In metal finishing, it’s all about the surface. It’s also about preparing the surface of the metal parts, and that involves cleaning. We hear a lot about "unintended consequences" in the manufacturing, economic, political, and regulatory arenas. With every cleaning step, with every process requirement, there are consequences, both intended and unintended. Our goal, in this and in upcoming columns, is to help you maximize the intended consequences and avoid or counteract the unintended ones.

Don’t Clean if You Don’t Have To
We are advocates of critical cleaning [1,2]. To understand why, let’s review how cleaning works. Soil, matter out of place, is an inevitable part of manufacturing. Cleaning is removing matter out of place. Many people clean parts because there is a sense that they have to, a sort of moral imperative. Of course, if current in-house process requirements require cleaning, you cannot simply change or remove the process. Similarly, if your customer mandates a particular cleaning step, or cleaning to a particular level, your cleaning process may seem to be set in stone. Even with a new manufacturing process, you may feel boxed in by economic, worker safety, or environmental constraints. We suggest that you question authority, that you determine the intended and the unintended or unanticipated aspects of cleaning. Similarly, in looking at regulations, you will find it productive to look at the motivations, both the written regulations, and the politics or political chemistry behind the regulations. Then, look at the consequences to your process, both positive and negative (see Table).

Clean Critically
Cleaning is often divided into "rough" cleaning and "precision" cleaning. The rough cleaning processes are the sort of "motherhood" cleaning steps--the steps you or your management assumes you ought to take but may have no idea why. After a part is machined, someone dips it into mineral spirits or runs it through an aqueous cleaning system. In precision cleaning, the steps are more likely to be clearly spelled out. There may be metrics to determine whether or not adequate cleaning has been achieved. The steps may be preformed in a limited-access controlled environment, such as a cleanroom. We think those distinctions do not truly reflect what is functionally needed.

Critical cleaning steps are the ones that make or break your product. If you are part of a supply chain, they are the steps that make or break the product of your customers. The critical step may occur early on in the process, perhaps right after machining. The intended consequences may be to make it easier to store the part or to cosmetically remove excess metalworking fluids. There may be unintended consequences of this process, both positive and negative, depending on the way this simple process is managed. One positive unintended consequence might be to minimize adherent residue. The longer soils remain in contact with the part, the more adherent they are likely to become. With multi-step processes, the final, so-called precision steps might not successfully remove these adherent, modified, caramelized soils.

There could also be unintended negative consequences. The cleaning chemistry could leave significant residue that interferes with later manufacturing steps. The process could add unnecessary costs. The cleaning chemistry might have significant levels of regulated or restricted chemicals such as VOCs (volatile organic compounds). Excessive use can impact the allowable budget for such chemicals , thereby restricting other processes throughout a manufacturing plant.

Look at the seemingly insignificant processes; they may actually be the critical cleaning process. For example, one group was having issues with their final cleaning process for molded metal parts. The cleaning process consisted of a wash/rinse/dry conveyorized system with overhead spray. Some of the parts were successfully cleaned, but there were intermittent, unexplained instances of surface defects in the final product. On closer inspection, we spotted a process, that the company termed “rough buff.” It was initially dismissed as unimportant. However, the process included an abrasive product, a wash step and a rinse step. We checked the production records, and we noticed that the product lines that did not go through the rough buff process were the ones that were more likely to show high surface defect rates. An unintended (but positive) consequence of this step was better soil removal. The immediate solution was to add the rough buff process for all product.

Regulatory Intent, Cleaning
If you are told you must perform a process a certain way, determine the reason.

Regulations, both safety and environmental, are often potent drivers in the decision of how to clean. One classic example is the divisions set up in the EPA SNAP program [3]. These divisions drive the way we conduct cleaning processes to this day. The EPA, in the program that regulates ozone-depleting compounds, divides cleaning into three basic categories: metal cleaning, electronics cleaning, and precision cleaning. Precision cleaning is exacting and has metrics. Electronics cleaning is concerned with removing a specific set of soils, fluxes. Metal cleaning is assumed to be rather unimportant. A bit of investigation goes a long way in understanding both the intended and unintended consequences of these requirements.

Back in the 1980’s, it was assumed that metal cleaning was relatively unimportant. People in the military let the EPA know that electronics assemblies were mission critical, that tests had to be run to determine replacements for CFC 113 and 1,1,1-trichloroethane. Precision cleaning, often in a cleanroom, was an easy “sell.” It was assumed that workers in the latter groups were doing important stuff and that the workers themselves were very sophisticated. In contrast, metal cleaning evoked images of guys clad in greasy denim, splashing parts in solvent.

In terms of solvent usage, the EPA may have decided that those cleaning metal do not need an aggressive chemical because the cleaning step is unimportant or because the workers are “unsophisticated” and are more likely to injure themselves or damage the environment. For the record, in our experience, people with advanced technical degrees working in high-tech applications may use chemicals very unwisely; people with relatively limited formal education often have a high level of street smarts when it comes to chemical management.

In any event, the intended consequences of SNAP are laudable. An untended consequence is that manufacturing is typecast. For many years, this picture of metal finishers has been inaccurate. Even if you are cleaning metal, you may actually be doing precision cleaning (or, as we would call it, critical cleaning). If you understand the intent of the regulations, you are better able to define how the regulations apply to your facility.

Regulatory Intent, Metalworking Fluids
Vanishing oil works because it leaves low residue. In fact, in the old days, it was touted as a way of avoiding the use of certain chemicals for cleaning. However, vanishing oil does not magically disappear--it evaporates, and this has the unintended consequence of introducing additional chemicals into the air. As we stopped using chemicals that decreased the upper (stratospheric) ozone, manufacturers started using metalworking fluids that increased lower (tropospheric) ozone--which resulted in increased smog.

In Southern California, local regulators, with the intent to meet Federal requirements to improve air, saw an opportunity to do so by changing the content of metalworking fluids. ILMA (International Lubricants Manufacturers Association), saw an opportunity to help develop workable regulations and to avoid an economically unsound plethora of products, some for sale in California and some for sale elsewhere. They developed a rule using thermogravimetric analysis (TGA) as a discriminator between low- and high-VOC coatings [4]--and this means that higher boiling metalworking fluids are favored in the regulation, and that products are being formulated accordingly. Higher boiling lubricants mean more adherent lubricants. The perhaps unintended consequence is that more adherent metalworking fluids will leave more residue; the residue is likely to be more adherent. The likely consequence is the need for more cleaning. The way to avoid unintended consequence is to determine how your own metalworking fluids will be affected. If reformulation is in the works, test the new fluids in terms of cleanability.

We take requests
Understanding critical cleaning is a key to success in metal finishing. Some of our best ideas for our technical columns come from readers. Maybe you have a problem, or just a vague, undefined worry or angst. Give us a call, send us an email. If you see us at a trade show, don’t hesitate to complain about the state of the world or manufacturing. We can explore problems and shine a bright light on impending issues. We can all make manufacturing better, safer, and more productive.

Table 1. At each step in the process, we have to consider both the positive and negative aspects of cleaning.
Coating adhesionUndesirable surface modification
Mechanical functionalityInadvertent increase in residue
Minimizing toxicsIncreased costs
 Additional regulatory constrains


  1. B. Kanegsberg, Preface to 2nd Ed., Handbook for Critical Cleaning, Second Edition, CRC Press (2011)
  2. B. Kanegsberg and E. Kanegsberg, “Contamination Control In and Out of the Cleanroom: Tipping Point Cleaning,” Controlled Environments Magazine, Feb. 2011.
  3. EPA Significant New Alternatives Policy (SNAP) Program,
  4. B. Kanegsberg and E. Kanegsberg, “Contamination Control In and Out of the Cleanroom: Finding the Optimal Analytical Test: Parts 1 and 2,” Controlled Environments Magazine, Nov. and Dec., 2010

About the Authors
Barbara Kanegsberg and Ed Kanegsberg Ph.D., “the Cleaning Lady and the Rocket Scientist” of Los Angeles-based BFK Solutions LLC (founded in 1994), are the industry leaders in critical/precision and industrial product cleaning. As independent consultants, they help manufacturers achieve rugged, trouble-free processes in areas such as metal forming and fabrication, aerospace, medical device manufacturing, electronics, optics, and consumer products. They are members of JS3, an interagency military/NASA working group involved with cleaning processes and Mil-spec development. Barbara and Ed also write regularly for trade journals in the U.S. and overseas. They are editors/contributors for the acclaimed, expanded two-volume Second Edition of the “Handbook for Critical Cleaning,” CRC Press, 2011. Contact: 310-349-3614 .