sealed in addition reference numeral 32 designates guide rollers disposed just in front of the front side wall 13 and these guide rollers 32 are rotatably mounted to the member 33 that is integral with the machine frame it is to be noted that the reason why the air sealing plates 19 and 20 are mounted in a vertically movable manner to the bottom end portions of the left and right side walls 12a and 12b and the air sealing plates 16 are mounted in a vertically movable manner to the bottom end portions of the front and rear side walls 13 is because it was contemplated to realize perfect sealing between the respective side walls and the canvas belt 7 even if a joining portion lacing portion of the canvas belt 7 should come to these side walls or even if a thickness or thicknesses of the corrugated cardboard sheet 8 the single faced corrugated cardboard sheet 1 and the liner 2 should vary now the operation of the double facer shown in fig1 to 4 will be explained in more detail after the liner 2 has passed a gluing machine it is preheated and conditioned by a preheat roller and then fed to the heating box hot plate section 11 on the lower side on the other hand.