A method and apparatus for cyclically shielding a work chamber opening (25) when loading and unloading workpieces using a conveyor device (10) that passes through the work chamber opening. A first shielding element (21) is placed at a workpiece loading station (11.1), and a second shielding element (22) is placed behind a second workpiece placement location (11.2), as viewed in the conveying direction. When the first workpiece is loaded into the work chamber (20), the first shielding element (21) is placed at or in the work chamber opening (25) by advancing the conveyor device (10). The first shielding element (21) is then removed from the work chamber opening (25) and placed behind the second shielding element (22). These steps are repeated with subsequent workpiece placement locations (11.2, 11.3, . . . ) of the conveyor device (10) and with respective cross-over changes of the shielding elements (21, 22).