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.

WD-40 is a lubricant dissolved in a solvent. While it can break down grease and oil to a certain degree, it also adds back some. This might be desirable if you are cleaning a hinge, conveyor, or corrosive-prone part, but not if you need it truly clean. For example, if prepping a surface before painting, cleaning with a cleaner/lubricant will lead to the paint dewetting (beading) or delaminating (flaking off). Chemtronics offers DPL for lubrication, and degreasers under the Eletro-Wash and Max-Kleen brands for high precision cleaning.

That depends on the requirements of your application. There are a number of factors that can have a big impact on performance and safety: flammability, dielectric strength, compatibility, toxicity, and environmental impact. Degreasers often contain very flammable alcohols and hydrocarbon solvents. They can be cheap and effective, but can dangerous without proper ventilation, or around open flames, sparks (e.g. welding), or hot surfaces. Nonflammable degreasers avoid these safety issues, but are generally more expensive. If you plan to powered equipment, or need to switch it on before the solvent has flashed off, consider a degreaser with a high dielectric strength.  More care needs to be taken when cleaning plastic packaging, plastic components, rubber gaskets and seals. If the degreaser is incompatible with the plastic, it can craze (create small cracks), embrittle, or soften the material. Rubber seals may swell, shrink, or dissolve if exposed to a harsh solvent. A new degreaser should always be tested before being used extensively. 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. All of this has caused maintenance facilities to reconsider their solvent choices, especially with manual cleaning when exposure tends to be higher. Volatile organic compounds (VOCs), solvents that add to smog, or solvents with high global warming potential (GWP) have been a focus of a number of regulators. Some state (e.g. CARB or California Air Review Board), municipal, and even industry-specific regulations restrict the use of high VOC or high GWP materials.

Yes, it is a good idea to use gloves when degreasing. The solvents used in degreasers do a great job at breaking down greases and oils, which also happen to exist in health skin. If your hands are exposed to a degreasing solvent for enough time, oils will be drawn from your skin leading to “defattening”. Your skin will become very dry and you could eventually develop dermatitis, which looks more like a rash. In addition, some solvents like N-Propyl Bromide (nPB), Trichloroethylene (TCE) and Perchloroethylene (Perc) are highly toxic, so can be absorbed through the skin and cause issues like cancer, or impact liver or kidney function. Please wear gloves and other PPE as required.

There are no degreasers that should be taken internally, but some ingredients are more harmful than others. 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.

Before you start spraying, shut down power to avoid the potential of sparks, electrical shorts or discharges, and other safety hazards. If disconnecting the power is not an option, look for degreasers with a dielectric strength above 30 kV (30,000 volts). Choosing a nonflammable cleaner would also add a layer of safety in case there is a spark.

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.