Manufacturing technology and performance of veneer strand flanged I-beam

以中密度纤维板或刨花板为卷材，采用热压法制备单板股绞线法兰工字钢。所提出的特殊金属模具成形压制方法具有以下特点：法兰同时成形并与腹板粘接；许多工字梁可以在一个单一的热压循环中生产，这种方法允许利用木材和木材复合材料工业的残留物和废物。结果表明，所提出的成形和压制方法在技术上适用于生产此类工字钢。腹板与翼缘的粘结质量对整个工字钢的强度有至关重要的影响。在常规热压条件下，采用不同的钢绞线尺寸组合、腹板与法兰之间的树脂种类、不同的压制时间和不同的木材树脂体系含水率对生产工艺进行了优化。在腹板和翼缘之间使用MDI树脂，除了尺寸稳定性有明显改善外，还能显著提高腹板与翼缘之间的粘结强度和断裂模量。将压制时间从20分钟缩短到12分钟是可能的。采用较低的木材树脂体系含水率会干扰法兰部分PF树脂的固化，导致梁的质量差，而木材树脂体系含水率为12%是生产具有平衡力学性能和尺寸稳定性的工字梁的最佳水平。对钢绞线密度和制备方法进行了优化，发现用锯制钢绞线生产的工字梁的性能优于用辊压分离法生产的工字梁。以异氰酸酯（MDI）树脂代替酚醛树脂（PF），在常规热压和注汽压两种情况下进一步缩短了压制时间。结果表明，在常规热压条件下，在钢绞线之间以及腹板和法兰之间使用MDI树脂，可以在最短的时间内（8.5分钟）生产出工字钢，而在使用PF树脂时则需要12分钟。此外，我们还发现，在注汽压制下，只要压制时间尽可能短（6分钟和8.5分钟），就可以生产出与上述材料性能相当的工字钢。少

Veneer strand flanged I-beam with MDF or particleboard as web material, was produced by hot pressing. The proposed forming and pressing method using special metallic mould has the following characteristics : flanges are formed and bonded to web at the same time ; many I-beams can be produced at a single hot pressing cycle and this method allows the utilization of residues and wastes of wood and wood-composite industries. The proposed forming and pressing method was found to be technically suitable to produce such type of I-beam. The bond quality between web and flange was found to have crucial effect on the strength of the whole I-beam. Optimization of the manufacturing conditions was investigated using different combinations of strand dimension, resin types between web and flange, different pressing time and different wood-resin system moisture content under conventional hot pressing. Using MDI resin between web and flange showed significant improvement in the bond strength between we … More b and flange as well as the modulus of rupture of the I-beam, besides distinguished improvement of the dimensional stability. Shortening pressing time from 20 to 12 minutes was found to be possible. Using lower wood-resin system moisture content was found to interfere with the curing of the PF resin at the flange part resulting in poor quality beams, while 12% moisture content in wood resin system was the optimum level to produce I-beam with balanced mechanical properties and dimensional stability. Optimizing the manufacturing conditions was continued regarding the strand density and preparation method, and it was found that the I-beams produced with saw prepared strands have superior properties over those of I-beams produced with roll-press splitter prepared strands. Further shortening of pressing time was investigated by replacing phenol-formaldehyde (PF) resin between strands by isocyanate (MDI) resin, under both conventional hot pressing and steam injection pressing. The main results showed that under conventional hot pressing, using MDI resin between strands as well as between web and flange made it possible to produce I-beam using shortest pressing time (8.5 minutes) instead of 12 minutes when PF resin was used. Also it was found that I-beam with comparable properties to those mentioned above can be produced under steam injection pressing using as short as possible pressing time (6 and 8.5 minutes). Less