The Study Of The Vertical Density Profile Of Fiber Board

The Vertical Density Profile is an important characteristic of structure, also one of indicators influence wood-based panels physical and mechanical properties (such as MOR,IB and MOE), different Vertical Density Profile can reflect the production process. By controlling of Vertical Density Profile may realize mechanical properties of reasonable arrangement, meet the expected performance requirements. To study the Vertical Density Profile of fiberboard, will benefit production enterprise to control product quality, production costs, promote industrial to power forward, the board will also promote sustainable ecological construction and economic development. Therefore Vertical Density Profile research has important social meaning and practical meaning.This research by single factor experiment discussed during hot-pressing process parameters on the effect of the Vertical Density Profile, including aimed-thickness, aimed-density, moisture content, temperature, closed-speed. Conclusions as follows:(1) The ideal Vertical Density Profile curve has the following characteristics:the pre-hardening thickness is thin, the curve of the density gradient from surface to core is smooth. In the actual production, heat transfer first begins from back surface, madding the Vertical Density Profile curve into asymmetric "saddle". Curve by four parts:the pre-hardening layer formed, the high-density areas in surface formed, the low-density in core formed, the density of transition zone between surface and inside formed.(2) The aimed-thickness increases, the face maximum density also increases, but lowest core density decreases, the density curve shape is more steep.(3) The aimed-density increases, the face maximum density and lowest core density also increases, the growth rate of surface density is lower than that of the core density. The aimed-density affect only the integral curve, not affect its shape.(4) With hot-pressing temperature increasing, the speed of surface fiber moisture evaporation and part of the adhesive polycondensation increase, the pre-hardening thickness is more thicker, the face maximum density and lowest core density increases. The curve of 160℃and 180℃is steep but 140℃is flat.(5) The moisture content increases is propitious to the thermal conductivity and fiber plasticity, hydrolysis reactions of cellulose and hemicelluloses, leading lignin to curing and melting point reducing. Moisture content has significant influences on pre-hardening thickness. The moisture content is higher, the pre-hardening thickness is thinner, the curve is more flat.(6) The closing-speed has an obvious effect on VDP. The closing-speed is fast, the difference value of surface-to-core is big, the curve is steep, which is helpful to improve stiffness and MOR; conversely, the difference value of surface-to-core is small, the curve is flat, the IB and edge unmatched grip are improved.