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Ultrasonic Cleaning Procedures for Sensitive Surfaces

Care must be taken when developing ultrasonic cleaning procedures on sensitive surfaces to remove processing contaminants such as solder fluxes, polishing media, or to prepare parts for further finishing operations such as anodizing, plating or painting.

Sensitive surfaces, in these instances, are surfaces that can be damaged due to low ultrasonic frequencies, excessive ultrasonic power or using an inappropriate ultrasonic cleaning solution.

Let’s look at these considerations and at equipment features that accommodate them.

How Ultrasonic Cleaning Works

A perfectly cleaned surface is required prior to chromium plating.

Generator-powered transducers create ultrasonic waves that produce countless minute bubbles in a cleaning solution. These bubbles are formed by a process called cavitation and implode on contact with parts immersed in the solution. A reason why ultrasonic cleaning is so effective is that cavitation bubbles penetrate cracks, crevices and other surfaces difficult or impossible to reach by manual scrubbing, and where manual scrubbing can damage delicate or highly polished surfaces.

Ultrasonic Frequency Selection

Transducers are designed to deliver sonic cleaning action at certain frequencies.  Examples are 25, 37, 45, 80 and 130 kHz. As the frequency increases cavitation bubble size decreases. Low frequencies produce comparatively larger bubbles that implode vigorously against surfaces and are used for cleaning heavily contaminated parts such as engine blocks.  But the same efficiency that low-frequency sonic cleaning applies to cast and fabricated components damages delicate and highly finished surfaces such as electronic components, PCBs, optical glass and polished aluminum. In these instances high frequency sonic cleaning should be specified. A variety of dual-frequency ultrasonic cleaners are available allowing users to broaden their cleaning capabilities. (See table)

Related to ultrasonic frequency is the distribution of cavitation action throughout the cleaning solution. A fixed frequency produces regions of relatively high and low cavitation in what is called the “normal” mode of operation. While the normal mode is useful in some applications such as mixing, dissolving and dispersing samples, it can cause etching or otherwise damage delicate surfaces. A “sweep” mode provides an automatic, continuous slight shift in frequencies that result in even cleaning. Some ultrasonic cleaners always operate in the sweep mode; others models have user-activated sweep or operate in the normal mode only.  It is important to be aware of this if you are cleaning delicate parts and select a unit that offers a sweep mode.

Ultrasonic Power

Ultrasonic cleaner power, which can be specified as watts per gallon of cleaning solution capacity, also can affect sensitive surfaces. Most benchtop cleaners operate at an average 50-100 watts per gallon. As power increases so does the number of bubbles, so increased power yields faster cleaning action but only up to a point. Beyond that you are not only wasting energy you also risk damaging parts being cleaned.

Because too much power can damage delicate products or surfaces, consider selecting a unit with adjustable power. This allows you to program your cleaner to provide the optimum cleaning cycle.

Cleaning Solution Formulations

Selecting the correct cleaning solution formulation is essential to the success of the cleaning job, both for removing contaminants and protecting the surface and integrity of what is being cleaned. An example is elma clean 260 dip & splash for metallic surfaces including aluminum and light metal alloys. A number of formulations are available. We invite you to contact our cleaning experts at 973-440-2191 to go over your cleaning challenges and suggest cleaning solution formulations and ultrasonic cleaner models that do the job.

Elma Model Series

Frequency kHz

Sweep

Normal

Adjustable Power

EH-EL

37

Permanent

No

SH-EL

37

User Activated

User Activated

No

PH-EL

37/80

User Activated

User Activated

30 – 100%

TIH

25/45*

User Activated

User Activated

10 – 100%

X-tra Basic

25/45

Permanent

No

*35/130 kHz available on request

FREE GUIDE TO ULTRASONIC CLEANING APPLICATIONS

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