General scheme for the production of ceramic products. Own business: production of ceramic dishes
The production of ceramic products includes the following main operations: mass preparation, product molding, drying, firing and decoration.
Materials used for ceramic production are usually divided into basic and auxiliary. The main ones include materials used for the preparation of ceramic masses, glazes, ceramic paints; to auxiliary - materials used for the manufacture of plaster molds, capsules.
The preparation of ceramic mass is carried out by the sequential implementation of a number of technological processes: cleaning of raw materials from harmful mineral inclusions, crushing, grinding, sifting through sieves, dosing and mixing.
Products are molded from plastic and liquid (slip) ceramic masses. Products of simple shapes (cups, plates) are molded from plastic mass with a moisture content of 24-26% in plaster molds using steel templates on automatic and semi-automatic machines.
The method of casting from a liquid mass (slip) with a moisture content of 30-35% into plaster molds is considered indispensable in the production of ceramic products, where the complexity and variety of forms preclude the use of other molding methods. Casting is carried out by manual or automatic methods.
Roasting is the main technological process. As a result of complex physicochemical transformations occurring at high temperatures, ceramic products acquire mechanical strength.
Roasting is carried out in two stages. For porcelain products, the first firing (scrap) occurs at a temperature of 900-950 ° C, and the second (poured) - at a temperature of 1320-1380 ° C. For faience products, the first firing is carried out at a temperature of 1240-1280°C, and the second - at a temperature of 1140-1180°C. Two types of furnaces are used: tunnel (continuous) and forges (intermittent).
decoration products - the final stage in the production of porcelain and faience products, which consists in applying special cuts to linen (unpainted semi-finished product) by two methods: manual and semi-mechanized.
Mustache, layering, tape are continuous circular strips (antennae 1 mm wide, layering - from 1 to 3 mm, tape - from 4 to 10 mm).
Stencil applied with an airbrush using plates made of thin tin or foil, having cutouts, the contours of which correspond to the applied pattern. It can be single color or multicolor.
cover the following types are distinguished: solid - the entire product is covered with a uniform layer of paint; semi-cover - the product is covered with paint with a width of 20 mm or more; descending - the paint is applied with a weakening of the tone to the bottom of the product; roofing with cleaning - a cleaning of the pattern was made along the continuous roofing; roofing with cleaning and coloring with paints and gold.
Seal is applied to the product from a printed impression on paper, while receiving a graphic one-color pattern, which is usually painted with one or more colors.
Stamp is the easiest way to decorate. The drawing is applied with a rubber stamp. More often stamps are applied with gold.
Decalcomania (decal) occupies a major place in the decoration of products. Transferring the design to the product using a decal made by a lithographic method, a sliding decal is currently used. A cellulose acetate film is attached to the lining paper, on which the pattern is printed. When wetting, the film with the pattern is separated from the paper and remains on the product. In the process of muffle firing, the film burns out, and the paint fuses with the surface of the product.
silkscreen is a promising way to decorate ceramic products. The pattern is printed through a silk mesh, on which a stencil is applied. The item to be decorated is placed under the silk mesh. A rubber roller with paint, passing through the mesh, pushes it into the cutouts of the stencil and thus the pattern is transferred to the product.
Painting works performed with a brush or pen by hand. Depending on the complexity, painting can be simple and highly artistic.
photoceramics reproduces on the product portraits of famous people, views of cities, it is especially effective in color.
Properties of ceramic products
The main properties of ceramic products are physical and chemical. The properties of ceramic products depend both on the composition of the masses used and on the technological features of their production.
The main properties include bulk density, whiteness, translucency, mechanical strength, hardness, porosity, thermal stability, sound wave propagation speed, and chemical resistance.
The bulk density of porcelain is 2.25-2.4 g/cm³, and faience is 1.92-1.96 g/cm³.
Whiteness is the ability of a material to reflect light falling on it. Whiteness is especially important for porcelain products. Whiteness is determined visually by comparing the test sample with a standard or using an electric photometer, as well as on the "Specol".
Translucency is characteristic of porcelain, which is translucent with a large thickness of the product, as it has a sintered shard. Faience products do not shine through due to the porous shard.
Mechanical strength is one of the most important properties on which the durability of the product depends. Specific mechanical strength, i.e. the ratio of the applied force to a unit of bottom thickness, is determined by the method of free fall of a steel ball along the bottom of the product. In faience, it is higher than in porcelain. The impact strength of the pendulum method, on the contrary, is lower for earthenware than for porcelain.
The hardness of the glaze layer according to the mineralogical scale for porcelain is 6.5-7.5, and for faience - 5.5-6.5, microhardness is determined by indentation of a diamond pyramid. Porcelain glazes are considered hard, majolica glazes are soft, and earthenware glazes are medium.
Porosity is determined by the method of water absorption, which is 0.01-0.2% for porcelain, and 9-12% for faience.
Thermal stability characterizes the ability of a product to withstand sudden changes in temperature. The thermal resistance of porcelain products is higher than that of earthenware. So, in accordance with the current GOSTs 28390-89 and 28391-89, the heat resistance of porcelain products should be 185 ° C, faience - from 125 ° C (for colorless glazes) and 115 ° C (for colored glazes).
The speed of propagation of sound waves for porcelain products is 3-4 times higher than for earthenware, therefore, when a wooden stick is struck on the edge, porcelain products make a high sound, and earthenware - deaf.
The chemical stability of glazes and ceramic paints used for household porcelain and faience products should be high, since they should not be destroyed when treated with weak acids and alkalis at ordinary temperatures or when heated to 60-65 ° C.
Classification and range of ceramic products
All ceramic goods are divided into coarse and fine ceramics. Rough pottery products have a non-uniform structure of the shard, which can be distinguished by the naked eye, in addition, the shard has a natural color - from yellow to brown tones.
For products of fine ceramics, a sintered finely porous shard with a homogeneous, dense structure is characteristic.
Fine ceramic products include two groups:
- products with a sintered shard(hard porcelain, soft, bone and frit porcelain, fine stone products);
- products with a porous shard(faience, majolica, semi-porcelain).
Hard porcelain is characterized by high mechanical strength, chemical and thermal resistance. Our factories produce mainly porcelain products from hard porcelain, which is prepared from a mass containing 50% clay substances, 25% feldspar and 25% quartz.
Soft porcelain has high translucency, but lower thermal and mechanical strength. The masses used in the production of soft porcelain contain 30% clay materials, 30-36% feldspar and 20-45% quartz. Soft porcelain is used in the manufacture of art products.
Bone china is made from a mass that, in addition to the usual components, includes 20-60% bone ash. Bone china is characterized by high translucency and low mechanical and thermal strength. It is used for the manufacture of souvenir dishes.
Frit porcelain is similar in composition to glass, as it does not contain clay materials. Due to the insufficient hardness of the glaze and the laboriousness of the technological process, this type of porcelain is rarely used for making dishes.
Fine-stone products have a color that depends on the natural properties of clay (light gray, cream). These products have high thermal stability. They make chemical fine stoneware, as well as mugs, coffee and tea sets.
Majolica is a type of faience with high porosity. Majolica products are usually covered with colored glaze.
Semi-porcelain in its properties occupies a middle position between porcelain and faience and is mainly used for the manufacture of sanitary products. Semi-porcelain products are cheaper than porcelain and higher in quality than earthenware.
Ceramic products are divided into dishes and artistic and decorative products. In turn, the dishes can be tableware, tea and coffee purposes.
Porcelain products are divided by wall thickness into ordinary ones with a wall thickness of 2.5 (cup) - 4 mm and thin-walled 1.4 (cup) - 2.5 mm, all the rest.
Depending on the size, ceramic products are divided into small and large.
In shape - hollow and flat.
The flat ones include saucers, dishes, plates, herring boxes, etc.; hollow - glasses, cups, mugs, bowls, teapots, coffee pots, sugar bowls, jugs, etc.
Depending on the presence of a glaze layer, glazed and unglazed (biscuit) porcelain products are distinguished.
According to the completeness of the product, there are piece and complete (services, headsets, sets). A feature of the products included in the kit is the unity of decorative design, design and shape.
By purpose, the assortment of household porcelain products is divided into dining, tea, household utensils and others.
Artistic and decorative products are especially highlighted.
The range of faience products is simpler and less diverse than similar porcelain products. A significant share is occupied by flat products (plates, bowls, herring boxes, etc.). There are no tea cups, teapots, coffee pots in the assortment of faience products. Basically, the assortment of faience dishes is represented by tableware.
The range of majolica products includes tableware and artistic and decorative items. For majolica products, cutting with various colored glazes (majolica glazes) and underglaze paints is typical.
Assessment of the quality of ceramic goods
Ceramic products must be durable, easy to use, and have a beautiful appearance. They are made in accordance with the samples approved in the prescribed manner. When evaluating the quality of ceramic products, attention is paid to the quality indicators of the sherd, glaze and decoration. Depending on the appearance, physical and technical indicators, the nature, size and number of defects, the dishes are divided into grades I and II according to the current state standards.
Whiteness, thermal stability, water absorption, acid resistance are determined according to the methods set forth in GOSTs.
The whiteness of porcelain products for grade I must be at least 64%, for grade II - 58%. For faience products, whiteness is not regulated.
Translucency is typical only for porcelain products, which are translucent in layers up to 2.5 mm thick. Porcelain and earthenware plates and saucers are considered to be mechanically strong if they are stored in piles for five days (the first 120 pieces each, and the second 100 and 150 pieces each) do not collapse.
The presence of defects is established during an external examination of the product. The whole variety of defects found on ceramic products is divided into defects in the shard and glaze and defects in decoration.
To defects in the shard and glaze include deformation of the product, potholes and crevices, glazed one-sided cracks, bald spots and assembly of glaze, zek and hair (cracks in the glaze layer), front sight (dark dots on the product), traces of skids, combs, incorrect assembly of product parts, undermining of attached parts, etc. .
To decoration defects- overburning and underburning of paints, assembly of decalcomania, overglaze paint blots, paint peeling, etc.
According to GOST, the number of permissible defects should not exceed for porcelain products for grade I - 3, for grade II - 6; for faience products, respectively - 3 and 6.
Marking, packaging, transportation and storage of ceramic products
Each porcelain and faience product is marked with a trademark, which is applied to the center of the bottom of the product with ceramic paint and fixed by firing. The trademark must be legible.
When packing dishes, they use: consumer containers (boxes made of cardboard, paper and combined materials); packs of cardboard, paper and combined materials, paper bags and of combined materials, auxiliary materials (wrapping and interlining paper, corrugated cardboard, heat-shrinkable materials, polyethylene film, polystyrene, wood shavings, etc.); transport containers (wooden boxes and corrugated cardboard boxes).
Cups with saucers are stacked in the following way: the cup is placed upside down on the saucer on the front side, previously lined with paper, and wrapped with paper. Then a stack containing from two to twelve products is formed, which is also wrapped with paper. It is permissible to mold feet made up separately from cups and saucers. Flat products are wrapped in paper through one product, and then in a bag of 25-40 pieces. The enlarged package is tied up with twine or sealed with paper tape and a label is attached indicating the manufacturing plant and its address, product name, number of products in the package, grade, packing date, packer number and GOST or TU number. When packing packages of services, sets, sets, products of the same grade and one decorative design are laid: each item is wrapped in paper. Then the dishes are placed in consumer and transport containers. Souvenir and gift products are placed in corrugated cardboard boxes, on which artistically designed labels are pasted.
The dishes are transported by all means of transport. Basically, the dishes are transported in railway cars and containers, the floor of which is lined with wood shavings in a uniform and dense layer. Rows of packages are also laid with shavings. On containers and railway wagons, the manufacturer must make the inscription "Caution glass".
Porcelain and faience products are stored in closed dry rooms on racks. In this case, heavier products are placed on the lower racks, lighter ones - on the upper ones. Plates can be stored in stacks (porcelain 120 pieces, earthenware 100 pieces).
Despite the widespread use of modern materials, which are characterized by a long service life and good consumer qualities, ceramic products are still relevant. Ceramic cookware is fragile and quite expensive compared to, for example, plastic. However, good thermal conductivity and, most importantly, environmental safety of this material compensates for all its shortcomings.
Competition in the ceramic tableware market is high, including among Russian manufacturers. The situation is complicated by the fact that the capacity of this segment of the Russian market can only be estimated approximately, since it is part of the home goods market and is estimated in conjunction with other segments. It is known that tableware makes up about a third of the total market for all household goods. It accounts for about $700 million.
Despite the fact that products from various materials are presented here - from glass to metal, nevertheless, until recently, ceramic and porcelain dishes were in the lead (about 70% of the total volume of tableware production).
The main trends that have been observed in the Russian ceramic tableware market over the past few years are the annual decline in production volumes (a particularly significant decline occurred in 2009-2010s) and the simultaneous increase in unit prices. On the other hand, in early 2009 2009, there was a sharp decline in imports of tableware due to the depreciation of the ruble and problems with import crediting. Now the volume of production of ceramic products in our country is about 250 million products and 2.6 billion rubles in value terms per year, and the annual growth rate of ceramics imports from other countries is 20-30%.
In general, the market growth rate is gradually declining. Experts say that not the best times have come for the production of ceramic and porcelain-faience dishes. Almost no new companies have appeared over the past year, apart from small semi-handicraft enterprises. Most of the factories are closed or redeveloped, as the workload of production is only 10%.
It should be noted that, compared with Western countries, the ratio of domestic production and imported from other countries (mainly China) has long been in favor of Russian companies, while abroad, local producers have long lost ground to Chinese enterprises. Experts explain this by the fact that since Soviet times, domestic products have been in great demand among consumers due to their high quality. Nostalgia and confidence in the safety of Russian ceramics also play a certain role. Now the situation has changed somewhat.
The main share of sales in the Russian tableware market falls on imported products (especially in the porcelain segment). According to analysts, the volume of porcelain production in our country is reduced by more than 2,000 tons per year. Experts explain this by the obsolescence of equipment and, as a result, low quality and high cost of finished products. Among the countries that supply their products to Russia, China is the leader (about 40% of total imports). And in the segment of products from ceramics and porcelain with an above-average value, European manufacturers prevail. The main importing countries of ceramics: Germany, Czech Republic, Poland, Japan, Great Britain. The share of imported porcelain products in the Russian market is 80%, but every year it is gradually decreasing, which cannot but please domestic manufacturers.
At the same time, the consumption of tableware made from these materials in our country is constantly growing (an increase of about 7% per year). Experts are confident that this figure will increase as the income of the population grows. This is largely due to the rapid development of the HoReCa professional tableware segment (hotels, restaurants, cafes), which accounts for about 20% of the market volume.
The increase in prices for ceramic tableware is mainly due to the increase in the cost of raw materials (the rate of this growth is about 30% per year). About 10% of the raw materials used by domestic ceramic manufacturers are imported from abroad (mainly from Ukraine). Selling price per ton of clay in our country is about $100. The cost of clay imported from Ukraine is almost two times lower. In addition, raw materials from domestic deposits are often inferior in quality to clays from Ukrainian deposits. In our country, several dozen enterprises produce ceramic and porcelain products. Most of it is exported to neighboring countries, as well as to the USA and Germany.
Experts note the following trends in the development of the domestic market of ceramic and porcelain products: consumers prefer glassware, demand is shifting towards the low and medium price segment, and demand is growing for everyday products and professional utensils for catering establishments.
There are several classifications of ceramic products. The broadest division - depending on the destination. So, they distinguish industrial and building ceramics, technical, artistic and decorative and household. The first categories include brick, facing and floor tiles, tiles, tiles. And for the second two - pottery, dishes (plates, salad bowls, cups, dishes, pots, pans, cocotte bowls, baking dishes, etc.) and decorative items made of porcelain, faience and majolica (aroma lamps, ceramic sculptures, decorative figurines, caskets , aquarium ceramics, vases, lamps, etc.).
Ceramic products, like glass, belong to the category of silicate products. These products are made from plastic clay materials that are fired to give them strength. Depending on the components that make up the composition of the mass, and the firing temperature, ceramics can be either solid or porous. Before firing, part of the products is covered with glaze, which is a thin layer of glassy mass. This is necessary not only for the aesthetic effect: the glaze resists the absorption of dirt and moisture by the ceramic.
Pottery is made from simple colored clays. They can also be glazed and unglazed. Porcelain and faience products are made from white clay and differ in structure: in faience it is porous, while in porcelain it is sintered (solid). Majolica is a product made of white or slightly colored clays with relief patterns on the body, covered with colored glaze. Experts divide ceramics into coarse and fine. The first includes pottery, and the second - products from porcelain, faience and majolica.
For the production of ceramic products, plastic and lean materials are used, as well as fluxes (another name is fluxes). Plastic substances include various types of clays and kaolin. Strictly speaking, kaolin is also a clay substance, usually white in color, which consists of kaolinite. Depending on the impurities that are part of the mixture, clays can have different melting points and a variety of colors.
If the color is associated with the presence of impurities of organic origin in the raw material, then, as a rule, during firing, such a product acquires a white color (such types of clay are called white-burning). These materials are very plastic, but after firing they harden and turn into a shard. Weakening materials are used to reduce the shrinkage of ceramic products. Clay shrinks during drying and firing, which, in turn, can lead to deformation and cracking of the product. Thinning materials, which include quartz, quartz sand, broken shards, etc., prevent this deformation, keeping the shape of the product almost in its original form. Fluxes or fluxes are used for faster and more reliable sintering of the components of the ceramic mass (especially in the production of products from solid ceramics). For this, as a rule, chalk, limestone or feldspar is used.
Opening your own large-scale production is unprofitable. It is much easier for small companies that work for a certain narrow segment or regional market to survive. Such production does not require large areas and expensive equipment. The main requirement: production facilities must be located on the outskirts of the city or outside it. In addition, there should be water, heating and electricity. In addition to production space, you will need space for a warehouse, a bathroom, showers.
The necessary equipment of the workshop includes: muffle furnaces, a rolling machine, a "carousel", a ball mill for the production of glaze. To work in the workshops, a minimum of 3-4 workers per shift will be required. In addition, you can not do without an accountant (you can turn to the services of an accounting firm). Responsibilities of a purchasing and sales manager can be taken over for the first time.
Raw materials (white clay), as mentioned above, are usually bought in Ukraine. Therefore, immediately lay down the costs of processing all documents and customs clearance. This procedure will take approximately one week.
Raw materials must undergo special processing: first, they are cleaned of harmful mineral inclusions, then crushed, ground, sifted through a sieve, mixed with other components. A slip is made on the basis of clay - a liquid clay mass with a moisture content of about 35%. It is poured manually or with the help of special equipment into molds and left there until completely solidified. Products of simple shapes (for example, plates) are molded from plastic mass with a moisture content of about 25% in plaster molds using steel templates.
After that, the products are removed from the molds, dried and washed. Drying takes place either naturally (ovens are quite expensive, and small industries do without them), or in convection ovens at a temperature of 70 to 90 degrees Celsius. Firing in kilns is carried out in two stages.
The pottery is then glazed and fired. The full production cycle takes from three to five days. The use of special ovens for drying reduces these terms at least twice. One small workshop produces about 1000 items of products in one cycle.
The impeccable quality of your products is the main condition for its popularity among consumers. When evaluating the quality of ceramic products, three main characteristics are of primary importance: the quality of the sherd, glaze and decoration. Most manufacturers are guided by the so-called "technological regulations for the production of ceramic products."
Decide in advance on the range of products that you will produce. Let it be better small (20-30 items), which will avoid large stock balances. Ceramic dishes (pots, cups, tureens, etc.) are in the greatest demand. Try to regularly update your assortment, removing obsolete models and offering new ones, focusing on the wishes of consumers and demand.
The business associated with the production of ceramic products is not considered seasonal, although this factor still has a certain influence on it. For example, in the southern regions of our country, dishes are in especially high demand from September-October to April. In the hot season, people cook much less often, respectively, the volume of sales of dishes decreases sharply. Also, the work of the production itself can be suspended at high humidity, since ceramics absorb moisture well, which leads to an increase in the number of defects. Consequently, production volumes in a rainy autumn or an overly warm winter will be lower than in other months.
It will take at least 3.5 million rubles to open its own production of ceramic products. The profitability of such a project is about 25-30%, and the payback period is from 3 years. You can buy an existing business (there are enough offers on the market). It will cost 6-7 million rubles (including the lease of production space).
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Despite all the variety of ceramic products and the raw materials used for their manufacture, the most important processes in their production, differing in details, are essentially the same. Obtaining ceramic products consists mainly of the following technological operations:
1) preparation of raw ceramic mass;
2) product molding;
3) drying products and finishing them in an unfired form;
4) firing products;
5) glazing of products (may precede firing or be performed after preliminary firing with subsequent firing to fix the glaze).
Preparation of ceramic mass. In general, the ceramic mass consists of four components: clay (or a mixture of clays); emaciator; flux and water. In some cases, with suitable natural clays, there is no need to use a leaner or flux. If it is necessary to obtain a porous shard, pore-forming materials are introduced into the mass.
In order to accurately dose and evenly mix with other components, the clay is first subjected to coarse and then fine grinding. A necessary condition for the normal operation of fine grinding units is the low moisture content of the clay (not higher than 7 ... 10%). Therefore, excessively wet clay is dried in drying drums immediately after coarse grinding with crushers or clay cutters.
With another method, all components are ground in wet ball mills. The resulting ceramic suspension is passed through a vibrating sieve and subjected to spray drying, obtaining press powder with a moisture content of 5...7%.
For the production of high-quality products, it is necessary to give the clay high uniformity, for which it is mixed in clay mixers, if necessary, additionally moistened and sometimes heated to increase plasticity.
The choice of the scheme for preparing the ceramic mass is carried out taking into account both the characteristics of the raw materials and the method of subsequent molding, for which the main point is humidity. W raw mix. There are three most commonly used methods for preparing ceramic body: semi-dry (W= 7... 12%), plastic (W= 17...22%) and wet (W> 30%).
Molding of ceramic products. The molding of ceramic products is carried out by a plastic method, semi-dry pressing and slip casting.
plastic molding (W- 17...22%) is carried out using screw (belt) press. A modern non-vacuum belt press is a complex unit, but the principle of its operation is extremely simple (Fig. 5.1). Ceramic mass through the funnel / and injection rolls 2 fed to the blades of the auger (worm) 4, which, rotating around its axis, captures the mass and moves it towards the tapering part - the head 5. At the exit from the head, a removable nozzle is installed - the mouthpiece 6, the hole in which has one or another shape, depending on the specific product. When making bricks, the mouthpiece has a rectangular hole measuring 250x120 mm. Under the action of pressure (1.6 ... 7.0 MPa) developed by the screw, the mass is squeezed out through the opening of the mouthpiece and comes out in the form of a continuous clay band, which is cut into individual bricks by steel strings.
The method of plastic molding is used to produce both solid and hollow (multi-hole) bricks, pipes, tiles and other products. In the production of ceramic pipes, vertically forming screw presses are used.
Semi-dry pressing is carried out at high pressure (25...35 MPa). In this case, the optimal moisture content in the working mass should be 7 ... 12%. Forming is carried out on mechanical and hydraulic presses. Pressing is carried out in a mold , where a portion of press powder is transferred from the bunker with the help of a carriage . At the same time, when moving to the right, the carriage pushes the molded raw material onto the receiving device.
When the carriage moves back (to the left), the lower die is released and the press powder fills the mold . After that, the upper stamp is lowered and enters the mold , by pre-compacting the mass at a pressure of about 2 MPa, as a result of which its volume is reduced by 30 ... 35% . Further pressing is carried out by the lower stamp in two stages. At the first stage, a pressure of about 9 MPa is created. After that, the lower stamp goes down, giving an outlet to the air squeezed out of the pressed mass. If this is not done, then the air, expanding after the pressure is removed, will loosen the molded product. The final pressing is carried out at a pressure of about 30 MPa.
Semi-dry pressing produces ceramic tiles, bricks, tiles. This molding method has an advantage over plastic molding - it practically does not require drying of products and they can be immediately sent for firing.
Slip casting of ceramic products based on the ability of hardened gypsum to absorb water. Three casting methods are used: drain; bulk; combined.
In the overflow method of molding, the liquid ceramic mass (slip) is poured into a gypsum mold, the porous walls of which absorb moisture, taking it away from the slip, as a result of which a continuous uniform layer of thickened mass is formed on the inner surface of the mold. . When this layer acquires the desired thickness, the excess slip is drained, and the product is left for some time in the mold to dry (drier), as a result of which it shrinks and easily lags behind the walls of the mold.
In the pouring method, the slip is poured into the space between the mating parts of the detachable mold. With this method, the mass compaction process proceeds faster, since moisture is taken from both the outer and inner surfaces of the workpiece. . In contrast to the drain method, the pouring method allows molding products of a more complex shape and with greater dimensional accuracy.
In some cases, it is advisable to use both methods (combined method). For example, at sinks and washbasins, the “body” of the bowl is pouring, and the hollow sides are draining.
The casting method is used to make thin-walled faience and porcelain sanitary ware, dishes, vases, figurines, chemical utensils and appliances. This method, unlike others, allows the manufacture of products of complex shape.
Drying products. Drying of products is carried out in dryers of various designs (chamber, tunnel). Drying of ceramic products is a labor-intensive stage of production, since during the drying process a large percentage of rejects is obtained due to the formation of cracks and deformation of the workpieces.
Glazing of ceramic products.icing called a thin glassy layer applied to the surface of a ceramic product in order to give it a beautiful appearance and at the same time increase water resistance and resistance to chemical and mechanical stress. In terms of composition and physical properties, glazes are varieties of glass. To prepare the glaze, natural materials containing silica and alumina (quartz sand, clay, feldspar, talc, etc.) are used, as well as salts and oxides of various metals: potassium, sodium, lithium, boron, calcium, magnesium, barium, zinc, lead, tin, etc. Metal oxides give the glaze one color or another, improve gloss and other properties, and lower the melting point of the glaze.
Glazes can be transparent and opaque (deaf). Both those and others can be colored and colorless.
Finely ground glaze is mixed with water to obtain a suspension with the consistency of cream (density 1350...1400 kg/m 3) and applied to the surface of the product by pouring, dipping or spraying. During firing, the glaze melts, spreads over the surface and, when cooled, turns into a glassy layer.
Firing of ceramic products. Firing allows the irreversible transformation of the ceramic mass into a solid stone-like body. This process is called sintering.
The firing processes begin with the evaporation of that part of the mechanically mixed water, which was not completely removed from the product during drying. With a further increase in temperature in the range from 500 to 800 °C, chemically bound water is released. In this case, for example, kaolinite passes into metakaolinite: A1 2 0 3 2Si0 2 2H 2 0 -»A1 2 0 3 2Si0 2 + 2H 2 OT. In the temperature range from 800 to 900 ° C, dissociation of clay-forming minerals occurs, for example, metakaolinite: A1 2 0 3 2Si0 2 -> A1 2 0 3 + + 2Si0 2, as well as calcium carbonate present in the mass: CaCO 3 -> CaO + CO 2 .
Calcium oxide, as well as other metal oxides, with a subsequent increase in temperature, begins to react with silica and alumina, forming low-melting mixtures of various silicates and aluminosilicates. The amount of melt formed increases as it is heated; in accordance with this, the properties of the shard also change. First, the porous shard begins to gradually compact and lose its porosity, turning into a dense clinker. To obtain porous products, firing is carried out at a low temperature. If it is necessary to obtain a product with a dense stone shard, then the temperature is raised to such a value at which the amount of melt becomes sufficient to fill all the gaps and voids between unmelted particles.
The firing temperature of various products of building ceramics ranges from 900 to 1700 "C.
Kilns used in the ceramics industry are mainly continuous. According to the shape of the furnace space, modern furnaces are tunnel and slotted.
tunnel kiln It is a long (100 ... 160 m) narrow canal, lined with refractory bricks from the inside. The firing zone in this kiln is located approximately in the middle. The products to be fired are placed on trolleys and rolled into the kiln one by one, forming a solid train. When a new trolley is pushed in from one end of the kiln, the entire train is mixed so that a trolley with already fired material is pushed out from the other end. Tunnel kilns are used in the production of bricks, ceramic pipes, and sanitary ware.
Slotted Furnaces are applied to firing of a ceramic tile and a tile. They work like tunnel ovens, but have a very narrow slit-like channel into which the products are fed by a roller conveyor. Channel width of slotted single-row furnaces - from 0.9 to 2.5 m, height - 0.6 ... 0.8 m; slot furnace length - from 24 to 65 m.
The production of ceramic dishes is considered an ancient folk craft.
Despite the availability of a wide variety of modern materials that make it possible to manufacture similar products, it does not lose its relevance even now.
This is due to excellent consumer characteristics, as well as a long service life. Ceramics are comparatively brittle compared to plastics, but their environmental friendliness and high thermal conductivity successfully compensate for this disadvantage.
Capital investment
In ancient times, clay pots were molded in almost every village. Aspiring entrepreneurs who want to set up their own ceramics production can either use long-standing traditions or come up with something of their own. The main advantage of this type of activity is that it does not require significant capital investments.
The fact is that only skillful hands and raw materials are needed to start work. Any special equipment for the production of ceramic dishes is not required - the presence of a kiln and a dryer is enough - you will have to pay the most for it. You can buy it or build it yourself.
In the first case, you will have to spend about 50 thousand rubles. As for the manufacture of the furnace, it can be ordered from some craftsman, and it will come out much cheaper than buying a finished one. It should be noted that they are of two types - tunnel (have continuous action) and forges (differ in periodic action).
Raw materials for production
The manufacture of ceramic dishes requires the use of basic and auxiliary materials. The first of these include raw materials for the preparation of ceramic masses, paints and glazes, and the second - the substances necessary for the production of capsules and plaster molds. But the main raw material in this case is sintering clay.
In addition to it, the composition of future ceramic products in the form of an additive should include kaolin, which serves as a property regulator. You can add fragments of broken or failed items, quartz sand and fireclay. The addition of alumina, talc, carborundum and dunite will significantly improve such indicators as strength, thermal conductivity and heat resistance.
Getting Pottery Skills
In order to independently master the beginning of the skill in the production of ceramic dishes, it is enough to sign up for courses or paid lessons given by professionals. For a person who has never done anything like this, you need to attend at least a few classes. Be that as it may, the time spent will not go in vain and in the future you will not have to learn from your mistakes those simple truths that mankind invented many centuries ago.
Manufacturing technologies
Currently, there is far from one technology for the production of pottery. Most often, the methods of performing work differ among themselves in the firing time, the presence of additives and the finish of finished products. You can understand the difference between them only after you try each of them in practice.
Basic operations
The production of ceramic utensils consists of several stages: preparation of clay mass, molding, drying, firing and decoration of finished products. At the first stage, it is necessary to clean the raw material from all kinds of mineral additives, then crush it, grind it and sift it with a special sieve. Next, we proceed to the formation of the future product. The mass can be any - plastic or liquid.
The advantage of the first is that it makes it possible to produce products of different sizes. As for the second method, casting into plaster molds is performed from a liquid mass, which is also called slip. Its humidity is not less than 35%. It is used under conditions of high complexity, when no other method is suitable.
As soon as the future ceramic products are preliminarily dried, it will be necessary to attach handles, spouts and other elements to them using an adhesive mixture of slip with dextrin.
The production of ceramics involves drying, which will ensure mechanical strength and resistance to soaking. It should be noted that drying is carried out at a temperature of about 80 ° C in dryers.
The tableware acquires the specified physical and technical characteristics during firing. In addition, it allows you to fix decor and glaze on the surface. As a rule, they are fired twice, and if the painting is applied to the glaze, three times. At the final stage, manual or semi-mechanized decoration is performed.
Product types
Such a concept as ceramic products is quite extensive. In addition to dishes, this includes a variety of household items (vases, flower pots), souvenirs, jewelry, toys, building materials, and so on. Based on this, a variety of types of clay can be used in the manufacture of products. In order to understand what kind of products will be in demand, it is advisable to first go through the outlets through which it is planned to organize their sale.
Sales of products
The production of ceramic dishes will not justify itself if it is not marketed. In the event that it is not possible to open your own store, products must be offered in other people's shops and outlets of souvenirs and utensils in the markets. Despite the availability of similar plastic products, buyers often prefer more reliable ceramics. In this regard, many entrepreneurs will agree to take such dishes for sale.
Be that as it may, it is more expedient to open your own store, because this will significantly increase income. It should be noted that in order to organize such business activities as the production of ceramic dishes and its sale, it is necessary to register with the tax authorities and obtain the status of a private entrepreneur or legal entity.
Among other things, the sale of dishes can be organized through the Internet site. The advantage of this option is the ability to save on renting a store space and work directly with customers. Do not forget that in this case, consumers can order products according to an individual project with an original painting, so there is no need to wait until someone buys this or that product.
Profit diversification
One of the main ways to increase financial income from the production of ceramic tableware is to increase the range.
Despite the fact that now it is mass-produced in industrial volumes, there are a large number of connoisseurs of handicraft.
Another interesting direction is working with specialists in landscape design. The fact is that lately all kinds of ceramic decorative elements, which are installed in the yards of country houses, cottages and restaurants, have been very popular. These include decorative lanterns, animal figurines, large flower vases and the like - it all depends on your imagination.
In the history of mankind, there are many materials that have accompanied people almost from the very beginning of civilization. The first thing that comes to mind is wood, but do not forget about ceramics - baked clay, dishes from which they began to make from time immemorial.
Such a material has enough positive qualities: ceramics are durable, resistant to chemical and high-temperature influences, are completely environmentally safe, and everything is in order with their appearance. In addition, the tile does not rot and is not covered with fungus, which allows it to be successfully used for finishing a wide variety of technological rooms and bathrooms.
In general, ceramics are dishes or other things made of clay (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 be used for ceramics:
- plastic base. This is just the same clay or kaolin (a rock consisting of kaolinite).
- Materials that minimize settling during firing allow the product to retain its shape. High-quality quartz sand, non-standard porcelain (battle), fireclay are used.
- Rocks that give a dense glassy mass during sintering. Ideal feldspar, pegmatite.
- Glaze. It can be used as a material from natural raw materials, as well as numerous analogs obtained by chemical synthesis.
Classification
So we learned that ceramics is a specially processed clay. As factors predetermining the consumer qualities of the product, the type of ceramics, the method of decorating or molding it are distinguished.
Distinguish between fine ceramics (fine granularity on the breaking of the shard), as well as rough (coarse granularity). Of the fine varieties, everyone is familiar with porcelain, semi-porcelain, as well as faience, tiles from which are found in almost every bathroom. Accordingly, rough ceramics (you will find a photo in the article) are pottery pots. The thing is not very common among us, but known from the deepest 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 against the light. The edges of the side (usually the bottom) are not covered with glaze due to the firing technology. Mainly used in the production of kaolin
Semi-porcelain is an intermediate option between the above-described porcelain and faience. Somewhat coarser, water absorption from 3 to 5%, most often used in the manufacture of household dishes.
As for the faience itself, it is distinguished by a thick porous shard, which has a slightly yellowish tint when broken. The ability to absorb water is high, within 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 influences, this type of ceramics is used exclusively in the production of inexpensive dishes for everyday use, as well as for household containers. For dressing, they take not too high-quality varieties of clay, chalk and quartz sand. The ceramic technology of this grade also allows the use (as a base) of broken porcelain. Of course, before starting production, it is crushed and finely ground.
Majolica is a very attractive outwardly ceramics. The price for it is about a thousand rubles for an average vase. A distinctive feature is a very porous shard that 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 using casting technology. As a rule, products are decorated with glazing, and decorative bas-reliefs are also often found. In the production of this type of ceramics, white-burning clays, quartz sand, chalk and floodplains are used.
Pottery (the photo of which is in the article). It is distinguished by a shard of a specific red-brown color (red-burning clay) and a very large porosity. Moisture absorption coefficient - up to 18%. For coloring, special clay paints, engobes, are used. To protect them from moisture, the products are covered with a thin layer of colorless glaze on top. 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. This is the name of bricks made of roughly fired clay. In the production of this kind of ceramics, special foaming agents are used, which dramatically increase the porosity of the material, and therefore its thermal insulation qualities become much better.
How is the production process going?
The production of ceramics itself can be easily divided into several stages:
- Extraction and related preparation of raw materials.
- Moulding, applying decorative patterns or making functional holes.
- Casting, semi-dry stamping.
- Editing, first drying.
- High temperature processing.
- Frosting.
- Re-burning.
- Decorative processing (warm ceramics and analogues do not need it).
The 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 therefore now let's discuss each of them separately. To prepare the initial ceramic mass, the following technological operations are performed: the raw material is thoroughly cleaned of foreign mineral and organic impurities, crushed and ground. After that comes the turn of mixing and adding various additives.
Product molding
Molding is carried out from liquid or plastic ceramic masses. Plastic molding has a number of 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. Pouring is done in plaster molds. 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. Pottery for it is 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 taken out of the molds, after which various decorative and functional elements are glued, for which special glue is used to attach them. In the past, clay dough was used for this purpose, but it did not provide very high strength.
Drying
Drying is the most critical stage, since both the mechanical strength of the product and its decorative characteristics depend on the correctness of its implementation. Of course, the correct distribution of glaze is also extremely important, on which the resistance of products to water, as well as chemical agents depends. Drying is a prerequisite for the production of ceramics. For it, conveyor, radiation and chamber dryers are used. The temperature throughout the process should not exceed 70-90 °C.
The only exception is tiles. The ceramic in this case is very thick, so in some cases it is possible to use the high temperature mode for a short time.
Firing
The second most important technological stage is the firing of ceramics. The goal is to form a crock with precisely specified physical and chemical properties, to fix the coloring composition and glaze on the surface. Firing is important because in its course many physical and chemical processes take place, which predetermine the main consumer qualities of the product. Usually firing is carried out in two stages, but if paint has been applied to the surface of the glaze, the so-called muffle firing (third stage) is carried out.
The first stage is carried out at a temperature of 900 to 1250 °C (depending on the type and grade of ceramics). 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, as the risk of cracking is high. If we are talking about the average red clay, then products made from it are often “burned” once, at a temperature not higher than 960-1020 degrees Celsius.
Two types of kilns for ceramics can be used for firing: periodic (forges), as well as continuous ones. There are a lot of varieties of the latter, but tunnel and roller ones are the most common.
About various defects
The specificity of the manufacture of ceramic products is that at various stages of production, a large number of a wide variety of defects may occur. There are damages to the shard, glaze or decorative coating. As for defects in the shard, they most often appear at the stage of primary molding and initial drying.
Some part of the manufacturing defect appears almost immediately, and stains or something like that appear only after firing. Due to 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
Glazes are 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 tile or dish 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 important for household utensils.
Decoration refers to the application of decorative coloring or patterns. Often in conditions curly stamps are used, with the help of which the mass production of the same type of products. A stamp roller is used to apply the pattern to the edges of the pot. Accordingly, the final operations are to eliminate minor defects, polish the legs and edges.
Some information about glazes and paints
Glazes are divided into transparent and opaque varieties, they are colored and completely colorless. Ceramic paints are used to decorate almost all types of baked clay products. They are based on either 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 houses.
Paints are divided according to the way they are applied: 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 a kiln. 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 making molds for firing and casting.
Information about the manufacture of foundry molds
To make sufficiently strong and high-quality molds, molding plaster is used. It is made by finely grinding the powder of calcium sulfate hemihydrate. The peculiarity of such gypsum is that when mixed with water, it should turn into a fairly plastic and elastic dough. But the main thing is that this composition must be set in precisely defined terms, which guarantees a really high-quality firing. If gypsum is not available for some reason, carborundum can be used. Other refractory materials may be used.
That's what ceramics is. This is a material without which it is impossible to imagine any kitchen or bathroom. However, there is another variety of it, products from which can be real decorations for any home.
Artistic ceramics
“Artistic” refers to items decorated with particularly fine relief or stucco work. Of course, there are actually no other differences from ordinary ceramics, but there are many subtleties in manufacturing technology. We will talk about them now.
Initial preparation of raw materials
As you understand, art ceramics differs little from their "household" counterparts, but in its manufacture it is necessary to be more demanding in the selection of raw materials. Everything is the same as in the previous case, but all operations are performed more subtly. In addition, only finely divided kaolin (particle diameter less than 2 µm) should be used.
What does it give? This approach makes it possible to obtain a much more plastic mass, and also at least doubles the strength of the dried products. In addition, only small ones should be taken, since it sharply reduces the draft of the finished product, which is extremely important for artistic ceramics.
Drying of art ceramics
As we already pointed out in the first part of the article, drying is one of the most important stages. If we talk about artistic ceramics, then this statement becomes even more relevant. You should be aware that shrinkage phenomena during firing of thin products proceed unevenly, which can lead to big troubles, up to damage to the entire product. Therefore, it is extremely important to choose the right heating mode so that artistic ceramics do not turn into a bunch of shards.
If the products are flat, then it is strongly advised to dry them exclusively in forms. First, they are slightly dried until the future ceramics acquire the required density, and only after that it can be removed and dried to a moisture content of 1-2.5%.
To carry out this process in large quantities, special conveyor dryers are used. In particularly difficult cases, drying is carried out in devices that operate on a periodic basis. This is done so that thin ceramics do not dry out and crack. Drying time ranges from 30 minutes to three hours.
So you found out, This is one of the oldest materials that has ever been produced by mankind. Despite its antiquity, ceramics are in great demand to this day.
