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The Relation of the Temperature of the Center Layer of Mat in the Hot-pressing Process to Mechanical Performance of MDF

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Tutor: XieLiSheng
School: Central South University of Forestry Science and Technology
Course: Wood Science and Technology
Keywords: MDF,Central layerˇŻs temperature,Hot-pressing,Mechanical performance
CLC: TS653.6
Type: Master's thesis
Year:  2008
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Abstract:
The heat-conduction of MDF in the hot-pressing is affected by a large number of factors, such as the hot-pressing temperature, moisture content of mat, density of panel, thickness of panel, and so on. Confirming hot-pressing technic mainly fixs the hot-pressing time under different hot-pressing condition. And the time of resin solidifying in the mat is the hot-pressing time in principle.Hot-pressing method was adopted to make dry-process fiberboard, and the temperature of the center layer of mat was measured continuously and automatically by advanced instrument in the hot-pressing process, and the mechanical performance of boards were measured by mechanical tester. Based on the analysis of the curves of temperature changing and the mechanics of MDF, some basic relations as follows of the central temperature of dry-process fiberboard to the mechanical performance was summarized:(1)When the orthogonal experimentation was adopted, the relations of the central temperature to mechanical performance is:˘ŮWhen maximum temperature of core is under 117ˇćand the hot-pressing time of central temperature after 105ˇćis less than 24s under different hot-pressing time, modulus of rupture (MOR)and modulus of elasticity(MOE)were strengthened obviously with the increasing of maximum temperature of core and the hot-pressing time of central temperature after105ˇć; When maximum temperature of core is over 117ˇćand the hot-pressing time of central temperature after 105ˇćis more than 24s under different hot-pressing time, modulus of rupture (MOR)and modulus of elasticity(MOE)were strengthened tardily with the increasing of maximum temperature of core and the hot-pressing time of central temperature after105ˇć.the results under different hot-pressing time is the same with the results under different hot-pressing temperature.˘ÚEffect of central temperature on MOE and MOR is very little under different moisture content and resin content; MOE and MOR are mainly affected by moisture and resin content.˘ŰWhen maximum temperature of core is under 118ˇćand the hot-pressing time of central temperature after 105ˇćis less than 24s under different hot-pressing time, internal bond strength is improved obviously with the increasing of maximum temperature of core and the hot-pressing time of central temperature after 105ˇć; When maximum temperature of core is over 118ˇćand the hot-pressing time of central temperature after 105ˇćis more than 24s under different hot-pressing time, internal bond strength is enhanced tardily with the increasing of maximum temperature of core and the hot-pressing time of central temperature afterl05ˇć.(2)when antitheses of single gene were adopted, the relations of the central temperature to mechanical performance is:˘ŮMechanical performance improved obviously with the increasing of aimed temperature, and then leveled off. When the central temperature was 115ˇć, mechanical performance had been up to the standard, but strength had not been very high. When the central temperature was 120ˇć, mechanical performance had been very high, and leveled off.˘Úwhen the central temperature was same, mechanical performance improved with the increasing of hot-pressing, moisture content and targeted thickness. When the thickness is thin, hot-pressing time can be prolonged properly.
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