Explosion-proof ultrasonic cleaners must be used when cleaning tasks call for the use of volatile solvents to achieve the desired results. See examples below. When low flash point flammable solvents are involved in an ultrasonic cleaning operation, a number of precautions are called for in addition to using an explosion-proof ultrasonic cleaner. This is because using these solvents creates what the NEC and NFPA term a hazardous location.
A flash point is the temperature at which a particular organic compound gives off sufficient vapor to ignite in air when given an ignition source. In view of this, selection of an ultrasonic cleaner must take into account that not only do volatile solvents evaporate, but the heat generated by the ultrasonic cleaning process accelerates solvent evaporation and vapor generation.
Other areas of concern are addressed later in this post.
Flash Points of Commonly Used Flammable Solvents
Louisiana State University has published a table of common organic solvents and their flash points. Examples of low flash point volatile solvents that require an explosion-proof ultrasonic cleaner are 1-propanol (IPA) at 53⁰F, acetone at -4⁰F and toluene at 40⁰F.
Explosion Proof Ultrasonic Cleaner Applications
Before describing equipment options here are real-life applications using explosion-proof ultrasonic cleaners.
- Surgical Implants. One of the most common applications is cleaning surgical implants. These are frequently cleaned using IPA. Reasons? It evaporates quickly, is relatively non-toxic, and residue-free but requires an explosion proof ultrasonic cleaner.
- Stainless Steel Filters to remove ferrous contaminants using IPA or acetone.
- Remove Machining Oils and Particulates from traveling wave tubes, xenon ion propulsion systems, electronic power conditioners and microwave power modules.
- Small X-ray tube components are cleaned with a volatile solvent in an explosion-proof ultrasonic cleaner to yield absolutely contamination-free results. In an example using three steps the first step uses the solvent to remove oils that are deposited on the stainless/Kovar assembly.
- Electronic Components. Printed circuit boards, motherboards and other electronic components may accumulate solder flux and other contaminants during manufacture that must be removed prior to shipment. PCB manufacturers may be requested to use a flammable solvent to accomplish this. The process is faster, safer and more thorough than using sprays and brushes, the latter of which could damage delicate soldered joints.
- Regularly cleaning powder coating nozzles is an important procedure to maintain quality coatings. A supplier of powdered coated parts to the transportation industry uses an IPA solvent in an explosion-proof ultrasonic cleaner to thoroughly remove powder residues that accumulate on nozzles.
Ultrasonic Equipment Options for Volatile Solvents
Ultrasonic cleaning equipment provider Tovatech has a number of options whereby ultrasonic cleaning energy can safely be employed when using flammable solvents. Here are 3 examples
Use an Explosion-Proof Ultrasonic Cleaner
For large scale operations the SOL XP flammable liquid ultrasonic cleaning systems in 2, 4, 6, 9, 15 and 33 gallon tank capacities are available from Tovatech. These are designed to be used with low flash point volatile solvents.
These 40 kHz ultrasonic frequency units are compliant with all Class I, Division 1 (CID1) code and zone requirements. Different only in tank dimensions and capacities they can be fitted with a cooling jacket around the upper tank perimeter to capture solvent vapor and reduce odor.
The SOL XP explosion proof ultrasonic cleaners can be ordered with an Intertek ETL Certification and are shipped with a remote electrical panel to be located outside the CID1 envelope.
Units are nitrogen inerted for additional fire protection. Other included and optional features can be found on Tovatech’s SOL XP flammable liquid ultrasonic cleaning systems page.
Isolate the Solvent from the Environment
This method works best when the parts to be cleaned are relatively small and cleaning is done on an occasional basis rather than as a full-time procedure.
Carefully place the parts in a flask or beaker and add just enough solvent to ensure they are fully immersed. Cover the container loosely to minimize the vapor that will result during the cleaning process.
In this instance you can use tap water with a surfactant in the ultrasonic cleaning tank. Before proceeding remember to degas the solution by selecting the “degas” mode (if equipped) or by running the cleaner for 15 to 20 minutes without a load or until bubbles no longer rise to the surface.
Flasks can be fixed into position in a mesh basket using flask clamps, and beakers can be supported using a beaker cover instead of a basket.
In either case, the bottom 1-2 inches of the containers should be immersed in the water. The ultrasonic energy will penetrate the glass walls and cavitation action will occur in the IPA. At the conclusion of the process carefully remove the parts which, when dry, will be residue free.
Tovatech offers flammable solvent beaker kits that are ideal for this option.
An Explosion Proof Ultrasonic Cleaner for Very Small Parts
Extremely small parts such as watch parts, micro-optics, and micro-machined parts are very effectively cleaned, rinsed, and dried in the Elmasolvex VA ultrasonic cleaner.
This ultrasonic cleaner is certified to be explosion proof when used with solvents with a flash point ≥ 12°C (53⁰F). Optimum cleaning results are achieved using a combination of multi-frequency ultrasonic cleaning, oscillation, and vacuum technology. Cleaned parts are completely residue-free.
View this video for a short tutorial on how the Elmasolvex VA ultrasonic cleaner works.
Other Safety Precautions when Using Flammable Solvents
As noted earlier operating ultrasonic equipment when cleaning with flammable solvents creates what is called a hazardous area due to cleaning solvent and solvent fumes.
Fumes must be vented using approved ventilation systems. Electrical equipment, wiring, lighting fixtures, outlets and similar equipment in the area must be rated as intrinsically safe by the National Electric Code, NFPA-70 Articles 500-503.
In short, all components and equipment must be listed by a nationally recognized testing lab such as Underwriters Laboratories or Factory Mutual.
Contact the ultrasonic cleaning professionals at Tovatech for information on selecting and using an explosion proof ultrasonic cleaner.
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