Abstract: A screen apparatus has a frame having a pair of spaced-apart longitudinal beams whose ends are bridged by a pair of spaced-apart transverse beams. A central longitudinal member or wall equidistant between the longitudinal beams has ends secured to the transverse beams. Transverse struts extend between the longitudinal beams and through the central wall and support a screen. The frame is mounted for limited displacement relative to a fixed support and a drive motor is fixed to the central member and carries an eccentric for limitedly displacing the frame and the screen in a vibratory or oscillatory manner.

Abstract: A sifting machine having vibration generators connected to the opposite ends of a sieve screen, the vibration generators being so constructed as to vibrate one end of the sieve screen at a relatively low frequency and a relatively high amplitude and to vibrate the other end of the sieve screen at a relatively high frequency and a relatively low amplitude.