Process for coating granular materials

Claim 1

A process for coating granular material having granules with a particle size within the range of 100 to 1,000 microns in a coating apparatus of the type having a rotatable dish, which dish is mounted in a stationary vessel, said stationary vessel having a rising inner surface contiguous to the periphery of said dish and curved upwardly therefrom to define a steadily rising surface from said dish, which comprises charging said granular material into said vessel and onto said rotatable dish while said rotatable dish is rotated at a predetermined speed, intermittently supplying a binding solution to said vessel by measuring the specific electro-resistance of a mass of said granular material by means of a detector including at least one electrode which is spaced from a portion of the rising inner surface of the vessel, feeding a signal indicative of the detected specific electro-resistance to a comparision circuit, comparing said signal from said detector with a reference value fed from a reference signal generator, said comparision circuit generating a control pulse only when said detected specific electro-resistance exceeds the reference value and continuing the generation of such control pulse during a period in which said detected specific electro-resistance is in excess of said reference value, said binding solution spraying being effected under a predetermined pressure onto the fluidized mass of said granular material by means of an electromagnetic valve opened by said control pulse during the duration of said control pulse, the electro-magnetic valve being closed to discontinue spraying when the detected specific electro-resistance is less than the reference value and no control pulse is generated from said comparision circuit, and feeding coating powder continuously throughout the coating operation onto the fluidized mass of said granular material within said vessel.