Modification Of China-fir And Its Manufacture And Structural Design Of Plywood

The china-fir (Cunninghamia lanceolata) veneer and thick veneer, which were treated by high temperature and high pressure steam, were researched in this paper. And the modified veneers and thick veneers were used for structural design to manufacture structure plywood. The results from the experiments showed:(1) With the ordinary press machine and steam press machine, the compression modification could enhance the strength of veneer, although it was not obvious.(2) The effect of modification on thick veneer with steam press machine was better than another method. The improvements of modification with two kinds of machines were all obvious, but the modification with steam press machine was better. The dimensional stability of former was better, and thickness swelling rate (TS) was only the half of the TS of thick veneer, which was treated with ordinary press machine. The along grain modulus of elasticity (MOE) and modulus of rupture (MOR) were enhanced greatly with the treatment of steam. The along grain MOE and MOR can achieve 14.28GPa and 150.98MPa respectively, which are three times and five times respectively higher than the material.(3) According to the results of L9(34) orthogonal design, the initial moisture content, compression ratio, press time, and the interaction between initial moisture content and compression ratio have an obvious affect on thick veneer's MOE and MOR. The compression ratio has a much more greatly affect than any other factors. Every factor, except press time, has a very significant affect on MOE, and press time has a significant affect on MOE, although it almost reached to very significant level. Compression ratio and press time have very significant affects on MOR, comparing to others have significant affects on MOR.The optimal parameters for modification of China fir thick veneer can be concluded that: initial moisture content 50%, compression ratio 60%, press time 16 minutes, steam pressure 0.5MPa , press temperature 180℃, pressure 2MPa.(4) Three optimal structures were gotten in this paper by the model of elastic modulus along the grain, elastic modulus in tangential direction, in-plane shearing modulus and laminate rigid:①0/90/0/90/0/90/0/90/0, the outside four veneer is modified, the along grain MOE and MOR are 8377MPa, 60.9MPa respectively; The across grain MOR is 35.1 MPa, and TS is 17.2%.②0/90/90/0/90/90/0, the outside two floors are modified thick veneer, the along grain MOE and MOR are 8800MPa, 67MPa respectively; The across grain MOR is 37MPa, and TS is 12.5%. ③0/90/90/0/90/0/90/90/0, the 1, 9 floors are modified thick veneer, 2, 3, 7, 8 floors are modified veneer, the along grain MOE and MOR are 9781MPa, 69MPa respectively; The across grain MOR is 41MPa, and TS is 18.2%.