UFC 3-280-03
23 JULY 2003
required can be determined. An example of this determination is presented in Chapter
5.
2-8
CONSTRUCTION MATERIALS AND INSTALLATION CONSIDERATIONS.
2-8.1
Construction Materials.
2-8.1.1
Filter Press Components.
2-8.1.1.1 Structural Frame. The structural frame is typically made of carbon steel. It
should be designed to provide a completely integrated structure sufficient to support the
entire weight of the filter plates and withstand the operating pressures. Coatings and
materials should also be selected to minimize corrosion. The structural frame should be
installed as discussed in Paragraph 2-8.2.
2-8.1.1.2 Plate Materials. Selecting the construction material for filter plates depends
on several factors. The key factors that should be considered are mass and strength.
Because mass and strength of materials are interrelated, the design should consider
tradeoffs between greater mass/less strength and less mass/greater strength.
a. The mass of the plate can affect the following items: ease of handling
during installation, cleaning, inspection, and changing filter cloth; cost and overall weight
of the press; and additional structural costs for the building that houses the press.
Although the current press may not require the heavier filter press plates, it can be
beneficial to include provisions in the initial building design to handle heavier plates for
the future.
b. Strength is an important aspect because of the high operating pressure.
Operating pressures can run from 690 to 1550 kPa (100 to 225 psi), and the potentially
uneven force distribution that may occur during the filter cycle can increase the pressure
that must be considered. Uneven distribution can deflect and deform the plates, cause
blowout, and increase filter wear. Overall these effects increase as plate sizes increase.
To compensate for these, plates of lower strength are typically constructed with larger
stay bosses, which reduce cake volume between plates. This reduced volume leads to
a larger number of plates required, added structural frame length, and additional
building space to achieve a given volume using plate materials of lesser strength.
c. Fixed-volume filter press plates are commonly available in polypropylene,
gray cast iron, ductile iron, and epoxy- or rubber-coated steel. Variable-volume press
plates are also commonly available in polypropylene, ductile iron, and steel, and are
equipped with an elastomeric diaphragm typically constructed of polypropylene. Poly-
propylene plates are the most common because of their excellent chemical or corrosion
resistance, their lighter weight, which eases handling, and their low initial cost. Plates
constructed of polypropylene are typically found in all sludge presses for pressures of
1550 kPa (225 psi) and below at temperatures less than 90 degrees C (200 degrees F).
Above these conditions, glass filled polypropylene or nylon plates are recommended.
Although the strength of polypropylene plates is less than those made from iron and
2-69
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