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Hard chromium plating on chromium
Sep 19, 2017

Hard chromium plating on chromium refers to the size of the parts did not meet the requirements of process design, or because of wear and tear caused by dimensional deviation, the need for chromium plating on the base layer and then repair a certain thickness of chromium layer. The process of hard chromium plating on chromium is more complicated than that of hard chromium plating on base material. Because some parts are just plated, some are placed for a long time, some have been processed and polished. The main reason is that the surface of the chromium coating is easy to form a passive film in the air. The existence of this passivation film affected the bonding strength between the coating and the base metal during the second chromium plating. Only the passivation film was removed, the coating could be obtained. Chromium plating in order to achieve a good combination of the overall coating, the key to do the pre plating treatment and surface activation.

Skim. Remove the oil from the surface of the parts by the conventional method. After polishing, polishing and using heavy oil for a period of time, heavier parts, such as grease and polishing paste, are especially important.

Grinding. The burr on the surface of the chrome plating layer needs to be polished by the whetstone; some parts are covered with chromate film and so on because of the longer time they are placed. It is not easy to remove with the general method and needs to be carefully polished with sandpaper.

Preheating. After the parts are hung in the groove, the preheating time is selected according to the size of the parts, so as to reduce the temperature difference between the parts and the chromium plating solution, and avoid the phenomenon of sudden skin falling and peeling off because of the expansion coefficient of the base and the chromium layer. This step is more important for chrome plated parts.

Anode treatment. There is a layer of chromium on the surface of the part, and the anode treatment is to make the surface more rough and increase the bonding force. The time of anodic treatment should be determined according to the thickness of the existing chromium coating. The coating is thin for a few seconds, and the coating is thicker, up to 2 ~ 3min.

Normal plating. The activation of chromium layer by step current is the most important step in the whole cladding process. First use 5A / DM2 current density processing 3 ~ 5min, and then 10 ~ 15min time, the current density gradually increased to 20 ~ 25A / DM2 between, in this current density l0min plating, and finally into the normal electroplating.