METHOD OF DETERMINING THE LIQUID PHASE CONTENT IN THE BRIQUETTED CHARGE FOR PRODUCING COMPACTS WITH THE MAXIMUM STRENGTH

Abstract

Researchers of the Nekrasov Iron & Steel Institute, National Academy of Sciences of Ukraine, conduct studies aimed at developing analytical methods for predicting the strength characteristics of pellets. These studies use analyses of phase interaction mechanisms within a free-flowing medium to develop theoretic ideas on the formation of strong bonds in the pellets through adhesion. This led to the establishment of local models of adhesion processes for two basic particle interaction schemes: ‘particle + particle’ and ‘particle + liquid phase + particle’. Experimental studies undertaken in laboratory premises of the Nekrasov Iron & Steel Institute for the ‘particle + particle’ interaction scheme provided the foundation for a method to determine the strength characteristics of pellets made from fine-grained materials with zero moisture, under pelletizing pressures ranging from 50 to 220 MPa. The first part of the paper justified methodological prerequisites for experiments to study strong bonds within the pellets for ‘particle + liquid phase + particle’ interaction scheme. The methodological prerequisites accounted for the peculiarities of mechanical, physical, and physicochemical interactions, both between individual particles of the pelletized material and between the components in the charge (liquid phase). A generalized analysis of the experimental findings allowed evaluating a range of potential adhesion processes for the ‘particle + liquid phase + particle’ interaction scheme, localizing their manifestation, examining their nature, and assessing the effect of introducing a liquid phase into the pelletized charge, considering the compaction pressures applied. This paper focuses on  the experimental findings for the ‘particle + liquid phase + particle’ interaction scheme, establishing analytical dependences between the strength characteristics of pellets and integral indicators of the adhesive bond formation mechanism in this interaction scheme (in particular, dependence between the bulk density (r₀) and moisture content (W) for materials in the first group of systematization. Additionally, an analytical relationship between the compaction factor for pellets produced at a compaction pressure (P) of 220 MPa (K_comp220), considering pellet loosening, and the bulk density of materials (r₀) in the first group of systematization was established for the first time. Analysis of the findings led to a hypothesis suggesting that the amount of the liquid phase (in particular, water) introduced into the material should be balanced by its potential displacement during compaction to achieve maximum pellet strength. Grounded on the hypothesis, a novel equation was derived to calculate the amount of liquid bonding agent (water) to promote the most favorable conditions for the adhesion processes, thereby imparting the maximum strength to pellets from materials in the first group of systematization. A comparative analysis between the experimental findings and calculations confirmed that the equation was correct. Consequently, an analytical method was proposed to determine the moisture needed in the charge to produce pellets with maximum strength from materials in the first group of systematization (r_pycn ≥ 4.64 × 10^–3).