Getting required results from ultrasonic cleaning cycles requires a clear understanding of your cleaning task or objective, an important one being how you define “clean.” This post takes a look at some of the ways “clean” can be defined – and examples of processes.
“What do you mean by ‘Clean?’”
This is a key question Tovatech’s ultrasonic cleaning professionals pose when customers ask for equipment, cleaning formula and procedure recommendations. At first the answer seems simple: “I just want to get the dirt off.” But then the follow up is “What’s the dirt?” then “What are you cleaning?” and perhaps the toughest: “Do standards govern the degree of cleanliness?”
In the latter instance, meeting measurable quality standards can qualify a product as being “technically clean.”
Different Applications Require Different Definitions of Clean
The definition of clean depends entirely on how the parts will be used after cleaning. Here are a few examples that go beyond typical ultrasonic cleaning applications such as cleaning dirty engine parts:
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Surface Preparation Before Coating
If a part will be anodized, powder coated, painted, or bonded with adhesive, it must be free of oils, grease, and other contaminants that could interfere with adhesion. A surface is considered clean when coatings bond uniformly without defects such as bubbles, pinholes, or peeling. -
Appearance is the Key Criterion
Some products are cleaned simply because they need to look good. Decorative parts, consumer products, jewelry, and display items may only require removal of visible dirt, fingerprints, and stains. -
Is Outgassing to be Avoided?
If the product will be placed in a vacuum where it cannot release any gasses, then it must be chemically clean. -
Are We Talking Medical and Surgical Implants?
Orthopedic implants and surgical instruments require much more than visual cleanliness. They must be free of microorganisms and other biological contamination before sterilization. -
Hydraulic Components
Hydraulic systems are highly sensitive to particulate contamination. Dust, metal particles, fibers, and sand can damage pumps, valves, and cylinders, reducing reliability and shortening equipment life. In these applications, cleanliness is measured by the quantity and size of particles remaining after cleaning.
As you see, there are many different uses, therefore many different definitions of clean. Some applications have industry definitions of cleanliness and specific regulated testing requirements, noted earlier as achieving “technical cleanliness.”
Pro Tip: In many cases, ultrasonic cleaning is often only one step in a complete cleaning process. Depending on the application, rinsing, drying, filtration, sterilization, or contamination testing may also be required.
Example 1: Surface Prep for Anodizing or Powder Coating
The Association of Materials Protection and Performance (AMPP, formerly the Society for Protective Coatings/Steel Structures Painting Council) has established standards for preparing surfaces for protective coatings. SSPC-SP1 – the first step after inspection to remove loose rust, old paint or other contaminants – calls for using solvents, alkaline cleaners or steam to thoroughly degrease surfaces. Without this step outgassing may occur causing bubbles, pinholes or other imperfections in the coating.
Ultrasonic cleaning excels as a means to thoroughly remove greases, oils and other contaminants from parts with complex geometries.
A mildly alkaline cleaning solution for degreasing prior to coating is Elma Tec Clean A4 diluted to 2% with water. This formula can be used with industrial ultrasonic cleaners. If low-flash-point flammable solvents are employed for surface preparation, an explosion-proof ultrasonic cleaner is required – along with conforming to local and national safety regulations.
Example 2: Removing Bioburden from Surgical Implants
ISO 19227:2018* states “Cleaning of orthopaedic implants is an essential step for achieving their biocompatibility as well as controlling the microbiological load required for their sterilization process.” The standard further states “… cleaning agents should be effectively removed unless it has been proven that they do not impair both the biocompatibility and the performance of the implant.” (Emphasis ours.)
One effective approach is cleaning with isopropyl alcohol (IPA). Because IPA evaporates rapidly, it leaves no residue, reducing or eliminating multiple rinse cycles.
However, IPA is classified by the NFPA** as a low flash point volatile solvent, creating what is called a hazardous area rating of Class I Division 1 or Class I Division 2. Three options to clean surgical implants using IPA are described in our post Selecting an Explosion-Proof Ultrasonic Cleaner.
*International Standards Organization; **National Fire Protection Association
When flammable solvents cannot be used, a highly alkaline aqueous solution provides an effective alternative. After ultrasonic cleaning, parts should be thoroughly rinsed with deionized water before sterilization and packaging.
Example 3: Measuring Cleanliness in Hydraulic Systems
The interior workings of hydraulic systems – tubing, pumps and cylinders – can be severely damaged by particulate contamination from dust, metal fines, sand, fibers and similar substances. Hydraulic components require more than contaminant removal—they require contamination measurement.
ISO 16232* notes “The presence of contamination in a fluid system is acknowledged to be a major factor governing the life and reliability of that system.” It states “In order to achieve reliable performance of components and systems control over the amount of particles introduced during the build phase is necessary and measurement of particle contaminants is the basis of control.” (Emphasis ours.)
*International Standards Organization
A common testing procedure includes:
- Ultrasonically cleaning the component
- Filtering the cleaning solution through a fine membrane
- Drying the collected particles
- Measuring their weight using gravimetric analysis. This method employs a calibrated analytical balance capable of weighing in milligrams.
- Examining the particles under a microscope
The size of the components being cleaned governs the size of the ultrasonic cleaner required. Suggestions on specifying a unit are found in Picking the Best Industrial Ultrasonic Cleaner.
Large Part and Production Line Ultrasonic Cleaning Equipment Options
Industrial applications often require more than a standalone ultrasonic cleaner. As suggested above, several steps may be required to achieve the desired degree of “cleanliness” when meeting standards.
Equipment suitable for cleaning large parts includes the line of mobile Elmasonic Xtra ST units offered in 6 capacities from 7.9 to 67.4 gallons. These units can be equipped with rinsing and filtering options to extend cleaning solution life. Cleaning larger parts can be accomplished in by the Shiraclean line offered in 6 tank capacities from 25 to 204 gallons.
Details on these options are found in our Tips on Selecting an Industrial Ultrasonic Cleaner.
High-volume manufacturing often benefits from cleaning systems that combine pre-wash, multi-stage ultrasonic cleaning, rinsing and drying, either with or without automation. These modular systems provide repeatable results for applications where cleanliness standards must be consistently met. Contact our professionals to discuss your specific requirements.
Selecting the Right Cleaning Chemistry
Choosing the correct cleaning solution is just as important as selecting the right ultrasonic cleaner. Cleaning chemistries are formulated to remove specific contaminants such as:
- Oils and grease
- Carbon deposits
- Polishing compounds
- Flux residues
- Biological contamination
- Metal fines and particulates
Using the proper cleaning chemistry can make the difference between a part that simply appears clean and one that meets technical cleanliness requirements. A comprehensive list of formulas and applications is found on our ultrasonic cleaning solutions page.
Related Readings Where Standards Apply
- Where the ultrasonic cleaner itself must be validated to meet FDA and CFR standards
- Meeting FDA guidelines for cleaning laboratory equipment
- Compliance with manufacturer-specified standards for equipment maintenance
The following links may be helpful in making correct decisions:
- How Ultrasonic Cleaners Work
- Frequently Asked Questions
- Ultrasonic Cleaner Benefits and Features that Deliver
- Glossary of Terms
Need Help Achieving “Clean?”
Contact the professionals at Tovatech for unbiased information on ultrasonic cleaning equipment, cleaning solution formulas and operating procedures aimed at achieving your goals.