First, let us congratulate you for asking this question. Any time flammable solvents are used for cleaning purposes there is risk of fire or explosion due to ignition of volatile vapors by a flash source. Ignition can occur from any source due to spills or as flammable solvent vapors spread. This post explains how you can safely use flammable solvents in an ultrasonic cleaner.
An example of a widely used flammable solvent is isopropyl alcohol (IPA). References to its use are presented in this post.
Things to Know about Flammable Solvents and Ultrasonic Cleaners
Before you select and use an ultrasonic cleaner for your application(s) you should be familiar with options available as well as other factors that go into the decision process. Here you will learn about
- the definition of “flash points”
- flash points of commonly used flammable solvents
- where ultrasonic cleaners are used with flammable solvents
- ultrasonic equipment options when cleaning with flammable solvents
- other safety precautions when using flammable solvents in an ultrasonic cleaner
What is a Flash Point?
As noted in our introduction, 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.
Flash Points of Commonly Used Flammable Solvents
A table of common organic solvents and their flash points has been published by Louisiana State University. Examples of low flash point volatile solvents are 1-propanol (IPA) at 53⁰F, acetone at -4⁰F and toluene at 40⁰F.
Because of its relatively low flash point IPA, when used in an ultrasonic cleaner, creates what is defined by the National Electric Code (NEC) as a hazardous location. This is because fumes or spilled solvents can be ignited by extraneous sources such as electrical equipment, associated wiring as well as an ultrasonic cleaner improperly used or not certified as explosion proof.
Examples where Flammable Solvents are used in Ultrasonic Cleaning
The following examples use IPA, but can apply to other volatile solvents.
- 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.
- Small X-ray tube components are cleaned in a volatile solvent 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. Following this cycle the tank is drained and filled with acetone for the second cycle. After the acetone is drained the tank is refilled with the solvent for the third ultrasonic cleaning cycle to achieve the extreme cleanliness required.
- 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 to thoroughly remove powder residues that accumulate on nozzles.
Ultrasonic Equipment Options for Flammable Solvents
Elma offers a number of options whereby ultrasonic cleaning energy can safely be employed when using flammable solvents such as IPA. Here are 2 examples:
1. 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.
Containers should never be tightly sealed as expansion due to heat created by ultrasonic cavitation could cause them to break.
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.
You can purchase flammable solvent beaker kits that are ideal for this option.
2. 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.
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 us for information on selecting and using an ultrasonic cleaner for flammable solvents.