Trade Journals for the Concrete Industry

Block making machines are complex technical pieces of equipment for moulding and compacting stiff concrete mixes. Within one production cycle, they fill the form with concrete mix, compact the same, and strip the formwork from the freshly poured concrete bodies – all completely automatically. The unit thus manufactured is then subsequently transferred to a transport system. Illustration 1 shows the layout in diagram form of the compaction device for a block making machine. Extremely great dynamic forces are generated by shock vibrations in such machines for compacting the stiff concrete mix. In this, the vibration system first moves in sinusoidal oscillations with synchronised opposed rotating unbalance waves, the so-called four-wave exciter. Illustration 2 describes how such an exciter functions. Depending on the process stage, these waves can reach rotational speeds between 1,800 rpm-1 and 4,200 rpm-1. On top of this, pulses are conducted into the mix for compaction by means of possible relative motions between the elements of the compaction device and by its impact on a solid plane, the baffle plate. In this way, stochastic movement functions are generated in a concrete block machine’s processing area. Accelerations can attain values up to 2,500 ms-2 depending on the rotational speed of the unbalances. The dynamic stresses arising from this for the com - pacting device components, chassis, and foundation in a concrete block machine constitute a unique case in technology. The design, manufacture and installation of concrete block machines is accordingly quite demanding. A descriptive overview of the moulding and compacting process for concrete block machines is given in [1].