Slab Quality Research Articles

Two Paradigms on Study Slab Continuous Casting Process with Mold Electromagnetic Stirring

Electromagnetic stirring (EMS) is an efficient technology to control the flow structure in slab continuous casting mold. But there is still an important opened problem to be answered firstly, that is, what kind of flow structure is our goal by using electromagnetic stirring in order to get good casting products, and how to optimize the flow fields in slab continuous casting mold with EMS? Two kinds of research paradigms are proposed in this study. One is based on causal relationship between the flow field and its effects on the mold flux entrapment and solidification process. Two parameters, named Mold Flux Entrapment Index and Velocity Uniform Index were proposed in order to evaluate the flow field in the mold. Based on these two indexes, optimization stirring parameters were proposed under different casting situation. The other research paradigm is machine learning big data model based on correlation analysis of nearly all the input parameters of casting machine and slab quality as an output parameter. Data acquisition from the continuous casting machine, data mining by machine learning algorithms and online automatic control parameters output are three main aspects in the second research frame.

Influence of Electromagnetic Brake on Hook Growth and Inclusion Entrapment Beneath the Surface of Low‐Carbon Continuous Casting Slabs

In the current study, the entrapment of inclusions by hooks under electromagnetic brake (EMBr) is investigated through hook reveal and inclusion detection at the subsurface of slabs. Simulation is performed to present the fluid flow and the temperature at the meniscus of the mold. With the application of EMBr in the simulation, the steel jet from the submerged entry nozzle (SEN) deflected upward, the speed of upper backflow increased, and the temperature of steel at the meniscus also increased. The measured average depth of hooks and the number density of >10 μm inclusions without EMBr are larger than those with EMBr. With the application of EMBr, the high temperature of the liquid steel at the meniscus prevented the growth of hooks, and small hooks could only capture few inclusions. Hence, the surface quality of slabs could be improved with EMBr.

Effect of Mineralogical Structure of Flux Film on Slab Quality for Medium Carbon Steel

In order to avoid the slab quality problems in the process of continuous casting, mineralogical structure of flux film for medium carbon steel was studied systematically and the reasonable mineralogical structure of flux film was confirmed by combining with the lubrication and heat transfer characteristics of the mould flux. The results showed that layered structures of flux film were mostly crystallization phase, and the dominating phase was akermanite, with a small number of cuspidine and wollastonite. The akermanites were distributed on the shell side, wollastonites were spread in the middle of the flux film, and cuspidines were scattered in the glassy layer which was adjacent to the mould side. According to the analysis, the crystallization rate of flux film should be increased and the contents of wollastonite and cuspidine should be reduced to avoid longitudinal cracks and sticking breakout in continuous casting.

Yield in eucalyptus slab for use in the obtainment of battens

The present work aimed to evaluate the yield in eucalyptus slabs for obtaining battens to be used as raw material in the production of higher added value products. For this purpose, 15 logs of E. grandis and 15 logs of E. saligna, which were separated into three diametric classes of five logs for each species, were used: diametric class 1 (25 - 32 cm), diametric class 2 (33- 39 cm) and diametric class 3 (> 40 cm). Afterwards, they were cubed and evaluated for their taper, and were deployed on a band saw. The slabs were removed to evaluate the quality, yield and yield of slabs obtained for each species studied. The obtained results indicated that a medium classification of the specific gravity obtained, with good dimensional stability of E. grandis and E. saligna wood. The taper of the logs and the yields observed were not significant in both species. However, the yields in slabs and yields in battens had a slight decrease by the increasing of the diameters of the logs. Thus, logs with greater yield in slabs had smaller yields in battens. Therefore, it is possible to use slabs for battens production mainly in the industries that process high amounts of logs.

Melting of Moving Strip during Steel Strip Feeding in Continuous Casting Process

Steel strip feeding into continuous casting mold is an innovative technology improving the slab quality through decreasing the melt superheat and increasing the proportion of equiaxed dendrites. To investigate the embedded complex melting and solidification processes, a mathematical model has been developed to model all the essential physical behaviors of the fluid flow, heat transfer, melting, and solidification during steel strip feeding into the mold. The enthalpy method is adopted to describe both the melting of steel strip and the solidification of slab. The complex heat transfer between cold steel strip and hot melt is considered. The melting of moving strip and the growth of solidified shell are compared with the experimental measurements and empirical equation, respectively. The validated model is then used to predict the melting and solidification characteristics during steel strip feeding into the mold. Based on the experimental and numerical findings, the whole melting process of steel strip can be divided into three periods: the steel sheath formation, steel sheath melting, and steel strip melting. Effects of the strip thickness (), melt superheat (), and strip feeding speed () on the melting of steel strip have been analyzed. An empirical equation is proposed to correlate the total melting time with aforementioned parameters: . Furthermore, sensitivity study has also performed to reveal the influence of the strip thickness, melt superheat, and strip feeding speed on the final strip tip position.

Research on the application of wheel pile foundation for transmission lines

Under the action of low pressure, the wheel pile foundation bears most or even all the downward pressure. When the wheel pile foundation is subjected to uplift force, the uplift force is supported by the short pile, and the ring frame and the 4 flange mainly play the role of transfer pulling force, while the main bearing force is short and short pile. When the wheel pile foundation is subjected to horizontal forces, the horizontal force is mainly borne by the flange and the ring frame. Therefore, only downward pressure and horizontal force should be considered for the ring frame and flange, while uplift force should be considered for the design of thin and short piles. The basic design is simple and the transmission path is clear. The ring frame, flange and short pile of the wheel pile foundation are prefabricated. The foundation can take different prefabricated installation methods with the mechanized construction conditions. It can not only guarantee the quality of the concrete slab, but also speed up the construction speed of the foundation. By comparing with the economic technology of the plate foundation, it is found that under the same geological conditions, the use of wheel pile foundation can reduce the concrete earthwork and the increase of the load, the decrease of concrete is also increased, and the amount of steel is saved, and the economic benefit is remarkable.

Estimation of Lubrication and Heat Transfer by Measurement of Friction Force in Mold

In the continuous casting process of steels, the mold flux infiltrated in between a mold and solidified shell plays an important role to optimize lubrication and heat transfer to establish not only stable operation but also good surface quality of slabs. Therefore, lubrication and heat transfer was evaluated by measuring friction force attributed to the mold oscillation along with a lubrication model. The friction force was measured with a slab caster equipped with hydraulic oscillators, to understand how the friction force was affected by continuous casting factors such as the mold oscillation conditions, mold flux properties and casting speed.

Damage assessment of semi-precast slabs using impact-echo method

Semi-precast slabs are widely used in precast concrete constructions in China nowadays.However the construction quality of them are often hard to control, and the constructoion quality of the upper in-situ concrete of them is difficult to be guaranteed, as a result, how to detect the construction defects correctly and timely become more and more important. In this paper a traditional method Impact-Echo (IE) method is used to detect the flaws between the precast concrete and the upper in-situ concrete of the semi-precast slabs. Firstly one experimental slabs with many designed flaws was constructed, and than IE method was used to detect these flaws, fially the detected results were analysed to evaluate the proposed method. The results were processed using a mapping strategy, which indicated suspicious points where core extraction was undertaken. All cores taken from points derived from IE method results were found to have flaws providing evidence. The experimental results show that IE method may be a suitable tool to assess the construction quality of Semi-precast slabs

Model predictive control of a dynamic nonlinear PDE system with application to continuous casting

Setting the value of the water flow rate in the secondary cooling zone of continuous casting systems plays a crucial role in the slab quality. The standard method to achieve it is unsuitable when the casting speed changes. Therefore, this paper focuses on model predictive control (MPC) for the continuous casting process, based on a heat transfer model described by a dynamic nonlinear partial differential equation (PDE). Realising this MPC is difficult, because some parameters in the nonlinear PDE are unknown. Hence the MPC scheme is designed in the following two steps. First, we introduce a new iterative algorithm to identify the unknown parameters with the help of measured data. Both synthetic and real data are used to illustrate the validity of this method. The experimental results show that this new algorithm reduces the number of iterations and running time as compared to the methods of Landweber and Cao. Second, the dynamic optimisation problem of the MPC strategy is described according to metallurgical principles. To obtain a more stable temperature, an adaptive step size quasi-Newton method is presented to solve this dynamic optimisation problem. The reliability and accuracy of our MPC approach is confirmed by simulation and real steel data.

A coupled model on fluid flow, heat transfer and solidification in continuous casting mold

Fluid flow, heat transfer and solidification of steel in the mold are so complex but crucial, determining the surface quality of the continuous casting slab. In the current study, a 2D numerical model was established by Fluent software to simulate the fluid flow, heat transfer and solidification of the steel in the mold. The VOF model and k-e model were applied to simulate the flow field of the three phases (steel, slag and air), and solidification model was used to simulate the solidification process. The phenomena at the meniscus were also explored through interfacial tension between the liquid steel and slag as well as the mold oscillation. The model included a 20 mm thick mold to clarify the heat transfer and the temperature distribution of the mold. The simulation results show that the liquid steel flows as upper backflow and lower backflow in the mold, and that a small circulation forms at the meniscus. The liquid slag flows away from the corner at the meniscus or infiltrates into the gap between the mold and the shell with the mold oscillating at the negative strip stage or at the positive strip stage. The simulated pitch and the depth of oscillation marks approximate to the theoretical pitch and measured depth on the slab.

15.17: Progress in the development of production of heavy plates. S355‐S460ML till 100 mm at NLMK DanSteel

ABSTRACTAt the end of 2012 a new 4200 mm rolling mill was put into service in Frederiksvaerk at NLMK DanSteel. Since then the company has focused on production of heavy plates for construction, offshore, shipbuilding and boiler purposes, i.e. steel plates with higher mechanical properties. The company is constantly expanding its product program assortment with regards to sizes and grades. As an example of this, the company in 2015 expanded the range of thermomechanical rolled heavy plates, of structural steel of strength category S355ML, S420ML, S460ML up to 100 mm and received the achieved approval for CE‐marking of these grades.The article presents slab quality requirements, some features of production technology for specified quality and thickness categories as well as enhanced mechanical test results, including evaluation of the anisotropy of the hardness gradient and toughness downp to −80°C both in longitudinal and transverse directions, showing the actual level of low temperature impact toughness properties in ¼ and ½ of heavy plate thickness.Some additional investigations of weldability of low carbon heavy plates were done. The micro hardness of the basic sections in the weld joint of micro alloyed low‐carbon steel heavy plates is investigated. Two‐coordinate measurements of the micro hardness in the basic HAZ are described. The influence of post weld heat treatment on the micro hardness of opposite walls of the weld joint is determined.

Slab Quality and Environmental Degradation with The Addition of Additives and Coagulant

: This research used ammonium chloride at doses of 0%, 0.15%, 0.30% and 0.45% with 0% dose, 0.15%, 0.30% and 0.45% while formic acid and liquid smoke coagulants. The objective of this research is to determine the effects of the addition of additives (NH 4 Cl) and the type of coagulants on the quality slab degradation. The observed parameters were the value of dry rubber content (%), initial plasticity (Po), plasticity retention index (PRI), ash content (%), volatile matter (%) and Mooney viscosity. The results showed that doses ammonium chloride and coagulants affected to the value of dry rubber content (%), initial plasticity (Po), plasticity retention index (PRI), ash content (%), volatile matter (%) and Mooney viscosity. The treatment dose 0.45% ammonium chloride with coagulant has the best combination treatment reason it produced slab with dry rubber content 46.517%, initial plasticity 45, plasticity retention index 94, ash content 0.278%, volatile matter 0.604% and Mooney viscosity 72. Keywords: Ammonium chloride, coagulants and slab. Abstrak (Indonesian) : Penelitian ini menggunakan amonium klorida dengan dosis 0%, 0,15%, 0,30% dan 0,45% sedangkan jenis koagulan asam format dan asap cair. Penelitian ini dilakukan untuk mengetahui pengaruh penambahan zat aditif (NH 4 Cl) dan jenis koagulan terhadap degradasi mutu sleb. Parameter yang diamati adalah kadar karet kering (%), plastisitas awal (Po), indeks retensi plastisitas (PRI), kadar abu (%), kadar zat menguap (%), viskositas Mooney. Hasil penelitian menunjukkan bahwa penambahan dosis amonium klorida dan jenis koagulan berpengaruh nyata terhadap kadar karet kering (%), plastisitas awal (Po), indeks retensi plastisitas (PRI), kadar abu (%), kadar zat menguap (%), viskositas Mooney. Perlakuan dosis amonium klorida 0,45% dengan koagulan asam format merupakan perlakuan terbaik menghasilkan kadar karet kering 46,517%, plastisitas awal 45, indeks retensi plastisitas 94, kadar abu 0,278% , kadar zat menguap 0,604% dan viskositas Mooney 72. Kata Kunci: Amonium klorida, koagulan dan sleb.

Optimization of traveling magnetic field for horizontal continuous casting of thin slab containing tin phosphor bronze

Abstract

Effect of Air-entraining Agent and Mineral Admixture on Thixotropy Property of Fresh Concrete

The elevation control of concrete bottom slab in curve line section of high-speed railway is difficult because fresh concrete cannot hold its shape and the slope of fresh concrete cannot maintain effectively before concrete hardened. To solve this problem, air-entraining agent and attapulgite clay mineral admixture were used to improve the thixotropy of fresh concrete. Results indicated when air-entraining agent and attapulgite clay incorporated simultaneously, the static yield stress of fresh concrete increased to 9.78 Nm, the dynamic yield stress decreased to 5.56 Nm, the ratio between the static and dynamic yield stress increased to 1.9, and the ability of holding the shape and slope was improved to 95.6%. This is mainly due to fibrous gel structure and orientation distribution of attapulgite clay and spherical air bubbles introduced by air-entraining agent in fresh slurry. These will provide valuable and useful references for quality and elevation control of concrete bottom slab of ballastless track in curve line section of ballastless track.

Deformation and Structure Difference of Steel Droplets during Initial Solidification

AbstractThe surface quality of slabs is closely related with the initial solidification at very first seconds of molten steel near meniscus in mold during continuous casting. The solidification, structure, and free deformation for given steels have been investigated in droplet experiments by aid of Laser Scanning Confocal Microscope. It is observed that the appearances of solidified shells for high carbon steels and some hyper-peritectic steels with high carbon content show lamellar, while that for other steels show spherical. Convex is formed along the chilling direction for most steels, besides some occasions that concave is formed for high carbon steel at times. The deformation degree decreases gradually in order of hypo-peritectic steel, ultra-low carbon steel, hyper-peritectic steel, low carbon steel, and high carbon steel, which is consistent with the solidification shrinkage in macroscope during continuous casting. Additionally, the microstructure of solidified shell of hypo-peritectic steel is bainite, while that of hyper-peritectic steel is martensite.

Research on Soft Reduction Amount Distribution to Eliminate Typical Inter-dendritic Crack in Continuous Casting Slab of X70 Pipeline Steel by Numerical Model

AbstractTo investigate the formation of one kind of typical inter-dendritic crack around triple point region in continuous casting(CC) slab during the operation of soft reduction, fully coupled 3D thermo-mechanical finite element models was developed, also plant trials were carried out in a domestic continuous casting machine. Three possible types of soft reduction amount distribution (SRAD) in the soft reduction region were analyzed. The relationship between the typical inter-dendritic cracks and soft reduction conditions is presented and demonstrated in production practice. Considering the critical strain of internal crack formation, a critical tolerance for the soft reduction amount distribution and related casing parameters have been proposed for better contribution of soft reduction to the internal quality of slabs. The typical inter-dendritic crack around the triple point region had been eliminated effectively through the application of proposed suggestions for continuous casting of X70 pipeline steel in industrial practice.

Half PC 슬래브의 건조수축 거동 예측에 관한 연구

최근에는 공사기간을 단축하기 위해서 데크플레이트 외에 half PC 슬래브의 사용도 점차적으로 증가하고 있는 실정이다. PC 슬래브 위에 후타설되는 topping concrete 의 건조수축 변형이 PC 슬래브에 의해 구속을 받게 되므로 topping concrete 에 건조수축에 의한 균열이 발생할 수 있다. 따라서 half PC 슬래브의 품질을 향상시키고 내구성능을 증가시키기 위해서 건조수축에 의한 half PC 슬래브의 거동을 사전에 정확히 예측하는 것이 중요하다. 하지만 아직까지 half PC 슬래브의 수축거동 예측에 관한 연구결과가 없는 실정이므로 본 연구에서는 half PC 슬래브를 대상으로 건조수축거동을 관찰하였으며, 크리프특성을 고려한 증분법에 의한 수축거동을 예측한 후 실측값과 비교하여 그 타당성을 검토하였다. 그 결과 건조수축의 구속작용에 의해 half PC 슬래브에 발생하는 인장변형률은 구속률 개념과 증분법을 적용하여 예측이 가능한 것으로 확인되었다. The use of half PC slab has been increasing to shorten construction period. Because the drying shrinkage of topping concrete is restrained by PC slab, the tensile stress is generated at the topping concrete and the cracks can be occurred at the topping concrete due to drying shrinkage. Therefore, it is important to predict the tensile strain of half PC slab due to drying shrinkage to improve the quality of half PC slab. However, there is no studies on prediction of shrinkage behavior of half PC slab yet. Therefore, in this study, half PC slab was made, and the predictability of tensile strain generated at half PC slab due to drying shrinkage was investigated. The step by step method considering creep was used to estimate the tensile strain of half PC slab. In result, good agreement was obtained between the analytical and experimental values.

Influence of Wiper Height on 7A55 Slabs

In this paper, weak water cooling technology by wiper is introduced for the casting of 520×1650 mm 7A55 alloy slabs. By analyzing from experiment comprehensively, it indicates that the position of wiper will exert big influence on slab quality. Under the conditions of the experiment, if wiper height is below the bottom of sump, there will be more than 70% possibility for slab to have cracks. If it is excessively higher than 80 mm, the top of the sump, porosity will incur and macro-segregation will be enlarged. The experiment determines the correct height of wiper.

Improvement of Castability and Surface Quality of Continuously Cast TWIP Slabs by Molten Mold Flux Feeding Technology

An innovative continuous casting process named POCAST (POSCO’s advanced CASting Technology) was developed based on molten mold flux feeding technology to improve both the productivity and the surface quality of cast slabs. In this process, molten mold flux is fed into the casting mold to enhance the thermal insulation of the meniscus and, hence, the lubrication between the solidifying steel shell and the copper mold. Enhancement of both the castability and the surface quality of high-aluminum advanced high-strength steel (AHSS) slabs is one of the most important advantages when the new process has been applied into the commercial continuous casting process. A trial cast of TWIP steel has been carried out using a 10-ton scale pilot caster and 100-ton scale and 250-ton scale commercial casters. The amount of mold flux consumption was more than 0.2 kg/m2 in the new process, which is much larger than that in the conventional powder casting. Trial TWIP castings at both the pilot and the plant caster showed stable mold performances such as mold heat transfer. Also, cast slabs showed periodic/sound oscillation marks and little defects. The successful casting of TWIP steel has been attributed to the following characteristics of POCAST: dilution of the reactant by increasing the slag pool depth, enlargement of channel for slag film infiltration at meniscus by elimination of the slag bear, and decrease of apparent viscosity of the mold slag at meniscus by increasing the slag temperature.

Construction Technology of Floor Slab for Deep and Large Top–Down Excavation in Soft Clay

The construction quality and elevation of floor slab obtained using the top–down construction method in soft clay may be affected by soil uplift due to excavation unloading and recompression settlement due to the weight of concrete. Based on the Shanghai EXPO axis and underground complex project (Shanghai EXPO axis excavation), soil uplift is studied by conducting centrifugal model test and numerical simulation. The soil uplift process for soft clay in Shanghai EXPO Axis excavation is mainly concentrated during the 14 days after excavation, attaining approximate 84 % of the final values. The configuration of soil uplift is serrated. The maximum soil uplifts for excavation depths of −1.08, −9.10, −12.80, and −17.30 m (WSEY) are 85, 127, 143, and 153 mm respectively. On-site monitoring reveals that the floor slabs and beams are settling during concrete casting. The settlement values are related to concrete weight, bearing capacity of soils under the excavation surface, and stiffness of scaffold. Based on these findings, exposure time duration between soil excavation and concrete casting and reasonable pre-camber values of scaffold are proposed. The results of this paper demonstrate that the application of these values is effective in controlling construction quality and elevation of floor slab and beam.