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