High-speed Casting Research Articles

Specific features of glass applied for high-speed micrometallurgical casting of microwires

The present paper provides a justification for the selection of the basic composition of the system SiO2–B2O3–MgO–BaO–Na2O–K2O; its additional alloying with such elements as oxides PbO, Na2O + K2O, ZrO2 and TiO2 alters the main characteristics of glass tubes for casting microwires. The proposed glass compositions vary significantly the range of metals and alloys used to produce cast microwires in glass insulation.

Development of EMBr/EMS Multifunction Mold

EMBr (ElectroMagnetic Brake) and in-mold EMS (ElectroMagnetic Stirring) have been developed to control molten steel flow in a continuous casting mold. EMBr is able to stabilize the molten flow in the mold. EMBr is usually used to prevent breakout during high speed casting of medium carbon steel. In-mold EMS is effectively to improve surface quality of the cast such as interstitial free steel by forced flow of the molten steel in front of initially solidifying shell. Suitable molten flow pattern in the mold is depends on its casting condition and components. However, ordinary electromagnetic device has only one function of EMBr or EMS, so a multifunction device which can be selected EMBr or EMS in the mold is desirable. It is difficult to obtain sufficient performance both EMBr and EMS in only one electromagnetic device because the necessary structure of them is different. EMBr needs to generate large magnetic flux density by large teeth of iron core. A lot of small teeth are necessary for EMS to generate travelling magnetic field along the mold side uniformly. The structure and current applied method of the EMBr/EMS multifunction mold has been developed by numerical analysis of electromagnetic field and fluid flow dynamics. The EMBr/EMS multifunction mold has been applied to Kashima No.3 CC.

Numerical Simulation of Turbulent Steel Cem® Mold Under High Mass Flow Condition

The POSCO has invented one of the most innovated steel manufacturing process called CEM® (Compact Endless casting & rolling Mill) which can continuously produce coils without cutting before the finishing mill. In this high throughput process between the casting and rolling processses, a material balance is essential. World-class throughput of CEM® has been achieved with high-speed casting technology (up to 8.0 m/min) and increased slab thickness (up to 100 mm). Many new advanced technologies are required to do this. For instance, instability of the meniscus in the mold is one of the important factors to be solved. Electro Magnetic Braking (EMBr) system has come into the spotlight to control mold surface profile and level fluctuations. Therefore, an accurate evaluation and improvement of EMBr is required. In this work, a numerical and experimental study was carried out to investigate high throughput conditions, to prepare for the next generation of CEM®. In order to effectively stabilize mold flow near the meniscus, a new SEN was designed, combined with a U-shaped EMBr invented by POSCO. The effect of EMBr current on the temperature in the mold is also studied. Numerical results are consistently agreed with plant measurements obtained using nail board tests. Stabilized mold level and temperature are the critical technologies needed to achieve stable casting operation.

The evolution of microstructure and mechanical properties during high-speed direct-chill casting in different Al–Mg2Si in situ composites

The effect of high-speed direct-chill (DC) casting on the microstructure and mechanical properties of Al–Mg2Si in situ composites and AA6061 alloy was investigated. The microstructural evolution of the Al–Mg2Si composites and AA6061 alloy was examined by optical microscopy, field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The results revealed that an increase of the casting speed substantially refined the primary Mg2Si particles (from 28 to 12 μm), the spacing of eutectic Mg2Si (from 3 to 0.5 μm), and the grains of AA6061 alloy (from 102 to 22 μm). The morphology of the eutectic Mg2Si transformed from lamellar to rod-like and fibrous with increasing casting speed. The tensile tests showed that the yield strength, tensile strength, and elongation improved at higher casting speeds because of refinement of the Mg2Si phase and the grains in the Al–Mg2Si composites and the AA6061 alloy. High-speed DC casting is demonstrated to be an effective method to improve the mechanical properties of Al–Mg2Si composites and AA6061 alloy billets.

ОСОБЕННОСТИ СТРУКТУРИРОВАНИЯ ПРИ МАССОВОЙ КРИСТАЛЛИЗАЦИИ РАСПЛАВОВ Al И Pb В УСЛОВИЯХ ВЫСОКОИНТЕНСИВНОЙ ПЛАСТИЧЕСКОЙ ДЕФОРМАЦИИ ПРИ ЦЕНТРИФУГИРОВАНИИ

Представлены экспериментальные результаты по кристаллизации Al и Pb в условиях высокоинтенсивной пластической деформации [e¢ = (102-104) сек-1] на границе раздела «твердое-жидкое» в аппарате центробежного литья нового типа при скоростях вращения ротора до 2000 об/мин. В объёме закристаллизованных металлов Al и Pb методом атомной силовой микроскопии обнаружены вакансионные кластерные трубки со средними диаметрами Al – 39 нм, Pb – 25 нм. Обсуждается физическая модель образования в металлах новой субструктуры в виде вакансионных кластерных трубок, полученных при высокоинтенсивной пластической деформации.

Evaluation of Solidified Shell Thickness by Thermocouple in Mold

High speed continuous casting technology has been developed to improve productivity. The method of real-time calculation of the solidified shell thickness by using multiple thermocouples embedded in the mold copper plates was tested at JFE Steel Kurashiki No.4CCM, and the possibility of detecting various types of breakouts in high-speed casting was demonstrated. The main results are summarized as follows.

Mechanical Properties of Cast Al-Mg5 Alloy Produced by Heated Mold Continuous Casting

To make the high strength and high ductility of the cast aluminum alloys, the Al alloy samples are created by the heated mold continuous casting (HMC) process. Because of the rapid and unidirectional solidification in the HMC process, tiny grains with uniformly orientated crystals are created. In this case, influence of the solidification speed of HMC on the mechanical properties of the Al-Mg-based alloy is studied. The microstructures are altered with the casting speed because of the different solidification rates. The mean secondary dendrite arm spacing (SDAS) for the HMC-Al-Mg alloy made at the high casting speed of 2.7 mm/s is about one-fifth of that for the conventional gravity cast Al-Mg alloy. Nonlinear relationship between the tensile properties (strength and ductility) and the cooling rate are obtained with σ UTS and σ 0.2 increasing and e f decreasing with increasing the cooling rate. The high strength of the HMC samples at the high cooling rate results from the existence of tiny microstructures. The high ductility of the HMC sample at the low cooling rate is affected by the uniform crystal orientation, where shear slips are facilitated by the uniform crystal orientation.

Estimation of surface heat flux in continuous casting mould with limited measurement of temperature

Continuous casting mould is exposed to high heat flux due to its contact with the hot molten metal. The state of heat transfer in a mould and steel solidification depends on the magnitude of the mould boundary heat flux. In the present study, a mathematical model is developed to determine the heat flux across the hot surface of continuous casting mould from limited temperature measurement. The model is based on two-dimensional inverse heat transfer technique that was solved using the conjugate gradient method. Direct problem which involves two-dimensional conduction in the mould is first solved and validated. The inverse problem was tested by using the simulated temperature data obtained from the solution of a direct problem, where good agreement between the actual and estimated boundary heat flux is found. The Gaussian noises are added to the simulated temperatures to mimic the temperature measurement errors for testing anti-noise ability of the inverse problem model. Further, boundary heat flux is also estimated for a continuous casting mould using actually measured plant data. The model is applied to three test cases with temperature data obtained under different operating conditions and the results are analyzed. It has been observed that the proposed methodology results in accurate boundary heat flux estimation. Higher boundary heat flux are obtained for cases with higher casting speed as compared to cases with lower casting speed.

Effects of Process Parameters on Solidification Structure of A390 Aluminum Alloy Hollow Billet

The effects of process parameters on the solidification structure of A390 aluminum alloy hollow billets prepared by direct-chill casting were investigated. The decrease of casting temperature deteriorated the homogeneity and increased the size of primary Si particles in the hollow billet. Although the average size of primary Si particles was not obviously affected by the increase of casting speed, the thickness of Si-depleted layer at the inner wall increased with the higher casting speed. The tensile strength of A390 alloy is a function of the percentage of coarse Si particles (larger than 35 μm) and the average size of primary Si particles. Higher and more stable tensile strength can be received in the hollow billet with the casting temperature of 1050 K (777 °C), because the fine and uniformly distributed primary Si particles were obtained in the hollow billet.

Distribution of macro-inclusions in low carbon aluminium-killed steel slabs

ABSTRACTMacro-inclusions in low carbon, aluminium-killed steel slabs were characterised by step-machining within a 10 mm zone from the slab surface using an ASPEX automatic inclusion analyzer. Dendritic structures within the cross-section of slabs were examined. The results show that alumina clusters and alumina associated with bubbles are the dominant macro-inclusions. Along the slab width direction, macro-inclusions were mostly found at the slab centre because of the deeper hooks and freezing meniscus surrounding the submerged entry nozzle. In terms of slab thickness, inclusions were mainly concentrated within the zone 3.5–6 mm from the top of the slab surface, where the columnar dendrites showed a relatively small inclination angle, indicating small cross-flow velocities at the solidification front. The number density of macro-inclusions were strongly dependent on the washing effect produced by the flow velocity. High speed casting promotes this behaviour and improves the surface quality of the slabs.

Bonding process and interfacial reaction in horizontal twin-roll casting of steel/aluminum clad sheet

Asymmetrical and lower heat transport caused by the cladding strip during twin-roll casting (TRC) of clad sheet makes the process window narrow compared with traditional TRC. The effect of pouring temperature on process stability is more remarkable when it is relatively high under high casting speed and casting speed becomes a leading factor when its value is low. The inter-diffusion zone width at the Al/Fe interface depends on the solid/semi-solid contacting time. The longer the time is, the wider the inter-diffusion zone. A widest zone of 3.8μm is attained under condition of casting speed of 1.25m/min and pouring temperature of 720°C. Bonding strength of clad sheet by TRC depends on inter-diffusion zone width and rolling reduction. Proper combinations of inter-diffusion zone width and rolling reduction can result in same high bonding strength. The highest bonding strength of 16N/mm is attained under a combination of rolling reduction of 29% and inter-diffusion zone of 3.7μm. The wetting of aluminum melt on steel surface is uneven and insufficient as a result of short contacting time in TRC. As a result, same rolling reduction in TRC induces lower bonding strength than in roll bonding process. Bonding strength of clad sheet by TRC decreases when the surface of the steel strip is brushed, as a result of decrement of actual contacting area.

Study of the Life of Replaceable Inserts During High-Speed Steel and Wear-Resistant Cast Iron Machining

Comparative analysis is provided for hard-alloy inserts from different producer firms based on studying their durability during machining mill linings, and also pump wheels and casings.

Understanding mould powders for high-speed casting

The development and application of mould powder for high-speed continuous casting of steel is described. For thin slab casting, the main requirements are proper powder melting, undisturbed slag infiltration, adequate strand lubrication and the control of mould heat transfer. For increased casting speeds i.e. up to 8 m/min, slag infiltration and in particular the control of mould heat transfer via crystallisation of the slag film becomes even more important. It was found that a low powder consumption and hence a thin slag film is no restriction for an undisturbed thin slab casting process. Given a stable casting process and machine condition, the mould powder properties are not as critical as widely assumed.

Microstructural Evolution of Al-Mn Based Alloy Fabricated by Vertical-Type High-Speed Twin-Roll Casting

For decades, twin-roll casting has been applied for manufacturing aluminum alloy sheets. This conventional process contributes to make thin aluminum sheets from the molten metal directly. Recently, vertical-type high-speed twin-roll casting (HSTRC) has been developed with much higher casting speed rather than the horizontal-type. Some modifications such as feeding nozzle and water-cooling system of copper rolls contribute to increase cooling rates. This characteristic leads to many metallurgical advantages like grain refinement, super-saturation of alloying elements and fine distribution of secondary particles. The objective of this study is to investigate the constituent particles in HSTRC aluminum alloy. The commercial Al-Mn alloy strip was successfully fabricated by HSTRC. Clearly different microstructure was found in thickness direction. Many constituent particles observed along the grain boundaries/cell boundaries as well as inside of Al matrix on the surface area, while eutectic structure around globular grain boundaries was observed in mid-central area. The morphology as well as chemical compositions of the constituent particles were investigated.

Large Eddy Simulations of the Effects of EMBr and SEN Submergence Depth on Turbulent Flow in the Mold Region of a Steel Caster

Transient turbulent flow in the mold region during continuous casting of steel is related to many quality problems, such as surface defects and slag entrainment. This work applies an efficient multi-GPU based code, CUFlow, to perform large eddy simulations (LES) of the turbulent flow in a domain that includes the slide gate, SEN, and mold region. The computations were first validated by comparing the predicted surface velocity with plant measurements. Then, seven LES simulations were conducted to study the effects of casting speed, electromagnetic braking (EMBr) field strength, and submerged entry nozzle (SEN) depth on the transient flow. The results show that EMBr has an important influence on flow inside the SEN, in addition to flow in the mold. With EMBr, an “M-shaped” flow profile is seen inside the SEN. The swirling flow behavior in the SEN and ports is more symmetrical at high casting speed and with higher EMBr strength. The position of the SEN ports relative to the peak magnetic field affects the EMBr performance. The results confirm and quantify how applying EMBr greatly lowers both the magnitude and turbulent variations of the surface velocity and level profile.

Estimation of the Heat Stability of Hardened Cr-V Cast Irons

The paper describes the structure, properties and heat stability of white cast irons containing 2.5 – 3.0 %C, 14 and 20 %Cr, 3 %V after the secondary hardness treatment (quenching from 1150 °C and double tempering at 560 °C). It is shown that after the secondary hardness treatment M23C6 carbides appear along with the M7C3 phase. Heat stability of the alloys is estimated according to GOST 19265-73 standard. The effect of the temperature and duration of holding at 520–620 °C on structural changes and softening of secondary hardness treated cast irons is considered in comparison with high-speed steel and cast irons of the same composition quenched for the maximum hardness (from 1050 °C). The processes occurring at higher temperatures and long holdings that are responsible for softening of secondary hardness treated cast irons are studied. It is shown that the alloys under consideration after the secondary hardness treatment achieve the hardness of HRC 60 and more, and are able of pertaining it when heated up to 540 °C for 20 hours. This allows using these alloys as wear-resistant materials in the said temperature range.

A Novel Manufacturing Process to Fabricate Double-Layer Membranes

A new method to fabricate double-layer membranes by using a specially design casting machine is described in this study. This machine is able to produce membranes with a double-layer structure via a single-casting technique with the use of a closed-loop feedback control system. The membrane casting operation is controlled by a programmable logic controller (PLC). Membranes produced from this simplified technique exhibit similar properties as the double-cast membranes, such as a macrovoid free structure and good porosity property. Results show that high casting speed is desired during the membrane fabrication process as the relaxed polymer molecular orientation and low polymer chain entanglement promote vertical swelling, and hence enhance the membrane porosity. Turbulent coagulant flow further improves the membrane porosity due to the high solvent–coagulant exchange rate during the phase inversion process. In summary, this machine simplifies the double-casting technique and produces membrane with similar advantages as the membrane fabricated via a double-casting technique.

The effect of tape casting operational parameters on the quality of adjacently graded ceramic film

For small length tape casting of ceramic slurries varying green film thickness is often a problem. To optimise this, the following parameters were investigated: single blade, double blade, using a pump system and a modelled speed change mode have been analysed. Advantages and limitations of every method are described here. The tape casting experiments were built to be generic in order to allow the control of various processing conditions.From these results, the single-blade technique was chosen for a study of side-by-side tape casting. The influence of the geometric parameters of partitioning the casting tank into chambers, on the quality of graded tape was studied. Tape casting experiments at different speeds and partition tongue lengths in combination with rheological tests revealed that high casting speeds and absence of the partition under the blade are detrimental to the formation of the smooth well-controlled interface between the co-cast slurries, required for most of applications.

Process and Quality Control during High Speed Casting of Low Carbon Conventional Slab

Based on the achievement of 2.5 m/min casting speed on Shougang Jingtang (SGJT) No. 3 slab caster, effect of casting speed on the parameters closely related to the casting conditions was discussed elaborately by plant trial, mathematical simulation and experimental study respectively. The results showed that mold level fluctuation, surface velocity, average heat flux, bulging of broad face, temperature of copper plate, solidification crater end and frictional force entirely increased while the powder consumption rate, subsurface inclusions and depth of hook structure decreased with the increase of casting speed. As a consequence, flow control mold (FC mold) was more significant to control the mold level than submerged entry nozzle (SEN) and powder B was more appropriate for high speed casting than powder A. And further, it is highly recommended that high speed casting should be considered as a potential application to improve the surface quality of cold coils.

Influence of the viscosity of self-compacting concrete and the presence of rebars on the formwork pressure while filling bottom-up

Self-compacting concrete (SCC) enables new casting techniques, filling formworks by pumping bottom-up. However, fundamental questions remain concerning the formwork pressure when following this advanced filling procedure. A new series of formwork filling tests, with SCC being pumped from the base of the formwork, have been performed in 2012 at the Magnel Laboratory for Concrete Research of the Ghent University (MLCR). Numerical simulations of these formwork filling tests have also been carried out for validation with the experiments. For the filling process of eight casts in total, the influence of several filling parameters on the resulting formwork pressures were tested, like the casting speed, the presence of steel rebars (leading to a reduction of the flow section inside a formwork) and the rheology of the SCC. The formwork pressures were measured at three different positions on the formwork wall with accurate electronic pressure sensors. These measured formwork pressures were finally compared with the computed formwork pressures. Both the experiments and the simulations performed in this study showed a very good agreement and they revealed that the formwork pressures during the filling tests were higher than the hydrostatic pressure for SCC pumped from the base of the formworks. This was due to the additional occurring hydraulic losses. In our experiments, these additional flow losses represented 7% up to 16% of the total wall pressure for the performed filling tests with steel rebars, depending on the viscosity of the SCC and the casting speed. An analytical calculation model for the formwork pressure has been derived and validated, using the experimental measurements and the numerical simulations of the filling tests performed at the MLCR. Finally, the quality of the cast concrete, investigated through a visual inspection of a series of drilled concrete samples taken at several relevant locations of the casts, revealed to be excellent considering the high casting speeds.