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Grinding Business Line

 Andrew Wilkinson

Metso TR Seminar 

27 April 2012

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Metso grinding mills world wide

 York (PA) USA

Product Center 

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Grinding mill sales in % USD$ world wide – 2007Representing 88,2 % of 2007 market

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Metso 41,6 %FLS 37 %

Krupp 1,4 %

Outotec 9,9 %

Citic 3,8 %

Others 6,3 %

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Size reduction mechanisms

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Size reduction is required to liberate theminerals of interest to recover them selectively

Ore Textures Require Different Grinding Strategies / Stages to liberate minerals

Massive Sulphide Net Texture DisseminatedTexture

Pyrrhotite (Waste)

Copper Mineral Serpentine (Waste)

Scale of pictures: each square represents rock 3.5mm x 3.5mm

Ni Mineral

Coarse Grind Req’d  Medium Grind Req’d  Fine Grind Req’d 

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Particle Liberation where economic mineral iscoloured red

Barren MiddlingLocked Liberated

Scale: particle images are from +53 or +75um size fractions

 A typical Mineral Processing Plant will be designed to maximize therecovery of minerals of interest / limited by the constraints of capital andoperating costs and required concentrate grade

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Typical Ball Mill Components

FeedChute

Head

Motor 

InchingDrive

Reducer 

Clutch

JackingCradle

DischargeChute

TrommelLiningMain

Bearing

Shell

Gear Guard

Gear 

Pinion Bearings

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Milling circuits

“Conventional” (traditional) milling circuit 

Wet

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The fine art of milling – “Grinding Mills” Basics

Wet grinding

Dry grinding

Open circuit

Closed circuit

Batch

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Material ground as a slurry

Percent solids by weight (60 to 80%)

Dependent on subsequent process

Requires less power compared to dry

Media and liners consumption higher than dry

Eliminates formation of dust

The fine art of milling – “Grinding Mills” Wet grinding

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 Ground in a dry state

Material less than 1% H20

Dependent on subsequent process

Requires 1.3 times power as wet

Media and liners consumption less than wet

Requires dust collection system

The fine art of milling – “Grinding Mills” Dry grinding

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One pass through mill

 Average 1.4 to 1.5 more power over closed circuit

Broad product distribution

Less control compared to closed circuit

The fine art of milling – “Grinding Mills” Open circuit

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Mill discharge is fed to a sizing device with oversize returning to

the mill

Oversize returning is called circulating load

Less kW per unit ground vs. open circuit

Product top size control

Used in both wet and dry milling

The fine art of milling – “Grinding Mills” Closed circuit

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Material retained for batch-wise charging and discharging

Specialty applications

The fine art of milling – “Grinding Mills” Batch

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Overflow mills

Grate or diaphragm mills

Peripheral discharge mills

The fine art of milling – “Grinding Mills” Discharge arrangements

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Performance profiles - Grinding mills

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 AG/SAG Mills

• Application- Primary grinding

• Types- Wet- Dry – Airswept

• 1,8 m. to 13,4 m. diameters

• 7 kW To 30MW

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40 ft. Shell

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Pebble Mill Grinding

Secondary grinding

Grinds product from primary grinding step, which isnormally; Rod Mill, AG-Mill or SAG Mill Grinding

Grinding media (Pebbles) consists of screened outfractions of the ore itself, synthetic pebbles or manufactured Al

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O3

. 50-90 mm in size, sometimes larger 

Grate discharge

Lower charge and pulp density than Ball Mill Grinding

Pebble Mills are larger than Ball Mills running at the samehorse power draw

Pebble consumption normally between 5-20% of the ore

quantity Speed: 75-85% of critical

No metal contamination

Grate discharge

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• 1,5m to 4,5m diameters

• 55 to 1500 kW

•  Application

- 5mm to 0,5mm product

• Types

- Wet trunnion overflow

- Dry peripheral discharge

- Dry center discharge

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Rod Mills

Overflow

End peripheraldischarge

Center peripheral

discharge

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Ball Mills

• Tumbling mill

• Steel media

• 1,2m to 8m dia

• 1,5 kW To 15,5 MW

• Minus 15mm feed

• Minus 0,5 mm to micron

sized products

Overflow

Grate discharge

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SALA Rubber Roller (SRR) Mills

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PROP&EST DEPTPRESENTATION – OCT.

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PRESENTATION  OCT.2007 – D.SHAFFER

Rendering By: George Geesey

Typical dry grinding

& air classifier system

(Medium to fine products)

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Metso Mill Types

•AG (Autogenous Mill)

• Pebble Mill

• SAG (Semi Autogenous Mill)

• Rod Mill

• Ball Mill

• SRR Mill (Sala Rubber Roller Mill)

• Hardinge Conical Ball Mill

• Vertimill• SMD (Stirred Media Detritor)

• VBM

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THANKS FOR YOUR ATTENTION