Black Oxide Pretreatment
Cleaning and acid pickling are the most important steps in the Black Oxide process. If oils, scale or rust remain on the steel surface the finish will be inconsistent and non-uniform. Selecting the best cleaner and using an additive in the acid can be the difference between rejects and an even jet black finish. Here are some things to consider:
- Cleaner – Oil Splitter or Emulsifier? If you have no way to remove oils a strong oil holding cleaner is preferred.
- Rinsing – Don’t drag alkalinity into the acid tank.
- Acid – Hydrochloric/Muriatic acid can be used but acid salts may be safer and as effective.
Blackening steel is one of the most basic finishing operations in the industry, but it still requires understanding and proper maintenance. Variables include:
- Types of oils on the parts – water soluble, paraffin based, soy based – may all require different cleaning strategies
- Rust and carbon scale – may require stronger acid concentration, longer time & and Ambienol C
- Surface conditions – machined surfaces act differently than raw cast surfaces
- Metal alloys – leaded steels and hardened steels may require different acid pickle times
Maintaining chemical concentrations, operating temperatures process times will help maintain quality and consistency. Developing a dump schedule for chemical process tanks based on production volume, tank cleanliness and chemical effectiveness will also help to minimize rejects.