Essential Guidelines to Automotive Cleanliness Testing
The automotive industry is still one of the fastest growing industries in the world. With different types of vehicles being released on a yearly basis, from many emerging car manufacturers releasing different versions of cars and other vehicles, one of the most important considerations for these cars is safety.
Different sets of automotive standards are currently being referenced for determining various aspects of safety. One of the most heavily cited automotive guidelines publications is the Verband der Automobilindustrie (VDA Volume 19.1, 2015) which with the ISO 16232 (2018), released a standard for automotive cleanliness testing. hese standards, however, have developed from their "roots" in 2009, when the first version for a standardized method for cleanliness testing for automotives parts was released by General Motors (GMW16037). Since then, these standards have been revised in 2017 and again in 2021.
This initiative of General Motors to develop an internal set of standards for the analysis and detection of particulates became the starting point of ensuring that automotive parts are free from particulates that may be a result of faults along the manufacturing process. Isolating these particulate residues can provide an insight on where, in the manufacturing process, faults usually occur, and will also provide an insight on future wear and tear of the cars. The 2009 version of the Automotive Cleanliness Testing standards only cited a gravimetric technique that specifies a 10um Nylon Membrane Filter, with a provision of using a 40um Nylon Membrane prefilter when necessary, upon the appearance of larger particles in the retentate that causes the vacuum filtration to exhibit a high back pressure. In 2017, GMW16037-2017 was released to not just include gravimetric analysis but also to include microscopy techniques. It also introduced two methods: Method A and Method B.
| Method | Description |
| A | Is typically applicable when measuring gross amounts of sediment such as foundry sand or in process parts that are rough machined. This method may also be used when there is a need to provide faster results for a large number of components or to reduce costs. |
| B | Based on the ISO 16232 methodology for measuring debris. This method uses more rigorous procedures resulting in a tightly controlled and repeatable methodology. It is typically employed for parts that are finished machined with interior passageways that require a higher lev |
New Standards for Automotive Cleanliness Testing
In the latest standards being shared by VDA 19.1, GMW16037 and ISO 16232, the specified Nylon membrane and its pore size became less strict. Recommended alternatives were provided for Method B: ive- or ten-micron PVDF, Nitrocellulose or Polyester Material, in sequence with a 40-to-150-micron prefilter that is compatible with a non-polar organic solvent. Sterlitech offers membranes for the Automotive Cleanliness Testing that can fit the leading Component Cleanliness Cabinets which typically use a 47mm diameter filter.
Table 1. Chemical Compatibility of Recommended Membranes for Automotive Cleanliness Testing
| Method | Wash liquid | |||||
| Aqueous | Isopropanol | Ethanol | Oils/Petroleums | Ketones | ||
| A | Nylon Cleanliness Test Filters, 47mm, 100/Pk | + | + | + | + | + |
| B | Cellulose Acetate Membrane Filters, 5.0 Micron, 47mm, 100/Pk | + | + | + | - | - |
| Nitrocellulose Mixed Ester (MCE) Membrane Filters, 5.0 Micron, 47mm, 100/Pk | + | - | + | + | - | |
| Polyester (PETE) Membrane Filters, 5.0 Micron, 47mm, 100/Pk | + | |||||
| Nylon Membrane Filters, 5.0 Micron, 47mm, 100/Pk | + | + | + | + | + | |
Reference: Sterlitech Corporation - Chemical Compatibility Chart
This flexibility and preference for Method B (as listed in the latest standards) makes Automotive Cleanliness Testing more accessible to car manufacturers and Automotive Quality Control testing facilities. This development also removes the limitations on the use of Nylon Specific methodology with the inclusion of recommended alternatives.
One important factor taken into consideration by the updated guidelines is the inclusion of blank testing. Blank testing ensures that no residuals of any kind, ranging from stray fibers to particles are present on the filter material.
Upon the selection of an ideal membrane filter suitable for the application, the membrane filters with the particulates are dried in an oven and are subjected to gravimetric analysis. Sterlitech membrane filters offer lot-to-lot consistency; Nylon, MCE, PETE, and CA also offer thermal stability within the oven drying conditions of 105 degrees Celsius o that the membranes do not disintegrate after gravimetric testing.
A suitable membrane filter also provides accuracy in weighing and achieving very low deviations ideal for accurate gravimetric data as well as for imaging studies when identifying and categorizing particulates under a microscope.
Once these particulates are differentiated and categorized, quality control measures can be put in place to confirm contamination sources. This confirmation can be used to support decision making, process improvement, and safety.
References:
- Faber, J., Brodzik, K., Nycz, M. Understanding technical cleanliness: importance, assessment, maintenance. Combustion Engines. 2021, 186(3), 41-50. https://doi.org/10.19206/CE-140531.
- International Standard ISO 16232 First edition 2018-12 Road vehicles — Cleanliness of components and systems.
- Test Method to Quantify Cleanliness of Engine and Transmission Components. (2017). General Motors Worldwide (GMW), 3rd Edition, July 2017, pp.1-10.
- Verband der Automobilindustrie, Quality Management in the Automotive Industry, Inspection of Technical Cleanliness, Particulate Contamination of Functionally-Relevant Automotive Components / 2nd Revised Edition, Volume 19, Part 1, 2015.
