Chapter 5. Gyratory and Cone Crusher

5. INTRODUCTION

Gyratory crushers were invented by Charles Brown in 1877 and developed by Gates around1881 and was referred to as a Gates Crusher [1]. The smaller form is described as a conecrusher. The larger crushers are normally known as primary crushers as they are designed toreceive run-on-mine (ROM) rocks directly from the mines. The gyratory crushers crush toreduce the size by a maximum of about one-tenth its size. Usually metallurgical operationsrequire greater size reduction, hence the products from the primary crushers are conveyed tosecondary or cone crushers where further reduction in size takes place. Here the maximumreduction ratio is about 8:1. In some cases installation of a tertiary crusher is required wherethe maximum reduction is about 10:1. The secondary crushers are also designed on theprinciple of gyratory crushing but the construction details vary.

Similar to jaw crushers, the mechanism of size reduction in gyratory crushers is primarilyby the compressive action of two pieces of steel against the rock. As the distance between thetwo plates decrease continuous size reduction take place. Gyratory crushers tolerate a varietyof shapes of feed particles, including slabby rock, which are not readily accepted in jawcrushers because of the shape of the feed opening.

5.1. Design of Gyratory Crushers

5.1.1 Primary crusherPrimary crushers are solidly built to receive large lumps of rock directly from the mines anddesigned for large tonnage throughputs. Basically gyratory crushers consists of a fixed solidconical shell or bowl (also called concaves) and a solid cone within the bowl called a breakinghead (Fig. 5.1). The breaking head is fixed to a central spindle, which is hydraulicallysuspended or mechanically held from a spider. The bottom end of the spindle usually rests ona hydraulically supported piston. The bottom end of the spindle is connected to a bevel andpinion arrangement with straight or spiral teeth which on rotating by a journal moves thebottom of the shaft eccentrically. In some models, the spindle is fixed at the top and bottomand is made to move side-ways to impart the crushing action. The entire assembly can bevisualised as a circular jaw crusher.

Fig.5.1 is a typical sketch of a large gyratory crusher used as a primary crusher to reducethe size of large pieces of rocks produced during blasting in mines. Variations in the designof the breaking head and the mantle have been adopted by different manufacturers. Suchvariations are adopted from studies on stress distributions of component parts endured duringthe crushing operation. Effort is also made to improve the efficiency of the mechanicalmovements of the eccentric shaft. Such details are best described in manufacturer's literature.

The rule of thumb for describing the dimensions of primary gyratory crushers may besummarised as:

129

set

bottom shell

drive

mantle

gape

top shell

spider

hydraulic support

mantle diameter

129

1. For sizes < 66 cm, the circumference along the opening = 8 - 10 x gape (measuredalong the outer perimeter),

2. For sizes > 66 cm, the circumference along the opening = 6.5 - 7.5 x gape (measuredalong the outer perimeter)

3. The ratio of mantle diameter to grape = 1.3-1.7:104. The feed size = 0.9 x gape (up to 2 m in diameter)5. The reduction ratio ranges from 3:1 to 10:1.

The angle of nip for large crushers varies between 21° and 24° (average about 22°) but forcurved surfaces it is about 27° to 30° [2]. The distance of openings between the concave andthe breaking head at the top and the bottom ends are usually used to describe the size of thegyratory crusher. The other modes frequently adopted are:

1. Bowl diameter at the discharge end x gape2. Bowl diameter at the feed end x gape3. Bowl circumference at the feed end x gape4. Maximum diameter at the head x gape

The designs of the breaking faces differ with different manufacturers.. In so doing thecrusher products have different size distributions. The movement of the mantle or conicalhead that performs the crushing action can be visualised in Fig. 5.2 where it can be seen thatas the feed drops down, the mantle squeezes it against the concave and fractures the rock.

top shell

mantle

mantlediameter

hydraulicsupport

bottomshell

drive

Fig. 5.1. Sketch of a Gyratory Crusher (Crusher size is designated by the gape and mantle diameter).

130130

Fig. 5.2. Section of Gyratory Crusher.

When the mantle moves away during its cycle of gyration, the crushed rock slips down to becaught again between the mantle and the concave on the next cycle, resulting in further sizereduction. The process is repeated until the sizes of the broken rock are less than the open setat the bottom of the crusher.

The sizes of commercially available gyratory crushers vary considerably. The sizes areusually designated as gape x diameter of mantle (breaking head) or referred to by gape only.For a particular requirement it is advisable to consult manufacturer's literature. As a roughguide Tables 5.1-5.2 summarises the designs and other general characteristics of gyratorycrushers manufactured by different manufacturers and distinguished by the lengths of theirshafts. The fixed spindle gyratory crusher characteristics are included in Table 5.3.

Table 5.1 Design Characteristics of Long Shaft primary Gyratory Crushers [3].

CharacteristicsSizeUseful height*Set rangeRev./minutePower, kW

Small63.5-71 lmm

0.48 m25.4-44.5 mm

7002.2

Large1829-2294 mm

10.5 m228 - 305 mm

175298

' Denotes distance travelled by particles down the crusher

Table 5.2 Design Characteristics of Short Shaft primary Gyratory Crushers [3].

CharacteristicsSizeSet rangeRev./minuteMotor rating

Small762-1524 mm50.8-152 mm

425149

Large2133- 2794 mm178-305 mm

275750

131

mantle

concave

131

Table 5.3 Design Characteristics of Fixed Spindle Gyratory Crushers [3].

CharacteristicsSize of receiver openingSet rangeRev./minutesMotor rating, kW

Small203.2-813 mm

31.7 mm75016.8

Large635 - 5538 mm

-48083.9

According to Weiss [4] long shaft crushers are presently not in use but are being replaced byShort Shaft models.

5.1.2. Secondary and Tertiary cone crushersCone crushers were originally designed and developed by Symons around 1920 and thereforeare often described as Symons cone crushers. As the mechanism of crushing in these crushersare similar to gyratory crushers their designs are similar, but in this case the spindle issupported at the bottom of the gyrating cone instead of being suspended as in larger gyratorycrushers. Fig. 5.3 is a schematic diagram of a cone crusher. The breaking head gyrates insidean inverted truncated cone. These crushers are designed so that the head to depth ratio islarger than the standard gyratory crusher and the cone angles are much flatter and the slope ofthe mantle and the concaves are parallel to each other. The flatter cone angles helps to retainthe particles longer between the crushing surfaces and therefore produce much finer particles.To prevent damage to the crushing surfaces, the concave or shell of the crushers are held inplace by strong springs or hydraulics which yield to permit uncrashable tramp material to passthrough.

The secondary crushers are designated as Standard cone crushers having stepped liners andtertiary Short Head cone crushers, which have smoother crushing faces and steeper coneangles of the breaking head. The approximate distance of the annular space at the dischargeend designates the size of the cone crushers. A brief summary of the design characteristics isgiven in Table 5.4 for crusher operation in open circuit and closed circuit situations.

concave

Fig. 5.3. Sketch of a secondary cone crusher.

132132

Table 5.4 Design characteristics of Standard Symons cone crashers [4].

Design Characteristics

Size, mmCrusher chamber size range, mm *Discharge setting (closed side)Power kW

Open CircuitMaximum305076-43222-38.1300-500

Minimum60025-766.4-15.825-30

ClosedMaximum

305076-1786.4-19300-500

CircuitMinimum60025-513.225-30

* Chamber sizes vary between 3-6 numbers within a particular designated crusher sizeto produce fine, medium or coarse sized product.

The Standard cone crushers are for normal use. The Short Head cone crushers are designedfor tertiary or quaternary crushing where finer product is required. These crushers areinvariably operated in closed circuit. The final product sizes are fine, medium or coarsedepending on the closed set spacing, the configuration of the crushing chamber and classifierperformance, which is always installed in parallel.

For finer product sizes, i.e. less than 6 mm, special cone crushers known as Gyradisccrushers are available. The operation is similar to the standard cone crushers except mat thesize reduction is caused more by attrition than by impact, [5]. The reduction ratio is around8:1 and as the product size is relatively small the feed size is limited to less than 50 mm with anip angle between 25° and 30°. The Gyradisc crashers have head diameters from around 900-2100 mm. These crashers are always operated in choke feed conditions. The feed size is lessthan 50mm and therefore the product size is usually less than 6-9 mm.

5.2. Gyratory Crusher Circuit DesignIn practice, large primary gyratory crashers are seldom installed underground. They are

invariably installed at the surface. The charge is preferably fed directly off trucks, tip-wagons,side dump rail cars, and conveyor belts on to a receiving hopper, which feed the crusherthrough a chute. Usually a grizzly is placed prior to the feed entering the crasher to removeextra large pieces, which tend to jam the operation. Gyratory Crushers are invariable operatedin open circuit.

When a choice has to be made to include a gyratory or a jaw crasher in a circuit, a generalrule of thumb is to examine the desired production rate. Where the production rate required isin excess of 900 t/h, gyratory crashers are always the preferred option.

The primary gyratory crashers operate in open circuit while the last stages, either thesecondary or tertiary crashers are invariably configured to operate in closed circuits in serieswith the primary crasher.

The need for the secondary crusher is dictated by the size of the product required. Theproduct size from a primary crasher is limited by the possible reduction ratio, which normallyis around 10:1. The feed size to a primary crasher from the mines could be 1 to 1.5 m thus themaximum product size possible is 10 to 15 cm which is normally too large for down streamprocessing for mineral liberation. Hence secondary and possibly tertiary crasher stages formpart of the crashing circuit design.

The final product size from the circuit depends on the close set of the secondary crasherand on the screen apertures. The same logic is used where the final product size requires theinstallation of tertiary crushers.

To develop a crashing circuit it is useful to remember that the ranges of reduction ratios ofcrashers are:

133133

• Primary crusher 3:1 to 10: 1• Secondary crusher 6:1 to 8:1• Tertiary crusher = 10:1

Thus if a project requires a final product size of say 3 mm, then maximum feed size totertiary crusher should be 30 mm. As this would be the discharge size from the secondarycrusher, the maximum feed size of the secondary crusher should be about 240 mm. Similarlythe feed size to the primary crusher should not exceed (about) 2400 mm. Once the feed sizesfor different stages of crushing are determined the sizes of the crushers can be estimated usingthe rule of thumb that the gape of crusher is usually 1.1 times the feed size. This rule ofthumb for sizing the gape of primary jaw crushers is applicable to crushers up to 2 meters indiameter. Once the gape is determined, the size of the primary crusher can be ascertainedfrom relations given in Table 1. Such considerations are very rough indicators on the possiblesizes of crushers that would meet the desired criteria in a crushing circuit. Considerableexperience is required to make the final choice of equipment. Mathematical modelling of anoperation can make prediction of product sizes easier. This aspect is dealt with in Chapter 11.

5.3. Gyratory Crusher OperationMost crushing operations are performed in dry conditions. Water is only used occasionally

as a lubricant to wash or flush the fines and sticking material on crusher surfaces. Gyratorycrushers can accept 8-10% moisture in operation, but the fine content should be preferablyless than 10%. The crushing action in gyratory crushers is regarded as rings or "helics"(spirals) of feed down through the crusher of which a single section may be regarded assimilar to the jaw crusher. Therefore computations leading to the performance of gyratorycrushers may be considered very similar to jaw crushers. Thus, as in jaw crushers, theperformance of gyratory crushers will be affected by:

1. Fines content (fine should preferably be less than 10%)2. Inherent and total moisture content in the ore/rock3. Feed distribution in the crushing area and the bulk density of the feed.4. Hardness of ore (Work Index).5. Recirculating load in the case of closed circuit crushing.

The operation of crushers depends on the gyrating speed and the open and closed setpositions. For a uniform size of the product it is necessary to charge uniformly and distributethe feed evenly around the spindle keeping a constant level of feed in the crushing chamber.Idling should normally be avoided as the idling load power consumption is about 0.3 timesthe full load power consumption.

The operation of gyratory crushers is subject to the gape size, diameter of the mantle, theopen set, throw and speed of gyration. It also depends on the ore characteristics including thework index of the ore. Manufacturers generally supply the operational characteristics ofindividual types of gyratory crushers in the form of characteristic curves. Limestone is theusual mineral used for comparative purposes. The performance of selected sizes of gyratorycrushers (Table 5.5) operating with ores of various work indices indicate a wide range ofperformance with different operational settings. For details manufacturer's literature shouldbe consulted.

134134

Table 5.5Gyratory crusher operation [3].

SizeGape x Dia. of

mantle, mm1219x 18791371x18791828x23111524x22681524x22681219 x 20571524 x 2591

LMAX(Open Set)

mm200

137-223194

200-275238-275175-188

225

LT(Throw)

mm34444437373734

Gyration/min

1351351111139293134

Capacity(Production)

t/h2200310027503200318013302290

Work Indexof OrekWh/t

--

1361210-

5,3.1. Gyrating Speed of HeadOne of the important factors in the operation of a gyratory crusher is to determine the speed ofgyration to attain a specific product size at a specific rate. In general, the speed of crushing isinversely proportional to the size of the feed. If the feed size is increased, the speed ofgyration has to be decreased. There is some evidence [6, 7] that the speed of rotation requiredto produce particles less than size d should not be less than that given by the followingexpression [8]:

665(sin8-ncos6)cycles per min (5.1)

where 6 = inclination of the cone to the horizontalu = coefficient of friction of the materiald = size of crusher product, cm.

For example, if 9 = 75°, d = 10.2 cm and JJ,= 0.2, then the gyrating speed, v, is given by:

v >[66.5 (0.966-0.2x0.259)]

V0.102190 cycles per min.

Eq, (5.1) gives a rough guide to the gyration speed of a gyratory crusher of knowngeometry. However, manufacturers should be consulted regarding details of crusher operationand recommendations based on data on individual models.

5.4. Capacity

5.4.1. Gyratory crushersThe mechanism of crushing is considered similar to that of a jaw crusher. The difference isthat instead of wedges, the elements of material in the process of being crushed can beregarded as rings or spirals of which a single section may be regarded as similar to that of ajaw crusher which is inclined at an angle 8 to the horizontal. The operation of a gyratory

135135

crusher involves only one-half of its surfaces while in jaw crushers the entire crushing surfaceis involved.

Using this concept early workers [6,7,9] derived expressions for estimating the capacitiesof gyratory crushers. Hersam's approach [9] has been described in chapter 4, but its use doesnot often tally with actual performance. The variation is probably due to the uncertainty in thevalue of K. Gauldie [6,7] theoretically derived an expression for capacity by considering theangle of inclination of the breaking head and the distance travelled by ore particles during asingle cycle of breakage. Gauldie's expression for optimum capacity is:

Q= 0.35 7rsine(LMAx+LM iN)gH(sine-ncos6)0 5 (5.2)

where LMAX = Maximum distance between gyrating head and concave

LMIN = Minimum distance between gyrating head and concave

9 = Inclination of cone to the horizontalg = Acceleration due to gravityH = Vertical height of the chamber

Gauldie's expression is difficult to apply in practice as the angle of inclination is difficultto measure. An easier method to estimate capacity is to apply the method advocated by Roseand English for jaw crushers.

5.4.2. BromanBroman [10] developed an expression for the capacity of gyratory crushers based on the samelogic used for jaw crushers. For deriving the expression, Broman considered a cross-sectionof a surface of material in a crusher and determined the time taken and distance travelledduring one cycle of the head. The optimum volumetric capacity of a gyratory crusher is givenby the expression:

Qv = ( D M - L M I N ) * L M I N L T 6 0 N K ^

tana

where Qv = volumetric capacity of the gyratory crusher, m3 /hDM = mantle head outer diameter at the discharge point, mLMIN = closed set, mLT = length of throw, (Stroke length), mN = number of gyrations per minute,K = material constant having a value between 2 - 3,a = angle of nip.

Broman suggests that the frequency should not exceed a critical value as it would result ina decrease in production and has shown that capacities calculated using Eq. (5.3) agree withpractice.

5.4.3. Rose and EnglishThe theoretical work of Rose and English [11] to determine the capacity of jaw crushers isalso applicable to gyratory crushers. According to Rose and English, Eq. (5.4) can be used todetermine the capacity, Q of gyratory crushers:

136136

W,Dp s . . /LM A X-LM I N (LMAX+LMIN)K= p=== tph (5.4)

where Wj = Bond's work indexD = Diameter of bowl at a given cross-section,LMAX = Maximum distance between bowl and lower edge of mantle,LMIN

= Minimum distance between bowl and lower edge (closed set)R = Reduction ratioK = Statistical factor

For soft materials, like coal and coke, K = 0.5For harder materials, like quartz and granite, K = 1

Capacities of gyratory crushers of different sizes and operation variables are published byvarious manufacturers. The suppliers have their own specifications which should beconsulted. As a typical example gyratory crusher capacities of some crushers are shown inTables 5.5 and 5.6.

Table 5.6Gyratory crusher capacity for a feed of bulk density 1600 kg/m3 at maximum throw [12].

Model

42-6550-6554-7562-7560-8960-110

Feed opening(G), mm

106512701370157515251525

LMAX

mm140-175150-175150-200150-200165-230175-250

Capacityt/h

1635-23202245-27602555-33852575-37204100-55505575-7605

5.4.4 Cone CrushersThe methods applicable for estimating the capacities of primary gyratory crushers are alsoapplicable to cone crushers. To select a cone crusher of a definite size, the maximum productsize from the primary crusher is first checked. The gape of the secondary crusher should be1.1 times larger than the largest particle in the feed and the feed should have 80% less than70% of the feed opening of the crusher. Reference to manufacturer's data on performance ofcone crusher sizes is useful. Table 5.7 indicates the performance of cone crushers operatingin open circuit. The product is defined as fine, medium and coarse which will depend on thecrusher set.

5.5. Power ConsumptionTo compute the power consumption of gyratory crushers, knowledge of the ore work index

and crusher capacity is necessary. In its simplest form, the power consumption is given by:

137137

P = W ; Q (5.5)

where P = Power, kWWi = Work Index, kWh/tQ = Capacity, t/hFgo = Size through which 80% of the mineral feed passesP8o = Size through which 80% of the product passes

Table 5.7Typical Capacities of Standard and Short Head Cone Crushers in Open Circuit [12].

Crusher

HP800Standard

HP800Short Head

MP1000Standard2392 mm

Type

FineMediumCoarse

FineMediumCoarse

FineMediumCoarse

Feed opening(open), mm

267297353

3392155

300390414

LMIN, mm

253232

51013

253238

Capacity, t/h

495-730545-800545-800

260-335325-425

915-1210

1375-1750

This expression has been used by Rose and English [11] to calculate the power required forjaw crushers. The expression is claimed to be applicable for gyratory crushers as well. Eq.(5.5) indicates that once the comminution parameters, F8o and P8o, are established, the powerconsumption is directly proportional to the capacity. Thus substituting the value of Q fromEq. (5.4) into Eq. (5.5), the power can be calculated.

Motz [5] suggested that when the work index is not known, a rough guide could beobtained from the expression:

Work Index = ° ' 0 4 8 5 (Average Impact Strength)

Ps

where the average impact strength is in J/m.

Motz [5] expressed the power requirements of gyratory crushers by the expression:

(5.6)

P =10

kW (5.7)

138138

When a range of particle sizes are charged for crushing, as is usual from run of mine ores, thepower required has to be considered for only those particles that are larger than the closed set.The particles smaller than the closed set will gravitate down the crusher chamber anddischarged without crushing for which no extra power is required, hi actual practice it hasbeen found that for primary crushers, the following rule of thumb applies;

Total kW = Crushing capacity x kWh/t x K (5.8)

For primary crushers, K= 0.75 and for secondary crushers, K = 1

The calculated power described often differs from that observed by manufacturer's ratingshence a material balance method advocated by Whiten [13,14] and subsequently developedand applied by Andersen and Napier-Munn [15,16] is now accepted. This method is describedin Chapter 11.

5.6. Problems

5.1A primary gyratory crusher was required to crush iron ore at the rate of 3000 t/h. The largestsize of the Run-of-Mine ore was 1000 mm. The required product size was less than 162 mm.Manufacturer's data indicated that the nearest size of gyratory crusher would be 1370 mm x1880 mm with a cone angle of 18°. The work index of the ore was 14 kWh/t, the S.G. 4.5 andthe coefficient of friction, 0.43.

Calculate:

1. The closed set required to produce the desired product2. The frequency of gyration.

5.2A conveyor belt fed a Run-of-Mine iron ore to a gyratory crusher, which had a gape of 356cm. The maximum opening at the discharge end was 15.0 cm and the close set 4.5 cm. 80 %of the feed and product was less than 15.0 cm and 2.4 cm respectively. The size distributionof feed and product was as follows:

Size, cm+360+180+90+45+25-25

FeedWt,% retained

1.032.038.212.36.5

10.0

Size, cm+4.5+2.4+1.2+0.6+0.3-0.3

ProductWt. % retained

20.235.413.811.88.4

10.4£100.0 £100.0

The gyration was 15° to the horizontal. Estimate:

139139

1. The optimum throughput of the crusher,2. Power required for material having a Bond Work Index of 13.4 kWh/t,3. Minimum frequency of gyration.

5.3Limestone having a mean particle size of 50 mm is crushed in a cone crusher the product sizeanalysed.

Size, mm12.08.06.03.0

Mass % retained0.38.0

42.018.0

Size, mm1.500.750.40

-0.4

Mass % retained10.012.05.04.7

Xi oo.o

The power consumed for the operation was 8.0 W/kg. The feed size was then altered to anaverage size of 20 mm. A product of 0.5 mm (mean size) was required. Estimate the powerconsumption after the change in feed size.

5.4A gyratory crusher was installed in a gold mine where it was expected to crush the ore at arate of 660 t/h. The crusher was arranged to gyrate at 140 cycles/min at an angle of 30° to thehorizon. Estimate:

1. Radius of the cone,2. Change in throughput when the crusher was switched to dolomite (S.G. = 2.8),3. The change required in the set to maintain the same throughput as the gold ore.

5.5A cone crusher of height 2.1 m, open side feed opening 30.4 cm and a closed set at 5.1 cmgyrated at 480 rpm to crush quarry limestone scalped at 20.3 cm opening screen. The crusherwas expected to crush at the rate of 1000 t/h. Calculate:

1. The level at which the charge has to be maintained2. Angle of the crusher head

5.6A gyratory crusher size 33-55 was designed to accept feed of size 68 cm x 178 cm. The openside setting of the discharge opening was 10.2 cm. The rate of gyration was 175 per minute.Calculate:

1. The capacity of crusher for an eccentric throw of 1.6 cm,2. What would the eccentric throw be if the crusher capacity had to be increased to 600 t/h

at the same setting,3. If the open side setting of the discharge opening was altered to a setting of 12.7 cm what

will be the per cent increase in production.

140140

5.7A gyratory crusher, 122 cm x 304.6 cm, required 300 HP to operate at a gyration of 135cycles/min. When the eccentric throw was 2.5 cm and open side setting 12.7 cm, it produced1023 t/h of crushed ore. The open side setting was gradually increased in steps of 1.3 cm to20.3 cm and tested for productivity during comminution of magnetite ore (S.G. of 5.3). Allother variables being the same, establish a relation between productivity and the set at thedischarge opening.

5.8A secondary crusher (size 16-50) with approximate feed opening of 41 cm x 40 cm had aneccentric throw of 1.9 cm. Gyrating at 225 rpm it crushed limestone with an open setting of3.8 cm. Calculate the per cent change of power required when the open setting was altered to9.0 cm.

5.9Dry limestone was crushed at a rate of 100 t/h. 80% of the feed passed a square screen havingan opening of 25.4 mm and 80% of the product passed a 3.2 mm square screen. The S.G. oflimestone was 2.66 and the Bond Work Index 12.74 kWh/t.Estimate: The HP required to crush (1 kW = 1.34 HP).

5.10The feed size to a gyratory crusher is 2.54 cm and nearly uniform. The product analysis isgiven in column (2) in the table below. The power required to crush the feed was 500 kW.The clearance between the crusher head and cone was then reduced yielding a product whosesize distribution was given in column (3) of the same table. Estimate:

1. The power required in the second operation2. The change in reduction ratio if the power was reduced by 10%.

Size microns

-4750+3350-3350+2360-2360+1700-1700+1180-1180+850-850+600-600+425-425+300-300+212-212+100-100+150-150+106-106

ProductAfter 1st

crush2.0

10.018.020.015.012.010.57.64.40.5

0.1

analysisAfter 2nd

Crush

2.710.013.220.120.214.28.07.04.00.40.10.1

Z100.0

141141

5.11A gyratory crusher received iron ore from the mines at 1.5 m top size. The work index of theore was determined as 12.5 kWh/t. The height of the bowl was 9.75 m and it was required toproduce 300 t/h of crushed material at 175 rpm. Calculate the required crusher set to satisfythe crusher throughput.

5.12A long shaft suspended spindle gyratory crusher 12.7 cm x 127 cm was commissioned tocrush limestone with a work index of 13.2 kWh/t. The crusher was adjusted to a throw of 0.7cm and the set at 2.54 cm. The average size distribution was:

Sizemass%

1040

.2

.2cm 7.6cm

23.85.1cm16.1

2.54 cm19.0

10

.27cm

.9

It was operated initially at 500 rpm and then at 600 rpm. Assuming a shape factor equal to 1,estimate:

1 The production at each speed of gyration,2. The difference in power required between the two speeds of gyration,3. The critical speed of gyration.

REFERENCES[I] S.J. Truscott, A Textbook of Ore Dressing, Macmillan and Co., London, 1923.[2] A.F. Taggart, Handbook of Mineral Dressing, John Wiley, 1954, pp. 4-14,4-29.[3] S.C. Westerfield, in Mineral Processing Handbook, N.L. Wiess (ed), SME/AIMME,

(1985) 1.[4] N.L. Weiss, Mineral Processing Handbook, AIMME, 1985.[5] J.C. Motz, in Mineral Processing and Plant Design, A.L.Mular and R.B.Bhappu (eds),

SME/AIMME, New York, 1980, pp. 203-238.[6] K. Gauldie, Engineering, London, Oct 9, (1953) 456.[7] K. Gauldie, Engineering, London, April 30 (1954) 557.[8] S.K. Mishra, Private communication (1980).[9] E.A. Hersam, Trans. AIME, 68 (1923) 463.[10] J. Broman, Engineering and Mining Journal, June (1984) 69.II1] H.E. Rose and J.E. English, Trans. Inst of Mining and Metallurgy, 76 (1967) C32.[12] Metso Minerals, Retrieved: on 18 January 2006 from http://metsominerals.com;

http://www.ckit.co.za/Secure/Brochures/Metso/Nordberg%20HP%20Cone%20crusher/Nordberg%20HP%20cone%20crusher.htm

[13] W.J. Whiten, 10th International Symposium on Application of Computer Methods inMin. Ind., Johannesburg, (1972) 317.

[14] W.J. Whiten, Control '84, J. Herbst (ed), SME, 1984, pp. 217-224.[15] J.S. Andersen and T.J. Napier-Mann, 3rd Mill Operators Conference, Cobar, NSW, May

(1988) 103.[16] J.S. Andersen and T.J. Napier-Mann, Mining Engineering, 3 (1/2) (1990) 105.