In a molding process wherein a pair of mold halves pivoted on respective axes flanking a mold-closing plane are closed together scissor-fashion on an extrusion issuing continuously down in the vertical mold-closing plane, each of the mold halves is displaced during closing of the mold halves away from its respective pivot axis. Such displacement away from the axis is effected by means of a cam arrangement during the last stages of closing in order to insure that the mold cavities remain perfectly aligned with the extrusions being closed in them.