SOME FEATURES OF POROUS PERMEABLE CERAMIC MOLDING
BY SLIP CASTING
B. L. Krasnyi,
T. S. Marinina,
and A. L. Galganova
Translated from Novye Ogneupory, No. 6, pp. 43 – 46, June 2015.
Original article submitted December 1, 2014.
Preparation of porous filter ceramic by casting from aqueous slips into a gypsum mold is studied. The effect of
different factors on casting porous filter ceramic and methods for controlling its properties are established.
Test filter ceramic is prepared and operating parameters are determined.
Keywords: slip casting, porous ceramic, filter element.
Currently an important problem for the mining and met-
allurgical industry is preparation of finely porous filter ce-
ramics in the form of sector type elements, which are often
used for equipping ore concentrate dewatering vacuum de-
vices of instead of tissue filters. The stiff competition in this
segment of industry among ceramic producers for vacuum
units predetermines a search for new methods for filter ce-
ramic manufacture in order to provide efficient concentrate
Each method for molding ceramic objects due to its own
features has the most effective field of application. Porous
permeable ceramic is traditionally manufactured by semidry
compaction in hydraulic and vibration presses, plastic mix
extrusion, hot plastified mix casting, and pneumatic spraying
of slip mixes. Casting from aqueous slips is traditionally
used for manufacture of sanitary ceramics and some forms of
dense ceramic for engineering purposes.
In order to prepare porous complexly shaped large per
meable ceramic with a finely porous structure casting from
aqueous slips into porous molds may appear to be a uniquely
suitable molding method. The simplicity of molding equip
ment formulation makes this molding method for porous per
meable ceramic especially attractive, in spite of difficulties
arising during molding equipment preparation and servicing,
i.e., gypsum molds. Objects prepared by slip casting have a
uniform structure, which in the case of porous ceramic
should have a favorable effect on filter properties. The possi
bility is demonstrated in our work of preparing by slip cast-
ing in gypsum molds a porous ceramic material and filter ob-
jects based upon it.
During development of filter element composition it was
supported by generally accepted principles for molding a po-
rous ceramic permeable material structure: the main mix
comprises a narrow fraction filler, bonded into a strong car-
case by ceramic binder in low-temperature firing .
Ceramic for filter elements of the sector type during op-
eration are subject to action of weak organic and inorganic
acid solutions, and therefore specifications for filter material
chemical resistance remain at a high level: not less than 98%
acid resistance, not less than 95% alkali resistance. This fact
limits choice of raw material for synthesizing ceramic.
During implementation of slip casting the quality of slip
is fundamental. In order to provide a normal path for the pro
duction process and preparation of high quality product the
following main specifications are laid down for castable slip:
low viscosity with minimum water content, slip resistance to
solid component layering and settling, capacity for quite
rapid water removal into a gypsum mold with formation of
strong castings, and low object shrinkage during drying in
order to avoid occurrence of stresses in an unsecured
workpiece . Mineral particle size and shape, composition,
structure, and surface properties within a ceramic mix affect
slip rheological properties.
Slip viscosity should be the minimum possible in order
to provide the required slip fluidity and high quality gypsum
mold filling. The viscosity required in practice is selected by
testing, measuring material moisture content and pH. An in
correct increase in viscosity leads to a reduction in mix set
Refractories and Industrial Ceramics Vol. 56, No. 3, September, 2015
1083-4877/15/05603-0292 © 2015 Springer Science+Business Media New York
ZAO Scientific-Technical Center Bakor, Shcherbinka, Moscow,