Abstract: The invention relates to an apparatus for cleaning viscous materials, more particularly melted down scrap synthetic materials in a recycling process. The apparatus of the invention comprises a cleaning screen in the form of a strip which can be moved at right angles to the direction of flow of the material to be cleaned, so that the soiled area of the screen may be replaced by a clean area. In order to prevent the synthetic material from escaping when the cleaning screen is advanced, the volume before the screen is enlarged. This reduces or eliminates the pressure upon the screen so that the strip can easily be displaced, with no escape of the viscous material from the gaps in which the cleaning screen is located.