CS240743B1 - Mixture for preparation of protective enamels on metals, especially steel - Google Patents

Abstract

The invention relates to the field of glass and solves the problem of the composition of mixtures for the preparation of protective enamels for metals, especially steel. The mixture includes glass frit and corundum powder, with an addition of 1 to 60 parts by weight of corundum powder with a grain size of 1 to 60 μΐη per 100 parts by weight of glass frit. The composition of the glass for the frit is defined. By using the invention, an enamel that is acid-resistant and alkali-resistant and has good resistance to mechanical and thermal shock is obtained.

Description

The invention relates to the field of glass and solves the problem of the composition of mixtures for the preparation of protective enamels for metals, in particular steel.

The mixture comprises a glass frit and corundum powder, with an addition of 1 to 60 parts by weight of corundum powder having a particle size of 1 to 60 μΐη per 100 parts by weight of the glass frit. The composition of the glass for the frit is defined.

By utilizing the invention, an acid-resistant and alkali-resistant enamel is obtained with good resistance to mechanical and thermal shock. _.....

The invention relates to a composition for the preparation of protective coatings for metals, in particular steel, the composition comprising a glass frit and corundum powder.

The enamels that treat the surfaces of metal objects are essentially low-melting glass to which other components are added, both on the basis of the base material, e.g., cast iron, steel, iron, copper, precious metals, etc., and on the assumed basis use of a metal object. The essence of enameling is to apply ground glass to the surface of the article, mixed with other components such as clay, bentonite, water, etc., to obtain suitable suspensions for spraying, dipping, etc., and to heat the article to melt. : Enamels, as mentioned eg in MS. 221 734. Enameling usually uses several coatings, on the one hand a base enamel, which compensates for the basic differences in the expansion between metal and enamel and increases the adhesion of the enamel to the metal, as well as covering or protective enamel, sometimes in several layers.

Metal protective coatings have a relatively high sensitivity to mechanical damage by impact or sudden temperature changes and, when exposed to corrosive environments, such as strong acids or alkalis, lower alkali resistance.

To increase acid resistance according to US AO US No. 833,824 frit, consisting of silica, SiO ₂ , zirconium ZrO ₂ , sodium Na ₂ 0, calcium · CaO, aluminum Al ₂ O ₃ , lithium Li ₂ O, ferric Fe ₂ O ₃ , titanium TiO ₂ and barium BaO and calcium fluoride CaF ₂ .

For the protection of chemical plants in acid environments and for increased alkali resistance, the coating according to AO USSR No. 914 520 additionally contains cobalt trioxide Co ₂ O ₃ , molybdenum MoO ₃ and potassium chloride KCl, or aluminum AlCl ₃ or sodium NaCl, the glass consisting of silicon dioxide SiO ₂ , zirconium ZrO ₂ , boron B ₂ O ₃ , aluminum · Al ₂ O ₃ , calcium CaO, strontium SrO, sodium Na ₂ O, potassium K ₂ O, lithium · Li ₂ O and chromium Cr ₂ O ₃ .

To increase the heat resistance, an acid-resistant enamel is disclosed in USSR AO No. 478,783 consisting of SiO ₂ , magnesium MgO, sodium Na ₂ O, lithium Li ₂ O and chromium Cr ₂ O ₃ , which additionally contains CaO and zinc ZnO.

To improve the corrosion resistant coatings of U.S. Pat. No. 4,196,004, crystalline powders of lithium, magnesium or calcium titanates, silicates and aluminosilicates are added to the frit to the glass frit. Alternatively, corundum granules or powder are added to the glass frit, namely double grain to obtain enamel with high abrasion resistance, e.g. France 2,060,609 or Austria 324,071. The inventive enamel is primarily intended for ceramic tiles.

However, most of the previously known and described instructions do not solve the problems of resistance of protective enamels in a comprehensive way, especially in connection with the reported mechanical and thermal properties in connection with resistance to strong acids and alkalis.

These disadvantages are eliminated or substantially reduced in the composition for the preparation of the protective enamels for metals according to the invention, which consists in that the composition contains, per 100 parts by weight of glass frit, 1 to 60 parts by weight of corundum powder having a particle size of 1 to 60 μΐη. The glass frit comprises, in weight concentrations of 55 to 72 ° / o of silicon dioxide SiO _2, 0.1 to 15% titanium dioxide TiO _2, 1-10% boron oxide B ₂ O ₃ "from 0.1 to 5% of aluminum oxide A1 ₂ O ₃ , 1 to 11% ZrO ₂ , 0.1 to 10% MgO and / or CaO and / or barium oxide BaO and / or zinc oxide, 5 to 25% alkali metal oxide lithium Li ₂ O and / or potassium oxide K ₂ O and / or sodium oxide Na ₂ O. The frit also contains 0.1 to 2 ° F of fluorine F.

By using the invention, very good resistance of the protective coatings is obtained, especially when applied to chemical apparatuses, which require strong acid and alkali resistance essentially provided by glass frit. Addition of corundum powder results in further improvement of the corrosion resistance properties and high resistance to mechanical and thermal impact.

The amount of corundum powder to be added also affects the resulting physicochemical properties of the compositions and for practical use it is always necessary to select the optimum addition depending on the technical conditions of application. Therefore, the optimum size of the corundum powder should always be verified experimentally in the present case. This also makes it possible to vary the physical and technological properties of the materials obtained using the same starting materials, which is a further advantage of the invention.

The effect of the invention is illustrated and described in the following examples, with reference to a table in which examples of compositions of glasses suitable for the preparation of protective enamels are given.

The advantageous properties of the coating compositions prepared according to the invention are apparent from the following examples.

Example 1

Of a frit consisting of 100 parts by weight of glass No. 4 and 20 parts of corundum having a grain size of 10 to 15 μπι, water was added, 2 parts of clay and 0.5 to 1 part of sodium nitrite as electrolyte were sprayed onto a mild steel substrate provided with a base. enamel. After firing, the coating was subjected to a chemical resistance test according to standards

DIN 51156. The acid loss was 0.04 mg / cm ² and the alkaline solution was 0.6 mg / cm ² .

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Example 2

The coating prepared in the same manner from 100 parts by weight and 10 parts by weight of corundum powder with a particle size of 15 µm on the CIBA-GEIGY specimens for determination of resistance to sudden temperature changes showed an average thermal resistance of 5 samples of 240 ° G with low scattering.

Example 3

The coating prepared from frit No. 5 with the addition of corundum powder with an average grain size of about 20 μτη at a weight ratio of 10: 3 achieved a temperature resistance according to the CIBA-GEIGY method of 270 degrees Celsius with low scattering values (5 samples, + 2.5 ° C).

Example 1 a d 4

Coating of No. 10 frit and corundum powder in a weight ratio of 5: 1 was applied to an 8 mm thick mild steel test plate coated with a base of enamel (0.2 to 0.3 mm) and tested for impact strength by dropping a standard body . The first breakage of the coating (crack) occurred only when the impact energy was greater than 0.8 J. The coating with corundum additive did not show flake, which is characteristic of glass enamels at a significantly higher impact (4 J), but only crushed the coating layer in place. contact with the test piece.

Claims (1)

Subject Mixture for the preparation of protective enamels for metals, in particular steel, comprising a glass frit and corundum powder, characterized in that it contains 1 to 60 parts by weight of corundum powder with a grain size of 1 to 60 μτη per 100 parts by weight of glass frit, ^iO to 72 / o of silicon dioxide SiO _2, 0.1 to 15 why. titanium dioxide TiO ₂ , 1 to 10% boron oxide B ₂ O ₃ , 0.1 to 5% Al ₂ O ₃ , 1 to 11% ZrO ₂ , 0.1 to 10% MgO and / or calcium oxide CaO and / or barium oxide BaO and / or zinc oxide ZnO, 5 to 25% lithium oxide Li ₂ O and / or sodium oxide Na ₂ O and / or potassium oxide K ₂ O, and further 0 , 1 to 2% of fluorine F.