DISCONTINUOUS WET-GRINDING OF RAW-MATERIALS IN THE PRODUCTION OF TRADITIONAL CERAMIC TILES

The paper reports a laboratory and semi-industrial study on the discontinuous wet-grinding raw-material process which is widely used in the ceramic tile industry for body preparations. It focuses on the importance of controlling the rheology and particle size distribution of the aqueous suspensions and the mineralogical characteristics and amounts of the grinding residues of three raw materials-two clays (named Badia and Riola), and one sand-and of their 1/1/1 mix, generally used in factories for the production of porous, single-fired ceramic wall tiles. The apparent viscosities of the electrostatically deflocculated slips strongly depend on the grinding times. The highest solids content of the slips, enabling a good industrial workability, is about 55 to 57 wt% for both the clays, 70 to 72 wt% for the sand, and 60 to 62 wt% and 66 wt% for the mix (body) examined in the laboratory and semi-industrial experiments, respectively In all the samples, the weighted grinding residues on the 45-mu-m sieves, formed of the hard unclayey materials. decrease with increasing grinding times, attaining practically constant values at about 20 and 150 min, respectively, in the laboratory and semi-industrial experiments. The optimum apparent viscosity values, which enable the best grinding action on a ceramic body in a drum ball mill, are greater than those required for moving the final slip to the spray dryer. The results suggest that the grinding action is exerted only on the nonplastic materials. Therefore, the individual grinding of the raw materials forming the ceramic body is strongly indicated for optimization of the wet-grinding process. Other useful hints for the rationalization of the wet-grinding process, which may contribute to increasing production, lowering costs, and improving quality, are suggested.