Gyratory reduction crushers- types and characteristics
In The Preceding pages we covered briefly the development of various types of reduction crushers of the gyratory family. Fig. 4 shows a modern gyratory reduction crusher, which introduced the cylindrical top shell, flared head, and reversible concaves. Even with the older style of straight concaves, with which this machine was originally fitted, it represented a distinct step forward in secondary crusher design, and the later introduction of non-choking con caves increased its efficiency and permitted the use of finer settings than were originally allowable. This type of machine, although it has been superseded in the fine-reduction field by more efficient types, still hates as a very excellent crusher for secondary work. It has good capacity at moderate settings, is ruggedly constructed, and has, for comparable sizes, relatively large receiving openings, as compared to machines designed primarily for fine-reduction work.
To show why this machine was a distinct step forward in secondary crusher design, it is interesting to compare the action of its crushing chamber to the standard crusher chambers already described. And to make clear the fact that the machine had certain advanced features, even before non-choking con caves were developed; we first show a diagram of its crushing chamber with the older type of beveled, straight-face concaves (Fig. 5). It should be mentioned that these beveled con caves were not the very earliest type used in this crusher; they were preceded by plain, straight concaves, which utilized the full rated receiving opening of the crusher, but had the same disadvantage we noted in connection with this type, as used in the standard gyratory-concentration of wear at the discharge-point. The beveled type spread the wear out somewhat, although at the cost of some reduction in the effective receiving opening.
The distinctive feature of the design shown in Fig. 5 is the decided slope of the line-of-mean-diameters away from the center-line of the crusher, as this line runs down through the crushing chamber. As the volumes of the successive rings of material are functions of their diameters, as well as their areas, it is apparent that these progressively increasing diameters tend to offset the decreasing areas; in other words, the flared head spreads the material as it moves downward, thereby tending to minimize the ratio-of-volume-reduction. The actual compression-ratio in this chamber is about 1.5:1, which is lower than in either of the diagrams previously discussed-and very much lower than the case of the standard crusher with straight concaves. That this departure from the older conventional design was a decided improvement for secondary crushing is apparent when we compare two machines of approximately equal head diameters, a logical comparison because the diameter of the bottom of the crushing head directly affects the area of discharge opening and, hence, the capacity of the crusher. The Superior McCully l0-in. reduction crusher, with its 40-in. head, compares closely, in this respect, with the 20-in. standard crusher, which has a 38-in. head. Using straight-face concaves, the permissible minimum open-side settings are 11h in. for the former, and 3% in. for the latter. With non-choking con caves these settings are, respectively, 1 1/8 in. and 21/4 in.
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