Precautions in barrel plating process
1. The current density varies greatly.
Although the cathode current density of barrel plating is large, due to the great difference in current density, most current is consumed on workpieces with high current density, and the average current density is very small. As a result, the cathode current efficiency is low. If there is a slight negligence in operation, it is difficult to ensure the coating thickness.
2. Chemical dissolution occurs simultaneously during barrel plating.
When the workpiece rolls, the current will be intermittent. It is required to thicken the coating and prolong the rolling time. However, the coating at some places is still difficult to thicken.
3. Adjust the main salt concentration in time
The main salt consumption in barrel plating solution is fast, which is mainly caused by insufficient anode area and large loss when the workpiece comes out of the tank.When the main salt content is too low, the current efficiency will decrease and the coating is difficult to thicken. Therefore, it needs to be adjusted in time according to the test and analysis data.
4. The pretreatment of barrel plating parts is difficult.
The barrel plated parts can only be pretreated in the basket, which will inevitably overlap, so it is difficult to completely remove the dirt.Therefore, the barrel plating solution is easy to be polluted. Because the barrel plating solution is sensitive to impurities, the purification workload of the solution is large, which is often easy to delay the production.
5. The solution heats up quickly.
During barrel plating, the current is large and the heat is released. Due to the small amount of bath liquid, it is difficult to dissipate heat quickly. When the temperature exceeds the allowable value, the dispersion capacity of the solution and cathode current efficiency will be significantly reduced, resulting in a sharp increase in the hardness and internal stress of the coating.
Another problem with high temperature is that some additives are not allowed to work at high temperature, otherwise the anode polarization performance will be reduced, and higher current density must be used to obtain fine crystallization, but a vicious cycle may occur at this time, and the temperature will rise again.
The cooling device of barrel plating can not be omitted, especially galvanizing.
6. The pH value of barrel plating solution changes greatly.
The change of pH value is more obvious especially in nickel plating.This is due to the intense hydrogen evolution in local parts during nickel plating.In order to maintain production, the pH value needs to be adjusted frequently.
7. Anode plate consumes fast.
The requirements for the anode area of the barrel plating process itself are large, the anode area is insufficient, and the current is not easy to increase, which is difficult to meet the requirements of the barrel plating process. Due to the large fluctuation of the barrel plating solution, the electrode plate at the junction of the liquid level is easy to dissolve. It is common that only the plate head is hung on the anode stem, and the plate tail has already fallen into the bottom of the bath. Attention should also be paid to this situation.
8. Relationship between barrel speed and coating quality
The rotating speed of the barrel depends on the hardness and geometry of the texture of the barrel plating part itself.
For soft coating or small parts, slow speed should be selected, which is generally controlled within 15r / rain; For hard coating or large workpiece, a faster speed should be selected, which is generally controlled above 15r / rain, but the speed should not be too fast, otherwise the deposition speed is slow.
9. Master the appropriate loading capacity.
Excessive loading affects the uniformity of plating thickness;If the load is too small, some work pieces are easy to be separated from the group. At this moment, in addition to losing the opportunity of discharge, some work pieces may also be chemically dissolved, and even be affected by the dual electrode because they are between the cathode and anode, resulting in the peeling of the continuous coating.
10. Pay attention to cleaning after plating.
A lot of solution will adhere to the surface of the barrel plating parts when they come out of the tank. In order to make full use of resources and reduce environmental pollution, the solution shall be recovered and multi-stage countercurrent rinsing shall be adopted. In order to prevent the coating from being damaged, the loading in the basket shall not be too much. During rinsing, it shall shake gently in water (it is strictly prohibited to shake away from the liquid level).