Vibrator for a block molding machine

A vibrator for a concrete block molding machine to make molded concrete blocks, comprising a resiliently supported vibrating table suitable for receiving board-like production pallets with a block mold thereon, said production pallets horizontally positioned on a plurality of support bars of said table, intermediate spring members positioned for forcing said pallets against impact bars which are fixed on the machine, and an unbalanced vibrating drive means designed as a directional oscillator which is adapted to be driven at different amplitudes and comprises horizontal, parallel, positively synchronized, counter-rotating vibrating shafts suitable for generating an outwardly effective vibrating force in only the vertical direction through the support bars so that the support bars knock against the bottom side of the production pallet, wherein the vibrating drive means comprises two pairs of unbalanced vibrating shafts supported side by side and parallel to a respective center line therebetween, said vibrating shafts being adapted to be driven at the same rotational speed in forced synchronization and contrary sense and being supported such that the center lines of the two pairs extend in parallel in a vertical central plane therebetween, a regulator and distributor transmission for the drive of the vibrating shafts, said transmission being connected by universal joint shafts to a vibrating shaft of each pair and permitting independent, infinitely variable adjustment of the phase relationship of the vibrating oscillations of the two vibrating shaft pairs with respect to each other, and a means by which the regulator and distributor transmission is adjustable from a first phase relationship for pre-vibration to a second phase relationship for main vibration.