Manufacturing technology and performance of veneer strand flanged I-beam

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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