METHOD AND DEVICE FOR PRE-HEATING A PRESSED MATERIAL MAT

The invention relates to a method for pre-heating a pressed material mat (2) before feeding same into a press (4)， in particular in the course of producing wood material boards. The pressed material mat (2) runs through a double-belt pre-heating device (3) with an upper continuously circulating gas-permeable transport belt (5a) and a lower continuously circulating gas-permeable transport belt (5b)， wherein the pressed material mat (2) is supplied with a heated fluid which contains steam， and the pressed material mat is thereby heated. The method is characterized in that the pressed material mat (2) is first supplied with a steam-air mixture with a set dew point in a first stage by means of a first heating unit (7) in the double-belt pre-heating device (3)， said steam-air mixture flowing through the mat from one surface to the opposite surface and thereby heating the mat to a temperature (T 1) over the entire thickness of the mat. The pressed material mat (2) is then supplied with steam or a steam-air mixture on both sides in a second stage by means of a second heating unit (9) in the double-belt pre-heating device (3)， whereby solely the top layers close to the surface are heated to a second temperature (T2) which is higher than the first temperature (T1).