Drawings and materials specifications for aerospace-related activities are quantitative. Too often, specifications covering cleaning requirements are most kindly described as ornate and steeped in tradition. Many cleaning requirements seem inherently illogical; they often reflect decades-old technology and cleaning agents that have not been produced for nearly a generation.
While industry standards for controlled environments and contamination control might be cited, it is not always clear how they relate to actual cleaning and performance requirements. The following attributes of counterproductive specifications are drawn from documents that are internal to specific companies, are provided by design agencies, or are industry standards and guidance documents.
Streamlining the process
Many large aerospace companies provide immense volumes covering specific cleaning requirements. Production groups physically located within the company, captive shops, and independent job shops are often expected to use only those cleaning agents and processes specifically listed.
Peruse such large specifications and you may find, as we have, illogical and unwise choices. Cleaning Agent A may be specified on one page; Cleaning Agent B, on another. From the perspective of a job shop trying to satisfy the needs of their potential customer, which one is correct? True, someone at the customer’s facility may be able to provide clarification. However, it would be more efficient and less subject to misinterpretation if a consolidated list of cleaning agents were provided.
One simple, productive step to streamlining is to eliminate specification of cleaning agents that are consumer or household products. They are generally not supported by their producers for manufacturing activities. They may contain lotions and fragrances that contribute to thin-film contamination. The soil-loading properties may be so extensive that soil is re-deposited onto the part; and the formulation is subject to change without notice.
The danger of nostalgia
Many specifications evoke waves of nostalgia. The authors see specifications we helped write in the mid-’80s that have never been changed; even long-standing typographical errors remain. Other specifications, going back to the 1970s or even earlier, prohibit the use of halogenated solvents — not because of any worker exposure or environmental concerns, but because of stability concerns. The issue of acid formation has been successfully addressed over the past few decades. Given that all cleaning agents have the potential to damage product, an overall proscription against a single class is unjustified.
Too many documents call out obsolete technology as the required or benchmark process. One notable example is the continued homage to ozone depleting chemicals (ODCs) that were phased out of production in the 1990s. In fact, their replacements may also either have been phased out or, like HCFC 225, are scheduled for a production and usage ban. Sometimes, it is assumed that a stockpile of the desired chemical is available. However, stockpiles deplete, and even stockpiled chemicals can break down over time.
Requirements to use or even to benchmark against legendary, obsolete cleaning agents have the potential to result in product damage. Over the years, newer process fluids and materials of construction may have been adopted. This means the soils may have different solvency properties, and the product may have different materials compatibility attributes.
Some specifications have wording allowing the use of effective alternatives; this is not sufficient. A required or benchmark chemical ought to be currently in production. If it is not currently produced, the spec needs to be updated.
Sometimes we are perhaps justifiably attached to a chemical that is no longer readily available, and it is tempting to keep it as a benchmark so that the information is not lost. There is some justification to the desire to retain tried-and-true processes. By analogy, the medical profession periodically rediscovers the rationale for an older “folk remedy.” Because newly developed cleaning agents may have properties that emulate those that are no longer available, it would seem reasonable for companies, agencies, and industry groups to move references to obsolete chemicals to an appendix where the information could be accessed. Using an appendix provides a means of retaining company lore, and at the same time provides an up-to-date spec.
Specification differences
Even within aerospace and related activities, specifications reflect the backgrounds and concerns of those involved in spec preparation. For example, we once saw a set of documents covering metal cleaning that addressed only levels of ionic contamination, because the metal comes in contact with water and, we suspect, because the documents were prepared by metallurgists. Problems arose; surface analysis indicated non-ionic contamination.
A specification in one aerospace application precludes the use of a specific halogenated solvent for cleaning metal. Another specification in a related application for cleaning the same metal uses the very same solvent that is proscribed in the first spec as a benchmark. The difference is the background and experiences of the people who wrote the documents. In both instances, the product is functional. Reading and understanding the rationale of documents in related fields might result in better specifications.
Logic and product quality
Aerospace engineers may assert that cleaning is an activity that is part of “company lore.” Therefore, if an engineer determined that a cleaning process worked at some point in history, there is no reason to ever question it. Nonsense! Critical cleaning requires the same rational thought process as any other part of product design and manufacture. Taking “company lore” under consideration is often prudent, but make sure the ideas are logical and that they are applicable for current requirements.
Delving through aerospace requirements for critical cleaning can feel like wading through primordial ooze.
Even more unpleasant, sub-optimal cleaning specifications impede production, cost money, decrease competitiveness, and are detrimental to product quality. This situation can change. However, change involves a critical re-evaluation of documentation.
Barbara Kanegsberg and Ed Kanegsberg (the Cleaning Lady and the Rocket Scientist) are independent consultants in critical and precision cleaning, surface preparation, and contamination control. They are the editors of The Handbook for Critical Cleaning, Second Ed., CRC Press. Contact: [email protected]
This article appeared in the February 2013 issue of Controlled Environments.
