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About anodizing

Basic Knowledge About Anodizing

Anodizing refers to aluminum surface treatment for artificially forming oxide film (aluminum oxide) by electrolytically treating aluminum at the anode (positive electrode).

Aluminum is likely to combine with oxygen to form a very thin oxide film when exposed to air. Aluminum is generally said to be difficult to rust, in short, rust-resistant because it is protected by this naturally formed film. However, because this film is very thin, aluminum may corrode because of a chemical reaction depending on the environment. For this reason, anodizing, a surface treatment for protecting aluminum surface, is needed.

Why is anodizing needed?

Aluminum is light in weight (Specific gravity: approximately one-third that of iron). On the other hand, it is characterized by being soft and scratches easily. When using aluminum for products, there are concerns that it may corrode or become scratched and worn without any treatment. That is why an aluminum surface needs to be hardened and treated to be resistant to corrosion.

Basic structure

Anodizing method

The jigs to which aluminum products are mounted are dipped in an electrolytic solution (sulfuric acid or oxalic acid).
The anode is connected to the jigs, and positive charges of electricity is put through them.
At the same time, electricity is also put through the cathodes.
(3) Through electrolyzation, an oxide film (aluminum oxide) is formed on the surface of the aluminum.

Structure of anodizing film: Pores refer to the holes in the oxide film, and each pore is 10 to 30 nm (nanometers) in diameter. Surprisingly, there are several billion to 70 billion pores in one square centimeter, which can be compared to the earth's population fitting easily into one square centimeter.

The basic structure of anodizing is like bundles of pencils

Putting electricity through aluminum dissolves (penetrates) minute bumps and dips on the surface, and the oxide film grows simultaneously, forming a steric structure called a cell as time passes.
It may be easily understandable if you imagine bundles of hexagonal pencils growing from an aluminum surface.

Because aluminum is an active metal, the oxide coating with a thickness of approximately 20 nm is formed naturally in the air.
Aluminum is oxidized in the electrolytic solution, and the oxide coating grows.
Because high dissolution occurs in the bumps on the coating surface, sulfate ions enter the bumps and the coating is partially eluted as aluminum sulfate. As a result, countless numbers of pores are generated on the surface.
(4) At the bottom of the pores, the oxidation reaction and coating elution reaction proceed simultaneously, creating a structure where pores are regularly elongated.
(5) The anodizing thickness is proportionate to the electrolyzation time.

Comparison of Anodized and Plated
Anodizing and Film

Anodizing and plating are totally different

In fact, anodizing and plating are totally different, although they are bracketed together as metallic surface treatments. In the case of anodizing, films grow upward from the aluminum surface (standard surface) as the growing coating and downward from there as the penetrating coating. Because they grow uniformly, if the original aluminum surface has bumps and dips, they are anodized as they are.

Anodizing does not have the effect of smoothing the surface like plating. In addition, if a material that has already been anodized is anodized again, the material thickness decreases.
It is because the whole Osmotic film needs to be removed chemically before re-anodizing. On the other hand, in the case of plating, other metals are put on an object to be plated in turn. Therefore, the theory is completely different.

Growth of anodized coating

Desirable shapes of edges

How the film is formed in the corners and on the angled parts

Dimensional change

If the film is formed on the inner diameter

If the film is formed on the outer diameter

Dimensional change after anodizing Automatic conversion of machining dimensions to be targeted

Entering values in fields (1) to (3) displays the machining dimensions to be targeted (theoretical dimensions)

Outer diameter (shaft)

	Lower limit	Upper limit
Coating thickness	0μ	0μ
Drawing dimension
Machining dimensions to be target	φ0.0000	φ0.0000

Inside diameter (pore)

	Lower limit	Upper limit
Coating thickness	0μ	0μ
Diameter after treatment
Machining dimensions to be target	φ0.0000	φ0.0000

Enter values using one-byte numbers.
Enter the upper and lower limits of the drawing dimension of the outer diameter as well as the lower and upper limits of the dimension of the inner diameter after treatment in millimeters (mm).
The values entered are displayed up to the third decimal place, and the value of the fourth decimal place is rounded.
Enter the thickness of the coating to be formed in microns (μ).
Units are inserted automatically.

Our unique anodizing technology

To add functionalities to anodized coating, it is necessary to control various factors, such as the amount of electricity put through the electrolytic solution, time spent for the treatment, and concentration and temperature of sulfuric acid. Even a slight deviation makes it impossible to add functionalities as desired. We can realize functionalities as expected by utilizing the expertise acquired through the many long years of experience and manufacturing system under strict control.

The thickness, hardness, and quality of the film are controlled by adjusting and combining various factors, such as the temperature and the concentration of the electrolytic solution, intensity of electricity, and the time spent for treatment.

Effects that can be added through anodizing

Wear resistance
Sliding performance
Corrosion resistance
Durability
Painting adhesion
Heat dissipation
Electricity resistance
Design

Kashima Coat

Optimal for sliding parts Lubricated hard anodizing
offering superior abrasion resistance

MD Process

Protecting products from corrosion Corrosion-resistant anodizing
for aluminum die-cast materials

Oxalic Acid Anodizing

Keeps the surface roughness unchanged after treatment Achieves superior heat resistance, corrosion resistance,
and a beautiful surface treatment

Kashima Coat Black

Putting on coal-black armor Kashima Coat originally had a distinctive blackened color
while maintaining its lubrication properties

Hard Anodizing

Standard anodizing by Miyaki Forms more robust film than anodizing

About anodizing

Basic Knowledge About Anodizing Treatment method - Explanation of film structure with graphics