You Know Materials Compatibility Problems When You See Them
Or do you? Materials compatibility problems can be manifested in an acute manner such as a gross weight change or product deformation; the product may even dissolve. Even more insidious, a subtle surface change can compromise product performance. Those involved in optics manufacture are probably all too aware of the phenomenon. But it gets better (actually, worse); product failure may occur weeks, months, or even years down the road.
Impact of Changes
As parts become smaller and with increasing use of complex materials of construction, such as composites, materials compatibility issues become more pronounced. With any change in the manufacturing process, consider the potential impact of that change on materials of construction. Consider the impact of changes in chemicals such as lubricants and other metalworking fluids, polishing compounds, as well as the impact of changes in process conditions. For ongoing processes, compatibility problems can be exacerbated by lot-to-lot variability, not only of chemicals but also of materials of construction. For example, while a batch of plastics or composites may meet the physical specifications, sometimes the only chemical specification is a melting range. Glass can also show lot-to-lot variability; the cleaning and deblocking processes for optics may have to be re-optimized for each batch.
Consider the impact of changes in the cleaning process on potential compatibility issues.1 To review cleaning, soil is matter out of place; and cleaning is simply removing matter out of place. When you clean, one goal is to avoid altering the surface of the product. Philosophically, zero surface alteration is impossible, sort of like achieving zero surface contamination or zero pollution.
Looking at commercial compatibility tables provided by cleaning agent suppliers is a good starting point, but it is not sufficient. Suppliers do not know precisely how you will use the cleaning agents. In addition, lack of surface damage, like cleanliness, is in the eye of the beholder. Therefore, it is critical that you set up customized compatibility studies relative to the product, the soils to be removed, and the cleaning process. Some factors influencing materials compatibility problems are indicated in Table 1. In looking over the table, you might notice that some of the same factors that promote more effective cleaning (chemistry, temperature, time, force) also exacerbate compatibility issues. Pay particular note that a blend of cleaning agents may act very differently than any of the components.2
Plan the process change
“The dose makes the poison” holds true for cleaning/compatibility. Materials compatibility is not just based on exposing a single material of construction to a cleaning agent (even a heated cleaning agent) for some arbitrary amount of time. Test for compatibility as you develop your critical cleaning processes. Materials compatibility studies have to be geared to your specific application. This means testing and analysis before you set up the new cleaning process.
- Eichinger, E., “Material Compatibility,” in “Handbook for Critical Cleaning,” Kanegsberg & Kanegsberg ed., CRC Press, 449 – 459, 2001.
- Stavroudis, C, “Azeotropes from A to Z,” WAAC Newsletter, May, 2006.
Barbara Kanegsberg and Ed Kanegsberg, Ph.D. “The Cleaning Lady” and “The Rocket Scientist,” are independent consultants in surface quality including critical/precision cleaning, contamination control, and validation. They are editors of The Handbook for Critical Cleaning, CRC Press; an expanded second edition is scheduled for publication in the 4th quarter of 2010. Contact them at BFK Solutions LLC, 310-459-3614; firstname.lastname@example.org.