JPS5983770A - Manufacture of enameled aluminum-coated steel sheet by powder method - Google Patents

Abstract

PURPOSE:To obtain the titled steel sheet excellent in the adhesiveness of a film, while inhibiting the formation of blisters, by omitting the step of finish heating a rolled steel sheet in a series of steps, and executing a baking step serving both as said finish heating to the steel sheet after being coated with glaze and then dried. CONSTITUTION:After a steel sheet is degreased, acid pickled and then electroplated with a thin zinc layer at first, the aqueous liquid suspension of Al powder is applied onto one or both surfaces of said steel sheet by a roll coater or the like and then dried. Said steel sheet is then subjected to rolling-degasifying heating-rolling or degasifying heating-rolling, to form an Al film. Hereon, said steel sheet is immediately degreased with a weak alkali liquid or the like and then optionally anodically oxidized or heated in air. Thereafter, glaze for Al is applied thereto. Said glaze is pref. one having a baking temp. of about 500- 600 deg.C and a thermal expansion coefficient equal to or slightly smaller than that of the steel sheet. After the glaze is applied and dried, baking serving both as finish heating is performed under the same condition as that of a conventional process.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a powder aluminum coating i1'1iil 4-layer film, and particularly (2-layer film)
1υ4 to a manufacturing method that is ψ1ψ curable and can omit steps.

It'd be said that a product made by coating a steel plate with an aluminum layer through an aluminum layer has a coating of %Q plate made of fused aluminum. This product is a product made by preheating an aluminum-plated steel plate with commercially available molten gamma and firing the powder below the melting point of aluminum to form a filtration process. It has the advantage that the reaction between the enamel and the steel plate is suppressed, and discoloration does not occur even if the enamel is not coated thickly with enamel, such as by applying two coats of enamel. Therefore, it is possible to use it as a bond, improving productivity in manufacturing, and it has the great feature that the coating does not peel off even when subjected to slight bending.

However, the fused aluminum plating plate has a problem of swelling and blistering. In other words, the purpose of applying heat treatment before coating the enamel as in 412 is to prevent blistering from occurring on the enamel surface, and to remove moisture and gas remaining in the pinholes of the aluminum film in advance. In this case, the heating temperature is preferably 500°C or higher, but at this temperature the aluminum films are pressed together, so it has been proposed to carry out heat treatment after rolling to lower the processing temperature. These improvement measures inevitably increase costs and are not sufficient to prevent blisters.

As described above, conventional melt-processed aluminum steel sheets have the drawbacks of high cost and blistering.

Therefore, there is a strong demand for the production of aluminum-plated steel sheets that do not easily blister, and the present inventors have previously studied aluminum-plated steel sheets that do not blister when coated with enamel, and have produced powder powder under certain conditions. It was discovered in 1982 that aluminum laminated steel sheets were suitable for this purpose.
-164981. However, the enamel manufacturing process is somewhat complicated, and the film adhesion is impaired when the firing temperature is high and the firing time is long.

A method of manufacturing these conventional powder-processed aluminum-coated steel sheets will be explained with reference to the accompanying drawings. After degreasing and pickling the steel plate, it is electroplated with a thin layer of zinc, followed by a suspension of aluminum powder applied and dried. If the thickness of the aluminum film exceeds 60 μm, the adhesion will deteriorate, so the film thickness needs to be 60 μm or less. After drying, as disclosed in Japanese Patent Publication No. 54-43978 and shown in the accompanying drawings, rolling--gas heating--rolling or degassing heating--finish heating after rolling is performed. Next, as a preliminary treatment for enameling the heated steel plate, only ordinary degreasing is sufficient, but anodizing or heating in air further improves the adhesion between the aluminum film and the powder, so it may be carried out as necessary. . The reason for the improved adhesion is thought to be that the surface of the aluminum film has irregularities, which increases the mechanical bonding effect. After the preliminary treatment, a water suspension of eucalyptus powder is applied and dried, and then fired at a predetermined temperature to obtain enamel. However, conventional powder-processed aluminum coated steel plates had problems with film adhesion.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a powder-process aluminum-coated steel sheet that eliminates the problems of the prior art, prevents the occurrence of blisters, and has excellent film adhesion.

The gist of the present invention is as follows.

That is, a step of "degreasing and pickling a steel sheet," a step of electroplating the pickled steel sheet with zinc, a step of applying aluminum powder to the galvanized steel sheet and then drying it, and a step of applying the aluminum powder and drying the steel sheet. a step of degassing heating and rolling the steel sheet; and a step of heating the rolled steel sheet in a
[Step, a degreasing step in the finishing heating step, and a step of anodizing or heating the degreased steel plate in the air if necessary,
A method for producing a powder coated aluminum coated steel sheet comprising the steps of applying a powder to the anodized or air-heated steel plate and then drying it, and firing the powder coated and dried steel plate. In this method, the powder coated aluminum coated steel sheet is produced by omitting the finishing heating step of the rolled steel sheet and performing a firing step which also serves as finishing heating on the powder coated and dried steel sheet.

The film adhesion of powder coated aluminum coated steel sheets is influenced by the adhesion at the interface between the powder and aluminum and the interface between aluminum and the steel sheet. Conventionally,
Aluminum powder is applied to a steel plate, and after drying, it is degassed and heated.
Although it is closely bonded to a steel plate by finishing heating after rolling, etc., when the interface between the aluminum and steel plate that is in close contact with each other is heated again for enameling, the adhesion generally tends to deteriorate. The degree of deterioration becomes more significant as the heating temperature increases and the heating temperature increases within a range that does not cause alloying.

Therefore, in order to reduce the degree of deterioration, it is necessary to lower the firing temperature or shorten the firing time, but the only way to do this is to change the type of powder, and this is generally difficult. The inventors of the present invention have noticed that the temperature during heating of the finish that brings the aluminum powder into close contact with the steel plate is similar to the temperature during firing of the enamel. By integrating the IC and performing a firing process that also serves as finishing heating, we were able to prevent the deterioration of adhesion between the aluminum and steel plates due to reheating in the conventional method, and were able to achieve the effect of omitting the process.

That is, in the method of the present invention, first, a steel plate to be coated with aluminum is degreased and pickled using a conventional method, and then a thin layer of zinc is plated using an electroplating method. Next, in step 1, an aqueous suspension of aluminum powder is applied to the pupil surface or both surfaces of the steel plate using a roll coater or the like to a thickness of 20 to 80 μm. If it is thinner than 20 μm, there will be many pinholes in the aluminum film, which will cause blistering during enamel firing, and if it exceeds 80 μm, the film adhesion will deteriorate. After coating the aluminum powder, it is dried and further subjected to rolling--gas heating--rolling or degassing heating--rolling to form an aluminum film. Next, unlike the conventional method, enameling is immediately applied without finishing heating. First, it is degreased with a weak alkaline solution or an organic solvent, then anodized or heated in the air as necessary, and then a regular coating for aluminum is applied.
It is desirable that the temperature is 00 to 600°C and the coefficient of thermal expansion is the same as or slightly smaller than that of the steel plate. After coating the powder, drying, and applying the aluminum powder, firing is performed which also serves as finishing heating, and the heating temperature and heating time can be carried out under the same conditions as conventional enameling firing.

Example A steel plate with a thickness of 0.6 plate was degreased, pickled, and galvanized to a thickness of 0.03 μm by electroplating. Then, an aqueous suspension of aluminum powder was applied with a roll coater, dried,
After degassing, heating and rolling, the thickness is 10~ as shown in Table 1.
A 90 μm aluminum film was formed, then degreased with a caustic soda aqueous solution, coated with the aqueous powder shown in Table 1, dried, and baked at 550°C for 2 minutes to reduce the thickness by the method of the present invention. Covered with enamel of 50 capes. For comparison, enamel was also manufactured using a conventional method in which aluminum powder was degassed, heated, rolled, then finished heated at 550°C, and then glazed.

These enamels ((with, 5
The film adhesion was tested by T-bending and the results are also shown in Table 1. Table 1 shows that there is no difference between the inventive example and the conventional example in terms of enamel blistering, but the results of the 5T bending test show that the inventive example has better film adhesion than the conventional row.

As is clear from the embodiments described above, the present invention provides a method for producing aluminum-coated steel sheets using the powder method by omitting finishing heating after application of aluminum powder and performing firing which also serves as finishing heating in the final process. By doing so, we were able to prevent zero deterioration of film adhesion and also have the effect of omitting a process.

[Brief explanation of the drawing]

The attached drawings are process diagrams showing a conventional powder method for manufacturing aluminum coated steel sheets. Agent Takeo Nakaji

Claims (1)

[Claims] (1) A step of degreasing and pickling the roots, a step of plating the pickled steel sheet with zinc F1 mole, a step of dropping aluminum powder on the galvanized steel sheet and then drying it, and a step of drying the aluminum The process of degassing, heating and compacting the powder-coated and dried steel plate, the rolling process (the process of finishing heating the first plate, the degreasing process of the finishing heating trll &, and the process of putting the degreased steel plate on a rack) A step of anodic oxidation or heating in air, a step of drying after applying Yuraku to the anodizing or heating in air, and a step of drying after applying Yuraku to the board
l-: Powder method aluminum coating jp (Powder method aluminum coating jp (board wa Urou no Ayumu), which publishes the process of coating and drying a steel plate with a powder coating and firing it.
In the 4-way method, the second heating process of the pressurized steel plate is omitted;
Powder method - A manufacturing method for aluminum-coated 419 plates, which involves performing a firing process that also serves as a sintering process.