Study on the melting performance of single screw extruder with grooved melting zone and barr screw

A novel melting mechanism for single screw extruder with grooved melting zone and barr screw was established. The whole solid-plug, which came from the grooved feed zone, was ruptured and melted mainly by continuously changing the volume of the screw channels and the barrel grooves in the grooved melting zone. A new single screw extruder platform with hydraulic-clamshell type barrels was constructed to investigate the melting performance of different combinations of barrels and screws. The melting model was verified by experiments. Compared with conventional single screw extruder, the melting started earlier and the melting length was shorter in the single screw extruder with grooved melting zone. The melting efficiency was improved by the grooved melting zone and the melting stability was improved by the barr screw. The dimensionless analysis of energy indicates that the heat convection and viscous dissipation are the main melting heat sources for the single screw extruder with grooved melting zone.     

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 以包钢含氟烧结矿中的硅酸盐粘结相为研究对象，考察了粘结相的熔化特性随粘结相组成的变化规律。通过试验探讨了不同碱度(w(CaO)/w(SiO2)以及MgO、CaF2和FeO含量粘结相的熔化特性。结果表明，碱度为118时，粘结相的熔化温度最低，熔化时间最短；添加197%MgO，粘结相的熔化温度最低，熔化时间最短；FeO和CaF2含量增加使粘结相的熔化温度降低，但熔化时间变长。     

烧嘴对蓄热式铝熔炼炉熔炼过程的影晌

结合蓄热式铝熔炼炉熔炼过程的特点,运用FLUENTUDF和FLUENTScheme混合编程,耦合用户自定义熔化模型和燃烧器换向及燃烧量变化模型,实现了蓄热式铝熔炼炉熔炼过程的数值模拟。依据优化原则,获得了熔炼时间随影响因子的变化规律：熔炼时间随着旋流数、燃烧器倾角、空气预热温度或天然气流量的增加而缩短;熔炼时间随着燃烧器间水平夹角或空燃比的延长,先减小而后增加：熔炼时间随着燃烧器高度的增加而延长。     

金属Cu体熔化与表面熔化行为的分子动力学模拟与分析

采用Mishin嵌入原子势,通过分子动力学方法模拟了金属Cu原子体系的体熔化和表面熔化行为,分析了体熔化过程中系统结构组态和能量变化以及表面熔化过程中固-液界面迁移情况．模拟结果表明：在体熔化过程中,结构组态与能量在1585K处发生突变;在表面熔化过程中,固-液界面在1380K保持静止．两种熔化过程的不同发生机制是导致体熔点1585K高于热力学熔点1380K的原因．在实际熔化中,表面熔化处于支配地位,实验测量的是热力学熔点．得到的热力学熔点与实验结果吻合良好,验证了本文所采用方法是正确和有效的,同时也说明了Mishin嵌入原子势适合处理复杂无序体系．     

熔模铸铝成型质量控制

通过对铝合金熔模精密铸造熔炼、浇注现场调研,发现了大炉工序在生产中存在的成型质量问题.根据分析,提出了成型质量控制要点及缺陷的控制方法.对熔炼工具、熔炼过程、变质剂、浇注过程等工艺参数都做了阐述.     

TiAl合金真空自耗熔炼过程的数值模拟

通过数值模拟研究了直径为180mm的TiAl合金铸锭的真空自耗冶炼过程,获得了TiAl合金真空自耗熔炼过程中熔炼温度、熔炼速度和冷却能力对金属熔池温度梯度、熔池形状和糊状区宽度的影响规律。结果表明,随熔炼温度升高,熔池深度增加,其形状由碗状向V形转变,熔炼温度对熔池中温度梯度和凝固前沿糊状区宽度影响较小;随熔炼速度增加,熔池中温度梯度显著减小,糊状区宽度和熔池深度则明显降低;随冷却能力增加,糊状区宽度明显减小,熔池中温度梯度和熔池深度略有减小。     

Melting thermodynamics of nanocrystals embedded in a matrix

A simple model, free of any adjustable parameter, is established for the melting temperature and melting entropy of nanocrystals embedded in a matrix where the interface between the nanocrystals and the matrix is coherent. The model is based on Lindemann's criterion for the melting, Mott's equation for the melting entropy of bulk crystals and our model for the size-dependent melting temperature. It is shown that the melting temperature and the melting entropy of nanocrystals embedded in a matrix increase as the size of the nanocrystals decreases. The above predictions are supported by available experimental results on Pb and In nanocrystals embedded in an Al matrix. On the basis of the model, the melting mechanism of superheating is discussed.     

Current processes for the cold-wall melting of Titanium

Conventional vacuum arc consumable electrode melting continues to play a large role in the production of titanium alloy ingots. Titanium melting will be performed by electron-beam and plasma cold-hearth melting in some applications, for the production of titanium rotor-grade ingots. The current reports indicate that hard-alpha defects and high-density inclusions can be eliminated through hearth melting. Automatic controls for electron-beam melting and plasma-arc melting will play an important part in their development for producing high quality titanium ingots. Processes such as cold-wall induction may be integrated into atomization, spray deposition and casting systems. Other combinations of melting techniques can be used for new titanium products in the future.     

NUMERICAL SIMULATION OF INDUCTION SKULL MELTING PROCESS FOR TITANIUM-ALUMINIUM BASE ALLOY

The mathematics model for temperature field of water-cooling copper crucible induction skull melting process was established. The program for simulating temperature field of melting process was developed with finite element method. The temperature field of the melting process for Ti-47Al-2Cr-2Nb aUoy was calculated. During melting period, the temperature is raised gradually along radius augmentation direction. The elements of the charge near the crucible wall are molten first. The center elements of the charge are molten last. The melting time of the center element is just that of all the charge melting. The melting time of Ti-47Al-2Cr-2Nb alloy is 15min. In which, the charge was heated by low power 80kW for 9min and by high power 300kW for 6min. When melting Ti-47AI-2Cr-2Nb aUoy,the loading power is nearly direct proportion to melt temperature. Increasing loading power may raise melt temperature. The best melting power of Ti-47Al-2Cr-2Nb alloy is 305-310kW. This is identical with the melting test and has guidance sense to the melting process of actual titanium aUoy.     

旋流数对铝熔炼炉熔炼过程的影响

针对现有的圆形铝熔炼炉,结合铝熔炼炉熔炼过程的特点,在铝熔炼炉热平衡测试的基础上,建立了合理的铝熔炼炉数学模型,并运用计算流体力学软件FLUENT实现燃烧空间和熔池的耦合物理场的数值模拟。同时分析了不同旋流数对铝熔炼炉熔炼过程的影响,依据提出的优化准则,确实旋流数大于0.6时能够获得最佳的熔炼性能。     

磁记录Fe,Co,Ni纳米晶体的熔化温度

本文提出了一个无自由参数的晶体熔化温随尺寸变化的模型。模型指出纳米金属晶体的熔化温度随着纳米晶的尺寸的减小而降低。     

熔炼条件对铝熔体质量的影响

从空气相对湿度、熔炼设备、炉料质量、熔炼温度和时间以及熔体转注方式等方面,论述了它们对熔体质量影 响的试验结果。指出由于铝熔体的化学活性很高,极易吸氢和氧化,故熔炼工序的各个环节都不可忽视。     

蓄热式铝熔炼炉熔炼过程的数值模拟

为了更好地研究和优化铝熔炼炉的性能,针对现有的蓄热式圆形铝熔炼炉,在建立合理的铝熔炼炉基本模型的基础上,通过耦合用户自定义熔化模型和氧化烧损模型,运用计算流体力学软件FLUENT实现燃烧空间和熔池的耦合物理场的数值模拟。着重研究不同固液区和不同孔隙率对铝及铝合金熔炼过程的影响。结果表明,该模型较好地反映铝熔炼炉的熔炼现象,可运用该模型进行铝熔炼炉熔炼过程工艺参数的优化研究。同时获得了固液区和孔隙率对熔炼参数影响规律:铝液温度在固液区上升缓慢,而离开固液相线时,铝液温度上升速度加快,炉膛温度和氧化层质量随着熔炼时间分别呈周期性增加和呈抛物线增加;随着氧化层厚度的增加,铝液温度随着孔隙率的增加而增加变得缓慢。     

TC4合金的电子束冷床熔炼热平衡计算

通过对TC4合金电子束冷床熔炼过程热平衡的计算和实验验证,为制定合理的熔炼工艺提供了理论依据。结果表明,对于100kg/h的熔炼速度,维持冷床液态熔池表面125℃过热和结晶坩埚内100℃过热的条件下,熔炼原料的功率为70kW,维持冷床内液态熔池的功率为122kW,维持结晶坩埚良好凝固温度的功率为62kW。在此功率熔炼时冷床内液态熔池表面温度和计算吻合。     

Inclusions in melting process of titanium and titanium alloys

This paper summarizes melting methods of titanium and titanium alloy, such as vacuum arc melting(VAR) and electron beam cold hearth melting(EBCHM), and the related inclusions formed when using these melting methods. Low-density inclusions are resulted from contamination of air, and high-density inclusions are caused by refractory elements. The formation process of inclusions was analysed. The removal mechanism of different kinds of inclusions was specified. Low-density inclusions are removed mainly by resolving. This is a comprehensive process containing reaction diffusion. The resolving rate of high-density inclusions is so low that these inclusions are mainly removed by sedimentation. The experiments and physical models of inclusions are detailed. In various melting methods, vacuum arc melting is prominent. However, this method cannot remove inclusions effectively, which usually results in repeat melting. Electron beam cold hearth melting has the best ability of removing inclusions. These results can provide instructions to researchers of titanium and titanium alloys.     

高强度灰铸铁熔炼技术发展趋势及最新研究成果

回顾了灰铸铁熔炼技术的发展历史,认为提高熔炼过程中石墨的形核能力是提高熔炼技术的重要途径。通过冲天炉与感应炉双联熔炼和感应炉增碳熔炼HT250材料的对比试验数据,说明采用感应炉增碳工艺可以有效地减轻铁液的收缩和白口倾向,减少灰铸铁的断面敏感性,改善石墨形态,提高材料性能。指出随着熔炼工艺水平的提高和铁液炉前处理技术的创新,HT300材料已产业化应用,HT350及更高牌号的灰铸铁材料也已经能够达到。     

焊剂组元间交互作用对熔化温度的影响

利用数理统计理论发展起来的混料优化设计方法,建立数学模型,研究了焊剂组成成分间交互作用对熔化温度的影响问题,揭示了埋弧焊陶质焊剂7组元间交互作用,对焊剂熔化温度的影响规律,得到了焊剂组成成分对熔化温度影响的定量描述回归方程.结果表明,MgO-TiO2-CaCO3-Al2O3的交互作用,能在熔渣中形成相当数量的钙钛矿和尖晶石,使焊剂的熔化温度提高,而一定数量的CaF2和SiO2、ZrO2的加入则可使焊剂的熔化温度降低.     

Influence of duplex melting process on melt quality and solidification of grey cast iron

Abstract

The quality of molten iron produced by two melting processes, the medium frequency induction furnace melting process and the shortcut duplex melting process with blast and medium frequency induction furnaces, has been studied comparatively. The shortcut melting process contributes to a higher undercooling tendency of base iron, and the extent of this tendency depends on other processing parameters such as ratio of charges, fluctuation in composition, superheating temperature and holding time, etc. When the shortcut melting process is used in the production of grey cast iron, there are no essential differences, with subsequent proper inoculation, in the microstructure and mechanical properties of castings compared with the conventional medium frequency induction melting process. Inoculation is a very effective method to alleviate and/or eliminate the negative effect when the shortcut melting process is used.     

影响高效MIG/MAG焊中焊接材料熔化效率的因素

针对高效MIG／MAG焊的熔化效率、熔化速率等概念进行了分析，提出了影响MIG／MAG焊接材料熔化效率的因素和提高焊接材料熔化效率的有效方法。     

Alloying behavior of the rare earth metals with gold: the Ho–Au,Er–Au and Tm–Au systems

Phase relationships have been established for the Ho–Au, Er–Au and Tm–Au systems by means of the experimental investigation of a number of selected compositions using X-ray powder diffraction (XRD), optical (LOM) and scanning electron microscopy (SEM), electron probe microanalysis (EMPA) and differential thermal analysis (DTA). The Ho–Au system is characterized by eight intermediate phases: Ho₂Au (incongruent melting at 1095 °C), HoAu (congruent melting at ≈1700 °C), Ho₇Au₁₀ (incongruent melting at 1360 °C), HoAu₂ (congruent melting at 1350 °C), HoAu₃ (congruent melting at 1250 °C), Ho₁₄Au₅₁ (incongruent melting at 1060 °C), HoAu₄ (incongruent melting at 950 °C) and HoAu₆ (incongruent melting at 840 °C). The Er–Au and Tm–Au systems present six iso-stoichiometric phases. For the Er–Au system they are: Er₂Au (incongruent melting at 1120 °C), ErAu (congruent melting at 1710 °C), Er₇Au₁₀ (incongruent melting at 1350 °C), ErAu₂ (congruent melting at 1385 °C), ErAu₃ (congruent melting at 1285 °C) and ErAu₄ (incongruent melting at 1000 °C). For the Tm–Au system the phases are: Tm₂Au (incongruent melting at 1160 °C), TmAu (congruent melting at 1720 °C), Tm₇Au₁₀ (incongruent melting at 1345 °C), TmAu₂ (congruent melting at 1430 °C), TmAu₃ (congruent melting at 1300 °C) and TmAu₄ (incongruent melting at 1035 °C). Crystal structure data and lattice parameters are given.