184719593 Ultrasonic Cleaning

8/12/2019 184719593 Ultrasonic Cleaning

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Ultrasonic CleaningBy-

Monsoon Dibragede (10ME01004)Abhilash Fulkar (10ME01041)


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Ultrasonic Cleaning

Cleanliness is an important issue in many industries.

Ultrasonic energy is used extensively in critical cleaningapplications to both speed and enhance the cleaningeffect of the cleaning chemistries.

Ultrasonic cleaning mainly works on the principle ofCavitation and Implosion .The most commonly used frequencies for industrial ultrasoniccleaning are those between 20 kHz and 50 kHz.

Frequencies above 50 kHz are more commonly used in smalltabletop ultrasonic cleaners such as those found in jewellerystores and dental offices.


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Cavitation

In elastic media such as air and most solids, there is a continuoustransition as a sound wave is transmitted.

In non-elastic media such as water and most liquids, there iscontinuous transition as long as the amplitude or "loudness" of thesound is relatively low.

As amplitude is increased, however, the magnitude of the negativepressure in the areas of rarefaction eventually becomes sufficientto cause the liquid to fracture because of the negative pressure,causing a phenomenon known as cavitation .

Cavitation "bubbles" are created at sites of rarefaction as the liquidfractures or tears because of the negative pressure of the soundwave in the liquid.


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Implosion

As the wave fronts pass, the cavitation " bubbles oscillateunder the influence of positive pressure, eventuallygrowing to an unstable size.

Finally, the violent collapse of the cavitation "bubbles"results in implosions, which cause shock waves to beradiated from the sites of the collapse.

The collapse and implosion of myriad cavitation"bubbles throughout an ultrasonically activated liquidresult in the effect commonly associated with ultrasonics.

Such implosions of cavitations results in high temperatureand high pressure at the implosion sites of cavitationbubbles


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Ultrasonics in cleaning process

Cleaning in most instances requires that thecontaminant to be dissolved , displaced orboth dissolved and displaced.

The mechanical effect of ultrasonic energy

can be helpful in both speeding dissolutionand displacing particles.

Residual cleaning chemicals are removedquickly and completely by ultrasonic rinsing.


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As the cleaning chemistry dissolves thecontaminant, a saturated layer develops atthe interface between the fresh cleaningchemistry and the contaminant.

Once this has happened, cleaning actionstops as the saturated chemistry can nolonger attack the contaminant.

Fresh chemistry cannot reach thecontaminant.


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Ultrasonic cavitation and implosion effectivelydisplace the saturated layer to allow freshchemistry to come into contact with thecontaminant remaining to be removed.

This is especially beneficial when irregularsurfaces or internal passageways are to becleaned.


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Some contaminants are comprised ofinsoluble particles loosely attached and heldin place by ionic or cohesive forces.

These particles need only be displacedsufficiently to break the attractive forces tobe removed.


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As a Superior Process

In reality, surfaces are seldom flat, instead being comprisedof hills, valleys and convolutions of all description.

The adjacent figure shows why ultrasonic energy has beenproven to be more effective at enhancing cleaning than

other alternatives, including spray washing, brushing etc.The ability of ultrasonic activity to penetrate and assist thecleaning of interior surfaces of complex parts is alsoespecially noteworthy.


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Ultrasonic Equipment

To introduce ultrasonic energy into a cleaning system requires an ultrasonic transducerand an ultrasonic generator or power supply.

The generator supplies electrical energy at the desired ultrasonic frequency.

The ultrasonic transducer converts the electrical energy from the ultrasonic generator intomechanical vibrations.


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Maximizing the Ultrasonic Cleaning Proce

Maximizing cavitation of the cleaning liquid is very important to the success of theultrasonic cleaning process.

Temperature is the most important single parameter to be considered in maximizingcavitation intensity. The viscosity of a liquid must be minimized for maximum cavitationeffect and the viscosity of most liquids is reduced as temperature is increased.

The amount of dissolved gas in a cleaning liquid is reduced as the liquid temperature isincreased. Gas dissolved in the cleaning liquid is released during the bubble growth phaseof cavitation and prevents its violent implosion which is required for the desired ultrasoniceffect.

As the Ultrasonic power is increased substantially above the cavitation threshold,cavitation intensity levels off.


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Conclusion

Properly utilized, ultrasonic energy can contribute significantly to the speed andeffectiveness of many immersion cleaning and rinsing processes.

It is especially beneficial in increasing the effectiveness of today's preferred aqueouscleaning chemistries and, in fact, is necessary in many applications to achieve the desiredlevel of cleanliness.


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Documents

184719593 Ultrasonic Cleaning