Search Results (34)

The formation mechanism of black streak defects in hot-rolled steel sheets was investigated to address the influence of the process parameters on the surface quality during the production of 304 stainless steels. Macro-/microstructural characterization revealed that the defect regions contained necessary mold slag components (Ca, Si, Al, Mg, Na, K) which originated from the initial stage of solidification in the mold region of the continuous casting process, indicating obvious slag entrapment during continuous casting. On this basis, a three-dimensional coupled finite-element model for the molten steel flow–thermal characteristics was established to evaluate the effects of typical casting parameters using the determination of the critical slag entrapment velocity as the criterion. Numerical simulations demonstrated that the maximum surface velocity improved from 0.29 m/s to 0.37 m/s with a casting speed increasing from 1.0 m/min to 1.2 m/min, which intensified the meniscus turbulence. However, the increase in the port angle and the depth of the submerged entry nozzle (SEN) effectively reduced the maximum surface velocity to 0.238 m/s and 0.243 m/s, respectively, with a simultaneous improvement in the slag–steel interface temperature. Through MATLAB (version 2023b)-based reverse optimization combined with critical velocity analysis, the optimal mold slag properties were determined to be 2800 kg/m³ for the density, 4.756 × 10⁻⁶ m²/s for the kinematic viscosity, and 0.01 N/m for the interfacial tension. This systematic approach provides theoretical guidance for process optimization and slag design enhancement in industrial production. Full article

Final electromagnetic stirring (F-EMS) effectively improves macrosegregation and central porosity in round bloom continuous casting, while the flow and solidification of molten steel under F-EMS have a direct impact on metallurgical properties. Fluid flow and solidification behavior in a 600 mm round bloom continuous casting process with F-EMS were simulated. The influence of the liquid fraction model on strand temperature distribution was investigated. The flow of molten steel was analyzed under both continuous and alternate stirring modes. The results indicated that in continuous stirring mode, the stirring velocity fluctuates between peaks and troughs over a specific period. The closer the F-EMS is to the meniscus, the larger the mushy zone area and the higher the stirring velocity. Due to the 10+ s rise time for current intensity, a 25 s forward and reverse stirring duration is recommended for Φ600 mm round bloom continuous casting with F-EMS. Full article

Herein, a three-dimensional mathematical model was established to investigate the metallurgical behavior of liquid steel in a funnel-shaped mold equipped with single-ruler electromagnetic braking (EMBr). The effects of mold thicknesses, electromagnetic intensity, and casting speed in flow behavior were investigated. The results indicate that with EMBr, multiple pairs of induced current loops are present in the horizontal section of the magnetic pole center, distributed in pairs between the jets and broad faces. The Lorentz force acting on the main jet, which impacts the downward and upward flow at adjacent broad faces, is opposite in direction. Increasing mold thickness results in a larger jet penetration depth, leading to a higher meniscus temperature near the narrow faces accompanied by elevated velocity and turbulent kinetic energy. EMBr can lead to a decrease in shell thickness and an improvement in its uniformity at mold exit. For the thickened mold, as the magnetic flux density increases and the casting speed decreases, the penetration depth of jets and velocity near the narrow faces and meniscus decreases. The shell thickness decreases as the casting speed increases, with the lowest non-uniformity coefficient of 6.78% observed at a casting speed of 5.0 m/min. Full article

In the continuous casting of special steel blooms, low casting speeds result in slow renewal of the molten steel surface in the mold, adversely affecting mold flux melting and liquid slag layer supply, which may lead to surface cracks, slag entrapment, and breakout incidents. To optimize the flow and heat transfer behavior in the mold, a three-dimensional numerical model was developed based on the VOF multiphase flow model, $k-ϵ$ RNG turbulence model, and DPM discrete phase model, employing the finite volume method with SIMPLEC algorithm for solution. The effects of casting speed, argon injection rate, and mold flux properties were systematically investigated. Simulation results demonstrate that when casting speed increases from 0.35 m·min⁻¹ to 0.75 m·min⁻¹, the jet penetration depth increases by 200 mm and meniscus velocity rises by 0.014 m·s⁻¹. Increasing argon flow rate from 0.50 L·min⁻¹ to 1.00 L·min⁻¹ leads to 350 mm deeper bubble penetration, 10 mm reduction in jet penetration depth, 0.002 m·s⁻¹ increase in meniscus velocity, and decreased meniscus temperature due to bubble cooling. When mold flux viscosity increases from 0.2 Pa·s to 0.6 Pa·s, the average liquid slag velocity decreases by 0.006 m·s⁻¹ with a maximum temperature drop of 10 K. Increasing density from 2484 kg·m⁻³ to 2884 kg·m⁻³ results in 0.005 m·s⁻¹ higher slag velocity and average 8 K temperature reduction. Comprehensive analysis indicates that optimal operational parameters are casting speed 0.35–0.45 m·min⁻¹, argon flow ≤ 0.50 L·min⁻¹, mold flux viscosity 0.2–0.4 Pa·s, and density 2484–2684 kg·m⁻³. These conditions ensure more stable flow and heat transfer characteristics, effectively reducing slab defects and improving casting process stability. Full article

Background/Objectives: After anterior cruciate ligament reconstruction (ACLR), a 6-month composite test is recommended during rehabilitation before the return to sport, and the influence of a meniscal tear is not known. The hypothesis was that the location and treatment of meniscus injuries could influence the results of the composite test. Methods: A retrospective single-center study was carried out of prospectively collected data involving 504 patients who performed a composite test 6 months after ACLR. Isolated ACLR was compared to ACLR with medial meniscus injuries (MM), lateral meniscus injuries (LM), and bimeniscal injuries (BM) using a composite test including a single-leg squat (SLS), a single-leg landing (SLL), a single hop for distance (SHD), a triple hop for distance (THD) and a side-hop test (Side-HT), isokinetic strength tests, and an assessment of the anterior cruciate ligament—return to sport after injury (ACL-RSI). Results: Compared with isolated ACLR, MM injury was associated with a quadricipital deficit at a velocity of 240°/s (14% ± 14% vs. 18% ± 18%, p = 0.02), hamstring deficit at 30°/s (14% ± 18% vs. 18% ± 18%, p = 0.02) and an increase in the hamstring/quadricipital ratio at 240°/s (68% ± 27% vs. 80% ± 67% p = 0.02). Furthermore, ACLR + MM or ML injuries in the operated knee generated an increase in the dynamic valgus frequency detected by the SLS, respectively (40% ± 49% vs. 51% ± 50%, p = 0. 05) and (40% ± 49% vs. 54% ± 50%, p = 0.02). Meniscal repair and meniscectomies showed no differences. Conclusions: These results show that meniscal injuries lead to muscle imbalance for MM injuries and impaired neuromuscular control for MM and LM injuries and suggest that meniscal repairs should be done. Moreover, rehabilitation must be adapted to meniscus injuries. Full article

Based on a physical water model with a scaling factor of 0.5 and a coupled flow–heat transfer–solidification numerical model, this study investigates the influence of the submerged entry nozzle (SEN) depth on the mold surface behavior, slag entrapment, internal flow field, temperature distribution, and initial solidification behavior in slab casting. The results indicate that when the SEN depth is too shallow (80 mm), the slag layer on the narrow face is thin, leading to slag entrapment. Within a certain range of SEN depths (less than 170 mm), increasing the SEN depth reduces the impact on the mold walls, shortening the “plateau period” of stagnated growth on the narrow face shell. This allows the upper recirculation flow to develop more fully, resulting in an increase in the surface flow velocity and an expansion in the high-temperature region near the meniscus, which promotes uniform slag melting but also heightens the risk of slag entrainment due to shear stress at the liquid surface (with 110 mm being the most stable condition). As the SEN depth continues to increase, the surface flow velocity gradually decreases, and the maximum fluctuation in the liquid surface diminishes, while the full development of the upper recirculation zone leads to a higher and more uniform meniscus temperature. This suggests that in practical production, it is advisable to avoid this critical SEN depth. Instead, the immersion depth should be controlled at a slightly shallower position (around 110 mm) or a deeper position (around 190 mm). Full article

To achieve uniform cooling and effective homogenization control in ultra-large beam-blank molds necessitates the optimization of submerged-entry-nozzle (SEN) structures. This study employed computational fluid dynamic (CFD) modeling to investigate the impact of two-port and three-port SEN configurations on fluid flow characteristics, free-surface velocities, temperature fields, and solidification behaviors. Subsequently, integrating numerical simulations with the non-dominated sorting genetic algorithm II (NSGA-II) and metallurgical quality-control expertise facilitated the multi-objective optimization of a three-port SEN structure suitable for beam-blank molds. The optimized parameters enabled the three-port SEN to deliver molten steel to the meniscus at an appropriate velocity while mitigating harmful effects such as SEN port backflow, excessive surface temperature differences, and shell thickness reduction due to fluid flow. The results indicated that the three-port SEN enhanced the molten-steel flow pattern and mitigated localized shell thinning compared with the two-port SEN. Additionally, the optimized design (op2) of the three-port SEN exhibited reduced boundary layer separation and superior fluid dynamics performance over the initial three-port SEN configuration. Full article

Background/Objective: The effects of concomitant meniscal tears and their associated treatment on strength, lower extremity balance, and functional status after anterior cruciate ligament reconstruction (ACLR) have not been widely investigated. This study aimed to compare the functional outcomes in patients who underwent ACLR with concomitant treatment of the medial meniscus repair versus meniscectomy when returning to unrestricted physical activity. Methods: A total of 85 patients who underwent primary ACLR with combined meniscal repair (MREP; n = 39) or meniscectomy (MRES; n = 46) were assessed. The dataset included the Functional Movement Screen^TM (FMS) outcomes and single-leg balance test (SLBT) with anterior–posterior, medial–lateral, and overall stability indexes. Isokinetic knee extension and flexion strengths were tested at velocities of 60 deg·s⁻¹ and 180 deg·s⁻¹. The peak torque-to-body weight ratio (PT/BW) and limb symmetry index (LSI) were calculated. Results: In the functional assessment, there was no significant inter-group difference in the composite score of the FMS (MREP: 15.08 pts vs. MRES: 15.13 pts; p > 0.05). The SLBT outcomes in inter-group and inter-extremity comparisons were irrelevant (p > 0.05), too. Significant differences emerged in the inter-group comparison of the knee extension strength in the non-operated extremity at both 60 deg·s⁻¹ and 180 deg·s⁻¹ (p = 0.02). Inter-extremity differences were significant in both the MREP and MRES groups for knee extension and flexion at both angular velocities (all p values < 0.05). For knee extension, the LSI values ranged from 82% to 87%, and for flexion, from 77% to 84%, with no significant inter-group differences. Conclusions: Patients undergoing ACLR with concomitant meniscal repair or resection did not exhibit differences in isokinetic muscle strength, lower extremity balance, and functional tests upon returning to activity. However, participants in both groups demonstrated significant differences between the operated and non-operated extremities as far as the knee joint extensor and flexor strengths are concerned. Therefore, rehabilitation protocols should prioritize equalizing inter-extremity strength differences after the ACLR with additional treatment procedures addressing the menisci. Full article

In this paper, the fluid flow, slag entrainment and solidification process in a slab mold were studied using physical modeling and numerical simulation. The effect of two types of submerged entry nozzles (SENs) was also studied. The results showed that the surface velocity for type A SEN was larger than that using type B SEN. For type A SEN, the maximum surface velocity was 0.63 m/s and 0.56 m/s, and it was 0.20 m/s and 0.18 m/s for type B SEN. The larger shear effect on the top surface made the slag at narrow face impacted to the vicinity of 1/4 wide face, while the slag layer at the top surface was relatively stable for type B SEN. Increasing the immersion depth of SEN decreased the surface velocity and slag entrainment. For type A SEN, the thickness of the solidified shell at the narrow face of the mold outlet was thin (12.3 mm) and there was a risk of breakout. For type B SEN, the liquid steel with high temperature would flow to the meniscus and it was beneficial to the melting of the mold flux. The thickness of the solidified shell at the narrow face of the mold outlet was increased. Furthermore, the surface velocity was also increased and it was not recommended for high casting speed. Full article

This paper presents a numerical simulation of the steel grade transition from the ladle nozzle to the solidification end of the bloom. The simulation is based on models encompassing fluid flow, solidification, heat transfer, an electromagnetic field, and solute transport. To validate the accuracy of the steel grade transition model, transition blooms of high-carbon steel are sampled. Subsequently, the model is applied to investigating the steel grade transition between medium-carbon steel and low-carbon steel. The findings indicate that the regions exhibiting significant differences between their molten steel flow velocity and bloom casting speed in the strand model are primarily concentrated within 1 m below the meniscus. Additionally, the mushy zone in the strand model possesses a substantial volume. Solute elements continuously permeate the liquid phase from the solid phase through the mushy zone. Consequently, the distribution of solute elements in the transition bloom is primarily influenced by the molten steel flow in the tundish and macro-segregation in the casting process. The segregation degree of each solute element varies among grades with different carbon contents. In the austenite phase, the segregation degree of each element follows the order C > Si > Mo > Mn > Cr > Ni, while in the ferrite phase, the segregation degree is ordered as C > Si = Mn. Considering macro-segregation, the transition bloom partition model proves to be more stringent than the original partition method. This results in longer transition blooms when a significant difference exists between the new and old grades. For example, in Scheme 1, the original plan transition bloom length is 8.88 m, whereas the new plan transition bloom length is 10.88 m. Similarly, in Scheme 2, the original plan transition bloom length is 34.64 m, and the new plan transition bloom length is 35.16 m. Conversely, shorter partition intervals occur when there is an overlap in the composition of the new and old grades. In Scheme 3, the original plan partition interval for the new and old grades is 4.08 m, while the new plan partition interval is reduced to 0.94 m. Full article

Punctal occlusion (PO) is considered to improve both tear-film instability and increased friction during blinking and may consequently affect blinks. The purpose of this study was to investigate the effect of PO on blinks. This study involved 16 eyes of 16 severe aqueous deficient dry eye (ADDE) patients (mean age: 65.7 years). In all eyes, tear meniscus radius (TMR), spread grade (SG) of the tear-film lipid layer (i.e., SG 1-5: 1 being the best), fluorescein break-up time (FBUT), corneal epithelial damage score (CED), conjunctival epithelial damage score, corneal filament (CF) grade, lid-wiper epitheliopathy (LWE) grade, and superior limbic keratoconjunctivitis (SLK) grade were evaluated at before and at more than 1-month after PO. Moreover, using a custom-made high-speed blink analyzer, palpebral aperture height, blink rate, upper-eyelid closing-phase amplitude/duration/maximum velocity, and upper-eyelid opening-phase amplitude/duration/maximum velocity were measured at the same time point. After PO, TMR, SG, FBUT, CED, and the CF, LWE, and SLK grades were significantly improved, and upper-eyelid opening/closing-phase amplitude and maximum velocity significantly increased (all p < 0.04). The findings of this study suggest that PO improves ocular surface lubrication and that blink-related parameters can reflect the friction that occurs during blinking in eyes with severe ADDE. Full article

Steel is mainly produced through continuous casting; molten steel flows into the mold from the tundish, where it cools and then enters the secondary cooling zone, ultimately solidifying into a billet. During the continuous casting production process, the quality of the casting billet is mainly related to the lubrication state of the coated slag. In the upper part of the mold, the consumption of liquid protective slag directly affects the friction state of the initial solidified billet shell. Therefore, the flow and fluctuation characteristics of coated slag in the meniscus area are very important. There is limited research on the flow and fluctuation characteristics of coated slag in the meniscus area, and little consideration has been given to the shape of the meniscus. In this work, a two-dimensional numerical model for the flow and fluctuation of coated slag in the meniscus region was established, and the transient flow velocity of protective slag and molten steel at each moment of the vibration cycle was obtained, as well as the fluctuation of the slag/steel interface in the meniscus region. The results show that when the surface mold vibrated upwards, the protective slag in the meniscus area flowed clockwise. When the mold moved downwards, the protective slag in the slag pool generated a counterclockwise flow vortex. When the mold was in a positive slip state, the negative pressure formed by the upward flow of the protective slag on the meniscus and the inertia force of steel liquid pushed the meniscus toward the inner wall of the mold. During negative slip, the flow of coated slag generated positive pressure on the slag/steel interface, pushing the meniscus toward the steel liquid, and at the initial moment of negative slip, the steel liquid overflowed into the slag channel. This model could provide a theoretical basis for the flow control of protective slag. Full article

A metallic wire mesh screen, wire diameter of approximately 50 μm, is folded into ~80 “accordion-shaped” mini-channels and placed inside the evaporator package of a novel passive thermal management device for cooling overhead light-emitting diodes (LEDs) used in factory floors and high-bay facilities. The thermal power dissipated via these devices ranges between 75 W and 171 W. The channel walls (screen) wick liquid water from the porous wick (located centrally above the screen) and facilitate its evaporation. The closed-loop tests on this device confirm that the two-phase mixture quality exiting the evaporator is approximately 0.2. This paper presents a steady-state numerical model of this separated liquid–vapor flow in a single mini-rectangular channel (900 μm × 2000 μm, 4 cm long) with wire mesh-screen walls. The primary objective of the model is to estimate the pressure drops occurring in this two-phase flow. The model initially assumes a flat liquid–vapor interface along the channel and uses an iterative approach to estimate its final meniscus shape (curvature). In addition to the temperature distribution along the screen walls, this paper also discusses the velocity and pressure distributions in both liquid and vapor regions. It also helps understand the liquid–vapor interfacial shear in this flow configuration and proposes a flow-limiting condition for the device by predicting flow reversal in the channel. Full article

In this paper, a fully coupled large eddy simulation model, including the volume of fluid model, the discrete phase model, the bubble-collision model, and the bubble-breakup model was used to simulate the spatial distribution of multi-size bubbles and its impact on the instantaneous two-phase flow in a slab continuous-casting mold. The influence of the bubble-interaction model on the bubbles’ three-dimensional spatial distribution and size distribution, as well as on two-phase flow was discussed. By comparison with the velocity on the meniscus and the average bubble diameter inside a continuous-casting slab water model, the appropriate numerical model was recommended to accurately simulate the two-phase flow and characteristics of discrete bubbles. The submerged entry nozzle and the area around it saw bubble coalescence and breakage more frequently than other areas. The key interaction between the bubbles was their bouncing in the deep region of the mold. In the mold, the average bubble diameter was 0.741 mm, and 44.5% of the total number of bubbles had an approximately average diameter. Full article

To optimize the submerged entry nozzle (SEN) for an ultra-thick slab mold, a mathematical model has been established. The molten steel flow and solidification, inclusion transports, and meniscus fluctuation have been investigated through the model. Compared with the concave-bottom SEN cases, the convex-bottom SEN decreases the imping depth of the jet flow and increases the horizontal velocity and temperature on the meniscus. However, the remelting of the solidified shell is dramatic for the convex-bottom case. The well depth of the concave-bottom SEN and the SEN’s submerged depth have little influence on molten steel flow and solidification. The effects of SEN port shape and port angle on the molten steel flow are significant. As the port shape changes from rectangle to square or the port downward angle decreases, the imping depth of jet flow decreases, the horizontal velocity and the temperature on the mold free surface increase. For the ultra-thick mold, a square-shaped-port SEN with a −10° downward angle is more beneficial by comprehensive consideration of molten steel flow and solidification, inclusion removal, and mold powder melting. The optimized SEN has been applied to the actual caster and its performance has been assessed, indicating that the SEN optimization is efficient. Full article