By Christine Banaszek
Pharmaceutical manufacturers rely on a range of high speed mixers to accomplish dispersion and emulsification. In the processing ophthalmic solutions, for instance, Ross High Shear Mixers are utilized for dissolving salts as well as dispersing viscosity enhancers, antioxidants and other additives. The basic single-stage design features a four-blade rotor turning at tip speeds around 3,000-4,000 ft/min within a close tolerance fixed stator. It imparts mechanical and hydraulic shear by continuously drawing product into the rotor and expelling it radially at high velocity through the openings in the stator. Built-in powder induction mechanisms like the Solids/Liquid Induction Manifold (SLIM) Technology extend the High Shear Mixer’s functionality by enabling more convenient raw material additions, faster dissolution/dispersion and more efficient hydration of thickeners.
More viscous ophthalmic ointments and pastes are more efficiently batched in Multi-Shaft Mixers. These versatile machines are equipped with two or more independently-driven agitators working in tandem to deliver a combination of high shear agitation and laminar bulk flow. One common configuration is the Triple-Shaft Mixer featuring a low-speed anchor, rotor/stator assembly and saw-tooth disperser blade. The agitators can be engaged in any combination and at any speed for any interval during the mixing cycle. Adjustable scrapers attached to the wings of the anchor agitator physically contact the vessel surfaces for tighter temperature control and more enhanced product turnover. The saw-tooth disperser generates a vortex in the liquid surface for quick incorporation of solid ingredients and, along with the anchor, continues to agitate the batch when it becomes too thick to flow through the rotor/stator.