GROUND COAT ENAMEL COMPOSITION, GROUND COAT ENAMEL LAYER, PRODUCTS CONTAINING SAME AND METHODS FOR PRODUCING SAME

Abstract

A ground coat enamel composition for production of an adhesion promoter layer between steel and at least one cover coat enamel for production of an enamel-based coating that is highly corrosion-resistant with respect to mechanical, thermal and chemical effects. The ground coat enamel composition includes boron oxide (B.sub.2O.sub.3) and alkali metal oxide(s), especially Li.sub.2O, Na.sub.2O and/or K.sub.2O, in percentage proportions by weight: a first main constituent, SiO.sub.2 from 35-70%, preferably 40-65%, and, as a second main constituent, from Fe.sub.2O.sub.3 5-28%, preferably in the range from 7-23% and particularly 8%-15% by weight. Also disclosed is a ground coat enamel layer produced from such a ground coat enamel composition. A highly corrosion-resistant article having such a ground coat enamel layer. A method for producing such a ground coat enamel layer and also a method for producing a highly corrosion-resistant article using such a ground coat enamel composition.

Claims

1. A ground coat enamel composition for production of an adhesion promoter layer between steel and at least one cover coat enamel for production of an enamel-based coating that is highly corrosion-resistant with respect to mechanical, thermal and chemical effects, wherein the ground coat enamel composition includes boron oxide (B.sub.2O.sub.3) and alkali metal oxide(s), especially Li.sub.2O, Na.sub.2O and/or K.sub.2O, in proportions by weight in accordance with the following table: TABLE-US-00006 Constituent [% by weight] B.sub.2O.sub.3 4-22 Sum total of alkali 7.8-22.5 metal oxide(s) and, as a first main constituent, SiO.sub.2 with a percentage proportion by weight in the range from 35% by weight to 70% by weight, and, as a second main constituent, Fe.sub.2O.sub.3 with a percentage proportion by weight in the range from 5% by weight to 28% by weight.

2. The ground coat enamel composition as claimed in claim 1, wherein the ground coat enamel composition further includes Al.sub.2O.sub.3 and alkaline earth metal oxide(s), especially calcium oxide, in proportions by weight in accordance with the following table: TABLE-US-00007 Constituent [% by weight] Al.sub.2O.sub.3 1.5-13  Sum total of alkaline 0.25-6   earth metal oxide(s)

3. The ground coat enamel composition as claimed in claim 2, wherein the ground coat enamel composition further includes at least one substance, especially ZnO, TiO.sub.2 and/or CaF.sub.2, for controlling a rheology of a melt of the ground coat enamel composition, in proportions by weight in accordance with the following table: TABLE-US-00008 Constituent [% by weight] Sum total of 0-14 ZnO and/or TiO.sub.2 CaF.sub.2  0-2.8

4. The ground coat enamel composition as claimed in claim 1, wherein the ground coat enamel composition is essentially free from adherence oxides, namely oxides of the elements nickel, cobalt and manganese, and also in particular essentially free from rare earth elements.

5. A ground coat enamel layer applied on a steel sheet, wherein the ground coat enamel layer has been produced from a ground coat enamel coating as claimed in claim 1.

6. The ground coat enamel layer as claimed in claim 5, wherein a steel-ground coat enamel contact zone includes iron silicate.

7. The ground coat enamel layer as claimed in claim 5, wherein the ground coat enamel layer has a layer thickness in the range from 0.05 mm to 0.8 mm.

8. The ground coat enamel layer as claimed in claim 6, wherein the iron silicate is crystalline, especially essentially in the form of fayalite crystals, Fe.sub.2SiO.sub.4.

9. The ground coat enamel layer as claimed in claim 6, wherein the iron silicate at the steel-ground coat enamel contact zone forms.

10. The ground coat enamel layer as claimed in claim 9, wherein a layer thickness of the crystal layer is in the range from 10 μm to 65 μm.

11. The ground coat enamel layer as claimed in claim 5, wherein the ground coat enamel layer, especially the crystal layer, is essentially bubble-free and especially CO— and/or CO.sub.2-free.

12. The ground coat enamel layer as claimed in claim 5, wherein the steel sheet, especially at the steel-ground coat enamel contact zone, has a carbon content in the range from 0% by weight to 0.5% by weight.

13. An article that is highly corrosion-resistant with respect to mechanical, thermal and chemical effects, having a ground coat enamel layer as claimed in claim 5 applied on a steel sheet and at least one cover coat enamel layer applied on the ground coat enamel layer.

14. The highly corrosion-resistant article as claimed in claim 13, wherein a total layer thickness of ground coat enamel layer and of the at least one cover coat enamel layer is in the range from 0.5 mm to 3 mm.

15. A method for producing a ground coat enamel layer by the following steps of: i. providing a steel sheet; ii. optionally superficially removing rust, especially loose rust; iii. applying a ground coat enamel composition as claimed in claim 1; iv. firing the ground coat enamel composition at a temperature in the range from 890° C. to 950° C., over a period in the range from 20 min to 80 min.

16. A method for producing a highly corrosion-resistant article, in particular newly producing or reconditioning a used highly corrosion-resistant article, as claimed in claim 13, characterized by the following steps of: a) providing a new article made from steel sheet or a used highly corrosion-resistant article which in particular has a damaged ground coat enamel layer and/or cover coat enamel layer; b) cleaning a surface of the article that is to be coated, in particular mechanically by for example blasting with at least one abrasive substance, in order to substantially remove any loose adhesions, such as for example rust, and/or one or more earlier, especially defective, coatings; c) once producing a ground coat enamel layer on the cleaned steel sheet to be coated in accordance with, or in analogy to, claim 15; d) applying a cover coat enamel composition slip for subsequent formation of a cover coat enamel layer on the ground coat enamel layer; e) drying the cover coat enamel composition slip; f) heating the article with the ground coat enamel layer and the cover coat enamel composition, or rather the dried cover coat enamel composition slip, to a firing temperature in the range from 780° C. to 870° C.; g) maintaining the firing temperature for a period in the range from 6 min to 125 min; h) cooling the article in a controlled manner; i) if required, repeatedly applying a cover coat enamel composition slip for subsequent formation of a further cover coat enamel layer on the preceding cover coat enamel layer.

17. (canceled)

18. A ground coat enamel composition for production of an adhesion promoter layer between steel and at least one cover coat enamel for production of an enamel-based coating that is highly corrosion-resistant with respect to mechanical, thermal and chemical effects, wherein the ground coat enamel composition includes boron oxide (B.sub.2O.sub.3) and alkali metal oxide(s), especially Li.sub.2O, Na.sub.2O and/or K.sub.2O, in proportions by weight in accordance with the following table: TABLE-US-00009 Constituent [% by weight] B.sub.2O.sub.3 4.5-21.5 Sum total of alkali 8.5-21.5 metal oxide(s) and, as a first main constituent, SiO.sub.2 with a percentage proportion by weight in the range from 35% by weight to 70% by weight and as a second main constituent, Fe.sub.2O.sub.3 with a percentage proportion by weight in the range from 5% by weight to 28% by weight.

19. The ground coat enamel composition as claimed in claim 1, wherein the ground coat enamel composition further includes Al.sub.2O.sub.3 and alkaline earth metal oxide(s), especially calcium oxide, in proportions by weight in accordance with the following table: TABLE-US-00010 Constituent [% by weight] Al.sub.2O.sub.3  2-12 Sum total of alkaline 0.4-5   earth metal oxide(s)

20. The ground coat enamel composition as claimed in claim 2, wherein the ground coat enamel composition further includes at least one substance, especially ZnO, TiO.sub.2 and/or CaF.sub.2, for controlling a rheology of a melt of the ground coat enamel composition, in proportions by weight in accordance with the following table: TABLE-US-00011 Constituent [% by weight] Sum total of 0.001-12  ZnO and/or TiO.sub.2 CaF.sub.2 0.001-2.3

Description

[0086] The invention shall be described hereinafter with reference to an exemplary embodiment that is elucidated in more detail on the basis of the drawing. In the drawing:

[0087] FIG. 1 shows a sectional view through a conventional highly corrosion-resistant article according to the prior art; and

[0088] FIG. 2 shows a sectional view through a highly corrosion-resistant article produced according to the invention.

[0089] In the following description, the same reference signs are used for identical and identically acting parts.

[0090] FIG. 1 shows a sectional view through a conventional highly corrosion-resistant article 10. The article 10 consists of a steel sheet 20, to which a ground coat enamel layer 30 has been applied. The ground coat enamel layer 30 adjoins the steel sheet 20 along a steel-ground coat enamel contact zone 60, where along the contact zone 60 a layer of iron oxide dissolved in the ground coat enamel has formed, which is adjoined by a heavily bubble 50-laden glassy ground coat enamel layer 30. Arranged above the ground coat enamel layer 30 are a plurality of likewise bubble-rich cover coat enamel layers 40.

[0091] FIG. 2 shows a sectional view through a highly corrosion-resistant article 10 that has been produced in accordance with the invention using a ground coat enamel composition according to the invention. The article 10 produced according to the invention thus comprises a steel layer in the form of a steel sheet 20, on which a ground coat enamel layer 30 has been applied. The ground coat enamel layer 30 for its part has, along a steel-ground coat enamel contact zone 60, a crystal layer 35 which covers the steel sheet 20 over the full surface and shields it with respect to effects from the overlying ground coat enamel layer 30 and also from a cover coat enamel layer 40 lying yet further above. The crystal layer 35 consists of fayalite crystals and is bubble-free. The thickness of the crystal layer 35 is essentially 50 μm. It can readily be seen from FIG. 2 that any bubbles present are so only in a region of the ground coat enamel layer 30 that adjoins the cover coat enamel layer 40, and the ground coat enamel layer 30 is otherwise bubble-free. Further bubble formation does not take place; instead, the region of the ground coat enamel layer adjoining the crystal layer 35 is also bubble-free.

[0092] Exemplary formulations for a glass composition according to the invention are given in tables below.

TABLE-US-00004 Formula- Formula- Formula- Formula- Formula- tion 1 tion 2 tion 3 tion 4 tion 5 Constit- % by % by % by % by % by uents weight weight weight weight weight SiO.sub.2 56.7 56.8 57.3 57.9 59.6 Na.sub.2O 9.4 8.1 10.1 8.8 10.4 K.sub.2O 3.1 1.3 2.7 1.8 2.1 Li.sub.2O 0.4 0 0.4 1.3 1.6 B.sub.2O.sub.3 8.1 9.3 8.7 9.3 6.5 MgO 1.3 0.1 1.1 0.8 0.7 CaO 0.4 0.6 0.6 0.6 0.4 SrO 0.3 0 0 0.1 0.1 BaO 1.1 2 1.4 0.3 0 Fe.sub.2O.sub.3 13.2 14.8 11.3 13.8 13.1 Al.sub.2O.sub.3 5.2 6.7 5.8 4.7 5.1 TiO.sub.2 0.4 0.1 0.3 0.4 0.1 CaF.sub.2 0.4 0.2 0.3 0.2 0.3 Sum total 100 100 100 100 100

TABLE-US-00005 Formula- Formula- Formula- Formula- tion 6 tion 7 tion 8 tion 9 Constit- % by % by % by % by uents weight weight weight weight SiO.sub.2 60.4 65.2 65.9 66.3 Na.sub.2O 8.3 9.5 8.5 9.6 K.sub.2O 2.6 1.8 1.7 1.1 Li.sub.2O 0 0 0 0.2 B.sub.2O.sub.3 8.8 6.7 6.5 8.3 MgO 0 0.2 0.5 1.3 CaO 2.7 0.4 0.3 0.4 SrO 0 0 0.2 0 BaO 0 0 0.2 0.2 Fe.sub.2O.sub.3 10.1 12.8 11.9 8.1 Al.sub.2O.sub.3 7.1 3 3.9 4.3 TiO.sub.2 0 0 0.2 0.1 CaF.sub.2 0 0.4 0.2 0.1 Sum total 100 100 100 100

[0093] It should be pointed out at this juncture that all parts described above taken alone and in any combination, especially the details illustrated in the drawings, are claimed as essential to the invention. Modifications thereof are familiar to those skilled in the art.

LIST OF REFERENCE SIGNS

[0094] 10 highly corrosion-resistant article (detail) [0095] 20 steel sheet [0096] 30 ground coat enamel layer [0097] 35 crystal layer [0098] 40 cover coat enamel layer [0099] 50 bubbles [0100] 60 steel-ground coat enamel contact zone