19 a first or rear press on roller 20 which belongs to a press on and advancing movement device fig4 is arranged on the shaft 17 it is supplemented by a second or front press on roller 21 which is arranged on the shaft 19 driven by the latter and connected with the first or rear press on roller 20 via a press on belt 22 the press on belt 22 and the front roller 21 as seen in the direction of travel have a width which approximately corresponds to the overlapping of the sheets f1 f2 i e the width of zone s however the rear roller 20 is narrower this will be discussed later with reference to fig4 it is supported on the shaft 17 between an approximately trapezoidal bearing plate 23 fig2 and a side wall 24 of the leg 2 the second or front press on roller 21 has exactly the same diameter as the first or rear press on roller 20 at the same time however it must be capable of absorbing any unevenness to be traveled over when the upper sheet f1 is pressed on the lower sheet f2 against the underline base or substratum by this roller 21 therefore the roller 21 which is likewise driven must be vertically adjustable or displaceable this is achieved by two lateral holders 25 26 the two holders 25 and 26 swivel around the shaft 17 on which they are.