What is Ceramic, How to Make?
What is ceramic, how to make? What are the ceramic materials that are an indispensable part of our lives? What are the stages of ceramic shaping, pressing, drying, glazing and firing processes? In our article, we examined important issues related to ceramics.
What is Ceramic, How to Make?
Ceramic; They are inorganic and non-metallic solid materials formed by metallic materials that are chemically ionic and/or covalently bonded to each other with non-metallic elements. Ceramic is obtained by grinding raw materials and mixtures in certain particle sizes, drying after shaping, subjected to a heat treatment determined as glazed and unglazed, with the effect of heat and then cooling, giving them technical properties suitable for use. Ceramics are mechanically hard and brittle. Ceramics are classified into two groups as traditional ceramics and advanced technology ceramics.
What Are Ceramic Materials?
Traditional ceramics: consist of natural raw materials and generally three basic components; clay, quartz and feldspar. Clay is the most indispensable raw material of traditional ceramics. It has the feature of giving plasticity due to its layered structure and containing water between layers. Quartz cannot be shaped, but it provides strength to products. Feldspars, on the other hand, are raw materials formed by the deterioration of rocks. For instance; building ceramics (brick, tile), covering materials (floor and wall tiles), tableware, porcelain refractories and glass. Ceramic production in general; preparation of raw materials and mixtures, shaping, drying, glazing and cooking stages. The main processes in the production of ceramic materials are powder preparation, raw material preparation, shaping, drying, glazing and firing.
Powder preparation; ceramic raw materials are crushed, crushed, ground to certain grain sizes, classified and shipped to stock areas and stocked. Raw material preparation (Masse preparation – Ceramic mud); Ceramic raw materials, which are reduced to certain grain sizes, are mixed in mills according to recipe specifications, homogenized, dry or wet ground in certain grain size ranges, the slurry (sludge) whose wet grinding is completed is discharged from the mills, rested in pools and made ready for shaping.
How is Ceramic Shaped? What is Ceramic and How to Make?
Ceramics can be shaped by more than one method. Ceramic forming methods are explained below.
Use of Gypsum Mold
Casting mud (sludge rested in pools) is poured into plaster molds at a rate of approximately 25-30% water. The water in the mud is absorbed by the porous plaster mold. The mud takes the shape of a plaster mold at a certain wall thickness. Molding and drying time can be 1 day. Pressure casting method is the latest technological method. The casting mud is pressed into a resin mold consisting of many fine holes under pressure. Mud water is removed from the holes. Wall thickness is formed in the mold in 10-15 minutes in a fast time.
Extrusion
For shaping with the extrusion (plastic forming) method, the moisture content of the mud (16-18%) is adjusted by passing it through filter presses. The ceramic paste is extruded by vacuuming the air. It is formed according to the mold mouth attached to the end of the extrusion device. Materials with fixed cross-sections such as perforated or non-perforated tube rods and bricks are produced. – For shaping with the press method, the mud is passed through spray dryers and turned into granules. Granules are kept in press-top silos to ensure homogeneous humidity (5-7%). Prepared granules are shaped by pressing at certain pressures in powder press molds.
Injection Molding Ceramic Forming, What Is Ceramics, How to Make?
Injection mold forming; Injection molding method is used to produce complex shaped products. No water is used. The ceramic mixture powder is mixed in polymers at a rate of 45-55% by volume by melting under vacuum and the polymer is turned into mud. This mud is injected under pressure into the mold to be shaped. The mud freezes and takes the shape of the mold. The ceramic product remains after the polymers are removed during the heat treatment.
Ceramic Pressing, Dry Pressing, Hot Pressing, Cold Isostatic Pressing, What is Ceramic and How to Make?
It is the shaping of a liquid or mud-like mixture by casting using a mold. Plastic forming: It is the process of forming semi-wet ceramics using pressure (Extrusion). Powder compaction: This method; It is based on the principle of shaping the powders (granules) filled in the mold cavity by applying unidirectional or bidirectional pressure.
The cooking process can be done in continuous or intermittent ovens. After the ovens are filled, the oven is turned off and the cooking process is started, when the cooking process is completed, the oven is cooled and new products are loaded again after the products are emptied. In continuous kilns, also called tunnel kilns, on the one hand, the product enters, on the other hand, the baked product comes out. The cooking process can take 20-50 hours. They can work with bottom or side heating. In the production of porcelain products, the products that come from shaping are subjected to a baking process at 1240 oC for 15-17 hours.
Here, the patterns are adhered to the relevant product and baked at 870 ᵒC for 2 hours on glaze, and for 2 hours at 1210 ᵒC on glaze. Pattern quality separation is made and the products are sent to the packaging department and stored.
Ceramic Dryer
Drying is the process of removing the physical water in the sludge at around 100 °C. It is the most important stage of production. There should be no cracks or deformation. Drying before cooking is done in order to prevent the material from breaking and cracking during transportation, the formation of water vapor during cooking, and the explosion of the material in the oven by giving the material the necessary strength.
Ceramic Glazing, Paint
Ceramic glazing gives the object a beautiful visual appearance and reduces water permeability. The glaze is actually a kind of painted glass sand. Glazed ceramic products have a longer life. All of the ceramic products used in the kitchen are actually glazed. Before applying glaze, you must clean the surface of the ceramic object. Smooth ceramic surfaces give better results in glazing. Because the dust on the surface prevents the glaze from covering the object, the defect becomes more obvious after it is baked. After glazing, cracks, scratches and bubbles may remain on the ceramic surface. Different methods of applying the glaze to eliminate these defects
you can try. You can use ceramic glazing processes such as applying the glaze with a sponge, using a compress, or dipping. After the glazing process, the ceramic object is fired. At high temperature, the glaze melts and a colored glassy layer is added to the ceramic surface.
Ceramic Baking
Ceramic baking; It is the process of reducing the pores, increasing the density and giving strength to the material by subjecting the grains in contact with each other to high temperature heat treatment in the shaped and dried ceramic material. The cooking temperature is kept below the melting point of the material and varies according to the usage area and recipe.
There may be slight differences between the production techniques due to factors such as the ceramic classes, the use of variable raw materials during the production phase, the use of additives, the variations in the processes, the temperature differences in the kiln sections, the methods applied specific to the facility, the production of the same products at different production temperatures and times.
Raw materials are generally stored in closed silos. Silicate raw materials can be used with their natural compositions in the production of bricks-tiles, floor-wall tiles; but it is used as enriched in porcelain and sanitary ware products. Tables showing the ratios of raw materials, additives and water used in the production of a ceramic product are called recipes. There are more than one raw material in ceramic production, especially traditional ceramics. Clay, feldspar and quartz minerals are mainly used in the production of ornaments, building materials, sanitary ware and porcelain.
Material groups used in ceramic production All processes applied to turn ceramic raw materials into a masse (sludge) suitable for shaping separately or as a mixture are called “ceramic masse preparation”. Crushing, Grinding, Separating grain groups, Reducing the water or completely drying, Dosing (Recipe creation), Wet Grinding, Casting sludge, ceramic paste or granulating, Transporting the granules by means of belts, Stocking in silos above the press.
The operations to be performed are determined according to the forming method. While the dry method, that is, dry crushing and grinding, is used in the production of coarse ceramic products, the wet method is used in the production of fine ceramics. Masses with an average size of up to a few mm in coarse ceramics are prepared, while in fine ceramics, they must be ground to less than 0.1 mm. The amount of water in the wet-milled mass should be reduced by plastic (17%) for molding (30%) by pressing (7%). In the production of rough ceramic products, dryly crushed and produced masses are sieved, separated into grain groups and stored in silos. Dosed grain groups are made ready for shaping by adding water and additives to provide the targeted consistency depending on the shaping process. Various mixers are used at this stage. The most common type of mixer is ball mills. What is Ceramic and How to Make?