Fundamentals of Vertical Density Profile Formation in Wood Composites. Part III. MDF Density Formation During Hot-Pressing
Keywords:Medium density fiberboard, MDF, <i>in-situ</i> measurement, density profile, pressing, OSB, compression, radiation, consolidation
AbstractThe formation characteristics of the vertical density profile of MDF are presented herein. Results of laboratory studies indicate that the vertical density profile of MDF is formed from a combination of actions that occur both during compaction and also after the press has reached final position. The methodology, which was used to describe the formation of the density profile for OSB that used two periods and five stages, can also be used to describe the density profile formation of MDF mats. There was a clearer surface layer consolidation stage for MDF mats when compared to OSB mats. At least 58% of the area in an MDF mat was in "spring status" when the press reached 120% of final panel thickness. The observed stress-strain response of MDF mats in hot-pressing with the one-step closing schedule was similar to OSB pressing. This was characterized by a long stress plateau followed by a rapid increase in stress, followed by an immediate reduction in stress after the press reached final position. Compared to OSB hot-pressing, the same pressing schedules (traditional or step-closure) did not result in similar MDF density profiles. It appears that high-density surface layers are easier to create in MDF than in OSB.
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