Size reduction basics — reduction ratio for fine grinders:\nIn comminution terminology, what is the typical reduction ratio achievable by fine grinders (i.e., equipment used for fine to ultrafine size reduction)?

Introduction / Context:
Reduction ratio is a quick way to characterise how much a size-reduction device can shrink particle size in one stage. It is defined as characteristic feed size divided by characteristic product size. Coarse crushers achieve modest ratios, while fine grinders (e.g., ball/tube mills with classifiers, jet mills) are designed to push the fineness much further. This question reinforces typical magnitudes so that you can rapidly select equipment during preliminary design.

Given Data / Assumptions:

• “Fine grinders” means mills intended to produce fine to ultrafine products (well below typical crusher product sizes).
• One-stage reduction performance is being compared qualitatively.
• Representative characteristic sizes (e.g., 80% passing) are implied.

Concept / Approach:
Jaw and gyratory crushers often deliver ratios around 3–8. Secondary/tertiary cone or impact stages may reach the teens. Fine grinding devices can achieve much higher ratios because the starting feed is already small and the product is pushed into powder ranges. In standard handbooks, fine grinders are commonly cited with reduction ratios up to about 100 in a single stage, depending on classifier efficiency and circuit configuration.

Step-by-Step Solution:

Verification / Alternative check:
Vendor data sheets for fine mills and closed-circuit systems frequently show feed in hundreds of micrometres reduced to single-digit micrometres, consistent with ratios approaching two orders of magnitude.

Why Other Options Are Wrong:

• 5–10; 10–20; 20–40: typical of crushers or coarse/intermediate grinding, not fine grinders.
• > 500 in one pass: unrealistic without multi-stage or extreme classification recycle.

Common Pitfalls:
Equating multi-stage cumulative reduction with single-stage capability; always check if the ratio refers to a single pass or an overall circuit.

Final Answer:
As high as 100