All grades of Bitumen emulsions are biphasic systems stabilized using suitable emulsifiers and additives. Since the stability and field performance of a bitumen emulsion depends largely on degree of fineness of bitumen droplets which remains suspended in water-emulsifier continuous phase, during production of same, colloid mill is used to achieve the lowest possible particle size of bitumen droplets and their effective coating with emulsifier molecules. 

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Colloid Mills are mechanical shearing machines which works on principle of passing the emulsifier solution with hot bitumen through a static base and a fast rotating metal rotor where very fast particle size reduction is achieved due to numerous collision of fast moving bitumen droplets with metal surface of both rotor and stator and finally discharged from the mill outlet while passing through a slit having very small gap between the two parts of the colloid mill. More number of stages ensure no big size particle passing through the machinery and into the final emulsion leaving the colloid mill which could result in poor quality emulsion with very low stability and separation of bitumen from water phase during storage. 

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In high efficiency colloid mills, the rotor part rotates at a very high speed (~6000 RPM) thus producing finest grade bitumen emulsions with very high production rates. Colloid mills can be laboratory scale which are able to produce very small quantity of fine emulsion (~ 0.5 to 1 Kg) or the commercial scale producing upto 10 MT Bitumen Emulsion per hour. The material of construction and the workmanship during production of the colloid mill dictate its efficiency and capacity.  

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