JPS60197885A - Manufacture of enameled aluminum coated steel sheet - Google Patents

Abstract

PURPOSE:To obtain an enameled Al coated steel sheet having superior adhesive strength to the enamel, superior heat and chemical resistances by applying enamel having a high softening point to the surface of an Al coated steel sheet and by baking it at the m.p. of Al or above to convert the Al into an Fe-Al alloy and to form an enamel layer. CONSTITUTION:Enamel having a high softening point and softening at the m.p. of Al or above is applied to the surface of an Al coated steel sheet, and it is baked at the m.p. of Al-1,000 deg.C to convert the Al into an Fe-Al alloy and to form an enamel layer on the surface. Thus, an enamelded Al coated steel sheet is manufactured. The enamel applied contains 15-60wt% PbO and/or 0.1- 50wt% B2O3.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for producing an enameled aluminum-coated steel sheet, which is used for a wide range of purposes including interior and exterior building materials.

(Prior art) Enameled aluminum-coated steel sheets, which are made by enameling the surface of aluminum-coated steel sheets coated with pure aluminum or aluminum alloy, such as hot-dip aluminum-plated copper sheets, aluminum-clad steel sheets, and aluminum electroplated steel sheets, have good adhesion to the base material. It has advantages such as good mechanical impact resistance and is widely used for interior and exterior building materials, blackboard surface materials, etc. However, the melting point of the aluminum coating the steel plate is 600 to 660°C, and when enamel with a high softening point, such as enamel for steel plate, which requires a firing temperature of 800°C or higher, is fired, the aluminum melts and flows, forming the enamel layer. Since there was a preconceived notion that the adhesion with the aluminum coating would deteriorate, conventionally, low softening point enamels, which can be fired at temperatures below the melting point of the coating aluminum, have been used for enameling aluminum-coated steel sheets. However, low softening point enamel contains a large amount of alkali metal oxides that adversely affect the enamel properties in order to lower the softening point, and has better heat resistance, chemical resistance, hardness, and
There is a drawback that the appearance and texture are inferior, and therefore, the enameled aluminum coated steel sheet has the drawback that these properties are inferior to the enameled steel sheet.

(Object of the Invention) The present invention solves the drawbacks of the conventional enameled aluminum-coated steel sheets and provides a method for producing enameled aluminum-coated steel sheets with improved properties such as heat resistance, chemical resistance, hardness, and appearance texture. It was completed with the purpose of

(Structure of the Invention) The present invention applies an enamel glaze having a high softening point that softens at a temperature higher than the melting point of the coated aluminum to the surface of an aluminum coated steel sheet, and then sintering the coated steel plate at a temperature higher than the melting point of the coated aluminum and lower than 1000°C. It is characterized in that it is made into an iron-aluminum alloy and its surface is coated with an enamel layer.

In the present invention, the aluminum-coated steel sheet serving as the original sheet can be a hot-dip aluminum-plated steel sheet, an aluminum-clad steel sheet, an aluminum electroplated steel sheet, an aluminum vapor-deposited steel sheet, an aluminum powder-rolled heat-treated steel sheet, etc. When using an aluminized steel plate, the aluminum coating layer contains 1 Si.
It is advantageous to use those containing up to 15% by weight. After the surface of such an aluminum-coated steel sheet is degreased, it is glazed with an enamel glaze having a relatively high softening point that softens at a temperature higher than the melting point of the coated aluminum without pre-firing. The melting point of pure aluminum is about 660°C, but the melting point of aluminum alloy is lower, about 600°C. Enamel glazes with relatively high softening points have not been used for aluminum-coated steel sheets. used. Preferred enamel glazes are those containing 15 to 60% by weight of PbO, and those containing B20. The composition contains 0.1 to 50% by weight of. The aluminum-coated steel sheet coated with enamel glaze is heated in the atmosphere to a temperature higher than the melting point of the coated aluminum to perform enamel firing, but at this time, the molten aluminum or aluminum alloy hardly flows and is bonded to the base steel sheet. reacts rapidly with Fe
A thermally stable iron-aluminum alloy consisting of one or more phases of A1+, FezAIs, FeAl, Fe, and AI is formed. This iron-aluminum alloy layer has fine irregularities with an Rmax of 5 to 25μ on its surface, which produces a strong physical bonding effect and chemical fusion effect with the enamel layer. ~60wt% PbO and 0°1~50wt% B
If a composition containing either or both of tOs is used, the adhesion to the enamel layer will be significantly increased. The reason for this is not necessarily clear, but it is thought that PbO lowers the surface tension of the glass component in the molten enamel glaze, causing the enamel to penetrate into the fine irregularities of the iron-aluminum alloy layer. It is also believed that the B,03 component increases the physical bonding effect between the enamel layer and the iron-aluminum alloy layer by corroding the surface of the iron-aluminum alloy layer. In addition, this effect is not remarkable for those with pbo less than 15% and those with B t O3 less than 0.1%, and those with pbo more than 60% and those with B2O3 more than 50%. Since it cannot satisfy the chemical resistance and hardness required for enamel glaze, it is not normally used except for special purposes. In addition to being added to the enamel glaze in advance, these components are partially decomposed after the enamel is fired to form PbO or B20.
For example, boric acid (H3B 03), metaboric acid (
KBO3), sodium metaborate (Na Bow, N
aBO2・4H*O), potassium metaborate (KBO2
), Boric anhydride (N az B a O,), Lead metaborate (P
b (Box) t ) etc. may be added as mill additives. It goes without saying that the temperature for firing the enamel should be above the melting point of the coated aluminum, but if it exceeds 1000°C, the distortion of the aluminum coated rope temporary base will become large and practicality will be lost, so the temperature should be below 1000°C.

Next, examples of the present invention will be shown together with comparative examples.

After degreasing a 0.8N hot-dip aluminized steel plate (one side plating thickness 16μ) with alkali, the N11L shown in Table 1 was applied.
~11 hll of enamel glaze was applied by spraying to a thickness of 70μ, and the enamel was fired for 3 minutes at temperatures of 660°C, 700°C, and 750°C, which exceed the melting point of the coated aluminum (about 600°C). However, ail is a comparative example, and only this one contains PbO, B, and O.

57 using an enamel glaze that can be fired at low temperatures and does not contain
Enamel firing was performed at 0°C. The obtained enameled aluminum coated steel sheet was evaluated for enamel adhesion, chemical resistance, hardness, and appearance texture, and the results are shown in Table 2. In addition, enamel adhesion was determined using a drop impact deformation test method using a punch diameter of 25.0 a.
Place the test piece between mφ and die 25.5 ms and weigh 1 kg.
The degree of peeling of the enamel layer was evaluated when a maximum deformation depth of 3 times was applied due to the impact of dropping a weight, and the chemical resistance was determined according to JIS.
The hardness was evaluated by the method of R4301 and measured by a Mohs hardness meter.

Table 1 Enamel composition However, mill additives are distributed externally.

Table 2 Evaluation results (◎: Very good, ○: Good, △: Poor)
．． A general rimmed steel plate with a thickness of 0.6 fin containing 0.4% by weight of C and a thickness of 20% made of aluminum with a purity of 99.9%.
An aluminum clad steel plate with a cladding layer of μ formed thereon was washed with water after normal alkali degreasing and
Enamel glaze of O was applied by spraying to a thickness of 100μ, and heated at 660°C, 700°C, and
When enamel fired at 50°C, an enameled aluminum-coated steel sheet with the same evaluation as in the first example was obtained (effects of the invention). Denying the conventional wisdom that the process must be carried out at a temperature below the melting point of aluminum, the surface of various aluminum coated steel sheets is coated with a high softening point enamel glaze and then fired at a temperature above the melting point of the coated aluminum. By converting the coated aluminum into an iron-aluminum alloy and coating it with an enamel layer, we have succeeded in obtaining an enameled aluminum-coated steel sheet with excellent enamel adhesion, heat resistance, chemical resistance, hardness, appearance texture, etc. It will greatly contribute to the development of industry as it solves the problems of conventional enameled aluminum coated steel sheets.

Patent applicant: Nippon Insulator Co., Ltd.

Claims (1)

[Claims] 1. After applying a high softening point enamel glaze that softens at a temperature higher than the melting point of the coated aluminum to the surface of the aluminum coated steel plate,
A method for producing an enameled aluminum-coated steel sheet, which comprises firing at a temperature above the melting point of the coated aluminum and below 1000°C to turn the coated aluminum into an iron-aluminum alloy and at the same time forming an enamel layer on its surface. 2. The method for producing an enameled aluminum-coated steel sheet according to claim 1, wherein the enamel glaze contains 15 to 60% by weight of PbO. 3. The method for producing an enameled aluminum-coated steel sheet according to claim 1, wherein the enamel glaze contains 0.1 to 50% by weight of BzO's. 4. Enamel glaze contains 15-60% by weight of Pbo and 0.1-5%
The method for producing an enameled aluminum-coated steel sheet according to claim 1, which contains 0% by weight of Boo.