Medium Density Board Performance Measurement Method
The main production process of medium density board is chipping hot grinding drying paving hot pressing sawing sanding plate embryo sorting packing out of storage. In the experiment of tracking and measuring the change trend of core temperature during hot pressing, the slab is divided into two layers equally and evenly, separated by yarn mesh in the middle (the purpose is to make the thermocouple contact to the core position accurately, so as to accurately measure the change of core temperature during hot pressing).
We mainly measure the absolute moisture content, density, plane tensile strength, static bending strength, water absorption thickness expansion rate of the density plate. Firstly, the water content of the sheet was measured preliminarily by the induction moisture meter, and the ratio of the difference of the quality of the sample before and after drying to that after drying was determined. The strength of the inner joint is the ratio of the maximum tensile force perpendicular to the plate surface and the area of the specimen. After microwave drying, the cross-section density distribution of MDP is very uniform, which is obviously different from that of conventional hot-pressing plate. This is because microwave preheating makes the temperature difference of each layer of the blank smaller. After microwave preheating, the minimum density of the plate is higher than that of the ordinary hot-pressed plate, and the percentage of low density in the core layer is higher than that of the plate without microwave preheating.
Because microwave preheating strengthens the heat transfer effect, reduces the temperature difference, and reduces the time required for the core to reach the curing temperature of the adhesive. If the density difference between the surface layer and the core layer decreases and the profile density distribution curve tends to be flat, the change of strength properties will be opposite. That is to say, the internal bonding strength will increase, the nail holding force of the material will increase, and the mechanical processing performance will be better, but the static curvature will decrease slightly. Microwave preheating can increase the density of the core layer and enhance the internal bonding strength of the density plate. The density of the surface layer of MDF plate is still higher than that of the core layer, which can maintain the hardness and good coating properties of the plate surface.