Showing papers on "Liquid metal published in 2001"

Semi-solid processing of engineering alloys by a twin-screw rheomoulding process

Abstract: Based on the extensive experience in injection moulding of polymeric materials, a twin-screw rheomoulding process has been developed in our laboratory for near net-shape production of engineering components. The rheomoulding equipment consists of a liquid metal feeder, a twin-screw extruder with closely intermeshing, self-wiping and co-rotating screws, a shot assembly and a central control unit. The fluid flow in the twin-screw rheomoulding process is characterised by high shear rate and high intensity of turbulence. The experimental results of rheomoulded Sn–15wt.% Pb and Mg–30wt.% Zn alloys have demonstrated that the twin-screw rheomoulding process is capable of producing small and near mono-sized solid particles distributed uniformly in a fine-grained eutectic matrix. Compared with other existing semi-solid metal processing techniques, the twin-screw rheomoulding process has the following advantages: small and spherical solid particles of near mono-size, chemical and microstructural uniformity throughout the component, accurate control over a large range of solid volume fractions, lower overall component cost due to low cost of feedstock materials, and shorter cycle time.

Contact temperature and erosion in high-current diffuse vacuum arcs on axial magnetic field contacts

Abstract: We have investigated the surface heating effects of drawn vacuum arcs for several industrial designs of axial magnetic field (AMF) contacts, using near infrared (IR) photography of the Cu-Cr arcing surfaces with an image-intensified charge-coupled device (CCD) camera and an IR pyrometer. This enables detailed contact temperature mapping immediately after a half-cycle of arc current. The very homogeneous temperature distribution observed at current zero stands in contrast to the visually nonhomogeneous high-current diffuse arc, which was studied in separately reported experiments using high-speed digital photography and arc voltage measurements. The peak temperature at current zero increased relatively linearly with the peak current I/sub P/, and reached well beyond the melting range. We combine the temperature maps with a heating model to determine the thermal sheath thickness after arcing and its dependence on I/sub P/. The results suggest that near the interruption limit of AMF contacts, the interaction of the stable high-current arc with the anode and cathode is dominated by processes induced by flowing liquid metal, which redistributes the heat input from the axially concentrated arc over most of the contact surface. Furthermore, the flow of liquid metal off the cathode and anode faces contributes to the overall contact erosion.

Rayleigh–Bénard convection in liquid metal layers under the influence of a vertical magnetic field

Abstract: The influence of a vertical magnetic field on the integral heat transfer and the temporal dynamics of liquid metal Rayleigh–Benard convection is studied in an experiment using a small Prandtl number (Pr≈0.02) sodium potassium alloy Na22Kr78 as a test fluid. The test section is a rectangular box of large aspect ratio 20 : 10 : 1 that covers a parameter range of Rayleigh numbers, 103

Metastable States of Liquid Metal under Conditions of Electric Explosion

Abstract: The paper deals with the simulation of the initial stage of tungsten wire explosion under the effect of a high-power nanosecond current pulse. The calculations involve the use of a semiempirical equation of state for tungsten, which allows for the effects of melting and evaporation at high temperatures. The laws of conservation that take into account the presence of a magnetic field and relative motion of the media are written at the liquid–vapor interface. It is demonstrated that a description fitting adequately the available experimental data is possible if one takes into account the possibility of realizing metastable states of liquid metal in the process of evolution of the system.

Microsecond Laser Polarimetry for Emissivity Measurements on Liquid Metals at High Temperatures—Application to Tantalum

Abstract: The aim of this work was to determine accurate and reliable thermophysical properties of liquid tantalum from melting up to temperatures of 5000 K. Temperature measurements on pulse-heated liquid metal samples reported by different authors have always been performed under the assumption of a constant emissivity over the whole liquid range because of the lack of data for liquid metals. The uncertainty in temperature measurement is reduced in this work by the direct measurement of emissivity during the experiments. The emissivity measurements are performed by linking a laser polarimetry technique with the established method for performing high speed measurements on liquid tantalum samples at high temperatures during microsecond pulse-heating experiments. A set of improved thermophysical properties for liquid tantalum, such as temperature dependences of normal spectral emissivity at 684.5 nm, heat capacity, enthalpy, electrical resistivity, thermal diffusivity, and thermal conductivity, was obtained.

Low temperature synthesis of semiconductor fibers

Abstract: This invention presents a process to produce bulk quantities of nanowires of a variety of semiconductor materials. Large liquid gallium drops are used as sinks for the gas phase solute, generated in-situ facilitated by microwave plasma. To grow silicon nanowires for example, a silicon substrate covered with gallium droplets is exposed to a microwave plasma containing atomic hydrogen. A range of process parameters such as microwave power, pressure, inlet gas phase composition, were used to synthesize silicon nanowires as small as 4 nm (nanometers) in diameter and several micrometers long. As opposed to the present technology, the instant technique does not require creation of quantum sized liquid metal droplets to synthesize nanowires. In addition, it offers advantages such as lower growth temperature, better control over size and size distribution, better control over the composition and purity of the nanowires.

Heat transfer to liquid metals : Specific features, methods of investigation, and main relationships

Abstract: The main periods of investigations of heat transfer to liquid metals are considered. The specific features of liquid metals as coolants for nuclear power installations are discussed. The methods and the technologies used in the experiments to determine the values of the heat-transfer coefficients are described. The regularities of heat transfer to the liquid metals in round tubes are analyzed on the basis of the original experimental data. It is noted that the most reliable results, which are free from the effect of the contact thermal resistance on heat transfer, can be obtained only from the measured temperature distribution in the flow.

Thermal Diffusivity of Iron at High Temperature in Both the Liquid and Solid States

Abstract: Thermal diffusivity measurements of pure iron have been made using a laser flash apparatus (LFA) over the temperature range 25 to 1 640°C. These measurements are compared with existing data and recommended values are given. In the γ-Fe phase region the thermal diffusivity can be represented by a=6×10 -6 +3.13×10 -9 ×(T-911). In the δ-Fe phase region the thermal diffusivity can be represented by the constant 0.07×10 -4 m 2 s -1 . In the liquid region up to 1 640°C, the thermal diffusivity can be represented by a=6.2×10 -6 ×1.79×10 -9 ×(T-1 538). Tin both equations is temperature in Celsius and the thermal diffusivity equation units are m 2 s -1 . To improve the LFA measurement characteristics of a metal, it is often coated with graphite. Unfortunately, due to the solubility of carbon in iron, at high temperatures, the coating does not remain on the surface of the iron. The effect of using a zirconia coating as opposed to a graphite coating was tested. The efficacy of this change was evaluated by comparing thermal diffusivity measurements on Cu using both coating materials.

Generation of Compression Waves by Simultaneously Imposing a Static Magnetic Field and an Alternating Current and Its Use for Refinement of Solidified Structure

Abstract: A new generating method of compression waves in a liquid metal has been proposed in which a static magnetic field and an alternating current are simultaneously imposed. The theoretical expressions of intensities and distributions of pressure and velocity accompanied with the compression waves have been derived. The pressure change in liquid gallium excited by the method proposed here was measured under different intensities of the magnetic field and the alternating current. The measured pressures approximately agreed with the theoretical evaluation. The structure of a Sn–Pb alloy that was solidified under the imposition of the compression waves, was completely refined.

Magnetic susceptibility of high-Curie-temperature alloys near their melting point

Abstract: An experimental set-up allowing the magnetic susceptibility measurement during the processing of metallic alloys at high temperature in high magnetic fields is described. Curie temperature, melting and solidification can be observed by the magnetic susceptibility variations. Results for a high-Curie-temperature Co–Sn alloy are presented, together with the effect of the field on the resulting microstructure.

Thermodynamic evaluation of surface tension of liquid metal-oxygen systems

Abstract: Thermodynamic equations have been derived to evaluate the surface tension of liquid metal-oxygen systems. On the basis of these equations, the effect of the oxygen on the surface tension of liquid metals has been evaluated by using the fundamental information on the oxygen solubility in the metals, the surface tension and the molar volume of pure liquid metals and oxides. The calculated results from these equations agree with the literature values of the surface tension of liquid Fe-O, Co-O, Ni-O, Cu-O and Si-O systems.

Systems for detecting and measuring inclusions

Abstract: The present invention relates to systems of methods of detecting and measuring inclusions in liquid metals. More particularly, non-metallic inclusions having a conductivity level different from the liquid metal melt are forced to migrate and are collected on a measurement surface using electromagnetic Lorentz forces. The inclusions and their concentrations are detected at the measurement surface using either an electrostatic detection system or an optical detection system.

Measuring velocity in high-temperature liquid metals: a review

Abstract: All fluid mechanics problems in metals-processing operations are associated with the measurement of fluid velocity. The development of various models of predicting fluid flow characteristics in complex engineering problems has increased the need for fluid velocity measurements. These measurements provide the necessary validation and tuning for model predictions. In addition, measurement of fluid velocity can be used as a tool for process control purposes. Moreover, the continuous push of metal industries for improved quality and efficiency in liquid metal processing operations, has further highlighted the need for liquid metal velocity measurements. This review presents the various techniques used so far to measure velocity in liquid metals. It outlines the advantages and disadvantages of each technique and provides the reader with information for critical analysis.

Technology for electroslag remelting with rotation of the consumable electrode

Abstract: It is known that metal which is produced by the method of electroslag remelting (ESR) has service properties superior to those of metal made by open refining and casting. This can be attributed to the better conditions which exist for refi ning in the specially chosen slag and for the crystallization of the metal in the case of ESR. However, the need for a two-stage metallurgical conversion (essentially requiring repeat refining) makes ESR metal more expensive than metal made by electric-arc refining. By resorting to out-of-furnace treatments, the content of harmful impurities in the latter product can be reduced to nearly the same level as in ESR metal. In addition, the consumption of electric power in the production of ESR ingots is more than three times greater than the level characteristic of steelmaking in electric furnaces. It is this circumst ance that is presently impeding the wider use of ESR [1]. The costs of producing ESR ingots could be reduced significantly by using an electroslag remelting technology that involves rotation of the consumable electrode around its axis. The General Metallurgy Department of South-Ural State University has already had many years of experience in developing and studying an ESR process that takes place in a centrifugal force field [2‐8]. Such a technology has several important advantages. Most significantly, it makes it possible to appreciably increase the productivity of the process (more than 25% in some cases) without increasing the amount of power that must be supplied to the slag bath. This is accomplished through a change in the hydrodynamic situation in the bath, a reduction in the height of the bath, and the forced removal of liquid metal from the electrode. The hydrodynamic pattern which exists during the melting of a rotating electrode is different from the pattern characteristic of an electrode that moves only vertically. An ascending slag flow is created in the zone near the consumable electrode as it rotates. While rising, the slag is heated and reaches its highest temperature in the immediate vicinity of the elec trode end that is being melted (Fig. 1 b). In the standard technology, slag washes over the melting conical portion of the electrode after it gives up heat to the water-cooled wall of the mold. Moving through the near-electrode region, the slag reaches its highest temperature at the boundary with the liquid metal bath (Fig. 1 a). The removal of liquid metal from the electrode as the latter rotates occurs mainly under the influence of centrifugal forces rather than gravitational forces, which is typical of the given (standard) remelting technology. When the electrode is melted in a centrifugal force field, the liquid phase (drops) are more shielded from the melting surface than when the electrode is not rotated. The melting end of the consumable electrode is flat when it is rotated. The slag level in the mold is thus lower than in the standard technology. In the latter, the slag bath is higher because slag is displaced by the conical end immersed in it. The decrease in the area of contact between the slag and the water-cooled wall of the mold also reduces heat losses by 9‐13%, the exact reduction depending on the parameters of the remelting process. The presence of a flat end makes it possible to ensure that the required distance is maintained between the electrode and the liquid bath with a 10‐15% decrease in the amount of flux which is used. In addition, rotation of the consumable electrode significantly improves the refining ability of the remelting process. This is due to the fact that the thickness of the layer of liquid metal (film) on the end of the electrode is uniform and mini

A carbon dioxide partial condensation direct cycle for advanced gas cooled fast and thermal reactors

Abstract: A carbon dioxide partial condensation direct cycle concept has been proposed for gas cooled fast and thermal reactors. The fast reactor with the concept are evaluated to be a potential alternative option to liquid metal cooled fast reactors, providing comparable cycle efficiency at the same core outlet temperature, eliminating the safety problems, simplifying the heat transport system and making easier plant maintenance. The thermal reactor with the concept is expected to be an alternative solution to current high temperature gas cooled reactors (HTGRs) with helium gas turbines, allowing comparable cycle efficiency at the moderate temperature of 650 C instead of 800 C in HTGRs. (author)

Liquid-solid rolling bonding method for different kinds of metals and the apparatus therefor

Abstract: The present invention relates to a liquid-solid rolling bonding method for heterogeneous metals and an apparatus therefor. The method comprises: pouring a liquid metal onto the surface of a heterogeneous solid base metal coated with a soldering flux; rolling the liquid metal and the solid metal under pressure; solidifying the liquid metal and making it bond to the surface of the solid base metal under rapid cooling to realize metallurgical bonding of the two or more metals. The apparatus comprises an unrolling machine, a soldering flux tank, a drying-heating apparatus, a pouring nozzle, an interior water-cooling rollers and a roll-collecting machine arranged in order, a pouring basket is disposed above the pouring nozzle and a base frame is disposed below the pouring nozzle. The present invention has the advantages of high bonding strength, lower production cost, high production efficiency, good product quality, fewer investment for the apparatus and lower consumption of energy. The method of the present invention can replace the convention rolling bonding method in solid-solid phase and is suitable for the production of various clad metal sheets and strip.

Method and installation for hot process and continuous dip coating of a metal strip

Abstract: The invention concerns a method for continuous dip coating of a metal strip (1) in a tank (11) containing a liquid metal bath (12), method which consists in: continuously unwinding the metal strip (1) in a sheath (13) whereof the lower part (13a) is immersed in the liquid metal bath (12) to constitute with the surface of said liquid metal a liquid pressure seal (14); producing a natural flow of the liquid metal from the surface of the liquid pressure seal (14) into two overflow compartments (25, 29) arranged in said sheath (13) and comprising each an inner wall extending the sheath (13) at its lower part and maintaining the level of the metal liquid in said compartments at a level below the surface of the liquid seal (14). The invention also concerns an installation for implementing the method.

Method of fabricating a mold-cast porous metal structure

Abstract: A method of fabricating a porous metal structure of a molten liquid metal within a casting chamber to form a porous solid structure upon controlled chamber cooling and depressurization. The method includes provision of a pressurizable stationary mold casting chamber having a gas pressure release valve, a gas pressure measurement sensor, and a plurality of sites with respective surface-temperature or heat flux sensors and respective independently operable temperature controllers for regulating each respective site temperature. A data base driven microprocessor receives pressure and temperature data and selectively and independently adjusts pressure and temperature in accord with algorithmic commands relative required pressure reduction for pore formation and cooling for solidification to chosen extents of porosity and of solidification over a time period terminating upon porous solid-structure fabrication.