successively produced mould parts or blocks are displaced on to a guide channel or conveyor pathway comprising a travelling grate or walking beam conveyor 2 and an endless rod belt 3 associated therewith in principle the travelling grate or walking beam conveyor 2 may be built up in the same way as disclosed in british patent specification no 1 419 592 with the modification that each set of grate bars comprises only two single bars 4 and 5 respectively the bars 4 are movable only in the vertical direction whereas the bars 5 are also reciprocable in the horizontal direction in the situation shown in the drawing both sets of grate bars are shown in their topmost position and the bars 4 are ready for being lowered whereupon the bars 5 are displaced to the left for advancing the mould not shown however the mould is not supported directly by the travelling grate 2 in fact this grate is surrounded or enclosed by endless rod belt 3 the upper run of which is supported and stepwise or intermittently advanced by the travelling grate with its upper side at exactly the same level as the bottom plate 1 of the pressing chamber in the embodiment shown the belt 3 consists of tubes 6 which are of substantially square section and so interconnected that the belt may be regarded as non extensible in the longitudinal direction this can be important for maintaining the required 34 weighting 34 or pressing together of the individual parts of the mould in the drawing the square.