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Metal micro-droplet 3D printing is an effective additive manufacturing technique to form micro pillar structures. However, the control mechanism of the pillar contour is still unclear. To form a pillar with uniform radius, it is essential to investigate the dependence of processing parameters on pillar contours. In this study, a 3D numerical model was employed to simulate and analyze the successive pileup processes of multiple droplets. The solidification angle of solidified new-coming droplets is defined to characterize the pillar contour. An analytic equation of solidification angle was established. In this case, the solidified morphology of the droplets could be feasibly predicted through thermophysical parameters and initial conditions. This work provides good physical understanding of the complicated mechanisms for fabricating a pillar structure by means of the successive pileup of molten metal droplets, and paves the way for pillar contour control.

The uniform droplets of gallium based eutectic alloys have been widely used to develop the electronic packaging. Therefore, a droplet generator has been designed for formation uniform droplets in a controlled way, which entails important technological advantages over existing techniques. The results indicated that, the uniform droplets could be produced by continuous-ink-printing and drop-on-demand based on the mode of pulse electromagnetic force; compared with the droplets generator using one elastic diaphragm for producing water droplets by continuous-ink-printing, the metal droplets could be produced without using elastic diaphragm. Therefore, this work provides a useful parameter-selection approach for droplets production.

A kinetic lattice Monte Carlo model is used to study the Ga droplets self-propelled motion along GaAs(111)A and (111)B surfaces during the initial stage of high-temperature annealing. An estimation of the droplet velocity, running along (111)A and (111)B surfaces, in a wide temperature range, is carried out. The mechanism of small Ga drops movement during high-temperature annealing is suggested. Different directions of droplets motion and the morphology of drop-crystal interface on (111)A and (111)B substrates are determined by a difference in the etching rate of (111)A and (111)B facets by liquid gallium. It is shown that metal droplets can cause step bunching.

A method is described to determine geometrical dimensions of electrode metal droplets depending on short circuit duration. It provides a quantitative evaluation of the electrode metal transfer and the energy impact on metal parts being welded. It is proved that using inverter power source decreases the size of droplets transferred to the welding pool by 24% in average if compared with a diode power source. It also reduces overheating of the droplets which improves efficiency of transferring chemical elements from the electrode to the weld metal.

One of the most efficient ways to eliminate the harm of chromium oxide in stainless steel slag is to reduce chromium oxide in stainless steel slag using aluminium. In the present work, the Al reduction of synthetic CaO–SiO2–Al2O3–MgO–Fe2O3–Cr2O3 stainless steelmaking slags at different conditions, including temperature, slag basicity and Al amount was investigated to get optimal conditions for the reduction and the metal–slag separation. It was found that the agglomeration of metal droplets and metal–slag separations were improved by increasing temperature. The reduction degrees of SiO2, Fe2O3 and Cr2O3 were enhanced with increasing basicity of slag. The addition of CaF2 in slag leads to better agglomerations of metal droplets and metal–slag separations. The highest reduction degree of chromium could reach 99% in slag with basicity of 2 at 1873 K.

In this paper, a theoretical analysis is carried out on the pneumatic diaphragm drop-on demand technology. The typical forming process of the droplet is analyzed, and the working principle of the pneumatic droplet injection is studied. The fluid calculation software FLUENT is used as the calculation platform to simulate the formation process of metal micro-droplets under gas pulse. Experiments demonstrate that this micro-jetting technology has a good performance on micron droplets generation and dispensing. And the experimental results agree well with the simulation results, which proves this simulation model and method is correct.

7075 aluminum billets were fabricated by micro droplet deposition manufacturing technique, and the influence of interfacial bonding between metal droplets on the tensile properties was studied. Three sets of samples were manufactured under different temperature conditions, and their mechanical properties were compared. The results show that the temperature of the metal droplets and substrate significantly affect the tensile strength of the sample. Moreover, with proper temperature setting, the 7075 aluminum billets manufactured by micro metal droplet deposition could achieve very good mechanical properties with a tensile strength of 373 MPa and an elongation of 9.95%, which are very similar to those of an extruded sample. Moreover, a metallurgical bonding diagram based on numerical calculations of interfacial temperature was established to predict the interfacial bonding state. In addition, the fracture morphologies of these specimens were observed. It is indicated that there was a significant transformation of failure mechanism with the improvement of metallurgical bonding, which agreed well with the numerical results.

Droplet solidification technique is important with respect to the fundamental study of strip casting given the common conditions of direct contact between cooling mold and solidifying metal. In this study, an improved droplet solidification technique has been developed for the in situ observation of the sub-rapid solidification phenomena of metal droplets impinging onto the water-cooled copper substrate. The heat transfer rates were calculated by the inverse heat conduction program (IHCP), according to the responding temperatures’ gradient inside the cooling mold. Meanwhile a charge coupled device (CCD) camera was placed beside the bell jar aimed to record the whole melting and solidification process of the steel sample, which also allowed the determination of the final wetting angel, during the dipping tests. Moreover, it was found that the heat transfer rate increased with decreasing final contact angle, which means better wetting condition between the liquid sample and the copper substrate.

Solder jetting is a growing technology for microelectronic packaging in diverse range of applications. In this paper, an electromagnetic jetting device is developed to direct deposit solder droplets. Experimental results show that the electromagnetic jetting is feasible to deposit solder, and uniform solder balls can be obtained. The process of jetting and deposition of solder droplets is analyzed, and the influence of the nozzle diameter on the droplet diameter is obtained. Our results show promise for electromagnetic jetting as a potential tool in fabrication of metal droplets.

The effect of injection of nepheline syenite (NS) together with CaC 2 and C on the iron losses in form of metal droplets in a slag during desulphurization of hot metal is investigated in industrial trials. The characteristics of different metal droplets (such as morphology, number, size and composition) in slags of trials without and with injection of a NS are investigated using SEM. All metal droplets in the slag are classified into three groups according to morphology: Type A-spherical/oval; Type B-spherical/irregular; Type C-irregular. It is found that the addition of NS influences the compositions of hot metal, slag and metal droplets in slag. As a result, the amount (area fraction) and size of metal droplets decreased for Type A and B and increased significantly for Type C droplets present in the slag. The effect of injection of nepheline syenite together with CaC 2 and C on the iron losses in form of metal droplets in a slag during desulphurization of hot metal is investigated in industrial trials. The characteristics and behavior of different metal droplets in slags of trials without and with injection of a nepheline syenite are investigated.

Laser-induced forward transfer is a direct-write process suitable for high precision 3D printing of several materials. However, the driving forces related to the ejection mechanism of the donor ma-terial are still under debate. So far, most of the experimental studies of nanosecond LIFT, are based on post process analysis of either the donor layer and/or the deposits, which were transferred to the receiving substrate. To gain further insights into the ejection dynamics, this article presents results of a series of imaging experiments of the release process of nanosecond LIFT of a 200 nm thick gold donor layer. Images were obtained using a setup which consists of two dual-shutter cameras. Both cameras were combined with a 50× long-distance microscope and used to capture coaxial and side-view images of the ejection process. Bright field illumination of the scene was accomplished by a 6 ns dual-cavity laser source. For laser fluence just above the transfer threshold, the formation of a jet and the subsequent release of a single droplet was observed. The droplet diameter was esti-mated to be about 2 μm. Analysis of the coaxial images indicates the emission of a spectral broad range light which was identified as thermal radiation.

Targeting micrometer sized metal droplets with near-infrared sub-picosecond laser pulses generates intense stress-confined acoustic waves within the droplet. Spherical focusing amplifies their pressures. The rarefaction wave nucleates cavitation at the center of the droplet, which explosively expands with a repeatable fragmentation scenario resulting into high-speed jetting. We predict the number of jets as a function of the laser energy by coupling the cavitation bubble dynamics with Rayleigh-Taylor instabilities. This provides a path to control cavitation and droplet shaping of liquid metals in particular for their use as targets in extreme-UV light sources.

The quest for the ‘when’ and ‘where’ of the world's earliest metallurgy has been dominating scholarly research on this topic for decades. This paper looks beyond the question of origins by discussing ‘how’ and ‘why’ metallurgy was invented. It looks into choices and skills involved in selection, experimentation and processing of distinctively coloured copper minerals and ores throughout c. 2000 years in the Balkans. The body of evidence is built around the currently earliest evidence for copper smelting, dated at c. 5000 bc and discovered in the Serbian Vinca culture site of Belovode. The ‘microstructure’ of a metal invention process is explored through optical and compositional analyses of a selection of copper minerals and metal production evidence: ores, slags, slagged sherds and metal droplets recovered from seven settlements in Serbia and Bosnia and Herzegovina, altogether dated between the late seventh and the late fifth millennia bc. This research suggests an independent technological trajectory of the emergence of metallurgy in the Balkans based on a unique technological meme, black and green mineral, which follows the evolution of early metallurgy from mono- to polymetallic within the fifth millennium bc.

This paper integrates archaeological, material, microstructural and compositional data of c. 7,000 years old metallurgical production evidence with the aim to address the knowledge of the world’s earliest metalworkers. The main focus is placed on copper minerals, ores, slags, slagged sherds and metal droplets coming from four Vinca culture settlements in Serbia and Bosnia and Herzegovina: Belovode, Plocnik, Vinca and Gornja Tuzla, all dated between c. 5400 and 4400 BC. Chemical study of copper minerals throughout all sites points at striking uniformity in selecting black and green minerals from the early days of the settlements’ occupation, some of which predate the metal smelting events. Microstructural examination of metal production debris showed convincing technological similarity throughout c. six centuries of copper making in the studied sites, as well as a consistent choice of black and green ores for metal extraction. We argue that black and green ores were intentionally selected as ingredients for the metal smelting ‘recipe’ in the early stages of Balkan metallurgy based on the knowledge related to their characteristic visual aspects. This finding demonstrates how important the adequate combination of colours was for the early copper metalworkers and suggests a unique technological trajectory for the evolution of metallurgy in this part of the world. It also illustrates the capacity that micro-research carries in addressing the how and why of the emergence of metallurgy, and outlines a methodology for future studies of early metallurgies worldwide.

Slag-metal emulsion plays an important role in the oxidation kinetics of metalloids in oxygen steelmaking. The importance of droplet generation rate, droplet size, and its residence time in the slag-metal emulsion on the overall reaction kinetics has become evident in recent times. Residence times of the droplets are strongly dependent on the decarburization rate, the CO bubbles giving a buoyant force to the droplets. The present work aims at developing a mathematical model for predicting the composition evolutions of the slag and the metal phases as the blow proceeds in an LD converter. The process dynamics are modeled by dividing the LD convertor into three separate continuous stirred tank reactors. Oxidation reactions are assumed to be primarily taking place at the interface between the slag and the metal phases in the emulsion. Among the different mass transfer and reaction steps controlling the kinetics, the mass transfer of FeO in the slag phase and that of the metalloids within the metal droplet are assumed to be rate-controlling. For a Fe-C-X (X = Mn, Si etc.) droplet, simultaneous removal of elements have been modeled by Gibbs' free energy minimization at the slag-metal interface. Effects of droplet size, mass transfer coefficient, and initial carbon content on the mean residence time of metal droplets in the slag-metal emulsion have also been identified. Mixing in the metal phase is simulated in terms of metal exchange rate and the reactor weight ratio between the upper and the lower parts of the bath. (C) The Minerals, Metals & Materials Society and ASM International 2014

Iron losses in slag during an intensive desulfurization of hot metal can reach 0.6-1.1% from the total amount of processed hot metal. The characteristics of different metal droplets (such as morpho ...

We present the drop-on-demand generation of liquid microdroplets from aluminum alloy melts with minimum diameters of 235 μm. The so-called StarJet technology, used to generate the droplets features a pneumatically actuated printhead that has been used to print microdroplets from solder (T me lt ≈ 220 °C) before. In this work a novel StarJet printhead is presented that can be operated at up to 950 °C and thus allows for printing of aluminum alloys. The printhead is compatible with chemically aggressive metal melts and can be operated in a standard laboratory environment. Experimental results regarding the generation of droplets and a printed aluminum structure are presented. To the knowledge of the authors this is the first time that aluminum alloy microdroplets of such small size (d = 235 μm) have been produced by drop-on-demand.

An efficient stainless steel making industry is defined by different factors such as an efficient utilisation of energy in the Electric Arc Furnace (EAF). This requires a good by slag foaming practice and an utilisation of waste products from own production facilities. In the following study, briquettes applied for a combined slag foaming and waste product recycling in the EAF were investigated in both laboratory and industrial scales. More specifically, briquettes were characterised and used for slag foaming in the EAF. The recipes of the briquettes were made based on a literature review and previous experience. Afterwards, the composition and density of briquettes were defined and compared to calculated data. Moreover, weight reduction experiments were made on a laboratory scale at temperatures up to 1500°C in an argon atmosphere in order to characterise the products (metal, slag and gas) produced by briquettes. The calculations were also compared to experimental data. Thereafter, briquettes with different densities and pet-coke addition were tested on an industrial scale to study slag foaming in the EAF process during a stainless steel production. The slag foaming tendencies were determined based on visual estimations of slag foaming, determinations of the slag density before and after additions of different briquettes, and by calculating a foaming index. Moreover, the influence of the main parameters of the briquettes (composition, density) and the furnace slag (composition, basicity and etc.) on slag foaming was studied. Investigation of briquettes made on laboratory and industrial scales provided the following main results: the density of briquettes can successfully be verified, briquettes have different mechanical properties depending on the materials used for production of briquettes, briquettes yield different amounts of metal and gas. Moreover, it was found that the heavy briquettes (containing FeCr) produce about half the amount of gas compared to the light briquettes (without FeCr). The main part of the gas was generated during the first 2-3 min. Also, the valuable metals can be recovered from briquettes; recipes of briquettes can be optimized based on the amount of metal droplets in briquettes and the total utilisation of carbon. In addition, it was found that both heavy and light briquettes can be used for slag foaming. The highest slag foaming rate was obtained for slags with a basicity in the range of 1.31-1.49.

Iron losses during calcium carbide based hot metal desulphurisation have been studied via large scale investigations of slag from the slag pit as well as slag sampling during desulphurisation at SSAB EMEA in Lulea. The desulphurisation slag, after injection of calcium carbide, is normally solid and contains large amounts of iron. An alkali containing mineral, nepheline syenite, was mixed together with the calcium carbide to form a more fluid slag as the iron losses originate from enclosed metal droplets in the slag as well as drawn off hot metal during slag skimming. The slag amount after slag skimming decreased from 28·1 to 25·1 kg t−1 hot metal with addition of 5 wt-% nepheline syenite to the calcium carbide, and the magnetic fraction of the slag from the slag pit decreased from 2·5 to 1·9%. Finally, no negative effect on the reagent efficiency was observed during the trials with addition of nepheline syenite.

The leakage of blast furnace tuyeres is an unpredictable incident, which happens several times at normal blast furnace operation. The reasons for BF tuyere damages were investigated and the liquid slag and hot metal were found as the main causes of the tuyere burn-out. Investigation was initiated in order to describe the accurate wear mechanism of tuyere erosion due to hot metal and slag. Metallographic tests were performed by analytically analyzing the removed noses of damaged tuyeres. Analyses showed Cu–Fe solid solution formation between tuyere material and the Fe-content of hot metal droplets. A thermodynamic model was prepared for the analysis of the thermal relations between the tuyere and the hot metal drop causing its damage; based on which, it can be stated that the conditions of the formation of Cu–Fe solid solution are given under the blast furnace circumstances.

The deposition of uniform metal droplets has attracted extensive interest for potential application in rapid prototyping and manufacturing. In this paper, a three-dimensional model based on a volume of fluid (VOF) method was developed to investigate the successive deposition of molten Al droplets on a horizontally moving substrate. In this model, protecting gas surrounding the droplets was treated as a void region, and then the droplets were considered as a single-phase fluid. The spreading, cooling and solidification processes of droplets were investigated under different substrate velocities. The simulated final morphology of droplets agreed well with experiments carried out under the same conditions. It was found that the molten Al droplets solidified in a layer by layer mode due to the high heat conductivity. A series of L-shaped ridges appeared on the surface of solidified droplets, which resulted from the integrated effects from solidification and oscillation consisting of alternately spreading and recoiling of droplets.

Despite many theoretical and experimental works dealing with the impact of dense melt droplets on the substrate during the process of thermal spray coating, the dynamics of the impingement of hollow melt droplet and the subsequent splat formation are not well addressed. In this paper a model study for the dynamic impingement of hollow droplet is presented. The hollow droplet is modelled such that it consists of a liquid shell enclosing a gas cavity. The impingement model considers the transient flow dynamics during impact, spreading and solidification of the droplet using the volume of fluid surface tracking method (VOF) coupled with a solidification model within a one-domain continuum formulation. The results for spreading, solidification and formation of splats clearly show that the impingement process of hollow droplet is distinctly different from the dense droplet. Study with different droplet void fractions and void distribution indicates that void fraction and void distribution have a significant influence on the flow dynamics during impact and on the final splat shape. The results are likely to provide insights for the less-explored behaviour of hollow melt droplets in thermal spray coating processes.

A sharp contrast of the density and size of Ga metal droplets (MDs) on strip patterned GaAs (100) is demonstrated through droplet epitaxy (DE) and photolithography technique. As clearly evidenced by scanning electronic microscope (SEM) and atomic force microscope (AFM), MD density between etched (patterned) and un-etched (un-patterned) surfaces can be sharply different up to one order of magnitude under an identical growth condition. Etched surface exhibits much higher density and smaller diameter and height of MDs.

A 2D axisymmetric model has been proposed to study the mechanism of the droplet generation by using a pneumatic drop-on-demand (DOD) generator. A proprietary pneumatic DOD generator was also applied to conduct droplet generation experiments. The validity of the proposed model was verified through the simulation results of droplet pattern, breakup length distance and droplet diameter, which were in good agreement with the experimental ones. Theoretical studies were conducted to characterize the metal droplet generation using pneumatic DOD technique. Theoretical analyses show that metal droplets break away from jets in front of the sphere ends due to the increase of the capillary disturbance at a very small Ohnesorge number (Oh

SnO 2 /ZnO hierarchical nanostructures were synthesized by a two-step carbon assisted thermal evaporation method. SnO 2 nanowires were synthesized in the first step and were then used as substrates for the following growth of ZnO nanowires in the second step. Sn metal droplets were formed at the surfaces of the SnO 2 nanowires during the second step and were acted as catalyst to facilitate the growth of ZnO nanowires via vapor–liquid–solid mechanism. Room temperature photoluminescence measurements showed that the SnO 2 /ZnO hierarchical nanostructures exhibited a strong green emission centered at about 520 nm and a weak emission centered at about 380 nm. The emissions from the SnO 2 were drastically constrained due to screen effect caused by the ZnO layer.

Recovery of novel metals such as Au, Ag and Ni from wastes PCB was investigated by slag treatments. The CaO-(-) and CaO-- slags were employed in the present study. The PCB/Cu ratio is recommended to be lower than unity. The use of CaO-- slag provided the more higher yield of Au, Ag and Ni than the CaO-(-) slag did, which was mainly due to the lower melting point and the viscosity of -containing slag. The terminal descending velocity of metal droplets in the slag phase increased with decreasing slag viscosity.

Soil layers at the Tunguska event site may have accumulated infalling extraterrestrial matter derived from the Tunguska Cosmic Body (TCB). Using mineralogical, textural, and chemical criteria, a set of metal and silicate spherules of probably cosmic origin was identified in the collection of spherules and rounded particles recovered from sites with high concentrations of magnetic spherules on a terrace above the floodplain of the Chunya River. The metal spherules consist of Ni(Cr)-bearing wustite and magnetite with Ni-rich metal inclusions. The silicate spherules are glassy, cryptocrystalline, barred, and porphyritic melted micrometeorites, some of which contain metal droplets. The number of spherules counted in our samples is higher than the background level, indicating the possible presence of the TCB material.

Electrostatic delivery of charged uniform metal droplets is a novel method to deposit metal parts with short process period and low cost. But the delivery process is unstable and delivery accuracy of charged droplets deteriorates because of actions of mutual interactions of closely charged droplets. A droplet generator with droplet charging and deflecting system has been established to find out the way for stably and accurately deflecting droplets. The parameters for generating uniform droplets were first studied. Then the droplet deflections and metal parts depositions with different charge methods were discussed. The results show that the unbalanced electrostatic repelling forces are the main factor to cause the unstable deflection of droplets. The droplets deflection distance can be predicted and controlled by balancing the repelling forces of charged droplets. The metal parts are stably deposited after combining the board charged pulse and substrate motion, indicating that the work can provide useful theoretical and experimental guide for droplet-based freeform fabrication.

In laser droplet generation from a metal wire a droplet is generated by laser heating of the wire-end. In the paper a problem of laser droplet sequence generation, which results in unsuccessful droplet detachment is considered. To solve this problem, a control system and strategy for laser droplet sequence generation are proposed. The control bases on in-process monitoring of the initial position and temperature of the wire-end are presented. The results show that by ensuring proper initial wire-end position and stationary wire-end temperature which can be influenced by laser pulse parameters, a reliable generation of a droplet sequence can be achieved.

The control of electrode metal transfer in arc mechanized welding and surfacing is one of the main problems in welding because transfer determines not only the quality of the welded joint but also ...

The main focus of the present work was to develop a sampler to obtain the physical description of the slag–metal interface in the presence of bulk flow. Industrial trial experiments were carried out in the ladles at Uddeholm Tooling, Hagfors, Sweden using the designed sampler. Samples of the slag–metal interface were successfully taken in both gas stirring and induction stirring modes. The similarities of the appearance as well as the micrographs of the samples suggested that the slag–metal interfaces in the two stirring modes were very similar except in the open eye area. In the case of both stirring modes, metal droplets were found in the slag bulk. On the other hand, no appreciable amount of slag was detected in the metal bulk. Further systematic investigation using a large number of samples is required to obtain a quantitative description of the interface.

The authors have developed two types of metal jet nozzles, i.e., a molten metal type and an electric-discharge type. In the molten metal type, the molten metal droplets are jetted through a hole in the nozzle by the action of a piezo-electric actuator. In the first half of this paper, the jetting mechanisms of metal droplets and the minimum droplet sizes able to be jetted are discussed. Some considerations show that an ultra-small droplet can be jetted in the case of the molten metal having a concave meniscus to nozzle material. On the other hand, it becomes very difficult to jet smaller droplets in the case of molten metal having a convex meniscus. These discussions are confirmed by experiments under several combinations between molten metals and nozzle materials. In the electric-discharge type, molten metal droplets are jetted intermittently by blowing out the molten balls which are formed at the end of a metal wire by the electric discharge. The mechanisms of the droplet formation are discussed. On the bases of the discussion and the experimental results, the minimum and maximum droplet sizes are then estimated under practical conditions.

Slag samples, hot-metal samples and hot-metal temperatures were obtained during tapping of two blast furnaces. Sampling was carried out at different time points during tapping of three separate hea ...

The deposition of metal droplets is of great engineering interest because of its practical applications to such various fields as spray forming, surface treatments, and solid freeform fabrication (SFF), etc. The objective of this work is to develop a new drop-on-demand generator of superheated metal droplets that is suitable for the selective infiltration manufacturing (SIM), a new SFF process for the direct fabrication of metal parts. The developed generator comprises a solenoid vibrator, a micro-drilled 130 μm diameter nozzle, an impulse-transmitting rod, and a tubular heating element. A parametric study showed that the diameter of droplets was 301 ± 10 μm when the superheating temperature of Sn–37Pb wt% was set at 260 °C, 299 ± 12 μm at 290 °C, and 301 ± 12 μm at 320 °C. Experiments showed that the developed generator is able to deposit superheated metal droplets according to the frequency of the vibrator.

A mathematical model for evaluating the residence time of metal droplets in slag-metal-gas emulsions through top gas blowing is proposed. The model is based on the equation of accelerated moving bodies in a moving fluid. The parameters used in the model are based on the available data from both room and high temperature experiments. Using the proposed model provides a formal way to extend the experimental results of the residence time of the droplets for an evaluation of the conditions in an industrial furnace. This connects theoretical understanding, experimental results and plant data in to a coherent and quantitative model of the process.On propose un modele mathematique pour evaluer le temps de sejour de gouttelettes de metal dans des emulsions de scorie–metal–gaz par soufflage de gaz vers le haut. Le modele est base sur l’equation des corps acceleres en mouvement dans un fluide en mouvement. Les parametres utilises dans le modele sont bases sur les donnees disponibles provenant tant d’experie...

Although numerical heat transfer and fluid flow models have provided significant insight about fusion welding processes and welded materials in recent years, several model input parameters cannot be easily prescribed from fundamental principles. As a result, the model predictions do not always agree with the experimental results. In order to address this problem, the approach adopted here is to develop and test a model that embodies a heat transfer and fluid flow sub-model and an algorithm for optimizing and learning the values of uncertain process variables from a limited volume of experimental data. The heat transfer and fluid flow sub-model numerically calculates three-dimensional temperature and velocity fields, the weld geometry and the shape of the solidified weld reinforcement surface during gas metal arc (GMA) welding of fillet joints. Apart from the transport of heat from the welding arc, additional heat from the metal droplets is also considered in the model. Alternative algorithms for optimization of uncertain welding variables are examined. The overall model is capable of estimating uncertain parameters such as the arc efficiency, effective thermal conductivity and effective viscosity from a limited number of data on weld geometry. Part I of this paper is focused on the details of the numerical model, optimization technique used and an examination of the important features of the model. In an accompanying article (part II), the application of the model to GMA fillet welding of mild steel is described.

In-rich InGaN quantum dot structures were grown by metalorganic chemical vapor deposition. Growth at low temperature made possible the growth of InGaN layers of high In content (over 70 InN%) with negligible formation of In metal droplets. The density, average diameter and height of typical InGaN quantum dots (QDs) were estimated at 8x10 9 /cm 2 , 80 and 1.2nm, respectively. The emission wavelength from the QDs could be controlled to the near ultraviolet (UV) region by variation of the growth conditions. This work demonstrates that In-rich InGaN QD active layers are very promising device structures for application as UV light-emitting diodes.

The new technology of rapid prototyping (RP) has been developed to reduce product development time and the cost of manufacturing. The science of stream break-up into uniform droplets has attracted academic and industrial interest for application. Using this technology, the metal droplets can be generated flexibly and controlled precisely. Net-form manufacturing of components or ingots based on precisely controlled metal droplets is gaining industrial interest due to the promise of improved component quality resulting from rapid solidification processing and the economic benefits associated with a structural component in one integrated operation.

This article presents a design and development of a drop-on-demand (DOD) droplets generator. This generator uses molten metal as a liquid and can be used in fabrication, prototyping and any kind of printing with solder droplets. This setup consists of a vibrator solenoid with tunable frequency to produce a semi-spherical shape of molten metal, close to the surface of fabrication. This design also has a nozzle with micro-size orifice, a rod for transmitting force and a heater to melt the metal and keep it in superheat temperature. This DOD can produce droplets in different sizes (less than 550 µm) by controlling the vibration frequency of solenoid. This ability together with the accuracy of the droplets in positioning (the error is less than ±20 µm for 1.5 mm amplitude) can be used in different applications. Moreover, in this paper, the impact of initial position of the head and temperature on the average diameter of droplets and the impact of the frequency on the shape of the droplets have been tested and discussed

A complete set of equations is proposed to model droplets of molten metal ejected from the contacts in a high voltage circuit breaker of the SF6 filled gas-blast type. The initial speed and diameter of the droplets are varied to characterize their behaviour and study the distribution of the metal vapour. A relation is derived that can be used in simplified arc models such as integral or two-zone models to take the effect of the droplets into account. It is found that, although the influence on usually measured quantities such as pressure and voltage is small, droplets affect velocity and temperature fields in the electric arc significantly and should not be neglected.

A new model which extends previous studies and includes the interaction between enveloping gas and an array of droplets has been developed and presented in a previous paper. The model incorporates the probability density function of atomized metallic droplets into heat transfer equations. The main thrust of the model is that the gas temperature was not predetermined and calculated empirically but calculated numerically based on heat balance considerations. In this paper, the accuracy of the numerical model and the applicability of the model as a predictive tool have been investigated by comparing experimental and calculated results for the powder particles of 12Cr-Mo-V steel. The study also focuses on some aspects of the process which are not available experimentally, for example the effect of undercooling and the gas/metal ratio on the solidification. The important effects of these parameters are illustrated. A comparison between the numerical model and the experimental results shows an excellent agreement and demonstrates the validity of the present model, for example the calculated gas temperature which has an important influence on the droplet solidification behaviour as well as the calculated cooling rate of the droplets is found to be in good agreement with the experimentally determined value. The fact that the present approach of modelling is more general than previous studies opens up new possibilities for a deeper understanding of such a process without the limitation of experimental input parameters, for example gas temperature. Finally, the present approach of modelling and its predication illustrate the fact that quantitative results and guidelines can be drawn from this model which can then be used as a tool for the optimization of the process.

In this study, the effect of slag's physical properties on the desulphurization process in electroslag remelting (ESR) was investigated. Three different steel grades were used as consumable electrodes in ESR. Each steel was remelted under three slag compositions with different physical and chemical properties. The results obtained showed the efficiency of ESR in removal of up to 68 % of the sulphur contained in the metal. This pronounced effect of ESR on desulphurization is a result of slag/metal and gas/slag reactions. Although the greatest portion of sulphur is removed by gas/slag reaction which is enhanced by using a low viscosity slag, the metal/slag reaction represents the rate controlling step over all the desulphurization process. Slag/metal reaction occurring at the metal droplets/slag interface is the most effective and enhancing by relatively high slag viscosity and high CaO content in the slag. Slag composition (mass contents in %) of 70 CaF 2 , 15 CaO and 15 Al 2 O 3 has a good combination of chemical reactivity and physical properties for attaining the highest degree of desulphurization among the three investigated slags.

Metal droplets separating in the magma ocean have the radius less than 1cm, and it takes about 106 seconds to separate in the magma ocean. Metallic liquid accumulated in the bottom of the magma ocean starts to fall into the lower mantle when the metal drops grow into the radius of about 1km. The present theoretical analysis implies that the small metal droplets falling into the molten magma ocean are thermally and chemically in equilibrium with the silicate magma ocean, whereas the large metal pools falling in the lower mantle are disequilibrium with the surrounding silicates. Therefore it may be possible to estimate the depth of the magma ocean from the conditions of the metal-silicate equilibrium. Abundances of Ni and Co in the mantle may be accounted for by the chemical equilibrium between metal and silicate at 40 GPa and 2500°C, suggesting existence of the primordial terrestrial magma ocean with the depth of 1200 km.