Crushing operation

Crushed stone for road building must be relatively strong and inert, and must meet specifications regarding size distribution and shape. Both size and shape are determined by the crushing operation. Table 20-29 lists specifications for a few size ranges. 

It is reported that between 10 and 11 million cars are taken apart every year in North America once the metallic portion has been recovered from the crushing operation, the remainder - representing over 20% of the total mass or 3.5 million tons - must be eliminated. Pyrovac, in collaboration with Universite Laval and under the sponsorship of E.T.P. Technologies, recently undertook a research programme to recover valuable products from this Automobile Shredder Residue. A process flow sheet for a 4000 kg/hr plant is presented, with fixed capital investment estimated to be 5 million US dollars. Details are given. 

The zirconium sponge thus obtained is highly pyrophoric. The industrial practice is to condition this sponge by the controlled admittance of air-argon mixtures at around 50 °C. Such a treatment results in the formation of a thin, protective oxide film on the sponge this eliminates any major fire hazard in subsequent handling and crushing operations. 

A demonstration by Berthollet in 1788 of replacement of potassium nitrate in gunpowder by the chlorate led to a violent explosion during the crushing operation which caused two fatalities. Later incidents involving factories for chlorate-containing explosives led to widespread destruction. 

The choice of a machine for a given crushing operation is influenced by the nature of the product required and the quantity and size of material to be handled. The more important properties of the feed apart from its size are as follows ... 

Crushing and Fermentation. Daily Equipment Cleaning and Sanitization. All equipment used in the crushing operation must be cleaned and sanitized daily. This is especially important in keeping the local population of fruit flies to a minimum and in avoiding early build up of volatile acidity from Acetobacter infections. Winery waste tends to putrify rapidly if allowed to stand. 

If one-step crushing (primary) is done, then the resulting particles are rather coarse. In order to produce finer particles, the crushing operation usually has to be repeated (secondary), or the material is subjected to grinding. This is the reduction of a material to a powdery state (pulverization) in devices based on friction (such as millstones ) or concussion or abrasion with metal balls (ball grinders), or pebbles (pebble grinders)... 

The modern battlefield is like a huge resting machinery, in which countless hidden eyes, ears and arms are unoccupied waiting for the minute on which it all depends. Then, as a fiery overture, a single red flare from one or other hole in the earth travels into the skies, and a thousand guns bellow simultaneously, and with one blow the work of destruction, driven by countless levers, begins its crushing operation.47... 

A typical cottonseed crushing operation will separate the seed into oil [160 kg/t (320 Ibs/t)], hulls [260 kg/t (540 Ibs/t)], meal [455 kg/t (910 Ibs/t)], and linters [83.5 kg/t (167 Ibs/t)] (1). The hulls and meal are sources of vegetable protein feed for animals and the linters are used as a chemical cellulose source in personal care products, in batting for upholstered furniture and mattresses, and in high-quality paper (2). 

In concentrating-mill operations, surface is fully as important in the concentrating department as in crushing operations. It is surface that limits the tonnage that can... 

Once the magnesite rock has been blasted, it is generally loaded onto trucks and transported to the primary crushing operation. Primary crushers are heavy-duty machines and handle dry run of mine feed material as large as 1 m. There are two principle types of primary crushers in operation— gyratory crushers and jaw crushers, with the gyratory type being the most common. 

Crusher-run aggregate is the unscreened product from a single crushing operation. 

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