Ultrasonic Cleaning

Every organization using hazardous chemicals within their facility has the responsibility to equip their facility and personnel to maintain exposure levels below the TLV. Personal monitoring badges can be used to measure exposure of a specific material. Then, depending on the threshold limit and the application, exposure can be controlled with PPE like masks, face shields, respirators, and even coveralls. If they don’t reduce exposure below the recommended limit, you will need to consider a special ventilation hood or even containment booth. As you can see, as the exposure limit gets down to a certain level, the equipment required to safely use the solvent can get impractical. At that point, your best option is to consider a safer alternative.

The personal hazard associated with a solvent is often defined using Threshold Limit Value (TLV), which is the recommended average exposure in an 8-hour day, 40 hour work week. The lower the TLV of a particular substance, the less a worker can be exposed to without harmful effects. TLV is stated on the SDS of chemical products, in additional to recommended personal protection equipment (or PPE). The threshold limit value of a solvent is generally set by the American Conference of Governmental Industrial Hygienists (ACGIH). The unit of measure is Parts Per Million (PPM).

If the chemistry is a good solvency match to the soil, less sonic agitation will be needed. This allows you to run your cleaning process more quickly, at lower temperature, and lower amplitude, decreasing the likelihood of damaging sensitive components. The following are characteristics to look for when reviewing options: 1) Solvency – Ability of the cleaner to breakdown and dissolve the soil. For a quick evaluation of solvency, place a drop of cleaner directly on the soiled part, let it sit for a few minutes, and they blot it dry. From this simple test, you can generally tell if the chemistry is a good match to the soil. If the cleaner just sits on the surface of the soil, and doesn’t wet and start to break down the soil, move on to the next cleaner. 2) Surface tension – This impacts how well a solvent can get into tight crevices, like under low stand-off components. 3) Density – Density can have a minor impact on how quickly the sonic waves travel through the liquid, and the amount of cavitation. A higher density material requires more energy to move, so could deplete the energy, thus the cleaning power, by the time it reach the part.

Several adjustments can be made to increase the cleaning performance of your ultrasonic process: 1) Frequency – This is the number of waves in a second, so how “tight” the wave form is. Lower frequencies provide more aggressive cleaning, but more potential of damaging sensitive surfaces and components. High frequency sonic waves can penetrate into tighter areas. As you get over 400 kHz, in the mega-sonic range, the bubble collapse is not as violent due to smaller spacing, so cleaning is often less effective in tight areas. 2) Amplitude – This is the height of the wave, or the loudness. Greater amplitude will generally increase cleaning effectiveness, but also the potential for damage of delicate surfaces or components. 3) Temperature – Increased temperature generally improves the cleaning performance of a solvent. Higher temperature can also reduce the viscosity of the cleaner and increase the surface tension, allowing the solvent to enter tighter areas. Cleaning performance increases significantly if the temperature of the solvent is above the melting point of the soil. 4) Time – Increase the time of the cleaning cycle to compensate for lower than optimal solvency. 5) Chemistry – If the chemistry has a good solvency match to the soil, less sonic agitation will be needed. This allows you to run your cleaning process more quickly, at lower temperature, and lower amplitude, decreasing the likelihood of damaging sensitive components.

An ultrasonic cleaning process utilizes equipment to transmit ultrasound waves, generally between 20-40 kHZ. The transducers send those sound waves through the liquid cleaner, which acts as a transfer medium from the transducers to the parts. At very high frequency, the waves may pass over the surface of the parts, creating agitation through a process called acoustic streaming. As the frequency is reduced, it creates cavitation within the liquid. These voids quickly collapse, generating heat and shock waves, which creates agitation in the cleaning process.

A degreaser is intended to clean a surface, so remove contamination. A degreaser is designed specifically to remove oils, greases, and lubricants. Sanitizers are intended to kill various pathogenic agents, like bacteria and viruses. There are materials that can do both, like 70% isopropyl alcohol (per CDC guidelines for hard surface disinfecting), but don’t assume all degreasers will kill pathogens.

The ingredients of a degreaser can vary wildly depending on the product. Generally speaking, they fall into 2 camps: 1) solvent cleaners – this includes alcohols (like isopropyl alcohol, or ethyl alcohol), hydrocarbons (like heptane and mineral spirits), ketones (like acetone and xylene), and more exotic compounds and blends. 2) water-based cleaners – these include ingredients dissolved or blended with water. Which is best for your application depends on the type of soil and various requirements like performance, evaporation rate, toxicity limits, and environmental regulations.

Windex (or other similar glass cleaners) could be considered a very light-duty degreaser. Glass cleaners can remove very light oils, like fingerprints, but will fall very short with heavier oils, greases and lubricants. Techspray offers a foaming glass cleaner (part #1625-18S) and water-based Eco-Shine (1505-QT) for light cleaning, and products like G3 Maintenance Cleaner (1630-16S), PWR-4 Maintenance Cleaner (3400-20S), and E-LINE Maintenance Cleaner (1620-10S) for more heavy-duty oils, greases and lubricants.

N-Propyl Bromide (nPB), Trichloroethylene (TCE) and Perchloroethylene (Perc) are highly toxic chemicals commonly used in degreasers to provide cleaning performance in a nonflammable formula. There are documented court cases where workers suffered major health effects when exposed to high levels of these chemicals. Workers reported headaches, dizziness, and even loss of full body control. There are also possible links to reproductive problems and cancer. All of this has caused maintenance facilities to reconsider their solvent choices, especially with manual cleaning when exposure tends to be higher.

Rigid plastics like ABS, polycarbonate (trade name Lexan), and acrylic materials like Plexiglass can be very sensitive to harsh solvents like toluene, xylene, and acetone. Alcohol and hydrocarbon based solvents tend to be better on sensitive plastics. Rubber, silicone or other seals or gaskets made of elastomeric (soft) materials can have a tendency to swell or shrink with exposure to harsh solvents. After the solvent flashes off, they may spring back to their original dimensions, or be permanently changed, impacting the effectiveness of the seal. Polyester or Teflon based gasketing materials are less prone to this type of damage from harsh solvents.

A degreaser is a cleaner designed to remove grease, oils, cutting fluids, corrosion inhibitors, handling soils, finger prints, and other contamination common in assembly, stamping, other types of metal fabrication, refineries, motor repair, airplane hangars, and many other applications. Degreasers go by a number of different names, including precision cleaner, maintenance cleaner, and specific for automotive repair, carb cleaner, brake cleaner. The objective for a degreaser is to remove the offending soil quickly, avoiding as much wiping and scrubbing as possible. Degreasing solvents are commonly packaged as an aerosol for convenience. Aerosols have the added advantage of providing a forceful spray that creates agitation and to penetrate all the crevices of the part.