Rotor stator milling shear rate

Colloid Mills. Colloid mills are another form of rotor stator mill. A colloid mill is composed of a conical rotor rotating in a conical stator (Fig. 8.5). The surface of the rotor and stator can be smooth, rough, or slotted. The spacing between the rotor and stator is adjustable by varying the axial location of the rotor to the stator. The gap can be as little as a few hundred microns to a couple of millimeters.18 Varying the gap varies not only the shear imparted to the particles but also the mill residence time and the power density applied. Particle size is affected by adjusting the gap and the rotation rate. It is possible to produce particles in the 1-10 pm size range. 

For the toothed rotor/stator mills, there are localized areas of high shear where the most energy is imparted to the particles, and breakage is believed to occur, through a combination of shear and collision. Therefore, useful parameters that quantify mill performance will reflect these effects. Three typical parameters used in rotor-stator mill scale up are tip speed (rotation rate of rotor x rotor circumference), shear rate (tip speed/distance between rotor and stator), and shear frequency (rotation rate x number of slots on rotor x number of slots on stator).Rotor-stator types typically differ in the number of rows of teeth and the number of teeth in each row of rotor and stator, though other geometric differences are possible. When rotor-stators of different design are available for study, shear frequency appears to have... 

Rotor/stator gap (gap width) Smaller gap increases shear forces, increases milling rate, and produces smaller particles. 

Crystallinity Impurity Solvate Incomplete dissolution pH Temp Amount Miscibility w/solvent Mixer type(high-shear in-line versus suspended mixer homogenizer) Mixer design Rotor/stator design and gap Tip speed S/AS flow rates and ratio Batch size Processing time Temperature Too slow Incomplete removal of solvent Temp. Time Air flow Humidity Shear/temp Milling mechanism... 

Colloid mill. This type of mill is used extensively in the food industry. A colloid mill is a conical rotator that turns in a stator of the same shape, leaving a very narrow gap between rotor and stator. The liquid is introduced from the top, and flows through the narrow gap. Due to the high rotation rate, and the small size of the gap, the shear forces are very intense, and small droplet sizes can be realized. The regime the mill operates at depends on the viscosity of the mixture. When the mixture is highly viscous, the flow will be laminar. The transition towards turbulent flow is given by the Reynolds number, which characterizes the flow ... 

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