Parameter Reference

Technical Physics Guide

Each parameter below directly influences the DEM (Discrete Element Method) physics simulation. The mill model computes critical speed from diameter, derives angular velocity, and applies gravitational, contact, and friction forces to every particle each frame.

Mill Geometry

Shell Inner Diameter

D1–12 m

The internal diameter of the mill shell, measured liner-to-liner.

Physics effect: Sets the simulation scale (pixel-to-mm ratio) and the critical speed Nc = 42.3 / √D. Larger mills need lower RPM to reach the same fraction of critical speed.

Rubber Lining

0 / 6 / 12 mm

Thickness of the rubber liner layer inside the shell (discrete options).

Physics effect: Drawn as an exact-thickness band. Reduces the effective interior radius used for charge-area and critical-speed calculations.

Shell Plate Left / Right

30–150 mm

Thickness of the steel shell plate behind the rubber lining, set independently for the leading (left) and trailing (right) sides of each lifter.

Physics effect: Between lifters the plate top ramps from the left thickness to the right thickness, forming an angled ball-tumbling surface. The average thickness feeds area and critical-speed calculations; the plate forms the lifter base.

Shell Plate Lip

10 / 15 mm

Reduced shell-plate thickness under each lifter bar.

Physics effect: Produces the stepped cross-section: angled plate thickness between lifters, lip thickness under lifters.

Lifter Bars

Lifter Height

hL50–400 mm

Radial height of each lifter bar protruding from the shell liner.

Physics effect: Taller lifters carry balls higher before release, increasing cataract flight distance and toe impact energy. Excessive height can pack balls between lifters.

Leading Edge Height

LEH30–165 mm

Height of the vertical leading face of each lifter, measured from the base.

Physics effect: Defines where the angled (raked) portion of the lifter face begins. A lower LEH angles more of the face; a higher LEH keeps the face vertical for longer.

Lifter Width

wL100–400 mm

Circumferential width of each lifter bar at its base.

Physics effect: Wider lifters increase the collision cross-section with balls, enhancing grip but reducing how many lifters fit the circumference.

Lifter Face Angle

α0–45°

Rake angle of the leading lifter face, measured from vertical (0° = vertical).

Physics effect: A steeper angle lifts balls more directly; a shallower angle releases them earlier. Drives the tangential velocity transfer at the lifter face.

Number of Lifters

nL6–60

Count of lifter bars equally spaced around the shell circumference.

Physics effect: More lifters increase ball-lifter interaction frequency and reduce the inter-lifter gap. The S:H guidance flags whether the spacing-to-height ratio lands in the working band (see S:H Ratio Guidance below).

S:H Ratio Guidance

Target Ideal (mid-life)

S:H*configurable

The target spacing-to-height ratio the liner is designed to hit at mid-life, per Malcolm Powell.

Physics effect: A new liner starts below the target and wears up through it. The suggested row count places the new liner at the lower edge of the working band (Target ± band width) so it lands on the target around 50% wear.

Band Width

±configurable

Half-width of the acceptable working band around the target S:H.

Physics effect: S:H inside [Target − band, Target + band] is Optimal (green). Just outside is amber (packing or slippage risk); far outside is red.

Whole-life Min / Max

configurable

Multotec internal tighter band shown as a brighter marker inside the working band.

Physics effect: Used as a whole-life design guide — the ratio should stay inside this inner band across the liner's full wear life.

Application Presets

SAG / Primary / Secondary

Industry-typical target + band presets, enabled by the application selector in Default Settings.

Physics effect: SAG target ≈ 2.9 ± 1.0; Primary Ball ≈ 3.0 ± 1.5; Secondary Ball ≈ 2.5 ± 2.0. Single (custom) uses your own target/band.

Progressive Wear

w0–100%

Optional slider that simulates liner wear from new to end-of-life.

Physics effect: Reduces the effective lifter height so S:H passes through the target at 50% wear, confirming the design tracks well over the liner life.

Charge

Total Charge Level

J+U0–45%

Combined volumetric fill of grinding media plus ore, as a percentage of the mill cross-section.

Physics effect: Sets the target free-surface height for the whole charge. Above ~45% restricts shoulder formation and grinding efficiency.

Grinding Media Level

J0–45%

Volumetric fill of steel grinding balls (clamped to ≤ total charge).

Physics effect: Determines media ball count. The ore portion is the remainder (total − media). Higher media fill increases collision frequency but reduces free flight distance.

Media Over-seed

1–3×

Multiplier on the target media area used at seed time.

Physics effect: Extra particles are seeded so that after gravity settling the pile packs up to the target media charge line. Higher factors fill more densely.

Ore Over-seed

1–3×

Multiplier on the target ore area used at seed time.

Physics effect: Controls how much ore is seeded around the media so the settled ore fills to its portion of the charge line.

Grinding Media PSD

PSD

Custom mix of media ball diameters and volume fractions (should total 100%).

Physics effect: Affects packing density and per-particle mass (m ∝ r²). Multiple sizes fill interstitial spaces for better grinding efficiency.

Ore PSD

PSD

Custom mix of ore particle diameters and volume fractions (should total 100%).

Physics effect: Controls ore particle sizes. Ore is seeded around the media and interlocks with it; finer ore packs more densely.

Speed & Slice

Critical Speed

% Nc40–100%

Rotational speed as a percentage of the theoretical critical speed — where centrifugal force exceeds gravity.

Physics effect: Drives angular velocity ω = −(%Nc/100) × Nc × 2π/60. Below 65% cascading; 65–82% cataracting (optimal); above 82% centrifuging.

Mill Slice Length

100–2000 mm

Axial length of the mill slice being modelled.

Physics effect: Used for 3D volumetric and mass calculations from the 2D cross-section. Does not change the 2D rendering.

Friction

Media-to-Media

μbb0.05–0.7

Friction between grinding-media particles.

Physics effect: Controls how the media pile shears internally. Higher values make the ball bed grip and rotate more as a body; lower values let balls slide over each other.

Media-to-Boundary

μb0.05–0.7

Friction between grinding media and the liner/lifter surfaces.

Physics effect: Scales how far the mill drags the media up the shell before slippage. Higher boundary friction lifts the shoulder higher.

Ore-to-Ore

μoo0.05–0.7

Friction between ore particles.

Physics effect: Controls internal shearing of the ore bed and how it interlocks with the media.

Ore-to-Boundary

μo0.05–0.7

Friction between ore and the liner/lifter surfaces.

Physics effect: Scales how far ore is dragged up the shell. Higher values carry ore higher into the cataracting zone.

Live Outputs

Motion Type — Cascading, Cataracting, or Centrifuging, derived from % critical speed. Shown as a coloured badge with the RPM in the floating panel.

RPM — Operating rotational speed, computed as %Nc × Nc where Nc = 42.3 / √D.

Derived Geometry — Effective diameter/radius, cross-sectional area, charge angle θ, chord, charge height (h1), centre-to-charge (h2), critical speed, and linear speed — all computed from the current parameters.

Particle Counts — Per-size media and ore counts and the renderable total, derived from the charge levels and PSDs.

Toe & Shoulder Markers — Blue block = toe (impact/landing side), orange block = shoulder (lift-off side) of the largest media, tracked as smoothed angular extremes of balls riding the liner.

Tracer Lines — Fading yellow paths of the largest media balls (a selectable 25/50/75/100% fraction), tracing the shoulder→toe cataracting trajectory.

Liner Damage Alerts — Impacts of the largest media above 3.5 m/s are tallied into Medium (3.5–4.5 m/s) and High (≥4.5 m/s) bands; an expanding red flash marks the impact point and the dominant band is reported with the worst impact speed.

Theoretical Trajectory — A red parabolic curve and impact square show the ideal single-particle flight from the lifter shoulder (MillTraj-style), plus theoretical shoulder/toe markers derived from charge level and speed — toggleable via the Theory button.