When the various process conditions exceed the control range, the degree of influence on the quality relationship of the anodized film, different symptom phenomena and corrective methods are discussed in the following questions.
How is the voltage controlled during anodization?
The voltage is adjusted depending on the temperature of the solution. When the temperature of the solution is low, the voltage of the specified upper limit should be used. This is because the oxide film obtained is dense at the lower temperature of the solution, and the resistance of the oxide film is large. It is necessary to adopt a higher voltage to thicken the oxide film, otherwise it is difficult to obtain normal oxidation. Film quality. When the temperature of the solution is high, the voltage is reversed. Otherwise, the film solution may be too fast due to the loose oxide film formed, and it is difficult to obtain a desired oxide film thickness.
For example, in the unit without cooling device, the temperature of the solution in summer will approach the limit temperature. If it still needs to continue working, the voltage should not exceed 12V. The temperature of the winter solution is lower than the lower limit of the limit temperature, and the voltage is raised to a high value, such as 18V.
Anodizing is an exothermic reaction. When the workload is full, the temperature of the solution will gradually rise, so it should be tested at any time as a basis for providing regulated voltage. If the temperature continues to rise, it is difficult to guarantee the quality when the voltage is below the specification. Production should be stopped at this time. Take corresponding measures to cool down, and then process it when it meets the process requirements.
How is the current density controlled during anodization?
Under normal temperature conditions (about 20 ° C), in addition to the special process formula, the current density of aluminum and its alloy anodizing is generally controlled between 1 - 1.5A / dm2.
Select according to the temperature of the solution, the concentration of the solution, the shape of the part and other relevant process conditions.
Under the possible conditions, appropriately increasing the current density is beneficial to accelerate the film formation speed, shorten the anodization time, increase the porosity of the film layer, and improve the coloring effect. However, when the current density is continuously increased, the anodizing process will be affected by the Joule heat, the thermal effect in the pores of the membrane is increased, and the local temperature rise is remarkable, thereby accelerating the dissolution rate of the oxide film, and the film forming speed is lowered, and the complex is encountered. The piece also causes uneven current distribution and affects the coloring effect. A loose oxide film which is easy to wipe off may be present on the surface of the article, or the film may be brittle, cracked, or have white marks, and may cause ablation of the article in severe cases.
Selecting a suitable current density can accelerate the growth rate of the film within a certain range, but when it exceeds a certain value, the film formation speed is rather lowered.
According to the above rules, in order to ensure product quality and improve production efficiency, the following methods can be adopted.
When the cooling conditions are good and the solution can satisfy the strong agitation, the upper limit of the current density can be used to improve the working efficiency.
Under the condition of no cooling device and no strong agitation, although the temperature of the solution is moderate at the time, the current density should be properly controlled to prevent quality problems due to excessive temperature rise during the anodization process, and may cause parts in severe cases. Ablation. The most effective method at this time is to reduce the volume current density.
The correct estimation of the surface area of anodized parts is also an important condition for reasonable control of current density and should be taken seriously.
The surface of the deep concave portion of the anodizing member should be distributed with the same current density as the other surfaces.