Abstract: Significant changes of chosen ore properties are the basic reason of concentrate quality unqualified of Washan dressing plant, point out middling regrinding ability deficiency and product size not controlled strictly, size of product of three stage magnetic concentrate screening classification is over thick, high frequency vibrating fine screen screening efficiency is low are the basic reason of cause the quality of concentrate not high, improvement scheme of strength secondary grinding ,increase three stage grinding, use Drake fine screen as preexamination screening of threestage grinding is proposed purposefully.

Key words: Grinding fineness, Optimizing and upgrading of process, Largescale ballgrinding machine, Fine screening