DESIGN SPECIFICS OF QUASI-ISOSTATIC MOLDS
M. I. Timokhova
Translated from Novye Ogneupory, No. 12, pp. 18 – 22, December, 2006.
Original article submitted July 19, 2006.
The author describes the specifics of molds for quasi-isostatic molding, which provide volumetric compres
sion of preforms made of powdered materials and their waste-free production technology. The advantages of
these molds compared to isostatic molds are discussed.
The method of quasi-isostatic molding developed by us
for producing a wide range of ceramic products is a simpli
fied variant of isostatic molding ensuring three-axial volu
metric compression of the material and, consequently, yield-
ing products of uniform density with good physicomecha-
nical and electric properties.
The medium transmitting uniform isostatic pressure is a
hard elastomer (synthetic caoutchouc), which simultaneously
acts as part of the mold forming the outer or the inner surface
of the preform. For instance, the elastic element in a mold
designed to produce ceramic rings is the core forming the
inner cavity of the ring, whereas in a mold for producing an
article shaped as a solid cylinder, such element is the bushing
that shapes the outer surface.
Figure 1 shows possible schemes of compressing the
matrix by means of the elastic medium: external compres
sion from the periphery toward the center (a, b, c); inner
compression from the center to the periphery (d, e); bilateral
compression (inner and external) to form articles with a sig
nificant wall thickness ( f ).
Molds for quasi-isostatic molding by their design, instal
lation method, and operating techniques resemble molds for
static molding. However, an article under quasi-isostatic
compression exists in a more complex volumetrically
stressed state than under traditional static compression, since
the usual system of forces acting in static molding here is
complemented by the reversible elastic energy of the
press-buffer volumetric compression and its deformation.
An elastic press-buffer is the main element in quasi-iso-
static molding; therefore, in designing these molds a very
significant issue is the choice of an accessible material for
the elastic pressing element, which would ensure compaction
of powder materials and reliable service of the mold in in-
dustrial conditions. We tested a wide range of elastomers in
molds for molding ceramic products. Based on molding test
results and data on physicomechanical properties, we have
chosen the elastomer SKU-7l as the optimum material pro
viding for articles with a uniform density throughout their
volume and a smother (less rough) surface. This material has
exceptionally high wear resistance and ability to operate
under high pressure; its residual deformation is equal to zero
Refractories and Industrial Ceramics Vol. 47, No. 6, 2006
1083-4877/06/4706-0344 © 2006 Springer Science+Business Media, Inc.
Remeko Company, Russia.
a b c d e f
Fig. 1. Schemes of material compressed by an elastic medium: a, sphere; b, cylinder; c, ring; d, rectangular shell; e, sagger; f, thick-walled
cylinder; D, d, outer and inner diameters of the preforms; h, preform height; R, pressure force; A, diameter or the side of the molding plane of the