- MULTI-MILL (DQ) COMPILED DOC
- MULTI-MILL (IQ) COMPILED DOC
- MULTI-MILL (OQ) COMPILED DOC
- MULTI-MILL (PQ) COMPILED DOC
A multi mill (also called a multi-mill, communiting mill, or multimill) is a high-speed size-reduction and granulation machine widely used in pharma to reduce lumps, de-agglomerate, and produce uniform granules/powders before blending, compression, capsule filling, or coating. It works by a rotating impeller/beaters that forces material through a screen (sieve), giving controlled particle size with relatively low heat generation when properly operated.
Typical pharma uses
- Wet granulation: milling damp mass to form uniform granules before drying.
- Dry granulation: sizing compacted ribbons/slugs.
- De-lumping: breaking lumps in API/excipients and dried granules.
- Co-milling: improving blend uniformity by reducing large particles (with care to avoid segregation).
Key parts and working principle
- Feed hopper → product enters the chamber.
- Rotor/impeller (knives/beaters) rotates at set RPM.
- Screen determines final particle size; smaller mesh = finer product.
- Discharge chute collects milled output.
Many models have variable speed drives, interchangeable screens, and optional forward/reverse rotation.
Critical process parameters (CPPs)
- Screen size/type (mesh, perforation pattern)
- Rotor speed (RPM)
- Feed rate and product load
- Knife/impeller condition and gap
- Moisture content (for wet mass)
These affect granule size distribution, fines generation, flow, compressibility, and content uniformity.
GMP/validation focus
- Cleaning and cleaning validation: multi mills can trap powder; inspect dead spots, screen housing, discharge chute.
- Cross-contamination control: dedicated parts for potent/allergen products; proper line clearance.
- Preventive maintenance: screen integrity, rotor balance, bearing wear, vibration and noise monitoring.
- Dust containment: use with dust extractor/isolator in dispensing areas to protect product and operators.
- In-process controls: sieve analysis of milled output, moisture checks, and documented parameter settings in batch records.
Common issues include excess fines (too high RPM/small screen), overheating, screen damage leading to metal contamination risk (mitigated by checks and magnets/metal detectors where applicable), and inconsistent granules from variable feed/moisture.