A Semi-Autogenous Grinding (SAG) Mill is a critical piece of equipment in mineral processing plants, used for grinding large chunks of ore into smaller pieces for further processing. It combines both ore and grinding media (typically steel balls) to break down material through impact and attrition.
Key Features of SAG Mills:
1. Grinding Mechanism:
– Uses a combination of ore (autogenous grinding) and a small charge of steel balls (typically 6-15% of mill volume).
– Larger rocks act as grinding media alongside steel balls.
2. Feed Size:
– Handles coarse feed (up to 250–300 mm) directly from primary crushing..jpg)
3. Product Size:
– Produces finer material (~80% passing 10 mesh / 2 mm), which feeds ball mills or flotation circuits.
4. Power & Efficiency:
– High energy consumption but reduces the need for secondary crushing stages.
– Operates at lower critical speed (~70-80%) compared to ball mills.
5. Applications:
– Widely used in gold, copper, platinum, and iron ore processing.
– Often integrated with ball mills in a two-stage grinding circuit (SAG-Ball Mill Circuit).
Advantages:
✔ Reduces overall comminution costs by minimizing secondary crushing stages.
✔ Handles wet or dry feed efficiently.
✔ Flexible operation—adjustable ball charge and mill speed optimize performance.
Disadvantages:
✖ High capital and operating costs due to large size & power demand.
✖ Sensitive to feed size variations—requires consistent ore hardness monitoring.
Components:
- Shell & Liners: Protect the mill from wear; liners are replaceable (rubber/metal).
- Drive System: Gearless (ring motor) or geared drives with pinion/girth gears.
- Discharge System: Grate or overflow discharge depending on product requirements.
- Ore hardness (Bond Work Index) affects throughput.
- Ball charge % impacts grinding efficiency.
- Mill speed (% critical speed) influences particle breakage.
Optimization Factors:
Would you like details on SAG mill circuit design or troubleshooting common issues?
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