Final Step Cleaning in Metal Fabricating

Product cleanliness is an important criterion for machine shops and metal fabricating shops producing parts meeting extremely tight tolerances.   Removing all traces of cutting oils, dust, chips, turnings, polishing residues and other contaminants is necessary to ready newly fabricated and machined parts for shipping.   Depending on the size of your facility an industrial or benchtop ultrasonic cleaner is your best solution to achieve optimum parts cleaning.

Ultrasonic cleaning is especially effective for fabricated or machined parts with intricate designs because the process acts on all surfaces immersed in specially formulated water-based biodegradable ultrasonic cleaning solutions.  Hand scrubbing with brushes in solvent-filled wash tanks not only is time consuming; it cannot reach small crevices, blind holes and other tight spots or restricted areas. Moreover, solvent baths can be a health hazard and present disposal challenges.

How Ultrasonic Cleaners Work

Cleaning is accomplished by what is called cavitation.  This is the implosion of countless microscopic bubbles on the surface of parts immersed in a tank filled with the cleaning solution.  Implosion dislodges and carries away surface contaminants.

Cavitation bubbles are created by generator-powered ultrasonic transducers bonded to the tank.  Bubble size is governed by the frequency of the ultrasonic transducers, which is measured in thousands of cycles per second or kilohertz (kHz).  Widely used equipment for the majority of metal cleaning applications operates at 35 or 45 kHz. A happy medium for cleaning newly fabricated or machined parts is 37 kHz generated by the Elmasonic E and S series available from Tovatech.

Higher frequency cavitation bubbles are better able to penetrate small orifices and blind holes.  If you manufacture parts with these characteristics a dual-frequency ultrasonic cleaner is the answer.  An example is the Elma TI-H series that can be set to operate at 35 kHz for primary cleaning then switched to 130 kHz to penetrate the orifices.   Because it is imperative that the cleaning solution penetrates these spaces you might require an oscillating cleaner. Contact us for more information.

The correct ultrasonic cleaning solution formulation is a critical part of metal parts cleanliness.  Generally you’ll look at an alkaline aqueous cleaner for removal of oils and coolants. We direct your attention to our post on selecting cleaning solutions and cleaning solution maintenance.

Other Important Ultrasonic Cleaner Features

Heaters allow you to set the proper temperature for the ultrasonic cleaning solution, a step that is necessary to remove coolant and cutting oils.  Timers allow you to operate the units without constant supervision.

Select equipment with a Sweep mode to provide homogenous distribution of cavitation throughout the cleaning bath, a step necessary to achieve thorough cleaning.  Sweep also avoids what are called “hot spots” or “standing waves” of ultrasonic cavitation that can damage highly finished surfaces.  High-end oscillating cleaners, mentioned above, are extremely effective to achieve thorough cleaning at high throughput.  Degassing is a convenient feature when preparing fresh cleaning solutions.  The process removes cavitation inhibiting entrained air.

These features work best when parts being cleaned receive the full benefit of ultrasonic cavitation.  For suggestions on improving cavitation efficiency check our post covering parts positioning.

Rinsing and Drying Metal Parts

Parts rinsing is required if cleaning solution residues are not acceptable.  Several rinsing systems are available for residue removal.  The simplest is a spray rinse using city water.  This too may leave unacceptable residues, in which case RO, DI, or distilled water can be used.  More elaborate systems have one or more rinse tanks adjacent to the ultrasonic cleaning tank. They have a shower rinse and an oscillating ultrasonic rinse tank to remove residues from complex shapes including crevices and blind holes.

If rusting is a concern a rust inhibitor such as elma-KS can be added to the rinsing bath.

When parts emerge from heated cleaning or rinsing baths they may be warm enough to flash dry.  Complex parts that hold water require systems that can range from simple hand-held hot air driers to electrically powered top- and front-loading industrial dryers.

For More Information:

The ultrasonic cleaning professionals at Tovatech are ready to help you specify an ultrasonic cleaning system, cleaning solution concentrates and cleaning procedures to meet your requirements for delivering machined and fabricated components of the highest quality.

About Rachel Kohn

So how did an MIT Ph.D. end up selling refrigerators? When I figured out that a lot more scientists buy lab refrigerators than innovative leading-edge instruments. I hope that my many years of lab experience will help you find the right equipment for your work. Before co-founding Tovatech I worked in business development and project management at Smiths Detection, Photon-X, Cardinal Health, and Hoechst Celanese. And before that I spent 12 years as an R&D chemist at Hoechst Celanese and Aventis working on advanced drug delivery systems, polymer films and membranes, optical disks, and polysaccharides. Some day, eventually, I’ll make enough money to develop an innovative technology that will change the world. Read More