- Thesecondaryscreensreceivethecoalfromthecrushersandremovethefines.Theoversizeisreducedbyrollcrusherstothecorrectsizeofcoal.Hugediggingmachineswereneededandcrusherstogetthegoldfromtherock.Theprevalenceofshell-crusherscoincideswiththeappearanceofotherd...
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