Black oxide is a conversion coating formed by a chemical reaction produced when parts are immersed in the alkaline aqueous salt solution operated at approximately 285 degrees F. The reaction between the iron of the ferrous alloy and the hot oxide bath produces a magnetite (Fe3 O4) on the actual surface of the part.
ADVANTAGES OF BLACK OXIDES
The unique anodized finish is the only one in the metals industry that satisfies each of the factors that must be considered when selecting a high performance aluminum finish:
- No dimensional changes: The as-formed dimensions do not change (as they do when plated or painted). Black oxide is a coloring of the base metal, no metal is removed or deposited.
- Dark black color: (No patina or rainbow effect) The surface of the part may be shiny or matte depending on the surface of the part and the after finish applied. For example, a polished surface will retain its luster after black oxidizing.
- The finish will not chip, peel, flake, or rub off: Black oxide can only be removed by mechanically or chemically removing the finish itself.
- Reduces light glare (reflection): Black oxide makes an excellent finished surface for moving parts such as hand tools and machine parts. The reduction in reflectivity reduces eye fatigue and is less distracting.
- Can be coated for additional protection: Black oxide finishes with supplementary treatments ("after-finishes") improve the appearance, abrasion resistance, and corrosion resistance of the part to which they are applied. The normal after-finishes are Oil, Wax, Lacquer, and Chromic Seals. The part configuration and the end-use will help to determine which after-finish to specify.
- Improved lubrication characteristics: Black oxidized parts have improved lubricity and anti-galling characteristics due to the after-finish (oil or wax) resulting in smoother running, mating parts.