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 thats formed, glazed and baked. Figure 1: Wall & floor tiles.
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
Glazing ProcessGlaze is a layer or coating of a vitreous substance which hasbeen fired to fuse to a ceramic object tocolor, decorate, strengthen or waterproof it.Without glazing, ceramics would remain porous and wouldremain unsuitable for holding liquids. Special glazingprocesses are used to make dinnerware, porcelain andstoneware beautiful.
Glazing ProcessComposition: Ceramic glazes generally contain silica to formglass, in combination with a mixture of metal oxides such assodium, potassium and calcium which act as a flux and allowthe glaze to melt at a particular temperature, alumina (usuallyfrom added clay) to stiffen the glaze and prevent it fromrunning off the piece.
glazing ProcessTo prepare glaze the raw materials are weighed,then mixed and dry or wet milled. The milled glazesare 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.
glazing ProcessWater fall glazing:Spray glazing:
Firing (sintering) ProcessBefore firing the ceramic piece is said to be GREEN.Means not fully processed or treated. This GREENpiece lacks hardness and strength, so it is heated tofix is shape and to achieve hardness and strength.Firing is the heat treatment process that sinters theceramic material it is performed in a furnace called akiln. In sintering , bonds are developed between theceramic grains, and this is accompanied byreduction of porosity.
Firing Process• Typical firing temperatures for alumina, mullite, andzirconia reach 2850 °F - 3100 °F.• Typical firing cycles can range from 12 - 120 hoursdepending upon the kiln type and product.• Ceramics shrink approximately 20% during thesintering process.•Unglazed ceramic ware is fired only once butglazed product s are fired twice. Fire the ware oncebefore glazing to harden the body of the piece, applythe glaze, fire the piece a second time to harden theglaze.
Finishing ProcessParts made of ceramics sometimes require finishing.In general, these operations have of the followingpurposes, 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.