JPS6044772A - Heat collecting plate for solar energy-powered hot water supplyer and its manufacture - Google Patents

Abstract

PURPOSE:To raise the manufacturing yield of products by enabling good solar energy absorptive film to be formed by a method in which the surface of a steel plate is treated so that a metal element-enriched layer in a reduced state is formed and then subjected to a bright annealing, followed by rust-proofing treatment before a selective absorption film processing. CONSTITUTION:A metal element(in reduced state)-enriched layer is provided on the surface of a stainless steel plate in a thickness of 50Angstrom depth at most. In forming a selective absorption film for solar energy collection, the steel plate is subjected to a bright annealing process under conditions to meet the relationships, 800<=y<=1,100, -70<=x<=-30, and 10x+1,390<=y, where (x) is the temperature of dew point in deg.C and (y) is the temperature of annealing in deg.C, in an atmosphere of ammonia decomposed gas, hydrogen, etc. Then, the steel plate is dipped in a solution composed of 10-50wt% sulfuric acid and 0-30wt% sodium bichromate at 80 deg.C for 30min at maximum.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a stainless steel plate for a solar heat selective absorption membrane and a method for manufacturing the same.

For the surface finish of cold-rolled stainless steel sheets, in addition to flattened 3 to JFA8 buffing finishes, BA finishes obtained by bright annealing (hereinafter referred to as BA) in a reducing gas (nitrogen dehydrogen) atmosphere are used.

By the way, with recent advances in steelmaking technology, 5US444 (1
8Cr-2Mo) BA finished steel sheets began to be produced, making it possible to obtain low-grade stainless steel. The main use of the steel plate in this BA finish is as a heat collection plate for solar water heaters, and in the BA finish, a chemical treatment is applied to the surface of the steel plate to form a solar heat selective absorption film in order to increase the heat collection efficiency. However, due to variations in BA processing conditions, there are cases where the selective absorption film formation process described above cannot be performed uniformly and reliably.
This results in a significant decrease in product yield.

Therefore, the present inventors investigated the surface properties of BA-finished steel sheets and
As a result of intensive research on the A treatment conditions, we discovered that if BA treatment is performed under specific conditions, a copper plate can be obtained that can reliably form a uniform selective absorption film.
This led to the present invention.

According to the BA processing method of the present invention, stainless steel sheet metal for solar heat collector plates can be obtained reliably, and the yield of the product is the same as 1, which greatly contributes to improving production efficiency.

Selective treatment of heat collector plates for solar mud water tank The film forming treatment is a surface treatment with a glaze, and in the temperature range below 110℃μ, for example, sulfuric acid bath, chromic acid-sulfuric acid bath, dichromic acid-sulfuric acid bath, etc. This is a method in which a film is completely deposited on the surface of stainless steel by immersing it in an acidic mixed solution containing selenium oxide and phosphoric acid in an acidic bath. In this treatment step, a dark blue film is formed on the surface of the stainless steel jJI4 plate through a chemical reaction. Therefore, whether or not this film can be formed reliably depends on the reaction rate of the chemical reaction on the stainless steel root surface in the solution. That is, this is due to the stability of the BA finished surface film, and the better the stability of this film, the faster the selective absorption film forming reaction will proceed.

The present inventors used X-ray photoelectron spectroscopy (ESCA), which can analyze the morphology of surface films, to analyze the surfaces of steel plates with good selective absorption films and steel plates with no good selective absorption films. The results shown in 1 were obtained. the result,
In the case of a steel sheet that can form a good selective absorption film, metal elements such as Fe%Cr% MO are present as simple substances, and niobium is reduced as NbO within a range of up to 50^ of the surface of the steel sheet that participates in the selective absorption film forming reaction. It was found that oxides exist in a highly reduced state with oxides on the surface of the steel sheet during BA treatment, which is an essential condition in order to ensure complete selective absorption membrane treatment. I gained knowledge.

As a result of various studies based on this knowledge, we found conditions that can be obtained by surface kBA treatment with the above-mentioned reduced state, and completed a method for manufacturing stainless steel plates for heat collection in solar lake water vessels.

The bright annealing performed in the present invention can reliably form a good selective absorption film for collecting solar heat if the following conditions are satisfied. As the annealing atmosphere, ammonia decomposition gas, hydrogen, etc. are used. Then, the dew point temperature is x (℃)
Bright annealing may be performed within a range that satisfies the following conditions: 3-800≦y≦1100 −70≦X≦−30 10x+4300≦y , where the annealing temperature is y (° C.). The selective absorption membrane formation process involves (10 to 50 wt%) sulfuric acid + (
0-30 wt%) sodium dichromate solution (80℃
) for up to 30 minutes.

As mentioned above, the reason 11 for limiting the annealing conditions in the present invention as described above is due to the results of the following examples shown in the attached drawings. The determination was made from the viewpoint of corrosion resistance and rust resistance during the period from BA treatment to selective absorption film formation treatment.

Hydrogen is used as the atmospheric gas to change its dew point, and H
BA treatment was performed under conditions where the A treatment temperature was changed. The obtained BA-treated steel sheets were evaluated as to whether the selective absorption film forming treatment was good or bad and were subjected to a rust resistance test. The results are shown as graphs in the attached drawings. The shaded summer region shown in this graph is the range of the present invention in which there is no risk of rusting between the BA treatment and the selective absorption membrane treatment, and a good selective absorption M can be formed. Region 1 is a range in which a good selective absorption film cannot be formed due to rusting, and region 2 is a range in which there is no rusting but a good selective absorption film cannot be formed. Therefore, by performing bright annealing under the conditions in region (3) in the graph of the attached drawing, the surface of the steel sheet is treated to have a metal element concentration layer in a reduced state, and rusting occurs during selective absorption film treatment 1 after BA treatment. Therefore, it is possible to form a good selective absorption film, which greatly contributes to improving the yield of products.

Note that similar results were obtained in the selective absorption membrane formation treatment using many of the other acid baths mentioned above.

The numbers in the symbols shown in the attached drawings are the values of current density measured by the method described below, and a selective absorption membrane with a good current density of 80 mA/ad or more was obtained.

The suitability of the selective absorption membrane is determined using an aqueous solution containing 10 to 50 wt% sulfuric acid and 0 to 30 wt% sodium dichromate at 15 to 50°C, as disclosed in Japanese Patent Application No. 58-80664. potential sweep speed of 50 m at a temperature of
The entire anode dispersion curve dl11 was determined under conditions of V/min or less, and those whose value exceeded 80 mA, Otsu-, were selected as suitable materials.

In addition, 1,1i11 rusting property was determined by performing a salt spray test in 5% saline solution at 35°C for 100 hours as specified in JISz2371, and visually determining whether or not there was any rusting on the surface.

Table-I BA treated stainless steel surface X-ray photoelectron spectroscopy analysis results

[Brief explanation of the drawing]

The attached drawing is a graph showing the relationship between the dew point of the atmospheric gas and the BA treatment temperature. Patent applicant: Kawasaki Steel Corporation 7-

Claims (2)

[Claims] (1) A heat collecting plate for a solar water heater characterized by having a metal element concentrated layer in a reduced state on the surface of a stainless steel plate up to a depth of at most 50X. (2) When manufacturing a heat collector plate for a solar water heater that has a metal element concentrated layer in a reduced state on the surface of a stainless steel plate up to a depth of at most 50X, the dew point of the atmospheric gas (total X (°C)), the bright annealing temperature ky ('C), the following conditions: 800≦y≦1100 -70≦X≦-30 10x+1300≦y A method for producing a heat collector plate for a solar water heater, characterized by performing bright annealing within a range that fully satisfies the following conditions: .