STUDY OF THE RHEOLOGY OF SINTERED GLASS CERAMIC MATERIALS
BY TORSION OF THIN-WALLED TUBES
D. V. Andreev
and A. I. Zakharov
Translated from Novye Ogneupory, No. 1, pp. 36 – 44, January, 2012.
Original article submitted October 13, 2011.
The capabilities of a newly developed method of rheological study of roasted semifinished articles in simple
shear and in shear combined with axial strain induced by additionally applied compressive or tensile stresses
are demonstrated. The method is based on the principle of torsion of thin-walled tubes realized in a newly cre
ated device and makes it possible to determine the mutual influence of the components of the strain rate tensor
of the material, where the strain may be a consequence of dilatancy, anisotropy, asymmetry of a mechanical
reaction or other factors. The rheological properties of semifinished articles belonging to the group of porce
lains which have been preliminarily roasted at 900°C, lithium-aluminosilicate glass ceramic, and sintered
semiporcelain are studied.
Keywords: porcelain, glass ceramic, sitall, strain, rheology, viscosity, simple shear, torsion, dilatancy, liq-
uid-phase sintering, shrinkage, roasting
Efforts have been focused on reducing the roasting time
and roasting temperature as a means of reducing energy con-
sumption in the production of ceramic articles. Active fusing
agents that form a liquid phase at low temperatures are basi
cally used for this purpose, though the probability of strain of
the article thereby grows and the precision of its dimensions
falls. In addition to technological methods of reducing strain,
which are always limited by the properties of the materials
and the particular mode of production, there also exists the
engineering capability for reduction of deformation by com
pensation of deformation with appropriate correction of the
shape of the model or by increasing the rigidity of the con
struction of the article; prediction of deformation is needed
to realize these capabilities.
In the traditional technology of staged manufacture of
new models of products where there is unacceptable defor
mation in roasting, correction of the dimensions of the model
together with repetition of all the stages is required. The time
spent on correction and fabrication of the mold may be sub
stantially reduced through the use of computer modeling.
CAD and CAE programs are used in the creation of the com
puter models of constructions and materials; it is also neces-
sary to know the characteristics of the roasted article.
In the course of roasting a semifinished ceramic article
experiences the effect of multidirectional forces caused by
stresses associated with sintering (shrinkage) and tempera-
ture expansion, phase transformations, and the effect of
deadweight. The rheological behavior of the material in the
course of roasting may be described by any one of the
well-known models (governing relations) in light of the
above factors. Any one of a number of different models may
be used to describe the rheology of a material, from simple
phenomenological models to complex theoretical models.
The latter types of models are generally on the basis of a par
ticular type of idealized mechanical models or, in the case of
great universality, are distinguished by a set of structural pa
rameters that are not amenable to determination with any re
quired degree of precision. The use of phenomenological
models is associated with difficulties in the realization of
three-dimensional schemes for testing the samples and for
this reason the most commonly employed models are
semi-empirical. Tests of samples in special cases of the
stress-deformed state are used to determine the phenomeno
logical parameters of these models while iterational calibra
tion, manual variation, etc. are used to determine the struc
tural parameters. In  porcelain plates and sanitary pottery
ware served as the subject of study and simulation; the di
mensions of the articles at different stages of sintering were
Refractories and Industrial Ceramics Vol. 53, No. 1, May, 2012
1083-4877/12/05301-0031 © 2012 Springer Science+Business Media, Inc.
FGBOUVPO Mendeleev Chemical Engineering University of
Russia, Moscow, Russia.