Parts cleaning, a major component of industrial operation, changed radically in the 1990s as we learned to use aqueous technology. It’s changed little since that time. Innovation is scarce, so I’m writing this column to propose some. My interest in this column is in cost reduction-by not having to purchase fresh cleaning products and then dispose of them as spent cleaning agents. Chemicals, and especially their disposal, are often the major component of operating costs for cleaning operations. So, how is one to get soil off parts and keep it off without cleaning agents? This column will examine when and how one might choose not to use cleaning agents for removing soils from parts and how to use steam to clean parts in metal finishing operations-as a test case for not using cleaning agents. This column is not a convention alone. It’s not about how work is done or should be done. It’s about change that we may or may not be able to believe in. My aim is to suggest different ideas in parts cleaning, and provoke readers to discuss them with suppliers. The answer to my previous question is found in the familiar image of a three-legged stool. Without the beneficial effects of cleaning agents, one has only two remaining factors to be implemented in a cleaning process: heat and mechanical force. In other words, one may consider contact with steam as a suitable cleaning process. Steam does provide both remaining factors.
CLEANING USES OF STEAM
Cleaning with steam has long been used in industries outside of metal finishing operations, including:
• Disinfecting of surfaces found in the home, for example, refrigerator door seals, toilets, filters, air conditioning coils, and the like.
• Non-industrial applications such as food service, agriculture, ready mix concrete, hazmat and decontamination situations, and military ground support.
• Industrial applications, including: cleaning engines, transmissions, drivetrains, and other equipment prior to performing service and maintenance work; degreasing dies and tools.
WHAT STEAM IS
Steam is produced by expansion of heated water compressed to a modest pressure (in the 100-250 psi range vs. 1,500-4,000 psi for the most common pressure washers). The water temperature is typically around 320°F. At this temperature, the water is in the liquid state at any pressure above about 90 psi. When the pressurized hot water is expanded across the spray nozzle at close proximity to the soiled area, some of it turns to vapour-stearn as the pressure is reduced below 90 psi. Evaporation of the liquid to make steam requires heat. That comes from cooling the main mass of water. The liquid temperature becomes the normal boiling point of water (to no surprise).
CLEANING WITH STEAM
Cleaning action is not performed by the steam, per se. The cleaning action is done by application of mechanical force, as in Figure 1. This is basically a spray cleaning machine. The force is provided by impingement of small water droplets entrained in the rapidly moving steam. The steam is rapidly moving because its volume has increased by about 1,500 times through expansion from the liquid to the vapor phase. The water droplets are hot. They heat oily or viscous soils, so they are much more easily removed from surfaces. The pressure nozzle is conical and designed to give the water droplets sufficient time to form, and be accelerated.
WHAT STEAM ISN’T
Steam cleaning is not cleaning with pressurized hot or cold water. That’s done by application of high-pressure water that may or may not be heated. If heating is done, it is to reduce the viscosity of the oily soils. The pressure nozzle is a wide-angle maximum coverage type for Acceleration of droplets comes not from their entrainment by evaporated water but from the huge pressure drop. Without heating, cleaning is done only with the application of mechanical force.
THE REAL ROLE OF CLEANING CHEMICALS
Yes, cleaning chemicals aid in soil removal, enabling the process to be done at low temperatures and without severe levels of mechanical force. But the real role of surfactants in cleaning operations is to tie up the soil materials so they can be removed from the cleaning bath without contaminating the parts. The “tie up” is often an emulsion, which is broken when the temperature is changed, releasing the soil. So cleaning without chemicals (and without their associated costs) means that the soils must be collected by the capabilities of the apparatus.
ABOUT THE FUTURE
This column is the first of several that will attempt to change our thinking about how a part cleaning is done-perhaps leading to innovation? Specifically, I have asked (but not answered) the question of whether or not cleaning with steam could replace the traditional approach of cleaning with chemicals. All comments and discussion from interested parties is appreciated.