|
 Glossary
Frost Resistance.
This is the frost resistance for ceramic
materials. The property depends on the distribution size of
the pores, of the geometric capillary form, of the elastic
module, of the bending resistance and of other factors related
to the production cycle.
CLAY. The most important characteristics are:
plasticity, hardening during the drying process, acquisition
of a rigid form after baking, shrinkage during the drying and
baking process, color change depending on the baking
cycle.
Double-firing.
This is divided into "fast double-firing
", with both the thermal cycles generally less than one hour
in the rolled furnace, and "slow double-firing or traditional
" in which both thermal cycles are for a number of
hours.
Baking
. Consists
generally of subjecting ceramic pieces to high temperatures
for a sufficient time period (from several minutes to a few
days) in order that the desired reactions materialize within
the ceramic body. The complete baking of the piece and its
vitreous covering or decoration may include more than one
thermal cycle, each of which occurs, in most cases (but not
necessarily), at temperatures inferior compared to the
previous thermal cycle. The baking cycles can thus give rise to single-fired,
double-fired or thrice-fired.
vetrified. Ceramic with vitrified stone, white or
colored, without enamel. Belonging to this category are also
the clinker, brined vitrified or fine vitrified for domestic
use.
vetrified stonewar. Tiles obtained by pressing, with total
porosity very low, made by a white-body that may also be fully
colored or varied with a mixture of dustings and granules of
differing sizes and colors. The composition of the mixture is
very similar to a vitrified white-body but the raw materials
are selected so as to maintain the percentage of oxide and
iron to a minimum. The mixture is pressed with specific
charges 50% greater than the vitrified white-body enamel. The
baking is performed with cycles of less than one hour and
temperatures of around 1200°C. The tiles can also be polished,
before or after the installation, in order to enhance its
esthetic qualities. It is resistance to frost, to acid and to
the bases and has a high mechanical resistance. It is a
product that has found widespread use in the tile industry,
where there are also present different types with low
applications of enamel and/or silk-screen processing that
consents a further esthetical appreciation of the
product.
mix. Homogenous mixture formed from components
of the ceramic body after the operations of grinding and
mixing; based on the content of water it can assume the aspect
of dust granulated by pressing, of a dense liquid for casting,
so-called “barbottina”, or of a mixture for plastic
processing.
Klinker. Small bricks or small sized tiles with
high thickness whose composite mixture is constituted by clay
and low quality kaolin, flux feldspathic and non-plastic
materials. A difference is made between vitrified
tiles for the heterogeneity of the mixture and for reduced
vitrification but frost-proof, unalterable to chemical attacks
and with a notable mechanical resistance to bending. The
products are obtained by pressing or extrusion and are baked
at over 1200°C with cycles for a number of hours. It is used
for external and internal paving. Clinker has its origins in
Germany around the 1930’s and this country is still the
largest producer.
single-fired. The ceramic tiles are subject to only one
thermal cycle during which all the chemical and physical
reactions occur in order to obtain the final desired
characteristics
.
The use of this term has now become
peculiar and almost exclusive to the production of ceramic
tiles, even if in fact single-fired cycles are found in other
similar production sectors such as, for example, refractory,
sanitary and roof tiling. A process of single-firing applied
to the production of tiles is generally fast (less than one
hour) while in the other sectors the thermal cycles are
realized over a longer period (even a number of
days).
tile. The Regulation UNI EN 87 defines ceramic
tiles as follows: “Thin slabs produced with clay, dioxide,
flux, coloring and other raw material minerals, that are
utilized as floor and wall coverings. They are produced
through grinding, sieving, mixing, humidification, etc. and
are formed by pressing, extrusion, casting and other
procedures generally at room temperature. They are first dried
and then baked at high temperatures. The tiles may be
enameled, non-enameled, or even slipped, they are
incombustible and unaltered by light”.
enameling. Application on ceramic pieces of a
vitreous cover that after baking constitutes its external
and/or internal surface.
enamel. Thin vitreous coat that had been applied
or formed on ceramic pieces and subjected to a thermal baking
cycle. This is constituted by a mixture of raw materials which
have the property to transform themselves in a continuous
vitreous coat when subjected to a thermal baking cycle. The
enamel can be of differing types that are summarized
below.
Thrice-fired. This
term was initially used to describe a thermal cycle made at a
maximum temperature not greater than 800°C. The definition of
thrice-firing originated from the fact that the ceramic
objects had already been subject to a first baking of the
ceramic body and a second baking of the enamel coat. The third
firing was destined, thus, to the baking of the final
decoration in the final production of tableware, dishes, and
more recently, of the ceramic tiles.
In
the case of the tile it is used especially for the so-called
"trim tiles ", through techniques aimed at giving the tiles an
appreciable esthetic effect.
| 
