JPH068512B2 - Coated steel plate for enamel - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a coated steel sheet for enamel, and particularly to provide a steel sheet that enables production of enamel products free from nail skipping and bubble defects.

(Prior Art) As is well known, defects in enamel products include nail skipping, bubbles, and poor adhesion, and defects are likely to occur when the combination of enamel steel plate and glaze or pretreatment is inappropriate.

Nail skipping is caused by the enamelling glaze at the time of firing or hydrogen generated by the decomposition of water in the atmosphere of the firing furnace enters the steel, and gathers at the interface between the steel plate and the enamel coating during cooling, and the enamel film is released by the pressure of the hydrogen gas. It is thought that it was caused by being splashed.

Therefore, as a method of improving the nail flying resistance, inclusions in steel,
A method of increasing the amount of precipitates and occluding hydrogen in the vicinity thereof has been conventionally known, and examples include Ti-C, Ti-S and Ti-REM.
In the -S system, there are JP-A-48-222, JP-A-52-131919 and JP-B-54-3447, and in the BN system, there are JP-A-58-1013.

On the other hand, bubble defects include copper heads, pinholes, etc. These are considered to be mainly CO in the steel [C] and carbide decomposed during firing to form COx gas, resulting in bubble defects. As a preventive measure or a measure for improving workability, decarburization is performed during molten steel or during firing.
53 and JP-A-51-6813.

However, it seems that inclusions on the surface of the steel sheet are related to the cause of the bubble-based defects, in addition to the [C] source, and it is not easy to completely prevent nail popping and bubble defects at the same time.

(Problems to be Solved by the Invention) The present invention is to provide a coated steel sheet for enamel, which is intended to simultaneously prevent nail skipping and bubble defects that occur when the enamel product is made.

(Means for Solving the Problem) In order to provide the above steel sheet, the present invention is characterized in that oil is adhered to the lower layer of the enamel glaze layer.
That is, a rust preventive oil layer has 0.2 to 5.6 g / m ^{2 on} one surface of a enamel steel plate having a surface roughness of Rmax of 7.2 to 55 μm, and has a enamel glaze layer on the layer. Another object of the present invention is to provide a coated steel sheet for enamel.

In general, enamel steel sheets are completely degreased and then pickled or Ni.
It is common knowledge to apply glaze after plating and neutralization, and it is essential to complete degreasing or a state close to it, so as in the present invention, it is used as the lower layer of the glaze of the glazed enamel steel plate. However, it is a product that cannot be thought of by conventional wisdom that makes oil adhere.

Hereinafter, the present invention will be described in detail.

By the way, the steel sheet of the present invention is a steel sheet for enamel whose surface roughness is adjusted, and (1) rust preventive oil and a glaze layer or (2) Ni on the surface thereof.
It consists of three or four components: a plating layer, rust preventive oil and a glaze layer.

First, as a steel sheet for enamel, the composition adjustment and decarburization or denitrification treatment in the steel making and annealing stage, heating, hot rolling finishing temperature, coiling temperature, cold rolling rate, annealing conditions and temper rolling, etc. Defects such as precipitates, inclusions and dislocations are adjusted to make them suitable for enameled steel sheets.

And, the surface roughness of these steel sheets is 7.2 to 5 in Rmax.
Adjust to 5 μm. The surface roughness is generally adjusted by pickling, dull roll rolling, polishing (grinding, paper, shot blasting, electric discharge machining, etc.) and grinding. Here, the surface roughness Rmax is represented by the average value of Rmax in the L and C directions on the front and back surfaces of the steel sheet. In the case of one-sided enameled, only the surface on which the enameled is applied is enough.

When the surface roughness is less than 7.2 μm in Rmax, the oil film thickness on the entire surface of the steel sheet tends to be uneven when rust preventive oil is applied on top of it, and when the enamel glaze is glazed and baked, the molten glaze Due to the surface tension, glaze shrinkage occurs, and a part with the glaze attached and a part without the glaze are produced on the steel plate.

In addition, the glaze easily floats due to the decomposition gas of oil during firing. In order to have the anchoring effect of oil and glaze on the steel plate, a roughness of Rmax of 7.2 or more is required, while the number of peaks per inch, PPI is about 25 to 300 peaks /
In inches, the centerline average roughness Ra is about 0.6-4.0 μm.

Rmax of more than 55 μm requires pickling, requires a long time, and a large amount of smut (dirt) adheres to the surface of the steel sheet, which easily causes bubble defects in the enamel product, and the roughness of dull rolls. If it is more than 55 μm, it is difficult to adjust the roughness of the roll surface and the wear of the roll surface during use is severe. Therefore, it is necessary to change the roll frequently, which is disadvantageous in terms of cost.

Furthermore, shot blasting is suitable for roughening the surface of the steel sheet, but in order to make Rmax over 55 μm, it is necessary to make shot injection pressure extremely high, which results in high cost in terms of equipment and power consumption. It is a disadvantage. From the above, the appropriate roughness is set to Rmax 7.2 to 55 μm.

Next, as rust preventive oil, JIS NP-0 ~ 11 and NP18 ~ 20
It is classified into 15 types, and those that are usually called rust preventive oil, lubricating oil, machine oil, etc. are included, and a vaporizing rust inhibitor is also considered to be effective.

The action and effect of the oil coating of the present invention is that the enamel glaze softens at about 500 to 600 ° C. at the time of temperature increase during firing, the oil decomposes and burns at a low temperature until it melts, and water and oxygen in the glaze are evaporated and removed. By doing so, it is considered possible to reduce or prevent the generation of the nail jump and the foam.

The appropriate coating amount is 0.2 to 5.6 g / m ^{2 on} one side.

If the amount of oil applied is less than 0.2 g / m ^{2 on} one side, a part that is not applied with oil may occur, or it may not change from a normal degreased steel sheet that is too small, and the oil burns during firing, which is the main effect of the present invention. Insufficient to dry water or expel oxygen in enameled glaze,
This is because the effect of oiling is lost.

Furthermore, if the amount of oil applied exceeds 5.6 g / m ^{2 on} one side, oil burning and a large amount of decomposed gas are generated during firing, and the enamel glaze floats above the steel plate, peels off, or partially floats up and glazes. Is likely to occur and the cost is high.

Among the above rust preventive oils, it is desirable to use one having a flash point of 98 ° C or higher. Oil with a flash point of less than 98 ° C is burned during firing, and a large amount of decomposed gas is generated in a short time when the temperature is low. The unmelted enamel glaze adhering to the upper surface of the oil is floated from the steel plate surface and peeled off. Therefore, it is recommended to use a small amount of oil or a mixture with high temperature flash point.

Oiling is generally performed by spraying, a roll coater, dipping, a flow coater, brush coating or the like. It is a spray for long objects,
After coating, use a roll to make the coating amount uniform. If a small amount is applied uniformly, electrostatic coating is used.

Alternatively, the steel sheet may be plated with Ni and then applied with oil. That is, after adjusting the roughness of the surface of the steel sheet, degreasing, pickling, and then heating at about 70 ° C., a few% NiSO ₄ aqueous solution (pH 2.5 to 3.
It is immersed in 0) for about several minutes for plating, then neutralized and dried, and the above rust preventive oil is applied. The effect of Ni plating is effective in preventing defects in enamel products, but particularly improves the adhesion of enamel film to steel sheets.

Next, the oil-coated steel plate is used as a flat plate such as a white plate or a panel, or is bent, pressed, welded or the like to be processed into a molded product for each application. In pressed parts and the like, sufficient oil remains in the recesses of the roughness of the steel sheet, which is sufficient as it is.

Thus, the enamel glaze is applied to the oiled steel plate for enamel. Enamel glaze is a glassy material (frit) that has been melted and crushed after quenching, and is then finely pulverized to about 200 mesh (slip) with a ball mill etc. by adding a floating agent, a coloring agent, and water. Depending on the application, various additives may be added.

Glazing includes spraying, dipping, electrostatic spraying, electrophoresis, etc., and is performed on one side or both sides of the steel plate. In general, there are two firings, two firings, one firing and one firing.
850 to 920 ℃ at high temperature, 800 to 870 ℃ at the top or once
It is baked at medium temperature.

After glazing, dry at room temperature to 100 ° C for several tens of minutes, about 800 to 920 ° C
Bake in an oven or dry, bake, and cool in a continuous oven to make enameled products.

For A and A plated steel sheets, a glaze that is fired at a low temperature of 400 to 600 ° C. is used.

Enamel products manufactured from the products of the present invention have corrosion resistance,
Excellent in heat resistance, abrasion resistance, chemical resistance, rich colors, etc., water heater, bathtub, stove, range, kettle, bowl, pot,
Used in pots, rice cookers, sinks, chemical or brewing containers, building panels, whiteboards, heat exchangers, etc.

(Example 1) From the steel sheet obtained by washing the 2.3 mm-thick hot rolled steel sheet for enamel with hydrochloric acid and the 0.8 mm-thick cold rolled steel sheet (0.8% temper-rolled) of the components (% by weight) shown in Table 1 to 150 A sample of × 100 mm ² was sheared, degreased with an alkaline solution, pickled in a 10% sulfuric acid bath for several minutes to adjust the roughness, and then neutralized. The rust preventive oil was uniformly applied with a bar coater by changing the seed and the amount of oil applied.

The glaze (slip) containing frit A and B as the main components in Table 2 was glaze sprayed, dried at 100 ° C for 30 minutes, baked, air-cooled, and various enamel properties were measured. The results are shown in Table 3 and Table 3. It is shown in Table 4. The conventional products are those produced without pickling rust preventive oil after pickling.

As can be seen from Tables 3 and 4, before glazing with enameled glaze, 0.2 to 5.6 g / m ^{2 of} one or a mixture of various rust preventive oils was applied on one side, and products enameled were copper. There was no head or nail jump, and the adhesion was good.

Contrary to this, the conventional manufacturing method, in which the degreasing and pickling is applied as it is and glazed and enameled, has many copper heads. Also, if the amount of oil applied is too large, such as more than 5.6 g / m ^{2 on} one side and 8 g / m ^{2 on} one side, glaze will occur. The adhesion is 8
0% or more is the standard for passing.

(Example 2) As in Example 1, the 0.8 mm thick cold and thin enameled steel plate of Table 1 was sheared to 150 × 100 mm ² , degreased, pickled, # 120 paper polished, shot, or a combination thereof. After adjusting the roughness of the front and back surfaces of the steel plate to 6.5 to 55 μm with Rmax, apply oil and glaze B enamel glaze B shown in Table 2 on the upper layer, and after drying 850
Table 5 shows the results of investigating various enamel properties after firing at ℃ for 3 minutes and air cooling. Incidentally, the comparative product is one which has been enameled in the usual enamel manufacturing process.

Table 5 shows the influence of the roughness of the enamel steel sheet before glaze, and when Rmax was set to a roughness of 10 to 55 μm, various enamel properties were extremely good.

(Example 3) In the same manner as in Example 2, the enamel glaze was applied to both sides once using the glaze C, and the drying condition after the glaze was 100 ° C for 30 minutes, 5 minutes.
It was baked at 0 ° C. for 30 minutes and at room temperature for 30 minutes (natural drying) and then baked. The results obtained in Table 6 are shown together with comparative products.

In Table 6, the product of the present invention was applied to both sides once.
Was good even at 7.2 μm. As the drying conditions for the glaze, normal temperature drying to 100 ° C. drying were also satisfactory.
Furthermore, the Ni-plating treatment gives good adhesion even if the enamel is applied once on both sides.

It should be noted that in the comparative method, due to roughness adjustment and selection of steel type,
Peeling of the enamel film and poor adhesion (less than 80%) have occurred.

(Effect of the invention) The enamel coated steel sheet according to the present invention has good enamel properties and can prevent enamel defects as compared with the conventional enamel steel sheet, so that its economic effect and work efficiency are extremely large.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kazuhisa Yamashita Kazuhisa Yamashita 1 Fuji-machi, Hirohata-ku, Himeji-shi, Hyogo Nippon Steel Corporation Hirohata Works (72) Inventor Masayuki Matsuda 1 Emitsu Edami, Hachiman-ku, Kitakyushu, Fukuoka -1-1 Inside the Yawata Works, Nippon Steel Corporation

Claims (2)

[Claims] 1. A rust preventive oil layer of 0.2 to 5.6 g / m ^{2 on the} surface of a enamel steel plate having a surface roughness Rmax of 7.2 to 55 μm.
A coated steel sheet for enamel which has one surface and has a glaze layer for enamel on the layer. 2. The coated steel sheet for enamel according to claim 1, further comprising a Ni plating layer between the steel sheet and the rust preventive oil layer.