A Case for Forged Mill Balls - EIZ Meeting, Livingstone, Zambia, 2008

8/14/2019 A Case for Forged Mill Balls - EIZ Meeting, Livingstone, Zambia, 2008

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By Ramoutar (Ken) Seecharran (MEIZ)By Ramoutar (Ken) Seecharran (MEIZ)

Plant Superintendent, Frontier Sprl, DR Congo

A CASE FOR FORGED MILL BALLSCASE FOR FORGED MILL BALLS


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FIRST QUANTUMFIRST QUANTUMs ACTIVITIESs ACTIVITIES


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PLACEFIX MAP SHOWING FRONTIER MINEPLACEFIX MAP SHOWING FRONTIER MINE


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BRIEF HISTORY OF FRONTIER MINEBRIEF HISTORY OF FRONTIER MINE

The deposit was known to exist, but not fully quantified

The Japanese had shown interest during the Gecamine erabut depressed copper price and high project cost curtailedproject implementation

First Quantum was operating the Lonshi mine to the south east

of this deposit, in the Pedicle, so logistically, it was easy forus to carry out extensive drilling

Once quantified, the board was committed to our development

of copper deposits in this part of Africa, and approved the project

The project was implemented at a cost of $US226m


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For the valuable mineral(s) of an ore to be economically separatedfrom the waste, host rock (gangue), the ore has to be broken downto a small enough size (comminuted), to liberate it (them) from therock matrix. Comminution represents the most expensive part of aplants circuit. At this point, we minerals engineers use our knowledgeof the properties of the various minerals to exploit noticeable differencesin those properties, between the valuable mineral(s) and their ganguecounterparts.

These differences in properties could be: Difference in specific gravity Difference in solubility in a suitable dissolving chemical Difference in magnetic susceptibility or,

Difference in surface properties

BEFORE THESE DIFFERENCES CAN BE EXPLOITED, WE MUSTPRESENT THE MINERALS TO THE SEPARATION STAGE INAS UNIFORM A SIZE AS POSSIBLE, IDEALLY, ALL OF THE SAMEGRAIN SIZE.OR AS NEAR TO THE SAME SIZE AS POSSIBLE


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So once broken, the grains of minerals in the ore must be sized.

Those which meet this size requirement progress to the separationstage, those failing, are given another chance to be broken.Therefore, the ideal sizing machine should be some form of a screen,however, the huge tonnages we treat these days will not make screening

feasible. Hydrocyclones are used as a practical compromise.A hydrocyclone utilises drag force to remove the fines through the vortexfinder in the middle of the cone while the coarser particles are actedupon by centrifugal force and forced outwards towards the wall. Theythen migrate downwards under gravity and get another chance tobe broken.


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THE NEED FOR COMMINUTIONTHE NEED FOR COMMINUTION


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POLISHED SECTIONS OF FRONTIERPOLISHED SECTIONS OF FRONTIERs OREs ORE

FREE CuFeS2LOCKED CuFeS2


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POLISHED SECTIONS OF CONGOLESE/ZAMBIAN Cu ORESPOLISHED SECTIONS OF CONGOLESE/ZAMBIAN Cu ORES


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Traditionally, comminution in a concentrator plant was carried out in afew well defined steps, namely:

Primary crushing.underground or on surface

Secondary crushing.on surface in the concentrator plant Tertiary crushing.in the concentrator plant, and in closed circuit witha screen

Ball milling.in the concentrator plant

Before the refinement of tertiary crushing, this function was performedby rod milling. Rod mills became unfashionable in the early 1960sas crusher bowl and mantle profile research enabled ore to be crushedsuccessfully to a size below 10mm without causing metal to metalcontact between the crushing faces.

Crushing and screening plants had numerous operational problemssuch as Bogged crushers, Blinded screens and Blocked chutes. A

phenomenon we plant operators called the three Bs!


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FRONTIERFRONTIERs OPEN PITs OPEN PIT


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PROCESS DESCRIPTION AT FRONTIERPROCESS DESCRIPTION AT FRONTIER

Run of mine ore is primary crushed and stockpiled Crushed ore at a size of 80% smaller than 112mm is fed to a

Semi Autogenous Grinding (SAG) mill SAG mill product is fed to a cluster of hydrocyclones (sizing device) wherethe fine product progresses to the separation stage and the coarse fractionis routed to a ball mill and given a second chance to be broken, the ball millproduct is fed to the same cluster of hydrocyclones, in order to close the circuit

Separation of valuable mineral from waste is carried out using froth flotation The copper minerals recovered is thickened and filtered to produce a solidcake containing about 9.5% moisture

The waste rejected (tailings) is thickened and disposed of in a responsible

manner in a tailings impoundment All water used in the plant is recycled in the process


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GYRATORY CRUSHER AT FRONTIERGYRATORY CRUSHER AT FRONTIER


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CRUSHED ORE STOCKPILECRUSHED ORE STOCKPILE


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SAG and BALL MILLS AT FRONTIERSAG and BALL MILLS AT FRONTIER


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INSIDE THE SAG MILLINSIDE THE SAG MILL


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SEPARATION UTILISING FROTH FLOTATIONSEPARATION UTILISING FROTH FLOTATION


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People being exposed to SAG milling for the first time often

underestimate the crushing forces present in these mills. Theyare normally of >32 feet in diameter. So the crushing force atthe toe of the crop load, the cataracting end, is phenomenal.Some studies suggest pressures as high as 20 bars are present.

Due to the shortage of suitable grinding media in Sub-SaharanAfrica, we were forced to start our plant with sub-standardgrinding media in October 2007. Time was of the essence as wewere faced with an entirely new work force and on-the-job

training had to be expeditiously carried out.


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POROUS CAST BALLPOROUS CAST BALL-- INVITING DISASTERINVITING DISASTER


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POROUS BALLS AFTER 20 Hrs OPERATIONPOROUS BALLS AFTER 20 Hrs OPERATION


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A WEEK LATER!!!!A WEEK LATER!!!!

EVEN THE BETTER QUALITY CAST BALLSEVEN THE BETTER QUALITY CAST BALLS

HAD THEIR OWN PROBLEMSHAD THEIR OWN PROBLEMS


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HAD THEIR OWN PROBLEMSHAD THEIR OWN PROBLEMS.caused by the intense pressure in the SAG mill


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BROKEN BALLS ARE DETRIMENTAL TO SAG MILLING OPERATIONSBROKEN BALLS ARE DETRIMENTAL TO SAG MILLING OPERATIONS

They take up useful space that could be occupied by ore. Beingstreamlined, they do not get flushed out easily

They are too light to have enough kinetic energy to break rock

They add to power consumption, by their weight and being pinnedto the mill shell, they get carried up to a point beyond which a wholeball leaves the shell on its trajectory, thus adding more load to the

motor

They add to steel consumption, Fe ions are detrimental to flotation.Sulphide minerals get depressed

When hammered against the discharge grate, they cause peening.Peening reduce the flow through a mill

They act as a cushion against which rocks are hammered by balls,

so breakage is less effective


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Cast balls are not suitable for a SAG mill

The outer crust is hard, typically in excess ofBrinell hardness 450. This quickly diminishes

towards the centre of the ball.

It is for this reason, when you open a SAG mill,in which cast balls were fed, you see balls ofpredominantly one size.


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DATA I COMPILED FOR ZCCM IN 1989DATA I COMPILED FOR ZCCM IN 1989under a different incarnation

BRINELL HARDNESS ACROSS BALL

050

100

150

200250

300

350

400450

500

1 2 3 4 5 6 7 8

PICTURE FROM INSIDE KANSANSHIPICTURE FROM INSIDE KANSANSHI SAG MILLSAG MILL


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PICTURE FROM INSIDE KANSANSHIPICTURE FROM INSIDE KANSANSHIs SAG MILLs SAG MILLNOTE BALLS OF ONE SIZE

EFFECTS OF SOFT CENTRE OF A CAST BALLEFFECTS OF SOFT CENTRE OF A CAST BALL


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EFFECTS OF SOFT CENTRE OF A CAST BALLEFFECTS OF SOFT CENTRE OF A CAST BALLuneven wear

EFFECTS OF SOFT CENTRE OF A CAST BALLEFFECTS OF SOFT CENTRE OF A CAST BALL


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EFFECTS OF SOFT CENTRE OF A CAST BALLEFFECTS OF SOFT CENTRE OF A CAST BALLdimpled ball


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WHAT WAS THE SOLUTION?.....FORGED BALLSThe bar from which a forged ball is made is cut into shots, reheatedand hammered at least 30 times. Compacting and hardening it. Theinitial hot rolling of the bar followed by rapid cooling, reheating and

subsequent hammering, also changes the microstructure from oneresembling pearlitic to that closer to martensitic. The steels grainstructure aligns and stretches in the forging process, thus creating astronger, more compact steel. The balls are then quenched and

reheated for tempering and stress relieving, respectively.

We therefore then get a ball which is of uniform hardness andweight. A ball which can withstand the harsh conditions in a SAG mill.The difference in weight between a well forged ball and an excellent

cast counterpart could be about 9%

Here networking helped us. ECLIPSE foundry in South Africa washelpful. I knew Humphrey, their Zambian representative for many

years, and studied at university in the UK with Jacob, their ex MDin South Africa.

PHOTOMICROGRAPHS OF STEELPHOTOMICROGRAPHS OF STEEL


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PHOTOMICROGRAPHS OF STEELPHOTOMICROGRAPHS OF STEEL

PEARLITIC MARTENSITIC

ECLIPSE FOUNDRYECLIPSE FOUNDRYs FORGED BALLs FORGED BALL


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ECLIPSE FOUNDRYECLIPSE FOUNDRY s FORGED BALLs FORGED BALL


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Although proved to be successful, the volumeof forged balls we required, ECLIPSE wasunable to supply.

So, armed with valuable information gathered from theECLIPSE trial, we went to the European Union, from

where our sister plant in Mauritania was sourcing theirSAG mill balls.

Long lead time and transport logistics remain a nightmare.

I was informed that ECLIPSE has plans to expand theirproduction capacity, we welcome such a symbiotic move.

FORGED MILL BALLS FROM SPAINFORGED MILL BALLS FROM SPAIN


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FORGED MILL BALLS FROM SPAINFORGED MILL BALLS FROM SPAIN

HAND FORGING IN CHINAHAND FORGING IN CHINA


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HAND FORGING IN CHINAHAND FORGING IN CHINA

MILLING INFORMATION SHOWN ON THE COMPUTERMILLING INFORMATION SHOWN ON THE COMPUTER


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MILLING INFORMATION SHOWN ON THE COMPUTERMILLING INFORMATION SHOWN ON THE COMPUTER

EMPHASIS ON CENTRE HARDNESSEMPHASIS ON CENTRE HARDNESS


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AERIAL VIEW OF THE PLANTAERIAL VIEW OF THE PLANT


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FINISHED PRODUCTIONFINISHED PRODUCTION


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CURRENT MILL BALL PROFILECURRENT MILL BALL PROFILE


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BENEFITSBENEFITS


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We have found that throughput has increased, as grindingis now more efficient

The quality of the ground ore has improved

Steel consumption has decreased, due to less

ball breakage and a more competent ball

Grinding cost has decreased, steel consumption droppedfrom about 550 g/tonne of ore milled to about 450.

It is currently running at about $US 1.15 per tonne of ore milledwe are confident that this will reduce as the circuit is optimised

MILL BALLS WORLDWIDEMILL BALLS WORLDWIDE


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ANY QUESTIONS????NY QUESTIONS????

HARDNESS TESTINGHARDNESS TESTING


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BRINELL - A hardened ball of specified diameter is impressedinto the materials surface, at a known pressure. The Brinell

hardness number results from calculations involving the loadand the spherical area of the balls impression.

ROCKWELL This method involves measuring the depth ahardened steel ball or a diamond penetrates into the materialbeing tested, under controlled loading.

STEEL MANUFACTURING PROCESSSTEEL MANUFACTURING PROCESSmicrostructure


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microstructure

STEEL MANUFACTURINGSTEEL MANUFACTURING


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HARDNESS OF MARTENSITE WITH CARBON CONTENTHARDNESS OF MARTENSITE WITH CARBON CONTENT


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FRONTIERFRONTIERs FLOWSHEETs FLOWSHEET


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BEST EVER DAYBEST EVER DAYs RESULTs RESULT


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FIRST QUANTUMFIRST QUANTUMs PRODUCTION PROFILEs PRODUCTION PROFILE


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15 YEAR COPPER PRICE15 YEAR COPPER PRICE


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OROGENESIS, MINERALS FORMATIONOROGENESIS, MINERALS FORMATION


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Cu PRICE IN JAN 2006 centsCu PRICE IN JAN 2006 cents


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NORMAL RUNNING and OVERLOADED MILL


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PEENING OF DISCHARGE GRATESPEENING OF DISCHARGE GRATES


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HYDROCYCLONESHYDROCYCLONES


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HYDROCYCLONE OPERATIONHYDROCYCLONE OPERATION


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Documents

A Case for Forged Mill Balls - EIZ Meeting, Livingstone, Zambia, 2008