Grinding power calculated using Bond grindability Index test in the Bond Equation

Grinding power calculated, when using work indices obtained from Bond grindability test in the Bond Equation, is for the following specific conditions: (2)

• Rod Milling – wet, open circuit grinding in a 2.44 meter (8’) diameter inside liners rod mill.
• Ball Milling – wet closed circuit grinding in a 2.44 meter (8’) diameter inside liners ball mill.
• Power calculated is the power required at the pinionshaft of the mill, which includes mill bearings and gear and pinion losses but does not include motor losses or losses in any other drive component, such as reducers and clutches.

The feed for Bond Grindability Test is: (2)

Red milling ore crushed to minus 13,200 micrometers (0.530”) or finer.

Bal milling ore crushed to minus 3350 micrometers (6 mesh) or finer.

Which have been to establish optimum rod and ball mill feed sizes.

There are eight efficiency factors that are applied to the calculated grinding power to allow for variations from the specified conditions and optimum feed sizes. The background and reasons for these have been published (1), (2), (3) and are not part of the discussion. The factors are:

• EF₁ Dry Grinding
• EF₂ Open Circuit Ball Milling
• EF₃ Diameter Efficiency Factor
• EF₄ Oversized Feed
• EF₅ Fine Grinding in ball mills to product sizes finer than 80%} passing 200
• mesh (75 micrometers)
• EF₆ High or low ratio of reduction rod milling
• EF₇ Low Ratio of reduction ball milling
• EF₈ Rod Milling