Patent ID: 8893402

Claim:
A method for controlling the protective gas atmosphere in a protective gas chamber for the continuous treatment of metal strips, the metal strip being guided into and out of the protective gas chamber by way of locks and at least one of the locks having two sealing elements for the metal strip running through, with the result that a sealing chamber forms between the two sealing elements, the gas pressure (P 2 , P D ) in the protective gas chamber and in the sealing chamber of the lock being measured and the pressure (P D ) in the sealing chamber being regulated, wherein the pressure (P D ) in the sealing chamber is regulated such that during operation the differential pressure (ΔP seal ) between the protective gas chamber and the sealing chamber is kept to the greatest extent above or below a predetermined value for the critical differential pressure (ΔP seal, k ), the critical differential pressure (ΔP seal, k ) being fixed as that value at which the gas flow between the protective gas chamber and the sealing chamber is reversed and the critical value for the differential pressure (ΔP seal, k ) being calculated by way of a mathematical model, which takes account of the speed of the metal strip, the gap opening of the two sealing elements, the properties of the protective gas and the thickness of the metal strip, and the value set during operation for the differential pressure (ΔP seal ) being kept as close as possible to the critical value for the differential pressure (ΔP seal, k ), with the result that the gas flow (F 2 ) from or into the protective gas chamber is minimized.