钢中喂铝参数的实验和理论研究

钢中喂入铝线的熔化速度取决于线径(φ)、钢水过热度(ΔT)和喂入速度(μ)。在50 kg感应炉内热模拟试验获得喂入铝线的开始熔断时间(τ)的经验关系式为 低熔点金属喂入熔点较高的熔池后,其熔化过程包括结壳、传热、熔破等过程,利用传热学理论进行数学模型描绘,与实验法研究结果相符。两种方法均可为生产条件下选择喂线参数提供依据。     

钢中喂铝参数的实验和理论研究

钢中喂入铝线的熔化速度取决于线径(φ)、钢水过热度(ΔT)和喂入速度(μ)。在50 kg感应炉内热模拟试验获得喂入铝线的开始熔断时间(τ)的经验关系式为 低熔点金属喂入熔点较高的熔池后,其熔化过程包括结壳、传热、熔破等过程,利用传热学理论进行数学模型描绘,与实验法研究结果相符。两种方法均可为生产条件下选择喂线参数提供依据。     

搅动熔池中沉浸球体表面流动及传热过程的研究

近年来,熔融还原技术已取得很大进展,但在熔态还原重要基础研究,如熔池的传热供热、传质等的研究还较薄弱。本文试图探讨球体位于熔池表面及涡流区内时,供气量、球体位置及初始直径对固液相对流传热系数的影响。为了研究熔态还原中金属球团在搅动熔池中的熔化及传热过程,本文以冰球—水体系为模型,通过求解一维非稳态动边界热传导方程,并结合水模型实验,考察了球体不在气泡流区时底     

球状金属颗粒在流动熔体中熔化过程的数学模型

针对冶金过程中常涉及到的固态金属在液态金属中的熔化过程建立数学模型,用焓法描述相变过程,采用有限体积法,对过热熔体中球状金属颗粒熔化过程及其影响参数进行研究.结果表明,金属颗粒的熔化受颗粒初始温度、熔体过热度以及熔体流动强度的影响.熔体流动对相变影响作用较大,受周围流体对流强度的影响,颗粒从表面凝固壳形成到熔化过程呈现非均匀性,在靠近上游的颗粒前端以及下游尾迹处颗粒熔化速度较快,而颗粒边缘熔化速度较慢.     

双电弧集成冷丝复合焊中冷丝位置对焊接过程的影响

搭建了双电弧集成冷丝复合焊接系统,研究了冷丝不同位置对焊接过程的影响机理,其中包括冷丝作用位置对其加热熔化作用及表面成形的影响。实验结果表明:冷丝从两引导焊丝正前方送入时,熔池前端对冷丝的加热熔化作用不充分,冷丝末端会顶触熔池底部,随着冷丝的持续送进和母材的向后移动,某一时刻冷丝回弹,焊丝末端的熔滴弹出落在母材表面形成大颗粒飞溅。当冷丝从侧面送入时,熔池一侧的温度较低,影响熔池金属的流动,导致最终的焊缝成形不对称分布。当冷丝从两引导焊丝正后方送入熔池时,冷丝始终插入熔池中,焊接过程稳定,是理想的冷丝作用位置。此外,随着冷丝送丝速度的增加,两种脉冲电流模式（同相和反相）下,熔敷率均随之增加,且相差不大。同相脉冲电流下电弧对冷丝的加热熔化作用最强烈,反相脉冲电流下次之,直流模式下最弱。      

电弧炉中金属颗粒熔化速率的数学模型

为了描述工业电弧炉中（EAF）金属颗粒的熔化动力学,开发了将计算流体动力学模型耦合到熔似凝固颗粒的拉格朗日模型,假定液态钢水占据整个计算领域。金属颗粒为直接还原铁（DRI）,为了评价三相EAF中加入的DRI熔化速率,采用2个以前的模型,即电弧模型以及流体流动模型,评价了初始颗粒尺寸、初始DRI温度、加料位置、加料速率、电弧长度以及DRI的冶金性能影响,此外,本模型也评价了熔炼过程前期形成的凝固壳。     

元素添加强化铍铝合金研究现状

铍铝合金具有密度低、比刚度高、比强度高、热膨胀系数低及易加工等优良性能,在航空、航天工业、计算机制造业和汽车工业中有着重要的应用.铸造铍铝合金由于铍、铝两相熔点差异大、互溶度低、几乎没有金属间化合物,使得其微观组织具有显著糊状凝固特征,高熔点铍相作为颗粒相被低熔点基体铝相包裹,进而使得铍铝合金兼具铝基复合材料特征,在性...     

回收渣中铬铁的跳汰制度选择

碳素铬铁是我厂的主要产品之一,在冶炼过程中,由于炉渣熔点高、粘度大,渣中夹带的金属颗粒和未熔化的铬铁较多。这种炉渣冷却后难以用人工的方法分离回收,过去我厂只好将这些炉渣废弃。1983年我厂开始对回收碳素铬铁渣中的     

铝钨系中间合金及其制备方法

本发明涉及合金技术，具体地说是一种铝钨系中问合金及其制备方法。按重量百分比计，其成分为：10—75钨、0～75铌、0～75钼、0～20钛、铝余晕。制备可以采用炉外点火冶炼法：原料烘干温度70～80％，配料时加人配料渣子，加入量为原料总重量的5～15％；亦可采用中频炉熔化法：按所述配比配料时加入防氧化剂和助熔剂。本发明铝钨系中间合金熔点远低于金属单质的熔点，使钛合金的制备熔炼过程稳定，避免了由于金属单质熔点不一致，所施加的熔炼电流忽高忽低不容易控制的现象；     

电渣重熔过程中金属熔池形状的数学模拟

本文利用了前人关于熔滴在渣池中行为的研究成果和渣池中有关传热规律的实验资料,确定了渣池—金属熔池界面上的边界条件。通过实验确定了输入功率与熔化速度的关系。而后建立了包括有金属熔池、两相区、凝固锭在内的电渣锭温度场的数学模型,最后进行数值计算,得到6种不同熔化速度和两种不同渣量的熔池形状,并与实验进行比较,其结果是令人满意的。     

Measurement of magnitude and direction of velocity in high-temperature liquid metals. Part I: Mathematical modeling

This article describes the development of a mathematical model that predicts the time required for a metal sphere to melt in a metal bath under different fluid flow conditions. The sphere is made from the same metal as the bath. The model solves numerically the pertinent momentum and energy equations in three dimensions, employing the SIMPLER algorithm. For the case of a pure metal, the model uses the heat integration algorithm to account for the latent heat of fusion. For the situation of a metal alloy with long freezing range, it incorporates the enthalpy method to account for the latent heat of fusion. The model is validated extensively: first, by using Paterson’s analytical solution; second, by using the experimental results of Gallium melting in a rectangular enclosure; and third, by using experimental results involving ice spheres melting in water. The practical use of this model is to study the influence of various parameters in the sphere melting system. This study facilitates the detection of liquid metal velocity using the sphere melting technique.     

Interaction of iron particles with a solid-liquid interface in lead and lead alloys

The interaction of iron particles with an advancing solid-liquid interface has been examined in lead and lead alloys. In the case of pure lead solidified with a planar interface, the particle distribution in the solid and quenched liquid was uniform, indicating particles werenot rejected at the interface. For interfaces with a cellular and dendritic structure the particles were concentrated in the cell walls and interdendritic regions. This concentration is accounted for on the basis of the particle velocity and convective flow in the melt during the particle interface interaction. A water model was examined which simulated the metal system, using nylon spheres for particles and a lucite cellular surface for the interface. The results confirmed that particles are concentrated at intercellular regions as a result of the particle velocity and fluid flow. On leave from Universidad Nacional de Misiones, Argentina.     

Solidification of Pb particles embedded in Al

Hypermonotectic alloys of Al-5 wt% Pb and Al-5 wt% Pb-0.5 wt% X where X = Mn, Cu, Zn, Fe and Si have been manufactured by chill-casting and melt-spinning. The resulting microstructures have been examined by a combination of optical microscopy, scanning and transmission electron microscopy, and electron probe microanalysis. The as-solidified hypermonotectic alloys exhibit a homogeneous bimodal distribution of faceted Pb particles embedded in a matrix of Al, with chill-cast Pb particle sizes of 1–2 μm and 5–50 μm, and melt-spun Pb particle sizes of 5–10 nm and 50–100 nm. The larger Pb particles are formed during cooling through the region of liquid immiscibility while the smaller Pb particles are formed during monotectic solidification of the Al matrix. The Pb particles exhibit a cube-cube orientation relationship with the Al matrix, and a truncated octahedral shape with {111} and {100} facets. The as-solidified Pb particle distributions are resistant to coarsening during post-solidification heat treatment. The equilibrium Pb particle shape and therefore the anisotropy of solid Al-solid Pb and solid Al-liquid Pb surface energies have been monitored by in situ heating in the transmission electron microscope over the temperature range between room temperature and 550°C. The anisotropy of solid Al-solid Pb surface energy is constant between room temperature and the Pb melting point, with the {100} surface energy 14% greater than the {111} surface energy, in good agreement with geometric near-neighbour bond energy calculations. The {100} facets disappear when the Pb particles melt, and the anisotropy of solid Al-liquid Pb surface energy decreases gradually with increasing temperature above the Pb melting point, until the Pb particles become spherical at about 550°C. The kinetics of Pb particle solidification have been examined by heating and cooling experiments in a differential scanning calorimeter. Pb particle solidification is nucleated catalytically by the Al matrix on the {111} facet surfaces, with an undercooling of 22K and a contact angle of 21°C. Ternary additions of Mn, Cu, Zn and Fe do not influence the Pb particle solidification behaviour, but Si is a potent catalyst and stimulates the Pb particles to solidify close to the equilibrium Pb melting point.     

Heat Transfer Modelling of the Melting of Solid Particles in an Agitated Molten Metal Bath

Abstract

The melting of solid particles in stagnant melt such as the melting of iron pellets in an electric arc-furnace has been the subject of many investigations. However, little work can be found in the literature about the modelling of heat transfer during the melting of solid particles in an agitated molten metal bath. The present work deals with the development of a heat transfer model for the melting of the solid pellets in a stirred melt, as melting in induction furnaces or gas-stirred vessels. First, the flow pattern in the liquid bath was obtained using a two-equation k–ε turbulent flow model which was further employed to obtain the particle's trajectory and its slip velocity. The heat transfer coefficient between the melt and particle was then calculated and used in the model to identify the rate of heat transfer to the particle. Parametric studies were carried out to evaluate the effects of such parameters as physical properties of particle and those of the melt on the melting rate of particle. © 1998 Canadian Institute of Mining and Metallurgy. Published by Elsevier Science Ltd. All rights reserved.

Résumé

La fonte de particules solides dans un liquide stagnant, telle que la fonte de boulettes de fer dans un four à arc électrique, a été le sujet de plusieurs investigations. Cependant, on trouve peu d'information dans la litterature sur la modélisation du transfert de chaleur lars de la fonte de particules solides dans un bain agite de métal fondu. Le present travail a pour objet le développement d'un modèle de transfert de chaleur de la fonte de boulettes solides dans un liquide agité, telle que la fonte dans les fours a induction ou les réacteurs à agitation gazeuse. Premièrement, on a obtenu le patron d'écoulement dans le bain liquide en utilisant un modèle d'écoulement turbulent à deux equations, k–ε, également utilisé pour obtenir la trajectoire de la particule et sa vélocité de glissement. On a ensuite calculé le coefficient de transfert de chaleur entre le liquide et la particule et on l'a utilisé dans le modéle pour identifier le taux de transfert de chaleur vers la particule. On a mene des etudes paramétriques afin d'evaluer l'effet de parametres tels que les proprietes physiques de la particule et celles du liquide sur le taux de fonte de la particule. © 1998 Canadian Institute of Mining and Metallurgy. Published by Elsevier Science Ltd. All rights reserved.     

Transport phenomena and penetrability of solid particles in hot metal during lance injection

Abstract

The transport phenomena in injection lance and the penetrability of solid particles into liquid metal at the lance tip during injection treatment was analysed by a one-dimensional mathematical model developed in this work. Mechanic interactions and heat transfers between a solid particle, carrier gas, lance and/or hot metal have been incorporated in the model. Temperatures and velocities of carrier gas and solid particles were examined for a typical hot metal desulphurisation process by granulated magnesium injection. The temperature of gas increases by several hundred degrees, while that of solid magnesium particles only by several degrees in the lance. The gas velocity is increased by thermal expansion in lance. At the lance tip, the magnesium particle velocity is slower than the gas velocity. The penetrability of a magnesium particle into the hot metal at the lance tip was analysed.     

Melting behaviour of In and Pb particles embedded in an Al matrix

Microstructures of melt spun hypomonotectic Al−7wt%In, hypermonotectic Al−5wt%Pb and near monotectic Al−2wt%Pb alloys have been examined by transmission electron microscopy and consist of 10–150 nm diameter faceted In particles and 5–150 nm faceted Pb particles homogeneously distributed in an Al matrix. As-melt spun In and Pb particles exhibit near cube-cube and cube-cube orientation relationships with the Al matrix respectively, and truncated octahedral shapes bounded by {111} and {100} facets. The melting behaviour of In and Pb particles in as-melt spun Al−7wt%In, Al−5wt%Pb and Al−2wt%Pb alloys has been investigated by heating and cooling experiments in a differential scanning calorimeter and in situ heating experiments in a transmission electron microscope. In and Pb particles embedded within the Al matrix grains melt at superheatings in the range 0–40 K above the bulk equilibrium In and Pb melting points. Superheating of In and Pb particle melting within the Al matrix grains is caused by a kinetic difficulty of nucleating melting which increases with decreasing In and Pb particle size. In and Pb particles along the grain boundaries of the Al matrix melt at undercoolings in the range 0–7 K below the bulk equilibrium In and Pb melting points.     

Model Experiments on Melting of Alloys with Low Melting Temperature in a Medium with High Melting Temperature

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Measurement of velocity in high-temperature liquid metals

There is a paucity of methods available for the measurement of velocity in high-temperature liquid metals. This is due to the hostile environmental conditions which characterize liquid metals. This article proposes and appraises a new velocity measurement technique for liquid metal flows at high temperatures. The melting rates of metallic spheres in metal baths of the same chemical composition as the spheres are studied under isothermal conditions. It is dem-onstrated that the metallic sphere can be used as a probe for measuring the average velocity in a metal flow system over a distance equivalent to the diameter of the sphere. The system that was chosen for study is the commercial purity aluminum bath. The experimental calibration setup examined three different elements: (a) it introduced a stationary sphere in a metallic bath of a given temperature and compared its melting rate with that of a moving sphere with known external velocity along the periphery of a circle in a metallic bath of the same temperature; (b) three different sphere diameters were used; and (c) a range of bath temperatures was investi-gated. By studying the effect of these three elements concurrently, it was possible to determine the interplay of these elements. Results showed that the sphere melting time was related linearly to the flow velocity for the range of velocities of 0 to 40 cm/s and for bath superheat up to 100 °C. In order to verify the accuracy of the results obtained by the proposed technique, a comparison was undertaken between mathematical predictions and experimental results of a fluid flow field obtained in an AC induction furnace with molten aluminum. These predictions were made by solving numerically the relevant differential equations under the appropriate boundary conditions. The experimental results attained using the proposed technique were in close agreement with those from the mathematical predictions. A.C. MIKROVAS, formerly Graduate Student, Department of Metallurgy and Materials Science, University of Toronto.     

Aluminium scrap melting under different liquid aluminium flow conditions: part-II: two phase flow

This experimental research work deals with aluminium (Al) alloy melting in an Al bath. In this liquid metal, nitrogen gas was introduced at specific locations and at different gas flow rates. The samples employed, along with their position in the liquid Al, and the procedure for melting detection, were identical with the ones utilised in Part I. The introduction of gas into liquid Al has different effects on the melting time of the immersed Al 6061 alloy cylinder. For the range of gas flow rates examined, the addition of gas into a stagnant Al bath (i.e. natural convection conditions) produces insignificant changes in melting time. However, when the liquid Al is moving (i.e. forced convection conditions), the gas addition leads to a sizeable reduction in melting time. The melting time reduction ratio is introduced as a way to compare the melting under single and two phase flow liquid Al conditions. It is found that this ratio is affected by the nozzle position and also by the gas flow rate. The concept of an equivalent single phase velocity is also introduced, and defines the single phase velocity of liquid Al which results in the same melting time of the cylinder as under two phase flow conditions. It is found that the equivalent single phase velocity is influenced by both the gas flow rate and the nozzle position. The parameter which most likely contributes to the acceleration of the melting rate in two phase flow is the turbulence intensity, which is expected to increase due to the nitrogen gas injection.     

The superheating and the crystallography of embedded Pb particles in f.c.c. Al,Cu and Ni matrices

Al-1.4 at.%Pb, Cu-3.2 at.%Pb and Ni-3 at.%Pb have been rapidly solidified to obtain a nanoscale dispersion of Pb particles embedded within the higher melting point Al, Cu and Ni matrices. Each Pb particle in Al and Cu matrices is a single crystal and faceted. The shape of the Pb particles in Al and Cu is a truncated octahedron bounded by 111 and 100 facets. The second phase Pb particles in Ni are not well faceted and the shape is a roughened truncated octahedron. A well defined orientation relationship is observed between the second phase Pb particles and the matrices. The melting behaviour of these particles is studied using a differential scanning calorimeter. The majority of the second phase particles in all the matrices start melting below the equilibrium melting point of the Pb with a broad endothermic peak. In Al and Cu matrices, a few Pb particles are seen to be superheated while in the Ni matrix superheating of the Pb particles is not observed. It is shown that the observed difference in the melting behaviour is not due to the size dependent behaviour of melting of the second phase. Our results suggest that the shape of the second phase particle strongly influences the superheating.