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WAVE THEORY

Reprinted from the ACJ - February, 1994

The story you are about to hear is true. The names have been changed to protect the innocent. And to keep me from getting sued for slander.

Once upon a time there was a radiator shop owner with a bum knee, an old football injury I'm sure. This man was no fool, and had seen many sports injuries treated in a hot whirlpool tub. He had also read where ultrasound was used to treat deep tissue injuries. He put two and two together and came up with the solution.

After changing the tank water and letting it heat up, he lowered his battle weary leg into the warm water. He leaned over, pushed the core he was working on out of the way and hit the switch. At last the investment in the ultrasonic cleaning tank was paying off. Warmth and massage comforted his sore knee. At least that is what he thought up until he noticed the slow trickle of blood coming from both his nose and ears. "This is strange," he thought. But he was sure that the next "Health Watch" article would explain everything.

The use of ultrasonic cleaning is widespread in industry and becoming more and more popular in the radiator repair business. The machines offer advantages that standard boilout tanks cannot. In addition, they add an air of high tech to our industry.

The simplistic explanation of how they operate is as follows. The liquid solution within the tank is made up of billions of molecules. These molecules are unbalanced in regards to the electrical and magnetic charges spread over their surface. A molecule is said to be "polar" if the negative charge accumulates on one end and the positive charge migrates toward the other end of the molecule. The ultrasonic cleaner uses this molecular polarity for cleaning. The waves sent out by the transducers in the bottom of the tank change very rapidly back and forth between positive and negative.

This attracts first one end of the polar molecule then the other end. So the liquid molecules pivot back and forth with the rapidly changing waves.

When a core, or a body part, is immersed in the liquid full of these molecules, the pivoting molecules scrape against the core surface thousands of times a second and clean it like millions of tiny scrub brushes or steel wool. The ultrasonic waves don't stop with the outside of the radiator. The liquid inside the core also vibrates against the walls and cleans the inside of the core. With this rapid vibration come a few side effects.

As you might imagine if you rub steel wool against a surface thousands of times a second, you will generate some heat. The same is true of molecules. As a matter of fact, on a molecular level, a rapidly dissipating heat of several hundred degrees occurs. Also with this vibration the pressure next to the molecule changes. As the molecule pushes and pulls, the pressure goes up and down, sometimes reducing the pressure enough to make the liquid next to the molecule boil and bubble. This pressure induced low temperature boiling is called "cavitation." Well fine and dandy, but how does this translate into blood trickling from someone's ears?

As with the core, the ultrasonic waves can permeate a body part and vibrate the tissue inside. The temperature of the blood goes up, but more importantly so does the pressure due to cavitation of the blood within the veins and arteries. This will raise the person's blood pressure enough to blow out the weakest blood vessel membranes, which in a healthy person are the vessels in our nose and ears. Membranes in your heart or brain can also give way with life threatening results. Simple lesson: Never place living tissue in an ultrasonic cleaning tank.

Therapeutic ultrasound units are completely different in frequency and power. These mysterious ultrasonic waves are a subject of some controversy. Doctors use a different sort of ultrasonic wave when they take a picture of a baby in the womb of its mother, a so-called ultrasound. Some doctors use this procedure like an instamatic camera, constantly snapping family pictures. Other doctors shy away from its use unless absolutely necessary.

This discrepancy is due to many conflicting clinical tests that may or may not show tissue damage as a result of direct application of ultrasonic waves. The New England Journal of Medicine analyzed these studies and came up with no concrete conclusions one way or the other.

My opinion is to treat the devices with respect. As with a microwave oven, don't spend hours staring at it. But at the same time, don't wrap yourself in a lead suit and run from the room like a dental assistant every time you turn it on. By the way, the ultrasonic waves are transmitted very poorly in air so they dissipate quickly outside of the cleaning tank. Pregnant mothers may want to be a bit more cautious. Several companies restrict pregnant women from working near ultrasonic waves just to be safe.

There is a much more mundane but probably more pertinent hazard associated with ultrasonic cleaning tanks: the solution within the tank. Usually the cleaning agent is some form of corrosive material. Sodium Hydroxide (caustic, lye), NaOH, is a clear favorite.

As we have discussed before, NaOH is a strong basic chemical that can cause deep chemical burns when it contacts living tissue. Skin, eyes, lungs and stomach linings can all be irritated or burned due to contact with the liquid or breathing the vapors. Always use gloves, goggles and a respirator fitted with a corrosive vapor arresting cartridge when working over the ultrasonic tank, as you would when working over a standard type boilout tank. Ultrasonic cleaning compounds are formulated using extra components that aid in the cleaning action of the caustic and the waves.

These additives act as accomplices in the hazards of the caustic solution. The purpose of the additives is to help clean the core surface of oils and dirt, thus allowing the NaOH to get right in there and eat away at the surface, lifting the lime and other buildup.

The same is true of your skin. The additives help facilitate maximum contact of the NaOH with your skin, thus making the irritation and burning that much more rapid and possibly severe. Wash any exposed skin thoroughly as soon as possible after contact.

The elevated temperature of the solution helps in cleaning but adds to the danger as well. The warmer the chemicals, the more reactive they are both in the tank and on your skin.

Like my grandmother used to say, "You have to take the bad with the good." Of course, she also used to call me by my brother's name, so maybe she is not such a reliable source.

In summary, treat your ultrasonic tank with the same respect that you would your boilout tank. Avoid contact with the solution and limit breathing the vapors. Wear the necessary protective gear when working over it. And don't forget to be careful of splashing the liquid and watch out for burns.

If you feel the need for ultrasonic hydrotherapy, go down to the health club. The facilities are cleaner and safer, you get to watch the beautiful people parade around in workout clothes and you probably won't have to share the tub with a gummed up three-row core out of an old Buick.


The above article was written by David M. Brown, Chief Engineer of Johnson Manufacturing Company, Inc. and is published by JOHNSON with the expressed approval of the National Automotive Radiator Service Association and the Automotive Cooling Journal. Other reproduction or distribution of this information is forbidden without the written consent of JOHNSON and NARSA/ACJ. All rights reserved.

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