Abstract: The invention relates to a reactor for the treatment of highly viscous plastic melts, comprising a horizontal, cylindrical container (2) with a vapour exhaust and chambers in the region of the melting bath, formed by the arrangement of panel walls, in which annular discs, fixed to a shaft (3) by spokes and serving as stirrer elements (4, 5) may be rotated, whereby, in the cavities of the annular discs (4, 5), two opposing scrapers (6, 7) are fixed to the inside of the container at an offset angle and run past at a small separation from the front faces of the annular discs and the sleeve of the shaft (3). According to the invention, the assembly and disassembly of the shaft and scraper is simplified by connection of the scraper to the inside of the container by means of a positive connection (13, 19).