Ultrasonic cleaners are genuinely capable machines. The cavitation process they generate reaches into blind holes, threaded surfaces, and complex geometries that manual cleaning simply cannot access. Used correctly, the best ultrasonic cleaners deliver a level of cleanliness that is difficult to match with other methods.
Used incorrectly, the same process that makes them so effective can cause parts to be damaged. Knowing what not to put in an ultrasonic cleaner is as important as knowing what the equipment can do.
What Not to Put in an Ultrasonic Cleaner: The Core Problem
Cavitation is powerful and precise, but it applies mechanical energy indiscriminately. It does not distinguish between a contaminant and a fragile substrate. If the part or material cannot withstand the implosion forces generated inside the tank, it will show that quickly.
Materials and Parts that Should Stay Out of the Tank
Some incompatibilities are obvious once you understand how cavitation works, while others are less intuitive. Here is a breakdown of the categories that consistently cause problems across industrial and precision cleaning applications.
Soft and Porous Metals
Pure aluminum, lead, and thin soft-metal alloys are vulnerable to cavitation erosion. The implosion forces pits and degrades soft surfaces over time, and in some cases, the damage occurs quickly. Plated surfaces face a similar risk: cavitation can cause the plating layer to separate or flake, defeating the purpose of cleaning and contaminating the tank solution.
Parts with Adhesive Bonds or Coatings
Ultrasonic energy attacks bonded interfaces. Parts assembled with adhesives, sealed with gaskets, or coated with functional surface treatments can potentially affect those bonds during cleaning.
The vibration works its way into any interface it can reach. If the bond holding two components together, or a coating on a substrate, is not rated for ultrasonic exposure, the cleaning process will find it.
Wood and Organic Materials
Wood is porous and absorbs cleaning solution under the pressure generated in the tank. The result is warping, swelling, and discoloration that cannot be reversed. Organic materials broadly, including ivory, leather, and certain natural composites, behave similarly. The cavitation process and the cleaning solution together create conditions that might damage these types of materials.
Soft and Treated Gemstones
Opals, pearls, emeralds, turquoise, and other soft or porous stones crack, craze, or lose their surface treatments under ultrasonic vibration. Organic gems like coral and amber degrade in similar ways. Even some harder stones can be problematic if they contain internal inclusions or fractures, as pressure waves can propagate existing damage. This matters in precision and laboratory contexts where instrument components pass through cleaning systems.
Parts with Loose Components or Unsealed Cavities
Any part with a component that is not securely fixed is a liability inside an ultrasonic tank. Loose stones, unsealed housings, unsecured fasteners, and parts with open internal cavities can create serious issues during cleaning. They can trap cleaning solution, suffer internal damage from cavitation, or come out of the tank in worse condition than when they went in. Inspection before cleaning is not optional when part integrity is uncertain.
Delicate Plastics
Soft acrylics, PVC, polycarbonate, and similar materials can warp, become brittle, or degrade structurally under sustained ultrasonic exposure. Harder engineering plastics tend to perform better, but plastic compatibility should always be verified before introducing new part types to an ultrasonic process.
A Note on Electronics
This deserves its own section because the question comes up regularly, and the answer matters. Ultrasonics are not used to clean electronics. Many components on circuit boards, including delicate wire bonds, crystals, surface-mounted resistors, microchips, and sensors, are generally vulnerable to the shock waves generated by cavitation.
Solder joints can weaken, microcomponents can dislodge, and moisture can become trapped in areas that are impossible to reliably dry. The risk of circuit failure or short-circuit is real, and it is not recoverable.
Anyone specifying a cleaning process for electronic assemblies should consider solvent-based defluxing systems, not ultrasonic equipment.
What Can You Not Clean in an Ultrasonic Cleaner When It Comes to Equipment Fit?
Part incompatibility is one side of the equation. Even with compatible parts, the wrong machine for the application creates problems.
Benchtop ultrasonic units are designed for smaller, lighter parts in lower-volume applications. Placing oversized or excessively heavy parts into a benchtop system stresses the tank, disrupts the cavitation field, and results in uneven cleaning. Parts that exceed the tank’s working volume or weight capacity should be directed to an industrial ultrasonic cleaner capable of handling them properly.
Frequency selection also shapes what the equipment can and cannot clean safely. Lower frequencies generate larger, more aggressive cavitation bubbles suited to heavy industrial soils on robust parts. Higher frequencies produce smaller, gentler implosions suited to precision components with tighter tolerances and more delicate surfaces.
Running a fragile part through a low-frequency system configured for heavy industrial cleaning is highly likely to result in damage.
Operating temperature is another variable that interacts with part suitability. Some materials that would survive ultrasonic cleaning at ambient temperature become vulnerable when the tank is heated. Certain plastics soften, some adhesives lose their bond strength, and specific surface treatments become unstable at high temperatures. Part compatibility needs to be assessed against the full operating condition of the tank.
Choosing the Right Application Means Asking the Right Questions First
Ultrasonic cleaning is a precise technology, and precision requires knowing its limits as much as its capabilities. The materials, geometries, coatings, and assembly methods of every part type passing through a cleaning system should be considered before the process is set up.
At Baron Blakeslee, we have been working through industrial cleaning challenges since 1920. Questions about equipment fit and part compatibility come up in almost every application discussion we have. Getting the answer right at the start saves significant time and cost downstream.
Reach out to our team if you are assessing a cleaning process. We are happy to help you find the approach that fits your parts and your process.
