| Screening
machines
Fast
production screening of dry materials
Screeners are self-contained
production screening machines for separating dry materials according to
particle size. Through their unique gyratory motion of the near-horizontal
screen surface, combined with a positive screen mesh cleaning system, the
screener provides unusually high efficiency and capacity - all the result
of continuing development for hundreds of applications throughout scores
of industries.
The screeners utilize a unique
screening action that provides accuracy of separation at high production
rates. As shown in the illustration below, material enters at top left
where it is distributed over the entire width of the screen surface and
conveyed toward the discharge end.
Larger particles remain above the screen surface, while smaller particles
pass through, as determined by the screen openings used for each
particular application.
The model illustrated here is
a typical two-surface machine, which separates material into three
different grades. Other models have one to five screen surfaces, producing
two to six separate grades.
2
separate actions - gyratory motion and bouncing balls
For low-cost screening on a
production basis, screening machines must perform two distinct functions:
1. Give undersize material maximum opportunity to pass through the
mesh openings but without the loss of oversize material at the same time.
2. Prevent the material from lodging in the mesh openings.
The screeners perform these two functions by employing two distinct
screening actions, thereby providing far more accurate separations and
greater product yields at higher production rates.
1. The unique gyratory motion
imparts a combination of actions to the material as it passes along the
screen surface.
It begins with a horizontal
circular motion at the feed end, gradually diminishing along the length of
the machine to an elliptical path, and finally to an approximate
straight-line motion at the discharge end. There ist no vertical component
to this motion - thus keeping the material in constant contact with the
screen surface.
Circular motion at feed
end
The gyratory motion at the feed end
of the machine immediately spreads the material across the full width of
the screen surface to maximize screen utilization even though the feed is
from a single point. At the same time, this motion stratifies the
material, causing the fines to sink down against the screen surface.
The particles that are appreciably smaller than the openings quickly pass
through at this part of the screen.
Changing to elliptical
motion at center
As the circular motion diminishes
into an elliptical path, the gentle near-horizontal motion causes the fine
particles closer in size to the screen mesh - the near-size particles - to
fall through the mesh openings.
Straight-line motion at
discharge end
The nearly linear recipro-cating
motion at the dis-charge end of the screener removes those particles
closest in size to the mesh openings while gently conveying the oversize
material off the screen. In addition the unique screener ability to
advance or retard material flow at the discharge end allows further fine
tuning to achieve the most efficient and accrate motion for the
application.
2. Bouncing balls ...
prevent binding
The second action is performed by
resilient balls confined in beveled pockets under each screen surface. The
machine motion causes these balls to be deflected against the underside of
the screen surface. This action keeps the screen surface clear of lodging
particles or binding.
Keeps the screen surface alive, providing agitation to aid particle
stratification and to separate particles that may tend to stick together.
This freedom from binding enables the screener user to choose screens with
the exact openings required to achieve the desired sepa-ration, resulting
in maximum yield of on-spec product. This highly efficient combination of
actions achieves the desired product deterioriation, so as to yield more
usable clean material per amount screened.
The screen deck is inclined at 4°, thus the material is exposed to the
full mesh openings, ensuring constantly sharp, well defined separations at
high production rates.
Totally-enclosed
design, positive sealing
The screen box is constructed so
that the screen frames nest completely within the box, one on top of
another, with the cover directly on top. Continuous sealing strips are
incorporated between all sections of the machine, preventing cross
contamination in the product fractions as well as leakage out of the
machine. When the cover clamps are engaged, the entire unit is completely
enclosed and secure.
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