Thompson Sizing Test Determine energy requirement for grinding mineral

Over the years some have developed and refined a laboratory grindabilitly determination known as a Thompson test, named for the man deeply involved in its development. The test is based on a mineral’s behavior during several steps of size reduction and is related to experience gathered in field operations of Marcy mills.

The Thompson test develops the energy requirement for grinding the tested mineral. It uses the ratio for the test mineral ands a “standard” ore, comparing the surface area increases achieved through grinding. This ratio is used to convert the data for the “standard” ore in the accompanying tables. An example will illustrates this method.

Example: An ore is to be processed at a rate of 2,000 st per 24 hours is a wet closet circuit. The feed size is 3% - 5% + 3/8” and the product size requirement is 3% + 65 mesh. What is the horsepower requirement for a grate ball mill?

The table on p. 15 shows that to grind from ½” feed to a 65 mesh product at 2,000 st per 24 hours will require a 10’ 6” diameter mill.

The table below shows that for a 10’6” diameter mill to grind from ½” to 65 mesh requires 7.6 kwh/ st. This figure of 7.6 kwh / will be called the “standard grindability”

In this example, the Thompson test determines there ore to be 9% easier to grind than the “standard” The “standard” 7.6 kwh / st multiplied by 91 to arrive at 6.92 kwh / st. The next step corrects for the difference in feed sizes between 3/8” for the ore being tested and the ½” of the “standard”. The graph on p.8 shows 43% for ½” feed and 51% for 3/8” feed. The difference is 8%. Therefore, the figure of 6.92 kwh / st is multiplied by 92 to arrive at 6.37 kwh / st as a final power requirement.

The actual horsepower required is calculated in the following manner:

The tables showing standard grinding data for a grate mill indicates that a 10’6” diameter x 11’ long mill is needed to supply the required horsepower. If the horsepower consumed calculation were not comparatible with a 10’6” mill, then a correction would need to be made for mill diameter. As an example, if the horsepower consumed calculation were not compatible with a 10’6” mill, the horsepower calculated were more in range of an 8’6” diameter mill. The calculations above would be repeated by selecting from the table below 8.3 kwh/ st instead of the 7.6 kwh/st used above for 10’6” diameter.

Standard Grindability Overflow Ball Mills

Standard Grindability Grate Ball Mills

Overflow Ball Mill Capacities Short Tons Per 24 Hr.

Grate Ball Mill Capacites

Rod Mill Capacities