Chromateplate process description

1. Chromate plating

• Definition: chromium is deposited as a coating on other metals.
• Passivation: the metal is oxidized by strong oxidizing agent or electrochemical method, so that the surface becomes inactive process, is to transform the metal surface into a state that is not easy to be oxidized, thus delaying the corrosion rate of the metal method, chromium metal is very easy to passivation in the air, the surface formed a thin passivation film.
• Hardness: has a high hardness, according to the composition of the bathing and processing conditions, its hardness can be changed in a wide range of 400～1200HV.
• Heat resistance: chromate plating layer has good heat resistance, heating below 500 centi-degree, its gloss , hardness have no significant change, the temperature is greater than 500 centi-degree began to oxidize and discolor, greater than 700 centi-degree then hardness began to decrease.
• Friction factor: the factor of friction is small, especially the dry friction factor, which is the lowest in all metals, so the chrome-plated layer has good wear resistance.
• Chemical stability: it does not function in alkali sulfide, nitric acid and most organic acids, but is soluble in hydrochloric acid (such as hydrochloric acid) and hot sulfuric acid.
• Gloss: the reflectance of chromium is about 65%, between silver (88%) and nickel (55%), and because chromium does not change color, it can maintain its reflectance for a long time when used, which is better than silver and nickel.

2. The process flow of copper/nickel/chromium system on steel matrix is：
Degreasing (ultrasonic)~ water washing~ etching ~ flash copper cyanide plating OR flash nickel plating (alkali copper plating)~water washing~acid copper plating~water washing~ bright nickel plating~water washing~chrome plating ~water washing~drying (oven).