For better or worse, it is human nature to resort to offensive or defensive force when the going gets tough. In manufacturing, if the soil sticks to the part, there is an automatic reaction to get angry – angry at the soil, angry at the cleaning process, angry at the world. You scrub a little harder, keep scrubbing for a little longer. Critical cleaning processes, on the other hand, require finesse and planning – think of it as diplomacy in manufacturing. You have to decide on the type of force, and then control the way that force is used. This includes the strength and duration.
Molecular Forces
At the molecular level, chemical forces define the solvency properties of a cleaning agent; and sometimes, simply exposing the product to be cleaned to the cleaning chemistry is enough to remove the soils in a timely manner. This happens sometimes, but not very often.
Usually, manufacturers combine chemical force with other more macro, physical forces to make soil removal easier. Here are examples of these forces along with some pros and cons.
Elbow grease
Some product has to be cleaned by hand. While in general, we suggest avoiding the elbow grease approach, there are a number of reasons to do hand cleaning. Perhaps the parts are too large to fit into the cleaning system. Maybe production volume for the particular build is very low. Perhaps a small number of parts require rework. An employee scrubs at the part using a cloth, a cleanroom wipe, a brush or sponge. You have to pay attention to the cleaning agent as well as the wipes or brushes used to apply that cleaning agent. One advantage to elbow grease is that a skilled operator can clean specific problem areas of the component. On the other hand, the process depends on the skill and even the mood of the operator. At the end of the shift, it is too easy to clean ineffectively. Further, there can be too much of a good thing. Overly-enthusiastic cleaning can result in surface damage.
Agitation Under Immersion
Rather than simply immerse the part in cleaning agent, some cleaning systems use immersion combined with mechanical agitation. One technique is mechanical turbulation in liquid where the part is placed on a platform and mechanically moved up and down or side to side. Other systems employ a spa-like approach, including air-bubbles and/or “Jacuzzi-like” jets. Such systems can be far more powerful than simple immersion. It is always best to test parts and inspect for surface damage prior to purchasing a system.
Spray in Air
Cleaning and rinse chemistries (including water) may be sprayed onto parts, some at very high pressure. Spray in air cleaning can be part of a solvent degreaser process. It is used often in water-based processes to enhance cleaning speed and effectiveness. However, spray is a line-of-sight process; if the cabinet washer has an overhead spray, cleaning along the side of a large, bulky part may not happen. Further, there can be too much of a good thing; blunt force trauma can happen. If the pressure is too high, we occasionally find components physically removed from parts. Some cabinet spray systems are manual; so you will see more variability depending on the technique used. This can result in ineffective cleaning and product damage.
Liquid and solid media polishing
Polishing can be in air or under immersion and often includes polishing cloths. Such processes tend to be thought of as buffing or polishing. They are not thought of as cleaning processes. However, it is important to identify where buffing or polishing is serving a cleaning function. As with other cleaning forces, media can damage the surface if used improperly; and, just as with cleaning agents, media has to be removed from product, including from areas where it might become entrapped or embedded.
Ultrasonics
Ultrasonics, cleaning with high frequency sound waves, can be effective. Sound waves travel through liquid (the cleaning or rinsing chemistry) producing microscopic vacuum bubbles or “tears.” When those bubbles implode, momentary high pressures and high temperatures occur. These forces serve to blast particles and thin film contaminants from the surface. Unlike spray which is unidirectional or line-of-sight, ultrasonics are omnidirectional. This means ultrasonics work particularly well with complex surfaces and blind holes. However, there is a down side. Ultrasonics can gradually erode the surface. How rapidly this occurs depends on a number of factors including the frequency, the power, time, chemistry, temperature, and the materials of construction of the part you are trying to clean.
Diplomacy
The tendency to expect that more is better extends to other cleaning variables. For instance, in “Some Like it Hotter,” our March 2015 column in Products Finishing Magazine, we discuss the pros and cons of higher temperature.
A little more can be better, but after a certain point, more can be counter-productive. The secret to successful critical cleaning is to use the engineering equivalent of finesse and balance. Consider the impact of all cleaning variables including the cleaning chemistries, force, temperature and time. Determine how those variables interact with the substrate and the soil.
