A SAG (Semi-Autogenous Grinding) mill is a type of grinding mill used in the mining industry to break down large rocks into smaller pieces for further processing. It combines ore, grinding media (typically steel balls), and water to achieve efficient size reduction.
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How a SAG Mill Works:
1. Feed Material:
– Large rocks (ore) are fed into the mill along with water and a small amount of steel balls (typically 6–15% of the mill volume).
– The ore itself acts as the primary grinding medium (hence “semi-autogenous”).
2. Rotation & Impact:
– The SAG mill rotates at a controlled speed (usually 70–80% of critical speed).
– As the drum spins, the ore and steel balls are lifted by liners and then cascade or tumble back down.
– This motion causes impact and abrasion, breaking down the rocks into smaller fragments.
3. Grinding Mechanism:
– Impact: Large rocks collide with each other and steel balls, fracturing into smaller pieces.
– Abrasion: Friction between particles further reduces their size.
4. Discharge & Classification:
– Ground material exits through a discharge grate at the end of the mill.
– Oversized particles are returned for further grinding, while finer material moves to downstream processes like ball mills or flotation.
5. Key Components:
– Shell & Liners: Protects the mill shell and enhances grinding efficiency.
– Drive System: Electric motor with gearbox/pinion or gearless drive (in large mills).
– Lift.jpg)
: Help lift ore and grinding media for effective cascading.
Advantages of SAG Mills:
– Reduced need for secondary crushing (lower energy consumption than conventional crushing/grinding circuits).
– Handles both wet and dry grinding (though wet is more common).
– Flexible feed size (can process large chunks of ore directly from mines).
Applications:
– Primary grinding stage in mineral processing plants (gold, copper, iron ore, etc.).
– Often used in combination with ball mills for finer grinding.
Would you like details on specific operating parameters or comparisons with other mills?