Melt Bath Research Articles

Using acoustic field energy to decrease dust discharge from the working space of the Vanyukov furnace

To organize in-furnace dust settling in the Vanyukov furnace at OAO SUMZ (Revda, Russia), acoustic emitter technology is used. The emitter design includes a nozzle tube, an air nozzle, a resonator, and a focusing surface. Starting from the surface area of the furnace melt bath and recommended specific acoustic power for in-furnace dust settling, the summary acoustic field sound power is calculated and the optimal amount and arrangement places of acoustic emitters are determined. To form the acoustic field in the Vanyukov furnace for melting copper sulfide zinc-containing feedstock and deplete liquid converter slags, four acoustic emitters are mounted in the end wall through an inspection window, two on the apothecary side and two on the loading side of charge materials. In general, six pilot modes of testing the in-furnace dust settling system with various operational settings of acoustic emitters and one base mode for comparing performance characteristics are implemented. The duration of pilot periods varies from 5 to 18 days, and the total aggregate service time is 68 days. The presence of the acoustic field in the working furnace space at any emitter operation settings promote a decrease in the concentration of dust particles after the chain of gas purifiers (in the commodity point). It is revealed by the experimental data that the minimal summary acoustic field sound power, which decreases the dust concentration due to the coagulation of dust particles inside the furnace space, is 800 W.

Wetting behaviors of the molten silicon on graphite surface

A theory which was proposed by Scheid et al. in 2010 (Scheid B, van Nierop E A, Stone H A 2010 Appl. Phys. Lett. 97 171906) suggests that very thin ribbons of molten material can be drawn out of a melt by adequately tuning the temperature gradient along the dynamic meniscus that connects the static meniscus at the melting bath to the region of the drawn flat film. Based on this theory, one-step manufacturing ultra-thin silicon wafer by pulling out from a molten silicon bath has attracted considerable attention in recent year due to its many attractive performances such as low cost, simple process, etc. By using this method, solar cell can have intensive applications due to its low cost and stable output efficiency. The results show that the thermal capillarity effect plays a great role in preparing the ultra-thin silicon. The thickness of the silicon wafer is sensitive to the capillary length and the strength of the surface tension variation as well. In order to reveal the mechanism for the effect of thermal capillary on the fabrication of ultra-thin silicon wafer, a thermal capillary finite element model is developed for the horizontal ribbon growth system to study the wetting behaviors of molten silicon on graphite. The mathematical model is established and simulated by using the commercial software; several parameters such as mass, viscous stress and capillary force are calculated. The wetting processes are tested by changing surface roughness (Ra=0.721 m and Ra=0.134 m), system temperatures (17371744 K), and durations (1030 s) at constant temperature on a high-temperature, high-vacuum contact angle measurement instrument. It is found that the wetting angle of silicon droplet on graphite decreases with surface roughness and temperature increasing; the wetting angle comes down with time going by (lasting 30 s) at constant temperature, which is consistent with the theoretical result of Wenzel. The influence of surface tension on wetting process is studied by analyzing the distributions of pressure and velocity field. It is shown that the differential pressure at the solid-liquid interfaces, induced by thermal capillary effect, decreases in the wetting process and reaches a balance which prevents the droplet from being wetted. At T=1700 K, the wetting angle and the shape of droplet change quickly within 0.4 ms and eventually become stable after 5 ms as shown in the simulation. The spreading length L and droplet height h at the steady-state are calculated with considering the influence of droplet radius on the wetting process. The results show that both L and h are directly related to the steady-state of wetting angle. The surface tension dominates the wetting process for droplet radius R0 5mm; while for R0 5 mm, the wetting process is dominated by gravity.

Determination of the True Temperature During Selective Laser Melting of Metal Powders Based on Measurements with an Infrared Camera

The recovery of the true temperature of a metal powder during selective laser melting is examined. A method is proposed for determining the temperature of the surface of the melt bath of a metal powder during selective laser melting based on measurements with an infrared camera. The influence of key melt parameters on the geometry of the melt bath is estimated.

Acoustic-Emission-Analysis of Dissimilar Laser-welds of Aluminium and Polyamide 6.6

A novel laser joining process for hybrid polymer-metal structures has proven a strong bond between polyamide and aluminium. This welding technique is strongly requested by the automobile producing industry for numerous applications within structure components. However, the joining quality exhibits a strong dependency on process-related variables, which highlights the need for an online inspection technique. The requirements for a chosen inspection technique are [1], [2]: 1. Showing the results on-line during the joining process; 2. Working non-destructive; 3. Working as an integral method; Being able to determine weld defects. In that case only the Acoustic Emission Analysis (AEA) as a Non-Destructive-Technique (NDT) can be used to guarantee reasonable results. During the first tests at the welding laboratory at the Laser Technology Competence Centre (LTCC) at the University of Luxembourg, AEA sensors are applied onto the surface of the test specimen which has to be welded. In this principle acoustic events, caused by welding defects, are recorded during the laser joining. The most important laser process parameters, like velocity, power and horizontal focal position of the laser spot, have been verified and evaluated by the AEA. It was observed that insufficient laser power can lead to the break of the melting bath, which is often not recognizable by non-destructive optical methods [2]. The AEA however was able to detect this lack of fusion. Using high laser power, the appearance of gas bubbles arising from the Polyamide 6.6 could be detected afterwards in a microscopic micrograph. The AEA signals related to this effect can be correlated clearly. Due to the high pressure of the gas bubbles, the aluminium weld is often interrupted, which can be traced back to the solidification of the aluminium molten mass. Due to the actual situation, the AEA is a well-working NDT online monitoring method and can be used for the correlation of acoustic events and welding defects within the mentioned joining method. Future tasks will develop some algorithms to separate the different defects by pattern recognition of the AEA signals and parameter

Fluoride Addition Effects on Voltammograms and UV-Vis Spectra of Neodymium Cation in Molten Chlorides

The modification of electrochemistry and electronic absorption spectra of neodymium in various molten chlorides depending on additional fluoride in the melt bath has been investigated. Disproportionation reaction is restricted by fluoride addtion and absorption spectra is highly modified in molten NaCl-2CsCl as compared with that in molten LiCl-KCl. These facts would be explained by modification of local structure around neodymium cation depending on fluoride addition.

Contributions to the Environmental Impact of the Process of Welding Work in the Environment of Protective Gases

Paper presents the main pollutants that appear Gas metal arc welding, the main chemical reactions take place in the melting bath where results the pollutants, determining the impact on the working environment by calculating the coefficient of pollution. The optimization of welding process gives a coefficient of minimum pollution and determines the influence of welding parameters of the system on the appearance of major pollutants elements.

Synthesis, characterization and antimicrobial activity of alkaline ion-exchanged ZnO/bentonite nanocomposites

Nanocomposites of zinc/bentonite clay were synthesized for use as an antibacterial material by a quick and simple alkaline ion exchange method. The synthesis of zinc doped bentonite nanocomposite was accomplished by placing bentonite in a melting bath of ZnSO4 for 10, 20, 40, 60 and 90 min. The complexes were characterized by XRD, SEM and DRS. XRD analyses and SEM observations confirmed the diffusion of zinc to the clay surfaces. Antibacterial activity tests against Escherichia coli showed that bentonite did not present any antibacterial properties, but after alkaline ion exchange treatment, inhibition was noted. The highest antibacterial activity was observed with ZnO/bentonite composite alkaline ion exchange for 60 and 90 min. Interestingly, the leaching test indicated that ZnO/bentonite did not present any risk for drinking water treatment.

Nonlinear properties of voltage and current transfer ratios for electric arc furnaces

A method of arc voltage gradient calculation for an electric arc furnace (EAF) is presented. The arc voltage gradient is the basic characteristic in study and simulation of an automatic power control system of an EAF. This characteristic is a strongly nonlinear multifactorial function that depends on electrical parameters of a power supply system, thermal conditions, and processes of arc heat exchange in an EAF melting bath. The method of arc voltage gradient calculation considers the relation between the electric and thermal conditions of an EAF in order to describe feasible nonlinear properties and to improve expressions for voltage and current transfer ratios as nonlinear multifactorial functions in particular. An EAF is regarded as a subject of control. Multifactorial properties are defined by the parameters of an equivalent electrical circuit of a furnace and by variable conditions of arc heat exchange in a melting chamber during steel melting. The method is effective for overcoming the uncertainty of the arc length in simulation of an EAR power controller. The unstable behavior of the furnace at a high impedance was explained using the obtained functions of the arc current and the arc voltage for various electrodes and the arc length. The minimum allowed arc current was found. The automatic power controller becomes unstable and the arc is extinguished under this value.

Temperature Controlled Laser Joining of Aluminum to Galvanized Steel

Reliable joining of 6000 series aluminum alloy to galvanized steel is a challenge for current manufacturing technologies. To control and limit the formation of brittle intermetallic phases, mixing of both metals in liquid state has to be avoided. It has been shown that laser weld-brazing is a possible process. Thereby the aluminum and zinc layer of the galvanized steel are molten and the steel remains solid during the process. In addition, to avoid zinc degassing, the aluminum melt bath temperature has to be below zinc boiling temperature of 907°C. To meet these requirements a temperature controlled laser process was developed, allowing to join the two materials without flux and filler material. The thickness of the intermetallic layer shows a dependency on the set temperature used to control the process. At optimum set temperature the thickness of intermetallic phases can be limited to about 5 μm. Tensile strengths of the joints of up to 75% of the aluminum base material were achieved.

The Technological Comparative Analysis between the Vertical MAG Welding with Solid Wire and with Cored Wire

The vertical welding is generally considered difficult because of the danger of the flow of the melting bath and the melted slag under the action of gravity. In the case of the MIG/MAG welding process, the technological measurements that are being regarded in the ascending and descending of the vertical welding refer to: the use of transfer modes through short circuit and pulsed current, the use of core wires instead of solid wires, the crossing from the semi-mechanized to automatic or robotical welding, that allows the use of complex radial oscillation systems, that assure a good control of the metal bath. The paper wants to make a comparative technological and economical analysis between the vertical ascendent MAG welding using solid wire or core wire. The advantages that are being presented are for the use of the core wire with a rutilic core for the vertical, ascendent welding from a technological, qualitative and economical point of view in the mechanical corner welding process of a 10 mm thickness steel plates.

3D µCT and SEM Analysis of Resolidified Tips of Cored Wires Used in Twin-Wire Arc Spraying

In twin-wire arc spraying (TWAS), the in-flight particles are atomized from a melting bath which generates an inhomogeneous spraying plume. This inhomogeneity is due to the fact that these particles are generated by the impingement of fast continuous flowing air upon the melting tips of electrically conductive wires. This work aims to contribute to the understanding of the initiation of such particles in the TWAS process. For this purpose, cored wires filled with W-rich particles were sprayed. After interrupting the TWAS process, the tips of these cored wires were imaged by 3D µCT and scanning electron microscopy in order to analyze how the filling powder interacts with the melted part of the sheath. The analysis of the 3D tomograms shows that the resolidified melting bath of the cored wires is interspersed with both spherical and irregular-shaped W-rich particles. This irregular shape suggests a partial melting of the W-rich particles.

Silicon Influence on the Cast Iron Structure

Chemical element silicon, placed in liquid iron behaves differently, through the influence they exert on the metallographic structure. The factors that define their influence are the melt temperature, melting bath temperature variation dynamics, the amount that is inserted into melting bath, chemical shape etc.Refining of metallographic structure was found when FeSi was used with 35% si 73% Si.

How to select a suitable shielding gas to improve the performance of MIG and TIG welding of aluminium alloys*

Welded aluminium alloy products are widely used in the construction and packaging sectors: in this context, in order to be competitive, the welding processes must offer valid solutions from both the productivity and quality viewpoints in addition to health-related aspects with regard to welders and operators. In this context, the technological goals of Air Liquide have been focused on improving the quality of welded joints made using the MIG and TIG processes. The approach adopted here is to examine the various gas mixtures from the viewpoint of influence on electrical parameters (voltage), regularity of filler metal transfer, the surface tension of the melt bath and the convection patterns present in the latter.

Formation of Cr-Bearing Species in Stainless Steelmaking Dust by Induction Furnace

Stainless steelmaking dust contains significant levels of Cr-bearing phases (typically 0.28~16.5%). In this study, stainless steel was produced in an induction furnace, dust generated during the smelting process is collected in order to classify dust formation mechanisms and effects of operation parameters of smelting process on the formation of Cr(VI) species in the dust. The results showed that approximately 60% of dust generated during stainless steelmaking process by induction furnace is due to entrainment of charge fines, about 30% of dust formed due to metal and slag splashing result in oxygen and argon injection, and only about 10% of dust are formed through vaporization from the melt bath. In addition, the Cr-bearing phases in the dust mainly generate due to slag and metal splash. It can increase Cr(VI) content in the dust by increasing the chromium content in the molten steel, the amount of slag former and temperature of molten. To accelerate the cooling rate during the sampling period will decrease the Cr(VI) content in the dust.

A LUMP-INTEGRAL MODEL FOR FREEZING AND MELTING OF A BATH MATERIAL ONTO A PLATE SHAPED SOLID ADDITIVE IN AN AGITATED BATH

A lump integral model is developed for freezing and melting of the bath material onto thesurface of a plate shaped additive immersed in an agitated melt bath. It exhibits the dependenceof this occurrence on independent parameters-the initial temperature, θai of the additive, the bathtemperature, θb , the Biot number, Bi the property ratio, B and the Stefan number, St and yieldsclosed-form solutions for time variant frozen layer thickness, ξ around the additive and heatpenetration depth, η in the additive. In the solutions, B, Bi, θb and θai appear as a conductionfactor, Cof that ranges from 0 to ∞. The frozen layer thickness per unit St with respect to Coftakes time τcmax=1/3 for its maximum growth whereas this maximum thickness ξ*cmax becomes(1- θai)/3. The total time of the growth of the maximum frozen layer thickness with itssubsequent melting, τct is 4/3 when the heat penetration depth reaches the central axis of theplate additive, η=1. When Cof →0 signifying highly agitated bath (h→∞) or additive preheatedto the freezing temperature of the bath material, no freezing of the bath material occurs. For thebath at the freezing temperature of the bath material, the frozen thickness is also obtained. Themodel is validated by reducing the present problem to heating of the plate additive subjected to aconstant temperature maintained at the freezing temperature of the bath material.

Influence of Laser Wavelength on Melt Bath Dynamics and Resulting Seam Quality at Welding of Thick Plates

Abstract CO2- and solid-state lasers are the most widely used beam sources. Owing to their different physical beam characteristics, these two types of laser differ fundamentally not only in how the beam is guided but also in their process behavior during deep penetration welding. Almost all industrial applications in thick material > 8 mm have to be full penetration welds to increase fatigue strength, for example in ship building, pipeline construction, train and rail construction or power-train, Holzer et al., 2011 . Therefore process behavior and limits at full penetration will be analyzed in detail for both beam sources.

Thermocapillary-assisted pulling of contact-free liquid films

We study the formation of a free liquid film that is pulled out of a bath at constant speed and stabilized by the action of thermocapillary stresses prescribed at the free surfaces. The basic concept was introduced recently by Scheid et al. [“Thermocapillary-assisted pulling of thin films: Application to molten metals,” Appl. Phys. Lett. 97, 171906 (2010)]10.1063/1.3505523. The theory suggests that very thin ribbons of molten material can be drawn out of a melt by adequately tuning the temperature gradient along the dynamic meniscus that connects the static meniscus at the melting bath to the region of the drawn flat film. In the present paper, we extend our original analysis by investigating the roles of inertia and gravity on the film thickness, and show how the results depend on heat transfer/conduction properties. Furthermore, we analyze the one-dimensional transverse stability of the free film with respect to the long-wave thermocapillary instability.

Experimental Trials of the Thin Shell Casting (TSC) Technology for Directional Solidification

In this paper a novel directional solidification process - Thin Shell Casting (TSC) is presented. According to this new technology a thin shell mould mounted to a chill is dipped through the floating baffle into the melt bath. By pulling up the shell mould, a directional solidification can be performed in a downward direction. Due to the use of extremely thin shell moulds and the application of gas cooling, an efficient heat extraction can be achieved in comparison to the conventional and modified Bridgman techniques. In the experiments with Cu- and Al-alloys, not only directional solidification (DS), but also single crystal (SC) growth can be successfully performed. This confirms the feasibility of the new technology, which will be further applied to the production of SC components of superalloys.

Freezing and melting of a bath material onto a cylindrical solid additive in an agitated bath

In melting and assimilation of a cylindrical shaped additive in an agitated hot melt bath during the process of preparation of cast iron and steel of different grades, an unavoidable step of transient conjugated conduction-controlled axisymmetric freezing and melting of the bath material onto the additive immediately after its dunking in bath occurs. Decreasing the time of completion of this step is of great significance for production cost reduction and increasing the productivity of such preparations. Its suitable mathematical model of lump-integral type is developed. Its nondimensional format indicates the dependence of this step upon independent nondimensional parameters- the bath temperature, ?b the modified Biot number, Bim denoting the bath agitation, the property-ratio, B and the heat capacity-ratio, Cr of the melt bath-additive system, the Stefan number, St pertaining to the phase-change of the bath material. The model provides the closed-form expressions for both the growth of the frozen layer thickness, ? onto the additive and the heat penetration depth, ? in the additive. Both are functions of these parameters, but when they are transformed to the growth of the frozen layer thickness with respect to the heat capacity ratio per unit Stefan number; and the time per unit property-ratio, B, their expressions become only a function of single parameter, the conduction factor, Cof consisting of the parameters, B, Bim and ?b. The closed-form expression for the growth of the maximum thickness of the frozen layer, its time of growth, the time of the freezing and melting; the heat penetration depth are also derived. When the heat penetration depth approaches the central axis of the cylindrical additive in case of the complete melting of the frozen layer developed Cof?11/72. It is found that the decreasing Cof reduces both the time of this unavoidable step and the growth of the maximum frozen layer thickness and at Cof=0, the frozen layer does not form leading to zero time for this step. If the bath is kept at the freezing temperature of the bath material, only freezing occurs. To validate the model, it is cast to resemble the freezing and melting of the bath material onto the plate shaped additive. The results are exactly the same as those of the plate.

Structure of Deposits Obtained from Urea-Based Melt Bath Containing Co and La

Electrodeposition was performed in an unagitated solution from a urea-based melt bath containing Co and La under galvanostatic (10­ 40mA·cm12) and coulostatic (10C·cm12) conditions at 403K, and the structure of the deposits was investigated. Co deposited in a metallic state at 10mA·cm12, whereas it was incorporated into deposits mainly as an oxide at high current densities of 30 and 40mA·cm12. La codeposited with Co as an oxide irrespective of current density. The content of La2O3 increased with current density. The deposits showed a granular crystal structure and became nonuniform crystals comprising large localized granules at high current densities. [doi:10.2320/matertrans.M2011379]