JPS6049820B2 - Manufacturing method of solar heat selective absorption stainless steel plate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses an acid oxidation method to produce a stainless steel copper plate that selectively absorbs solar heat. This is a stainless steel plate that selectively absorbs solar heat by polishing and immersing it in acidic oxidation to form a solar heat selective absorption film only on the mechanically polished surface, which has excellent resistance weldability as well as solar heat collection properties. This relates to a manufacturing method.

Conventionally, a heat collecting surface with high solar heat absorption efficiency and low re-emission rate of absorbed thermal energy is called a selective absorption surface, and the solar heat selective absorption plates that have been researched and developed to date are:
A chromic anhydride-sulfuric acid bath (U.S. Pat. No. 3,210,222 ) or an acidic oxidation method using a chromate-sulfuric acid bath (chromate 100-400911) sulfuric acid 400-800yIl) JP-A No. 52-3865 (Japanese Patent Publication No. 52-3865) has been proposed.

However, when these acidic oxidation baths are used, local corrosion (mainly intergranular corrosion) of the stainless steel base plate occurs during film formation, although this varies slightly depending on the concentration ratio of chromic acid anhydride or chromate and sulfuric acid. This causes problems such as a decrease in selective absorption and a deterioration in rust resistance in an atmosphere where chlorine ions are present, such as in a salt spray test.
The present inventors previously disclosed a method for solving the problems in the known acidic oxidation method in JP-A No. 57-79177.
However, as a result of further research, the method of the present invention was obtained.

In general, the method of manufacturing solar heat collector plates using acid oxidation method using stainless steel plates is to resistance weld the concave portions (between the water channels) of two stainless steel plates press-formed into mountain-shaped unevenness, and then perform acid oxidation. There are cases in which selective absorption coating treatment is performed by immersing in a bath, and cases in which resistance welding is performed after selective absorption coating treatment.

In the former method, the press-formed product is subjected to J-immersion treatment, so there are processing problems such as the number of sheets to be processed is limited compared to the case of processing unformed steel sheets, and uneven coloring is likely to occur in the welded part. In addition, the latter has slightly higher electrical resistance than the untreated board (material), resulting in inferior resistance weldability, and a selective absorption film is also formed on the back side of the solar sunset heat collecting surface (water channel side). It has the following problems. In the latter case, the present invention provides a method for manufacturing a solar heat selective absorption stainless steel plate with excellent resistance weldability, and in which only one side of the stainless steel plate has a roughness of RaO. After mechanical polishing to a thickness of 3 to 0.7 μm, 70 to 90 yIe of chromate
The present invention provides a method for manufacturing a solar heat-absorbing stainless steel sheet, characterized in that a selective absorption film is formed only on the mechanically polished surface by immersion treatment in an acidic oxidation bath containing 550 to 630 y1f of 1 sulfuric acid.

That is, the present inventors, when forming a selective absorption film on the surface of a stainless steel plate using the above acidic oxidation bath,
Focusing on the fact that the formation time of a selective absorption film is significantly shorter on a mechanically polished surface of a copper plate than on an acid-finished surface, we developed a stainless steel plate in which only one side of the stainless steel plate was mechanically polished. , Due to the time difference in the formation of the selective absorption coating, it is possible to treat only one side of the selective absorption coating, and the surface roughness can be adjusted to RaO. When the film is formed by mechanical polishing and adjusted within the range of 3 to 0.7 μm, the emissivity does not increase significantly, the absorption rate improves significantly, and subsequent resistance welding is easy. The present invention was completed by investigating this fact. The reason why the film formation time is significantly shorter when the mechanically polished surface is in an acidic oxidation bath is that the acidic film formed after mechanical polishing is a thinner oxide film ( This is because the reaction with the acidic oxidation bath is quick because it is an AlrfOrmed film).

Roughness is RaO. The reason for specifying 3 to 0.7 μm is that 0.
If the thickness is less than 3 μm, the absorption rate decreases, and if it exceeds 0.7 μm, the emissivity increases significantly and a clear black film cannot be obtained.

3. Also, regarding the method of adjusting the surface roughness,
A method using shot blasting (Japanese Unexamined Patent Publication No. 1124/1983) has been proposed as a pretreatment for solar heat absorbing stainless steel sheets, but in this case, unlike the case of surface polishing, the surface of the stainless steel sheet is Formed during pickling3. Because a dense passive film remained, a stainless steel plate that had been shot blasted on only one side was
Even if the steel sheet is treated in an acidic oxidation bath as described in Japanese Patent No. 79177, a steel sheet with a selective absorption film formed on one side cannot be obtained.
4CAlso, even if you use a stainless steel plate that has been mechanically polished on only one side,
A chromate monosulfuric anhydride bath (chromic anhydride 250yIe monosulfuric acid 500y1') and a chromate monosulfuric acid bath (chromate 100-00 da Iel sulfuric acid 400
-800y1', Japanese Unexamined Patent Publication No. 52-3865), it is not possible to obtain a steel sheet with a selective absorption film formed on one side. The advantages of having a stainless steel plate with a selective absorption film formed on one side are as follows. Compared to single-sided film coated plates, the electrical resistance is as low as that of the raw material, making resistance welding easier.

2. Because the film formation treatment is performed only on the surfaces necessary to absorb solar energy (mechanically polished surfaces), the reaction area with the acidic oxidation bath is reduced, which is advantageous in terms of the life of the treatment bath.

In the present invention, the electrical resistance of the steel sheet treated with the selective absorption coating was measured using the method shown in FIG.

That is, as shown in Figure 1, the diameter is 4.577r! T.L.
Rod-shaped electrodes 1, 1 of 200k9 are placed above and below the sample 2.
The resistance value was measured 3 seconds after applying a current of 1 A. According to this measurement method, 0.
3Tmm thick 19Cr-2M0 steel 0.32n1ΩIc
It is about A. If this resistance value is 1.6 mΩ or less, preferably 1 mΩIcTl or less, resistance welding is possible, but if the resistance value is 1.6 to 15.9111ΩIclt, welding may be difficult, and 15.9111ΩIc! t
It becomes impossible to weld. The method of the present invention will be explained below based on Examples. Example 1 19Cr-2M0 steel and SUS3O4O. 3Tfr!
An n-thick NO2B finished steel plate was mechanically polished using emery paper and treated in an acidic oxidation bath (80f1'Na2Cr2O7
After chemical conversion treatment at -600y1f1 (2S04108℃) for 17 to 18 minutes, heat collection characteristics (absorption rate and 100%
Emissivity ε100 considering the radiant energy distribution at °C
The measurement results are shown in Table 1.

Those having roughness within the range of the present invention have an absorption rate of 0.90.
Above, the emissivity ElOO is 0. Good heat collection properties were obtained with the roughness being below the ratio, but as shown in the comparative example, the roughness was 0.2μ
Below m, the emissivity ε100 is as low as 0.13 or less, but
The absorption rate is 0.87 or less, which is not good for heat collection characteristics.

Further, when the thickness is 0.8 μm or more, the absorption rate is relatively good, but the emissivity is significantly high at 0.30 or more, which is not good as a heat collection property. Example 219Cr-2M0 steel N
O2B finished steel sheets were subjected to selective absorption film formation treatment in various acidic oxidation baths, and the electrical resistance was measured. Table 2 shows the results.

NO. Samples 1 to 3 have a selective absorption coating formed on one side using the method of the present invention. Numbers within 0 are those with selective absorption films formed on both sides without mechanical polishing. The film formation treatment was performed with a bath composition of 1 to 3.
Those that were subjected to double-sided film formation treatment also showed electrical resistance values that were relatively close to those of the raw material, but those that were subjected to one-sided film formation treatment using bath compositions 1 to 3 of the present invention showed electrical resistance values that were comparable to those of the raw material. This value is significantly lower than that of Comparative Examples 4 and 5, indicating that the electric resistance weldability is excellent.

As explained above, the solar heat selective absorption stainless steel plate produced by the method of the present invention can form a selective absorption film on only one side without resorting to complicated processing means, and therefore has excellent weldability, making it suitable for solar heat collection. It is possible to form a solar heat selective absorption film on the surface of the stainless steel plate before welding and assembling the plate, making it possible to easily manufacture solar heat absorbing plates, resulting in significant cost reductions. etc., the effect is extremely large.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a method for measuring the electrical resistance of a plate treated with a selective absorption coating.

Claims (1)

[Claims] 1 One side of the stainless steel plate has a surface roughness of Ra0.3 to 0.
．． After mechanical polishing to within the range of 7μm, chromate 70-90g/l, sulfuric acid 550-630g
1. A method for manufacturing a stainless steel sheet for selectively absorbing solar heat, characterized in that a selective absorbing film is formed only on the mechanically polished surface by immersion treatment in an acidic oxidizing bath containing /l.