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This work focuses on ultrasonic melt treatment (UST) in a launder upon pilotscale direct chill (DC) casting of 152-mm-diameter billets from an AA6XXX alloy with Zr addition. Two casting temperatures (650°C and 665°C) were used to assess their effect on the resulting microstructure (grain size, particle size, and number density). Structure refinement results show the feasibility of UST in the DC casting launder. This is quantified through the corresponding reduction of grain size by around 50% in the billet center, or more towards the billet surface, reduction of the average Al 3 Zr particle size, and increase in the particle number density. A higher Al 3 Zr particle density was obtained when the alloy was cast at 665°C. Numerical simulation results and suggestions on how to improve the treatment quality of UST in DC casting launder are also provided.
This study concerns the numerical simulation of two competing ultrasonic treatment (UST) strategies for microstructure refinement in the direct-chill (DC) casting of aluminium alloys. In the first, more conventional, case, the sonotrode vibrating at 17.3 kHz is immersed in the hop-top to treat the sump melt pool, in the second case, the sonotrode is inserted between baffles in the launder. It is known that microstructure refinement depends on the intensity of acoustic cavitation and the residence time of the treated fluid in the cavitation zone. The geometry, acoustic field intensity, induced flow velocities, and local temperature are factors which affect this treatment. The mathematical model developed in this work couples flow velocity, acoustics modified by cavitation, heat transfer, and solidification at the macroscale, with Lagrangian refiner particles, used to determine: (a) their residence time in the active zones, and (b) their eventual distribution in the sump as a function of the velocity field. This is the first attempt at using particle models as an efficient, though indirect, alternative to microstructure simulation, and the results indicate that UST in the launder, assisted with baffle separators, yields a more uniform distribution of refining particles, avoiding the strong acoustic streaming jet that, otherwise, accompanies hot-top treatment, and may lead to the strong segregation of refining particles. Experiments conducted in parallel to the numerical studies in this work appeared to support the results obtained in the simulation.
Although the adverse health effects of poor indoor air quality on occupants from mold and dampness in indoor environments are well described, there is no reliable empirical tool to evaluate indoor mold and dampness levels in the home for use by the medical profession and health safety regulatory bodies. The economic impact to society approaches $40 billion a year in North America alone from the cost of health care and workplace lost productivity. Mobilizing corrective action necessitates an acceptable home environment evaluation method. This paper proposes a reliable empirical model and tool, the Holistic Environmental Assessment Lay Tool for Home Healthiness, and develops guidelines for its use as a tool to evaluate and rank mold and dampness related indoor environmental conditions associated with known respiratory health outcomes. HEALTH2 was calibrated using theoretical homes and then validated using data from 269 home evaluations where occupant health and the home environment factors were collected. Results suggest the model can be used as an early detection tool to assist in determining indoor environment risk factors associated with respiratory illness from mold and dampness. Empirical modeling and this tool can assist environmental professionals in determining improvement scenarios beyond general industry prescription and assist regulatory bodies in setting home health guidelines. The HEALTH2 model challenges the dominant view and suggests that damp and moldy environments are measurable and the impact to society is sufficient to necessitate prompt medical and regulatory action.
A promising strategy for upscaling ultrasonic melt treatment (UST) during direct-chill (DC) casting is through a strategically-placed flow management system in the launder. This aims at improving the melt residence time and acoustic pressure distribution, which ultimately optimizes the treatment efficiency. This work focuses on observing the effect of partitions and UST on the resultant grain refinement upon DC casting of an AA6XXX aluminum alloy with Zr additions. Billets 152-mm in diameter were cast in a pilot-scale DC casting facility: cases with and without partitions and with and without UST were compared. The effect of partitions on the UST efficiency was quantified through macro-and microstructure observations and supported with acoustic pressure measurements. The positive impact of partitions on the grain refinement upon UST is demonstrated.
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