are mainly aimed for those processes requiring a precise and constant feeding
of the production line in order to obtain high quality products. The systems
have a maximum flow rate of 20 ton per hour and their dosage sensitiveness may
reach the 0,2% of this maximum flow rate. The quantity of gravimetric metering
devices in the extrusion lines for the production of master batch and compounds
may vary in the following way. From two, the simplest solution, i.e. one for
the polymer in powder or granule, and the other for the rest of the mixed additives,
up to a maximum of 12, enabling a widely varied dosage and the selection of
the diverse extrusor positions. A control program has been developed for these metering devices. This program is based on an analog electronic system capable of adding the necessary corrections in only one second rather than in 15 as normally required by digital systems. A series of screens enable the access and necessary modification of production formulae, the command parameters and production start-up. The operative parameters may be varied during functioning by means of these screens. The modification of flow rates and dosage percentage is also possible. All these operations may be fulfilled by the automatic adaptation of process parameters or in completely manual mode. In addition to gravimetric systems, the company has developed a series of high precision single- or double-screw volumetric metering devices, continuous and discontinuous of low, medium and high flow rate to dose powders and granules of diverse type and flow capacity, dry and wet. The modular construction enables a simple and efficient cleaning and a vast line of auger conveyors of diverse profile guarantees the excellent adaptation to any application. The clots-breaking device in the container maintains the product in motion thus guaranteeing a regular feeding to the auger conveyors. The space between the auger conveyor and clots-breaking device arm has been reduced to the minimum possible value in order to prevent vacuum formation.
In the case of double-screw metering devices, the auger conveyors are restrained one to the other thus providing an auto cleaning effect that prevents crust formation and enables the emptying of the container while greatly reducing the times involved in the product change and the minimization of the residual losses.
The retaining funnels applied to the metering devices have inclined walls in order to facilitate the product flow towards the metering device. Stirring devices, pneumatic vibrators and plasticizers contribute to their best performance. By adding a load cell balance to a metering device of either type or by means of a microprocessor regulator, a continuous gravimetric dosage or batch dosage is possible.