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 – 2007 Representing 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 the
minerals of interest to recover them selectively
Ore Textures Require Different Grinding Strategies / Stages to liberate minerals
Massive Sulphide Net Texture Disseminated Texture
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 is
coloured red
Barren Middling Locked Liberated
Scale: particle images are from +53 or +75um size fractions
A typical Mineral Processing Plant will be designed to maximize the
recovery of minerals of interest / limited by the constraints of capital and
operating costs and required concentrate grade
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Typical Ball Mill Components
Feed
Chute
Head
Motor
Inching
Drive
Reducer
Clutch
Jacking
Cradle
Discharge
Chute
Trommel Lining Main
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 is
normally; Rod Mill, AG-Mill or SAG Mill Grinding
Grinding media (Pebbles) consists of screened out
fractions of the ore itself, synthetic pebbles or
manufactured Al2O3. 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 same
horse 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 peripheral
discharge
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 DEPT
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