The special feature of the machine is the integration of two distinct functions in a single system; the first allows the compaction of slabs of bituminous mixtures to a controlled density, the second is for performing the wheel tracking test. A "kneading" system is used for compaction and consists in positioning between the roller and bituminous mixture a series of sliding metal plates that are free to move vertically, guided by the internal mould surfaces. The wheel tracking test apparatus is the "small-size" type prescribed in the Standard. The integration of the two functions is made possible by the particular machine design (patented); the cylindrical roller is replaced with two coaxial disks rolling along lateral projections of the sliding plates. On removing the plates, the disks are lowered over the two other edges of the mould, so contact between the bituminous mixture surface and the wheel of the wheel-tracking apparatus is made. As for the mechanics, the machine is composed by a horizontal axis driven by a brushless motor coupled with a ball-screw assembly and by a vertical axis driven by a Bellofram cylinder controlled by a pneumatic servo-valve. There are three sensors installed in the machine: an incremental encoder for the horizontal axis position, a magnetostrictive sensor for the vertical axis position, and a load cell for force. Each of these sensors can be used as reference by the closedloop, computer controlled system with feedback; the user interface ...
Keywords: Filmato, eng, tecnotestitalia
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