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Breif Introduction to Ball Mill

The following article describes types of ball mill, affecting factors, ball mill grinding media, and working principle.

The final stages of comminution are performed in tumbling mills using steel balls as the grinding medium and so designated “ball mills.” Since balls have a greater surface area per unit weight than rods, they are better suited for fine finishing. The term ball mill is restricted to those having a length to diameter ratio of 1.5 to 1 and less.

Ball mills in which the length to diameter ratio is between 3 and 5 are designated tube mills. These are sometimes divided into several longitudinal compartments, each having a different charge composition; the charges can be steel balls or rods, or pebbles, and they are often used dry to grind cement clinker, gypsum, and phosphate. Tube mills having only one compartment and a charge of hard, screened ore particles as the grinding medium are known as pebble mills.

They are widely used in the South African gold mines. Since the weight of pebbles per unit volume is 35-55% of that of steel balls, and as the power input is directly proportional to the volume weight of the grinding medium, the power input and capacity of pebble mills are correspondingly lower. Thus in a given grinding circuit, for a certain feed rate, a pebble mill would be much larger than a ball mill, with correspondingly higher operating cost. However, it is claimed that the increment in capital cost can be justified economically by a reduction in operating cost attributed to the lower cost of the grinding medium. This may, however, be partially offset by higher energy cost per tonne of finished product.
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Ball Mill Working Principle

Specification of Ball Mill

Ball mill is key equipment for grinding in mineral processing plant, it is widely used in cement, silicate, new-type building material, refractory material, fertilizer, ore dressing of ferrous metal and non-ferrous metal, glass ceramics etc.  There are dry grinding and wet grinding, ball mill can be divided into tabular type and flowing type according to different forms of discharging materials.

Ball Mill Working Principle:

The ball mill is a horizontal rotating device transmitted by the outer gear. The materials are transferred to the grinding chamber through the quill shaft. There are ladder liners and ripple liners and different specifications of steel balls in the chamber. The centrifugal force caused by rotation of barrel brings the steel balls to a certain height and impact and grind the materials. The ground materials are discharged through the discharging board thus the grinding process is finished.

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Autogenous and Semi-Autogenous Mills

Autogenous (AG) and Semi-Autogenous (SAG) milling has seen increased use in recent years, especially in large mineral processing operations. These mills typically have a large diameter relative to their length, typically in the ratio or 2 or 2.5 to 1. AG mills employ ore as the grinding media. However, one the challenges with AG mills is that properties, such as hardness and abrasiveness, of the ore can vary, resulting in inconsistent grinding behavior. The addition of steel grinding balls rectifies this situation. This approach is then termed semi-autogenous grinding and the total amount of balls in these mills ranges between 5 and 10 percent of the volume.