Mill Liners | SAG Ball VRM Parts | ATF

Grinding Mill Liners and Components: Materials, Profiles, and Charge Dynamics

Grinding mills — semi-autogenous (SAG) mills, autogenous (AG) mills, and ball mills — are the largest energy consumers in mineral processing, often accounting for 40–60 % of a concentrator's total electrical load. Liner systems directly govern grinding efficiency by controlling charge motion, ball trajectory, and energy transfer from the rotating shell to the ore being ground. ATF manufactures shell liners, head liners, grate panels, discharge grates, pulp lifters, and feed-end components for mills up to 12.8 m (42 ft) diameter, using chrome-molybdenum steel, high-chrome white iron, and rubber-steel composite materials.

Chrome-moly steel is the dominant alloy for SAG and ball mill shell liners. ATF's standard liner grade contains 0.45–0.55 % C, 2.0–3.0 % Cr, and 0.3–0.5 % Mo, quenched and tempered to 325–375 BHN. This microstructure — predominantly tempered martensite with finely dispersed alloy carbides — provides an effective combination of wear resistance and impact toughness (Charpy V-notch values of 20–30 J at ambient temperature). For mills processing highly abrasive gold or copper ore, we offer a higher-chrome variant (5.0 % Cr, 0.5 % Mo) at 375–425 BHN that reduces liner consumption by 15–20 % but requires more careful installation to avoid cracking at bolt holes.

Liner profile design governs the trajectory of the grinding charge. Lifter bars (or lifter rows) protrude from the shell surface and raise the charge to a cataracting or cascading trajectory depending on their face angle, height, and spacing. ATF uses discrete-element-method (DEM) simulation to design liner profiles before committing to pattern manufacture. Key parameters include lifter face angle (typically 15–30 degrees from radial for cataracting action), lifter height-to-spacing ratio (H/S ratios of 0.3–0.5 for SAG mills, 0.2–0.3 for ball mills), and Hi-Lo lifter sequencing — alternating high and low lifter rows that promote a wider distribution of impact points and more uniform liner wear.

Rubber-steel composite liners combine a structural steel insert with a vulcanised rubber shell. This construction reduces liner weight by 40–50 % compared with all-steel designs, which translates to faster installation and lower crane requirements — a significant advantage in remote mine sites with limited lifting capacity. ATF supplies rubber-steel composite lifter bars for SAG mills and full rubber shell liners for ball mills in secondary and regrind service where impact energy is low enough that rubber provides adequate wear life. The rubber dampens noise levels by 10–15 dB and also protects mill shells from direct metal-to-metal contact that can cause shell fatigue cracking over long campaigns.

Grate panels and pulp lifters manage the discharge of ground slurry from SAG and AG mills. Grate-panel aperture size controls the transfer size between the SAG mill and downstream ball mills; typical apertures range from 10 mm to 30 mm depending on the circuit configuration. ATF casts grate panels in chrome-moly steel with wear-resistant inserts around the aperture perimeters, where erosive slurry flow is concentrated. Pulp lifters are fabricated from wear-resistant steel plate and lined with rubber or chrome-moly wear plates. Our pulp-lifter designs include both radial and curved configurations, with the curved design offering improved slurry transport efficiency and reduced back-flow (pebble recycling) that can choke mill discharge.