Analysis of chromium plating failure: high plating voltage, no bubbles at the cathode, cracks and hook marks on the plating layer
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1 During electroplating, the voltage is high, but there are no bubbles on the cathode Chromium plating During production, sometimes after stopping plating for a period of time, when the power is turned on again, the voltage will be very high, the current will be very small or even no current, and there will be no bubbles on the cathode The resulting phenomenon. The possible reasons for this type of failure are: poorly conductive lead chromate is formed on the anode surface; poor circuit contact; the anode area is too small or the electroplating power supply is faulty. When this type of failure occurs, first check the area of the anode. If the area of the anode is sufficient, turn on the power, hang the hanger from the cathode, and then use a copper wire or thin wire to connect one end to the conductive part of the cathode hanger. The other end touches the anode and strokes. If a spark occurs at the stroke, it indicates that the circuit is in good contact. Otherwise, there is no electricity between the anode and the cathode, and the poor contact parts should be found and corrected. If it is not that the circuit is in poor contact, then take out the anode and observe whether there is yellow lead chromate on its surface. If there is a yellow film on the surface of the anode, take out all the anodes, brush off the yellow film with a wire brush, and then hang it into the cell for electrolysis when it is energized. If the voltage drops and the ammeter pointer can rise when energized after this treatment, it indicates that the fault is caused by the formation of poorly conductive lead chromate on the surface of the anode. If it is not for the above reasons, it may be that the electroplating power supply is faulty, and the power supply should be checked and the fault should be eliminated. 2 There are obvious cracks on the chromium layer Decorative chrome plating often has network cracks, but such cracks are not easy to detect with the naked eye. The crack referred to here is a crack that can be discerned by the naked eye. The possible reasons for this kind of cracks are: too low temperature and too high cathode current density, too high sulfuric acid content or too low chromic acid content in the chrome plating bath, too much chloride ion content or too much stress on the underlying nickel. The cracks of the chromium layer usually become thicker with the concentration of chromic acid, the ratio of Cr03/H2S04, the decrease of temperature and the increase of cathode current density. So when there are obvious cracks in the chromium layer, first check the temperature, cathode current density, Cr03 and H2S04 content. If it is not the above reason after inspection, check whether the chloride ion content in the plating solution is too much. Generally speaking, too much chloride ion content will also cause poor brightness and blooming of the chromium layer. If these phenomena do occur, electrolysis can be used to remove C1 one for a period of time to observe whether the cracks in the chromium layer are alleviated. If the cracks are not alleviated and the chromium layer is very bright, then it may be that the stress of the bottom layer of nickel is relatively large. It is necessary to find out the reason for the high stress of the bottom layer of nickel, and then correct it (generally speaking, the bottom layerExcessive chloride ions, secondary brighteners, iron impurities and organic impurities in the nickel plating solution will increase the stress of the nickel layer). 3 After chrome plating, there are obvious hook marks on the parts Some parts have obvious hook marks after chrome plating. The possible reasons for this failure are: there is a hook print before chrome plating; the contact point of the hook is too thick; the anode area is too small or the conductivity is poor, the chromic acid content in the chrome plating solution is too low; there are too many trivalent chromium or foreign metal impurities; Or there may be NOF and so on. When analyzing the fault, first check the condition of the hook mark on the plating layer before chrome plating. The reason for this phenomenon is sometimes due to abnormal bright sulfate copper plating solution, and the plating layer is not bright at low current density, resulting in obvious hook marks, sometimes bright nickel plating A certain amount of copper or zinc impurities in the liquid, or too much secondary brightener will also produce obvious hook marks on the bright nickel layer. When there is such a fault, check it layer by layer. As long as you observe carefully, this phenomenon can be distinguished. If the fault originated in the chrome plating process, check the contact point of the hook, the anode area and anode conductivity, and the chromic acid content in the chrome plating solution. If the fault has not been eliminated after inspection and adjustment, then use electrolysis to remove NO3 or reduce trivalent chromium. After a period of electrolytic treatment, try plating to observe whether the fault phenomenon is improved. If it improves, continue electrolysis until the fault is eliminated. If the above correction is improved, but there are still some less obvious hook marks, you can add about 0.5g/L of fluorosilicic acid to the chrome plating solution, and at the same time add an appropriate amount of CrO3. Generally speaking, this can make the hook mark shrink or disappear. |