Q. We have a five-stage wash system using an alkaline cleaning package. Some of the rust inhibitors coming in on parts are not water-soluble. Should they be?—H.S.
A. Rust inhibitors can come in a variety of types and efficiencies. In general, water-based rust inhibitors are only applied where short-term, indoor rust protection is required. These will often be used in manufacturing plants that have a relatively short work-in-process time of a few days.
If you are shipping significant distances over several days in addition to the in-process storage time, and there is possible exposure to the elements during transit, it may be that a water-based rust inhibitor will not provide effective protection. In that case, a light, oil-based rust preventative should be used. This category of rust preventative, which is somewhat similar to WD-40, often utilizes a water-displacing additive in a solvent base.
The rust preventatives in the third category are actually oil-based and also incorporate water-displacing additives. Its advantage is that the water-displacing additive will orient and be adsorbed by the steel surface, while the oil base provides added corrosion protection. As would be expected, this last category of rust preventative is the most difficult to remove from the part, especially with extended storage times and elevated temperatures.
There are a number of different types of corrosion inhibitors available for industrial use. The more effective a rust inhibitor, the more tenacious it will be to remove from the steel surface. So when you ask if your customers should be using a water-based inhibitor, the answer depends on the degree of rust inhibition they require. Based on the previous explanation of rust inhibitors, you may believe that the customers are applying a rust inhibitor that is excessive for the situation. If that is the case, you may want to initiate a dialogue with them on their rust-inhibitor requirements and how this is affecting your processing of their parts. It may be possible that this conversation could result in potential time and cost savings to you and benefit to your customers.