Ball Mills

Ball Mills, and other forms of tumbling mills such as tube mills, rod mills and batch mills form a significant type of equipment used for the size reduction of a wide variety of materials such as minerals, ores, coal, carbon products and general chemicals. Generally used in high volume applications, there are a many types, sizes and system configurations and British Rema has long experience in the selection, design and sizing of such systems.

Operating Principles:

Ball mills operate by introducing the material to be milled into a rotating vessel which contains a grinding medium (eg high-density balls or rods) and the material is ground (wet or dry) by attrition through the tumbling action of the mill. Slow rotational speeds combined with simple and robust construction make them ideal for grinding hard and abrasive materials where continuity of service, low maintenance and minimum downtime are a necessity. Ball mills can be designed to operate continuously (fed at one end of the system and discharged at the other), or on a batch basis for smaller, or intermittent, volumes.

System configuration:

Ball mills can be operated either on a stand-alone basis (“open-circuit grinding”) or in conjunction with a classifier which returns oversize product to the mill for further grinding (“closed-circuit grinding”). With open-circuit systems, finished product is obtained from a single pass through the mill which typically produces a relatively wide particle size distribution. Special care has to be taken selecting the geometry of the mill (length, diameter, rotational speed etc) to ensure that the desired particle size is obtained. If operated in conjunction with the correct air-classifier (closed-circuit), the grinding system is capable of achieving a much narrower particle size distribution, with an accurate control of top-size. A closed system minimises over-grinding, resulting in improved efficiency, and allows a smaller mill to be used for any given capacity.

Air swept milling:

Applicable to dry closed-circuit milling only, a further variation can be the introduction of an air flow through the mill (“air-swept milling”). This provides a form of elementary pre-classification and typically produces narrower size distributions but less fine particles than its non air-swept equivalent. Typically suitable for end product falling in the range of 50 to 200 microns, this system can also be used to achieve a limited drying capability, handling product of up to 8% moisture content.

More Information:

A PDF datasheet is available for this product

Ball Mills.pdf (344KB)