Granite mill's working principle is similar to that of Raymond flour mill, but its grinding unit is furnished with 1000 - 1500 kg pressure spring. When it works, the grinding roller, under the action of high pressure spring and centrifugal force, rolls and closes up to grinding ring, its rolling pressure ratio is 1.2 times of that of Raymond flour mill given an identical condition, but its output may increase 20% to 30%.