(70bd) Scaling-up of Ceramic Body Grinding with Reference to Grinding Rate

Results of the research carried out in a pilot-plant ball mill for ceramic body grinding applied in floor and wall tiles are presented.

The feed was a mixture of feldspar and clay with anti-emulsifiers. Wet grinding of the feed was applied. The content of feldspar and clay depended on tile production technology. Experiments were made in a batch ball mill. During the experiments particle size distribution and ball diameters were changed. Grinding balls were made from Al₂O₃. Water capacity of the mill was 0.116 m³ and its inner diameter 0.5 m.

During grinding, product samples were taken at different compositions of the grinding medium and particle size analysis was carried out. Process parameters of mill operation were selected so that when the ball composition was changed, complete filling of the mill with feed and grinding medium was 45 and 90% of the total water capacity of the mill, respectively.

The main aim of the research was to determine the effect of changes in the number of contact points of the balls on the ceramic body grinding rate. Additionally, the influence of mill filling with the feed on specific grinding rate of particle fractions was identified. Basing on the particle size analysis, percentage of each size fraction for time intervals specified in the experimental procedure, was determined. A change of particle size distribution in time allowed us to calculated the grinding rate for particular size fractions. In the calculation we used the Gardner and Austin equation in a differential form for discrete values of the percentages, assuming an ideal mixing of the material being ground.

To determine the function of particle size distribution b_i,j the following equation was used:

Constants g, b depended on grinding process conditions.

Using correlation equations, a change of grinding rate of every size fraction for the tested times of grinding was described. In the description of changes in the specific grinding rate of size fractions, the following equation was applied:

High correlation of the experimental data with results obtained analytically by means of the above mentioned equations, allowed us to formulate a general relation that determined the specific rate of grinding of the size fractions. This rate was dependent on the number of contact points of the balls with material being ground.