Research Of Hot-Pressing Technology For Medium Density Firberboard(MDF)

Research of Hot-Pressing Technology for Medium Density Fiberboard(MDF)Optional design and control of the hot-pressing technology for medium density fiberboard with the expected vertical density profile (VDP) , since the VDP may leads to the final quality property, will improve the technology with automatic control system so as to make the processing line more efficient with lower cost than before. The study adopted continuous temperature and pressure on-line testing method on the testing of traditional hot-pressing technology and its effects, also physical and mechanic process when the mattress was pressed were tested systematicly. Mathematical models includes experimental analysis to reflect those processes were established, and a new theory of hot-pressing technology for medium density fiberboard was advanced.The main results and innovations in this paper are shown as following:1.Explicited the defects of traditional hot-pressing technology, a new train of thought of hot-pressing technology was advanced and a serials of new equipments were developed and applicated. Traditional hot-pressing technology based on the pressure controlling involves defects such as press speed could't be controlled, press closing time could't be defined. Study advanced a new approach based on the thickness controlling, and based on the sencor technology and program control technology, a serials of new equipments include hot-pressing machine, temperature acquisitor system, pressure of vapour in the mattress acquisitor system were developed and applicated. The temperature profile, stress and vapor pressure in the mattress were tested and analyzed systematicly.2.Based on the heat and mass transfer of porous theory and non-equilibrium thermodynamic theory, a nonlinear mathematical model of MDF mattress pressing was established.The coupled heat and mass transfer phenomena was considered enough in the model. Furthermore, the research analyses of the temperature and moisture's effect on the phase-only coefficients based upon the definition of chemical potential.3. Based on the machincs of porous theory and the classical viscoelasticity theory, mathematical models to describe the viscoelasticity of mattress were established. The viscoelasticity of mattress were divided into two parts: press phase and after the mattress comes to the designed thickness, and three constants reflects the hot-pressing parameter were involved in the models.4. The experimental data Of hot-pressing and the formation mechainism of Vertical Density Profile of MDF mattress was analyzed and a simulation model was established, its make up the basement of, new hot-pressing technology of MDF. The period of hot-pressing decided by the time needed by the center of mattress comes to the cure temperature of resin and the property of resin. The formation of VDP start from the beginning of pressing, ended by the resin's cure, and results of simulation show: with higher press temperature, proper moisture contents and higher pressing speed, temperature of mattress center will rise quickly, the press period could be shorten. Under the condition of same average density, with higher press speed, higher press temperature and proper moisture contents, the peak density of VDP would move towards surface of mattress, with lower press speed, lower press temperature and higher moisture contents, the curve of VDP would be smoothly, it tallies with the experimental data.5.Based on the testing methods of machanics of MDF, the wreck mechanism of MDF was analyzed. Conclusions of MOE decided by. density of the firstly wreck point and MOR decided by density of the lastly wreck point were proofed experimentally and theortically.