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Film testing on an ultrasonic bath – reliably testing function and cavitation

With the Foil test The operation of an ultrasonic bath can be checked easily and clearly. Aluminium foil makes the intensity and distribution of cavitation in the vibrating tank visible.

When carried out regularly under comparable conditions, the film test helps to detect changes in the ultrasonic effect at an early stage and to assess the functionality of the ultrasonic bath.

Your benefits at a glance:

Simple functional test of the ultrasonic bath
Visually assessing cavitation
Comparing test results
Document the examination in a way that is easy to follow
Suitable film test frames for different tub sizes

What is a film test?

The The foil test is a method for testing the functionality of an ultrasonic bath in accordance with IEC TR 60886. Its purpose is to visualise the intensity and distribution of cavitation within the vibrating tank.

To do this, a thin aluminium foil is stretched over a foil test frame and placed in the prepared ultrasonic bath. During the ultrasonic treatment, the cavitation events generated by the ultrasonic waves act upon the foil. This results in visible perforations and holes.

The resulting perforation pattern provides information on how cavitation is distributed within the tested area.

What does the film test check for?

The film test helps in assessing,

This makes the film test particularly suitable for the regular functional and process monitoring of ultrasonic baths.

Why should an ultrasonic bath be checked regularly using a film test?

The cleaning effectiveness of an ultrasonic bath is largely determined by the resulting Cavitation determined. However, without the film test, it is not possible to reliably determine whether and how this is distributed within the vibrating trough.

The foil test makes the effect visible.

BANDELIN recommends carrying out a test before the first use and then at regular intervals, for example quarterly. The actual frequency of testing required depends on the specific application and is the responsibility of the operator.

1. Check that it is working

The perforation in the aluminium foil indicates that cavitation is acting on the test surface.

2. Compare results

If the test conditions are kept constant, current film tests can be compared with previous results.

3. Recognising changes

Significant deviations in the perforation pattern may give cause to examine the operating conditions or the ultrasound device more closely.

4. Document the test

The test date, device and result can be recorded and archived for future comparison.

Carrying out a film test: step by step

To ensure that the results of different film tests remain comparable, the tests should, where possible, always be carried out under the same conditions.

The validated process, step by step:

1.Filling the ultrasonic bath

Fill the vibrating tank with water and a suitable ultrasonic cleaning agent up to the designated fill level mark, using the dosage specified by the manufacturer.

2.Degassing the ultrasonication fluid

Before testing, degas the freshly prepared ultrasonic cleaning fluid in accordance with the ultrasonic bath’s instructions for use.

3.Stretching aluminium foil

Stretch the aluminium foil (household foil, 10 μm to 25 μm thick) over the foil test frame. Depending on the size of the tray, the frame may protrude. It is sufficient to stretch the part of the foil test frame that will be covered by the ultrasonic liquid.

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4.Position the film test frame

Place the film-covered test frame diagonally in the centre of the vibrating trough.

Secure it if necessary.

5.Sound the film

Switch on the ultrasonic device and apply the ultrasonic waves to the film until a visible perforation or hole appears.

As a guide, the film should be at least one minute ultrasonic treatment. For sturdier, thicker or coated films, a longer ultrasonic treatment time of up to approximately three minutes may be required.

6.Remove the film

Switch off the ultrasonic cleaner, remove the foil test frame from the tank and then carefully remove the aluminium foil.

Leave the film to dry.

7.Assess the result

Following a successful foil test, there should be a clearly visible perforation in the aluminium foil.

If the expected perforation does not occur, the test conditions should be checked first. If this does not identify the cause, a technical inspection of the ultrasound scanner is recommended.

8.Document the film test

Label and document the result, for example, as follows:

Test date
Device or serial number
film used
Duration of sound exposure
Test conditions
Results or any abnormalities

The test film can also be photographed, scanned or archived.

9.Cleaning the swing tray

Rinse the vibration tank thoroughly after the foil test to ensure that no aluminium particles that have come loose remain in the tank.

What is important to bear in mind when carrying out a film test?

A single film test shows the current condition during the test. However, the method becomes particularly meaningful when several tests can be compared with one another under conditions that are as identical as possible.

To ensure that film tests are reproducible, the following parameters in particular should therefore be kept constant and documented:

✓ Fill level of the vibrating trough
✓ Temperature of the ultrasonication fluid
✓ Degassing time
✓ Position of the film test frame
✓ Type and thickness of aluminium foil
✓ Duration of sound exposure
✓ Type and concentration of the ultrasound contrast agent

Mnemonic:
No two slides need to look exactly the same – what matters is that the tests are carried out under comparable conditions and that any changes in the results can be detected.

Analysing a film test: What does the perforation pattern tell us?

During ultrasonic treatment, cavitation acts on the taut aluminium foil, creating characteristic perforations.

In the event of repeated tests under the same conditions, the perforated areas should be examined with regard to Extent and distribution are roughly comparable . However, a completely congruent hole pattern is not to be expected.

Consistent or comparable result

The pattern of perforations largely corresponds to previous reference results in terms of extent and distribution.

A significantly different result

If the current perforation pattern differs significantly from previous tests, all test conditions should first be checked.

Insufficient perforation

If no perforation is detectable despite the test having been carried out correctly, the ultrasonic bath should be inspected for technical faults.

Document foil tests and compare results over the long term

Clear documentation makes it easier to carry out regular functional checks on the ultrasonic bath.

In addition to the test parameters, particular attention should be paid to the Test date and the serial number of the ultrasonic bath be documented.

The aluminium foil used can then be kept or digitally archived – for example, as a scan or photograph. This makes it easier to compare current results with previous foil tests.

BANDELIN Film Test Documentation Sheet

The BANDELIN documentation sheet can be used to record the key test conditions and results in a structured manner.

The right products for every application

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FAQ – Film Test

What is a film test?

The foil test is a simple method for checking the functionality of an ultrasonic bath. A taut aluminium foil is exposed to ultrasonic waves and perforated by the resulting cavitation. This makes the intensity and distribution of the cavitation effect visible.

How often should a film test be carried out?

BANDELIN recommends carrying out a film test before the first use and then at regular intervals, for example every quarter. The specific frequency of testing depends on the application and is determined by the operator.

What type of film is used for a film test?

Suitable aluminium foil can be used for the foil test. BANDELIN states that standard aluminium foil has a thickness of approximately 10 to 25 µm. Pre-cut foil sheets are also available for various foil test frames.

How long does a film test take?

The actual ultrasonic treatment usually lasts at least one minute, or until a visible perforation or hole appears. With more robust films, a longer ultrasonic treatment time may be required.

What does a successful film test look like?

After the sound exposure, the aluminium foil should be clearly perforated. In repeated tests carried out under the same conditions, the extent and distribution of the perforated areas should be roughly comparable.

Do two film tests have to look identical?

No. The perforation patterns do not need to be identical. What is crucial is that the test conditions are comparable and that there are no noticeable changes in the extent or distribution of the perforated areas.

Why does the ultrasonic bath need to be degassed before the film test?

Dissolved gases in freshly prepared cavitation fluid can affect the formation of cavitation. The fluid should therefore be degassed in accordance with the instructions for use before the film test.

What should you do if the film does not perforate?

First, check the test conditions, such as liquid level, degassing, positioning, film, sonication duration and the ultrasonic specimen. If the expected perforation still does not occur, the ultrasonic device should be checked.

How can a film test be documented?

In addition to the test date, device or serial number and test conditions, the film used can itself be archived. Alternatively, it can be photographed or scanned. The BANDELIN film test documentation sheet facilitates structured documentation.

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We - a Berlin-based family business in its third generation - specialise in the development, manufacture and distribution of ultrasonic devices, corresponding accessories and application-specific cleaning and disinfection preparations. The high vertical range of manufacture, a modern production facility and motivated employees distinguish us and are guarantors for constantly new quality products.