摘要
为了研究平压法热压中密度纤维板过程中板坯含水率分布和热压曲线对板材断面密度分布(VDP)的影响,制取平坦型和陡平型VDP板材,该文通过改变板坯含水率分布以及热压曲线,热压不同VDP的中密度纤维板,分析各工艺参数对板材表面质量、表层厚度、表心层密度比、心层最低密度的影响。结果表明:适当增大板坯的含水率,可以改善板材的表面质量,提高表心层的密度比,降低心层密度;在高压阶段不超过压机闭合时间的前提下,提高高压压力,增长高压作用时间,有利于提高表心层的密度比;第一次降压压力的存在,使得表心层密度比减小,心层密度增加;当高压压力较小、作用时间较短时,采用较低的第一次降压压力,可以使得表层厚度增加、表心层密度比减小,有利于制取平坦型VDP板材;当高压压力较大、作用时间较长时,控制第一次降压压力的大小,使得表层最高密度基本不变、表层厚度减小、心层密度增加,有利于制取陡平型VDP板材。
MDF samples with different vertical density profiles （VDP） were fabricated under controlled mat moisture distribution and hot-pressing curve. The effects of hot-pressing parameters on MDF surface quality, surface layer thickness, surface-inner density ratio, and the lowest inner layer density were investigated. The results indicated that moderately increasing the moisture content would improve the surface quality, increase the surface-inner density ratio, lower down inner layer density. On the hot-pressing curve, moderately increasing the ＂high pressure＂ value and extending the hot-pressing time in ＂high pressure＂ region would increase the surface-inner density ratio. The pressure for the 1st pressure dropping tended to decrease the surface-inner density ratio and increase the inner layer density. When decreasing the ＂high pressure＂ value, shortening the hot-pressing time, and applying the lower pressure for the 1 st pressure dropping, surface layer thickness was increased, surface-inner density ratio was decreased, and this was more favorable to fabricate the ＂fiat pattern＂ VDP panel; while increasing the ＂higher pressure＂ value, extending the hot-pressing time, and controlling the pressure for the 1 st pressure dropping would keep surface density peak staying put, and lower down the surface layer thickness, increase inner layer density, which were more favorable for fabricating the ＂sharp-flat＂ VDP panel.
出处
《北京林业大学学报》
CAS
CSCD
北大核心
2009年第4期118-122,共5页
Journal of Beijing Forestry University
基金
"十一五"国家科技支撑计划项目(2006BAD18B0904)
"948"国家林业局引进项目(2006-4-106)
