Electromagnetic mill manufactured by ELTRAF company is currently used in industry for dry milling, with gravitational transport of material. In such a circuit, the milling chamber is deflected from the horizontal position by a proper angle to move the feed material along the milling chamber due to gravitational force.
To improve, among others, the control over residence time of the material in the working chamber, the partners in the Consortium jointly developed the idea how to carry out the milling process in the electromagnetic mill using pneumatic transport. Two patent applications were filed that are related to this concept: one regarding the method of dry milling in electromagnetic mill, the other regarding the means of parametrization of a pneumatic classifier integrated with the mill.
The concept which was the basis for building the installation in Institute of Automatic Control, Silesian University of Technology, assumes vertical position of electromagnetic mill's working chamber. From the top of the chamber, feed material is supplied with a screw feeder and from the bottom, a stream of transport air is delivered. Above the working chamber and integrated with it there is located a preliminary classifier, which forms an internal recycle. Material of proper (small enough) granularity is carried upwards, towards the precise classifier, which divides the stream of milled material into final product and recycle stream. The final product on the output of the precise classifier is separated from transport air in a cyclone and is collected in a tank.
Currently, transport air is drawn by the main blower and air velocities in particular streams are set via suppression, using controllable valves. In the installation, appropriate measurement points were prepared as well, for measuring quantities such as: velocity, pressure, humidity and temperature of air, temperature and moisture of material, mass of material in individual tanks, valves position and rotation speed of motors.
The whole circuit is managed by automatic control system which bases on PLCs and SCADA system interfaced through a PC touchpanel. In the PLCs there are implemented direct control layer algorithms for supply of feed material and grinding media, pneumatic transport system and milling system. The SCADA system allows to manually select the tuning parameters of individual control systems or to switch on the automatic mode of operation with supervisory control layer algorithms, which choose proper operating points of the installation.