I don’t think most of us would consider using motor oil to moisten our dry skin. By the same token, we wouldn’t use body oil in our car’s engine. The notion seems to persist in the cleaning industry, however, that oil is oil. We often neglect to differentiate between oils when it comes to developing or recommending a cleaning process or chemistry. In fact, there are probably thousands of different oils each with its own set of characteristics which can have a great impact on the process and chemistry required to remove them.
Oils can be distillates of crude oil, man-made or synthetic oil, animal oil, or vegetable oil or mixtures of any of these. Additives including wetting agents, stabilizers, emulsifiers and a host of others are added to give the oil the properties required for a particular application. As an example, let’s look at a two classifications of oil, their general characteristics and what impact those characteristics might have on removing them from a substrate.
Lubricants, in general, are oils designed to penetrate into capillary spaces and remain in place for a long period of time. They are not water soluble and have relatively low surface tension to allow them to penetrate and wet the surfaces being lubricated. However, their surface tension needs to be high enough to prevent their continued migration too far beyond the location requiring lubrication. They also have low volatility to slow evaporation so that they will continue to lubricate over the long term. In some cases they must be able to resist high temperatures. Viscosity is tailored depending on the application. Because of their relatively low surface tension, lubricating oils are best removed by a chemistry that will emulsify them into solution. Finding a chemistry that will preferentially wet the substrate (“splitting” the oil) is not generally an option.
Coolants and some types of cutting oils are usually emulsions of oil and water. A surfactant is used to assist in the emulsification process. The primary purpose of a coolant is to cool the cutting tools and substrates during a machining process. In general, the lubricating function, although important, is a secondary characteristic. Coolants are usually delivered in large quantity to completely flood the area where machining is taking place. The oil component of a coolant usually leaves a thin coating of lubricant on the surface while the water component cools the surfaces. Because of their relatively low surface tension, coolants are often best removed using a chemistry that “splits” the oil from the substrate. The benefit to using a “splitting” chemistry is that the chemistry is not consumed or depleted during the cleaning process. In some cases, the recovered oil can even be re-used.
The list of industrial oil classifications goes on to include penetrating and/or water-displacing oil, hydraulic oil, rust inhibitors and many others such as the oil used for dampening in shock absorbers. Add to this the classifications of oil used in non-industrial applications such as skin care and pharmaceuticals and the list becomes almost limitless.
The “take away” here is that removing oil from parts is far beyond a case of “no brainer” solutions. Just because a process is effective in one oil removal application does not mean that is going to work in any other even if the two appear to be similar. Knowing the type of oil being removed and its inherent characteristics is critical to success.
– FJF –