bediscussed in the following pages.These are:1. The Blake-type crusher.2. The Dodge-type crusher.3. The single-toggle type crusher.

Blake Type CrusherBoth chronologically, and by virtueof its standing in the field of heavy-duty crushing, the Blake-type crusher

stands first in the list. All of the large,heavy-duty primary crushers of thejaw type are built around the Blakeprinciple which, for simplicity andbrute strength, is unsurpassed by anymechanism thus far devised for rockand are breaking.A sectional view of a jaw crusher

which incorporates the Blake double-toggle mechanism is shown in Fig. 1.The Blake crusher in common with allmachines of the jaw family is builtinto a rectangular frame, at one endof which is located the crushing cham-ber; in fact, the end of the box-frameconstitutes the stationary jaw. Themovable or swing jaw is suspendedfrom a cross-shaft (swing jaw shaft)at its upper end, this shaft in turnbeing supported at each end in bear-ings at the top of the two sides of thecrusher frame.The actuating mechanism consistsof the eccentric-shaft (also supportedin bearings in the sides of the frame),the pitman, and the pair of toggles,which span from swing jaw to pit-.man, and from pitman to rear end ofthe frame. The motion of the eccen-

tric-shatt is transmitted through thepitman to the inner ends of the tog-gle pair, and through their action tothe lower end of the swing jaw, whichpivots around the supporting shaftat its upper end. The motion is simi-lar in one respect to that of the stand-ard gyratory crusher, in that it isgreatest at the dlscharge opening, andgradually decreases toward the upperpart of the chamber.Jaw-crusher frames have been thesubject of considerable variety in de-

tails of design and have been built ofseveral different materials. Originallyall frames were of cast iron, as wasthe case with all of the early gyra-tory machines. Then, as larger sizeswere developed, cast steel became thecommon medium for all large and me-dium size crushers. When the Superiorline was designed, semi-steel was se-lected for the frame, and steel rodsextending through the side membersfrom end to end were provided to ab-sorb the tensile stresses. This type ofconstruction is used in all sizes of this

line, except in the 84-in. machines,where cast steel has been used ex-clusively up to the present time, thesecast-steel "frames being reinforced forheavy-duty applications in the samemanner as the semi-steel frames ofthe smaller machines. Of recent yearsthe trend has been very definitely to-ward the use of welded design, withside members of rolled steel plate, re-inforced by stiffening ribs.In past years both chilled cast ironand manganese steel were used in jawplates for" the Blake crusher, depend-ing upon the kind of rock to be crush-ed. The chilled iron plates did not pos-sess the requ isite strength to resistbreakage. even when used on com-paratively soft rock; in our case wehave abandoned them in favor of man-ganese steel ou all of our jaw crush-ers, regardless of size.The Superior crusher is representa-tive, in its general proportions, of theprevailing practice in Blake crusherdesign for a number of years. In this

respect it is probably just as well en-

f

------~"--------- -------- -

cFig_ I: c..... seUlon .. 1 detail of mode.n type double-toggle crusher

A _ ,.

18


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titled to be classed as a "standard"type as the gyratory crusher whichgoes by that title. 'It is true that re-finements have been made in almostevery detail, as compared to earlymodels, but the basic action and thegeneral proportions of the crushingchamber are much the same.As a matter of fact, aside fromthese refinements in mechanical de-

tails, the only important departuresfrom the original Blake design thathad been tried, until quite recently,consisted of: (1) alterations in therelative positions of stationary andswing jaws with respect to the ver-tical i (2) the introduction of curved(non-choking) jaw plates. .The original Blake crusher was de-signed with a vertical stationary jaw.

Probably the first departure from thisarrungc ment was an 84- x 66-in.crusher, bui l t in 1914. This machine

IL ---'84 x 66-inch iow (rush"r built in \9\4_

incorporated a reversal of the con-ventional design, in that the swingjaw was made vertical. Later, whenthe Superior line was developed, acompromise between these two ex-tremes was used in several of thesizes; that is, both jaws were sloped.Each of these three arrangementshas certain features which are ad-vantageous, and others which are un-favorable. Present indications are thatthe original arrangement, with ver-tical stationary jaw, will continue tohold a leading position.Crushing angles in standard Blake-type machines generally run in theneighborhsod of 27 deg. at the mini- .mum open-side discharge setting. The

ro-----'R~ECEIV~ING_..j~OPENING ) \V \

J

.::..::::.!!l.=!""; '!- C L0 5E - 5 1 D E_.r-,'f--OPEN- SIDE

Fig. 2: Diagram of slraigkt jaw plale crusher

ratio-of-reduction at minimum recorn-mended settings and with straight jawplates average about 8:1, in the rangeof sizes from 15- x lO-in., to 60- x48-in., inclusive.

Straight Jaw PlatesFig. 2 shows a diagram of a stand-ard type of Blake crusher with regu-lar or straight jaw plates .. This typeof plate has been the standard fromthe time of its inception, emulating,in this respect, the straight concavesin the gyratory machine. And it willbe noted that the theoretical action inthis straight-plate jaw chamber fol-lows quite closely the pattern of theaction in the straight-concave gyra-tory chamber.Calculations for the jaw crusherchamber are somewhat simpler thanin the case of the gyratory because thevolumes included between the succes-sive pairs of horizontal lines are rec-tangular in plan, whereas, in the gy-ratory we have to deal with annularvolumes (actually, a descending spi-ral, rather than flat rings). But, whenthe line-of-mean-diameters in the gy-ratory chamber parallels-to a closeapproximation, at least-the center-line of the crusher, the general char-acteristics of the two crushing cham-

bers, with respect to ratio-of-volume-reduction and concomitant reductionin percentage of voids are similar.Crushing angles and throws would ofcourse have to be the same for thecomparison to be exact.:rhere is one readily discernible dif-ference between the two diagrams weare comparing j the drop per stroke

in the jaw crusher diagram is notice-ably smaller. This difference is mostpronounced in the upper part of thechamber. The reason for the differ-ence is two-fold. In the particular ma-chines selected for these diagrams,there is a difference of several de-grees of crushing angle in favor of the

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'j;.mmlV[ UCENING OPE II \KG WI 1H NOK-RMJ lS l II l!PLATES-11 ' 0 U FE crlV E P . CE IV IN G O PI 'H I~ G W ItH R E. VE RS IB LE .PLATES

Fig. 3: Diagram of law crusher with non-chok-;"9 Iwin!J lo w plale

gyratory; this accounts for the aver-age difference over the full depth ofthe chambers. Secondly, the motionof the swing jaw, at the top of thecrushing chamber is, proportionately,smaller than the movement at the topof the gyratory chamber. The reasonfor this is that the distance from thetop of the crushing chamber to the ful-crum-paint-as compared to the totallength from discharge-point to ful-crum-point-is smaller in the case ofthe jaw crusher. This is .generallytrue of Blake-type crushers as com-pared to gyratories except for thevertical swing jaw type, in whichthe swing jaw is carried up some dis-tance above the top of the stationaryjaw.The close proximity of the fulcrum-point to the receiving opening givesthe type of crusher we are consideringenormous leverage on large blocks ofstone, and the small motion tends todecrease the shocks incidental to grip-ping and shattering such blocks. Fromthe capacity standpoint, the smallerdrop per stroke is compensated for bythe fact that the jaw crusher speed,for comparable sizes, is higher thanthe eccentric-speed of the gyratory.

Non-choking Jaw PlatesWhen the non-choking concave dem-

onstrated its capabilities in the gy-ratory crusher, it wa.s only naturalthat the principle should be applied tothe jaw crusher. But, inasmuch as theBlake-type jaw is used very largelyfor primary breaking, where maxi-mum receiving opening is, more oftenthan not, a controlling factor, the ap-plication of non-choking plates tostandard machines of this type hasone unfavorable aspect, as will beevident from an examination of Fig.3, "Standard Blake jaw crusher-non-choking swing jaw plate." Thisdiagram shows the same machine as


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RECEIVINGOPENING

CHOKE-POINT

Fig. 4: Diagram ot new type crushing chamber

the last one considered, except thatthe swing jaw is fitted with a curvedjaw plate.These non-choking jaw plates havebeen developed in two styles, reversi-ble and non-reversible. The advantageof the reversible design has been out-lined in connection with its applica-tion to the gyratory reduction crush-er. For both types of jaw plate, the ef-fective receiving opening is reduced,as compared to the standard, straight-plate setup. For the non-reversibleplate, this reduction is determined bythe actual increase in depth of theplate, resulting from the introductionof the curve. For the reversible plate,it is established by the point wherethe tangent to the curved surface coin-cides with the maximum angle of nipfor the material being crushed. Simi-lar restrictions were outlined in ourdiscussion of non-choking concaves ingyratory crushers.Regarding the reversible plate, it

should be noted that, while that por-tion of the chamber above the point ofnip does no crushing, it does consti-tute an "active" receiving hopperand, as such, is of definite value inminimizing bridging across the re-cerving opening. For applicationswhich do not require the full rated re-ceiving opening of the crusher, non-choking jaw plates offer a substan-tial improvement in performance, animprovement comparable to that re-sulting from the substitution of non-choking concaves in the gyratorycrusher. While this is readily appar-ent from a comparison of the two dia-grams we have presented, more con-crete evidence is contained in the tableof capacity ratings, which gives rat-ings for both types of jaw plates, for

sizes up to, and including, the 60- x48-in. machine.High-Capacity Blake CrusherWhen the non-choking feature wasbeing applied to existing crushers of

the gyratory type, it was found thatin several machines, the attendantreduction in receiving opening conoidbe partially offset by sloping thestraight portion of the concaves at awider angle than that for which thetop shell was originally designed, be-cause some of these older machineswere designed with very conservativecrushing angles. Generally speaking,however, this was not true of existinglines of jaw crushers. It is true thatprevailing angles could be widened incertain cases, and for certain appli-cations; but the jaw crusher, morethan any other type of crusher, iscalled upon to handle very hard, toughmaterials, and standard designs mustbe based on that kind of duty. Fur-thermore, as was pointed out in ourdiscussion of gyratory crushers, a cer-tain amount of slippage occurs in allcrushing chambers, and the jawcrusher, which is not essentially ahigh-capacity machine, could ill af-

ford to have any additional slippagebuilt into it.A study of these factors convinceddesigners that, to fully realize theadvantages of the non-choking featUrein the Blake-type crusher, it would be

necessary to develop a new line, withcrushing chambers designed specific-ally for that type of plate. It wasrealized, that improved performance-particularly on hard rock-wouldresult from a substantial decrease inthe prevailing practice with regardto crushing angles. And, thirdly, in-asmuch as the jaw crusher is prepon-derantly a primary breaker, it wasdesirable that these improvements beincorporated without sacrificing valu-able inches of receiving opening.These ideas were given concrete

form in a new line of all-steel Blake-type jaw crushers, with frames ofwelded design, and several interest-ing and important refinements in me-chanical details, including an im-proved system of lubrication.Fig. 4 shows a diagram of the

crushing chamber in one of the newtype crushers. This diagram covers amachine of the same receiving-open-ing size as the standard type on

CRUSHER JAW CAPACITY IN TONS (2000 lS.) PER HOURSIZE R.P.M. MOTION H P . @ OPEN SIDE SEHINGS OF:(IN.) (IN.I 4' 4V 2 5" sYi 6" eYi' 7" 7h_" s, 9" lOW

36 X 2.5 2.10 I-lj'6 60-75 200 220 240 250 260 280 290 300f.--- ..._.- - ------ ----- ---- ----- ----- - - _ . --- --- --- ---__42 X 32. 2.00 1-31 1 6 100 2.50 270 2!10 310 33 0 340 .360 380 400f.---.- -- - --~ -_~ _ ~ ___ L - .,.. .._- .- ~.- - .. - _ - -- --~- ~ --48 X 42 18 0 1-1j2. 125-150 380 400 42.0 450 470 49 0 510 540 580X48 - 1-71 1 6 ------ -- 1 5 7 060 17 0 150-250 450 4 80 50 0 530 550 61 0 660

ICRUSHE.R JAW CAPACITY- TONS (2.000LB)PER HOUP-.SIZ.E R.P.M MOTION H P. .: @SETTING

(IN.) (IN.) 1/2." 3/4' I" IYi '4 X 6 275 1/2 3 Y 4 '/2. 1~---.--. _.- .13116 -. .._ - - - ..-~-7 X 9 235 6 I 2. 38 X 12. 220 19/32 10 I Y 2 . 3 4II X 15 200 -T "':5 /8 - 15 2 4 6

CRUSHER JAW CAPACITY IN TONS (2"00 LB ) PER HOURSIZ.E R . P . M . MOTION HP . @OPEN SIDE SETTINGS OF:(I N.) (IN.) * 2" 3" 4" 5" 6" 7" 8" S" 10 " II" 12"

2 . 4 - X 15 2.10 7/8 35 A 19 34 - 48 62 .----- _._-, --- -- -- .-----.75 B 30 50 70 9036 X 24- 15/ ,6 1---210 7S A 45 66 89 1101------.- -- - ..- -- ------~~ ---- -- --S 80 10 0 13 0 170 ~~~------ _ -- --'---- --- -- ;-- -- -~42 X40 190 I 12.5 A 90 120 15 2 lal 230.~--~ -- .._-, --- -_. -- - ._ .--S 140 190 230 270 32048 X42 19 0 1- Y 1 6 -- I~ --_I--- -~-- --- --ISO A 135 173 215 262--- f.--. --~ --B 210 250 30 0 35060 X 48 I-VB- ~ 1-_- f..--- -- ------ -~1-170 2.00 A 155 2.15~:~BS 325I- I----B 270 320 450 510*A-- CAPACITY WITH STRA.IGHT JAW PLATESB-- CAPACITY WITH CURVED JAW PL.ATES

CamparisDn ~h,uts af, frDm top to bottDm: Bloke-type crusher, Dodge-type c .... her, and single-toggle type crusher

20


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which the two preceding diagramswere based. A brief comparison willimlicate why 'the new crusher hasdistinctive performance characteris-tics.At first glance, the most strikingd itf'crunce lies in the depth of thecrushing chambers, due partly to thenon-choke design, and partly to the de-creased crushing angle. This diagramwas laid out for the same jaw-mo-tion as the standard-crusher dia-g ram. anrl it will be noted that aboutthe same number of strokes are l'e-qu ied to move the material downfrom reccivinrr-opcniug to discharge-opening'. However, it will also be notedthat the areas between successive linesare substantially grc::ttel', which is adirect indication of the relative thea-reticai capacities of the two crushers.In addition to this theoretical differ-ence, there is an" imponderable" assetwhich accrues to the decreased crush-'ing ang-Ie-an asset which is 110t sub-ject to pre-calculation, but which con-

tributes in no small degree to the ex-cellent performance of the new ma-chine, not only in increased capacity,but in reduced rate of wear on thejaw plates.Ratings of the developed sizes ofthe new crusher are given in a table.Naturally, it costs money to buildsuch characteristics into a crusher,and, for that reason, it is hardly to beexpected that this improved designwill entirely supersede existing stand-ani models of the Blake crusher. Invery many applications, receivingopening, rather than optimum ca-pacity, is the predominant factor. Forsuch applications-especially for thoseinvolving soft, or medium-hard ma-terial-the lower-cost standard crush-er will probably continue in favor.

The Dodge CrusherA sectional view of the Dodge-typejaw crusher is shown in Fig. 5. Themechanism of this machine is so sim-ple that it is hardly necessary to en-large upon what can be gained froman examination of the cut.In one respect, the Dodge machineis a reversal of the actions we havebeen discussing; its movable jaw, be-ing pivoted at a point below the dis-charge opening, has minimum move-ment at that opening, and maximummovement at the receiving opening.Because the choke-point and the pointof least motion coincide in this crush-er, it is to be expected that it wouldbe lacking in capacity, as compared tosimilar sizes of the Blake-type crush-er, The Dodge machine has the vir-tues of simplicity, low cost, and easeof adjustment and maintenance, but,due to its low capacity, its field is re-stricted to rather narrow limits.By reason of the small movementat the discharge opening, the natural

.)

JJ;J91JZ IZ 14

fig. 5 : Dodge-type crusher par'" 11) Frame, 121 Main bearing cop, 131 Oil ...ell cover, 141 Oil wellcover spring, 15) Swing jaw shott box, 161 Breaking plate, 171 Shim, 181 Pitman. I,}I Pitman cap,ilO) Pitman pin, (11) Pitman eye bolt, (12) Pilm .. n jaw sprjng cop, (13) Swing law and Pitm .. Roil well eovar, il41 Swing jaw spring, (15) Swing jaw, 1161 Flywheel. !l7) Eccentric 'haft, (181loase pulley, 1191 Tight pulley, (21) Swing jaw .hall, 1221 Left hand ,ide liner, (2)) Ri~ht handoide liner, 124) Plain .tatlanary jaw plate, Il~ I Plain swing Ja'" plate, (26) Hopper, 12,}1 5to-tianary jaw plole bolt, (301 Swing jaw'ptote bait, 131 I Dog bolt; 132) Outboard bearing, 1331

Outboard bearing cap

expectation would be that the Dodgecrusher would deliver

Crushing Practice and Theory

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