Authors: Yun Zhong Liu, Yuan Yuan Li
Abstract: A novel spray forming process was developed to produce large billets, wide plates or
thick tubes with excellent microstructures and high cooling rates. Its uniqueness lies in a
combination of the wide-range reciprocating movement and the swing scan of a gas atomizer, and
the externally forced cooling of substrate during this spray deposition procedure. Its basic concept is
that both good sticking and rapid solidification can be achieved if droplets with high liquid fractions
impact a cold substrate, spread fully and then deposit on the surface. In order to control and
optimize this new process, the thermal histories of droplets and deposits for spray forming of
aluminum alloy billets were simulated with a set of new numerical models. Through shortening
spray distance and raising melt superheat properly, the liquid fraction of droplets before deposition
will increase and their spread on the deposit surface can improve for good sticking. Simulation
results show that the optimal liquid fraction of droplets for deposition is about 0.2 higher than that
in the conventional Osprey process. Its optimum spray distance is about 0.25m, which is nearly half
as that in the Osprey process. In addition, this new process increases the mushy layer area and the
specific surface area of heat extraction during deposition. Together with the forced cooling of
substrate, it results in higher cooling rates. A high-quality large billet can be obtained by controlling
the atomizer movement, the droplet liquid fraction and the deposit surface temperature properly in
this new process.
1171
Authors: Ya Li Guo, Rachid Bennacer, Sheng Qiang Shen, Wei Zhong Li
Abstract: The shape and surface texture of a liquid droplet were studied in two-dimension when a droplet impinges on a solid substrate under isothermal condition. The lattice Boltzmann moment model was applied to simulate the fluid dynamics considering the adhesive interaction between fluid particles and surfaces. The results show the influence of wetting on the process and the drop shape. For the hydrophobic surface, the process after impinging may be divided into two stages: the spreading process driven by inertial forces and the subsequent oscillation (recoiling process) driven by surface tension forces. While for the hydrophilic surface, the droplet will only deposits on the surface and there is no the recoiling stage. In addition, the effects of the impinging speed on the shape and texture of the droplet were studied. The spreading speed and the maximum diameter of the spreading droplet increase with the rise of the impinging speed.
303
Authors: Yan Jin, Zhi Bing Tian
Abstract: Because the dynamic soft reduction of continuous casting process is based on the computation of the solidification end point, using model to simulating the steel solidificating process is more and more interesting. Especially, the influence of the heat flux to the solidification end point is needed to research thoroughly. In this paper the heat transfer model for the simulation of the solidification of steel droplet is established. The simulation reveals that the steel droplet (the radium is 7.2 mm) is solidified quickly in 4.3 seconds on water cooling copper plate, and in 3 seconds there is half of the droplet is frozen to solid. If there are materials resisting heat transfer inserted between cooling plate and liquid steel, the solidification end position would be moved to the deeper place below the shell in obvious extent, and the influence of heat flux to the ratio of mushy zone is weaker than that to solidification end point position.
3936
Authors: Sheng Dong Gao, Yang Wang, Hong Bo Wang, Yan Wu
Abstract: An experimental device capable of producing uniform metal droplet stream and electric charging and deflecting has been developed. Uniform spherical powder of 180μm in diameter was obtained after cooling and solidification. Numerical models of heat transfer and solidification of droplets were established. The thermal history including solid fraction of droplets in uniform droplet spray process were calculated. Under the common processing conditions, the cooling rate of a droplet of 180μm diameter is of the order of 103−104°C/s. To obtain homogeneous and dense preforms, the substrate should be positioned at a distance of 1.1-1.3m from the nozzle.
519
Authors: Feng Liang Yin, Sheng Zhu, Jian Liu, Yuan Yuan Liang
Abstract: A two-dimensional mathematical model has been developed to simulate the impinging and solidification process of a single droplet onto substrate in uniform droplet spray rapid prototyping. Droplet free surface is tracked by volume-of-fluid (VOF) algorithm. The effect of surface tension on the droplet is taken into consideration by means of considering surface tension to be a component of the body force. The governing equations are solved using a finite volume formulation. The calculation results predicted the final shape of a molten droplet impacting onto a solid substrate, and revealed that the solidification process began at the leading edge with the spread process of droplet. The simulation results provide insight and information not easy available from experimental. Keywords: numerical simulation, droplet, rapid prototyping
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