Fuel cell technology can make a sustainable contribution to the energy transition. When hydrogen – produced using wind or solar energy, for example – reacts with oxygen, it produces electrical energy. Water is then the only and clean emission. The reaction occurs in a fuel cell, part of which are so-called bipolar plates. Fuel cells’ performance and lifespan depends strongly on the mechanical quality of these plates, such as their surface roughness, unevenness and other defects.
In the European Interreg project Super Surf, Demcon developed and realised a measuring system for the quality control of bipolar plates. Fuel cell producer Nedstack in Arnhem needed a simple, accurate and fast system for validating its production process. The measuring system had to cover the entire plate, operate contact-free, and be able to handle plates easily.
Demcon researched a range of optical measuring principles for Nedstack, and concluded that their suitability depends on the type of material. Bipolar plates are made of (highly reflective) metal or (dull, slightly reflective) graphite. Optical triangulation turned out to be the most suitable method for the quality control of graphite plates. Light is projected in a straight line onto the plate’s surface at an angle, and the reflected light is detected at a different angle. Height differences in the surface caused by roughness or defects can then be seen in a ‘ripple pattern’ of the reflected line.
Two linear actuators move the plate step by step under a set routine with exposure, optics and camera, each time effecting a line scan. All scans combined create a height map, where all ‘irregularities’ in the surface can easily be read. A high resolution can be achieved by limiting the vertical scanning range to 3 millimetres. Calibration with known etched patterns shows that a step height of 2.5 microns can be detected in the surface. Measurement repeatability is 5 microns, and the pitch between successive line scans can be set to a minimum of 10 microns.
The optical measuring system can measure a plate (size 18 x 25 cm) entirely within five minutes, at high resolution. Another option is to perform the measurement at a limited number of points. This shortens the measurement time and reduces the volume of measurement data. The Super Surf project has enabled Demcon to develop a working measurement system for graphite plates. This system participates successfully in quality control at Nedstack, and may contribute to a breakthrough in fuel cell technology.