CRUSHERS IN THE 20TH CENTURY

The incentive to build large primary gyratory crushers came in the 1920s with the devel­opment of open-pit mines for copper and iron ores. The aggregate producers’ demand for a machine that would control the size distribution and shape of pebbles at a high pro­duction rate offered the incentive to build cone crushers, which had specially designed crushing chambers to minimize blockage. In a cone crusher, the closed side settings could be adjusted to control the product size during operation. When necessary, these machines could be made larger and stronger to crush hard, abrasive ores of metallic minerals for further grinding. Limestone used for making cement is usually crushed with a jaw or gyratory crusher in the quarry and a cone or impact crusher in the plant ahead of the roller or ball mills.

Primary Crushers

By 1910, the need to crush high tonnages of rock from open-pit mines led to a spectacu­lar growth in crusher size. In 1905, a large jaw crusher was 0.77 m x 0.61 m and was driven by a 34-kW motor, and a large gyratory crusher was 0.46 m x 1.61 m with a 75-kW motor (Louis 1909). Within 15 years, a large jaw crusher was 2.15 m x 3.07 m and a large gyratory crusher was 1.84-m. Both machines required 375-kW motors (Tag­gart 1927). The growth of copper mining led Allis-Chalmers to build six all-steel gyra­tory crushers with 1.54-m feed openings for a copper mine in Chile in 1926-1927. They weighed 500 tons each and were the height of a two-story building. Figure 5.13 shows one of these crushers.

The increasing demand for iron also affected crusher design. The high-grade pock­ets of hematite in the Iron Range in Minnesota were depleted during the world wars, and the underlying low-grade taconite ore, which is a hard, abrasive siliceous ore containing magnetite, had to be mined. Larger and stronger crushers were needed, and Traylor, Nordberg, and Allis-Chalmers all built high-capacity, heavy-duty primary and secondary crushers that incorporated improved lubrication systems and more reliable drives and bearing elements. The maximum power that could be drawn by the improved 1.54-m primary gyratory crushers was increased to 750 kW.

By 1970, crusher plants were operating that handled more than 100,000 tpd, and by 2000, plants could be built to crush any tonnage of ore. These plants are immense struc­tures that require deep excavations to achieve good gravity flow of the pebbles. Figure 5.14 is a sketch of the primary crusher at Bougainville Copper Limited (Papua New Guinea), which handled 120,000 tpd of low-grade copper ore. Developments on Bougainville Island added much to knowledge of crushing systems.

Updated: 24.03.2016 — 12:06