Color technology and process flow of stainless steel chemical coloring

Color technology and process flow of stainless steel chemical coloring

Experiments show that, within the effective coloring range, the film thickness continues to increase with the coloring process. At first, the thin oxide film shows blue and brown, then the film shows golden yellow and red with medium thickness, and then the film shows green with thick film. There are altogether 4 primary colors and about a dozen intermediate colors.

(3) the influence of the composition change of the surface oxide film on the composition change of the surface oxide film, will change the refractive index of the oxide film, even if the surface thickness is the same, the color of the interference color will also change.

4. Chemical coloring of stainless steel

In 1972, the Inco process was proposed by the European research and development center of Inco.

This process is to dip the polished stainless steel into the mixture of chromic acid and sulfuric acid at 80~90℃. With the extension of time, the oxide film of different thickness will be generated on the surface, and different colors will be produced due to the interference of light.

When the composition and temperature of the solution inevitably change slightly during the working process, the color with good reproducibility cannot be obtained.

In order to overcome this problem, inco adopted the potential difference control method based on Evans' research, and the color stainless steel coloring process started on the road of industrial development.

At present, more than a dozen companies in Britain, America, Germany, Italy, France, Australia and other countries have adopted intech technology patents, forming a large-scale production.

As a result of solving a series of problems, finally make the obtained color stainless steel with bright colors, ultraviolet radiation resistance, wear resistance, corrosion resistance and good processing performance and other outstanding advantages.

So that the color stainless steel in 1976 after the real development.

Colored stainless steel has become a widely used material in foreign countries.

Companies in a number of countries have set up bases for production, and those who have mastered the technology have built up a complete set of stainless steel surface hangings, patterns and colors with the greatest commercial potential.

In 1980, the British knin company produced 100,000 square meters of colored stainless steel, and Japan took the leading position in the production of colored stainless steel when it reached 170,000 square meters (1000t).

(1) composition and process conditions of chemical coloring solution by genetic method

Solution composition: sulfuric acid (h2SO4,d=1.84) 490g/L

Chromic acid (CrO3) 250g/L

The color solution temperature is 70~90℃

Depending on the time of immersion, the order of colors produced is: bronze, blue, gold, red, and green.

There are two control methods for coloring

(2) time control coloring method will be immersed in the stainless steel coloring solution for a certain amount of time, you can get a certain color.

For example, when the temperature is 70℃, the color can be blue for 15min, golden yellow for 18min, and purple or green for 20~22min.

This time - controlled method does not yield repeated colors.

This is because the temperature of the coloring solution changes slightly, so the control is not very accurate, and the chemical composition of the chemical coloring solution may also change due to water evaporation, both of which can affect the reproducibility of the color obtained.

(3) potential control staining method when stainless steel with platinum electrode immersed in the fluid of the color, as shown in figure 1 stainless steel coloring device schematic, potential recorder on the stainless steel connections, even on the platinum electrode potential correction instrument, the coupling between the two wires, due to the stainless steel and platinum electrode potential, the potential difference, as the coloring of stainless steel chemical reaction process, increasing the thickness of the oxide film, with potential change.

In the whole process of coloring, that is, the time curve of coloring potential was measured.

FIG. 1 schematic diagram of stainless steel coloring device

Potential - point B on the time curve indicates that the potential of the stainless steel has reached the most negative point.

B is called the pick up potential.

Pick up refers to the stainless steel surface began to appear black marks, indicating that has formed a layer of light interference caused by oxidation film, began to change color direction.

Pick up potential from point B, with the extension of time, the potential of stainless steel gradually decreased to point C, point C called coloring potential.

B, C = Δ bits, referred to as the colouring potential difference.

FIG. 2 potential-time curve of stainless steel coloring

All sorts of color of colouring potential difference Δ bits is as follows:

Blue Δ bits = 8 ~ 11, mv film thickness of 0.09 microns

Yellow Δ = 13.5 ~ 16 bits of mv, film thickness of 0.15 microns

Red Δ bits = 17.8 ~ 18.5 mv, film thickness of 0.18 microns

Green Δ bits = 20.8 ~ 21.6 mv, film thickness of 0.22 microns

Certain color appears in a potential difference, and the relationship does not change with the change of temperature and solution composition of the color solution. This is the reason why the color can be colored by the control potential difference method. The control time has good reproducibility.

(4) stainless steel coloring process microcomputer control equipment color adjacent potential difference is very small, only a few millivolts, need precision voltmeter (such as TH - V digital voltmeter) to distinguish.

This will bring great inconvenience to the actual operation, which requires the equipment to have very high precision and anti-interference, otherwise the error of the instrument itself will lead to control errors.

If mass production, more to consider the use of microcomputer automatic control.

The use of electronic computer automatic control, when reaching a potential difference, in line with a certain color requirements, immediately issued instructions, start the lift, take out the colored stainless steel, as shown in figure 3.

At present, the main gap between China and advanced countries is the color of electronic monitoring equipment.

This kind of equipment has been used in industrial production abroad and can get repeated colors, but it has not been reported to be used at home. Therefore, it is urgent to develop electronic monitoring equipment for coloring.

FIG. 3 microcomputer control equipment system diagram of stainless steel coloring process

1 -- dyeing solution;

2 -- P1 reference electrode;

3 -- stainless steel sample;

4 -- digital millivoltmeter;

5 - microcomputer;

6 - digital-to-analog converter;

7 -- analog recorder