Production of Submicron Particles by Autogenous Grinding with a Stirred Mill.

Abstract

The stirred mill is regarded as one of the most efficient devices for micronizing materials and have come to be actively used for preparation of fine particles. Recently, a demand for ultrafine particles is increasing in many kind of industries.In this paper, based on frictional action of feed material each other, an autogenous grinding to get submicron or micronized particles have been carried out using a stirred mill (Attritor-type D). The mill used was made of stainless steel and its volume was about 5.5 liters. The mill held 12 impellers. In the present work, two operating parameters such as stirring speed and feed size of limestone were used. The feed mass was 5 kg and three different feed size were chosen for this experiment: 6.7-10, 10-13, 13-20mm. The rotational speed of impeller examined were 69, 103 and 139 rev/min. The ground products were sieved in the size range from feed size to 149, u m, and from 149 to 0.17, a m, the size distributions were measured by a laser diffraction and scattering methodThe torque reading were recorded during each experiment, and the area under the torque vs. grinding time curve was used to give a measure of the total energy input to the mill. The grinding time were 2, 4, 10, 25, 40, 60 and 180 min. The progress of grinding was evaluated by the increasing rate of submicron or micronized particles in products.The results are summarized as follows(1) The zero-order equation was applicable to the increasing rate of submicron particles in earlier grinding time. (2) The energy consumption to get submicron particles decreased with increase in the feed size at all speed of impeller.(3) It was minimum when the feed size was 13-20mm, that is, close to the distance between the top edge of impeller and the wall of mill. (4) The following experimental equation was obtained. Q1= (5.6×10-9-3.2×10-11n) E·xfm where Qi is the mass fractiom finer than 1μEm, n the rotational speed of impeller, E the energy consumption and xfm the maximum size in the feed.(5) It was found the an autogenous grinding with a stirred mill is an effective method producing submicronized limestone.