重载纤维模塑材料热压成型的水分传递过程

目的探究各工艺因素(热压温度、热压压力、初始含水率、定量)对重载纤维模塑材料水分传递过程的影响,揭示重载纤维模塑材料热压成型的水分传递机理。方法采用隔层设计测得纤维模塑板坯不同位置的水分变化;引入t检验与F检验法检验对称位置水分变化曲线的差异。结果热压过程中,水分在重载纤维模塑板坯中对称分布,水分变化可划分为2个阶段,即快速下降段(Q段)和集中汽化段(L段)。水分梯度主要发生在L段,其水分传递依次满足菲克第一定律的稳态扩散和菲克第二定律的非稳态扩散,扩散速率由表及里逐渐减慢。在Q段与L段,提高热压温度、增大热压压力或减小定量均能加快芯层水分下降速率,初始水分含量对水分下降速率无明显影响。结论热压过程中,重载纤维模塑材料由表及里先后完成干燥。降低初始含水率、提高热压温度、增大热压压力或减小定量均能缩短重载纤维模塑材料的干燥时长。

Moisture Transfer Process of Hot-Press Molding of Overloaded Molded Fiber Material

The work aims to study the effects of various process factors (hot-press temperature, hot-press pressure, and initial water content and basis weight) on the moisture transfer process of overloaded molded fiber material, and reveal the mechanism of moisture transfer in hot-press molding. The moisture change of molded fiber slab at different positions was measured in the method of interlayer design. The T test and F test methods were introduced to test the difference of water change curves at symmetrical position. During the hot-press process, the moisture content was symmetrically distributed in overloaded molded fiber materials and the moisture change could be divided into 2 stages: the rapid descending section (section Q) and the centralized vaporization section (section L). The moisture gradient mainly occurred in section L and its moisture transfer in turn met the steady state diffusion of Fick''s first law and the unsteady state diffusion of Fick''s second law. The diffusion rate gradually decreased from the outside to the inside. In sections Q and L, the increased hot-press temperature and pressure or the decreased basis weight could accelerate the descending rate of the moisture content of the core layer. The initial moisture content had no significant effect on the descending rate of moisture content. In hot-press process, the overloaded molded fiber material is dried from the outside to the inside. Reducing initial moisture content, improving hot-press temperature and pressure, or decreasing basis weight can shorten the drying time of overloaded molded fiber material.