In the history of mankind, there are many materials that accompanied people almost from the very beginning of civilization. The first thing that comes to mind is a tree, but do not forget about ceramics - burnt clay, dishes from which they began to make from time immemorial.
Such material has enough positive qualities: the ceramics are strong, resistant to chemical and high-temperature influences, they are completely environmentally friendly, and their appearance is all right. In addition, the
burnt clay tile does not decay and is not covered with a fungus, which allows it to be successfully used to decorate a wide variety of technological rooms and bathrooms.
In general, ceramics are dishes or other clay things (with or without mineral additives) obtained by molding and subsequent high-temperature firing. To make the appearance of such products more beautiful, they are glazed.
What materials can be used in production?
We have already said that clay is mainly used for these purposes, but there are exceptions. So, the following materials can go to ceramics:
- Plastic base. This is just clay or kaolin (a rock consisting of kaolinite).
- Materials that minimize sludge during firing, keep the shape of the product. Quality quartz sand, substandard porcelain (battle), chamotte are involved.
- Rocks giving a dense vitreous mass during sintering. Feldspar, pegmatite is ideal.
- Glaze. Can be used as a material from natural raw materials, and numerous analogues obtained by chemical synthesis.
Classification
So we learned that ceramics is a specially processed clay. The factors that determine the consumer qualities of a product are the type of ceramics, the way it is decorated or molded.
Distinguish fine ceramics (fine grit on a broken shard), as well as coarse (coarse grit). Of the subtle varieties, porcelain, semi-porcelain, as well as earthenware, tiles of which are found in almost every bathroom, are familiar to everyone. Accordingly, rough ceramics (see the photo in the article) are pottery pots. The thing we have is not too common, but known from antiquity.
Properties of different types of ceramics
A distinctive feature of porcelain is a thin, dense and white fine-grained shard. The material absorbs moisture very poorly (up to 0.2%). Valuable vases or cups (very thin) can be viewed in the light. The edges of the rim (usually the bottom) do not glaze due to the firing technology. For production, kaolin and
feldspar are used mainly
.Semi-porcelain is an intermediate option between the porcelain and faience described above. Somewhat coarser, water absorption from 3 to 5%, most often used in the manufacture of tableware for household purposes.
As for the faience itself, it is distinguished by a thick porous shard, which on the scrap has a slightly yellowish tint. The ability to absorb water is high, in the range of 9-12%. It is precisely because of this, and also because of the high porosity, that any ceramic products of this type are necessarily covered with a layer of thin glaze.
Since the glazing used is very unstable to thermal effects, this type of ceramic is used exclusively in the production of inexpensive utensils for everyday use, as well as for household containers. For dressing, grades of clay, chalk and quartz sand that are not of high quality are taken. Ceramic technology of this variety also allows the use (as a basis) of beaten porcelain. Of course, before starting production, it is crushed and finely ground.
Majolica is a very attractive ceramics. The price for it is about a thousand rubles for an average vase. A distinctive feature is a very porous crock, can absorb up to 15% moisture. Despite this, the products are distinguished by thin shiny surfaces, have a small wall thickness. The latter is due to the fact that majolica is made by casting technology. As a rule, products are decorated with glaze, and decorative bas-reliefs are also often found. In the production of this variety of ceramics, white-burning clays, quartz sand, chalk and meadows are used.
Pottery ceramics (photo of which is in the article). It differs in a shard of a specific red-brown color (red-burning clay) and a very high porosity. Moisture absorption coefficient - up to 18%. For coloring, special clay paints, engobes are used. To protect them from moisture, on top of the product are covered with a thin layer of colorless glaze. As for the scope of use, the range is represented not only by decorative pots, but also by quite practical utensils for the household.
In addition, warm ceramics belong to the same category. So-called bricks made of roughly burnt clay. In the production of this kind of ceramics, special foaming agents are used, which sharply increase the porosity of the material, and therefore its heat-insulating qualities become much better.
How is the production process going?
The production of ceramics itself can easily be divided into several stages:
- Extraction and appropriate preparation of raw materials.
- Forming, applying decorative patterns or making functional holes.
- Casting, semi-dry stamping.
- Editing, first drying.
- High temperature treatment.
- Frosting.
- Re-firing.
- Decorative processing (warm ceramics and analogues do not need it).
Quality indicators of the finished product are determined by the characteristics of the appearance, full compliance with the functional purpose, as well as durability.
Manufacturing technology
We talked about the main stages of production, and so now let's discuss each of them separately. In order to prepare the initial ceramic mass, the following technological operations are carried out: the raw materials are thoroughly cleaned of foreign mineral and organic impurities, crushed and ground. After this comes the turn of mixing and adding various additives.
Product Forming
Molding is made of liquid or plastic ceramic masses. Plastic molding has several advantages. First of all, this is expressed in the fact that you can make products of almost any shape and size. In addition, even the simplest and most technologically advanced equipment can be adapted for their manufacture.
As for casting, a mass with a moisture content of 34-36% is used for this. Filling is made in plaster forms. This is an indispensable method for the manufacture of truly complex ceramic products, the shape of which physically does not allow the use of other molding methods. In addition, this is how tiles are made. Ceramics for it are not made from the best grades of clay (below the requirement), but the thickness of the finished products should be as uniform as possible.
Casting can be either manual or fully automated. After the initial drying, the products are removed from the molds, after which various decorative and functional elements are glued, for the connection of which special glue is used. In the past, clay dough was used for this purpose, but it did not provide too high strength.
Drying
Drying is the most important stage, since both the mechanical strength of the product and its decorative characteristics depend on the correctness of its conduct. Of course, the correct distribution of the glaze, on which the product's resistance to water, as well as chemical agents, is extremely important. Drying is a prerequisite for the production of ceramics. For her use conveyor, radiation and chamber dryers. The temperature throughout the process should not exceed 70-90 ° C.
The only exception is tile. Ceramics in this case are very thick, so in some cases it is allowed to use the high-temperature regime for a short time.
Burning
The second most important technological step is the firing of ceramics. The goal is the molding of a crock with precisely specified physicochemical properties, fixing the coloring composition and glaze to the surface. Burning is important because in its course there are many physical and chemical processes that determine the main consumer qualities of the product. Typically, firing is carried out in two steps, but if paint has been applied to the surface of the glaze, so-called muffle firing (third step) is carried out.
The first stage is carried out at a temperature of 900 to 1250 ° C (depending on the type and type of ceramic). The second stage requires a temperature regime from 1020 to 1410 ° C. The latter value is used exclusively for porcelain. Other ceramics are rarely fired in this mode, since there is a high risk of cracking. If we are talking about the average red clay, then products from it often even “burn” once, at a temperature of no higher than 960-1020 degrees Celsius.
For firing, two types of ceramic furnaces can be used: periodic (kilns), as well as continuous. There are a lot of varieties of the latter, but tunnel and roller are most common.
About various defects
The specifics of the manufacture of ceramic products is that at various stages of production, a large number of a wide variety of defects can occur. There are damage to the shard, glaze or decorative coating. As for the defects of the crock, they most often appear at the stage of primary molding and initial drying.
Some part of the manufacturing defect appears almost immediately, and spots or something like that appear only after firing. In connection with the “capriciousness” of the final product, there is a requirement to strictly control the cleanliness of all tools used in production.
Description of basic concepts
Glaze is a special melts that are applied to the surface of the finished product. Their thickness is 0.12-0.40 mm. The purpose of glazes is quite diverse. Firstly, the surface of the tiles or dishes is covered with a dense decorative layer, which not only contributes to a pleasant appearance, but also significantly increases the mechanical strength. In addition, the coating provides reliable protection against physical and chemical influences, which is especially true for household dishes.
Decoration refers to the application of decorative coloring or patterns. Often in industrial production , shaped dies are used, with the help of which mass production of similar products. A stamping roller is used to apply the pattern to the edges of the pot. Accordingly, the final operations are to eliminate minor defects, grinding the legs and edges.
Some glaze and paint information
Glazes are divided into transparent and opaque varieties, they are colored and completely colorless. Ceramic paints are used to decorate almost all varieties of baked clay products. They are based either on metals or their oxides. When heated, they form stable compounds that are not only beautiful, but also very durable. Such ceramics, reviews of which are always excellent, have long been an adornment in many wealthy homes.
Paints are divided according to the method of their application: either on a layer of glaze, or under it. As you can understand, in the latter case, the coloring composition is applied directly to the shard. Only then it is covered with a layer of glaze, and the product is fired in an oven. If the composition is applied directly to the glaze layer, it is fixed with a temperature of at least 600-850 ° C.
As for auxiliary materials, they are used for the manufacture of forms for firing and casting.
Mold Production Information
To make sufficiently strong and high-quality molds, molding gypsum is used. It is made by finely grinding powder of calcium sulfate hemihydrate. The peculiarity of such gypsum is that when mixed with water it should turn into a sufficiently plastic and elastic dough. But the main thing is that this composition must be set in precisely defined terms, which guarantees really high-quality firing. If for some reason there is no gypsum, refractory chamotte carborundum can be used. Allowed to use other refractory materials.
This is what ceramic is. This is such material, without which it is impossible to imagine a single kitchen or bathroom. However, there is another variety of it, products from which can be real decorations of any home.
Art ceramics
Under the "artistic" refers to products decorated with a particularly delicate relief or stucco. Of course, there are practically no other differences from ordinary ceramics, but there are many subtleties in the manufacturing technology. We’ll talk about them now.
Initial preparation of raw materials
As you know, artistic ceramics are not much different from their "household" counterparts, but in its manufacture it is necessary to more demanding approach to the selection of raw materials. Everything is the same as in the past case, but all operations are performed more subtly. In addition, exclusively finely ground kaolin should be used (particle diameter less than 2 microns).
What does it give? This approach allows you to get a much more ductile mass, and also at least doubles the strength of the dried products. In addition, only fine quartz sand should be taken , since it sharply reduces the precipitation of finished products, which is extremely important for art ceramics.
Drying art ceramics
As we have already indicated in the first part of the article, drying is one of the most important stages. If we talk about art ceramics, then this statement becomes even more relevant. You should be aware that shrinkage phenomena during firing of thin products occur unevenly, which can lead to great trouble, up to and including damage to the entire product. Therefore, it is extremely important to choose the right heating mode so that art ceramics do not turn into a bunch of shards.
If the products are flat, then it is strongly advised to dry them exclusively in molds. At first they are slightly wilted until the future ceramics acquire the necessary density, and only after that it can be removed and dried to a moisture content of 1-2.5%.
To conduct this process massively, use special conveyor dryers. In particularly difficult cases, drying is carried out in devices that operate on a periodic basis. This is done in order to prevent fine ceramics from drying out and cracking. The drying time ranges from 30 minutes to three hours.
So you have learned what ceramics are. This is one of the oldest materials that has ever been produced by humanity. Despite its antiquity, ceramics are still in high demand to this day.