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The grinding circuit is among your largest capital investments and greatest operating costs. SGS can reduce your risk by combining different test procedures and design methodologies to ensure that you optimize this critical part of your plant.

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Our philosophy is to first determine the variability of your ore using rigorous comminution testing, including Bond tests for ball and rod mills. We conduct a small number of expensive tests that require a larger sample size, such as the Bond Ball Mill Grindability Test. The results are used to calibrate a large number of less expensive tests that require only a small sample, such as the Modbond Grindability Test.

Here is an overview of the Bond Tests available at SGS:

Modbond Grindability Test

Similar to a Comparative Work Index, this test is an open circuit dry batch grindability test run in the standard Bond Ball Mill for a set time. It can be used at mesh sizes from 65 to 200 mesh (normally 100 mesh). The test requires calibration against the standard Bond Ball Mill Work Index test to estimate the Work Index. It is used to show the orebody hardness profile and to predict throughput in a ball mill circuit.

SGS created the Modbond grindability test and has a large proprietary database. The small sample size enables many tests to be conducted, resulting in extensive variability information that our experts use to efficiently design your grinding circuit.

Feed Sample Requirements
1.2 kg of minus 6 mesh ore.

Bond Ball Mill Grindability Test

The test determines the Bond Ball Mill Work Index which is used with Bond’s Third Theory of Comminution to calculate net power requirements*. Various correction factors may have to be applied.

W = Wi (10/√P – 10/√F)

Where  W = Net power consumption in kWh/t 
            Wi = Bond work index (either Imperial or Metric units)
            P = The 80% passing size of the ground product in µm
            F = The 80% passing size of the feed in µm

The test is a closed circuit dry grindability test performed in a standard ball mill. It can be performed at mesh sizes ranging from 28 mesh to 400 mesh. The normal finishing size is 100 mesh.

Feed Sample Requirements
10 kg of minus 6 mesh

* Bond F. C., “Crushing & Grinding Calculations”, Reprint from British Chemical Engineering, Allis-Chalmers Publication 07R9235B

Bond Low Energy Impact Test

The test determines the Bond Impact Work Index which is used with Bond’s Third Theory of Comminution to calculate net power requirements when sizing crushers*. It is also used to determine the required open-side settings (jaw crushers and gyratory crushers) or closed-side settings (cone crushers) for a given product size.

P80 = 25400 x Oss x (0.04Wi + 0.40)

P80 = 25400 x Css x 7Ecc x (0.02Wi + 0.70) / (7Ecc - 2Css)

Where  Oss = Open-side setting in inches 
            Css = Closed-side settings in inches
            Ecc = Eccentric throw in inches
            P80 = Aperture through which 80% of the product will pass.
            Wi = Work Index

The impact apparatus consists of two pendulum-mounted hammers, mounted on two bicycle wheels so as to strike equal blows simultaneously on opposite sides of each rock specimen. The height that the pendulum is raised is increased until the energy is sufficient to break the specimen.

Feed Sample Requirements
At least 10 pieces of minus 3” plus 2” ore (20 pieces recommended).

* Bond F. C., “Crushing Tests by Pressure and Impact”, Trans AIME, Vol 169, 1947, pp 58-66.

Bond Rod Mill Grindability Test

The test determines the Bond Rod Mill Work Index which is used with Bond’s Third Theory of Comminution to calculate net power requirements when sizing ball mills*. Various correction factors may have to be applied.

The test is a closed-circuit dry grindability test performed in a standard rod mill. It can be performed at mesh sizes ranging from 4 mesh to 65 mesh. The normal finishing size is 14 mesh.

Feed Sample Requirements
15 kg of minus 1⁄2” ore.

* Bond F. C., “Crushing & Grinding Calculations”, Reprint from British Chemical Engineering, Allis-Chalmers Publication 07R9235B