Crushing and Grinding

Crushing and Grinding

Crushing and Grinding

Crushing is the low-energy phase of the comminution process, and grinding is the high-energy phase. Crushed products for direct use are known as aggregates, which are hard inert materials used for mixing various-sized fragments with a cementing material to form concrete or mortar.

Aggregates are used in commercial centers, homes, airports, highways,dams,and streets. When aggregates from natural deposits were not available, they were made from rocks by hammer and chisel, or sometimes even in a mortar pestle, and later in crushers developed for the purpose.

The whole secret of the efficient reduction of material lies in a suitable crushing unit of the right capacity. This, I suppose, is obvious, but when one looks at some of the reduction plants in operation one is inclined to the belief that obviousness of such a statement has escaped at least a few. The best way to reduce any material is also the cheapest:the energy must be priportioned to the work in hand, otherwise either the work is not being done property or energy is being wasted.

During the second half of the 19th century,investors responded with jaw and gyratory crushers that are still used today,among them the blake jaw crusher that was patented in 1858 and the Gates gyratory crusher that was patented in 1881.

By 1850,Smooth double rolls for grinding ores driven by 15-kw motors were operating at 50 rpm and grinding 60tpd of siliceous ores. These rolls had come a long way from the ones that Taylor used in Cornwall in 1805. From 1890 to 1910, the cyanide and flotation process were established, and reliable fine crusher were required to grind ores at high rates to less than 5 mm, which was suitable then for ball mill feed. Roll crushers were the answer, and models were built that were stronger and more compact than those previously available and operated at high speed. By 1925, rolls were 1.8m in diameter and 0.53 m wide and were powered by 112-Kw motors.They typically ground siliceous ore to -3mm.

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