Recycled algae paper density control system for quality screening with adjustable light source wavelength

. One of the biggest challenges in paper recycling is to ensure even density over the entire area of the sheet. The result is influenced by several parameters: 1) the technology used to prepare the pulp, 2) the equipment, especially the pulp feed mechanism and levellers, 3) the raw materials, such as pulp, its substitutes and, in the case of recycled paper, fillers. A common control method is to scan a sheet of paper against a light source. In this way, changes in density in one sheet can be detected and changes in density of paper pulp can be visually assessed. However, this is not enough for automated production, where information needs to be stored to control the quality of many sheets or large areas of paper, as well as to provide feedback to automated line executives. In a small laboratory environment, numerical quality control makes it possible to objectively compare the design results with changed initial parameters: pulp concentration, raw material fineness, application thickness, smoothness, temperature, etc. For fine quality control, a wide range of visible light wavelengths can provide information. In a situation where the longitudinal dimensions of the fibres are in the order of 10-200 μm, their cross - section is comparable to the wavelength of the light used. In this case, the difference between the sheet scans at 420-450 nm (blue light) and 680-720 nm (red light) shows the proportion of fine fractions in the soft pulp used, which in turn causes changes in the physical parameters of the resulting paper (abrasion resistance, tensile strength, water resistance). Our device allows to automatically measure the differences in the intensity of transmitted light at different wavelengths, which allows us to draw conclusions about the compliance of the applied parameters with the expected result.