an apparatus for the production of plastic pipes with transverse grooves comprising half shells each having a mold recess which are arranged on a machine bed driven in a cycle . the half shells are assembled in pairs in a molding path to form a complete mold , the injection head of an extruder being arranged at the beginning of the molding path . furthermore , the half shells are provided with vacuum channels , each vacuum channel being connected to a respective mold recess . the vacuum channels are joined into vacuum connections formed in the machine bed , and the half shells are provided with cooling channels which join into cooling water inlets and outlets in the machine bed . in order to ensure an exact setting of the half shells during the molding operation , the cooling channels , on the one hand , and the vacuum channels on the other hand , in a given half shell are completely separated from each other .