Abstract: A method of and apparatus for melting a thermoplastic material in order to obtain an at least nearly homogeneous molten mass, according to which a granular or similar material is melted while it is being transported e.g. by a screw conveyor through a space between a housing of circular cross section and a body rotating in the housing. The transfer of heat to the granular or similar material takes place over at least an axial section of the space between the above mentioned housing and the rotatable body. This space is divided into alternating inlet and discharge channels by first ridges fixedly connected to the rotating body over the above mentioned distance and extending along the inside surface of the housing so as to at least nearly block the passage of molten material, and by second ridges respectively arranged between the first ridges and extending at least substantially parallel to the first ridges while being fixedly connected to the rotating body.