A triple roller mill is used to mix semisolids while preparing ointments, creams, pill masses, wet mass for making granules, etc.
Principle
The material experiences a high shear developed by the differential speed and the narrow space between the rollers.
Under the influence of this shear, aggregates, and particles get crushed, and the drug gets distributed uniformly throughout the semi-solid base.
Construction
A triple roller mill consists of three rollers of equal diameters and is made up of hard abrasion-resistant material (stainless steel usually).
These rollers are arranged parallelly and are horizontally fixed to a rigid frame.
The pressure and gap between the rollers can be adjusted.
A hopper is fixed between the first two rollers, and the last roller has a scrapper attached.
Working
- The last two rollers are adjusted so that the distance between them is less than between the first two rollers.
- The first roller is the receiving roller, which rotates at a speed slower than the second roller, which rotates at a speed slower than that of the third roller, the discharge roller.
- The feed introduced is made to pass through the gap between the first and second rollers.
- The aggregates and particles are crushed and abraded by the rubbing action of the rollers; this action develops due to different rotation speeds.
- A film of the feed of desirable thickness is produced.
- The feed introduced passes from the slow-rotating roller to the fast-rotating one.
- The gap between the second and third roller is small. Thus, a thinner film of feed is produced. The Speed of the third roller can be increased to compensate for the reduction of cross-sectional area.
- Finally, the material removed by the scrapper from the last roller is collected in a receiver or transported through a suitable conveyor.
Application
· It is used for mixing solid powders with an ointment base.
Merits
¨ It is used in pharmaceutical industries for preparing uniform dispersion of semisolid drugs and bases.
¨ It is also used in continuous processes for preparing semisolid dosage forms
Demerits
It is not suitable for liquid material whose viscosity is 5 Pa/Sec, such as glycerin, castor oil, etc.
