Internal and external cleanliness of products

Product cleanliness testing is a very important element in the quality assessment of many components, especially those having contact with operating fluid. Such tests are carried out in a clean room of ISO 6 cleanliness class (according to ISO 14644).
The basic factors determining the purity of the tested object are: mass of insoluble impurities, mass of soluble impurities, amount of insoluble impurities of a certain size and type of contamination. In the case of insoluble (solid) impurities, it is possible to divide them according to their nature: metallic, non-metallic and fibers, as well as by chemical composition. In order to determine these properties, an appropriate extraction liquid is selected (it must be compatible with the component material) and method of pollutants extraction is selected: agitation, pressure washing, ultrasonic techniques, washing on functional test benches reflecting the working parameters of the test object. The choice of the extraction method depends on the characteristics of the tested object and on the specified properties: internal/external/overall purity.
Extracted pollutants are analyzed by the following methods:
  • gravimetric – the mass of contaminants
  • microscopic – the quantity and size of the contaminants
  • scanning electron microscopy (SEM)– the chemical composition of the impurities
  • infrared spectroscopy – the chemical composition of organic impurities



BOSMAL is the only laboratory in Poland accredited for testing of cleanliness according to ISO 16232, VDA 19.1 and DIN 8964-1


Testing norms

  • ISO 16232
  • DIN 8964-1

Testing norms from the industry and customers’ own norms

  • VDA 19.1, QV 11111, DBL 6515, DBL 6516, PV 3347, PV 3370, PV 3336, VW 01134, VW 01137, Volvo STD 107-0002, Scania STD 4189, GMW 16037, NW 22-10-202, SAE J1726, Continental TST N 002 02.22, Wabco JED 593, BWS 42001, Renault 34-07-012, Renault 34-07-025 and others.

Evaluation of cleanliness by surface tension test

One of the simple and fast methods of determining the cleanliness of surfaces is to test the surface tension by applying test inks / markers.
Surface contamination, especially that resulting from metal alloys which are formed in the course of production process, reduces adhesion of paints, adhesives or galvanized coatings.
Clean surfaces have a material- specific surface tension. Clean surfaces have high surface energy, while in case of contaminated items surface energy proves to be much lower. 
It is assumed that a correct value of surface tension for metallic surfaces should be min. 44 mN / m for processes such as gluing, welding or coating to be effective. Typically, for cleaned surfaces, depending on the cleaning process applied, the surface tension ranges from 38 mN / m to more than 70 mN / m. In case of oily surfaces, the surface tension ranges from 25 to 35 mN / m.
The cleanness assessment technique related to surface tension consists in applying a test ink with an appropriate value of the surface tension to the tested surface. Observing the behaviour of the stroke of ink on the surface allows to determine the minimum value of the surface tension of the tested item.
Document No. Title/Description
ISO 16232 Road vehicles - Cleanliness of components and systems
VDA 19.1 VDA Volume 19 Part 1, Inspection of Technical Cleanliness - Particulate Contamination of Functionally Relevant Automotive Components
DIN 8964-1 Circuit components for refrigerating systems - Part 1: Testing