Ultrafine grinding involves the use of various dry and wet size-reduction equipment to achieve very fine particle sizes. Equipment selection depends on feed size, desired product size, and whether the process is carried out in dry or wet conditions.
Grinding efficiency is largely related to the surface area created, and multiple grinding mechanisms are used sequentially to achieve ultrafine sizes.
Process / Selection Criteria
- Feed particle size
- Desired final particle size
- Dry or wet processing requirement
- Equipment availability and cost
- Material characteristics
Operational Principles
Grinding Mechanisms
- Pressure crushing (coarse stage)
- Mechanical impact (intermediate stage)
- Particle attrition (ultrafine stage)
Wet Grinding Methods
- Uses grinding media to apply force in liquid suspension
- Efficiency improved by external classification and recycling (for coarser stages)
- Wet classification becomes difficult below 10 µm
- Requires:
- Multi-stage grinding
- Progressive reduction in media size
Grinding Media
- Coarse grinding: 80 mm to 20 mm
- Medium to fine grinding: down to ~8 mm
- Practical minimum media size: ~12 mm
Performance Factors
- Shear stress from agitators
- Force multiplication by grinding media
- Particle concentration in system:
- Solid volume / gas volume (dry)
- Solid volume / liquid volume (wet)
- Particle interaction and clearance during processing
