Fiberboards 2847 



platens themselves are also heated, by steam or hot water, but only to a tempera- 

 ture slightly above 212°F to avoid condensation on the surfaces of the board. 

 A press size of 5 x 18 feet seems to be particularly suitable for the application 

 of high-frequency heating. The power requirements increase with the number of 

 openings. In one of the newer medium-density fiberboard plants a single-open- 

 ing high-frequency press 8 feet wide and 65 feet long has been installed. It seems 

 to be generally accepted that the use of high frequency reduces press cycle time 

 and thus increases the output of a given press configuration. Capital costs and 

 operating costs per unit output are higher than in the case of a press heated with 

 either steam or hot water. 



CONTINUOUS MENDE PROCESS 



The Mende process (fig. 23-77) was developed in Germany and introduced in 

 the United States in 1971 in an attempt to produce thin particleboard on a small 

 scale economically. By 1976 fifty Mende plants were in operation, ten of them 

 in the United States and four in Canada. Most are particleboard plants, but the 

 machine can handle fibers as well. One of the U.S. installations is a fiberboard 

 plant (Louisiana Pacific Corp., Oroville, Calif.) 



The heart of the Mende process is the continuous press, comprised of a 10- 

 foot-diameter, heated and rotating drum against which the mat is pressed by a 

 steel band (fig. 23-77 and 23-78). Widths, i.e., drum lengths, available are 4, 5, 

 6, 7 and 8 feet. After less than one full revolution of the drum, the continuous 

 board leaves the press and is cut to size. As the steel band carrying the mat 

 approaches the press section, it is heated from below by infra-red heaters, which 

 elevate the steel band temperature to about 250°F. Pressure is first applied as the 

 mat passes between entrace roll and press drum (fig. 23-78), both of which are 

 oil heated to a temperature of 355°F. The temperature at the press drum surface 

 is about 300°F. Between entrance roll and heated return roll additional infrared 

 heaters are installed to maintain the temperature of the steel band. 



Between return roll and heating drum, pressure on the mat reaches a maxi- 

 mum. This pressure depends on the tension of the steel band, which can be 

 controlled by adjusting the tension roll. As the band bends around the heating 

 drum, it passes two more infrared heaters and two unheated pressure rolls, which 

 press the mat to the final board thickness. As the band turns around the drive roll, 

 the board is fully cured and is returned in the reverse direction over the forming 

 station. The temperature of the board as it leaves the heating drum is 230°F. 



Since the heating drum is in direct contact with the mat and therefore forms 

 the surface, protection of the drum surface from scoring is essential. Several 

 rotating brushes clean both drum and steel band. The steel band returns to the 

 forming station via a water-cooled roll, which reduces its temperature to about 

 150 to 160°F, to prevent curing of the resin before the mat enters the press 

 section. 



The heating oil recirculates through a boiler heated by gas or other fuels. 

 Temperature of each drum can be controlled separately. Table 23-8 shows the 

 line speed for various board thicknesses. 



