To a more significant degree than in other comminution devices, SAG Mill Liner Design and Configuration can have a substantial effect mill performance. In general terms, lifter spacing and angle, grate open area and aperture size, and pulp lifter design and capacity must be considered. Each of these topics has had a considerable amount of research, and numerous case studies of evolutionary liner design have been published. Based on experience, mill-liner designs have moved toward more open-shell lifter spacing
AG and SAG mills are now the primary unit operation for the majority of large grinding circuits, and form the basis for a variety of circuit configurations. SAG circuits are common in the industry based on:
- High single-line capacities (leading to capital efficiency)
- The ability to mill a broad range of ore types in various circuit configurations, with reduced numbers of unit operations (and a corresponding reduction in the complexity of maintenance planning and coordination)
- Favourable operating costs (with contributions from reduced liner/media consumption relative to conventional circuits)
Though some trepidation concerning AG or SAG circuits accompanied design studies for some lime, such circuits are now well understood, and there is a substantial body of knowledge on circuit design as well as abundant information that can be used for bench-marking of similar plants in similar applications. Because SAG mills rely both on the ore itself as grinding media (to varying degrees
The video below graphically explains the common problem of Coarse Ore Stockpile Segregation. This topic relates to SAG Mill tonnage and the bad habit of putting bulldozers “dozers” on ore stockpiles.
Plants designed using The Barratt Method as published in the Book Mineral Processing Plant Design, Practice, and Control Proceedings, include:
- Batu Hijau
- Cadia (one consultant among others)
- Clarabelle (Inco)
- Collahuasi (line 1 & 2)
- El Teniente SAG 1
- Ernest Henry
- Freeport 95K expansion
Numerous benchmarking exercises to operating grinding circuits in mines are published online.
The Drop Weight tests (DWT) by JK is now replaced by the JKMRC Rotary Breakage Tester. It is faster as confirmed by Tony and now used by many since its intro http://www.min-eng.com
In an AG/SAG mill there are two main mechanisms of breakage, namely impact (high energy) and abrasion (low energy). The industry accepted JK
impact breakage parameters, A and b, can reliably be determined using the new generation high throughput JK Rotary Breakage Tester® (JKRBT®).
Here is a download link to a pre-build Excel file you can use in testing for with a Rotary Breakage Tester to obtain the data
Beginners might ask what grinding test data is required in order to properly size a grinding mill. After the grind requirements are established, testing for the selection of comminution circuits and mill size can be initiated and can include the following:
- Primary Autogenous Media Competency
- Primary Autogenous and Semi-Autogenous Pilot Plant
- Secondary Autogenous (Pebble) Testing
- Impact Crushing – Bond Work Index
- Rod Mill Grindability – Bond Work Index
- Ball Mill Grindability – Bond Work Index
- Abrasion Index
- Crushing, Grinding and Concentration Pilot Plant
SAG & AG Mills can be sized according to any of the most appropriate methods of rock hardness testing like SPI, JK, Barrett and Starkey.
This discussion will be limited to testing for selection of rod and ball mills. Rod and ball milling, using grinding media of known quality, are well established and require much simpler grinding test
This design of SAG mill feed chute lasted 9 months seeing 90,000 TPD. It is 600 brinell chrome steel.
With the big liners on the bottom of the chute you need to get a Chevron cast into the top to push the feed out to the sides for the first little while and then as the chevron wears it will start to come back into the centre. This will make the wear life longer and more even on that piece. The 100mm wide x 100mm high chevron need be included in the casting.