Mold Wall Research Articles

Electromagnetic Stirring and Joule Heating in Continuous Casting Mold

"It has been developed a 3-D transient model of in-mold electromagnetic stirring in a continuous casting mold. The magnetohydrodynamics model was used to couple the time-varying electromagnetic field with fluid flow, and the solidification of liquid steel was analyzed using the enthalpy-porosity technique. The fluid flow was modelled with turbulence using a realizable k-ε turbulence model. The effect of Joule heat in steel at different frequencies of the electromagnetic stirrer has been predicted using Joule heating caused by induced current inside the mold. Preliminary research indicates that electromagnetic stirring retards the initial start of solid shell formation at the mold wall and transforms the liquid core present at the strand's center into the mush of the liquid-solid interface. Joule heating is observed to be limited in the stirring zone, with a maximum value observed close to the mold wall. The total Joule heat in the strand is found to be less than 1% of the total heat loss from the strand during the solidification process. An increase in frequency though increases the Joule heat in the strand, it is found to be dominant near the wall in the stirrer zone. The liquid core present above the stirrer position is found to expand marginally along the horizontal direction because of Joule heating.

Controlling the Thermal and Rheological Properties of Silicate Glasses for Development of Advanced Mold Flux Systems

Development of the advanced mold flux is always mandatory to enhance both the quality and productivity of continuous casting of steels. Especially, the increasing demands for high alloy steels production and high speed casting reveals serious contradiction between two principal functions of mold flux: lubrication and controlling heat transfer. In order to overcome this problematic needs, some innovative research activities are being carried out. MAE (Mixed Alkali Effect) has been examined in alumino-borosilicate-based mold system to stabilize alkali cation and aluminum association, which enables chemically stable glassy mold flux film during casting of high alloy steels. Non-Newtonian mold fluxes could be developed by addition of Si3N4 or SiC due to the increase of stiffness of polymeric structure, which would be beneficial to satisfy the contradictory requirements of viscosity at mold top surface and mold wall. Some innovative ideas for controlling mold heat transfer without deteriorating the lubrication have been examined by dispersion of nano-size metallic particles and by modification of prenucleation motif. All these trials are closely related with glass science and engineering. Therefore, it should be highly beneficial to enhance the collaborative research activities between glass and metallurgy society for further development of advanced functional mold flux systems.

Optimization of catheter's implementation in the mold, in the case of vaginal HDR brachytherapy treatment.

BackgroundThe purpose of this study was to evaluate and compare results obtained in high dose rate (HDR) brachytherapy treatment of vaginal cancer. Different catheters distributions inside the custom mold were explored. The difference between those distributions is the position of the posterior catheter located near the rectum in the actual custom mold applicator used in different hospitals, each one having a catheter displacement of 0.5 which is equal to the length of a step position. The best catheters distribution offering an optimal dose distribution: better coverage of the clinical target volume (CTV), while reducing the dose received by organs at risk (OARs), were discussed.Materials and methodsA group of 60 patients treated with HDR brachytherapy, alone or in combination with external radiotherapy, was investigated. A custom mold is normally used for HDR brachytherapy vaginal cancer treatment. Three different geometrical positions of the catheters (G1, G2 and G3) and, consequently, 3 different dosimetries were simulated out for each patient on the CT images, using the Oncentra planning system. The coverage of the CTV was studied.ResultsThe average volume treated was 30.46 cc (min = 9.8 cc, max = 70.86 cc). The total prescribed dose, including external and internal radiotherapy, was 80 Gy. We evaluated conformity index (CI), dose homogeneity index (DHI) and conformality index (COIN) indices for the three implantation geometries to reach the same coverage criteria of the CTV. The D2cc parameter allowed the evaluation of the dose received by the OARs. For the rectum, a dose reduction of 9.67% (range 0.29–32.86) was obtained with the second geometry of implantation compared to 10.14% (range 1.43–28.33) with the third geometry. For the bladder, the second geometry of implantation showed a better preservation for this organ [15.93% (range 0.86–58.71) vs. 8.35% (range 0.33–30.43) with the third geometry]. The sigmoid was more protected using the second plan of implantation as well [6.33% (range 0.14–40.71) for the second implantation compared to 5.95% (range 0.33–36) for the third implantation].ConclusionsG2 and G3 catheters’ distribution, having catheter position farther from the mold wall and so from the vaginal wall compared to the catheter position applied showed a better protection for the OARs while giving the same prescribed dose for the CTV.

The Microstructure Formation in Slag Solidification at Continuous Casting Mold

The microstructure of slag film solidified on the inner wall of mold in continuous casting of low carbon steel has been examined experimentally and analyzed theoretically. A puzzle for the crystallization sequence has been solved by this work, which is useful to guide the modification of slag microstructure in efficient casting of advanced steels. The experiments observed three crystalline bands, each containing an initial block-shaped crystal sub-band and late-developed dendrite sub-band. The grain size and morphology change monotonically across the crystalline layers to form a gradient structure. The reason for this is that the solute segregation causes considerable surging of viscosity and constitutional undercooling in the liquid phase. This is rarely seen in the casting of alloys and have not been pointed out previously in the casting of oxide mixtures.

Annealing-induced phase transitions in a Zr–Ti–Nb–Cu–Ni–Al bulk metallic glass matrix composite containing quasicrystalline precipitates

Abstract The phase formation of a copper-mold-cast Zr60Ti2Nb6Cu14 Ni9Al9 alloy has been investigated upon cooling from the melt as well as upon annealing of as-cast specimens. The different states of the samples are characterized by X-ray diffraction, optical and electron microscopy, and differential scanning calorimetry. The cooling rate as realized upon copper-mold casting leads to micrometer-sized quasicrystals, which are embedded in a glassy phase. The thermal stability ΔTx of the supercooled liquid state of the glassy phase that forms near to the wall of the copper mold, differs from that of the glassy matrix in the center of the rod due to different compositions of the glassy phase. This is a consequence of the change in local cooling conditions, which affects the phase formation upon solidification as well as the subsequent transformation behavior of the alloy upon constant-rate heating.

Отсекающий УФ-светофильтр для предотвращения отрицательного наклона стенок мастер-штампа мягкой литографии

The general-purpose polymers formation issues are solved using micro- and nanoelectronic technologies of new generation, for example a nanoimprint lithography. One of its subspecies, soft lithography, includes topology formation using soft master die fabricated by hard mold imprint. Therefore, engineering study of possibility of hard molds self-dependent fabrication for the purposes of optoelectronic data bus formation for new generation printed circuit boards using general-purpose polymer materials is a priority. In this work, to rationalize the purchasing cost of an expensive hard mold of soft lithography, an original technological process for a hard mold fabrication based on the SU-8 photoresist has been developed and implemented. During the performing of the proposed technological process, the reason for the negative slope (T-topping) formation of soft lithography hard mold walls made of SU-8 photoresist was determined. A series of cut-off UV filters for optical wavelengths less than 350 nm has been developed and fabricated to eliminate T-topping. Based on the UV radiation intensity experimental measurements data from the i-line mercury lamp of the automated alignment and exposure system EVG620 NT, the UV radiation intensity attenuation dependences on the functional layer thickness of the developed optical UV filter for 365 and 400 nm wavelengths are plotted. The developed UV filters application effectiveness has been proven due to T-topping elimination during the technological process of producing the soft lithography hard mold test topology. The use of soft lithography will make it possible in the future to create a new generation printed circuit boards with a built-in optoelectronic data bus in the form of a polymer planar optical waveguides array and optical input / output elements.

Experimental investigation on influence of mould wall thickness and hardness on green sand mould permeability

The green compression strength, mould permeability and hardness are the three important properties of the green sand mould. These mould properties are influenced by the sand type, sand grain size, grain shape, clay type, water content, ramming and mould wall thickness. The poor mould permeability and hardness value result in gas related casting defect and poor casting surface finish. Hence in this work, to predict the green sand mould permeability, the exponential models are developed for mould permeability, mould wall thickness and mould hardness value. The mould specimens of 50 mm diameter, 30/40//50/60/70 mm thickness with the hardness value of 87, 90 & 93 are prepared from the moulding sand. The permeability and hardness tests are carried out in the prepared specimens. Using these test results, graphs are plotted between the permeability and mould wall thickness for 87, 90 and 93 hardness values. The exponential model for each hardness value is developed to predict the permeability value for the different mould wall thicknesses.

Aluminum metal composites primed by fused deposition modeling-assisted investment casting: Hardness, surface, wear, and dimensional properties

Fused deposition modeling -based three-dimensional printing techniques, when merged with the investment casting process, is one of the most innovative techniques for developing functionally graded metal–matrix composites in high-performance industrial applications. In this study, Al–Al2O3 matrix composites have been prepared by the combined route of fused deposition modeling and modified investment casting processes. In the first step, the Al–Al2O3 particles have been reinforced into nylon 6 thermoplastics for the preparation of fused deposition modeling-based feedstock filaments (in two configurations: C1 (60% nylon 6–30% Al–10% Al2O3) and C2 (60% nylon 6–28% Al–12% Al2O3). In the next step, the investment casting patterns of the fused deposition modeling process of nylon 6–Al–Al2O3 composites were prepared. Furthermore, the investment casting has been performed by controlling the proportion of nylon 6–Al–Al2O3, the volume of pattern, the density of pattern, barrel finishing media weight, barrel fining time, and number of mold wall layers considering Taguchi L18-based experimental design. Finally, the functional aluminum matrix composites were subjected to testing to investigate average surface roughness ( Ra), deviation inside the cube, average wear, and average hardness. The study results have suggested that maintaining a higher proportion of Al2O3 in three-dimensional printed parts leads to higher Ra, higher dimensional deviation, and higher hardness of investment cast parts. On the contrary, solid patterns have provided low wear rates and low-density patterns resulting in increased wear rates in final investment casted products. Furthermore, the responses are optimized concurrently with the “technique for order of preference by similarity to ideal solution–Taguchi” technique while considering the analytical hierarchical process and entropy weights of significance.

Rotomoulding release agent preparation for auto part fabrications

As it produces parts with intricate details and finishes, minimal waste, few stress points, and excellent wall thickness uniformity, rotational moulding is one of the commercial shaping processes for manufacturing polymeric automotive parts. Use of a mould release agent is critical for a demoulding approach in rotational moulding, and the main requirement for typical use of a mould release agent is suitability in work environments at very high temperatures (>200 °C). Surprisingly, Thailand has approximately 2000 mould manufacturers, which can be attributed to the high demand for mould release agents; however, a vast majority of release agents are imported from abroad. This research aims to formulate the semi-permanent water-based release agents for shaping engineering plastics via a rotational moulding process. The main functions of the produced release agent include allowing the resin to become attached to the mould wall during the initial heating phase of the moulding cycle, ensuring that the fully molten skin of the rotomoulded part remains in close contact with the mould wall throughout the heating cycle. The rotomoulded part must remain in close contact with the mould wall during the initial part of the cooling cycle until the part has enough cohesion within its structure to resist collapse when the release process begins. The release agent used to aid in the quick release of rotomoulded parts while minimizing surface abrasion damage. First, chemical characterizations were performed using Fourier-transform infrared spectroscopy. Next, processability, surface characteristic, thermal stability, adhesion performance, and rheological characteristic were observed via Fourier-transform infrared spectroscopy, contact angle, thermogravimetric analysis, differential scanning calorimetry, adhesion tester, and rheometer, respectively, to inspect the possibility of using the produced release agents for a rotational moulding process. Experimental results confirm successful formulated rotomoulding release agent, however; the repetition of using a release agent needs further improvements for cost reduction.

An approach to accelerate the convergence of SIMPLER algorithm for convection-diffusion problems of fluid flow with heat transfer and phase change

A new segregated pressure-based algorithm is developed to solve two-dimensional incompressible fluid flows with convective heat transfer and liquid to solid phase change by the finite volume method. The predictive-correction scheme is based on the SIMPLER algorithm with n added iterative cycles to increase the accuracy of pressure in satisfying the discretized continuity equation. The performance of SIMPLERnP is compared with SIMPLER and IDEAL in the solution of the laminar fluid flow in a lid driven cavity, natural heat convection inside a square cavity, convective heat transfer in the annular space between two concentric cylinders and conjugate natural heat convective solidification of a binary alloy that included the transient heat conduction in the thick mold walls. The results indicate that the proposed algorithm is highly stable, even when a value of 0.99 is used for the under-relaxation of the velocity components, and allows significant improvements in the reduction of the number of iterations and time of computation.

Evolution of solidification structure, primary phase and wear properties of Sn–11wt%Sb alloy ingots under permanent magnet stirring

ABSTRACT An experimental investigation has been conducted with respect to the influence of permanent magnet stirring (PMS) under different rotation speeds (0, 60, 120, 180 rpm) on the evolution of solidification structure, primary Sn4Sb3 phase and wear properties of Sn–11wt%Sb alloy. The results revealed a significant increase in the flow intensity of the liquid, improvement in the grain and eutectic microstructure refinement, and decrease of solidification cavities with increasing rotation speed. Besides, when the rotation speed increased from 0 to 180 rpm, the difference in the area proportion of the Sn4Sb3 phase between upper and lower parts of the alloy ingots decreased from 17.05% to 0.41%, resulting in a more uniformly distributed primary phase along the longitudinal direction. In addition, with enhanced stirring intensity, a primary phase-rich layer was formed at the surface of the ingot close to the mould wall, and the average equivalent diameters of the primary phase were increased. Moreover, tribological test results suggested that magnetic stirring could improve the wear resistance of the alloy by decreasing the friction coefficient from 0.77 to 0.72 and reducing the width of the worn surface from 1.51 to 0.81 mm due to the PMS-driven uniform distribution of the reinforcing primary phase.

The Computational Fluid Dynamics Investigation on the Solidification of Aluminum Cast in Moulds with Different Thickness and the Influence of the Moderate Press

The influence of applying an external distributed pressure along the upper surface of the molten metal (Aluminum ) during the solidification process on the temperature reduction profile was studied including the time of solidification of the cast and the phase change moving boundary location for two mould wall thicknesses (10mm and 15mm). A 3D model was built up by Solidworks and simulated by ANSYS FLUENT; each mould wall thickness was discussed for two press cases (1bar and 3bar) sequentially, comparing with no press cases. The discussion includes the ambient temperature effect, which is taken (300K then 310K), the overall cases that studied was 7 cases. The study shows a remarkable effect of press on the temperature reduction profile especially when mix with the mould thickness effect as well as the ambient temperature which has a great order in guiding the results. The results showed that the heat reduction increases by increasing the mould thickness as well as the applied pressure. Moreover, this effect will reduce the solidification time and the moving of the boundary of phase change become faster in appearance.

Experimental determination of the shell thickness within the primary cooling zone in the continuous casting process

ABSTRACT The correct thickness of the shell solidifying within the primary cooling zone of the continuous casting machine is among the most important parameters assuring the safe operation of the casting process. The main problem is related to the fact that the actual measurement of the thickness of steel solidifying in the mould is impossible. Available continuous casting process monitoring systems allow us to calculate its approximate value on the basis of the mould wall temperature reading, and often these systems ensure failure-free steel casting. In this paper, the authors show the results of long-term research carried out when assessing anomalies occurring during the steel continuous casting process. As a result of this research, shell thickness was measured experimentally. On the basis of experimental data, a new model was proposed to describe heat transfer in the primary cooling zone.

Effects of wall compliance and light-curing protocol on wall deflection of simulated cavities in bulk-fill composite restoration

Background/purposeCuspal deflections in composite restoration have been investigated with considering wall compliance of human tooth cavity and light-curing protocol. The purpose of this study was to investigate effects of mold wall compliance and radiant emittance of LED light on the wall deflection of simulated aluminum mold cavities restored with a bulk-fill composite.Materials and methodsSixty aluminum molds simulating a class II mesio-occluso-distal (MOD) cavity (6 W × 8 L × 4 D mm; W, width; L, length; D, Depth) were prepared and allocated to three groups with varying mold wall thicknesses of 1, 2, and 3 mm. The molds were bulk-filled with a bulk-fill composite and photo-cured. Four light-curing protocols were used: three duty ratios/exposure times: 100%/20 s, 50%/40 s, or an increasing mode (0 → 100%)/40 s with a pulse width modulated (PWM) LED curing light and one 20 s exposure time with a commercial LED light.ResultsMean mold wall deflection at 2000 s decreased with increasing mold wall thickness (1, 2, and 3 mm) (p < 0.05). Wall deflections with 1- and 2-mm-thick molds exhibited no statistically significant differences among light-curing protocols (p > 0.05). However, in the 3-mm-thick mold, wall deflections with low radiant emittance were significantly lower than those with high radiant emittance (p < 0.05).ConclusionIn composite restoration of class II MOD cavities, lowering the radiant emittance of LED light can reduce the mold wall deflection only in low compliance cavities.

Application of the stress interaction failure criterion in platelet composite compression molded parts

AbstractThe stress interaction failure criterion was applied to three compression‐molded sheet molding compound (SMC) materials. Two are epoxy‐based compounds with randomly oriented carbon fiber tows, and the third material consists of glass fiber bundles randomly oriented in a vinyl ester resin. The failure surface was built using tensile test results at different orientations with respect to the flow direction, resulting in combined loads in the principal stress coordinate system. Three unknown variables arise from using only tensile strength values. Solving a system of three equations derived from the criterion function and using the failure values obtained from destructively testing at three different orientations, the unknown variables as well as the interaction strength components were determined. Results show good agreement for all three materials. Overprediction was found in some instances, attributed to the effect of fiber orientation distribution in the part, and to the complex interactions of the filled structures. To allow a more direct comparison between predicted and experimental data, the resulting failure surface was translated to the global coordinate system (σxx) and compared to the data derived from destructive tensile tests. Good agreement for all materials was observed, with underprediction noted for some orientations, attributed in part to the equation solving method and the nature of the mesostructures of the composites, where interactions between the tows, resin, mold walls, and fibers are present. The results of this work show that the methodology described permits the development of a failure surface for SMC materials when limited data is available.

Influence of the Submerged Entry Nozzle’s Bottom Well on the Characteristics of Its Exit Jets

In vertical continuous casting machines the liquid steel from the tundish is poured into the mold through the Submerged Entry Nozzle (SEN). The shape and direction of the SEN exit jets affect the liquid steel dynamics inside the mold. This work quantifies the effect of the SEN pool on the principal characteristics of the jets emerging from it, precisely, the shape, the spread angles, and the mold impact point. Experimental and numerical simulations were carried out using a SEN simplified model, a square-shaped bore nozzle with square-shaped outlet ports whose length is minimal. These experiments showed two well-defined behaviors. When a single vortex dominates the hydrodynamics inside the simplified SEN, the exit jets spread out and are misaligned about the mold’s central plane. On the contrary, when the inner flow pattern shows two vortexes, the exit jets are compact and parallel to the mold wide walls. The measured difference on the jet’s falling angles is 5°, approximately, which implies that in an actual casting machine, the impingement point at the narrow mold wall would have a variation of 0.150 m. This hydrodynamic analysis would help design new SENs for continuous casting machines that improve steel quality.

Revealing the mechanisms for the nucleation and formation of equiaxed grains in commercial purity aluminum by fluid-solid coupling induced by a pulsed magnetic field

This study considers the factors controlling the grain structure of commercially pure aluminum when a Pulsed Magnetic Field (PMF) is applied during solidification. It is revealed that PMF of pure metal forms equiaxed grains by different nucleation and growth mechanisms depending on the casting conditions. One mechanism occurs when PMF is applied from above the melting point. On reaching the melting point copious nucleation occurs on the mold walls and these small grains are detached by pulses occurring every 100 milliseconds. Convection due the PMF generated Lorenz force distributes the grains in the melt resulting in a refined equiaxed grain structure throughout the casting. Another mechanism is nucleation of the columnar grains that form a shell on the walls of the mold before PMF is applied and once applied fluid-solid coupling develops due to the Lorenz force. Depending on the shell thickness, this fluid-solid coupling detaches the columnar shell or, for thicker shells, only the top few millimeters of the shell from the mold wall. The detached shell is then fragmented into large blocky grains due to a lower melting point iron-rich liquid phase on the grain boundaries. In this case a bimodal grain structure is produced because the exposed wall generates fine grains as described above filling the gaps between the large blocky grains. The optimal condition for uniform refinement is when PMF is applied from above the melting point ensuring that a refined equiaxed grain structure forms throughout the casting.

Microstructures and Macrosegregation of Al-Zn-Mg-Cu Alloy Billet Prepared by Uniform Direct Chill Casting.

In this study, large-sized Al–Zn–Mg–Cu alloy billets were prepared by direct chill casting imposed with annular electromagnetic stirring and intercooling; a process named uniform direct chill casting. The effects of uniform direct chill casting on grain size and the alloying element distribution of the billets were investigated and compared with those of the normal direct chill casting method. The results show that the microstructures were refined and the homogeneity of the alloying elements distribution was greatly improved by imposing the annular electromagnetic stirring and intercooling. In uniform direct chill casting, explosive nucleation can be triggered, originating from the mold wall and dendrite fragments for grain refinement. The effects of electromagnetic stirring on macrosegregation are discussed with consideration of the centrifugal force that drives the movement of melt from the central part towards the upper-periphery part, which could suppress the macrosegregation of alloying elements. The refined grain can reduce the permeability of the melt in the mushy zone that can restrain macrosegregation.

Influence of local convective heat flux on solidification, contraction and wall detachment behavior of molded chocolate during air cooling

The cooling process is an important step during chocolate production. It influences final product quality characteristics such as gloss, texture and melting behavior. Furthermore, it is a high energy consuming operation and its optimization leads to an increase in energy efficiency of the chocolate production. Dark chocolate was cooled in a pilot-scale cooling tunnel with cooling air temperatures of Tair = 2, 12 and 18 °C and air mean velocities of vin = 1.5, 3.5, and 6.0 m s−1. Convective heat transfer coefficients at the top and the bottom of the mold were received from model calculations applying a CFD model. Crystallization and detachment behavior from the mold walls were newly analyzed by measuring the damping characteristics of ultrasound waves transferring the filled molds during cooling. In addition, for this-like treated well-tempered dark chocolate, the crystallization and detachment behavior were analyzed in further detail. The convective heat transfer from the bottom of the mold increases in flow direction due to the existence of a typical mold geometry-dependent recirculating zone of the cooling air below the chocolate mold and also dependent on the local air velocity. It was shown that depending on intensity and homogeneity of the heat transfer in the air-cooling phase, the structure density of the chocolate can be increased which has a positive impact on resulting product quality characteristics. Moreover, the detachment of the chocolate from the mold wall was demonstrated to have an optimum for typical chocolate plate formats with 125 g weight at an apparent heat flux of 550 W/m2, for which the time until detachment reaches a minimum.

Numerical modeling of copper macro-segregation in the binary alloy Al-4Cu

In this paper, the modeling of the solidification of Al-4Cu alloy was studied. The calculation code is developed to model the equiaxed globular solidification of the Al-4Cu alloy in a square mold. The mold walls are subjected to constant temperatures and the velocity components are equal to 0, the exchange coefficient ’H’ between the interface of the melt and the mold is estimated at 500 W/( m2 K) and the initial melt temperature ’T0’ is equal to 900 K. The resolution method used is finite differences, the upwind scheme for convective terms, and the space-centered scheme for diffusive terms. The calculated profiles are temperature, solid fraction, concentration and macro-segregation of copper. At the beginning of cooling, the solidification of the Al-4Cu alloy started in the four corners of the plate. The grains formed at the walls could not move in the studied surface. With cooling time, the solidification of the casting developed rapidly in the lower part; because, the grains formed away from the walls sedimented and accumulated in this part of the plate. On other hand, the liquid was located mainly in the upper part. The segregation of copper in the two-phase mixture is due to its continuous rejection from the solid to the liquid.