A rod mill is a type of tumbling mill used in grinding (comminution) processes, primarily in the mining and mineral processing industries. It is similar to a ball mill but uses long cylindrical steel rods as the grinding media instead of balls.

 Key Features of Rod Mills:
1. Grinding Media: Uses steel rods (typically 50–100 mm in diameter and slightly shorter than the mill length) instead of balls.
2. Particle Size Reduction: Produces a more uniform particle size distribution with fewer fines compared to ball mills, as rods grind particles by line contact rather than point contact.
3. Operation: Operates at lower rotational speeds (~60-75% of critical speed) to prevent rod tangling and promote cascading motion.
4. Applications:
   – Primary grinding stage (coarse grinding).
   – Preparing feed for ball mills in wet or dry circuits.
   – Used in cement, coal, and chemical industries (less common than ball mills).  
 Advantages:
– Less over-grinding of fine particles compared to ball mills.
– Better control of particle size distribution.
– Suitable for brittle materials like coal and limestone.  

 Disadvantages:
– Not ideal for very hard materials (rods wear faster than balls).
– Requires careful operation to avoid rod breakage or tangling.  
 Comparison with Ball Mills:
| Feature          | Rod Mill                          | Ball Mill                        |
||-|-|
| Grinding Media   | Steel rods                       | Steel or ceramic balls           |
| Particle Size    | Coarser, more uniform            | Finer, wider size distribution   |
| Speed            | Lower (~60-75% critical speed)   | Higher (~70-80% critical speed)  |
| Over-grinding    | Less likely                      | More likely                      |  
Rod mills are often used in open-circuit grinding or before ball mills in a two-stage grinding process, particularly in mineral processing plants handling ores like tungsten, tin, or gold.
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