Rust or corrosion can lead to significant damage to bearings. Corrosion is caused by environmental facts such as water, salt water, acid/alkaline solutions or by chemical facts (galvanic action caused by dissimilar metal contact). Minebea applies various surface treatment methods, depending on the materials. It not only prevents corrosion but also advances the anti abrasion ability of bearings. Surface treatment advances overall performance ability of bearings.
Cadmium, Zinc, Chrome Plating
Although zinc plating is most commonly applied for industrial applications, cadmium plating has higher resistance against salt water. The low cost is a great advantage of zinc plating. Usually chromate treatment is applied after cadmium and zinc plating, as well as Zinc-Nickel Plating. The chromate treatment enables to give various types of color. Depending on the purpose, color choices of white, yellow, green or black are possible with zinc plating. Stainless steels can also be plated when anti corrosion is crucial. For instance, the combination of 440C ball with chrome plating and 17-4PH race with cadmium plating are generally chosen for marine applications.
Zinc-Nickel Plating
Zinc-Nickel Plating is a Zink Plating containing High Nickel. It has less affect on the environment compared to Cadmium Plating and offers an excellent corrosion resistance solution. It is widely used on bearings for aerospace application.
Passivation
The passivation method is useful with stainless steel to maintain its corrosion resistance capability. After cleaning the surfaces with alkali, they are soaked in a nitric acid and dichromate mixture. The substance not only cleans the surface, but also creates an inactive layer on the surface to advance corrosion resistance capacity. It is an effective corrosion prevention especially after cleaning off metal particles, which adhered during the machining process.
Anodizing
Pure aluminum is said to have a high corrosion resistance, as construction of the oxide Al2O3 is very elaborate, which prevents the oxidation. Aluminum alloy for sleeves, have a lower corrosion resistance compared with pure aluminum, therefore they are treated with anodizing or chemical conversion coatings. Anodizing means Anodic oxidation coatings, or more generally it is called alumite.
Table 20 : List of common surface treatments
| Treatment | Spec | Characteristics | Color | Application for Minebea Bearings |
|---|---|---|---|---|
| Chrome plating |
AMS-QQ-C-320 | Good surface hardness, Good wear resistance, Thick plating possible |
silver white | Ball surface Body I.D. |
| JIS H 8615 | Same as above Good for industrial robots |
silver white | Ball surface | |
| Cadmium plating | AMS-QQ-P-416 | Most common for air-craft steel alloy, good resistance against sea water | depending on chromate Type I white Type II yellow |
3 Piece body Race for Sph. bearing sleeve |
| Zinc plating | JIS H 8610 | Generally used for industrial applications | depending on chromate, white, yellow, green, or black | 3 Piece body |
| Zinc-Nickel Planting |
AMS2417 | High corrosion resistance equivalent of Cadmium planting, amd good fpr environment. | dark green - light blue depending on chromate |
3 Piece body Race for Sph. bearing sleeve |
| Passivation | AMS2700 | Improving corrosion resistance of stainless-steel, especially remarkably effective under 200 °C. | No color | 3 Piece body |
| Anodizing | MIL-A-8625 | Preventing corrosion of aluminum & Aluminum alloy. Type III is used on sliding surface of bearing | gray white greenish | sleeve aluminum alloy ball |
| Alodining | MIL-C-5541 | Preventing corrosion of Aluminum & Aluminum alloy. Used as primer for bearing to be painted later | yellow or white | sleeve Aluminum alloy race |