Хонинговальные головки

The advent of steam power greatly improved the efficiency of flour mills. In 1786, two 37-kW steam engines were connected to drive 20 stone mills (1.5 m in diameter) at the Albion grain mill in London (Fischer 1944), and for the next 100 years, grain was ground mainly in steam-driven querns. A flour mill that […]

Impact breakage processes are used to reduce the size of hard, brittle materials but are not useful for reducing soft or elastic materials unless the materials can be cooled to the point at which they become brittle. This is where cryogenic breakage is becoming very important. Its main use is in recycling processes for plastic […]

The discovery of fine-grained gold ores on the Witwatersrand in South Africa in 1886 highlighted the importance of finding a new method to extract the gold, because the losses with the amalgamation process used at the time were excessive. Chemists had known for 100 years that gold could be dissolved in potassium cyanide. A patent […]

Wet Mills In the early 1930s, the economic depression was in full force, and the only interest in new grinding machines was for milling gold ores, because gold was the only metal that was not falling in price. In 1933, gold rose from $21 to $35/oz. Alvah Hadsel, a mechan­ical engineer in California with considerable […]

Figure 9.2a shows the Dorr classifier as it was in 1940, and it has changed little since then. Mineral companies quickly accepted the rake classifier and thickener, and closed — circuit wet grinding became part of mineral processing technology. With its reciprocating rakes, the Dorr classifier soon had competition from the Akins classifier (Figure 9.2b), […]

By 1900, rock drilling had reached the point at which hammer drills were available that operated at several hundred cycles per minute, worked at any angle of inclination, had the cutting head held at the rock face by an air cylinder, and had the chips and fine detri­tus continually removed from the working zone by […]

Although John Bennett had a flair for mathematics at school, he did not take the scholar­ship he won to Oxford University. Instead, when World War I started, he joined the Royal Engineers at the age of 17. After the war he lived in Turkey and Greece for 15 years, where he worked as a diplomat […]

Until the 15th century, all the major developments in size reduction were for the food preparation industry—for the grinding of grain to make flour. Although there were demands for minerals, particularly gold, copper, zinc, and lead, and for construction materials, the demands were small, and the methods used to grind grain were adequate. When manually […]

The 20th century ended with the mining and stone industries using the same types of primary crushers that were invented by Blake and Gates and used at the end of the 19th FIGURE 5.24 Typical size-reduction circuit for a cryogenic scrap tire-processing plant (Reschner 2002; reprinted by permission from Recovery Technologies Ltd.) TABLE 5.2 Sizing […]

The background to the flotation process was similar to that for the cyanide process. The reserves of ores containing coarse-grained minerals were dwindling, and ores containing fine-grained minerals—which were difficult to extract by the processes of the time— needed to be mined. The cyanide process was unsuitable for ores containing lead, zinc, and copper, all […]