Fine and very fine screening

Summary: As the screening practice reached the range of fine and very fine classification in the 20^th century, also comprising difficult-to-screen materials, such as in ore or salt processing and recycling as well, increased screening forces and screen deck accelerations were required. Thus, the aeration of the material to be screened should be increased and obstructing or clogging of the screen deck be reduced on the one hand, and larger specific throughputs be achieved on the other hand [6]. The technical inventions described in the following for the direct excitation of the screen deck by means of bumper, impactor bar, flip-flop or even ultrasound excitation met the new process requirements to a great extent [9, 11, 12].

1. Throw screening machines directly excited by means of bumpers or impactor bars

The development of bumper-type screens [1], which had begun in America at the beginning of the 20^th century, was continued with some efficient new developments mainly in Germany from the middle of the 20^th century. These screens were used for mean and fine sizing, in some cases even for very fine sizing. The knowledge acquired in the basic research of special processes proved to be an advantage for this development [2, 3, 13, 14].

The heavily inclined bumper-type screens (the inclination of the screening surface...