Ask the Stamping Expert: How can I evaluate the performance of recycled lubricant in-house?

Q: I have an issue regarding the consumption of stamping lubricant in our facility. The toolroom is requesting to use only new lubricant rather than recycled, as well as a richer lubricant mix in some tools. This is increasing our lubricant and disposal costs. Is there a test that I can perform in-house to evaluate lubricant performance without damaging tooling or taking production time for testing?

Note from Ask the Expert columnist Tom Vacca: This topic is outside my area of expertise, so I am deferring to lubricant specialist Paul Bosler, who is product manager, mill applied corrosion preventatives/metalforming lubricants for Fuchs Lubricants Co.

A: It’s not easy to answer your question without additional information. But yes, there are methods you can use on-site to determine the relative condition of recycled or used oil. I would also suggest that a lab be involved too. The type of lubricant also plays a role. For example, is it neat oil, water-emulsifiable oil, or a water-soluble synthetic?

The first step is to determine some parameters of the virgin mixture: color, odor, pH, viscosity. If there is any level of extreme-pressure (EP) additives in the mixture, determine a benchmark. EP additives can be critical to the forming process, but they are consumed and even can emit corrosive acid when degraded.

The next step is to determine the mixture’s resistance (or lack thereof) to microbial growth. Perhaps the recycled lubricant is inherently resistant to microbial growth, or it might have a biocide to help control this growth. You also need to establish the mixture’s capacity to prevent rust. We use a humidity chamber in our lab, but you could run a simple cast-iron chip test (CICT) to obtain similar information. If you are using coated or soft metals, you need to test the anticorrosion properties on those metals.

Once you have established these parameters, run the material for a period of time and monitor the level of fresh mixture that is required to maintain applicator reservoir levels. Lubricant typically is consumed as it travels as a residue on parts. We like to see a constant addition of new to old; as a rule, the best rate is 25 percent new to 75 percent old. We also like to promote efficient lubricant application, so it’s possible that not enough mixture would be consumed to maintain this replacement ratio. If that is the case, a well-designed recyclable lubricant should not experience problems. If it does, you can use additives to maintain alkalinity or even kill microbes. Adding fresh lubricant renews EP additives, corrosion inhibitors, and biocide that have been consumed.

Once you have established a pattern, you can probably maintain the system through simple checks of the concentration and the pH using a hand-held refractometer and/or titrations. In our lab, we use analytical methods to provide an accurate reading of water versus lubricant. We provide training for use of field models too.

There are even more elaborate tests, such as an acid split to determine tramp oil contamination. But that type of test is best left to a lab. Your lubricant supplier should still analyze samples on a regular basis, too, to ensure that the recycled product continues to meet the benchmarked parameters. Some suppliers do this at no charge to the customer.

Last, be sure you are using a lubricant that is designed for recycling. It might be important to use a lubricant that can split tramp oils so they can be skimmed off. Also, it is important that the product provides a long sump life and a stable pH.