Testwork: Drop weight test

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Testwork: Drop Weight Tests

The JK drop weight testing machine is used to generate data sets for two different comminution models:

  • A fitted "A" and "b" for the "ECS versus T10" test result, which is used in JK SimMet to generate particle size distributions (ergo, the appearance functions).
  • A fitted "drop weight index" (DWI and Mia) test result, which is used in the Morrell SMC power model to predict the specific energy consumption of particle breakage for "standard particle size distributions" of a process feed and product streams.

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. The size and quantity of the specimens is different in the JK SimMet and Morrell SMC (DWI) procedures. Generally, the DWI procedure requires fewer specimens of smaller sizes, but is much quicker (and less expensive) to operate.

Sample Requirements

The drop weight test for use in JK SimMet, referred to here as the "full drop weight test", requires approximately 100 kg of material with a top size of 75-100 mm. When using drill core, this requires whole-diameter PQ core.

The drop weight test for use in the Morrell SMC model requires minimum 8 kg with sized between 27-32 mm (though smaller dimensions can be substituted if the coarser material is not available).

Test Inputs

Not applicable

Test Outputs

  • The "full" JK DWT returns a separate value for the fitted parameters A and b (which are frequently multiplied together and reported as A×b),
    • A table of Appearance values for a crusher model are provided. (not used in SAGMILLING.COM)
    • A companion tumbling test is conducted that returns a ta value.
  • The SMC test returns a Drop-Weight Index DWI value and several related inferred values.
    • Inferred A, b (and A×b) and ta are provided for people who intend to use the JK SimMet software.
    • Output value DWI (drop weight index), kWh/m3
    • Derived output values for Mia (for SAG milling), Mic (for crushing) and Mih (for high-pressure grinding rolls) are provided for doing power-based calculations, such as those in SAGMILLING.COM.

Extra fields available for modelling

  • SMC indicates whether this is a SMC test (value of 1, boolean=true). Otherwise, is a full JK drop weight test (value of 0, boolean=false).
  • 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.


JK SimMet, which is a population-balance model, uses the A and b values to predict the t10 generated by a certain breakage energy ECS. This t10 is then extended to create an appearance matrix used to predict the particle size distribution of a breakage event.

In the SAGMILLING.COM version of a Morrell SMC model, the Mia value is used to predict the specific energy consumption of a SAG mill. When combined with an Mib value (obtained as a modified output of a Bond Bond ball mill work index test), the total specific energy consumption of a grinding circuit can be predicted.

Trademarks & Licensing

  • JK SimMet and JK DWT are trade marks of the Julius Kruttschnitt Mineral Research Centre, Indooroopilly, Australia. Laboratories performing this test pay a royalty when submitting raw results for interpretation.
  • SMC Test and DWI are trade marks of SMC Testing Pty Ltd, Chapel Hill, Australia. Laboratories performing this test pay a royalty when submitting raw results for interpretation.