A travelling mold has mold blocks formed by opposing mold block sections which open and close relative to one another. The mold sections travel horizontally around a continuous track which is fitted with a plurality of side-by-side mold block carriers on which the mold block sections are releasably supported. The mold block carriers are provided with carrier gears which engage with the main drive gear of the mold so that the mold is driven by engagement of the drive gear with the carriers and not the mold block sections.