General Description Of Design

There are many different colloid mills commercially available, but each share some common elements. Colloid mills usually consist of a rotor and a stator (Fig. 1). The rotor is a disk that can have many different forms and surfaces, but it is most commonly conical. This disk rotates at a high speed, usually between 1,500 and 20,000 rpm depending on the particular design. The speed of the rotor is more commonly in the intermediate range of3,000 to 10,000 rpm for smaller machines and roughly half that range for larger machines. The rotor may be directly connected to the motor, or it may be driven by a gear or drive belt system. The stator is a fixed surface that is close to the rotor. However, colloid mills have been designed with many variations of these elements, such as two rotors spinning in opposite directions close to each other; and rotors and stators with slots, channels, flutes, teeth, projections, corrugations, steps, and intercalating ridges forming a sinuous passage (2). The diameter of the rotor may range from 1 to 21 inches (2.54-53.3 cm). In operation some colloid mills require a feed pump, whereas others are self-pumping.

Flowing between the rotor and stator is a thin film of liquid that is subjected to a very high shear field. The thick-

Figure 1. Basic components of a colloid mill: a rotor attached to a rotating shaft and a stator close to the rotor with a small gap between them.

ness of this layer of liquid is typically between 0.001 and 0.050 inches (0.0254—1.27 mm). It is characteristic of a colloid mill that the intensity of the shear field can be adjusted so as to achieve the desired process result. This adjustment is most often made by varying the thickness of the gap between the rotor and the stator.

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