Study On The Mechanism Of Vertical Density Profile Of Fiberboard And The Relationship With Mechanical Properties

Density is an important indicator of fiberboard products, the Vertical Density Profile can accurately reflects the quality and performance of fiberboard. Controlling Vertical Density Profile rationally is an important method of the guarantee cost-saving and quality of fiberboard. Researching mechanism of Vertical Density Profile, impact factors and the method of control is very important.This paper choose different hot-pressing curves to make fiberboard through adjust technical parameters just as the most pressure , the least pressure, the time of keep the pressure and the time of reducing pressure. We get the curve of Vertical Density Profile and mechanical property, analyzed the main hot-pressing technology factor of affecting Vertical Density Profile of fiberboard and the relationship with mechanical properties. The results showed that:(1)The Vertical Density Profile curve of fiberboard decided to hot-pressing technology, its shape is symmetrical saddle-type. The Vertical Density Profile can be divided into four parts: pre-cured layer formed, high-density areas in surface formed, the density of transition zone between surface and inside formed, the low-density areas inside formed which are formed in the phase of rapid increase the pressure, the phase of high-voltage and the pressure-holding time, the phase of low-voltage and the pressure-holding time and the phase of pressure gradient and its corresponding time.(2)During the progress of hot-press, the pre-hardening thickness decided to the rate of increase pressure, the surface density increases with the increasing of high-voltage, and increasing of low-voltage, the core density increases. The surface thickness increases with the increasing of pressure-holding time in high-voltage. The core thickness increases with the increasing of pressure-holding time in low-voltage.(3)The mechanical property of fiberboard is decided to the Vertical Density Profile, when the average density in the same conditions, the internal bond strength increases with the increasing of the lowest density and increases with the increasing of modulus of uneven。The bend strength increases with the increasing of the highest density and increases with the decreasing of modulus of uneven。The average density play a balanced and harmonious role to the impact of density factor.(4)The Ideal Vertical Density Profile curve is symmetrical saddle-type, the pre-hardening thickness is thin, the curve of the density gradients from surface to core is smooth, no phenomenon of sandwich. The difference density numerical value of the surface and core decides different use.