Design and performance of horizontal ribbon mixer for microingredients of corn feed with different particle sizes

Lab scale horizontal double ribbon mixer with capacity of 15 kg was developed to investigate the effect of particle size on mixing operation for animal feed. Corn powder with five different fineness of 0.002 (corn starch), 0.429, 0.588, 0.698 and 1.139 mm and salt with fineness of 0.273 mm were selected as carrier and tracer respectively. The experiment was performed under five different agitator rotating speed, i.e., 19.5, 30, 45, 60 and 80 rpm; and the mixing degree expressed by coefficient of variation was separately detected at 0.5, 1, 2, 3 and 6 min each time. The coefficient of variation of salt concentration in ten samples which were taken from mixer at random position was determined by measuring conductivity of sample solution. Moreover, two material flow parameters, i.e., angle of repose and angle of wall friction were measured and applied to study the relationship between flowability and mixing operation. Convective and shear movement play a major role during mixing processing in double ribbon mixer. The experiment shows that particle size of materials and agitator rotating speed have no significant effect on final mixing degree within the fineness range of animal feed. The mixing rate is obviously affected with alternation of fineness and rotating speed. The higher mixing rate is achieved when small fineness is applied. The high rotating speed is always favorable for obtaining higher mixing rate. Particle size distribution is expected to have important effect on mixing rate. Particle size has significant effect on operation parameters. The optimum rotating speed ascends with increasing of fineness. At low speed (about 30 rpm), mixing time for both "satisfactory mix" and "best mix" ascends obviously with increasing of fineness. At higher speed, there is not significant difference among mixing time with alternation of rotating speed. Moreover, The particle size has significant effect on angle of repose and angle of wall friction. Good flowability of materials is not always necessary for achieving satisfactory mix. The ability carrying tracer particle is more important.