Contactless Ultrasound Generation in a Crucible

Bojarevics, Valdis; Djambazov, Georgi; Pericleous, K.

doi:10.1007/s11661-015-2824-5

Cited by 28 publications

(20 citation statements)

References 13 publications

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“…Recent developments in electromagnetic processing may offer a solution when the high-frequency vibrations imposed on the melt by a contactless coil result in resonance conditions inside the crucible with a cavitation zone formed inside the melt volume, while low-frequency electromagnetic field induces the stirring of the melt on the macroscopic scale [34].…”

Section: Typical Mistakes and Misconceptionsmentioning

confidence: 99%

Ultrasonic processing of molten and solidifying aluminium alloys: Overview and outlook

Eskin

2017

Materials Science and Technology

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Abstract. Ultrasonic melt processing attracts a lot of interest both from academic researchers and industry. Despite a long history of the subject, with first accounts dating back to the 1930s, the physics, mechanisms and practical applications are still under development. In the second half of the XXth century, pilot-and industrial scale applications of ultrasonic processing of light alloys were demonstrated for melt degassing, filtration, grain refinement, melt atomisation, and zone refining. In the last 10 years the interest to ultrasonic melt processing grew with regard to understanding the underlying mechanisms of previously established effects, developing numerical models of ultrasonic cavitation and the development of nanocomposite technology. This review paper summarises the mechanisms involved in the ultrasonic melt processing, including cavitation, flows, nucleation, activation, fragmentation and their consequences for degassing, structure refinement and particle dispersion. Some typical mistakes made by researchers in performing experiments and in interpretation of the results are discussed. New advanced methods of studying ultrasonic treatment and phenomena are considered. The paper also gives an outlook to future developments and challenges.

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Section: Typical Mistakes and Misconceptionsmentioning

confidence: 99%

Ultrasonic processing of molten and solidifying aluminium alloys: Overview and outlook

Eskin

2017

Materials Science and Technology

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“…This is equivalent to Tc/10, so C=1, 0.5 and 0.1 corresponds to modelling collision in 10, 50 or 100 time-steps. The ratio between the collision and fluid-particle time-steps is then Δ Δ = 10000 (6) Which totally justifies the multi-scale approach.…”

Section: Collision Time-scalementioning

confidence: 86%

“…The elastic forces, friction and cohesion between the particles dictate whether the clusters of particles form or break in the case of MMCs, while in the second case the efficiency of decontamination largely depends on the ability of the particles to adhere to the walls. The EM stirring is typically quite slow (5-10 cm/s, [5], [6]). In order to trace the particles during the stirring, at least one full cycle of stirring should be simulated, which is of the order of 1s for a 10 cm crucible.…”

Section: Introductionmentioning

confidence: 99%

Multiple Timescale Modelling of Particle Suspensions in Metal Melts Subjected to External Forces

Manoylov¹,

Djambazov²,

Bojarevics³

et al. 2016

Proceedings of the VII European Congress on Computational Methods in Applied Sciences and Engineering (ECCOMAS Congress 2016)

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Electromagnetic (EM) fields are widely used in metallurgy in order to stir conducting metals without the risk of contamination or causing an instability or chemical reaction. During the manufacturing of metal matrix composites (MMC), ceramic micro-and nano-particles are added into the metal melt, and ultrasonic (US) processing and EM stirring are used to break the agglomerates and to enhance the dispersion of the particles. EM stirring can also be used to remove the unwanted particles from liquid metal by pushing them towards the walls of the crucible where they adhere and can be easily removed. A model has been developed to account for the complex interaction of the particles with each other, with the walls, as well as with the flow of the metal melt. Particles are modelled as elastic spheres with adhesion. Adhesion is incorporated in the model using the Johnson, Kendal, Robert (JKR) and Derjaguin, Muller, Toporov (DMT) theories. The case of the oblique impact of the particles is modelled according to the Thornton and Yin method based on the partial-slip theory developed by Mindlin & Deresievics. The developed particle model is then coupled with the magneto-hydrodynamics (MHD) code PHYSICA in order to demonstrate the effect of the EM stirring and vibration. Multiple timescales are used which permits modelling the realistic time range of metalprocessing and at the same time capture the individual collisions between particles with sufficient precision. Several methods of predicting the particle collisions are employed and their efficiency is compared for the case of removing contaminating particles from liquid metal.

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“…1 The use of an electromagnetic coil as a contactless source of ultrasound has been demonstrated to work in aluminum crucibles 19,20 containing up to 10.5 kg of metal. This process, using a high-frequency induction coil suspended close to the liquid-free surface 21 resulted in grain refinement and degassing after 2-4 min of treatment. Given that the high-frequency field does not penetrate the melt for more than a few millimeters, acoustic resonance is sought to achieve the pressure threshold required for cavitation in the treatment volume.…”

Section: Introductionmentioning

confidence: 99%

Contactless Ultrasonic Treatment in Direct Chill Casting

Tonry

Bojarevics

Djambazov

et al. 2020

JOM

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Uniformity of composition and grain refinement are desirable traits in the direct chill (DC) casting of non-ferrous alloy ingots. Ultrasonic treatment is a proven method for achieving grain refinement, with uniformity of composition achieved by additional melt stirring. The immersed sonotrode technique has been employed for this purpose to treat alloys both within the launder prior to DC casting and directly in the sump. In both cases, mixing is weak, relying on buoyancy-driven flow or in the latter case on acoustic streaming. In this work, we consider an alternative electromagnetic technique used directly in the caster, inducing ultrasonic vibrations coupled to strong melt stirring. This ‘contactless sonotrode’ technique relies on a kilohertz-frequency induction coil lowered towards the melt, with the frequency tuned to reach acoustic resonance within the melt pool. The technique developed with a combination of numerical models and physical experiments has been successfully used in batch to refine the microstructure and to degas aluminum in a crucible. In this work, we extend the numerical model, coupling electromagnetics, fluid flow, gas cavitation, heat transfer, and solidification to examine the feasibility of use in the DC process. Simulations show that a consistent resonant mode is obtainable within a vigorously mixed melt pool, with high-pressure regions at the Blake threshold required for cavitation localized to the liquidus temperature. It is assumed that extreme conditions in the mushy zone due to cavitation would promote dendrite fragmentation and coupled with strong stirring, would lead to fine equiaxed grains.

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Contactless Ultrasound Generation in a Crucible

Cited by 28 publications

References 13 publications

Ultrasonic processing of molten and solidifying aluminium alloys: Overview and outlook

Ultrasonic processing of molten and solidifying aluminium alloys: Overview and outlook

Multiple Timescale Modelling of Particle Suspensions in Metal Melts Subjected to External Forces

Contactless Ultrasonic Treatment in Direct Chill Casting

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