Study On Microwave Preheating MDF Mat

Microwave technique has been used widely in wood industry. But it has seldom been applied in MDF. Producing thick MDF consumes most energy because of the limitation of equipment. This article not only provides the feasibility of microwave technique applying on MDF, but also theoretical bases for the further study on the MDF processing.In first part of this article, the influence is described that microwave preheat MDF mat and redistribute moisture in MDF mat. The effect of the height of mat, the time of microwave heating and initial moisture content of fiber on redistribution of water in thick MDF mat was experimented and analyzed. The results indicated that the moisture content in the face layer was higher than in the center, when reducing the height of mat, increasing the time of microwave preheating and moisture content of mat. This moisture gradient can improve the mass and heat transfer during hot pressing.As the second part of the article, the temperature distribution and influence of microwave power on the temperature in the centre of mat were carried on an investigation in. The result showed that the temperature in the centre of the mat is higher than on the surface layer of the mat. Microwave pre-heating not only increases the overall mat temperature with high-energy efficiency within a very short period of time, but also most importantly redistribute the moisture content within the mat, creating a potentially favorable moisture content gradient. The result also indicated that the more the microwave power is, the fast the temperature in core of panel increased.At the last, the physical and mechanics properties of MDF are studied. The results showed that1) The curve showed that the density profile keep quite smooth in the panel center, which was preheated by microwave, than the one, which was not preheated.2) If the mat was preheated by microwave, reducing the height of the mat can increase IB of the panel; there were no obvious differences on the product properties of medium density fiberboard, which was not preheated by microwave through changing the height of mat.3) Through the result of orthographical experiment, the optimum processing is that the initial moisture content of fiber was 11%; the time of microwave heating was 100s; the height of mat was controlled in 3cm and the hot pressing time was 5 min.4)During hot pressing, the temperature could attain 103℃ in mat center which was preheated by microwave and rise quicker than the one which was not preheated. And the longer time of preheating carry out the less time of hot pressing.