Construction and Operation of a Rod Mill
A rod mill is a type of tumbling mill used in mineral processing and grinding operations. It utilizes long steel rods as the grinding media instead of balls (as in a ball mill). Rod mills are particularly effective for coarse grinding and are commonly used in the first stage of grinding circuits.
—
## 1. Construction of a Rod Mill
A rod mill consists of several key components:
A. Shell (Cylindrical Body)
– Made of rolled steel plates welded or bolted together.
– Lined with replaceable wear-resistant liners (rubber, steel, or composite materials).
– Typically longer in length compared to ball mills (L/D ratio ~1.4–1.8).
B. Feed and Discharge Ends
– Feed End: Where raw material enters the mill.
– Discharge End: Equipped with a trunnion or grate discharge system to allow ground material to exit while retaining rods.
C. Grinding Media (Steel Rods)
– Made of high-carbon steel, typically 50–100 mm in diameter.
– Length is slightly shorter than the mill’s working length (~25–150 mm less).
– Charge fills about 35–45% of the mill volume.
.jpg)
D. Drive System
– Consists of an electric motor, gear reducer, and pinion gear.
– Operates at lower speeds than ball mills (~60–75% critical speed).
.jpg)
E. Bearings & Support Structure
– Supported by trunnion bearings at both ends.
– Foundation must withstand dynamic loads from rotation.
—
## 2. Operation of a Rod Mill
A. Working Principle
1. The mill rotates, lifting rods by centrifugal force.
2. As they cascade down, rods crush and grind ore by line contact rather than point contact (as in ball mills).
3. Coarse particles are broken first, while finer particles pass through gaps between rods.
B. Key Operating Parameters
| Parameter | Typical Range |
|———–|————–|
| Speed | 50–65% of critical speed |
| Rod charge | 35–45% of mill volume |
| Feed size | Up to 50 mm |
| Product size | 0.5–10 mm (coarse grind) |
| Power consumption | Lower than ball mills for coarse grinding |
C. Advantages Over Ball Mills
✔ Better control over particle size distribution (less