Melt Stream Research Articles

Survey of melt stream infrared radiation parameters at various stages of steel tapping from basic oxygen furnace

Current world economic recession and high competition in the market of ferrous metallurgy products make the issue of improving the efficiency of the steel-making process especially pressing. One of the ways to improve the efficiency of a steel-making unit is to provide the sufficient minimum content of furnace slag in a pouring ladle. It can be achieved by permanent real-time monitoring of the melt stream during tapping from the steel-making unit. The most efficient way to monitor the melt stream is the method based on control of infrared radiation from the steel being tapped. The article offers the analysis of arrays of infrared radiation values from operating steel-making units of the largest smelters of Russia. The authors give some practical design recommendations for monitoring systems of melt stream in the process of tapping from the steel-making unit. They also describe the rule of slag detection in the melt stream.

The identification of an accurate simulation approach to predict the effect of operational parameters on the particle size distribution (PSD) of powders produced by an industrial close-coupled gas atomiser

Powder metallurgy (PM) refers to a range of engineering techniques whereby net shape or near-net shape bodies are produced through the aggregation of a powder substrate. Specifically, the emergence of Additive Layer Manufacturing (ALM) is an exciting development in this field. However, the quality of any product produced by ALM is highly dependent upon the quality of the powder used. Gas atomisation is a specialised processing route in the PM field for the production of fine, spherical powders directly from a molten metal melt. The close-coupled gas atomisation process involves a melt stream being impacted by high velocity, under-expanded gas jets which initiate its break-up in two distinct phases; the second critical in determining the final particle size distribution (PSD) of the powder produced. However, fully understanding the mechanisms at work and exerting a high level of control over any produced powder is a challenge faced by the powder manufacturing industry; highlighted by the stringent requirements of the new ALM manufacturing technique.Utilising Ansys Fluent v14.5 computational fluid dynamics (CFD) software, a 3D axi-symmetric simulation has been developed of a close-coupled atomising gas jet nozzle configuration utilised by a powder manufacturer. Through the two-way coupling of the CFD with a Discrete Particle Model (DPM) using the Euler–Lagrange approach, an assessment has been made of the effect of process parameters on the final PSD of the metal powders produced. The most appropriate model for the simulation of the secondary break-up phase has been identified from the Kelvin–Helmholtz (KH), Kelvin–Helmholtz Rayleigh-Transport (KHRT) and Taylor Analogy Break-up (TAB) models. Subsequently, the validated simulation approach has been used for the qualitative assessment of the effect of altering the atomising nozzle geometry and process conditions on the average size of powders produced i.e. finer or coarser. It was also established that there is potential for the model to be used as a quantitative predictive tool of powder size; useful for quality control especially when manufacturing powder for use in ALM. However, further development and validation is required for confirmation of this function.

Dependence Of The Structure And Magnetic Properties Of Cast Plate-Shaped Nd60Fe30Al10 Samples On Their Thickness

Abstract The hard magnetic Nd-Fe-Al alloys are inferior to Nd-Fe-B magnets as far as the magnetic properties are concerned, but their great advantage is that they need no additional annealing to achieve good magnetic properties. These properties depend on the cooling rate from the melting state, and on the thickness of the sample - the best values are achieved at the quenching rates at which the samples have a thickness of 0.3-2 mm. The present study is concerned with the correlation between the magnetic properties of the plate-shaped Nd60Fe30Al10 samples and their size - thickness. Two casting ways: with the melt stream perpendicular direction and parallel to the surface of the plates were used. The plates were produced by pressure casting and suction casting. The studies have shown that the cooling rates depends on local propagation on liquid metal in the mold resulting in heterogeneity of structure and properties.

On the Stability of the Melt Jet Stream during Casting of Metallic Glass Wires

The factors that affect the stability of the melt stream during the casting of wire directly from the melt have been investigated. It is shown that the criticality of process parameters centres mostly on the forces imposed on the melt stream at confluence with the cooling water. The analysis of these forces indicated that the shear component of the disturbance is dependent on the ratio of the velocity of the melt stream (vm) to that of the cooling water (vw) in accord with results obtained from previous experiments. The role of oxide-forming elements in widening the process parameters range is attributed to the increased stability of the melt stream due to the additional shear force resistance offered by the solid oxide layer. The roles of Cr and Si oxides in stabilising the melt stream are confirmed by X-ray photoelectron spectroscopy (XPS) of wire indicating the presence of these oxides on fresh as-cast wires. Melt superheat and nozzle clearance distance are not strictly stream stability factors, but rather their role in glass formation prescribes optimal limits for fully amorphous wire.

Weld line improvement of short fiber reinforced thermoplastics with a movable flow obstacle

ABSTRACTShort fiber reinforced (SFR) thermoplastics are ideal materials from which to manufacture complex technical parts in high volumes with low energy expenditure. The orientation of the fibers, and hence their reinforcing effect, depends strongly on the nature of the cavity and on the injection molding process. One disadvantage of SFR thermoplastics is a significant decrease in mechanical properties in the areas of the weld lines, due to suboptimal fiber orientation as the melt streams reunite at these points. Common mold‐based and process‐based optimization techniques alter the fiber orientation after the formation of the weld line. The mold‐based approach presented here, on the other hand, operates at the time the weld line is formed: by redirecting the melt streams, it moves the weld line and improves the fiber orientation. A prototype mold is described, and samples produced from it with both standard and modified weld lines are compared with flawless specimens. The new technique yields a large rise in flexural strength and a smaller but significant improvement in tensile properties. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42025.

Radiocarbon distribution and the effect of legacy in lakes of the McMurdo Dry Valleys, Antarctica

The water of the ice‐covered lakes of the McMurdo Dry Valleys is derived primarily from glacial melt streams and to a lesser extent permafrost seeps and subglacial outflow. The result is a mixture of radiocarbon ages that reflect both the end‐member water source and the biogeochemical processing of waters as they migrate to the lake‐water column. Samples were collected from various locations within perennially ice‐covered Antarctic lakes and the streams that feed them, and they were analyzed for radiocarbon abundance of organic and inorganic carbon. Stream gradient and length were shown to affect the degree of equilibration of water with the modern atmosphere prior to entering the lakes. Stream microbial mats assimilate inorganic carbon flowing over them. Seasonal ice‐free ‘moat’ water dissolved inorganic carbon (DIC) is largely dependent on the amount of meltwater input from streams (modern) vs. that from direct glaciers input (old). Under the ice cover, 14C ages of lake‐water DIC and organic matter are dependent on lake history, composition, and quantity of particulate matter fallout. Bottom waters of the west lobe of Lake Bonney have a DIC age of µ 27,000 14C yr before present, which we believe are the most radiocarbon‐deficient lake waters on Earth. Comparison of the radiocarbon profiles in the two lobes of Lake Bonney, along with previously published geochemical data, provides a new chronology of the evolution of these two waterbodies and shows that currently deep saline water is being displaced over the sill separating them.

Locating an ice-covered Antarctic landfill using ground magnetometry

AbstractAt former Antarctic research stations, legacy waste often remains in situ and concealed by ice. Consequently, the location, characteristics and potential environmental impact associated with legacy waste remains poorly documented. This study applies ground magnetometry to map the spatial extent of the landfill at the abandoned Wilkes Station. Magnetic anomalies indicate that the landfill extends north-west to south-east and is close to, and perhaps prograding into, the ocean. The landfill is characterized by large magnetic variations of > 1500 nT with asymmetrical magnetic anomalies which suggest variable orientations of material and random dumping. Magnetic susceptibilities > 0.02SI units beyond the landfill area reveal elevated magnetic properties of the basement geology. However, a contrast in anomaly shape reliably distinguishes large anomalies generated by landfill material. Surface and subsurface melt streams (observed at the shoreline) flowing from the survey area suggest elevated potential for metal contamination of the nearshore and marine environment. The survey demonstrates a cost-effective and non-invasive method for gathering information to guide the clean up of landfills beneath ice.

Climatic control on extreme sediment transfer from Dokriani Glacier during monsoon, Garhwal Himalaya (India)

In the Himalayas, most of the glaciers are covered by thick debris, especially in the ablation zone. Supraglacial debris cover might play an important role for sediment budget of the glaciated area or for the ablation of ice masses mantled in debris. During summer season, proglacial meltwater carries considerable amount of suspended sediment. The deglaciated area provides a ready source of sediment during Indian Summer Monsoon (ISM). The heavy sediment load from the glaciers affects the hydropower generation, irrigation and drinking water supply. Therefore, to understand the sediment delivery from glaciated basins, characteristics and variation of the suspended sediment concentrations in the proglacial meltwater stream, Dokriani Glacier, have been monitored during the ablation season (May–September). Suspended sediment samples were collected near the snout of Dokriani Glacier, Garhwal Himalaya, in 2010 and 2011. Results show that mean monthly suspended sediment concentrations (SSC) were 1499, 2303, 3845 and 1649 mg/l for the months June, July, August, and September, respectively, indicating highest concentration in August followed by July. Over the period of recording, daily mean suspended concentration in the melt stream varied from 13–9798.2 mg/l, which is very high, caused due to a flash flood event during the monitoring period. The mean daily suspended sediment concentration was computed to be 2196 mg/l. The suspended sediment concentration begins to increase with discharge from May and reduces in September. Present study provides TRMM (Tropical Rainfall Measuring Mission) derived and field based hydro-meteorological insight about severe rainstorms during the years 2010 and 2011 in the study area, which transported large amounts of sediment.

Effect of Compositional Changes on the Mechanical Behaviour of Grey Cast Iron

The effect of varied alloying elements onthe mirostructure hardness and tensile properties of gray cast iron has been investigated. 0.1wt%, 0.2wt% and 0.3wt% of ferro-silicon inoculants were added to the stream of the iron melt during tapping for uniform dissolution and later poured into prepared sand mould. The cast samples were prepared for metallographic analysis. Hardness and tensile test were determined with standard samples. Mechanical properties are shown to be a function of the matrix, graphite or carbide forms. The increase in inoculants addition increases the carbon equivalent, but the tensile and the hardness properties were found to decrease. Hardness properties decrease from 58.9HRC to 44.70HRC from un-inoculated to 0.3wt% inoculated grey iron respectively

Characterization and comparison of potential denitrifiers in microbial mats from King George Island, Maritime Antarctica

Cyanobacterial microbial mats are highly structured communities commonly found in Antarctic inland waters including melt streams. These benthic microbial associations comprise a large number of microorganisms with different metabolic capacities, impacting nutrient dynamics where established. The denitrification process is a feasible nitrogen loss pathway and a biological source of nitrous oxide, a potent greenhouse gas that also promotes ozone depletion. Potential denitrifiers from five microbial mats were characterized using a PCR-DGGE (denaturing gradient gel electrophoresis) approach. Molecular markers encoding for key enzymes in the denitrification process (nirK, nirS and nosZ) were used. Fingerprints were obtained for the five sampled mats and compared for two successive years. Distance analysis showed that despite the sampled year, the denitrifying genetic potential was similar between most of the sites when represented in Euclidean space. The number of dominant denitrifiers detected for each sample ranged between 6 and 18 for nirK, 4–10 for nirS and 6–17 for nosZ. The seventy-two sequenced phylotypes showed 80–98 % identity to previously reported environmental sequences from water column, sediments and soil samples. These results suggest that Antarctic microbial mats have a large denitrification potential, previously uncharacterized and composed by both site-specific and common phylotypes belonging mainly to Alpha-, Beta- and Gammaproteobacteria.

Influence of coextrusion die channel height on interfacial instability of low density polyethylene melt flow

The effect of side stream channel height on flow stability in 30° coextrusion geometries was investigated. The studies were conducted on a Dow LD150R low density polyethylene melt using a single extruder to feed a flow cell in which the delivered melt stream was split before, and rejoined after, a divider plate in a slit die. Wave type interfacial instability occurred at critical stream thickness ratios. Reducing the side stream channel height broadened the layer ratio operating range before the onset of interfacial instability, therefore improving process stability. Stress fields were quantified and used to validate principal stress differences of numerically modelled flow. Stress field features promoting interfacial instability in each of the die geometries were identified. Interfacial instability resulted when the stress gradient across the interface was asymmetric and accompanied by a non-monotonic decay in the stress along the interface from its inception.

Pressure Variation during Interfacial Instability in the Coextrusion of Low Density Polyethylene Melts

Abstract Pressure variation during the coextrusion of two low density polyethylene melts was investigated. Melt streams were delivered to a die from two separate extruders to converge in a 30°° geometry to form a two layer extrudate. Melt flow in the confluent region and die land to the die exit was observed through side windows of a visualisation cell. Stream velocity ratio was varied by control of extruder screw speeds. Layer thickness ratios producing wave type interfacial instability were quantified for each melt coextruded on itself and for the combined melts. Stream pressures and screw speeds were monitored and analysed. Wave type interfacial instability was present during the processing of the melts at specific, repeatable, stream layer ratios. Increased melt elasticity appeared to promote this type of instability. Analysis of process data indicates little correlation between perturbations in extruder screw speeds and stream pressures. The analysis did however show covariance between the individual stream pressure perturbations. Interestingly there was significant correlation even when interfacial instability was not present. We conclude that naturally occurring variation in extruder screw speeds do not perturb stream pressures and, more importantly, natural perturbations in stream pressures do not promote interfacial instability.

Assessment of suspended sediment concentration and load from a large Himalayan glacier

An assessment of suspended sediment concentration (SSC), load, yield and erosion rate has been undertaken for the Gangotri Glacier drainage basin (nearly 50% glaciated) located in the Garhwal Himalayas. Data were collected for four ablation seasons (2008–2011). Mean monthly SSCs, for May, June, July, August and September during the study period was 1,011, 1,384, 1,916, 1,675 and 567 ppm, respectively, indicating highest SSC in July, followed by August. For the entire melt season, the mean daily SSC was computed to be 1,320 ppm. Similar trends were also found for the sediment load and about 67% of the total suspended sediment load of the melt period was transported during the months of July and August. Sediment yield for the study basin was computed to be about 2,863 tonnes km–2yr–1. For the entire ablation period, the erosion from the Gangotri Glacier basin is estimated to be about 1.0 mm. There was a poor relationship between SSC and discharge and hysteresis effect was prominent in the melt stream. The average percentages of clay, silt and sand were found to be 3, 67 and 30%, respectively, which suggest maximum content of silt followed by sand.

Role of the Interphase in the Interfacial Flow Stability in Coextrusion of Compatible Multilayered Polymers

This work aims to highlight the importance of interphase triggered from interdiffusion at neighboring layers on controlling the interfacial flow instability of multilayer coextrusion based on a compatible bilayer system consist of poly(methyl methacrylate) (PMMA) and poly(vinylidene fluoride) (PVDF) melt streams. A fundamental rheological measurement on the bilayer structures provides a good strategy to probe the mutual diffusion process occurred at neighboring layers and to quantify the rheology and thickness of the interphase generated thereof. By implementing steady shear measurements on the multilayer’s, subtle interfacial slippage can be observed at a condition of short welding time and rather high shear rate due to the disentanglement of chains at the interphase. Pre-shear at an early stage on the multilayer was found to greatly promote the homogenizing process by inducing branched structures and hence increasing interfacial area. In coextrusion, some key classical decisive parameters concerning the interfacial instability phenomena such as viscosity ratio, thickness ratio and elasticity ratio, etc. were highlighted. These key factors that are significant in controlling the interfacial stability of coextrusion in an incompatible system seem not that important in a compatible system. In comparison to the severe flow instability observed in the coextrusion of PMMA/PE incompatible bilayer, the coextrusion of PMMA/PVDF compatible bilayer appears to be smooth without apparent interfacial flow instability due to the presence of the interphase. Interdiffusion can reduce (even eliminate) the interfacial flow instability of coextrusion despite of the very high viscosity ratio of PVDF versus PMMA at low temperatures. Indeed, in the coextrusion process, on one hand, the interdiffusion should be studied by taking into account of the effect of polymer chain orientation which was demonstrated to decelerate the diffusion coefficient. On the other hand, the interfacial shear stress was able to promote mixing and homogenizing process at the interface, which favours the development of the interphase and guarantees the stable interfacial flow. The degree of the interphase is related to a lot of parameters like contact time, processing temperature, interfacial shear stress and compatibility of the polymers, etc. Therefore, apart from the classical mechanical parameters, the interphase created from the interdiffusion should be taken into consideration as an important factor on determining the interfacial instability phenomena.

Use of free-falling stream of melt for making nanocrystalline magnetically hard Fe – Nd – B materials

A method for hardening from liquid state is developed and used to design and create a commercial prototype facility for supercooling melts of Fe – Nd – B alloys to produce rapidly hardened flakes. Optimum modes for hardening of alloy Fe – 28.5% Nd – 1.4% B – 1% Zr in this facility are developed and rapidly hardened flakes with high magnetic properties are obtained. The phase composition and the structure of the alloy are studied.

Differing source water inputs, moderated by evaporative enrichment, determine the contrasting δ18OCELLULOSE signals in maritime Antarctic moss peat banks

AbstractOxygen isotope palaeoclimate records, preserved in moss tissue cellulose, are complicated by environmental influences on the relationships between source water inputs and evaporative conditions. We carried out stable isotope analyses of precipitation collected from the maritime Antarctic and cellulose extracted from co‐located Chorisodontium aciphyllum dominated moss peat bank deposits accumulated since 1870 A.D. Analyses of stable oxygen and hydrogen isotope composition of summer precipitation on Signy Island (60.7°S, 45.6°W) established a local meteoric water line (LMWL) similar to both the global MWL and other LMWLs, and almost identical to the HadAM3 isotope‐enabled global circulation model output. The oxygen isotopic composition of cellulose (δ18OC) revealed little temporal variation between four moss peat banks on Signy Island since 1870. However, δ18OC followed two patterns with Sites A and D consistently 3‰ enriched relative to δ18OC values from Sites B and C. The growing moss surfaces at Sites A and D are likely to have been hydrated by isotopically heavier summer precipitation, whilst at Sites B and C, the moss banks are regularly saturated by the isotopically depleted snow melt streams. Laboratory experiments revealed that evaporative enrichment of C. aciphyllum moss leaf water by 5‰ occurred rapidly following saturation (ecologically equivalent to post‐rainfall or snow melt periods). In addition to the recognized source water‐cellulose fractionation extent of 27 ± 3‰, such a shift would account for the 32‰ difference measured between δ18O of Signy Island precipitation and cellulose.

Electrospun PLA: PCL composites embedded with unmodified and 3-aminopropyltriethoxysilane (ASP) modified halloysite nanotubes (HNT)

Electrospinning is a simple and versatile fiber synthesis technique in which a high-voltage electric field is applied to a stream of polymer melt or polymer solution, resulting in the formation of continuous micro/nanofibers. Halloysite nanotubes (HNT) have been found to achieve improved structural and mechanical properties when embedded into various polymer matrices. This research work focuses on blending poly(e-caprolactone) (PCL) (9 and 15 wt%/v) and poly(lactic acid) (PLA) (fixed at 8 wt%/v) solutions with HNT at two different concentrations 1 and 2 wt%/v. Both unmodified HNT and HNT modified with 3-aminopropyltriethoxysilane (ASP) were utilized in this study. Fiber properties have been shown to be strongly related to the solution viscosity and electrical conductivity. The addition of HNT increased the solution viscosity, thus resulting in the production of uniform fibers. For both PCL concentrations, the average fiber diameter increased with the increasing of HNT concentration. The average fiber diameters with HNT-ASP were reduced considerably in comparison to those with unmodified HNT when using 15 wt%/v PCL. Slightly better dispersion was obtained for PLA: PCL composites embedded with HNT-ASP compared to unmodified HNT. Furthermore, the addition of HNT-ASP to the polymeric blends resulted in a moderate decrease in the degree of crystallinity, as well as slight reductions of glass transition temperature of PCL, the crystallization temperature and melting temperature of PLA within composite materials. The infrared spectra of composites confirmed the successful embedding of HNT-ASP into PLA: PCL nanofibers relative to unmodified HNT due to the premodification using ASP to reduce the agglomeration behavior. This study provides a new material system that could be potentially used in drug delivery, and may facilitate good control of the drug release process.

Experimental investigation of flow induced molecular weight fractionation phenomenon for two linear HDPE polymer melts having same Mn and Mw but different Mz and Mz+1 average molecular weights

In this work, flow induced molecular weight fractionation for two linear HDPE polymers having the same polydispersity index (Mw/Mn) but different Mz and Mz+1 molecular weight averages, has been experimentally investigated. It has been revealed that first, onset as well as intensity of slip–stick instability and flow induced molecular weight fractionation are in direct relationship, i.e., low molecular weight polymer chains start to fractionate from the main polymer melt stream at the onset of slip–stick flow regime initiating formation of low viscosity layer at the die wall, which leads to its consequent unwanted accumulation at the die lips–die drool phenomenon. Second, due to enhanced melt elasticity (by the presence of long linear chains of linear HDPE polymer), the flow induced molecular weight fractionation is more effective which results in narrow molecular weight distribution of die drool sample containing small amount of long chains. Third, buildup ratio sensitivity to apparent shear rate is the highest in the slip–stick regime and its value increases with increased content of very long chains. Finally, the flow induced molecular weight fractionation takes place only in a very thin layer near the die wall (i.e., within less than 8% of the channel radius for the studied processing conditions and HDPE polymer samples).

Three-dimensional simulation of primary break-up in a close-coupled atomizer

Until now much of the modelling activity around close-coupled gas atomization has been mainly focused on gas-only flow with discrete phase interaction using Lagrangian-based models. However, this approach is unable to supply valuable information regarding the primary break-up mechanism of the melt being injected. Furthermore, much of existing numerical work is based on two-dimensional axisymmetric geometries, and therefore suffers the absence of three-dimensional flow features. In order to overcome these aspects the authors have carried out an analysis using a three-dimensional geometry by means of an Eulerian, Volume of Fluid, model to accurately present the early stages of melt stream behaviour at the atomizer’s melt inlet. The study investigates the mechanisms associated with primary break-up, and the results obtained highlight three modes under which a close-coupled atomizer may operate.

Formation of Metallic Glass Nanowires by Gas Atomization

Gas atomization which is a conventional technique in powder metallurgy is adapted for the formation of metallic glass nanowires. This approach is able to produce a large quantity of nanowires with diameters in the 50-2000 nm range. Experiments performed with different conditions and alloy compositions confirm that the key mechanism of the nanowire formation is the spinnability which increases exponentially when the melt stream is supercooled from the liquid state.