PRODUCTION AND EQUIPMENT
ADVANTAGES OF QUASI-ISOSTATIC PRESSING
FOR POWDER MATERIALS
M. I. Timokhova
Translated from Novye Ogneupory, No. 6, pp. 24 – 28, June, 2012.
Original article submitted March 23, 2012.
The first technology for quasi-isostatic pressing that does not use costly isostatic presses has been developed
in Russia. The pressing operation is performed in quasi-isostatic molds on conventional hydraulic or mechani
cal presses normally used for static pressing. This article examines the advantages that quasi-isostatic pressing
has over hydrostatic and static pressing.
Keywords: quasi-isostatic pressing, advantages, static pressing, hydrostatic pressing, mold, cubic compres
sion, polyurethane, elastic buffer, service life, metal content of molds, mass production.
Quasi-isostatic pressing is well-known as a technology
that ensures the manufacture of high-quality products. Liq-
uids, gases, powdered graphite, melts of metals or glasses, or
various gels can serve as the pressing medium, but liquids
are the medium that is most often used in practice.
The most extensive research on hydrostatic pressing has
been carried out in the insulator industry. We have developed
a technology for the production of an entire range of stay in
sulators, condenser insulators, stopper couplings, lead-in in
sulators up to 720 mm high, and thin-walled cones for rock
ets. The cones have a 5-mm-thick wall and a height of up to
500 mm. A system of expanding limiters has also been de
veloped, this system making it possible to produce ribbed in
sulators by hydrostatic pressing.
The research done on isostatic pressing over the last 15
years has shown us that this technology has a whole range of
deficiencies which are impeding its broad introduction as a
means of mass production. Specifically, it is energy-intensive
and requires a large capital investment, a large amount of
space, and expensive hydrostatic presses that can be made
only by specialized factories. The process is also character
ized by low productivity, and the massive size of the hydrau
lic presses precludes vibration of the molding powder during
the pressing operation. When the technology is being used to
obtain large products, the ends of the products are not
pressed because the pressing pressure is applied radially.
That requires the subsequent use of lathes to remove the un
pressed sections from the ends of such products . The
above shortcomings of the technology and its complexity
have engendered a search for a simpler, more productive, and
more cost-effective process.
We have developed a new method for the isostatic press-
ing of ceramic and refractory materials — quasi-isostatic
pressing. The new method provides for cubic (triaxial) com-
pression of the material being pressed and combines the ad
vantages of hydrostatic radial (biaxial) pressing and static
uniaxial pressing [2, 3].
The pressing operation is performed without the use of
costly isostatic presses . It is performed in quasi-isostatic
compression molds that are similar in design, method of as
sembly, and regimes of operation to the conventional metal
lic compression molds used in static pressing. Each mold
consists of a floating steel die, an elastic element — the
buffer — a steel punch, and a steel ejector. Whereas a steel
core is used to form the internal cavity of a ring or sagger
(for example) in static pressing, in quasi-isostatic pressing
the same function is performed by the elastic buffer. The
elastic element simultaneously serves as a part of the mold,
providing for internal or external compression of the material
being pressed. Bilateral compression can be used to make
thick-walled products [5, 6].
The principle behind quasi-isostatic pressing is that the
medium which transmits uniform isostatic pressure during
the pressing operation is a hard elastic material — polyure
thane — which behaves similarly to a highly viscous liquid
(quasi-liquid). The pressure that the press applies to the elas
Refractories and Industrial Ceramics Vol. 53, No. 3, September, 2012
1083-4877/12/05303-0147 © 2012 Springer Science+Business Media New York