Millipore testing: 9 questions every engineer wants answers to

Have you ever wondered why your finished components fail to pass millipore testing? You’re not alone.

There are thousands of variables that go into achieving the desired millipore value. Therefore, it can be challenging to understand why you’ve landed outside your specifications.

We’ve worked with engineers and manufacturers, testing various industrial fluids, and learned much about millipore testing. Please click here to learn about Innovation Filter System.

More importantly, this experience has led us to create this blog that manufacturers will find helpful.

If you’re struggling to achieve the desired millipore values, contact us today!

Estimated reading time: 8 minutes

What is Millipore?

Manufacturers use millipore testing to determine the cleanliness of a finished component. It tests the presence of any solid particles or other non-soluble contaminants.

Interestingly, the test gets its name from Millipore Corporation, making filters often used as the media in these tests.

The filters are small, flat discs acting as sieves to trap different particles.

Why is millipore testing necessary?

Millipore testing is a crucial quality-control measure. Manufacturers can also use these tests to validate that tools and other parts have undergone proper cleaning. Also, to test the effectiveness of their filtration systems.

Millipore in auto-industry

The auto-OEMs and auto-component manufacturers use millipore testing to validate the cleanliness of fluid systems and other components.

Particle contamination can lead to inefficiencies, safety concerns, and significant engine wear over a vehicle’s lifetime.

To counteract this, manufacturers use automotive parts washing and millipore cleanliness testing to establish quality standards.

Millipore in pharma-industry

Likewise, because of regulations and safety standards, pharmaceutical industry manufacturers must be aware of the cross-contamination risks.

Hence, these companies must be aware of potential contaminants in their machine tools. Therefore, testing with millipore is essential.

Millipore test standard

Any accredited testing laboratory should specify the test standard as a basis for their results.

The universally accepted testing standard for cleanliness of components and systems is ISO 16232:2018.

The ISO 16232:2018 test standard aims to improve the results’ quality and make them more comparable. Moreover, it also defines a standardized way of measuring and expressing cleanliness specifications in the automotive industry.

Millipore test procedure

The ISO 16232:2018 document gives details of the procedure and test apparatus required to arrive at the Millipore value. In practice, the millipore testing procedure is as follows-

1. Take a component whose millipore value is to be determined.
2. Wash this component with a component cleaning chemical and collect the chemical in a beaker. One liter of the fluid sample is sufficient.
3. Take a filter paper of known pore size- 5 microns, 2 microns, 0.5 microns.
4. Clean the filter paper using heptane. Then dry it in an oven at a set temperature.
5. Remove the paper from the oven after a set time and note the ‘before’ weight of the paper.
6. Pass the dirty chemical sample (collected in step 2) through filter paper using the test apparatus.
7. The filter paper will trap the contamination greater than its pore size.
8. Once all dirty chemical passes through the filter paper, the paper is again washed using heptane and dried in the same oven at the same temperature for the same time.
9. Check the weight of the dirty filter paper on the same scale; this is the ‘after’ weight of the paper.
10. The difference in after and before weight of the filter paper gives the dirt weight on the component.
11. Thus, we get dirt weight (usually in milligrams-mg) per liter of chemical. Mg/liter or parts per million (ppm) is the millipore value of the component.

Here is an excellent video showing the test procedure and millipore test equipment.

Millipore test report format

How do you test for the millipore value of a finished component? You use a test kit, usually known as a patch test kit. Many companies have an in-house testing facility. However, some companies prefer sending their samples to a lab.

Interpreting the test reports

Below are images from millipore test reports we had done for one of our customers to validate our coolant filtration solution.

(We have removed the customer’s name for privacy purposes. However, kindly email us if you want us to provide the original report. Please click here to get our email address.)

Following are the essential points to note about the test report-

Sample collection

We must conduct the same test on the ‘before’ and ‘after’ samples collected from the same source or location. In the above case, our engineers had collected the coolant sample ‘before’ passing it through our filtration system and ‘after’ passing it through our filtration system.

Test standard

The report should clearly state the standard or method used to conduct the tests. The lab adopted the ASTM D 4807 test method in the above example.

Filter patch

The report should also state the filter paper porosity. You can specify the porosity you want and even test on 0.5 microns paper. The lab used 47 mm diameter filter paper with 5 microns porosity paper.

However, note that the patch porosity you choose would decide the size of contaminant it will trap. The above example assumes that the 5-micron patch will trap all particles above 5 microns.

The results will be different if we conduct the test of the same sample on a different porosity paper.

Unit of measurement of millipore value

The unit of measurement of a millipore test using ‘gravimetric analysis‘ is mg/lit.

Mg. or a milligram is a unit of weight and liter is the unit of volume of the fluid sample.

Thus, from the above example, we can conclude that 76 milligrams of contaminant are present in a liter of clean coolant sample.

There are two ways a customer can interpret the above results-

• Firstly, you can compare the ‘after’ value with the desired specified value or process parameter.

In the above example, suppose the process demands that the clean coolant have no more than 50 mg/lit contamination (above 5 microns in size). In that case, we should reject or consider improving the filtration system.

However, the above clean coolant sample is acceptable if the process demand was 100 mg/lit (on a 5 microns patch).

• Secondly, you can specify the quantum of contamination reduction between the ‘before’ and ‘after’ samples.

For example, you can specify that the filtration system should reduce the contamination in a dirty fluid sample by at least 50% or even 90%.

Millipore test specification

Verification of test results

What could lead to a high millipore value?

If the millipore values are higher than expected, verifying the validity of the testing is relatively easy.

Firstly, ensure that you perform the procedure exactly as specified. It’s easy to miss the details if there’s a change in personnel or equipment.

Secondly, run the test without the components; since they’re the intended source of contamination, the result should show no contamination at all!

If not, your specification may need some tweaking, or your collection procedure isn’t working correctly. Either way, it’s worth running a “dummy” test before making any changes to your system.

If all the above is satisfactory, then it’s worth looking at other aspects of the test-

Solvent

For the solvent you use during testing, it’s essential to ensure that it is pure and well-filtered. If not, there could be contaminants in the solvent, which could wrongly increase the millipore value.

Clean equipment

Please make sure you clean the equipment before you use them for testing. You must ensure that the entire test kit is cleaner than the parts you are testing.

Dry patch

When performing the test, it’s crucial to ensure that the filter patch is dried adequately before weighing it. Check that you set the oven temperature correctly and that drying time is sufficient.

What could lead to a low millipore value?

Suppose your dummy test produces a result lower than the specified value. In that case, you should test one of the proven parts that meet the specification.

Alternately, you could run tests on a single part repeatedly. Each time, the measured level of contamination should trend lower as each iteration removes some of the initial contamination on the component.

If the millipore values are much lower than expected, you may want to ask some questions. Either the parts are cleaner than they used to be (a good thing), or something is missing from the collection process for some reason.

Things to consider in case of historically low millipore values-

• Low spray pressure
• The location of collecting the samples may be incorrect
• If the part is not demagnetized properly, it will hold particles

Conclusion

So, what have we learned?

We know that millipore testing is essential to achieving desired finished product quality. We also know that it’s important to understand the millipore test, its standard, and how we can use it to achieve our desired output.

The bottom line: don’t leave your millipore testing up to chance! Use this information to help you achieve your desired output. Then, ensure consistent results with each batch of products you manufacture.