The standard of Ball mill and Rod mill

1. Scope

This standard specifies the following scope of ball mills and rod mills, their type and basic parameters, technical requirements, test methods, inspection rules, marking and instructions for use, packaging, transportation and storage.

This standard applies to ball mills and rod mills(Hereinafter referred to as mills) for grinding ores, rocks and other suitable grinding materials of various hardness in wet and dry processes.

2. Type of mills and basic parameters

2.1 Type of mills

2.1.1 Mills are divided into ball mills and rod mills according to different grinding media; ball mills are divided into grate type and overflow type according to discharge form, and grate type ball mills are divided into dry type and wet type. The structure type is shown in Figure 1, Figure 2, Figure 3, Figure 4 and Figure 5 respectively, and this figure does not determine the specific structure. Among them, Figure 1 discharge end cover structure is recommended for grate ball mill with diameter no more than φ3200mm, and Figure 2 discharge end cover structure is recommended for grate ball mill with diameter no less than φ3600mm.
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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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What is ball mill?

Ball mills are a similar shape to that of the rod mills except that they are shorter with length to diameter ratios of 1 to 1.5. As the name implies, the grinding media in these mills are steel balls. The particles size of the feed usually does not exceed 2.5 cm. The grinding is carried out by balls being carried up the side of the mill such that they release and fall to the point where they impact the ore particles in trailing bottom region of the slurry. If the mill is rotated too fast, the balls can be thrown too far and just strike the far end of the mill and conversely, if the mill is rotated to slow, the efficiency of the grinding process significantly reduced. Ball mills are suited for finer grinding as larger particles do not impede the impact on to smaller particle as in rod mills.

What is Rod Mill?

Rod mills are long cylinders filled with steel rods that grind by compressive forces and abrasion. The length of the cylinder is typically 1.5 to 2.5 times longer than the diameter. As the mill turns, the rods cascade over each other in relatively parallel fashion. One of the primary advantages of a rod mill is that it prevents over-grinding of softer particles because coarser particles act as bridges and preferentially take the compressive forces. Rod mills can take particles as coarse as 5 cm. Many of the newer operations tend to install ball mills in combination with SAG mills and avoid rod mills due the cost of the media, the cost of replacing rods and general maintenance costs. Many older operations have rod mills in combination with ball mills.