Abstract: A grinding apparatus in which lignocellulose-containing material such as wood chips is ground in a grinding space defined between cooperating disc segments carried by a rotating disc and a stationary disc in close spacing tolerance. In order to counteract the deflective centrifugal force exerted on the rotating disc segments, the peripheral portion at the rear of the rotating disc is formed with an annular bulge having an annular channel therein for receiving mercury in an amount calculated to generate during the rotation of the bulging disc a counter centrifugal force equal to the deflecting centrifugal force exerted on the rotating grinding segments to thereby maintain the close tolerance spacing between the cooperating grinding segments.