The reduction ratio (RR) of a ball mill is a measure of the size reduction achieved from the feed material to the final product. It is calculated as:
\[
\text{Reduction Ratio (RR)} = \frac{\text{Feed Particle Size (F80)}}{\text{Product Particle Size (P80)}}
\]
Key Definitions:
– F80: The particle size at which 80% of the feed material passes (in microns or mm).
– P80: The particle size at which 80% of the product material passes (in microns or mm).
Steps to Calculate:
1. Determine F80 (from sieve analysis of feed material).
2. Determine P80 (from sieve analysis of ground product).
3. Divide F80 by P80 to get the reduction ratio.
Example Calculation:
– If the feed has an F80 = 1000 µm and product has a P80 = 100 µm, then:
\[
RR = \frac{1000}{100} = 10
\]
Typical Reduction Ratios for Ball Mills:
– Ball mills usually achieve a reduction ratio between 5:1 and 20:1, depending on:
– Mill type (wet/dry, open/closed circuit).
– Grinding media size and material.
– Feed hardness and fineness requirements.
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