Engineers will look at the volume required for the parts being cleaned, the proper frequency, the ideal temperature and the type of filtration required when developing proper ultrasonic cleaning system for a specific application.
As important as all of the above specifications are, however, chemistry is still one half of the total solution. Chemistry is the key. I like to say that the ultrasonic cleaning machines are the hardware and chemistry is the software. You can make up for some shortcomings in the hardware equipment, if you apply the best possible software, or chemistry, to the equation.
Let me give you an example. An ultrasonic cleaning tank generates millions of microscopic sound bubbles per second that implode upon contact with a hard surface. Each bubble contains a vacuum pressure. When the bubble hits a surface, the bubble bursts-but it does not explode, it actually implodes.
Implosion means the internal vacuum pressure releases and it actually sucks water and surface debris into itself. Somewhat similar to what a black hole does. It collapses on itself and takes everything around with it. Under a microscope, you can actually see a vortex in the middle of the bubble acting like a tornado, which pulls fluid into the center of the collapsing wave. This is a very effective way to clean a variety of items.
Why is chemistry so important if the ultrasonic cleaning machine can do so much? What the proper chemistry and correct water temperature do is create a slight wedge just underneath the dirt particle and between the surface of the part being cleaned to loosen the bond between the dirt and machinery surface. The soap and water are not removing the dirt, but they are loosening and softening it for the ultrasonic cleaning machine to dissolve the dirt away.
You can certainly take a part, place it into a static tank with hot soapy water and you might see a slight amount of debris float away. If you were to take a part that was just as dirty in an ultrasonic cleaning tank, you will literally see dirt flying off from the ultrasonic waves hitting the dirt.
There are many components to chemistry. The most basic is pH. Most of the colleagues in this field are aware the pH of water is usually 7 to 7-1/2%. This pH level is considered neutral. Can parts be cleaned in water? The answer is yes in some instances. There are many applications where water or de-ionized water is the only cleaning solution allowed. You see this in many electronic wafer and chip manufacturing applications.
Some applications allow only a neutral based cleaning soap. Why do you need a neutral based cleaning soap if water is neutral? Because the surface tension of water is essentially high, this is not conducive to cavitating strong ultrasonic action. Soaps containing nothing more than surfactants that lower the surface tension of water, also known as “making water wetter”, are used simply to increase ultrasonic activity in a tank.
Most applications however require higher or lower pH depending on the specific type of dirt but also taking into account the surfaces being cleaned.
If we are talking about oils, soot, greases, carbon, polishing compounds, grime and just run of the mill dirt, a higher pH or alkaline detergent is required. How high? The level depends upon the surface we are cleaning. The higher the pH, the better. Let’s say the level is 13, which is considered caustic.
Caustics mixed with water clean very well but if we are cleaning a cast aluminum surface, the elevated pH will cause the aluminum to pit, scar, and even turn black. If the surface is stainless steel, a pH level of 13 is not a problem. Cleaning steel at a pH level of 13 won’t be an issue, but with if you clean the steel with water you will get flash rusting.
So the soap must have rust inhibitors in it — usually silicates to protect this flash rusting. Water temperatures above 180F cause silicates to separate out of the bath so that is something that must also be accounted for.
If inks are being removed, pH is only part of the equation. The very high pH isn’t the only key, it’s the specific cleaning detergents required just for ink.
If scale, calcium deposits or light to medium surface rust is the culprit, then an organic acid based cleaner is the best solution. Acids fall into the lower pH range of 2-4. Acids can actually remove surface layers of metals facilitating the removal of these types of contaminants.
If 2 pH is good, isn’t 1 even better? No way! Extreme acids such as hydrochloric actually destroy stainless steel welds, which do not allow cleaning systems to hold up long term. Not to mention the danger of working with these extreme acids. However, applications exist where hydrochloric acids are necessary, but precautions with the tank must be maintained.
Passivation is a process removing iron molecules from stainless steel. This is required in all aerospace and medical products. A citric acid blend can be used to remove only the very finest outer surface of metal-mainly the iron ore.
Enzymes exist which do a good job of removing oil and actually eating and digesting the petroleum molecule off as carbon dioxide. These are living protein cells but they have serious limitations. Operate them at elevated temperatures such as 150F-they become dormant. Boil them-they die. This small temperature differential leaves very little wiggle room. Enzymes also don’t work well with ferrous metals that rust as they offer no degree of protection against flash rusting.
Cleaning solder flux and electronic items is accomplished using a medium pH product in the 9.5-10 range. Again the higher pH will damage the thin copper substrates, so this product is in fact an alkaline light, kind of like a light beer. With electrical items, using a good de-ionized rinse water and thorough drying are paramount.
Water based chemistries give us many software solutions to our cleaning needs. It’s a matter of matching those applications to the proper soaps. Many applications have been tested and documented so matching up is easy. You just have to do your homework. Those parts that are different or modified can easily be tested. Contact Omegasonics to schedule a test part cleaning.
Interviewer’s Questions
Frank, I know that you have an engineering background. How did you learn about using chemistry to optimize the services OmegaSonics offers?
Where did you go to school?
Everyone one of the technologies OmegaSonics utilizes seems so unique. How did you dream them up and what is your research and development process?
What is the biggest mistake your competitors use when they bring chemistry into an equation where principles of engineering are king?
What new products do you have that use chemistry to make OmegaSonics the best ultrasonic cleaning company out there and why should people choose you as a vendor?
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