spacing between the rolls. It is necessaryto set the opening between the rollsslightly closer than the top product sizerequired. With two coarse corrugatedshells (fig. 6-7), the tip-to-tip settingproduces a product larger than two smoothshells set at the same distance.In the NCF, thehydrocone crusher isnormally used as the secondary unit. Thesemachines have a conical or domed crushingmember called a cone, head, or sphere,which moves in a small circle around avertical axis inside a fixed bowl ormantle.The cone may be relativelystationary at the top and move at thebottom only, or be mounted so that thehead can wobble as well as gyrate. Thecrushing head is free to turn under thethrust from the material being crushed.The fineness of the product is adjusted byraising or lowering the mantle.Effective feed and dischargearrangements are essential to theoperation of any cone type of crusher. Formaximum crushing efficiency, feed must besupplied to the crushing chamber in theoptimum amount and distributed evenlyaround the entire crushing area.NOTE:Material received by thehydrocone crusher must be evenly distributednonsegregated feed. This means that thematerial entering the crusher is evenlydistributed around the entire crushingchamber, with fine and coarse materialwell intermixed in the feed. Unevenlydistributed or segregated feed resultsin poor manganesewear, reducedcapacity, and high stresses within thecrusher. These problems can cause shortbearing life and possible failure ofmajor components. An evenly distributed,nonsegregated feed results in maximumcapacity, a uniform product, and asmooth running machine.A pressure gauge is standard on allhydrocone crushers. Erratic hydroset controlpressure and motor amperage (horse-powerdraw) readings are evidence of poorfeeding conditions and uneven feeddistribution in the crushing chamber. Thepressure gauge enables the operator toread high, average, and low pressures inthe hydroset control and take correctivemeasures against erratic and high-pressureconditions. The pressure gauge should bechecked regularly when the crusher isreceiving the full or maximum amount offeed.NOTE: When excessive fluctuations occurin the pressure in the hydroset control andhorsepower drew, determine and eliminate thecause immediately. Operating the crusherunder these conditions can causeFigure 6-7.—Shell combinations for dual roll crushers.6-6
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