Misting, graying, or blackening of the electroplated coating on electric heating tubes

Misting, graying, or blackening of the electroplated coating on electric heating tubes

This fault mainly occurs in the low current density area, with many factors causing it and a higher frequency of occurrence.

(1) High or low concentration of main salt can easily occur. Too high, fast deposition rate, good coating brightness, no scorching in high current density areas, but fogging, graying or blackening in low current density areas; If it is too low, the deposition rate and brightness will decrease. Can analyze the plating solution for adjustment, or conduct Hull cell tests. Do not blindly add main salt, as slight carelessness may make it difficult to remove faults.

(2) The concentration of conductive salt is low, and the coating in the low current density area has high voltage and low current opening, except for fogging, graying, and blackening; The current is slightly higher, the coating in the high current density area is burnt, and the brightness is lower. Both analytical adjustments and Hull cell tests can be ruled out.

(3) When the concentration of the cylinder opening agent is low, the dispersion ability and deep plating ability decrease, and the coating in the low current density area will become foggy, gray, and black. Accurate judgment can be eliminated by adding appropriate supplements, but avoid adding too much.

(4) There are many foreign metals and organic impurities in the plating solution. If it is impurities such as copper and lead, additives have hidden functions and do not need to be treated. Generally, it is caused by excessive decomposition products of additives. At this point, the solution becomes slightly cloudy and requires the addition of activated carbon for filtration and removal.

1.4 Rough coating

(1) There are many solid particulate impurities in the solution, mainly from insoluble substances produced by anodic dissolution. The organic decomposition products of additives are best treated and filtered with activated carbon.

(2) Fe3+increases in the plating solution, which is generated by oxidation of the main salt Fe2+. In the oxidation reaction, H+in the solution decreases due to consumption, and the pH value increases. Fe3+generates insoluble hydroxide solid particles from the colloidal state, and adsorbs on the coating, resulting in roughness. Fe3+is abundant, and the solution is turbid, showing a slightly brownish yellow color. In severe cases, it appears brick red. At this point, add 0.5-1.0gL of reducing agent to reduce Fe3+to Fe2+, restore the solution to clarity, and eliminate the malfunction.

(3) The content of additives (carrier brightener) is too low. Add the cylinder opening agent to the new tank at a rate of 12.

(4) The relative distance between the anode copper rod and the cathode copper rod is too close, resulting in a distance of less than 150mm between the zinc plate (anode) and the hanging tool (cathode). Change the hanging fixture design to adapt.

(5) If the content of zinc chloride in the main salt is too high, the solution can be diluted appropriately, and conductive salt and brightener can be added accordingly.

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