S.V. Komarov

Characterization of acoustic cavitation in water and molten aluminum alloy

High-intensive ultrasonic vibrations have been recognized as an attractive tool for refining the grain structure of metals in casting technology. However, the practical application of ultrasonics in this area remains rather limited. One of the reasons is a lack of data needed to optimize the ultrasonic treatment conditions, particularly those concerning characteristics of cavitation zone in molten aluminum. The main aim of the present study was to investigate the intensity and spectral characteristics of cavitation noise generated during radiation of ultrasonic waves into water and molten aluminum alloys, and to establish a measure for evaluating the cavitation intensity. The measurements were performed by using a high temperature cavitometer capable of measuring the level of cavitation noise within five frequency bands from 0.01 to 10MHz. The effect of cavitation treatment was verified by applying high-intense ultrasonic vibrations to a DC caster to refine the primary silicon grains of a model Al-17Si alloy. It was found that the level of high frequency noise components is the most adequate parameter for evaluating the cavitation intensity. Based on this finding, it was concluded that implosions of cavitation bubbles play a decisive role in refinement of the alloy structure.

Numerical and Experimental Investigation on Heat Propagation Through Composite Sinter Bed With Non-Uniform Voidage: Part I Mathematical Model and Its Experimental Verification

The mechanisms of heat transfer through the sinter beds of the MEBIOS process are discussed and their comprehensive mathematical model is proposed. The MEBIOS process, the concept of which has been proposed earlier by the authors, allows using both coarse and fine particles of iron ores in the same sinter bed. The study includes two parts. The first part describes the model content and the results of its experimental verification. The model accounts for coal combustion, limestone decomposition, moisture evaporation/condensation, and melting/solidifying of solid phases. The model predictions are in good agreement with the experimental data. Typical numerical results of the sintering process and the key parameters influencing the process efficiency are discussed in the second part of the study.

Investigation of Acoustic Streaming in Aluminum Melts Exposed to High‐Intensity Ultrasonic Irradiation

The purpose of the present work is to investigate characteristics of acoustic streaming in aluminum melts experimentally and by numerical simulation. In ultrasonic casting of aluminum alloys, the acoustic streaming is of considerable importance because it can affect the metal flow causing both positive and negative influences on the alloy solidification structure.

A Novel Ultrasonic Casting Process Using Controlled Cavitation and Melt Flow in Hot Top Molds

The present work introduces a novel ultrasonic DC casting process which allows producing billets of hypereutectic Al-Si alloys with greatly refined and uniformly distributed particles of primary Si. In the process, ultrasonic vibrations are introduced into an Al-17Si-0.01~0.03P melt in a hot top positioned on the mold by using a high-amplitude ceramic sonotrode. The hot top design and sonotrode arrangement provided a highly effective cavitation treatment of the melt in the hot top and well-controlled flow in the sump. A simplified model is proposed to explain the obtained results.

Development of Large‐Size Ultrasonic Sonotrodes for Cavitation Treatment of Molten Metals

This work presents results of the development of large-size high-amplitude ceramic sonotrodes destined for use in cavitation treatment of molten metals. The sonotrodes were characterized for their vibration amplitude, erosion resistance and cavitation-producing ability in aluminum melts. The ability of the sonotrodes to refine the grain structure was examined by applying them to the DC casting of Al-Si hypereutectic alloys. The results showed that the sonotrodes have excellent performance characteristics, and they possess far superior erosion resistance and endurance than those made of such high-resistance refractory metals as Nb alloys.

Numerical and Experimental Investigation on Heat Propagation Through Composite Sinter Bed With Non-Uniform Voidage: Part II Prediction of Process Efficiency

The results of numerical simulation of the mosaic embedding iron ore sintering (MEBIOS) process according to the model presented in the first part of the study are introduced. The main objective of the second part is the elucidation of key factors influencing the process efficiency, particularly the sintering completeness, velocity of the heat wave propagation and maximum temperature achievable in the pellet during the wave propagation. Numerical results reveal that the mass fraction of coal, diameter of coal particles and air inlet velocity are of prime importance in determining efficiency of the MEBIOS sintering process.