Gyratory crusher operation

The work index may be round experimentally from laboratoiy crushing and grinding tests or from commercial miU operations. Some rules of thumb for extrapolating the work index to conditions different from those measured are that for dry grinding the index must be increased by a factor of 1.34 over that measured in wet grinding for open-circuit operations another factor of 1.34 is required over that measured in closed circuit if the product size Xp is extrapolated below 70 [Lm, an additional correction factor is (10.3 + Xp)/l.l45X . Also for a jaw or gyratory crusher the work index may be estimated from... 

The development of improved supports and drive mechanisms has allowed gyratory crushers to take over most large hard-ore and mineral-crushing applications. The largest expense of these units is in relining them. Operation is intermittent so power demand is high, but the total power cost is not great. 

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. 

Crushers are slow-speed machines for coarse reduction of large quantities of solids. The main types are jaw crushers, gyratory crushers, smooth-roll crushers, and toothed-roU crushers. The first three operate by compression and can break large lumps of very hard materials, as in the primary and secondary reduction of rocks and ores. Toothed-roll crushers tear the feed apart as well as crushing it they handle softer feeds like coal, bone, and soft shale. 

Cone crushers are increasingly being used as secondary and tertiary crushers and are frequently operated in closed circuit (i.e. with over-sized particles being screened out and recycled to the crusher) to produce a well-defined top size, with minimum fines. They have similar reduction ratios to gyratory crushers (4 1 up to 6 1) and produce a more slabby product than impactors. 

Gyratory crushers, which are used as first-stage machines when very hard and coarse feed material has to be reduced, can receive the material direct from the truck, without the interposition of a feed hopper (Fig. 19). As the preliminary crusher delivers a product in the 300-500min size range, the second-stage crusher can function under less severe operating conditions than if the size reduction had to be performed all in one stage. 

Cone crushers operate on the same principle as gyratory crushers. This allows a gradual reduction of the area between the two cones. The rotating cone or mantle is inclined, thus providing a combination of impact loads and compression loads. By comparison with the gyratory crusher, the outer bowl is inverted, and the mantle rotates at much higher speeds. There are two types of cone crushers ... 

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