A black oxide finish imbues a worked ferrous component with an attractive ebony coating. The process transforms a thin layer of surface metal into iron oxide, so no deposits are called for here, just a chemical reaction that enhances corrosion resistance. As advantageous as this supplementary feature undoubtedly is, black oxide failure does occur, so we need to stay abreast of the common problems incurred by this oxidizing process.
Assessing Process Variables
As with any high-end engineering process, numerous variables are at work during a black oxide coating sequence. They all subscribe to a disciplined control methodology, a tightly regulated series of organized steps, but it only takes a single unbalanced ingredient to undermine everything. Black oxide failure happens when an ingredient is poorly applied or the process isn’t performed according to an exactingly conferred operational doctrine, but chemical composition isn’t the only factor that’s causing trouble.
Black Oxide: Common Failure Causes
The conversion technique, as already determined, isn’t a depositing technique. Rather, it’s a means of oxidizing the surface of a metal part, of transforming a predetermined layer so that it exhibits a uniform deep black finish. When it fails, that finish is corrupted at a molecular level. That’s a slightly worrying prospect, especially when we’re attempting to control an oxidization process. Fortunately, we can troubleshoot the issue. Common problems in application processing stations include the following:
- The oxide does not wipe off
- Cast or hue change issues
- Blotchy coverage problems
- The oxide layer rubs off as a coarse stain
- No black oxide finish whatsoever
Calling All Blackening Solutions
This list contains the worst processing culprits, so, in offering a solution, we’ll also solve the bulk of all other common and atypical problems. First of all, this is a relatively complex technique, one that “cooks” the ingredients in a precise manner. Timing issues and temperature ambiguities will obviously affect the final result, so correct oxidizing timing when the component is dipped into the salt bath. Likewise, maintain the temperature of the oxidizing tank at a predetermined level. Finally, turn to the part when the coating won’t convert the surface properly. Clean the part, desmut it, and return it to the bath for a second attempt.
Black oxide failure submits to a coordinated troubleshooting strategy, so restore all processing systems to their default settings. If this doesn’t work, then assess the part and clean it until it’s in virginal condition and ready for its oxidizing bath.