CONTROL OF GRANULATION OF POLYDISPERSE CHARGES AND POWDERS BY METHODS OF COMPACTION AND PELLETIZING BASED ON RHEOLOGIC MODELS

摘要

Use of disperse media in powder form in the chemical and allied branches of industry frequently fails to conform to technological and ecological requirements (dusting during transport, lack of friability, delamination, and deterioration in storage). Products with improved properties are formed during granulation of these materials. Compacted structures (pressings) of a given density, strength, and shape are obtained when disperse media are subjected to forces in granulating equipment (drums, plates, roller presses, powder-tableting machines, extruders). The products undergoing granulation are polydisperse, and consist of a large number of materials with dissimilar physicochemical properties (powders, charges), which are characterized by a different content of elastic, brittle, plastic, and hygroscopic components, as well as the existence of various special additives. Some of the materials have a minimum moisture content, while liquid binders should be added to the others. The introduction of additives or binders lowers inter-particle friction, and alters the plasticity and cohesiveness of the system, as a result of which a more complete wetting of surface particles by the liquid phase and a reduction in their hardness is ensured, while structural changes occur during solid-phase or other reactions, and new phases are formed [1]. Powder materials acquire new rheologic properties, whereupon they may go over from one state to another (from granular to plastic, from elastic to viscoplastic, etc.) in different stages of processing.