JPS5912745B2 - Pretreatment method for enameling of molten aluminized steel sheets - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for pre-enameling a molten aluminized steel plate, and more particularly to a pre-enameling method for a molten aluminized steel plate with extremely few bubbling defects on the surface of the enamel when enameled. .

When enameling a molten aluminized steel sheet, only degreasing is required as a pretreatment, so the pretreatment cost is low, and as a glaze, its thermal expansion coefficient is close to that of the steel sheet, and the composition is close to that of the glaze for aluminum. By using this method, the firing temperature can be lowered than when enameling is performed directly on the steel plate, so it is less likely to cause irregularities, and has been used in recent years for blackboards, shielding boards, building materials, etc. that require flatness. It's starting to look like this. However, when directly enameling a molten aluminized steel plate as produced, significant bubbling may be observed on the surface, making it impossible to use it for products that require a high-quality appearance. This is because when a molten aluminized steel plate is microscopically observed, microscopic defects such as pinholes, minute non-plating, and indentation scratches occur on the surface of the molten aluminized steel plate, no matter how small, and these microscopic D-order defects occur. It is thought that the air, moisture, etc. contained therein expand during firing of the enamel, causing bubbles to form on the surface of the enamel. Looking at it from another angle, it is thought that in heat-resistant components, which are the main uses of hot-dip aluminized steel sheets, minute defects that pose no problem in terms of quality can have a significant impact on the appearance during enameling. 10 However, the present inventors have found that, as a method that is effective in preventing foaming on the enamel surface, before performing enamel D-roeing, a molten aluminized steel plate is heated at a temperature of 500 to 600°C for a predetermined period of time to reduce the amount of bubbles contained in micro defects. Patent Application No. 5135-1851 discloses that the air, moisture, etc.
No. 7, the heating temperature in this method is too high for molten aluminum plated steel sheets, and if a molten aluminum plated coil is heated in a tight coil state, there is a risk that the plated layers will weld to each other. However, heating had to be carried out in an open coil state, resulting in poor workability and the problem of diffusion of iron particles into the plating layer.

Therefore, the present inventors conducted extensive research to lower the heating temperature, and as a result, they found that skin-passing before heating is effective in preventing foaming even if the heating temperature is lowered.

Therefore, the object of the invention is to prevent bubbling on the enamel surface by skin-passing the steel plate after molten aluminizing and before heating, which allows the heating temperature to be lower than the temperature disclosed in Patent Application No. 51-18517. The purpose is to provide an effective enameling pretreatment method for molten aluminized steel sheets, the gist of which is to skin-pass the molten aluminized steel sheets before enameling, and then to
It is characterized by heating in the range of 480°C.

The purpose of the skin pass before heating in the present invention is to crush minute defects existing on the surface of the molten aluminized steel sheet and mechanically push out air, moisture, etc. contained therein. is the surface roughness Rnlax of the skin pass roll (JISBO6O
1) and the rolling reduction rate play a major role.

The skin pass crushes most of the microscopic defects on the surface of the molten aluminized steel sheet, and also pushes out most of the air and moisture contained therein, greatly preventing bubbling during enameling, but still. Since extremely small defects containing air, moisture, etc. remain, it is essential to dissipate the air, moisture, etc. contained therein after the skin pass. However, since the remaining micro defects are limited to the very surface layer of the plating layer, the heating temperature is
It does not require high temperatures as disclosed in No. 17.
Next, the present invention will be explained in detail with reference to Examples.

[Example 1] To investigate the skin pass conditions, enameling was performed without skin pass or heating, and the following three materials were confirmed to have bubbles on the enamel surface: (1) Plated in a bath without silicon added; Molten aluminum plated steel plate with a plating thickness of 22μ on one side.

(2) A molten aluminum plated steel plate plated in a silicon-added bath, with a plating thickness of 22μ on one side and a plating layer containing 7.5% by weight of silicon.

(3) A molten aluminum plated steel plate plated in a silicon-added bath, with a plating thickness of 11μ on one side and a plating layer containing 7.5% by weight of silicon. After skin-passing each of them by changing the surface roughness and rolling reduction of the skin-pass roll, they were heated in the air at 250°C for 8 hours or at 300°C for 6 hours, and then the composition was 22O% SlO, 5% B, O, ，
Na2O+K, O2O%, PbO28%, TiO, 25
%, CaO2% (both weight %) glaze is applied,
This was fired at 570°C for 5 minutes, and the number of bubbles generated on the enamel surface was counted. Tables 1, 2, and 3 show the results for materials 1), (2), and (3), respectively, and the numbers in the tables indicate the number of bubbles per 1 d. Regardless of the plating thickness of each material and the presence or absence of silicon in the plating layer, the smaller the surface roughness RJnaX of the skin pass roll is, the more effective it is in preventing the generation of bubbles on the enamel surface. preferable. Also, the larger the rolling reduction rate, the more effective it is, especially at 0.
．． It is preferable to set it to 5% or more. Therefore, if the hot-dip aluminized steel sheet is plated in a bath that does not contain silicon, or in a bath that contains silicon in a normal amount, the plating thickness will not exceed the standard thickness. In this case, the skin pass is preferably performed using a skin pass roll having a surface roughness Rmax of 20 μm or less and applying a rolling reduction rate of 0.5% or more. Naturally, the upper limit of the skin pass rolling reduction is within the range of the skin pass rolling reduction that is normally performed. [Example 2] In order to investigate the interrelationship among plating thickness, heating time, and heating temperature, the following three materials were found to foam when enameled without skin pass or heating, namely (1)
Surface roughness Rmax after plating in a bath without silicon addition
The rolling reduction rate is 2.00 with a skin pass roll of 1.0μ! )
A molten aluminum plated steel plate that has been skin-passed and has a plating thickness of 20μ on one side after the skin-pass.

(2) After plating in a silicon-added bath,
) A molten aluminium-plated steel sheet skin-passed under the same conditions as 2009-2012, the plating layer contains 7.5% by weight of silicon, and the plating thickness on one side after the skin-pass is 20 μm.

(3) A molten aluminum plated steel sheet having the same history as (2) above, containing 7.5% by weight of silicon in the plating layer, and having a plating thickness of 10 μm on one side after skin pass.

Each was heated under different heating conditions, and then enameled in the same manner as in Example 1, and the number of bubbles generated on the enamel surface was counted.

Tables 4, 5, and 6 show materials (1), (2), and (
The results for 3) are shown, and the numbers in the table indicate the number of bubbles per 11. The heating temperature after the skin pass is in the range of 250 to 480°C, regardless of the plating thickness and the presence or absence of silicon in the plating layer, for each material, 225°C is insufficient even if the heating time is prolonged. If the heating time is adjusted according to the heating temperature, the number of bubbles generated on the enamel surface will be reduced. As is clear from Tables 4 to 6, this heating time can be made shorter as the heating temperature is higher and the plating thickness is thinner. Therefore, if you want to reduce the number of bubbles to 1 or less, the minimum heating time Z (hours) and the plating thickness x (
μ) and heating temperature y (℃), Z=x
The equation (0,000016y2-0.0128y+2.5) holds true.

No matter how long you heat it for longer than the time calculated by this equation at 480°C or less, no diffusion of iron into the plating layer will be observed, so there is no need to specify an upper limit for the heating time, and the enameling process will work. There is no adverse effect on

In the present invention, it is possible to perform heating at a temperature exceeding 480°C, but in this case, since the micro defects are limited to the very surface layer, the air, moisture, etc. contained therein must be dissipated. The effect remains the same, but on the other hand, if the coil is heated in a tight coil state, there are concerns about welding of the plated layers to each other and diffusion of iron into the plated layers.

The heating atmosphere in the present invention is not particularly limited as long as it is an atmosphere that can dissipate air, moisture, etc. from minute defects.

In addition, if oil or dirt has adhered to the surface of the molten aluminized steel plate due to handling or processing after heating and before enameling, remove as necessary to improve the adhesion and appearance of the enamel. All you need to do is to clean the surface by degreasing or washing with water.
The following points can be mentioned as effects of the present invention.

(1) As the micro defects are crushed by the skin pass, the air and moisture contained therein are pushed out, and only extremely small micro defects exist on the surface layer. It is economical because it does not require high-temperature heating to dissipate water and water.

(2) Since the heating temperature can be as low as 250 to 480C, the iron content will not diffuse into the plating layer and develop an alloy layer, so the workability of the plating layer will be improved before heating. Furthermore, even if the coil is heated in a tight annealing manner, there is no welding of the plating layers to each other, and the heating efficiency is significantly improved.

(3) The present invention can be carried out regardless of whether or not the plating layer contains silicon.

(4) Depending on the change in plating thickness, the equation Z=x(0.
Since the heating time and temperature can be determined by 000016y2-0.0128y+2.5), products of stable quality can be obtained.

(5) Even if the heating temperature is lowered by skin-passing,
Since foaming during enameling can be significantly prevented, the yield of enameling is improved, which is of great industrial benefit and can be used in applications where a high quality appearance is required.

Claims (1)

[Scope of Claims] 1. A pre-enameling treatment method for a molten aluminized steel plate, which comprises skin pass processing and then heating in a range of 250 to 480°C before enameling the molten aluminized steel plate. . 2 Surface roughness Rmax (according to JISB0601) is 2
．． The method for pre-enameling a molten aluminized steel sheet according to claim 1, wherein the skin pass process is performed using a skin pass roll having a diameter of 0μ or less. 3. The enameling pretreatment method for a hot-dip aluminized steel plate according to claim 1 or 2, wherein the rolling reduction rate in the skin pass process is 0.5% or more. 4 When the heating time is Z hours, the single-sided plating thickness after skin pass is xμ, and the heating temperature is y℃, the formula Z=x(0.0
00016y^2-0.0128y+2.5) Claims 1 to 3 in which heating is performed for a time longer than the time calculated by
A pre-treatment method for enameling a hot-dip aluminized steel sheet according to any one of paragraphs.