Corrugator with intermeshing overlapping moldblock halves

A corrugator for molding externally ribbed and corrugated thermoplastic pipes, including two trains of moldblock halves circulating respectively in two endless paths containing a straight forward run in which the halves cooperate with each other in the directions of their circulation and perpendicularly to the latter, to form a travelling mold for the thermoplastic pipe, a return run and two semi-circumferential guide tracks for transferring the halves between said runs, the halves having intermeshing elements hooking the halves of the two trains together across the travelling mold, the improvement wherein the halves of one said train are biased in relation to and overlap the halves of the second train along the travelling mold in such a manner that each half of one train bridges and extends into two halves of the second train along the travelling mold, in order to withstand tensile forces of molding acting to make gaps between the halves of the same train along the travelling mold.