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Tube mill

Tube mills are used for wet grinding iron ore, gold/copper ore, nickel ore and other ores, as well as for grinding lime/limestone for flue gas desulphurisation systems, coal and other raw materials.

Depending on the required product quality, wet grinding tube mills operate in either open or closed circuit. Operation in closed circuit leads to a product with a narrow granulometric distribution, while operation in open circuit results in coarser products, flatter grain size distribution curves and possibly oversize particles.

Wet grinding tube mills are normally designed as overflow mills or, in special cases, as mills with end discharge diaphragms or as two-compartment mills. They have a grinding media charge (balls, rods) of between 30 % and 40 %.

Wet mills are equipped with rubber linings. In the case of tube mills that are operated as primary mills, steel linings are also used if the chemical properties of the pulp permit.

Tube mills normally have a L/D ratio of about 1.3 to 2. Depending on the hardness of the feed material, the typical maximum feed size is between 5 and 10 mm but in special cases it may be up to 20 mm. If the mill is operated in closed circuit, the product fineness will be between 20 µm and 250 µm, while an open circuit mill will have a product fineness of 100 µm to 500 µm.

Rod mills are also used as primary mills. They are operated in open circuit to grind a product with a steep grain size distribution curve.

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