RU2161146C1 - Method of making porcelain ware decorated with cobalt - Google Patents

Abstract

FIELD: manufacture of porcelain products decorated preferably with cobalt. SUBSTANCE: in order to manufacture highly artistic products decorated with cobalt paint having improved properties, what is claimed is optimum mode of third period of gazed firing is 1020-1120 C and 1120-1220 C with carbon monoxide carbon content of 1.78-1.8% and 1.24-1.32% in gas medium; optimum thicknesses, when applying layer of cobalt paint onto porcelain ware, range from 20 to 240 mcm; layer of glaze applied is 80-300 mcm; cobalt oxide content in paint varies from 1.25 to 2.50 mg/sq.cm and dextrin content varies from 8 to 14%. EFFECT: more efficient preparation method. 6 cl, 2 tbl

Description

 The invention relates to a technology for the production of porcelain, mainly art, decorated with underglaze painting.

 Distinctive features of porcelain - white color, lack of porosity, strength, heat resistance and chemical resistance, translucency, are determined both by the composition of the feedstock and its processing technology [1].

 Known methods for the production of porcelain, decorated with overglaze and underglaze cobalt painting [2, 3], the technology of which includes the following basic operations: preparation of ceramic mass, molding, drying, firing, painting, glazing, firing, etc. - approximately the same in many enterprises. The technology of the underglaze method is characterized by increased waste (up to 1.5-2%) during annealing of products as compared to overglaze.

 The well-known "Method of decorating porcelain products" (ed. St. 483374, class C 04 B 33/34), relating to underglaze painting.

The classical double-firing system (the first one is fired and the second one is watered, reflects the nature of the gas environment in the furnace), which is the main process for the production of porcelain products, includes (with various parameters of gas composition, temperature and heating rate) periods:
The 1st proceeds in a gas oxidizing medium when the temperature rises T = 50-920 ^o C, it is characterized by a constant (or with small deviations) to T = 920 ^o C and an oxidizing gas medium, which contributes to the burning of carbon CO from the skull, which should be completed before the start of the next recovery period, when the glaze layer is sintered and compacted, the carbon adsorbed by the skull should completely burn out by the beginning of the recovery period. If this condition is not reached, then the CO: CO ₂ ratio will become less than 0.1 and carbon burnout will begin again, with the only complication being that by that time a glaze melt will form on the skull,
gas medium - reducing,
The 2nd layer proceeds at 920-1020 ^o C, intense burning of carbon in the skull and oxidation of iron compounds occur and a reducing gas medium is created, if the oxidizing medium is accidentally replaced by a reducing medium during the first exposure, then re-carburization of the skull will occur, when a high CO content can cause not only carburization of the skull, but also the reduction of heavy metal oxides, sometimes introduced into the glaze, the environment is reductive-oxidative,
The third begins at 1020-1250 ^o C, in this interval T, the recovery process is carried out and intensive shrinkage of the mass occurs, while the capillaries and pores in the skull are gradually closed, and gas diffusion in the skull gradually fades, as a result, the recovery process does not reach to the end, the main sintering processes are completed at T = 1350-1410 ^o C, proceeds in a neutral gas medium.

 The third period of firing is a specific feature of porcelain production, it even differs from the others in the classical version, for example, in the claimed technology for the subject of the invention.

 The above temperature limits are not unchanged, they depend on the composition of the porcelain cash register, the composition of paints, the type of painting, etc.

In the gas mode of firing the tunnel kiln, it is advisable to maintain the concentration of carbon CO (with drop-free firing) in the range of 1000-1100 ^o C in the amount of 3-4%, and from 1100-1250 ^o C 6-8%. The ratio of carbon monoxide and carbon dioxide CO: CO ₂ should be greater than 0.3 during this period [1]. The indicated ratio is valid for the technology of the Dulevo Porcelain Factory. For other enterprises, the given ratios are 3-3.5 and 3.5-4.5%, respectively. For the method of manufacturing porcelain products decorated with cobalt (underglaze painting), the ratios given, i.e. CO: CO ₂ must be less than 2% depending on the firing temperature.

 The sequential course of temperature changes (rise, exposure, its decrease and the nature of the gas medium in the furnace) are noted in the firing mode, assigned in accordance with those reactions that must be carried out to obtain the skull with the required properties.

At the porcelain factories of the Russian Federation, the CIS and foreign countries, the used range of temperature for poured firing, in which porcelain acquires all its valuable properties, ranges from 1320-1400 ^o C [2]: 1160-1180 ^o С (Bagdanovichsky), 1320-1350 ^o C ( Baranovsky, Poltava), 1350-1380 ^o C (Dmitrovsky), 1380-1400 ^o C (Kuzyaevsky, Dulevsky), etc.

In most Western European factories, the firing temperature of household porcelain is 1380-1410 ^o C [2].

Known methods for the manufacture of products decorated with cobalt, in which both in the coloring of ceramic products and tinting of the masses, and in obtaining different colors, in the overglaze painting of art products cobalt oxide CoO (GOST 18 671-85) is widely used. In the underglaze painting, cobalt paints, unlike art paints, withstanding the high temperature of poured firing (up to 1460 ^o C), also give the product a limited range of colors. They are exposed to intense fire during firing and partially dissolve in the glaze. The color palette is limited by the resistance of paint systems to high temperatures in different gas environments. Therefore, the set of such paints is extremely limited in domestic and foreign practice of porcelain production.

 For example, on porcelain products decorated by hand with blue known paints of the German company Degussa containing cobalt, their strong dissolution in the glaze, a higher intensity of its coloring compared to the cobalt paint of the applicant, is observed. The reasons that impede the use of this technical result include the fact that metallization occurs almost always on the surface of the glaze.

In fundamental works on the technology of porcelain production (Budnikov P.P. Heat engineering in the production of porcelain and faience .- M: 1972, Budinkov P.P. Selected works.- Kiev, 1960, Budnikov P.P.- Roasting of porcelain.- M .: 1972, Bulavin I.A. Technology of porcelain and earthenware production.- M., 1975, Avgustnik A.I.- Ceramics.- L., 1975, Moroz I.I. et al. Handbook of the porcelain industry. 1,2, M., 1960, Vizir V.A. and Martynov M.A. Ceramic paints .-- Kiev, 1964, Mills M., Lauske R. Porcelain painting.- M., 1971 and others) information, in parts of the consideration or mention of issues yazannyh a second firing porcelain and metallization no. In foreign literature, for example [4, p. 49-60, section "Defects of ceramic decor"], the specific causes of the appearance and elimination of metallization are interpreted as follows: "The defect occurs on products decorated with blue cobalt and appears on the surface of the glaze as dirty stains of copper color.This is usually caused by excessive cobalt in the paint, insufficient flux, too thin a layer of glaze or a thick layer of paint.From a baked product, metallization can be eliminated by wiping the stains with Pb ₃ O ₄ and exposing re-firing. To prevent metallization, reduce the cobalt content in the paint or apply a thinner layer of underglaze paint. The described methods for removing metallization are used, for example, in Czech and Slovak porcelain factories in Dalovishte, Stara Role, Karlovy Vary China, etc. . " However, the above recommendations on eliminating this defect require time and cost, but they lack the main thing - quantitative and qualitative recommendations - eliminating it in the third period of watered firing due to the regulation of the concentration of carbon monoxide CO and the ratio CO: CO ₂ .

The metallization effect (Meissen) also includes triple firing: first, piece-dressing, poured, is painted on the product of poured firing, then firing in an electric furnace at T = 1300 ^o C. However, this technology reduces the juiciness of cobalt paint.

 The patent materials also did not find information related to this issue, with the exception of cobalt paint and glaze, for example, in ed. St. 1542921 "Ceramic pigment of blue color" (CL 5 C 03 C 1/04). In the available materials, the questions of the influence of the purity of the blue tone, the decrease in the firing temperature are not linked to metallization.

 In the CIS and abroad, drawing is performed using hand-painted and a pen. The latter allows you to get very thin contours, it is used only for products of small series, for products of large series the effect of drawing with a pen is given by screen printing or printing from a metal plate. Paint for working with a pen is diluted more strongly.

 Domestic underglaze blue paints, for example, the composition of underglaze blue paints NN 28-35 [3, p. 299], have a charge mixture containing cobalt oxide (!!) (7.5-50%).

 The content of pegmatite, dolomite, and porcelain shard specified in the paint formulation N 30.31% increases the total% content of calcium and iron oxides in the chemical composition of the formed decor, which reduces the blue tonality of the decor and the transparency of the melt of the paint suspension. For a given% content of ceramic masses in the paint compositions N 30.31, the presence of aluminum oxides, which chemically interact with cobalt oxides (CoO) during the heat treatment of shards or upon calcination of the mixture during preparation of a suspension of blue paint, decreases in the chemical composition of the components, high temperature acquires a greenish tint, characteristic of this mineral pigment, which as a result degrades the purity of the blue decor tone, reduces the quality of the product - paint shedding (“cobalt flight”), causing t metallization on the surface of the calcined product. The probability of occurrence of defects is significantly affected by the temperature regime of 3 periods of watered firing.

The firing regimes of porcelain products made from domestic raw materials differ from foreign modes by longer heating in the range of 900-1040 ^o C [2], for example, the modes used at the Meissen porcelain factory.

The closest method of the same purpose to the claimed invention in terms of features is a method of manufacturing porcelain products decorated with cobalt, used by the Leningrad Porcelain Factory named after Lomonosov (LFZ) with a firing temperature of products of 1380-1410 ^o C [2], decorated with paint N 3 of the Dulevo paint factory, produced according to the standard "Underglaze paints TU 2362-008-00303833-95" with the addition of dextrin, in which by preparing ceramic mass , molding, drying, glazing and subsequent watered firing in a furnace with natural gas.

Currently, cobalt paints are produced by the Dulevo colorful plant [2, 380 p.]. However, the finished paint N3 at a high firing temperature up to 1350 ^o C does not give the juiciness of the color scheme and shades inherent in cobalt oxide. The cobalt oxide of the Nizhne-Ufaleysky plant used by this plant has the following chemical composition, wt.%: Co 71.19; Ni 0.78; Fe 0.08; Mn 0.039; Cu 0.009; S 0.011 [3]. Underglaze paint also includes dextrin.

The porcelain mass formulation LFZ contains ingredients, wt.% [3]: pegmatite 9.4, clay 12, kaolin 40, feldspar 9.6, silica sand 26.5, technical alumina 2.5, with the following chemical composition, wt. %: SiO ₂ 68.02; Al ₂ O ₃ 21.48; CaO 0.3; TiO ₂ 0.39; MgO 0.15; K ₂ O 2.0; Fe ₂ O ₃ 0.3; Na ₂ O 1.15; PPP-6.2.

Moreover, in the 3rd period of poured firing at T = 1040-1120 ^o C, the CO content is 2.5-3%.

The formulation of the underglaze blue paint of LFZ (painting is done with a pen grid) slightly reduces the quality of the melt and the purity of the color tone, the content of pegmatite, dolomite, and porcelain shard increases the overall composition of the decor% of calcium and iron oxides in the chemical composition, which reduces the blue tonality of the decor and the transparency of the melt paint suspensions, which during the heat treatment of shards or during the calcination of the mixture during the preparation of a suspension of blue paint chemically interact with cobalt oxides (CoO), while part of Latter high T = 1380-1410 ^o C acquires a greenish hue characteristic of this mineral pigment, as a result deteriorates the purity and juiciness tone blue decor, reduces the quality of products "cobalt flight", causing the metallization on the surface of the calcined product. In addition, the upper range T = 1410 ^o C requires an increase in energy consumption.

 The reasons that impede the achievement of the technical result indicated below when using the known method adopted as a prototype include the fact that the known method also does not take into account a frequently encountered defect in the porcelain manufacturing process - metallization, which sharply reduces the quality of porcelain products and depends on the oxidation -restoring conditions for 3 periods of poured firing, uneven application of a layer of paint, organic additives, etc. In chamber furnaces of the same design, under the same firing conditions, the output of defective products with the same ornament due to the metallization of cobalt is different.

 When implementing the claimed invention "Method for the manufacture of porcelain products decorated with cobalt", the operational characteristics of the redox roasting of decorated products are optimally used, taking into account their characteristics of physical processes associated with: manual cobalt decoration and the formulation of underglaze cobalt paint containing an organic bond.

 The technical result of the described method for the present invention is the release of highly artistic porcelain products, decorated with underglaze cobalt paint with minimal defects and improved whiteness, as well as reducing energy consumption.

There is a direct correlation between the set of features listed in the claims, and the above technical result. The proof is a solution to the compromise problem: working out the recovery periods of the watered firing at Т = 1020 - 1120 ^o C, selection taking into account the physicochemical processes in relation to the selected porcelain mass, the compositions of glaze and cobalt paint, closely linked to the content of dextrin in it, and the manufacture of products limited by temperature upper limit. Underglaze, brushstroke hand-painted with cobalt products determines the entire technological process, including recipes for cobalt paint and glaze, temperature 3 periods of poured firing, as well as issues related to the limitation of T max. firing no higher than 1410 ^o C. At higher T there is a sharp increase in energy consumption, deterioration in the quality of cobalt paint (blurred contours of the picture).

The specificity of the paint formulation used for decoration is such that cobalt oxide / !!, !!! / Co ₃ O ₄ (or CoO + Co ₂ O ₃ ) is used as the main ingredient, which can withstand only a neutral environment in the recovery period, so how cobalt oxide is prone to reduction.

It was found that a burnable organic binder, dextrin С ₆ H ₁₀ O ₅ , under conditions of a reducing environment (3 periods of watered annealing) decomposes with the release of pure carbon. The latter provides conditions for a strongly reducing gas medium close to equilibrium.

 The specified technical result in the implementation of the invention is achieved, as in the known method of manufacturing porcelain products decorated with cobalt, includes the preparation of ceramic mass, molding, drying, baking, glazing, hand painting (mesh) and subsequent watered firing in a kiln with natural gas.

The peculiarity of the method lies in the fact that the optimal mode of the third period of poured firing is 1020-1120 ^o C and 1126 -1220 ^o C, respectively, the optimal thickness of the layer of cobalt paint on porcelain is 20-240 microns, the glaze layer is 80-300 microns, which is the best the quality of porcelain products is ensured when the content of cobalt oxide in the paint is 1.25-2.50 mg / cm ² , the amount of dextrin in the paint composition is 8-14%, the likelihood of metallization on the surface of the products when the carbon monoxide content is 1.48-1.8, respectively and 1.24-1.32% in a gaseous environment almost equal to zero.

 An analysis of the state of the art by the applicant, including a search by patents and scientific and technical sources of information, and identification of sources containing information about analogues of the claimed invention, made it possible to establish that the applicant did not find a source characterized by features that were identical (identical) to all the essential features of the claimed invention. The definition from the list of identified analogues of the prototype, as the closest in the totality of the features of the analogue, made it possible to establish a set of significant distinguishing features in relation to the technical result perceived by the applicant in the claimed method set forth in the claims. Therefore, the claimed invention meets the condition of "novelty."

 The claimed technical solution in terms of temperature conditions (3 periods of poured firing) firing is most optimal for achieving a technical result, manufacturing of underglaze blue paint, glaze taking into account the composition of the used porcelain mass and dominating the final result: the quality of the painting in terms of the purity of the achieved tone and reduction of marriage of porcelain .

 In the technique of hand painting, when applying the drawing, the painter applies special strokes, bringing them to one point, with different thicknesses of paint. It turns out, as it were, the imposition of layers on each other. An excess of dextrin accumulates in this place when painting products, a funnel forms on the glaze, which is explained by the fact that the glaze in the reducing medium becomes more fusible and less viscous, which contributes to enhancing the absorption of the melt into ceramics. With an increase in the amount of dextrin (within 10-30%) in the paint, the wetting angle decreases from 90 to 30 degrees. This explains the intensification of the process of impregnation of a porous ceramic body. Reducing the glaze layer above the site with a high dextrin content provides carbon monoxide access to the cobalt oxide of the paint, which helps to restore cobalt ions and the formation of an undesirable metallization defect.

 When firing is poured, when the paint is under a layer of glaze, during the pyrolysis of dextrin, a reducing medium is created that promotes the formation of lower oxides that make up the glaze and dye, having lower melting points, and most importantly, significantly reduces the viscosity of the glaze melt. This contributes to the strong absorption of the low-melting melt by ceramics, and at the place of the increased dextrin content the glaze layer becomes thin, therefore, the gas reducing atmosphere of the furnace opens up to cobalt oxide, which is reduced to lower oxides or even metal. The reduction of ions to a neutral metal is affected by the conditions of poured firing (3 periods), the organic dye bunch and the thickness of the cobalt paint and glaze layer. At the locations of the paint layer, the glaze is colored, metallization appears in the form of crystals of various shapes and drop-shaped metal sections. Metallization, depending on the firing conditions, uneven application of the paint layer, organic additives in the composition of dextrin paint, appears not only on the surface of the glaze, but also near the surface and in its depth, the thickness of the applied paint layer varies from 20 to 240 microns depending on the painting technique and the thickness of the layer of glaze is from 80 to 300 microns.

The optimal thickness of the paint layer and the glaze, in which cobalt paint is completely dissolved in the glaze at T = 1000-1200 ^o C, which eliminates metallization, significantly affecting the quality of porcelain, is provided when the content of cobalt oxide is not less than 1.25 mg / cm ² , and with a content of more than 2.5 mg / cm ² , metallization appears. It was found that the optimal layer contains 1.25 - 2.50 mg / cm ² cobalt oxide.

 A significant effect on metallization is exerted by the gas environment of the furnace. The content of carbon monoxide CO, which contributes to the recovery of not only cobalt ions, but also other metals that make up the glaze and ceramics, depends on the furnace pressure and T firing. On the other hand, the presence of carbon C in the organic bond of the paint, dextrin, affects the reduction of the oxides that make up the glaze and paint. The latter decomposes under the conditions of the reduced medium with the release of carbon, which enhances the action of the reducing medium, transferring it to the discharge of a highly reducing medium close to the equilibrium gas medium. Thus, the limiter of the upper limit of the firing temperature is cobalt metallization, its increase is associated with an increase in temperature and the content of carbon monoxide, deterioration in the quality of cobalt paint.

The most important feature of regime 3 of the period of poured firing is the need to establish the ratios of CO: CO ₂ = 1.78 - 1.8% and 1.24 - 1.32%.

 For this, the firing process is clearly divided into the indicated periods with different compositions of gases, T and heating rate.

The applicant has a CO content of: in the 3rd period of watered firing, 1.78-1.8 and 1.24-1.32% at T = 1020-1120 ^o C and 1120-1220 ^o C, respectively, in the indicated period there is a complete absence of metallization on porcelain products. In the neutral mode of 4 periods, the CO content is 0.4-0.6%.

The concentration of CO in the range of 1020-1120 ^o C in the range of 1.78-1.8, and from 1120-1220 ^o C - 1.24-1.32.

 Due to the control of the gas regime of redox firing, taking into account the peculiarities of the cobalt paint formulation, glaze and the improvement of the technology of manual application of it to products, it is difficult to control a defect — metallization — that will improve its quality.

 Example.

 A feature of this method for the production of porcelain is the uniqueness of the underglaze cobalt painting that defines the entire process, including shaping, decoration, glazing, firing.

 The technology of the method for manufacturing porcelain products decorated with cobalt includes the following operations: preparation of porcelain, underglaze paint and glaze, casting, molding or pressing of products, drying, first firing, decoration, applying colorless glaze and the second with watered firing of products.

 Porcelain cake mix used for slurry preparation is mixed in a mixer, in which softened water and electrolytes are poured in advance (soda ash 0.1-0.2 and liquid glass 0.2-0.4%). The cleaned foundry slip under pressure is fed to the foundry tables. When mixing gypsum plastic dough, the dosage of water and gypsum is strictly observed, which ensures the production of gypsum castings with normal porosity depending on the wall thickness of the products, type of molds.

With a given moisture content, viscosity and structure factor, the slip is poured into the internal cavity of the gypsum form, as a result of which the moisture is redistributed between the slip, which gives off moisture, and the gypsum form, which absorbs this moisture: the clay mass goes into the state of plastic dough. The molded hollow ceramic product is dried in molds to a moisture content of 18%. The product is dried under natural conditions and in a chamber at T = 60 ^o C. At the end of the batch firing at T = 920-940 ^o C, underglaze painting is manually applied to the surface of the product, the features of which are described in detail above.

 In the inventive method, a porcelain mass containing pegmatite, quartz sand, clay, kaolin, skull 1 and 2 of firing is additionally used to add waste from china production, while these ingredients have the following wt. %: pegmatite 21.0 - 25.0, quartz sand 18.0 - 21.0, clay 4.5 -5.0 kaolin 32.0 - 35.0, skull 1 roasting 3.0 - 4.0, skull 2 firing (porcelain battle) 1.0 - 2.0, waste from china production 13.0 - 17.0.

 This porcelain mass in its basic physical and technical indicators (ductility, mechanical strength, whiteness, etc.) meets the basic technological requirements for the production of decorative and artistic porcelain.

Used recipe for underglaze blue paint contains the following ingredients, wt. %: cobalt oxide (!!, !!!) Co ₃ O ₄ (or CoO + Co ₂ O ₃ ) 47-53, silica sand 22.0-31.0, kaolin 13.0 - 18.0, pegmatite 5 -7.0, porcelain skull 0.5-1.0, dolomite 1.0 - 2.0, and also optional dextrin, casein and technical glycerin glue with the following% content in the suspension of underglaze blue paint: dextrin 8-14, glue casein 1.0 - 3.0, technical glycerin 0.5-1.5.

The firing temperature in the 3rd period of watered firing is raised to 1220 ^o C and create a reducing gas environment (described in detail above). The reduction of iron oxide, calcium and sodium begins under certain conditions and ends before the pores are closed, after which carbon monoxide CO will not be able to freely penetrate into the product material. Recovery conditions are created by increasing the concentration of CO at 1020-1220 ^o C. An increase in the content of CO is undesirable, because at the same time, soot is formed in the combustion products, which is deposited on the products. When it burns out on the surface of the glaze, a defect such as pricks may appear. In the neutral mode of firing СО 0.4-0.6%.

 In the table. 1 shows the optimal quantitative and qualitative indicators of the proposed method, which satisfy the quality of 1 grade of porcelain.

In the table. 2 shows the optimal data of the experimental results, which should be excluded in practice. With an increase in the CO: CO ₂ ratio _of more than 0.2 (in the 3rd period of poured firing at Т = 1020-1120 ^o C and over 0.15 at T 1120-1220 ^o C) metallization is observed, i.e., the production of non-sorted products is defective .

In studies, decorated products were evaluated on dried shards with a capacity of 250-600 cm ² .

Assessment of the surface quality of the decor was assessed by metallization (by the number "p" - pcs. Diameter "f" - mm) on the decor area with a product capacity of 250 cm ² according to TU N 5991 - 102-2953050 96 "Porcelain art products" with reference to the firing temperature. Evaluation of the quality of the blue tone corresponds to the reference sample with a bright blue tonality of the decor, as well as to the obtained chemical composition of the underglaze paint, taking into account the examples (see Table 1).

 The composition of the underglaze blue paint is optimal in terms of the purity of the painting and the purity of the blue tone, the yield of marriage, which is confirmed by the chemical analysis of the composition, and contributes both to an improvement in the purity of the tone and to an improvement in the quality of the painting on the porcelain surface.

 In the experiments, the compositions of the underglaze blue paint were prepared with the presence of an aqueous solution of dextrin (mainly potato); glue of casein and glycerin, components in suspensions prepared on the basis of the compositions: dextrin -8-14, casein glue - 1.0-3.0 and glycerin - 0.5-2.0. At the indicated% content of the aforementioned components, the obtained paint suspensions had greater elasticity: improved adhesion to the decorated surfaces of the products, while the color (blue) tone of the painting and the cleanliness of its surface did not change, there were no paint defects during glazing and watered firing, the products mainly met the requirements 1 varieties.

 Spreading of the paint causes a small amount of dextrin, which is introduced into the paint for fixing on the surface of the unglazed product before glazing.

The manufacturing technology of the underglaze blue paint is as follows: wet grinding of all previously prepared components is performed: cobalt oxide, quartz sand and kaolin, pegmatite, porcelain shard, dolomite; grinding is carried out to a dispersion characterized by a residue on a sieve N 0056 - 0.1% - “traces”, then the resulting solution is mixed with a parallel prepared organic binder consisting of dextrin, casein glue. Then they are mixed with the addition of glycerin, defended and poured through a No. 0056 sieve, absorbing excess moisture into dry gypsum forms, and dried to a moisture content of 32-42%. The finished blue (pure) paint with high hiding power and good resistance to the action of molten glaze is applied to the surface of porcelain; the latter are dried and fired at a temperature of 1020-1250 ^o C taking into account the regulation of CO. The firing cycle is 17 hours.

 Underglaze blue paint for painting art porcelain products corresponds to the color and shade of the standards, the surface of the finished products is smooth, glossy; the paint has a high hiding power and increased stability in the glaze melt; the probability of a paint defect during painting, glazing and firing is negligible; the color gamut meets the requirements of standards and the buyer, does not contribute to the reduction of grades; paint has the necessary properties for painting - a set of shadows, the continuity of the line during layering, etc .; the formed porcelain painting has a lively, pure blue tone and a clean surface, it has a strong shine and blue color, from dark to light blue, depending on the thickness of its applied layer (20-290 microns) and concentration. Metallization is eliminated by controlling CO.

 Glazing is performed according to the scheme: glazing of the product with cobalt and colorless glaze; impregnation of its surfaces with hydrophobic substances or glazing by dipping into the glaze suspension; layer thickness 0.1-0.2 mm.

 Products are painted in one color - blue underglaze paint (very durable, with beautiful shades of halftone) on a white porcelain background, applied with quick, wide strokes in combination with a delicate graphic rendering of details.

 The similarity of the porcelain mass and the glaze of the compositions in the described technology leads to the formation of a natural transition at the place of the combination of the glaze and porcelain layer, which is favored by the introduction of porcelain watered shards during grinding in amounts of 3-13%, silicate module (4.5-5.8; optimal value - 4.2-6.2 - [1]) indicates a good chemical stability of the composition used. The selected ratio of the components of the glaze composition better contributes to the cristobalitization of the glaze.

 The glaze composition for coating porcelain products has sufficient chemical resistance, mechanical strength, microhardness, heat resistance, has a transparent and good gloss, even spill and is well fused, and also less prone to subsidence.

 The mixture for the preparation of glazes contains, wt.%: Pegmatite Chupinsky 53.0-66.0, quartz sand 10.0-20.0, porcelain watered skull 3-13, dolomite 11-20, kaolin prosyanovsky 2-6%.

Partial firing is carried out in chamber furnaces of the PKV type (the environment in the furnace is oxidizing, the rise of T due to the flow of gas and air of the burner, the firing time is 8 hours) at T = 920-940 ^o C; then operations: control and marking of a trademark; underglaze hand-painted and glazed products (density of the glaze suspension: for colorless 1.3-1.32; for cobalt glaze 1.5-1.58 g / cm ³ depending on the range of products); watered firing in chamber furnaces (rise time T = 920-940 ^o C for 5-6 hours); oxidative aging proceeds from 920-940 ^o C to 1020 ^o C at an ascent rate of T 20 ^o C / h with a holding time of 4 hours with a gas sharply oxidizing environment; the beginning of the recovery period at T = 1020-112 ^o C with the completion at T = 1120-1220 ^o C at an ascent rate of T 40-50 ^o C / h During this period, the furnaces are under pressure, and in 3-4 hours the iron oxide turns into nitrous oxide, which gives the shard a white color; the beginning of the neutral period with T = 1120-1220 ^o , the completion - at 1410 ^o C for a period of 3 hours with a final exposure of 1-2 hours; medium slightly reducing alternating oxidative. The range of maximum firing temperatures of porcelain masses is 40-50 ^o C.

Firing products after decoration is carried out at T = 1220-1410 ^o C, its violation leads to improper shrinkage of porcelain and deformation of the form, to the violation of the color sound of cobalt.

 Aerodynamic parameters are regulated directly in chamber furnaces. With an increase in the volume of gases, their pressure in the furnace increases. With a narrow interval of porcelain sintering, an increase in pressure in the furnace chamber leads to a relatively sharp rise in T, the products are subjected to thermal shock, which leads to the appearance of a “pimple” marriage. In addition, a certain shift in the redox equilibrium is noted, as a result of which a weakly reducing medium is formed in the furnaces during the oxidative period, and a strongly reducing one is formed in the reducing period, which occurs due to the conversion of natural gas used as fuel.

 Thus, the method of manufacturing porcelain products decorated with cobalt meets the basic technological requirements for the production of decorative and artistic porcelain in accordance with the requirements of GOST "28399-89" Porcelain products ", TU 5991-102-2953050-96" Porcelain art products ", with white 60-69%; the parameters for the release of lead and cadmium from the inner surfaces of hollow and flat products do not exceed the requirements of GOST 28390-89.

 As raw materials used for this method of production of porcelain products, apply materials permitted by the sanitary and epidemiological surveillance services of the Russian Federation.

Thus, the above information indicates that when using the claimed method the following set of conditions:
- tool and technology: embodying the claimed method in its implementation, is intended for use in the ceramic industry, in particular in the production technology of porcelain, mainly artistic, decorated with underglaze painting;
- for the claimed method in the form described in the independent clause of the claims, the possibility of its implementation using the means and methods described in the application is confirmed;
- the claimed technical solution is disclosed in the application materials with the completeness sufficient for its implementation, and ensures the manufacture of porcelain utilitarian and decorative purposes.

 Therefore, the claimed invention meets the condition of "industrial applicability".

Sources of information
1. Augustinian A.I. Ceramics.- L.: Stroyizdat, ed. 2nd, 1975, 392 p.

 2. Technology of porcelain and earthenware production .- M.: Light Industry, 1975. / Ed. I.A. Bulavina, 444 p.

 3. Reference on the porcelain industry. I.I. Moroz et al. - M.: Light Industry, 1980, v. 2.

 4. Hladek I. et al. Dressing of china. -M .: Legprombytizdat, 1990, 160 p.

 5. Lisienko V.G. and others. Mathematical modeling of heat transfer in furnaces and units. - Kiev, Naukova Dumka, 1982, 232 p.

Claims (5)

1. A method of manufacturing porcelain products decorated with cobalt, including the preparation of porcelain mass, molding, drying, baking, dressing, glazing and subsequent watered firing at temperatures up to 1410 ^o C, including four processing periods, characterized in that the optimal mode of the third period is poured firing is 1020 - 1120 ^o C and 1120 - 1220 ^o C, respectively, with a carbon monoxide content of 1.78 - 1.8% and 1.24 - 1.32% in a gaseous medium.  2. The method according to claim 1, characterized in that the optimum thickness of the applied layer of cobalt paint on porcelain products is 20 to 240 microns.  3. The method according to claim 1, characterized in that the optimal thickness of the applied layer of glaze on porcelain products is 80 - 300 microns. 4. The method according to claim 1, characterized in that the best quality of porcelain products is ensured when the content of cobalt oxide in the paint is 1.25 - 2.50 mg / cm ² .  5. The method according to claim 1, characterized in that the amount of dextrin in the paint is 8 to 14%.

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