Controlling Titanium Acid Pickling Variables with Acid Management

Porter, Rick

R.L. Porter^1., D. Chew^1., S. Wolfe^1.

Abstract

Acid pickling of titanium alloys for aerospace, industrial and medical applications in HF / HNO₃ solutions is commonly utilized as part of in-process conditioning, metal finishing, part chem milling and inspection processes. Titanium producers, fabricators, part, and component manufacturers use pickling solutions which are typically made to customer or internal specifications dictating acid control ranges, temperatures, dissolved metal contents, and other key parameters. Baths are maintained and solutions are monitored, and additions made until dissolved metals concentrations reach pre-determined limits or etch rates diminish to unacceptable levels (long immersion times, hydrogen pickup, poor surface quality) at which time solutions are discarded for neutralization and disposal. This process of making acid solutions for short term use and disposal results in increased acid costs, waste, process downtime and reduced overall efficiency. To optimize these processes and maintain desired etch rates (in addition to temperature, agitation etc.), acid concentrations and dissolved metal contents have to be controlled. Different methods and commercial analyzers are available to monitor acid and dissolved metal concentrations within limits. By using a combination of acid filtration to remove suspended solids, and acid purification, acid / metal separation with high efficiency is possible. These technologies allow dissolved metal concentrations to be controlled within a desired range achieve acceptable removal rates and maintain bath life for extended periods of time reducing overall acid usage. In addition to immediate cost savings achieved from acid recovery, environmental savings (i.e. reduced CO₂ and other greenhouse gas emissions generated during the production of fresh acid) are significant.

^1.Scanacon, Inc. Hartville, OH USA