Abstract: An apparatus for heat treatment of oblong articles, such as monofilaments, multifilaments, tapes or webs of plastics, comprises a fixed bottom member (2) and a cover member (3) hingedly secured thereto along one long side, where the cover member (3) in the closed state together with the bottom member (2) define a hot-air channel (12). This hot-air channel extends lengthwise through the apparatus between the bottom member (2) and the cover member (3) from an inlet (14) to an outlet (15) in their respective ends in the apparatus. Means are provided for sealingly closing the slit (17) between abutting portions of the bottom member (2) and the cover member (3). These means for closing the slit (17) on the side of the apparatus being opposite the hinged side of the cover member (3) comprise a sluicing means (16). The sluicing means (16) is adapted to allow a lateral introduction of separate oblong articles into the hot-air channel (12) through a feeding track without completely opening said channel.