Rust Inhibitors – Keeping Rust Out Of The Finishing Process

It is no secret that rust causes rejections and failures of manufactured metal parts. The application and use of rust inhibitors are critical to reducing the cost of corrosion during the manufacturing process. A rust inhibitor is a chemical compound that decreases the corrosion rate of metal alloys. A rust inhibitor forms a thin film or passivation layer on the surface of the metal that hinders the access of the environment to the metal surface. This chemical layer retards either oxidation or reduction of the metal. The effectiveness of a rust inhibitor depends on many factors, including but not limited to concentration, environment, and time.

It can be surprising just how fast the corrosion process can occur. The timed experiment in the photo shows how fast the electrochemical corrosion process happens. A light bloom of rust will quickly turn into a beautiful bouquet of yellow and brown corrosion by-products. Once the corrosion process has initiated, it is hard to reverse.

Flash rust is seen starting on the unprotected cast iron part (left) almost immediately from being pulled from the cleaning solution.

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In the manufacturing process, rust inhibitors can be classified as “in-process rust inhibitors” or “long-term rust preventatives." In-process rust inhibitors are designed to prevent corrosion during and between the manufacturing processes, while long-term preventatives provide a shelf life of 30 days to 1 year or longer.

Precision Finishing manufactures Chemtrol aqueous “water-based” in-process inhibitors and long-term preventatives. The aqueous in-process inhibitors are safe to use and environmentally acceptable. The inhibitors are formulated into soluble lubricants, coolants, cleaners, straight inhibitors and, other processing compounds.

A unique advantage of some types of in-process inhibitors is the ability to coat or paint over the inhibitor without affecting adhesion. This saves you the cleaning step, which in turn, saves time and money. Many long-term preventatives contain oil or oil-like chemicals. Ever rising oil prices and escalating environmental costs associated with disposing of oil make using a water-based preventative extremely attractive. Water-based preventatives are now available for up to 1-year shelf life.