Heat-treating vehicle bodies

In order to obtain uniform intensity distribution in a movable tunnel-like structure (12) used for heat-treating newly enamelled surfaces of a vehicle body (10), the tunnel-like structure is provided with a secondary radiator (32) which embraces the vehicle-body profile at a given distance therefrom, and carries in mutually spaced relationship longitudinally of the movement direction of the tunnel-like structure a plurality of IR-radiators (36) operative in the medium-wave band. The shape of the secondary radiator (32) is substantially determined by circular-arcuate lines (44, 45), and the primary radiators (36) are so mounted that the radiation therefrom is directed onto focus axes through centres (42, 43) of the circular-arcuate lines. The extent to which the tunnel is moved with the heat-emitting sources activated is controlled with respect to vehicle-body designs and the nature of the treated surface, while the speed at which the tunnel-like structure is moved is determined with respect to the absorption and reflection capacity of the enamel or paint used.