In mining industry, a crusher is an indispensable component of all mining and quarrying operations, for reducing large blocks of rocks to smaller fragments (~ 0.5 m to ~ 0.01 m). There are seven general phases of the mining process as shown in Figure Follow. Rock fragmentation is involved in both extraction process and beneficiation process. The energy consumption in rock fragmentation in mining is the most significant. As estimated in “Energy and Environmental Profile of the U.S. Mining Industry” by the U.S. Department of Energy, the crushing and grinding process consumes 75% of the energy in beneficiation operations, which takes 39% of the total energy consumption in mining. Similarly a report titled “Energy Efficiency Trends in Canada, 1990 to 2007” by the Office of Energy Efficiency at the Natural Research Canada showed that in deep mining, rock drilling and crushing operations consume 10% of the energy in extraction, which constitutes 19% of the total energy consumption in mining. The rock crushing process also dominates the energy consumption in aggregate manufacturing in the construction industry. For instance, in 2006, the United Kingdom consumed approximately 209 million kWh energy to produce 127 million tons of crushed aggregate (Lowndes and Jeffrey 2008). Understanding of rock fragmentation process, including its physical mechanism and optimization method, is thus critical to improve productivity, to reduce cost, and to indirectly reduce greenhouse gas emission. However, the physical process during rock crushing is not well understood, although several empirical approaches are in current use.
In the beneficiation operations, the first step is the crushing process and a crusher represents the first element. There are four common types of crushers: jaw crusher, gyratory crusher, cone crusher and vertical shaft impact crusher.
The Crushing Process
The crushing process generally consists of two or three stages. primary crushing, secondary crushing, and tertiary crushing stages (if necessary). In the primary crushing stage, the size of ores is reduced from around 1 m into around 0.2 m, and the rock is further crushed to around 0.02 m size in the secondary crushing stage. If finer product than 0.02 m should be required, the tertiary crushing stage will become necessary. Generally, jaw crushers and gyratory crushers are normally used in the primary stage, and cone crushers and impact crushers are commonly used in the secondary/tertiary stage.