Aerostatically sealed non-contacting paperboard porosity measurement device

Measurement of paperboard porosity on-line during the manufacturing process allows controlling the process with a shorter feedback loop than when measuring samples from the end of the process offline in a laboratory. In a previous study, the authors proposed a paper porosity measurement instrument based on sealing the paperboard sample with an air bearing and presented measurement results for stationary samples of paper. This study expands on the previous study by introducing a measurement device, that requires access to only a single side of the measured sheet. The investigated device seals a measurement volume against the paper sheet with a porous aerostatic bearing, and uses a vacuum groove to control the gap height between the measurement device and the measured sheet. The performance of the device was investigated with two paper samples of varying permeability and varying seal supply pressure. Additionally, the air gap height was measured with a laser displacement sensor. The results of the study show that the seal supply pressure has an effect on the measured permeability value. The gap heights for the measured samples were 2.5 μm and 4.4 μm. The study provided corroborative evidence for viability of the investigated device.