Testwork: Bond crushing work index

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Testwork: Bond Crushing Work Index

The Bond low-energy impact crushing work index (more informally, the Bond crushing work index) is not as common as the Bond ball mill work index, and it is a notoriously noisy test.

The test is a 'per-specimen' test where individual specimens of prepared rock are hand-picked by the test operator and placed into the apparatus. Typically twenty specimens are chosen to represent a sample and the result reported is the average of those specimens.

There is a high-energy impact work index which is a different (and incompatible) test. The high-energy test has fallen into disuse and any recent (post year 2000) test labelled as a "crushing work index" can confidently be assumed to be the low-energy impact test.

Sample Requirements

The test requires 20 large lumps, minimum dimension 75 mm. When using drill core, use whole-diameter HQ or PQ size core.

Test Inputs

Not applicable.

Test Outputs

SAGMILLING.COM uses only metric work index units; if the laboratory reported work index in "short ton" units, multiply that value by 1.1023 and enter the result.

The laboratory will report the following information:

  • N° specimens: The number of specimens tested (typically 20)
  • min The metric work index of the sample with the lowest result
  • max: The metric work index of the sample with the highest result
  • stdev: The standard deviation of metric work index of all the samples
  • WiC: The arithmetic average of the metric work index of all the samples
  • density: The water-displacement density of the specimens prior to testing, in kg/L (also referred to as 'specific gravity')

Extra field available for modelling

  • synthetic indicates whether this is a real test result, or just a synthetic one that should only be used for modelling. If this column contains a value of '1' (boolean=true) for a test, then that test is understood to not be a real test result and is therefore not shown on the testwork comparison charts. Synthetic values are available when running circuit model simulations and do show up in the list of model results.

Wi of a single specimen in the test is measured based on the thickness of the test specimen and the potential energy of the hammers where the specimen broke.

 Wi_{C} = 48 \times 1.1023 \times \frac{110.2 \times cos (\alpha)}{d \times sg}

The average Wi values of all specimens within a sample is then reported as the WiC. Usually a test consists of 20 specimens.


Crushing mill work index is used in the SAGMILLING.COM Bond/Barratt specific energy consumption model.

The work index is used to calculate the energy requirement to break rocks in the coarse size range, from >100 mm down to about 10 mm - 20 mm.