2. The Basics
• Ceramic means “fired clay” and tile means
“covering.”
• Common raw materials are sand, clay, talc,
feldspar.
• A typical example of ceramic powder metallurgy.
• A ceramic tile is just clay that's formed, glazed
and baked.
Figure 1: Wall & floor tiles.
3. Preparation of Powder
• Rock lumps reduction to powder through
crushing and grinding.
• Crushing – reduction of large lumps to smaller.
Jaw breaker, gyratory crushers, roller crushes,
hammer mills. Picture
• Grinding - further reduction to fine powder. Ball
mill.. Picture
• Wet milling - Water, alumina, silica, binders and
lubricants mixed in ball mill with powder to form
a slurry.
• Spray drying – Slurry is dried using a rising
column of hot air.
• The raw materials are mixed in specific
proportions according to weight. The specified
mixture is achieved by varying the speed of
conveyors that feed the master conveyor belt
Video
5. Glazing Process
Glaze is a layer or coating of a vitreous substance which has
been fired to fuse to a ceramic object to
color, decorate, strengthen or waterproof it.
Without glazing, ceramics would remain porous and would
remain unsuitable for holding liquids. Special glazing
processes are used to make dinnerware, porcelain and
stoneware beautiful.
6. Glazing Process
Composition:
Ceramic glazes generally contain silica to form
glass, in combination with a mixture of metal oxides such as
sodium, potassium and calcium which act as a flux and allow
the glaze to melt at a particular temperature, alumina (usually
from added clay) to stiffen the glaze and prevent it from
running off the piece.
7. glazing Process
To prepare glaze the raw materials are weighed,
then mixed and dry or wet milled. The milled glazes
are then applied by following methods.
1. In centrifugal glazing or discing, the glaze is fed
through a rotating disc that throws the glaze onto
the tile.
2. In the waterfall method, a stream of glaze falls
onto the tile as it passes on a conveyor
underneath.
3. Sometimes, the glaze is simply sprayed on.
4. For multiple glaze applications, screen printing
method is used.
10. Firing (sintering) Process
Before firing the ceramic piece is said to be GREEN.
Means not fully processed or treated. This GREEN
piece lacks hardness and strength, so it is heated to
fix is shape and to achieve hardness and strength.
Firing is the heat treatment process that sinters the
ceramic material it is performed in a furnace called a
kiln. In sintering , bonds are developed between the
ceramic grains, and this is accompanied by
reduction of porosity.
11. Firing Process
• Typical firing temperatures for alumina, mullite, and
zirconia reach 2850 °F - 3100 °F.
• Typical firing cycles can range from 12 - 120 hours
depending upon the kiln type and product.
• Ceramics shrink approximately 20% during the
sintering process.
•Unglazed ceramic ware is fired only once but
glazed product s are fired twice. Fire the ware once
before glazing to harden the body of the piece, apply
the glaze, fire the piece a second time to harden the
glaze.
13. Finishing Process
Parts made of ceramics sometimes require finishing.
In general, these operations have of the following
purposes, to
(1) increase dimensional accuracy,
(2) Improve surface finish, and
(3) make minor changes in part geometry. Finishing
operations usually involve grinding and other
abrasive processes.
