JPS62135707A - Measuring method for chromate film adhesion quantity of chromate treated steel sheet - Google Patents

Abstract

PURPOSE:To easily measure and with a high accuracy the thickness of a film by reading a color difference of the film by a coloar-difference meter, and executing a treatment, based on a correlation of a measured value of the color- difference meter and the thickness of a chromate film. CONSTITUTION:A chromate film on the surface of a steel sheet shows a prescribed correlation between said film and a film which is measured by a color- difference meter. As for its color difference measurement, it is desirable that a correlation a shown in the figure is formed between a color difference (DELTAb) of a series (b) and the film thickness. Its coefficient of correlation is high such as >=about 0.95. That is to say, the vertical axis shows the film thickness (adhesion quantity: Cr-mg/m<2>), and the horizontal axis shows a color-difference meter measured value (DELTAb) in the series (b). A chromate treatment is done on a hot-dip galvanized steel, and results shown by a round mark and a black round mark in the figure show a clear correlation between the film thickness and the color- difference mater measured value respectively. Accordingly, by using this relation, its film thickness can be derived immediately from the color difference measured value of the film of the chromate treated steel to be measured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for measuring the amount of a chromate film deposited.

[Conventional technology]

Cold-rolled steel sheets and plated steel sheets (for example, galvanized steel sheets) are subjected to chemical conversion treatment such as chromate treatment or phosphate treatment as a base for painting or for temporary rust prevention.

Chromate treatment uses hexavalent chromium (CrO: +, Na
The treatment liquid is an aqueous solution whose main components are zc r 207 ・2 H2O, etc.) and an inorganic acid (mainly sulfuric acid), and the metal base is corroded by the acid, and some of the hexavalent chromium is reduced.
An insoluble hydrated oxide containing trivalent chromium is generated and deposited on the metal surface, forming a film. The film is amorphous gel-like and generally pale yellow to yellowish brown in color.

This chromate treatment is performed by a roll coating method or a spray method. The chromate treatment using the roll coating method is explained using Figure 2. (1
) is a processing liquid tank, (2) is a pickup roll (the lower surface of its body is immersed in the processing liquid in the processing liquid tank (1)), (3) is an applicator roll, and (4) is a steel plate guide. It's a roll.

The steel plate (S) is transferred along the circumferential surface of the body of the guide roll (4) in the direction of the arrow, and the treatment liquid (L) is transferred to the surface of the body of the applicator roll (3) via the pickup roll (2). From the applicator roll (3), it is applied to the surface of the fence plate (S) which abuts and transitions to the cavity surface.

Phosphate treatment, which is a typical chemical conversion treatment method along with chromate treatment, uses an aqueous solution containing primary phosphate as the main ingredient, and the free radicals that are generated when the main ingredient decomposes are used as the treatment solution. It consists of the corrosive action of phosphates on iron and the subsequent reaction to form poorly soluble phosphates (secondary and tertiary phosphates), which deposit on the steel surface and form a film. Become. This phosphate treatment is performed by passing the untreated steel plate through a treatment liquid tank and bringing the surface of the steel plate into contact with the treatment liquid.

It goes without saying that the film thickness formed by these treatments should be appropriately controlled and managed during the treatment so that the film does not shift in thickness or thinness and has a predetermined thickness.

Phosphate treatment is a reaction-type chemical conversion treatment as mentioned above, so the film thickness depends on the concentration and temperature of the treatment liquid and the rate of transfer of the steel plate into the treatment liquid (reaction time). /
If the tropism and liquid temperature are constant, the required constant film thickness (for example, 1.0 to 1.2 g/
It is possible to form a film of =>, and the film thickness can be controlled. ff1l
・There are no particular problems with management.

On the other hand, the thickness of the film formed by coating-type chromate treatment depends on the concentration and temperature of the treatment liquid, the circumferential speed of the roll,
It depends on the gear knob between the pink up roll/applicator roll and the applicator roll/steel plate, etc.
These become the film thickness control'+Wl factor.

[Problem to be solved]

However, in chromate treatment, even if the peripheral speed of the roll, the roll gap, the gear between the roll and the mouth plate, etc. are adjusted using the concentration and temperature of the treatment solution as indicators, the film cannot be formed to the desired thickness. Formation is extremely difficult in practice.

To deal with this, it is necessary to measure the thickness of the formed chromate film and feed it back to the roll coating device to control the circumferential speed of the roll, etc. in a timely manner.

The film thickness can be measured by dissolving and collecting the film formed on the surface of the steel plate with a chemical solution, quantifying the amount of chromium in the sample by atomic absorption spectrometry, and calculating the film thickness from the amount of chromium. There is a method of calculating the film thickness by spectroscopically analyzing the film using fluorescence X'+3. However, since the former measurement method using atomic absorption spectrometry is an off-line measurement method, it is not possible to control processing conditions by timely feed-hacking of measurement results during processing. On the other hand, the latter type of fluorescent X-ray analysis can be carried out online, and processing conditions such as roll peripheral speed can be controlled11 to obtain a predetermined film thickness based on the measured testis, but equipment costs are high. It is extremely expensive, and introducing J13 into an existing processing line poses many layout problems.

The present invention aims to provide a film thickness measuring method for solving the above problems.

Means for Solving the Problems] The method for measuring the amount (thickness) of a chromate film according to the present invention is to obtain the JIA H from the color difference of the film, and read the color difference of the film with a color difference meter. The method is characterized in that the thickness of the chromate film is determined based on the correlation between the color difference meter measurement value and the chromate film thickness.

[Effect]

The thickness of the chromate film on the surface of the steel sheet shows a certain correlation with the color difference of the film measured by a color difference meter. The color difference measurement is preferably performed in the range from yellow to blue, that is, in the b-series color difference (Δb), and a clear correlation is established between the b-series color difference (Δb) and the film thickness. Its correlation coefficient (r) is as high as about 0.95 or more.

The correspondence relationship between the thickness of the chromate film and the measured color difference value depends on the type of chromate-treated fence plate or the history of the steel plate, for example, whether it is a cold-rolled steel plate, a plated steel plate, or a galvanized steel plate. 1 (In the case of anti-galvanized metal, it is galvanized (like anti-alloy, it has been subjected to alloying treatment EIV after plating, or the plated metal has been subjected to spangle removal treatment (minimist spangle formation) Although there are differences in degree depending on the situation, the situation may differ depending on the situation.

Ru.

Therefore, by using a chromate-treated steel plate of the same type as the measurement target as a reference plate, and finding the correlation between the color difference measured on the reference plate and the chromate film thickness, and plotting this in a diagram, the chromate-treated steel plate of the measurement target can be calculated. The film thickness can be immediately determined from the color difference measurement values of the film.

〔Example〕

FIG. 1 shows an example of the correlation between the thickness of the chromate film and the measured value with a color difference meter. The vertical axis is +12 thickness (adhesion amount, Cr-■
/m), the horizontal axis is the color difference meter measurement value (Δb) in the b series
It is. The chromate-treated steel sheet is a hot-dip galvanized steel sheet (coating weight: 305 g/bo), and is marked with "○" in the figure.
The mark is a galvanized mesh plate that has been subjected to chromate treatment after being galvanized, and the plating layer is then cooled and minimized to spangles.The "・" mark is a plated layer that has been alloyed by heat treatment after galvanizing. This is a chromate-treated galvanized steel sheet. All chromate treatments are
A solution containing chromic acid as the main component and an organic substance or silica gel was used as the treatment liquid.

As is clear from the figure, there is a clear correlation between the film thickness and the color difference meter measurement values. The correlation coefficient is “
The symbol "○" indicates r = 0.986 (n = 30), and the symbol "." indicates r = 0.985 (n = 30).

〔Effect of the invention〕

According to the method of the present invention, the thickness of the chromate film can be easily and accurately determined from the color difference measurement values of the chromate film.

Therefore, by measuring the color difference of the chromate film and controlling the roll circumferential speed, roll gap, etc. in the roll coating device in a timely manner based on the measured value, the thickness of the chromate film can be easily and accurately controlled. be able to. The color difference measurement and control device is relatively simple and has low cost, so it can be easily introduced into existing chromate processing equipment.

Traditionally, reaction-type phosphate treatment has been used exclusively as a chemical conversion treatment for the coating base of galvanized steel sheets.
Recently, as a countermeasure to the problem of intergranular corrosion of galvanized layers and the resulting deterioration of coating film quality (bending workability, peeling resistance, etc.), efforts have been made to reduce the lead (PB) content of zinc plating. , Along with this, chromate treatment is being performed in place of conventional phosphate treatment. In order to cope with such a trend, the present invention has extremely great industrial significance.

[Brief explanation of the drawings] Figure 1 is a graph showing the relationship between the film thickness (adhesion amount) of the chromate film and the color difference measurement value of the film, and Figure 2 is a schematic illustration of chromate treatment using a roll coating device. . 1: Treatment liquid tank, 2: Pink asoprole, 3 Neabrifier roll L: Treatment liquid, S: Steel plate.

Claims (2)

[Claims] (1) Measure the color difference of the chromate film using a color difference meter,
A method for measuring the amount of chromate film deposited on a chromate-treated steel sheet, characterized in that the amount of chromate film deposited is determined based on the correlation between a color difference meter measurement value and the amount of chromate film deposited. (2) The method for measuring the amount of chromate film deposited according to item 1 above, which comprises measuring the color difference (Δb) in the b series.