Ultrasonic cleaning is suitable for a variety of industrial parts and metals such as bearings, aluminum, and stainless steel, to name a few. However, some of the surfaces are highly sensitive and demand specialized care. For example, steel is vulnerable to rusting when exposed to water-based chemistries, so it requires either an additional rinse in a rust inhibitor or an integrated rust inhibitor in the cleaning solution.
(Pixabay / aixklusiv)
In this article, we’ll share some tried-and-true tips to help you get the most out of the ultrasonic cleaning process.
A Quick Word on Ultrasonic Cleaning
Ultrasonic cleaning utilizes sound waves (mechanical vibrations) in a liquid to perform the cleaning (a process referred to as cavitation). The generation of sound waves present in the liquid creates bubbles that burst or collapse on contact with parts’ surfaces, which helps in the removal of grease and soil. The ultrasonic tank is built to produce millions of bubbles, each carrying vacuum pressure that push surface debris and water onto itself from rigid surfaces. This is why the procedure can even be used to clean hard-to-reach areas effectively.
The 5-Step Process for Getting the Greatest Benefits
1. Select the correct cleaning solution
This is a critical step in the ultrasonic cleaning process. There are various liquid-concentrated cleaning detergents available that can be used for ultrasonic cleaning. Choosing the incorrect one may cause serious damage to sensitive industrial parts. First, let’s look at the two major categories of ultrasonic cleaning solution formulations:
Emulsifying formulations
These formulations are typically used in low-volume cleaning operations as they collect oily contaminants that will remain in the solution. This can cause a build-up in the cleaning equipment over repeated cleaning cycles that will eventually inhibit cleaning efficiency. In addition to this, residue may be left behind on the surfaces of the products, so post-cleaning rinsing operations may be required.
Demulsifying formulations
When cleaning solutions with demulsifying formulations are used, oily contaminants will float to the surface of the solution during the cleaning process. By skimming off the floating contaminants before removing the cleaned products from the solution, the need for post-cleaning may be eliminated. Because of this, demulsifying formulations are typically used in high-volume cleaning operations.
Now that we’ve established the two main categories of formulations, let’s look at a few common cleaning solutions that may be used in ultrasonic cleaning operations:
Alkaline solutions
These solutions are usually phosphate-free, with a typical pH balance of about 11.0. Because they have a lower strength and slightly elevated pH, they can be used for general cleaning to remove dirt, dust, oil, grease, and carbon deposits.
Acidic solutions
Acid-based cleaning solutions typically have a pH balance of about 4.0, though some can go even lower. These cleaning solutions are highly effective in removing scale, oxidation, and tarnish.
Citrus-based solutions
These mildly acidic formulations are especially popular in the aerospace, medical, and food industries. They are very effective in passivating metals such as stainless steel and titanium, a process that involves removing free iron molecules to create rust-free surfaces.
Enzymatic solutions
This is another cleaning solution commonly used in the medical and food industries as it is very effective in removing protein-based contaminants such as blood, mold, and bacteria. However, it can also be useful in the industrial sector due to its effectiveness in removing cutting fluids and oils from parts. Furthermore, it dissolves the contaminants it removes, eliminating the need for post-cleaning operations.
De-ionized water
Though it is not specifically a type of detergent, de-ionized water can remove surface contaminants such as flux residue, mildews, and mineral deposits from parts.
How to choose the correct cleaning solution
The following factors should be considered when choosing which type of ultrasonic cleaning solution to use:
- The nature of the contaminant that needs to be cleaned
- The nature of the materials that the contaminated parts are made of
- The amount of parts that need to be cleaned
2. Choose the correct time and temperature
Softer metals such as aluminum can sustain damage from temperatures that are too high. However, to successfully remove tough contaminants such as burnt-on carbon, temperatures as high as 180 degrees Fahrenheit may be required. For the most part, cleaning industrial parts in a temperature range of 135 to 150 degrees Fahrenheit is ideal. When lower temperatures are called for, parts should remain in the cleaning solution for longer periods.
3. Ensure that the correct output frequency is used
Industrial part cleaning operations are usually performed at a frequency of 40kHz, which means that the ultrasonic tank produces 40,000 microscopic bubbles per transducer per second. This rate is effective in sufficiently cleaning parts, as well as increasing the lifespan of the ultrasonic equipment.
For weighty parts, or parts that are heavily contaminated, a lower frequency of about 20 to 25 kHz can be used to produce fewer but stronger cleaning bubbles.
High frequencies of 68 to 170 kHz are mainly reserved for the cleaning of submicron debris, especially in medical and electronic applications.
4. Use a basket
Though it may seem like a good idea to place the parts directly into the ultrasonic tank, it definitely is not. Doing so may lead to serious issues as the weight of the parts can interfere with the moving diaphragm of the tank. Not only will this result in less effective cleaning, it may also damage your parts as well as your equipment. This is why ultrasonic cleaners usually come with a stainless-steel basket or rack that can be attached to the unit.
5. Determine whether post-cleaning is necessary
Sometimes the need for post-cleaning rinsing may arise, especially if emulsifying cleaning solutions were used. Parts that are covered in residuals after ultrasonic cleaning can be rinsed with water or immersed in an ultrasonic rinsing tank. It’s advisable to thoroughly rinse products that are painted, plated, or powder-coated.
Conclusion
Ultrasonic cleaning is an effective and convenient method when it comes to the cleaning of industrial parts, especially since these parts usually contain hard-to-reach places such as crevices that are difficult to clean manually. However, you should take special precautions in order to avoid damaging components and ensure that you maximize your ultrasonic cleaning equipment’s lifespan.