Part III: An Investigation into the Surging of Ball Mills

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Abstract
The problem of surging in ball mills has been investigated by the use of small-scale models and, although a complete analysis of all the variables has not been made, a criterion has been obtained by use of which it is possible to determine, whilst the design is still on the drawing board, whether the charge of a proposed mill is likely to surge. The validity of the proposed criterion has been demonstrated by comparison with the published results relating to industrial mills; this comparison showing that all the mills considered are operated under conditions which are in accordance with those laid down in the present work. So far as is known, such a criterion has not previously been propounded, and it is believed that it is of considerable value to the designer and to the mill operator. For the purpose of predicting the existence or non-existence of surging in a mill, it is only necessary to establish within which of two possible zones on a certain graph the point corresponding to the operating conditions of the mill falls; the relevant graph having for the abscissae the value of the ratio of the mill diameter to the ball diameter and for the ordinate the product of the mill filling and the mean coefficient of friction of the ball and powder charge of the mill. Thus, in order that a mill shall not surge, it is necessary that the mill filling and the ratio of mill diameter to ball diameter shall be so chosen in relation to the coefficient of friction, which is fixed by the nature of the material being ground, that the operating point for the mill shall fall within the non-surging zone on the graph mentioned. It is suggested that if a mill can be operated under ‘non-surging’ conditions, then, for lower first costs and maintenance costs, plain liners should be adopted, but if the mill cannot be operated under these conditions, then heavy lifters should be provided to suppress surging—even though the cost is thereby increased.

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