How does the work index of an ore influence the selection and sizing of crushing equipment?

The work index (Wi) of an ore is a measure of its resistance to crushing and grinding, and it significantly influences the selection and sizing of crushing equipment. The work index represents the amount of energy (in kilowatt-hours per short ton, kWh/ton, or kilowatt-hours per metric tonne, kWh/tonne) required to reduce a material from a very large feed size to 80% passing 100 microns (0.1 mm). An ore with a high work index is considered hard and requires more energy to crush than an ore with a low work index. When selecting crushing equipment, the work index is used to determine the power requirements of the crusher. Ores with high work indices require crushers with higher power ratings and more robust designs. For example, a hard, abrasive ore with a high work index might require a jaw crusher or a gyratory crusher as a primary crusher, while a softer ore with a low work index might be suitable for a cone crusher or an impact crusher. The work index also affects the sizing of the crusher. For a given throughput rate (tons per hour), a higher work index will require a larger crusher or a crusher operating at a higher power level. If the crusher is undersized for the ore's work index, it will not be able to achieve the desired throughput rate or product size distribution. The work index is typically determined through laboratory tests, such as the Bond work index test. This test involves crushing a sample of the ore and measuring the energy required to achieve a specific reduction in size. The work index is then used in empirical equations to estimate the power requirements of crushing equipment.