Research On The Precise Wet Classification Of Super-fine Powder

Aiming at the problems exiting in grain classification at present, a vertical multistage waterpower device was developed to realize abrasive narrow-grade-classification. The experiments shows: (1) dispersing is a prerequisite to classification; (2) designing a powerful and steady force field is the key to classification, and (3) the guarantee to classification is to let the product be in time gotten rid of. This paper consists of two parts. The first part is about dispersing of super-fine powder. For the two kinds of abrasive grain—ordinary abrasive and ultra hard material, carborundum and diamond were chosen as samples for dispersing experiment. The law of dispersion behavior of diamond and carborundum in medium of water was studied. The influence of the pH, dispersants and surface-active agent on the dispersion behavior of particles was researched. By calculation of potential energy the essence of dispersion behavior of particles in water was analyzed. The interactions between particles were discussed based on DLVO and EDLVO theories. Experiment results show the effect of the pH on the dispersion is due to the repulsion interactions of electrical double layer; and addition suitable inorganic dispersant or organic macromolecule dispersant results in improvement the stabilization of the dispersion. The main action of the inorganic dispersants is to increase the repulsion interactions of electrical double layer and the main action of organic macromolecule dispersant is to increase hydration shell and steric hindrance. The compound dispersant is superior to the single dispersant. The dispersion action of the surface-active agent mainly embodies in particle surface wettability adjustment. The loss with time was put forward to value dispersion. The second part is about classifying the super-fine powder. Due to the abrasive grain being hard, seriously wearing the equipment and requiring the narrow-grade, a new-type of vertical multistage waterpower system was developed. The main characters of this system are (1) a vertical multistage classifier, (2) continuous feeding and putting out, (3) dynamical dispersion, (4) system of pacifying rising water and (5) the short distance efflux. The effect of the shape of particles, the density and velocity of feeding, grain size distribution and temperature to the efficiency and precision of classification were studied. According to the effect of size distribution to classification, the idea of pre-classification and two times classification was proposed, which, to great degree, reduces the effect of tail flowing and drift flowing and improves the precision of classification. Shape-coefficient can be determined by the ratio of the particle lengthand diameter. System concentration is decided by the density and velocity of feeding which must satisfy with the condition of Stokes' formulae, that is, to guarantee the freedom subsiding of particle among the fluid medium. Under different temperature the system has different viscidity and surface tension, and a digital temperature-controller can keep the constant temperature of the system. Experiments show this system can classify 5μm super-fine powder, and the product can accord with the China national standard and Soviet Union standard of W7. An auto-controlled idea was put forward to reduce the influence of human factors, and a mathematics model of multistage classification efficiency was designed for the reference to value the efficiency of multistage classifier.