Press cake is generally captured in an open-top container or a tarpaulin. Press liquor in a 5-
gallon pail or 55-gallon drum. If the press liquor goes to a pit or tank, the change in depth
can be timed.
Sometimes it is possible to collect only one flow, either press cake or press liquor. In these
cases, it is possible to estimate the press throughput if the solids content of the inbound
material and press cake are measured.
Screw Life
A screw can last anywhere from six months to twenty years. It depends on the material being
pressed and how hard it is being pressed. Two good indicators of a worn screw are:
1. Decreased throughput
2. Increased moisture in the press cake
You can stop the press and clean out the discharge area and visually check for a worn screw
by seeing how close the screw flights are to the screen. Be sure de-energize and lock out the
press before doing so.
Premature screw failure can arise from several causes. Some are:
1. The press is allowed to run continuously with no material being fed into it
2. Very low flow is consistently fed into the press
3. Abrasive material is dewatered with high cone air pressure
Extending Screw Life:
1. Various grades of hardsurfacing rod can be used to protect the flights of a screw. For
abrasive materials, Vincent will typically use a combination of colmonoy and
tungsten carbide, weld applied to the face of the flights at the discharge end
2. Using a VFD in combination with a level sensor
If a worn screw is suspected, shut down and lock out the press, open the cone, and dig out the
cake until the tips of the last two flights can be seen or felt. Check how badly the tips are
worn. If there is 3/8" between the tips and the screen, wear is evident. It is also an indication
that the sharp edges of the flights throughout the press may have worn, becoming rounded.
This can cause the flights to act like a putty knife, plastering solids against the screen,
preventing water from coming through.
Worn screws are either restored locally or returned to Vincent for rebuilding. The maximum
cost of a screw rebuild is around one third the cost of a new screw.
Pie Cutting
Sometimes the compression of a screw is reduced, in the field, in an operation called "pie
cutting". This involves cutting pie-shaped segments from certain flights of the screw, leaving
a butterfly (end view) configuration. The modification is done to avoid excessive
compression and jamming. (The "Sterile cut" is more drastic.) Consult the factory for
assistance before making this modification.
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