共查询到20条相似文献,搜索用时 31 毫秒
1.
An investigation into mold filling during the lost foam casting process taking into account the appearance of low-frequency
pulsations of liquid metal in the mold is carried out on the basis of a mathematical model of the kinetics of mold filling.
The pressure in the gas space (GS), where the thermo-destruction of expanded polystyrene (EPS) occurs, is calculated with
allowance for low-frequency pulsations. It is shown that the stability of the mold depends on the metal feed rate, the vacuum
in a flask, the section of a riser, and the gas permeability of the sand and the anti-burning-on coating. Pressure pulsations
in the GS begin at its maximum. Then pulsations dampen and their amplitude is higher at a smaller gas permeability of the
sand and refractory paint (at high coefficients D). The period of pulsations is commonly 0.3–1.5 s and increases during filling. The calculated dependences satisfactorily
coincide with the experimental data. 相似文献
2.
Based on an analysis of the thermal destruction of cellular polystyrene (CPS), an investigation into filling the mold during
casting by gasified models is performed. A mathematical model of the process developed on the displacement of gaseous products
of the thermal destruction of CPS from the region of gasifying the model by excess pressure in a gas gap between the CPS and
liquid metal is made. The results of calculations are compared with the available experimental data on the time dependence
of the pressure in the gas gap and measurements of the duration of the pouring time of actual castings. The satisfactory similarity
of the calculated dependences and characteristics with experimental ones is shown. The formula for the calculation of the
pressure in the thermal destruction region is suggested. This pressure determines the stability of the form and conditions
of obtaining suitable castings, as well as the method for calculation of the filling time of the mold. 相似文献
3.
The cooling of liquid metal in the process of filling the mold during foundry by gasified models is investigated based on an analysis of the equation of thermal conductivity during thermal destruction of the model material. It is shown that crystallization of metal is expanded top-down, and the intensity of cooling increases as the pouring rate increases and rarefaction in a casting box increases. An equation for calculating the temperature of the metal surface that takes into account the energy of thermal destruction of the model material, pouring rate, initial temperature of metal, rarefaction in the casting box, and the cross-section area of the casting during foundry by gasified models is suggested. 相似文献
4.
This study aims to propose suitable simulation methods, which enable to reduce the major differences between water model and real caster, such as the gradually decreased flow space, flow mass in the casting direction, and the momentum decay in the mushy zone. With consideration of solidified process, the method is concerned with the change of flow space and flow mass at the casting direction in water model. The level fluctuations, stimulus–response curves, velocities of liquid surface, and distributions of liquid slag have been changed in the water model to study the differences of flow character and the variation of fluid flow in molds. The mold with a solidified shell leads to significant differences in flow behaviors, such as higher level fluctuations, higher surface velocities, and worse liquid slag distributions. Neglecting the solidified shell causes unrealistic lower surface velocities and level fluctuations in water model. The mold with consideration of flow mass balance has higher level fluctuations and surface velocities than the mold without shell, and has lower level fluctuations and surface velocities than that of mold with a shell. The results indicate that it is necessary for water model to take the solidified process into account to acquire more accurate and reliable experiment results, especially for thinner slab. 相似文献
5.
Shan-Guang Liu Fu-Yang Cao Tao Ying Xin-Yi Zhao Jing-Shun Liu Hong-Xian Shen Shu Guo Jian-Fei Sun 《Metallurgical and Materials Transactions B》2017,48(6):2826-2835
A surface crack defect is normally found in low pressure castings of Al alloy with a sudden contraction structure. To further understand the formation mechanism of the defect, the mold filling process is simulated by a two-phase flow model. The experimental results indicate that the main reason for the defect deformation is the mismatching between the height of liquid surface in the mold and pressure in the crucible. In the case of filling, a sudden contraction structure with an area ratio smaller than 0.5 is obtained, and the velocity of the liquid front increases dramatically with the influence of inertia. Meanwhile, the pressurizing speed in the crucible remains unchanged, resulting in the pressure not being able to support the height of the liquid level. Then the liquid metal flows back to the crucible and forms a relatively thin layer solidification shell on the mold wall. With the increasing pressure in the crucible, the liquid level rises again, engulfing the shell and leading to a surface crack. As the filling velocity is characterized by the damping oscillations, surface cracks will form at different heights. The results shed light on designing a suitable pressurizing speed for the low pressure casting process. 相似文献
6.
为研究生产高精度薄壁黑色金属铸件方法,采用将真空密封造型的铸型放在压力下充型和凝固的铸造工艺,测量其在不同压力下真空密封造型铸型的抗压强度、抗剪强度、硬度、薄膜烧损、型腔内的反压力特性和对浇注金属液充型能力的影响。结果表明:此工艺方法生产的铸型,其强度、硬度远高于一般铸型,适合于生产尺寸精度高的铸件。此工艺既可防止金属液飞溅,又有利于充型流动,是一种生产薄壁、高尺寸精度铸件的方法。 相似文献
7.
The tilt pouring and gravity top pouring of an Al-4.5 pct Cu alloy have been studied. A computercontrolled rollover casting
wheel was used to perform the tilt pouring. Filling sequences with tranquil or turbulent flow patterns have been visualized
using real-time X-ray video radiography and modeled using a computational fluid dynamics (CFD) code. The area of the free
surface film entrained into the bulk of liquid metal in different filling conditions has been calculated using a filling sequence
free from surface turbulence as a baseline. The tensile properties of the castings have been quantitatively assessed for reliability
using a two-parameter Weibull distribution function. The study reveals that the liquid metal flow in the mold filling process
can be accurately simulated using a CFD code. In addition, the computed total surface area of the entrained surface film can
be used as a criterion to judge the deterioration of reliability. The high Weibull modulus achieved by filling a mold without
surface turbulence was reduced by a factor of 2.5 of its original value by entrained surface films. Entrainment of bubbles
required surface turbulence, but folded films could be entrained simply by contraction of the free surface, creating excess
surface film that necessarily folds inward. 相似文献
8.
Analysis of the flow of liquid metal in the mold during continuous casting is a challenging mathematical problem. Nevertheless, precise solutions have bene found for some cases. Such analytical solutions may be used to verify numerical solutions. In the present work, the melt flow in the mold is studied numerically on the basis of the finite-difference approximation of the initial system of equations. This method is relatively universal: it has been successfully used in continuum mechanics, in mathematical modeling of the stress–strain state of shells in casting, and in other industrial contexts. In the present work, it is applied to the hydrodynamic and thermal fluxes of liquid metal in steel casting in a rectangular mold in a continuous-casting machine. The three-dimensional mathematical model that is obtained describes the liquid-metal fluxes in the mold. The processes that accompany the filling of the mold with melt are simulated by means of Odissei software. The calculations are based on the fundamental hydrodynamic equations, a formula from mathematical physics (the heat-conduction equation with allowance for mass transfer), and a familiar numerical method. The resulting system of differential equations is solved numerically. The region investigated is divided into finite elements. For each element, the system of equations is written in finite-difference form. Solution yields the field of flow velocities of the metal and the temperature field within the mold. The algebraic equations obtained by this means are solved by means of numerical algorithms. On that basis, a program is written in Fortran-4. The mathematical model permits variation of the mold dimensions and the cross section of the metal outlet from the submersible nozzle. It may also assist in understanding the motion of the cast metal, which affects the heat transfer by the mold walls, and in finding the optimal parameters of the liquid metal as it leaves the submersible nozzle. As an example, steel casting in a rectangular mold (height 100 cm) is considered. In casting, the metal leaves the submersible nozzle symmetrically on both sides, in the horizontal plane. The results are graphically displayed. The motion of the metal flux is shown in different cross sections of the mold. Regions of circular flow are identified, as well as regions of vertical motion in the mold. The magnitude and intensity of these regions are determined. The temperature field indicates a local hot zone at the mold wall. That may be attributed to the direct flux of hot metal from the aperture in the submersible nozzle. 相似文献
9.
10.
This article develops a theoretical model of the two-chamber pressure casting process. In this process, a molten metal drop,
formed by arc melting a solid ingot, falls into a conical crucible attached to a gas-filled, porous cast mold. An energy-based
formulation of the mold-filling process is developed which focuses on the drop’s motion within the crucible and mold cavity
and on pressure evolution within the mold cavity. The model shows that drop acceleration into the mold depends on three dimensionless
parameters, the Euler number, Eu, the Froude number, Fr, and the pressure loss coefficient, K, across the crucible exit. These parameters are in turn determined by the mold’s permeability to the process gas, the characteristic
initial pressure difference between the interior and exterior of the mold, the mold thickness, the process gas viscosity,
and the metal density. Drop acceleration into the mold compresses trapped gas within the mold cavity; under most conditions,
pressure decay due to leakage of the trapped gas through the mold occurs at a faster rate than inertial compression. Under
these circumstances, a downward acting pressure force, having a magnitude determined by the Euler number, acts on the drop.
At low Froude numbers, however, gas compression occurs at a faster rate than leakage-induced decay and the pressure force acts upward, again with a magnitude determined by Eu. Scaling arguments
show that friction and evaporation recoil forces are negligible in determining drop motion, while surface tension, pressure,
drop inertia, and gravity are dominant. In addition, solidification effects are shown to be negligible. 相似文献
11.
Seong-Jai Cho Suk-Joong L. Kang Duk N. Yoon 《Metallurgical and Materials Transactions A》1986,17(12):2175-2182
The effect of an inert gas entrapped in isolated pores on liquid flow into them during liquid phase sintering has been studied.
An analysis of the balance between the capillary pressure of the liquid menisci and the gas pressure shows that the entrapped
gas delays the pore filling and produces bubbles. If the gas pressure exceeds a critical level, the pores remain intact and
the critical point for their filling will never be reached. These predictions are confirmed by experimental observations on
large spherical pores produced artificially in an Fe-Cu alloy. Argon gas is trapped in the pore by first sintering in Ar-H2 mixture gas and then in H2 after the isolated pores are formed. The entrapped inert gas of even low pressure is thus shown to cause a substantial porosity
in liquid phase sintered specimens.
Formerly a Doctoral Student at the Korea Advanced Institute of Science and Technology. 相似文献
12.
13.
Ramnik Singh Brian G. Thomas Surya P. Vanka 《Metallurgical and Materials Transactions B》2013,44(5):1201-1221
Electromagnetic braking (EMBr) greatly influences turbulent flow in the continuous casting mold and its transient stability, which affects level fluctuations and inclusion entrainment. Large eddy simulations are performed to investigate these transient flow phenomena using an accurate numerical scheme implemented on a graphics processing unit. The important effect of the current flow through the conducting solid steel shell on stabilizing the fluid flow pattern is investigated. The computational model is first validated with measurements made in a scaled physical model with a low melting point liquid metal and is then applied to a full-scale industrial caster. The overall flow field in the scale model was matched in the real caster by keeping only the Stuart number constant. The free surface-level behaviors can be matched by scaling the results using a similarity criterion based on the ratio of the Froude numbers. The transient behavior of the mold flow reveals the effects of EMBr on stability of the jet, top surface velocities, surface-level profiles, and surface-level fluctuations. 相似文献
14.
金属管材是工业领域中结构承重、输送气体和液体的重要部件。自由弯管成形技术有助于实现管件生产的高精度、高性能、高效率和数字化,其精度控制理论和成形技术的研究具有重要的工业应用价值。本文选择直径 30 mm 壁厚 2.0 mm 的铝合金管材6061为仿真优化对象,通过相关基础实验获得材料的基本力学数据,用于仿真模型参数的表征。同时,结合管材压弯实验验证本构模型成形预测的有效性。在完成仿真模型表征和验证的基础上,对铝合金管材的自由弯曲成形过程进行仿真模拟,分析对比了影响自由弯曲成形的各工艺参数,确定了该工况下最优的移动模与管材间隙大小、摩擦系数和进给速度等。该研究有助于优化管材空间自由弯曲成形工艺,具有一定的工业应用价值。 相似文献
15.
Hyo-Hoon Park Seong-Jai Cho Duk N. Yoon 《Metallurgical and Materials Transactions A》1984,15(6):1075-1080
Models for liquid flow into isolated pores during liquid phase sintering are described qualitatively. The grains are assumed
to maintain an equilibrium shape determined by a balance between their tendency to become spherical and a negative capillary
pressure in the liquid due to menisci at the specimen surface and the pore. With an increase of grain size, the grain sphering
force decreases while the radius of liquid menisci increases to maintain the force equilibrium. When grain growth reaches
a critical point, the liquid menisci around a pore become spherical and the driving force for filling the pore rapidly increases
as liquid flows into it. The critical grain size required for filling a pore increases linearly with pore size. Experimentally,
filling of isolated pores has been investigated in Fe-Cu powder mixture after liquid phase sintering treatment and after dipping
into a molten matrix alloy. The observed pore filling behaviors agree with the qualitative predictions based on the models.
In Fe-Cu alloy, pore filling is terminated by gas bubbles formed in liquid pockets.
This paper is based on a presentation delivered at the symposium “Activated and Liquid Phase Sintering of Refractory Metals
and Their Compounds” held at the annual meeting of the AIME in Atlanta, Georgia on March 9, 1983, under the sponsorship of
the TMS Refractory Metals Committee of AIME. 相似文献
16.
Doru M. Stefanescu G. Upadhya D. Bandyopadhyay 《Metallurgical and Materials Transactions A》1990,21(3):997-1005
A close examination of the recent developments in the field of computer simulation of solidification process reveals that
a combination of both macroscopic and microscopic models is necessary in order to accurately describe the solidification of
castings. Currently available macroscopic models include models that describe heat transfer from metal to mold, fluid flow
of liquid metal during mold filling, and stress field in the casting. At the microscopic level, the models should include
more intricate issues such as solidification kinetics and fluid flow in the mushy zone. Although significant progress has
been accomplished over the years in each field, the task of including all of these models into a comprehensive package is
far from being complete. This paper describes the state of the art on coupling the macroscopic heat transfer (HT) and microscopic
solidification kinetics (SK) models and introduces thelatent heat method as a more accurate method for solving the heat source term in the heat conduction equation. A new method for calculation
of fraction of solid evolved during solidification based on computer-aided cooling curve analysis (CA-CCA), as well as a method
based on nucleation and growth kinetics laws, is discussed. A new nucleation model based on the concept of instantaneous nucleation,
which is used to describe equiaxed eutectic solidification of commercial alloys, has been introduced. It is demonstrated that
the instantaneous nucleation model agrees well with the experimental results in terms of cooling curves and of evolution of
the fraction of solid during solidification. Validation results are also shown for SK models that are based on CA-CCA coupled
with HT models for eutectic Al-Si and gray cast iron alloys. 相似文献
17.
Yehia Mohamed Shash Tarek El Gammal Mohamed Ahmed El Salamoni Friedrich Alexander Denkhaus 《国际钢铁研究》1988,59(6):269-274
Most of the metallurgical effects resulting from electroslag remelting of metal may be divided into two groups, namely, the effects due to the slag/metal reactions taking place and the effects due to the special solidification conditions characteristic of this process. Solidification of ESR ingots takes place progressively as heat is removed from the liquid metal pool via the mold walls. By careful matching of the melting rate with the freezing rate, the desired shallow metal pool is attained, leading to the well known directional solidification pattern with consequent improvement in properties of the steel. The choice of power parameters is limited by a compromise between the need for a high melting rate for economic reasons (costs) which may tend to give a rather deep metal pool and the need for a shallow metal pool to obtain optimum metallurgical properties. In this process only a relatively small amount of the total energy input is actually utilized to melt down the metal. The major part of the energy is lost from the slag and metal pool to the water cooled mold. In this paper the results of numerical and experimental investigations are presented, setting out a simple method of saving energy and controlling the solidification pattern of the ingot. This method involves the addition of solid particles to the melt to utilize the surplus energy evolved in the central area of the slag bath. 相似文献
18.
LIFENG ZHANG SUBO YANG KAIKE CAI JIYING LI XIAOGUANG WAN BRIAN G. THOMAS 《Metallurgical and Materials Transactions B》2007,38(1):63-83
Fluid flow in the mold region of the continuous slab caster at Panzhihua Steel is investigated with 0.6-scale water model
experiments, industrial measurements, and numerical simulations. In the water model, multiphase fluid flow in the submerged
entry nozzle (SEN) and the mold with gas injection is investigated. Top surface level fluctuations, pressure at the jet impingement
point, and the flow pattern in the mold are measured with changing submergence depth, SEN geometry, mold width, water flow
rate, and argon gas flow rate. In the industrial investigation, the top surface shape and slag thickness are measured, and
steel cleanliness including inclusions and the total oxygen (TO) content are quantified and analyzed, comparing the old and
new nozzle designs. Three kinds of fluid flow pattern are observed in the SEN: “bubbly flow,” “annular flow,” and an intermediate
critical flow structure. The annular flow structure induces detrimental asymmetrical flow and worse level fluctuations in
the mold. The SEN flow structure depends on the liquid flow rate, the gas flow rate, and the liquid height in the tundish.
The gas flow rate should be decreased at low casting speed in order to maintain stable bubbly flow, which produces desirable
symmetrical flow. Two main flow patterns are observed in the mold: single roll and double roll. The single-roll flow pattern
is generated by large gas injection, small SEN submergence depth, and low casting speed. To maintain a stable double-roll
flow pattern, which is often optimal, the argon should be kept safely below a critical level. The chosen optimal nozzle had
45-mm inner bore diameter, downward 15 deg port angle, 2.27 port-to-bore area ratio, and a recessed bottom. The pointed-bottom
SEN generates smaller level fluctuations at the meniscus, larger impingement pressure, deeper impingement, and more inclusion
entrapment in the strand than the recess-bottom SEN. Mass balances of inclusions in the steel slag from slag and slab measurements
show that around 20 pct of the alumina inclusions are removed from the steel into the mold slag. However, entrainment of the
mold slag itself is a critical problem. Inclusions in the steel slabs increase twofold during ladle changes and tenfold during
the start and end of a sequence. All of the findings in the current study are important for controlling slag entrainment. 相似文献
19.
Utilizing ANSYS CFX commercial software and volume fraction of fluid (VOF) model, fluctuation behav- ior of steel/slag interface was numerically simulated in continuous casting mold with static magnetic field, and the influence of metal jet characteristics on the behavior of steel/slag interface was investigated. The results indicated that the behavior of steel/slag interface is similar at different process parameters, which is closely related to the characteristic of the flow field. The steel/slag interface has an obvious trough characteristic, which can be divided in- to three zones: frontal valley zone, back valley zone and horizontal zone~ as the magnetic flux density increases, the fluctuation of liquid level increases firstly and then decreases, and a reasonable magnetic flux density can make steel/ slag interface obtain a relatively flat interface, which can prevent slag from being entrapped into liquid steel. For a thin slab continuous casting process, when the casting speed is 4 m/min, a reasonable magnetic flux density is about 0.5 T, and the interfacial fluctuation is weaker. No matter the position of magnetic field is horizontal or vertical, for different operating parameters, there is a corresponding reasonable magnetic field position where the steel/slag inter- face fluctuation can be properly controlled and slag entrapment can be prevented. 相似文献