System for reducing the wiping gas consumption in an air knife

A device for controlling the thickness of a coating made of a liquid film on a moving strip (3), comprising a nozzle (1) fed with a pressurized gas (11) in a chamber (5) of the nozzle, said chamber (5) being terminated by nozzle lips making an elongated opening (4) for discharging the pressurized gas onto the moving strip (3), said elongated opening (4) being provided with automated means for reducing gas flow at each transversal side of the nozzle (1) outside the strip width, characterised in that said automated means for reducing the gas flow at each of said nozzle sides comprise a moving carriage (10) guiding a retractable cable (9) able to be applied respectively onto and out of the gas discharge opening (4), inside the nozzle chamber (5), and in that, at each transversal side of the nozzle, a transition, between an external nozzle section where the gas flow is reduced and an internal nozzle section where the gas flow is not reduced, is assured by two together-moving grooved wheels or pulleys (6, 7) connected to the moving carriage (10), located side by side and having their axis perpendicular to the nozzle, so that the cable (9) is successively located against the opening (4) on an external side of the first pulley (6), between the two pulleys (6, 7) and distant from the opening (4) on an internal side of the second pulley (7).