The Atritor Microniser is a Spiral Jet Mill also known as a Pancake Mill and is one of a wide range of types of Fluid Energy Mill.

The use of compressed gas - typically 6-10 bar g supply - to mill materials represents one of the most energy intensive form of milling and is therefore only to be considered when the fine product can command the added value from energy costs in the market place.

Typical Specific Energy consumption varies from 500 to 2,000 kWh/t. Throughputs on the Atritor range - 50 mm to 900 mm diameter - vary from a few grams to around 500 kg/h.

Spiral Jet Mills use a form of static spiral classification relying on a centrifugal effect which keeps larger heavier particles in the main body of

the mill while the finer lighter particles can escape through the central outlet annulus on the air stream.

Because of its simplicity, with no moving parts at the milling stage the Spiral Jet Mill has been used extensively in the pharmaceutical industry and also for the general contract micronising of a wide range of chemicals and minerals where cleaning between batches should be as simple as possible.

To provide a suitable feed to such a mill, materials should be fine enough to be successfully accelerated in a jet stream which as general rule should be all less than 1 mm with a large % < 0.5mm. Larger particles would need to be pre-milled on eg. a Cone Mill before feeding to the Jet Mill.

Because the Spiral Jet Mill generally has no form of dynamic classifier the product particle size distribution, when represented on an RRS log/log diagram is spread widely. In other words, for a given cut point, eg. d97 = 12 µm, the product will have a high proportion of fine material below say 6 µm, whereas Jet Mills with dynamic classification are capable of steeper particle size (RRS) distributions with lower ultra-fine percentages. The RRS diagram (Rosin Rammler) is a recognised means of graphical representation of particle size distributions. On its vertical axes it represents both % passing a given micron mesh and % retained, and on its horizontal axis the particle size in microns. Both axes are in logarithmic form which gives a characteristic distribution curve.