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Measures to reduce chromic acid regeneration and prevent aging by chromium plating

Ⅰ. Because of the accumulation of metal ions in chromium plating solution, especially the formation of trivalent chromium and trivalent iron, the PH value of chromium plating solution increases, which will eventually lead to the aging of chromium plating solution and cause the chromic acid solution to be scrapped or need to be treated with chromic acid regeneration.

Ⅱ. The accumulation of metal ions will deepen the color of the solution, increase the resistance and increase the cell voltage, which will eventually lead to the deterioration of the brightness of the coating, the decline of the depth ability, the roughness of the chromium layer and the deterioration of the adhesion, which not only seriously affects the chromium plating quality, but also increases the power consumption;

Ⅲ. The accumulation of metal ions mainly comes from the following aspects:

1. The effective area of anode in chromium plating bath is small, the current density of anode is large, and the reduction rate of trivalent chromium can not keep up with the production rate of trivalent chromium in cathode;

2, Poor or uneven conduction of anode affects the reduction efficiency of trivalent chromium;

3. The chrome-plated workpiece produces too many burrs, especially the tip effect at the upper and lower ends and the junction of bandaging leads to a large number of burrs. With the lengthening and densification of burrs, a large number of trivalent chromium will be produced inside the burrs;

4. The special deep hole in the exposed steel part of some complex workpieces is the place where more trivalent chromium is produced;

5, When the current efficiency of the solution is low, the formation rate of trivalent chromium is faster;

6, When sulfuric acid is too high, trivalent chromium will be produced in large quantities;

7, The dissolution of other metals in chromium plating bath will not only lead to the increase of trivalent chromium, but also cause the accumulation of these metal ions;

8, The ripple coefficient of power waveform is too large;

9, Chromic anhydride raw material has many metal impurities and high sulfuric acid content;

10, Reflux of chromium mist condensate;

11, Easily oxidized things or other dirt are brought into chromium plating bat

Ⅳ. In order to prevent the aging of chrome plating solution, the following preventive measures can be taken:

1. Make sure that the area ratio of the anode to the cathode is at least 2 to ensure the uniform conduction of the anode. Note that the current distribution of the anode is not uniform due to the distortion in the chrome plating slot. Only when the anode conducts uniformly and is always in a low current density state can the reduction efficiency of trivalent chromium be guaranteed.

2. Effectively prevent long-term shaving of workpieces, exclude discharge at the tip as far as possible, and also consider the excessive concentration of current when doing electrode protection. If the requirement of chrome thickness is very thick and leads to long chrome plating time, it is recommended to remove the shaving in the middle of the live state.

3. For deep holes, protect them by blocking as much as possible while keeping chrome plating unaffected.

4. Increase the current efficiency, pay attention to the combination of temperature and current, sulfuric acid and chromium anhydride content, and also add some chromium plating additives to improve the efficiency.

5. Prevent other metals from entering the slot, especially anode and cathode hooks, protective electrodes, bare metals, bipolar electrodes, etc. In addition, attention should be paid to the dissolution of metal impurity ions in the lead anode.

6. Pay attention to the ripple of chrome plated power supply. Excessive ripple factor not only causes chromium trivalent to rise, but also reduces the current efficiency, and ultimately affects the hardness and color of chromium layer.Therefore, in addition to choosing a rectifier with small ripple, we should always pay attention to whether the rectifier is out of phase due to burnout insurance (mainly older rectifiers) and whether the silicon tube is burned out.For large workpiece changes, try not to use thyristor voltage regulator rectifier;

7. High quality primary chromium anhydride is recommended.It is best to sample each batch of chromium anhydride before use and put it into use after meeting the requirements.

8. After the chromium fog from the exhaust fan has condensed, its sulfuric acid content and trivalent chromium content are also very high. It is recommended to centralize the treatment and return to the trough for use.

5. In summary, the existence of impurity ions is unavoidable, but how to prevent their rapid accumulation is especially important for chrome plating. Although it can be treated by various methods such as chromium acid electrolysis, it will affect production after all.If the design of chrome plating equipment, mastery of process and control of operation are processed dynamically to keep the chrome plating slot in a benign state for a long time, it will be of great benefit to the chrome plating production.

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