Causes of Black Spot on MDF Boards Surface
Medium density board black spot is a very headache problem, especially in winter and spring, there are many black spots on the density board, which not only caused huge economic losses to enterprises, but also damaged the reputation of enterprises, making people very distressed. What is the reason for the black spot on the density board? Here is how the small edition comes to everyone. .
Black spots are prone to occur in the manufacturing process of MDF in one year, which occurs frequently in winter and spring. The phenomenon of black spot is very serious when the temperature is below 13 C in winter, but it will be more serious when the air humidity increases in spring, when the air humidity exceeds 60%. The area of black spot is larger. The density plate with black spot will increase greatly compared with winter. In this way, the production of black spot on density plate has a very big relationship with temperature and air humidity.
In fact, black spots are produced by the accumulation of wet powdery fibers on the density board. In winter and spring, due to the lower temperature, higher air humidity and higher temperature of wood fibers after drying, the temperature difference between the two is large, and the maximum temperature can reach 40-60 degrees C. Even after drying, the moisture content of wood fibers can still reach more than 10%, and the moisture in wood fibers will evaporate continuously, so that it will be produced in the future. During the process, it contacts with the inner wall of the ice-cold conveying pipeline, and when the temperature of the pipe wall drops below the dew point temperature of the wet air, the moisture in the wet air continuously precipitates, forming condensate water on the pipe wall of the conveying pipeline, while the dried fibers fly around under the action of the airflow, and the raised powder fibers contact with the condensate of the conveying pipeline and bond on it to produce wet powder. In the process of fibre transportation, because of the constant collision and friction between fibers, the wet fibers on the pipe wall are scraped off from the pipe wall. These wet fibers on the pipe wall can not be sorted out and then sent to the forming pavement like normal fibers. These wet fibers are scattered on the slab surface during hot pressing. The degree of acid hydrolysis and thermal degradation during hot pressing is much greater than that of normal wood fibers, and water-soluble substances will appear. On the drying machine, the density board is fully air-dried, and the fibers are eventually dried, resulting in black spots on the surface of the density board.