3.2. Penetration probability
In this work the simulated screen decks were divided into six
sections along the longitudinal axis. The deck is numbered from
the feed end to the discharge end. The dynamic screening efficiency,
gd, for each section during the three vibration modes is
shown as Fig. 5. The term gd is defined as the ratio of the undersize
weight to the total weight of small and near-mesh size particles in
the deck layer at time t. The corresponding average screening efficiency
for each deck at the steady state is tabulated in Table 2.
At the beginning of the screening process, the screen deck is not
entirely covered with particles. Consequently, the first two sections
of the deck have a very high screening efficiency with no
oversize material being produced. The screening efficiency of the
remaining section is null with no undersized particles being produced.
The screening process gradually reaches a steady state
when particles reach the discharge end of the screen and start to
produce oversize material. The time to reach the stable state for
the different vibration modes differs. Linear and elliptical screening
modes reach a stable state more rapidly taking about 2 s due to the
fast particle traverse speed. The circular mode stabilizes after
about 2.5 s.
Fig. 5 and Table 2 indicate that the screening modes have a significant
influence on the distribution of screening efficiency along
the deck. For each section both the screening efficiency and the
increment of screening efficiency at a stable screening state