Classification of Grinding Mills – RuiNian Cast and Forged Steel Balls

There are several ways to classify grinding mills, with the most practical classification based on the type of grinding media: mills that use metal balls as media are called ball mills; those that use steel rods as media are called rod mills; those that use the ore itself as media are called autogenous mills; and those that use ore or gravel as media are called pebble mills.

Based on the shape of the grinding cylinder, grinding mills can be classified into cylindrical and conical types. At present, the production of conical mills in China has largely ceased; therefore, cylindrical mills are the primary type manufactured, which in turn include short-cylinder and tubular mills. In short-cylinder mills, the ratio of cylinder length to diameter is less than 1; autogenous mills fall into this category. Tubular mills (often simply referred to as tube mills), by contrast, have a length-to-diameter ratio greater than 2, with ordinary cement mills being a typical example.

Based on the discharge method, grinding mills can be broadly classified into three types: (1) overflow-type mill: the milled product overflows freely through the hollow journal at the discharge end; (2) grate-type mill: the milled product is discharged through the apertures in the grate plate at the discharge end and then flows out via the hollow journal; (3) peripheral-discharge mill: the milled product is discharged through openings around the periphery of the discharge-end cylinder. In addition, there are the open-type low-level discharge configuration used in rod mills and the air-flow discharge method employed in dry grinding.

According to the transmission method of the mill shell, there are three types: peripheral gear drive, friction drive, and central drive (Figure 1). Among these, the peripheral gear drive is the most widely used, while the central drive is mainly employed in tube mills.

According to the support method of the mill shell, there are three types: bearing support, roller support, and a combined bearing–roller support (Figure 2). Among these, bearing support is the most widely used, while the other two are employed only in ball mills and gravel mills with relatively short shells.

Grinding mills can also be classified into dry and wet types based on the grinding process. Currently, wet grinding mills are generally used in mineral processing operations, while dry grinding mills are rarely employed.

The classification of the conventional grinding mills mentioned above is shown in Table 1. In addition, a variety of specialized mills have also seen significant development, including high-pressure roller mills, disc mills, vibration mills, colloid mills, wrist-type mills, vertical cement mills, column mills, generalized mills, and stirred mills, among others.

Typically, rod mills are used for coarse grinding, while ball mills are employed for fine grinding but are also frequently used for coarse grinding. Autogenous mills are widely utilized in Chinese mineral-processing plants, generally for grinding after ore crushing, thereby eliminating the need for intermediate and fine crushing stages. Pebble mills, by contrast, are rarely used in Chinese mineral-processing plants and are typically reserved for fine grinding.