Analyze one by one: the reasons for the blooming and fogging of the chrome-plated layer!

There are many reasons for the blooming or fogging of the chrome layer, most of which are caused by the underplating layer or other external reasons. For example, there is too much saccharin in the nickel plating solution; the linear velocity of the nickel layer is polished; the polished part chrome plating has oil on the front surface Or there is a polishing paste; when nickel plating is out of the tank, a bipolar electrode is formed; the hanger does not spring tightly during chrome plating; the tin content in the copper-tin alloy bottom layer is too high; the temperature during chrome plating is too high; there is a problem with the chrome plating power waveform or the chrome plating solution Too much chloride ions, etc.

When analyzing the fault, you can take a batch of chromium-coated parts in other chrome-plating baths, and immerse the parts that are not blooming or fogging in the faulty chrome-plating bath for trial plating. If there is no other chrome-plating bath in this unit, you can just Good bright nickel-plated (unpolished) parts are immersed in newly prepared 5% (weight) sulfuric acid for 2 minutes, and after full activation, they are directly covered with chromium.

1

If the chromium layer obtained by applying chromium in this way is good, and there is no blooming or fogging, then the fault originated before chromium plating and has nothing to do with the chromium plating solution and the chromium plating power supply.

If it originated before chrome plating, different measures should be taken according to the specific conditions of each unit. If bright nickel plating is used to directly cover chromium, check whether there is too much saccharin in the nickel plating solution; whether there is a bipolar electrode phenomenon when the bright nickel is plated out of the tank, and whether the time between the bright nickel out of the tank and the chrome plating is too long and before chrome plating Whether the concentration of the sulfuric acid activation solution is too dilute or too high.

Too much saccharin in the nickel plating solution causes the chrome layer to bloom, which is generally more obvious on the tips and edges of the parts. At this time, the electrolysis method can be used to correct the chromium layer blooming caused by the bipolar electrode, which regularly appears on one side of the part (that is, near the side of the other cathode when the nickel plating is out of the tank).

At this time, turn off the power when the nickel plating is out of the tank or take out the parts when the current is adjusted to the minimum, or take out all the parts on the cathode at the same time for inspection and correction. The time between the bright nickel plating of the parts and the chrome plating is within 2 minutes. Generally, it is not necessary to perform sulfuric acid activation and directly cover the chromium. If the time interval is more than 2 minutes, it is best to use 3% to 5% sulfuric acid to activate the chrome. .

If you have doubts about the concentration of the activation solution, you can adjust it according to the analysis or replace it with a new solution.

2

If the parts are plated with dark nickel or semi-bright nickel and polished with chromium, pay special attention to the size of the polishing wheel and the degreasing and activation of the parts after polishing. Because the nickel layer is easy to passivate, the polishing wheel is too large, the rotating speed is too fast or the operator presses the parts on the polishing wheel when polishing, which will cause the nickel layer to increase in temperature during polishing and passivation. Covering chromium on the passivated nickel layer will cause blooming. This phenomenon is more likely to occur in summer.

The polished parts must be degreasing and activated. If the oil or polishing paste on the surface of the part is not completely removed, the chromium layer plated on the part is misty. If the concentration of the activation solution is too dilute, the nickel layer cannot be fully activated, which will cause the phenomenon of blooming similar to covering chromium on the passivated nickel layer; if the concentration of the activation solution is too high, there is no ability to activate the nickel layer, and It is oxidized, so the sulfuric acid activation solution with too high concentration will also make the chromium bloom. If the concentration of the activation solution is too high, it can be adjusted according to the analysis.

3

If the parts are copper-plated tin alloy polished and covered with chromium, in addition to checking the oil removal and activation after polishing, check whether the tin content in the copper-tin alloy coating is too high. high. Because the tin content is higher than 1 5%, using the general method to cover the chromium will produce the phenomenon of blooming. The method of inspection and correction is to immerse the polished and degreasing copper-tin alloy plated parts in 5% HF solution for 0.5min~lmin for activation and then cover the chromium, or put the copper-tin alloy plated parts in cyanide before chromium plating. Copper cyanide is flash-plated in the copper electroplating bath for about 10 seconds, and then chromium is applied.

4

If the fault originated in the chrome plating process, first check the temperature of the plating solution, whether the jigs are tight, and the waveform of the plating power supply. The current waveform of chrome plating is generally better to adopt pure DC, three-phase full-wave or six-phase double reverse star power supply. If one phase of the three-phase full-wave rectifier is broken, it will cause the chrome plating to bloom.

If after inspection, there is no problem in the above-mentioned aspects, then it may be that there are too many chloride ions in the chrome plating bath, and electrolytic chlorine treatment can be carried out.