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| Q - What is "cavitation"? |
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| "Cavitation" is the rapid formation and collapse of millions of tiny bubbles (or cavities) in a liquid. Cavitation is produced by the alternating high and low pressure waves generated by high frequency (ultrasonic) sound. During the low pressure phase, these bubbles grow from microscopic size until, during the high pressure phase, they are compressed and implode. |
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| Q - How do I tell if my ultrasonic cleaner is working right? |
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There is no universally accepted standard for evaluating the performance of an ultrasonic cleaner. Several methods are available which will detect day to day variations in relative ultrasonic intensity.
The classic "aluminum foil test," removing graphite from a ceramic surface and various hydrophone-type devices are the most commonly used for this purpose. When using any of these, it is important to duplicate conditions as closely as possible to assure that any change indicates a true variation in the ultrasonic performance and is not related to a change in temperature, soil loading, chemical concentration or any of several other variables.
For critical applications and where the expertise is available, an alternative approach is to evaluate the transducer condition by measuring its capacitance and resistance and to monitor the generator power by measuring its input current, input power or output power. If the transducer characteristics are within specifications and if the generator is drawing the correct power from the AC lines or delivering the correct power to the transducers, the probability that the ultrasonic cleaner is working right is very high. |
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| Q - Which frequency is best for cleaning? |
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Different cleaning requirements require different ultrasonic frequencies. Lower ultrasonic frequency means larger cavitation bubbles and more intense cavitation implosions. At higher frequencies, the cavitation bubbles are smaller, and although the cavitation implosions are individually less intense there are more of them.
Frequencies below 80kHz are commonly used for industrial cleaning applications where contaminants are relatively heavy and the parts being cleaned are robust. Frequencies above 80kHz are more frequently used to clean more delicate parts that require a higher degree of cleanliness.
Multiple frequency ultrasonics is indicated when a wide range of particle sizes and types need to be removed for the highest degree of cleanliness. Refer to the papers entitled "About Ultrasonic" of this website for additional information. |
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| Q - Why aren't my parts getting as clean today as they did yesterday? |
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The simple answer is that something has changed. The change, however, is not always found at the cleaning station. Once temperature, chemical concentration and all other cleaning parameters have been ruled out, the search should proceed back through the manufacturing steps. Common sources of problems include a change in lubricants, manufacturing processes and even raw materials.
Cleaning problems may also be caused by clogged filters, mis-directed coolant nozzles and improper machining or finishing practices. A change that is considered inconsequential by manufacturing may result in a huge difference in part cleanability. |
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| Q - Can I use solvents in my ultrasonic cleaner? |
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Flammable solvents MUST not be used in any cleaning system not specifically rated for use with them. In the Blackstone-NEY Ultrasonics line, only the model HT-1306 IPA (HT-1306 IPA) is rated for use with flammable solvents and then only in a controlled environment.
Other solvents should be used only with extreme caution and ONLY in equipment specifically intended to be used with them.
Most solvents require special equipment considerations to cavitate effectively because of their physical characteristics. The use of small amounts of solvent in glass beakers suspended in a water bath in an ultrasonic cleaner is the preferred method of handling any occasional need for small volume solvent cleaning. |
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| Q - How much ultrasonic power do I need in my cleaning tank? Can I have too much power? |
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The right amount of ultrasonic energy (usually expressed in watts per gallon) depends on the size of the cleaning bath and the difficulty of the cleaning requirement. Tanks in the one to two gallon size range often provide up to 200 watts per gallon of ultrasonic power. Achieving the same cleaning effect in larger tanks requires less energy density.
Excellent cleaning has been demonstrated in tanks having 2,000 gallons capacity with only 5 to 7 watts per gallon. The more difficult the application, the greater energy density is required for effective cleaning. Too much ultrasonic power may result in cavitation erosion occurring on delicate or highly polished parts that are near the transducer radiating surface. Aluminum, copper, brass and other soft metals are especially susceptible to cavitation erosion. |
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| Q - Can ultrasonics cause damage to hearing? Are there any other effects on the body? |
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Ultrasonic cleaning equipment utilizes high energy sound waves at frequencies above those audible to humans to enhance the chemical and mechanical cleaning effects of liquids. The ultrasonic energy, although high in power, has no measurable impact on human auditory senses - in fact, there are no established time weighted average exposure limits for frequencies above 20kHz (20,000 cycles per second) . The frequencies of concern are the audible sub-harmonics of the ultrasonic primary frequency.
These are produced due to sympathetic resonance of various components of the ultrasonic equipment which may include the cleaning tank, the enclosure panels, lids and other features. Pumps, blowers, and other ancillary equipment also contribute to the overall noise produced by the unit.
In that regard, ultrasonic cleaning equipment is no different than a machine tool or any other piece of equipment found in the industrial environment. Ultrasound of the intensity that can be transmitted through the air has no known effect on body tissue. Ultrasound, in fact, is commonly used for imaging of the human body. |
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| Q - Which is better, Magnetostrictive or Piezoelectric transducers? |
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This often asked question is driven primarily by the promotional efforts of the manufacturers who each tout the benefits of their particular type of equipment. Piezoelectric equipment is by far the most prevalent in use due to its relatively low cost, high efficiency and adaptability to a wide range of frequencies and waveform characteristics. Neither construction has proven superior to the other from a reliability standpoint although metallurgical attachment of either type by vacuum brazing or silver brazing likely provides longer life expectancy under adverse conditions in heavy industrial equipment.
A fact of physics is that when an ultrasound wave is traveling through a cleaning tank, it is not possible to tell what type of transducer produced this sound wave. However, it is also a fact of physics that the less massive piezoelectric transducer can respond to more rapid frequency changes than can a magnetostrictive transducer. This allows the piezoelectric equipment to produce special sweeping ultrasound waveforms that are advantageous in precision parts cleaning. To learn more about piezoelectric and magnetostrictive transducers, visit the technical information section of this website. |
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| Q - Will ultrasonic cleaning damage electrical components? |
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Concerns about damage to electronic components as a result of ultrasonic cleaning can be traced back to the 1950's when a single incidence of damage to early generation semiconductors was described in a report issued by the air force.
Today's semiconductor devices are designed to withstand the rigors of space travel and are not easily damaged by vibration. Furthermore, today's advanced ultrasonic cleaning equipment is able to prevent part resonance due to recurring harmonic vibration at any frequency making the cleaning of semiconductor devices completely safe and trouble free. |
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| Q - Why do I need to rinse parts after cleaning? |
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Rinsing is as important as cleaning in many applications and should be given the same attention as cleaning. Rinsing removes residues of the cleaning chemistry and the contaminants it has loosened to leave a part completely free of residue. Parts properly rinsed in de-ionized water or water processed by reverse osmosis will dry completely without water spots.
Rinsing can be improved by increasing water flow or by adding more cascading rinse tanks. See the paper entitled "Ten Minutes to Better Rinsing" in the technical information section of this website for additional information. Further enhancement of rinsing can be realized by adding ultrasonics to the rinse tank(s). |
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