Particle Size Reduction
British Rema offers a range of size reduction mills and micronisers capable of manufacturing to the most demanding particle size and size-distribution specifications. Applications range from the production of active pharmaceutical powders through fine chemicals to large-scale mineral processing plant.
Air micronisers (or “jet mills”) are applied to the superfine grinding of a wide range of materials, particularly where the feed material is already relatively fine. The technique relies on particle-on-particle impact to break down the material. There are two types of mill: (i) a spiral flow jet mill which is commonly used in pharmaceutical applications due to the absence of any moving parts; (ii) an opposed jet mill which can handle harder materials with classification achieved by means of a high speed rotor.
Rotary impact mills, also known as beater mills, employ high-speed rotors with a rotor tip velocity of up to 120 m/s. Grinding takes place through the impact of the powder particles on the rotating and fixed grinding surfaces. Typically used for softer materials of up to 3 Mohs hardness, an impact mill provides a operationally cost-effective solution when hardness and particle size parameters fall within its range. British Rema also offers a classifier mill: based on the rotary impact mill principle, this range incorporates two-stage grinding with an integrated classification step, and the consequent recycling of oversize material enables finer particle sizes to be achieved than with a conventional impact mill.
Ball mills, and other forms of tumbling mills such as tube mills and rod mills, comprise a cylindrical shell slowly rotating around a horizontal axis, partially filled with a grinding medium (such as ceramic or steel balls) to which the material to be milled is introduced. Typical in the ores, minerals, paints and general chemicals industries, ball mills can be designed to operate continuously (fed at one end and discharged at the other), or on a batch basis for smaller, or intermittent, volumes.