A-Plate Seal Assemblies
Variable Frequency Drives (VFDs)
In this era of dropping costs, Vincent recommends the use of an inverter VFD to start,
protect, and operate the screw press. With a VFD it is possible to establish the optimal
combination of screw speed and discharge cone air pressure. The VFD also can be used to
reverse the press in case of a jam or to slow it down or speed it up during upset conditions.
VFDs can be programmed to automatically stop and reverse the screw at set intervals. This
is a good feature when the material tends to blind the screen. Reversing the screw will wipe
the screen clear and liquid draining will return to normal. The auto-reverse function is also
useful for applications where long stringy material wraps itself around the screw. The
reversing action will knock free (untie) the stringy material.
Vincent is also more frequently using level controls, particularly in those applications where
the flow to the press can vary substantially. The level controls can be tied to the VFD or a
control system to speed up the press when it reaches a certain level or to gradually increase
screw speed or decrease backpressure to increase press throughput.
Vincent Cone Timers (VCTs)
For some applications a timer is used to periodically open the cone. There are two timer
settings on the cone timer. Timer 1 determines the interval between cone openings. Timer 2
determines how long the cone remains open. Both are set by trial and error, manually
opening and closing the cone using the cone positioning valve and then setting the timers
accordingly to make it automatic.
Cone timers are most frequently used when there is no level sensor. With abrasive materials,
low flow to a press maintained under compression will prematurely wear the screw and
screen at the discharge. As an example, we had a location where flow to the press would
stop for hours and the wood waste material would get completely dry, creating a "Presto
Log". When the flow started again, the presto log would not move, blowing out the screens
and bending back screw flights.
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