A Chili mill, also called a Chilean mill, uses upright rollers that travel around a circular grinding bed. A central carrier moves their radial axles around the shaft while the rollers turn on those axles. This model shows the three-roller arrangement illustrated by Hiscox.
Chili Mill Interactive Calculator
Set the inner and outer radii of the runner’s contact edges and the carrier speed. The animation shows orbiting and rolling motion; the calculator compares the two edge paths per orbit and per minute.
Equation Used
- A rigid cylindrical runner spans the entered radial contact width.
- The carrier runs at constant entered rpm.
- Wheel spin in the illustration assumes rolling at the mean contact radius.
- Wheel diameter and the pan housing are illustrative; they are not sizing outputs.
- Individual edge slip depends on actual wheel speed and contact conditions.
Geometric comparison of the paths at the two radial edges of a cylindrical runner. The mill view uses three rollers and an illustrative wheel radius. No crushing capacity, torque, wear rate or part-clearance result is inferred from path difference.
Rollers travel around a circular bed
Hiscox figure 1239 shows three upright rollers carried around by a central shaft and a three-armed carrier. Material is worked beneath the rollers and the ground product leaves through an annular collection trough.
The animation exposes the circular bed and radial axle arrangement. The carrier rotation moves each wheel around the pan. Marks on the wheel faces make their simultaneous rotation on the axles visible.
The near and far radial edges of a wide cylindrical wheel follow different circumferences. A single wheel spin cannot provide pure rolling at every radius across that contact width.
Understanding an edge-runner mill
This model explains the kinematics of an ore-grinding arrangement. It can be used to compare how radial contact width and carrier speed change the difference between the two edge paths.
The same inputs cannot predict product size, ore recovery, throughput or motor power. Those depend on material, feed, runner load, surface condition and the particular mill design.
Compare the two circular paths
A contact edge at radius r travels 2 pi r in one carrier orbit. Subtracting the inner circumference from the outer gives 2 pi (r2-r1). Multiplying by carrier rpm gives the path difference per minute.
This geometric difference is sometimes associated with differential grinding slip, but it is not the actual sliding distance at either individual edge. If the cylindrical wheel rolls at a chosen neutral radius, the inner and outer edges have opposing departures from pure rolling.
For illustration, wheel spin uses the mean radius as that neutral radius. The displayed wheel radius is schematic. The calculator’s four numerical outputs do not depend on that illustrative wheel size.
Default runner paths
For inner radius 0.9 m and outer radius 1.5 m, the edge paths are about 5.65 m and 9.42 m per orbit. Their difference is about 3.77 m per orbit.
At 20 carrier revolutions per minute, the difference rate is about 75.4 m/min. Doubling speed doubles that rate without changing either path per orbit.
If the outer radius is equal to or smaller than the inner radius, each circumference remains calculable, but the contact-width comparison is invalid. Enter an outer radius larger than the inner radius for a positive radial contact width.
Kinematic comparison rather than mill sizing
Runner load and contact mechanics determine how material is crushed and how the wheel slips. A geometric path difference alone cannot establish those forces or predict wear.
The animation uses three equally spaced rollers, an exposed bed and a simplified central carrier. Housing, discharge hardware, drive gearing and structural details are omitted. Extreme selected widths may require a different mechanical arrangement; this model does not validate clearances.
Calculator questions
Which speed does the rpm input describe?
It is the carrier’s speed around the central shaft. The wheel’s spin on its axle is a separate motion.
Are these the wheel’s inside and outside diameters?
No. They are the distances from the central mill shaft to the two radial edges of the contact width.
Does the path difference equal actual sliding distance?
No. Actual edge sliding also depends on wheel spin and contact behavior. The calculator compares the geometric circumferences.
Why are there three rollers?
The illustration follows the three-roller arrangement in Hiscox figure 1239. Other mills use different runner counts.
Separate actuator positioning tasks
The mill’s central carrier uses a rotary drive. The edge-path calculation does not size that drive, determine crushing force or select a linear actuator.
If a separate actuator positions a feed gate or other auxiliary component, calculate that component’s load, travel, mounting geometry and cycle requirements. The FIRGELLI actuator force calculator and linear actuator specifications can help compare such a positioning task; the mill geometry shown here does not establish an actuator’s suitability.
References & Further Reading
- Hiscox, Mechanical Movements, Powers, Devices and Appliances, printed page 305, figure 1239: three-roller Chili mill and central carrier.
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