The range of operating conditions for decorative chromium plating is relatively narrow, and the operating conditions need to be changed accordingly with the shape of the plated parts. If you do not pay attention to the plating layer, different defects will occur, and it needs to be stripped and then plated. However, no matter what method is used to remove the original coating, it cannot be directly re-plated, otherwise the chromium layer will not be deposited, or the chromium layer will be bloomed. For example, the chromium layer cannot be directly deposited on the nickel surface after the chromium is removed by the anodic method in the alkali solution. This is because the surface of the nickel layer is oxidized during the anodic treatment process. It will bloom. However, if the following measures are taken, it can be solved very well.
(1) Removal method in dilute hydrochloric acid. First wipe off the oil and other dirt on the surface of the stripped piece, then bind it with nickel-plated copper wire, strip it in 1:1 clean hydrochloric acid, take it out from the acid after stripping, rinse it with clean water and dry it. Instant chrome.
Note: After the chrome layer is removed and between the chrome plating, the plated parts should not be in contact with the dirt. The hydrochloric acid used must be clean. , a replacement layer will be produced, which can only be removed by mechanical polishing, and the replacement layer cannot be removed where the polishing cannot reach.
(2) Combined removal method of anode and cathode in lye. This method can be carried out directly in the electrochemical degreasing solution. After the chromium layer is completely removed, the polarity is exchanged, so that the plated parts are in the negative pole, energized for 5-10S, and then rinsed with running water, weakly corroded, etc., and then re-chrome-plated. .
(3) Combined anode in lye and cathode in acid solution. After the chrome layer is completely removed, move the workpiece to the aluminum anodizing tank for cathode treatment after rinsing: voltage 8-10V, time 3-5S.
(4) Anode stripping in lye, combined stripping method of galvanizing and dilute hydrochloric acid stripping. After the chromium layer is removed, it is rinsed and moved to the chrome plating bath for 1 min of zinc plating at the normal current density, then removed with dilute hydrochloric acid, and re-plated. The method of adopting the combined stripping method is to use the atomic hydrogen generated during the zinc stripping activation in the reducing acid to activate the surface of the nickel, and to plate chromium on the activated nickel layer, and the effect is quite good. Even so, it is necessary to prevent the contamination of the stripping solution from affecting the cleanliness of the surface of the stripped part, and the bound copper wire needs to be plated with nickel for 1-2 minutes first, so as to avoid binding marks when bound with bare copper wire.
Replating after hard chrome stripping is often difficult, or even partially or completely free of chromium deposition. This is mainly due to the severe hydrogen permeation of the plated parts during the first chromium plating process and the release of a large amount of carbon during the chromium stripping process. The situation is particularly serious for chrome plating of castings. Since castings contain a large amount of carbon, and there are shrinkage cavities, pores, cracks, slag inclusions and sand holes, etc., the hard chrome layer should be removed and then plated according to specific conditions.
The thin layer of chromium on the general carbon steel material can be removed by referring to the electrolytic removal method of decorative chromium, and this method will not cause problems when re-chrome plating. It is difficult to plate chromium after the chromium plating layer is thick, or the chrome plating layer on the surface of cast iron parts or alloy steel parts is removed. Often only hydrogen and oxygen are violently removed without seeing the deposition of chromium, resulting in The reason for this phenomenon is mainly due to the hydrogen permeation during the initial chromium plating, which leads to a smaller hydrogen overpotential during chromium plating after stripping.
The only way is to add a hydrogen drive process after the original chromium layer is removed. The hydrogen drive method can be baked in an oven as usual, or it can be treated in the bluing solution for 1-2 hours according to the normal bluing process, and then retreat Hair removal film. Chromium plating after hydrogen displacement treatment by one of the above two methods can obtain satisfactory chromium plating layer
