VDA 19 originally described the testing of technical cleanliness exclusively by means of extraction procedures with liquid extraction media. However, wet extraction is rather unsuitable for components that are not likely to come into contact with liquids during use or that can be damaged by liquids. This applies in particular to the testing of electronic components, for parts of the intake tract of engines, air filters, or also for logistics packaging such as blister packs, small load carriers. The dry extraction method can ultimately also ensure that the components can be reused after testing.
In the VDA 19, there are therefore new "dry" extraction methods since 2015: In addition to flow-through air extraction, also air jet extraction, in which the components are air-blown in a closed chamber and can thus also be sampled dry.
Air jet extraction by blowing off according to VDA 19 comes very close to pressure-rinsing with liquid media, because a jet of compressed air is used to blow off the components manually in an extraction cabinet. The particles are deposited on the wetted walls of the cabinet and are then rinsed off the walls by liquid extraction and transferred to the analysis filter.
Accordingly, air jet extraction is a combination of dry primary extraction with subsequent wet secondary extraction, which is similar to the final rinse procedure of a pressure-rinsing extraction.
The component can be removed dry from the extraction.
Due to the closed extraction cabinet, the component size that can be tested is limited by the size of the cabinet and meets specified limits, especially for battery systems in the field of e-mobility.
Suction extraction is a variant of air jet extraction that has been further developed by CleanControlling. Suction extraction is characterized by the fact that the components are not blown off, but sucked off.
By means of a vacuum generated by a suction module, the paticles are collected from the component surface via a suction nozzle. It is important to ensure that the suction nozzle is guided very close to the component surface so that the particles are effectively collected. This is usually assisted by the attachment of a brush to the nozzle, which mechanically assists in the removal process. The surface of the component determines whether a standard nozzle or specific suction nozzle geometry or specific brushes are used.
The system has several options for separating the particles from the suction stream. The particles can be separated from the suction stream via the cyclone and deposited in a laboratory bottle. Optionally, the suction hose can also be connected directly to a filter holder and the particles separated onto the analysis filter. For analyses directly in the production process, the particles can also be deposited via the cyclone directly onto a particle trap, which can then be easily and quickly exchanged, labeled and placed under the microscope without further preparation.
Compared to manual air extraction, suction extraction is particularly suitable for mobile use on large components or directly in the process environment. The component remains dry, does not have to be sampled in the laboratory and can be reused afterwards.