Simulation Glossary

A grinding process where the ore itself acts as the grinding media - larger rocks tumble and break smaller ones, without added steel balls. Used for competent, hard ores.

The total volume of steel grinding balls inside the mill, expressed as a percentage of the mill internal volume. Typically 25–40% for ball mills.

The mix of particle sizes in the charge, defined in the PSD editor as diameter/percentage rows that total 100%. Multiple sizes fill interstitial spaces for better grinding efficiency. Separate PSDs are set for grinding media and ore.

A charge motion regime below ~65% critical speed. Balls roll and slide down the charge surface continuously. Grinding occurs mainly by attrition. Gentle - suitable for coarse feed.

A charge motion regime between 65–82% critical speed. Balls are lifted by lifters, detach from the shell, and fall in projectile arcs - impacting the toe zone with high energy. Optimal grinding regime.

A charge motion regime above ~82% critical speed. Centrifugal force exceeds gravity, pinning balls to the shell wall. No effective grinding occurs. Must be avoided.

The total fill of grinding media plus ore/slurry, expressed as a percentage of mill internal volume. Typically 30–45%. Exceeding 45% reduces grinding efficiency.

The rotational speed at which centrifugal force on a particle at the shell equals gravity. Calculated as Nc = 42.3 / √D RPM (D in metres). Mills operate at a percentage of this speed.

Discrete Element Method. A numerical simulation technique that tracks every particle individually - position, velocity, and collisions - to predict bulk charge behaviour.

See Charge Level. The combined volume of media and ore as a percentage of mill volume.

A dimensionless coefficient (0.05 slippery → 0.7 sticky) representing grip between surfaces. The simulator models four independent coefficients: media-to-media, media-to-boundary, ore-to-ore, and ore-to-boundary. Higher boundary friction lifts the charge further up the shell before slippage.

A mill discharge design using a grate with slots. Only particles smaller than the slot width can exit, controlling retention time. Used in SAG and primary ball mills.

The kinetic energy released when cataracting balls strike the toe zone or liner. Proportional to ½mv². Higher impact energy means more effective breakage but faster liner wear.

A raised bar on the inside of the mill shell that lifts balls as the mill rotates. Height, width, face angle, and spacing all affect charge motion and grinding efficiency.

The height of the vertical leading face of a lifter bar, measured from the base. Below LEH the face is vertical; above it the face rakes back at the face angle. A lower LEH angles more of the face.

The rake angle of the lifter's leading face, measured from vertical (0° = vertical). Steeper angles lift balls more directly and higher. Shallower angles release balls earlier in the rotation.

A 1–10 scale of mineral scratch hardness (1 = talc, 10 = diamond). Used to characterise ore abrasiveness and predict liner wear rates.

The volume of ore plus slurry as a percentage of mill internal volume. Typically 10–30%. Must leave room for the grinding media to move.

Curved vanes behind the grate that carry slurry from the grate to the discharge trunnion. Efficient pulp lifter design reduces backflow and slurry pooling.

The average time material spends inside the mill. Longer residence time produces finer grind but lower throughput. Controlled by feed rate and discharge design.

A tumbling mill using long steel rods as grinding media. Operates in cascading regime. Used for coarse grinding ahead of ball mills.

A wear-resistant natural or synthetic rubber layer inside the mill shell. Absorbs impact energy, reduces noise, and outlasts steel in low-impact applications.

Semi-Autogenous Grinding mill. Uses a combination of ore and a small percentage of steel balls (typically 6–15%) as grinding media. Common in primary grinding circuits.

The structural steel plate forming the mill shell, behind the rubber lining. Thickness (30–150 mm) is set independently for the leading (left) and trailing (right) sides of each lifter, so the plate top ramps from left to right between lifters into an angled ball-tumbling surface. The average thickness feeds area and critical-speed calculations; the plate forms the lifter base.

The reduced shell-plate thickness sitting under each lifter bar (10 or 15 mm). Produces the stepped cross-section: full plate thickness between lifters, lip thickness under lifters.

Lifter arc pitch (S = π·D_pitch / N) divided by effective lifter height (H_eff). A key lifter-design metric. Per Malcolm Powell the target S:H is aimed at mid-life of the liner — a new liner starts below the target and wears up through it. Application presets (SAG ≈ 2.9, Primary Ball ≈ 3.0, Secondary Ball ≈ 2.5) with a working band, plus a progressive-wear slider, are configured in Default Settings.

A multiplier (1–3×) applied to the target media or ore area at seed time. Extra particles are dropped under gravity so that after settling the pile packs up to the target charge line.

Detected when a large grinding-media ball strikes the liner above 3.5 m/s. Classified into Medium (3.5–4.5 m/s) and High (≥4.5 m/s) severity bands. An expanding red flash marks the impact point and the dominant band is reported with the worst impact speed.

A fading yellow path that follows a selectable fraction (25/50/75/100%) of the largest-diameter media balls, recording their shoulder→toe cataracting trajectory. Newer segments render brighter and thicker.

The angular position where the ball charge reaches its highest point during rotation. In the simulator an orange block marker on the liner tracks the shoulder of the largest media.

A mixture of ground ore particles and water. In the simulator, slurry particles have reduced gravity and lower restitution to simulate liquid behaviour.

A pool of liquid slurry that forms at the bottom of the mill when slurry is enabled. Pools slosh with rotation and dampen ball motion at the toe.

The angular position where cataracting balls land - the primary impact zone. A blue block marker on the liner tracks the toe of the largest media. Directly correlates with liner wear patterns; Multotec uses toe angle to optimise lifter design.

The hollow cylindrical supports at each end of the mill through which ore enters and slurry exits. The mill rotates on trunnion bearings.

The region of the shell liner that experiences the most material loss over time. Predicted by the impact heatmap - typically the toe / impact zone in cataracting mills.