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Dry Screening (Dry Granulation) - Problems and Remedies

Excess Fines

Causes: Remedies
  • Granulation Overdried: Decrease drying time/temperature, Establish optimum moisture content
  • Screen size too small: Use a larger screen size
  • Rotor/screen clearance too close: Adjust rotor clearance
  • Overloading of mill or Granulator: Slow feed of material to mill or granulator
  • Weak granules:
  1. Increase granulating fluid
  2. Increase binder content
  3. Increase wet massing time

Difficult to Screen

Causes: Remedies
  • Granules too hard: 
  1. Decrease drying temperature (case hardening)
  2. Decrease water content (use alcohol/water)
  3. Decrease binder content
  4. Use a weaker binder
  • Moisture in granulation:
  1. Increase drying time
  2. Establish optimum moisture content

Poor Color Distribution

Causes: Remedies
  • Dye migration to granule surface nonuniformity of color throughout granule)
  1. Use lakes instead of soluble dyes (will minimize but not eliminate the problem)
  2. Decrease the size of the wet granules
  3. Decrease thickness of granulation bed; stir granulation bed frequently during drying to expose fresh surfaces at the top of the wet mass
  4. Use Avicel PH-101- reduces or eliminates dye migration in wet granulation

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