How is particle analysis with microscopes important for cleanliness analysis?
Nicol Ecke: In contrast to gravimetric measurement or manual measurements of the largest particles with a microscope, automated particle analysis with a microscope provides a complete size distribution of all particles, different measurement parameters, such as length and width, as well as objective and reliable measurement results. Choosing the correct analysis system depends on the requirements and specifications of the components. Microscopes are proven to be good analysis systems, because the particles are easy to detect, due to their high contrast from the filter surface, and can be automatically evaluated. A particle’s potential to cause damage can be characterized with the determination of its length, width, and amount. In addition, metal or corundum (sapphire or aluminum oxide) particles, which have a higher potential for damage than, for example, soft plastic particles or fibers, can be distinguished. Particles can be, in accordance with the analysis, re-localized, examined, and documented. They can also be inspected by the optical imaging system using different magnification values and contrast methods.
Leica Microsystems offers a suitable solution for every cleanliness requirement. For the standard analysis according to VDA19 or daily analysis of particles greater than 30 µm, the DMS1000 digital microscope is an ideal solution. Compound microscopes, such as the DM4 M and DM6 M microscope, offer a higher resolution. Here, even particles as small as 5 micrometers, in addition to larger particle sizes, can be evaluated in compliance with standards. This capability is important, for example, when checking the purity of oils or if the components have strict specifications. For these cases, to be able to make evaluation in accordance with standards, higher optical resolutions are needed, as described in ISO16232, VDA19, and DIN 51455.
Compared to particle counting flow meters, which are based on light scattering and provide neither information about the true geometry (length and width) nor the nature of the particles (metallic or non-metallic), microscope based solutions provide detailed and reproducible results. Results and images can be documented in a report at the click of a button. Also, a problem that can occur with flow meters is inaccurate results, for example, oil droplets or air bubbles can be counted as solid particles. Large, heavy particles can fall to the bottom of the liquid and then are often not counted. Therefore, the microscope solution offers decisive advantages, because all the particles can be accurately detected, assessed, analyzed, and documented.