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Ultra sonic cleaner testing and information.

Many workshops will have a bench top ultra sonic cleaner, on the whole they will work well for years but if they do break down it may not be obvious until you realise that things put in to clean are not being cleaned properly.

You can buy a piece of test equipment that you immerse into the cleaning solution and it tells you how strong the cavitation is. We used to use one to test the ones we had around the hospital but they are not cheap and you are unlikely to have one, apart from that it would be difficult to justify one if you only have one or two units in your hospital

Fortunately there are two other ways of testing that can be done without that sort of test equipment.

Firstly a little information just for your interest, and mine.

How do they clean?

The following is thanks to Hilsonic makers of a variety of Ultra sonic cleaners.

In a process termed “cavitation”, micron-size bubbles form and grow due to alternating positive and negative pressure waves in a solution. The bubbles subjected to these alternating pressure waves continue to grow until they reach resonant size. Just prior to the bubble implosion, there is a tremendous amount of energy stored inside the bubble itself. Temperature inside a cavitating bubble can be extremely high, with pressures up to 500 atm. The implosion event, when it occurs near a hard surface, changes the bubble into a suction jet about one-tenth the bubble size, which travels at speeds up to 400 km/hr away from the hard surface. With the combination of pressure, temperature, and velocity, the jet frees contaminants from their bonds with the substrate. Because of the inherently small size of the jet and the relatively large energy, ultrasonic cleaning has the ability to reach into small crevices and remove entrapped soils very effectively.
Some have heaters and some do not, the best temperature is between 50oc and 75oc

Cleaning solution to add to the water.

Soils adhere to the parts… if they didn’t, the soil would just fall off the parts! The purpose of the solution is to break the bonds between parts and their soils. Water alone has no cleaning properties. The primary purpose of the ultrasonic activity (cavitation) is to assist the solution in doing its job. An ultrasonic cleaning solution contains various ingredients designed to optimise the ultrasonic cleaning process. For example, increased cavitation levels result from reduced fluid surface tension. An ultrasonic solution will contain a good wetting agent or surfactant.

At its most basic you can use a small amount of washing up liquid.

Testing your unit.

Degassing your cleaning solution.
You need to degas the solution in your cleaner when you first fill it up with a clean solution. This needs to be done in general use and not just for testing.

Once filled with water the ultrasonics should be left operating for a few minutes so that excess air is driven from the liquid. Tiny bubbles will be seen to rise to the surface but this is gaseous cavitation and not suitable for cleaning. At the end of the de-gassing period, a hissing sound and a churning of the liquid surface (cold boiling) should occur indicating vaporous cavitation.

The glass slide test.
Wet the frosted portion of a glass slide with tap water and draw an “X” with a No. 2 pencil from corner to corner of the frosted area. Making sure that the tank is filled to the fill line, immerse the frosted end of the slide into fresh cleaning solution. Turn on the ultrasonics. The lead “X” will begin to be removed almost immediately, and all lead should be removed within ten seconds.

The foil test.
Cut three small pieces of aluminium foil about 4″ x 8″ each. Fold each piece over a rod that you will use to suspend the foil in the tank. A clothes hanger works well. Your cleaner should be filled with an ultrasonic cleaning solution, degassed, and brought up to normal operating temperature. Suspend the first “square” in the centre of the tank and the other two a couple of inches from each end of the tank. Make sure that the tank is filled to the fill line, and turn on the ultrasonics for about one minute. Remove the foil and inspect: All three pieces of aluminium foil should be perforated and wrinkled to about the same degree.

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