Signs of metal corrosion can be roughly divided into concave signs, convex signs and convex-concave signs. Basic requirements of corroded signs: beautiful pattern, clear lines, appropriate depth, flat bottom, full color, uniform drawing and consistent surface color. Characteristics of corrosion marks: strong weather resistance and solvent resistance; Even if the paint falls off, it still serves as a nameplate. Stainless steel is a special material, which has good corrosion resistance to atmosphere and fresh water. Good decorative effect can be obtained through wire drawing, corrosion and polishing. But the corrosion of stainless steel is much more difficult than that of copper plate and aluminum plate. The fastest corrosion method is electrochemical corrosion, also called electrolytic corrosion. Because electrochemical corrosion will make the ink fall off in the sign corrosion, the sign is not suitable for electrochemical corrosion, especially for fine patterns. We have to choose chemical corrosion. Chemical corrosion can be roughly divided into two types: strong acid corrosion and ferric chloride corrosion. Because the formula of strong acid corrosion is complex, maintenance is difficult, a lot of smoke is produced, and air pollution is harmful to human body, so manufacturers without purification equipment cannot use it. Ferric chloride corrosion formula is simple and easy to maintain and regenerate.

Formula of ferric chloride corroding stainless steel: ferric chloride, activator and water. The Baume degree of ferric chloride in the formula should be kept at about 42, and 0.8- 1.2 ml of active agent should be added to every liter of ferric chloride solution. The bottom surface of stainless steel corroded by this formula is smooth and flat, without black passivation film and pitting.

The factors affecting the corrosion of stainless steel by ferric chloride solution are as follows:

A. the influence of concentration. Chemical corrosion is also called microbattery corrosion. The more positive the redox potential, the faster the corrosion rate. With the increase of concentration, the redox potential becomes positive and the corrosion rate increases. Industrial grade ferric chloride has low purity and negative redox potential. When Baume degree is above 42, the redox potential can meet the requirements of stainless steel corrosion.

B. Effect of PH value of solution on corrosion rate. Low PH value is corrosive to stainless steel; When the PH value is too high, ferric trichloride is hydrolyzed into ferric hydroxide precipitate, which loses its corrosive effect. When corrosive liquid is used to a certain extent in production, the PH value should be adjusted.

C. influence of corrosive liquid temperature. The higher the temperature of corrosive liquid, the faster the corrosion rate. However, considering the bearing capacity of corrosion-resistant ink, the temperature should be controlled between 30-40℃.