Casting Stage Research Articles

Методика дослідження зародження кристалів у розплавах краплинним методом

The purpose of this work is to develop scientifically based ways of influencing the process of nucleation of crystallization centers in metal melts to control the formation of the cast structure and the properties of their blanks at the first stage of metal product production (at the casting stage). The possibility of controlling the nucleation of crystals in their melts was studied on transparent model environment (paraffin and salol) using the drop method, and the dependence of the crystallization kinetics of droplets with a dispersion of 100÷200 μm on their overheating temperature, the duration of exposure in an overheated state, and the degree of supercooling was established. Physical modeling on transparent environment made it possible to display images on a laptop screen with the help of a digital camera mounted on a microscope and to observe the nucleation and growth of crystals in real time, to determine the duration of solidification of all observed drops, depending on the experimental conditions. The criteria for evaluating the crystallization process of the investigated environment were the curves of the crystallization kinetics of drops from their melts. The nature of the change in the crystallization kinetics curves of the experimental environment, in our opinion, confirms the assumption about the decisive role of impurities in the crystallization processes of any alloys. The logical confirmation of the hypothesis about the decisive role of impurities in the processes of crystallization from the same positions of heterogeneous nucleation is the dependence of the number of solidified drops of experimental environment of the same diameter on the degree and duration of their overheating. It is likely that with greater overheating of the melt (or longer exposure to this overheating), partial deactivation (dissolution) of the impurities present occurs and the number of solidifying drops changes for the same supercooling. The analysis of the obtained results indicates a heterogeneous mechanism of crystal nucleation even in drops of microscopic size (~100 μm). The developed method of studying the processes of nucleation and growth of crystals in model alloys depending on their mass (size) can be applied in real conditions of mass crystallization. Keywords: model environment, droplet method, crystal nucleation, crystallization kinetics.

A novel roughness parameter for more precise estimation of the shear strength of concrete-to-concrete interfaces

Concrete-to-concrete interfaces are common in new reinforced concrete structures with different casting stages and or with precast members with cast-in-place parts, as well as in rehabilitation of existing reinforced concrete structures. Their longitudinal shear strength has been studied in the last five decades. Today, it is established that this is ensured by a combination of adhesion, aggregate interlock, friction, and dowel action. Being all these resistant mechanisms, but mainly friction, highly dependent on the surface roughness, the quantification of the latter is of paramount importance.This paper investigates the correlation between the friction coefficient and the surface roughness of concrete-to-concrete interfaces. An experimental campaign of direct shear tests, performed on specimens with different surface treatments (smooth, rough and corrugated), was carried out. The surface’s texture was analysed using a 2D Laser Scan and different roughness parameters (extreme, mean and segments) were calculated, then correlated with the corresponding shear strength and, lastly, based on the latter, correlated with the friction coefficient.Results showed that the extreme roughness parameters, as well as the peaks’ height related parameters, have poor or no correlation with the magnitude of the friction coefficient. The average roughness of the profile, its mean square, the mean valley depth, and the mean peak-to-valley height turned out to have the strongest positive correlation with the friction coefficient. Based on these, a novel combined roughness parameter with an optimized correlation with the friction coefficient was derived and proposed.

Experimental studies of the reusable steel deck forms for concrete slabs

Recently, many flyover steel bridges have been built due to high demand of transportation development mega cities in Vietnam, especially in Ho Chi Minh City and Ha Noi City. The steel bridges are selected as effective solutions in urban area because of their advantages such as rapid construction, aesthetic design, high performance. For the construction method of concrete deck slab, wood panels, plastic panels, and precast concrete panels are often used to reduce construction costs. From actual construction projects, these form solutions may not be suitable for large span over 2.0 meters and take more time to install and to dismantle. This study aims to develop an improved solution with reusable steel deck forms for bridge slabs which has been used as permanent deck forms in buildings. Experimental studies are conducted to investigate the frequency of reusability and to verify the bending capacity of the steel deck after many times of reuse. The experiments are separated into two phases including concrete casting stage and strength tests in laboratory. Bending strengths of reused forms are compared with that of new one. Results shows that steel deck forms are still in good condition and provide sufficient bending capacity after 10 times of concrete casting comparing. Therefore, reusable steel deck forms can be effectively applied in the construction of bridge slabs to optimize the construction time and cost.

A Self-Learning Based Dynamic Multi-Objective Evolutionary Algorithm for Resilient Scheduling Problems in Steelmaking Plants

Scheduling is one of the most important missions for plant-wide optimization in steelmaking manufacturing systems. In the context of dynamic scheduling, the decision-maker should simultaneously minimize economic objectives within the decision space and violation penalty out of the decision space. In this study, we introduce a resilient scheduling model in steelmaking plants, which provides flexible decisions, including buffering times in between stages and controllable processing speeds in the casting stage, to enable the solution to absorb random disturbances and recover quickly. We formulate the dynamic steelmaking scheduling problem with resilient responding strategies, which is a variant of dynamic multi-objective optimization problems (DMOP), and propose a resilient scheduling optimization framework to solve it over time. First, we employ a vector with problem-specific knowledge to map the whole decision space to sub-schedules in the casting stage, which contains casting priority, casting speed and scaling ratio. Next, we form a multi-objective linear programming model to evaluate these problem-specific vectors. Last but not least, we develop a self-learning based dynamic multi-objective differential evolutionary algorithm to solve the variant DMOP, in which a hypothesis-testing technique is used to detect and identify environmental changes. The sensitivity analysis and algorithm comparisons are performed on a wide range of problem instances under dynamic environments. Experimental evidence validates that the proposed resilient model and the optimization framework is effective to solve the dynamic scheduling problem in steelmaking plants. Note to Practitioners—This paper investigates a dynamic scheduling problem that comes from steelmaking manufacturing systems and is extensively studied in existing works. Because a decision-maker only has incomplete knowledge about the realistic environments, this paper simultaneously considers that both the decision and objective space of a scheduling problem dynamically changed over time. We develop a resilient scheduling model which can absorb the different types or scales of disturbances caused by unforeseen events, and recover rapidly to the original state. We formulate the resilience scheduling model and propose a dynamic multi-objective algorithm based on the self-learning differential evolutionary algorithm to solve it. The effectiveness of the proposed model and algorithm is validated via sensitivity analysis and comparison to other well-known algorithms. Furthermore, the resilient scheduling model and its optimization framework can also be applied to dynamic scheduling problems in other industries.

The influence of NbB inoculation on dendritic spacing and grain size of an aluminum 2017 alloy at different cooling rates

The Al-4Cu-Mg 2017 alloy is a significant Al extrusion alloy. As a result, knowing its behavior in terms of grain refining during casting stages becomes critical for the next processing steps. In the face of the shortcomings exhibited by TiB inoculants, the addition of NbB could be tested for this alloy as an alternative. The present article investigates the effects of NbB addition on grain size (GS), on secondary dendrite arm spacing (λ2), and on hardness of centrifugally cast (CC) and directionally solidified (DS) 2017 alloy samples, encompassing a broad range of cooling rates and solidification conditions. The λ2 did not change much as a result of the NbB inoculation, either for DS or CC samples, decreasing from 7.2 to 7.0 μm in the case of the 4-mm-thick CC samples and increasing from 17.0 to 22.5 μm in the case of the DS samples. The average GS, on the other hand, reduced from 293 to 136 μm for the NbB-containing CC samples and from 756 to 313 μm for the DS samples associated with cooling rates of 10 K/s. Both processes can achieve nearly the same GS reduction ratio, namely 2.2 for the CC and 2.5 for the DS. This implies that GS reduction ratio was barely affected if similar cooling rates were compared while taking the experimental range for both processes into account. Moreover, Vickers hardness results revealed that GS had little influence on this property for both alloys studied. The experimentally obtained data translated a variety of solidification condition outlines for the 2017 alloy. Through this data, the understanding of an alternative inoculant in a significant Al alloy series advanced significantly.

A unifying framework and a mathematical model for the Slab Stack Shuffling Problem

The Slab Stack Shuffling Problem (SSSP) consists of retrieving slabs, stored in stacks in a warehouse, to efficiently satisfy a processing order. The problem is relevant in the steel industry as the slab yard serves as a storage buffer between the continuous casting stage and the rolling mill. Notably, the SSSP also arises in cutting/assembly centres within the shipbuilding supply chain, where already rolled slabs must undergo further production stages. The different slabs managed in these facilities confer the problem novel practical features, such as the existence of slabs' typologies and deadlines, i.e., a maximum time beyond which their quality certifications expire and are no longer usable. In such a context, the goals of the present paper are twofold: (i) providing a comprehensive taxonomy of the main aspects involved in the problem; (ii) proposing an original mathematical formulation for the SSSP. Specifically, the model is cast as a bi-objective multi-period program, seeking to minimise the number of shuffles and expired slabs. Computational tests on randomly generated instances prove the relevance of the trade-off between the above-mentioned objectives and the impact of the yard's configuration on the retrieval process, suggesting the most suitable storage strategy to adopt under different operational settings.

Microstructure and corrosion resistance of commercial purity aluminum sheet manufactured by continuous casting direct rolling after ultrasonic melt pre-treatment

During the new continuous casting direct rolling (CCDR) process for manufacturing commercially pure aluminum sheet for foils, casting defects tend to arise as the raw material with huge mass flow rapidly solidifies under a high cooling rate, which generates negative effects on the formability of aluminum sheets and the performance of final foil products. Therefore, melt pre-treatment during continuous casting is very essential to improve the quality of the billet. In this study, multi-source ultrasonic field was employed to pretreat an Al melt during the continuous casting stage in a Hazelett CCDR strip production line. The Ti content distribution in the melt, the microstructure and corrosion behaviors of the rolled sheet with and without ultrasonic melt pre-treatment (UMPT) were investigated. The microstructure of the rolled sheet was refined due to the increased Ti content and uniformly distributed Al3Ti particles under UMPT. In addition, the morphology of the Fe-containing secondary phase was modified from an aggregated to a scattered structure, with reduced continuity. As a result, under the combined effects of the refined α-Al grains and secondary phase, the corrosion resistance of the rolled sheet was improved. The underlying mechanisms for the modifications of the microstructure and corrosion resistance after UMPT are also interpreted, which gives theoretical guidance on the practical applications of the ultrasound-assisted continuous casting in industrial production.

Study of the Mechanical Behavior of Steel-Hybrid Composite Beams Constructed by Suspension Bracing Method

The construction process of steel–concrete composite girders was simulated using a 3D finite-element model and suspension-bracing method. The influences of multiple factors such as self-weight of suspension bracket, wind load, longitudinal spacing of suspension points, concrete deck slab thickness, concrete casting process, and suspension bracket removal on the mechanical properties of the main steel girder and the composite girder were analyzed. The mechanical behavior of the steel–concrete composite girders during the construction process using the suspension-bracing method was revealed. The results show that (1) the normal stress and displacement of the steel girder increases with the increase of the weight of the suspension bracket, and they have a relatively large impact on the increase. (2) The wind load during the construction process will produce large transverse displacement of the main steel girder, the transverse wind load should be considered in the load combination analysis, and necessary measures should be taken to limit the transverse displacement of the main steel girder during the deck casting process. (3) The displacement and stress of the main steel girder will show a parabolic change with the change of the longitudinal spacing of the suspension points, so the optimal value of the longitudinal spacing of the suspension points is recommended to be 4 m. (4) The maximum midspan displacement and stress of the main steel girder increase with the increase of the deck slab thickness, and the weight of the deck slab occupies the main position in the whole system force. (5) In the process of casting deck slabs with the suspension-bracing method, the stress and deformation of the main steel girder increase with the concrete construction stage of the deck slabs. To ensure that the geometric shape of the bridge at each stage is consistent with the theory result, the design elevation of each section should be preraised during the construction process according to the vertical displacement and deformation of the main steel girder caused by the construction of each casting stage. In addition, the upward rebound of the main steel girder caused by the removal of the suspension bracket must be fully considered when setting the prearch of the steel–concrete composite girder.

A method for considering the influence of distinct casting stages in the flexural design of prestressed concrete cross sections

ABSTRACT Composite elements are structures of concrete, or other materials, constructed in different casting stages that act jointly under external loads. These elements are used when it is intended to combine the constructive advantages of precast structures with the monolithic behavior of cast-in-place structures. In regular civil engineering applications, such as the construction of a bridge or viaduct, the precast section is used as shoring before casting the slab in place. This process leads to imposed deformations prior to the ultimate limit state and a discontinuity in the specific strain of the composite cross section. This work proposes a methodology to design composite cross sections, built in two casting stages, evaluating the specific strain provided the construction process that can be easily implemented in precise computational routines. From applying the methodology on study-case numerical example, it is observed that the beam casted in two stages presents a factored moment resistance smaller than an identical beam casted in a single stage. However, further investigations should be conducted to assess the extent of this difference.

Study of Investment Casting Process For 3D Printed Jewellery Design

Manufacturing processes are increasingly complex with the growing demands of advanced technology in the production processes, especially in the handicraft industry. The complex jewellery designs are complicated to be produced by hand, considering the international demand and dynamics in the jewellery industry. However, advanced production processes and 3D printers are changing the way jewellery designers and manufacturers work and making it easier to produce quality products with fewer production and labour input hours. This study examines the investment casting process of 3D printed design as an option for jewellery manufacturing. The research aims to access jewellery manufacturing processes and its technology application by using trending 3D printing as a rapid prototype. It used the design and production process of 'OneCent Africa' as a case study to describe the process in the investment casting of jewellery products. The investment casting was conducted by prototyping, and the lost wax jewellery casting stages using the vacuum casting machines and burnout oven, with the casting process monitored in parts. This research results led to a better understanding of the experimental casting outcomes and described the potential for the future technological development of jewellery businesses.

ПРОБЛЕМЫ РАЗВИТИЯ ЛИТЬЯ ПОД ДАВЛЕНИЕМ ТВЕРДОЖИДКОГО МЕТАЛЛА В РОССИИ

The methods of powder and granular metallurgy are rapidly improving, granulation and spheroidization of solid phase particles is carried out “in–situ” at the stage of alloy preparation, which precedes the casting stage, and on this basis, a new generation of technologies is born and developed. dubbed Thixo – (casting, molding, forming) and PowderInjectionMolding (РIM (МIM, СIM)) technologies. All of the above technologies are united by the term Semi–Solid Processing (SSP), and the mandatory code prefixes Semi–Solid Metal (SSM) and MetalInjectionMolding (MIM) have appeared in the designations of alloys prepared for processing in a solid–liquid state.

Study of Conditions for Improving Chemical and Structural Homogeneity of Ferritic Class Hot-Rolled Steels

Redistribution of carbon and other elements, and formation of the structure, composition, and properties of low-carbon Nb, Nb–Ti, Nb–V, Nb–V–Mo and Ti–Mo microalloyed steels during hot rolling is studied using metal of five laboratory melts. It is established that by selecting the temperature for the beginning of rolling in the finishing group of stands according to steel composition (microalloying system) it is possible to achieve a significant improvement in the homogeneity of the composition, structure, and set of rolled product properties. Therefore, it is demonstrated by experiment that chemical and structural heterogeneity of metal formed in the billet casting stage may be largely eliminated during hot rolling on the basis of controlling carbide (carbonitride) precipitate formation.

Hall-Sensor-Based Position Detection for Quick Reversal of Speed Control in a BLDC Motor Drive System for Industrial Applications

This paper proposes the novel idea of eliminating the front-end converters used indirect current (DC) bus voltage variation, thereby allowing for control of the speed of the brushless direct current (BLDC) motors in the two-quadrant operation of a permanent magnet brushless direct current (PMBLDC) motor, which is required for multiple bi-directional hot roughing steel rolling mills. The first phase of steel rolling, the manufacture of plates, strips etc., using hot slabs from the continuous casting stage, is carried out for thickness reduction, before the same is sent to the finishing mill for further mechanical processing. The hot roughing process involves applying high, compressive pressure, using a hydraulically operated mechanism, through a pair of backup rolls and work rolls for rolling. Overall, the processes consist of multiple passes of forward and reverse rolling at increasing roll speeds. The rolling process was modeled, taking into account parameters like roller dimensions, angle and length of contact, and rolling force, at various temperatures, using actual data obtained from a steel mill. From this data, speed and torque profiles at the motor shaft, covering the entire rolling process, were created. A profile-based feedback controller is proposed for setting the six-pulse inverter frequency and parameters of the pulse width modulated (PWM) waveform for current control, based on Hall sensor position, and the same is implemented for closed loop operation of the brushless direct current motor drive system. The performance enhancement of the two different controllers was also evaluated, during the rolling of 1005 hot rolled (HR) steel, and was taken into consideration in the research analysis. The entire process was simulated in the MATLAB/Simulink platform, and the results verify the suitability of an entire-drive system for industrial steel rolling applications.

A Branch and Price Algorithm for Crane Assignment and Scheduling in Slab Yard

In a steel industry, a slab yard plays a role of a buffer between continuous casting stage and rolling mill. An effective assignment and scheduling of cranes can guarantee the operation efficiency in the slab yard. This work studies a multicrane scheduling problem with noncrossing constraints of slabs. A mixed-integer programming model is used to formulate the problem that minimizes the whole traveling distance of all the cranes and ensures the workload balance among cranes. As it is an NP-hard problem, classical programming mathematical methods are difficult to get an optimal solution for large-size instances. Thus, we develop a branch and price algorithm to solve this problem. First, we formulate the model as a generalized set covering problem and a set partition problem. Then, we solve them and combine the solutions to obtain the solution of the original problem. Finally, we conduct computational experiments based on real data from an iron–steel plant. The comparisons of proposed methods with an exact solution method show its effectiveness. Note to Practitioners —This work deals with a multicrane scheduling problem. Aiming to minimize the total traveling distance of all the cranes, it establishes a mixed-integer programming model with a workload balance constraint on cranes. It presents a branch and price algorithm to solve the problem whose solution complexity grows exponentially with problem size. The integration of crane assignment and scheduling enables the better utilization of cranes and faster service in iron–steel enterprises and, hence, improving customer satisfaction. The experimental results reveal the effectiveness of the proposed approach. It can readily be put into use in the steel industry.

The Antler Cycle and Fecal Testosterone of Male Sambar Deer Rusa unicolor unicolor at the Horton Plains National Park in Sri Lanka.

This study is aimed at evaluating the relationship between endogenous testosterone levels and antler development in male sambar deer (Rusa unicolor unicolor) inhabiting the Horton Plains National Park, Sri Lanka. Seven antler growth stages of sambar were documented based on phenotypic observations for the first time in Sri Lanka as (a) cast, (b) growing 1—single spike, (c) growing 2—antler fork into a Y as the second tine appears, (d) growing 3—velvet begins to harden as the third tine appears, (e) growth completed—velvet shedding begins, (f) hard antler, and (g) casting. Fecal samples were collected every month for a period of eighteen months from male sambar deer in different stages of the antler growth cycle, feeding in the wet patana grasslands of the park, and the fecal testosterone level was estimated by radioimmunoassay. Ten animals were randomly selected from each antler stage for the experiment. The results disclose that the highest concentrations of testosterone were recorded in the hard antler stage. Velvet shedding was preceded by an increase in the testosterone level, and it is the sudden drop in the testosterone concentration which triggers the antler casting. The casting stage corresponded with the lowest mean testosterone concentration. Although the study was able to conclude a clear relationship between the fecal testosterone levels of the male sambar deer in the Horton Plains National Park and their antler stages, there is no clear seasonality for the antler cycle.

Optimization of casting means and heat treatment routines for improving mechanical and corrosion resistance properties of A356-0.54Sc casting alloy

In this paper, the effect of different casting means and heat treatment routines on the mechanical and corrosion resistance properties of A356-0.54Sc casting alloy was comprehensively studied. Three different molds, including graphite mold, steel mold, and copper mold, were employed. Both the grain size and secondary dendrite arm space of primary α-(Al) in the casting A356-0.54Sc alloy with copper mold are the finest. Three different heat treatments, i.e., T4, T5, and T6, were then applied. With the T4 treatment, the eutectic (Si) particles transferred from the as-cast fibrous structure to the isolated spherical one, leading to a significant increase in ductility. After aging, the alloys in the T6 state always own the best strength properties. The strong heredity of microstructures from the casting stage to the subsequent heat treatments was observed. Moreover, the corrosion resistance of alloys was studied by the salt-spray corrosion experiments. The experiments showed that the pitting corrosion mostly occurs in the interface between the eutectic (Si) and primary α-(Al). It was finally concluded that the alloys casted using the copper mold and treated with the T6 routine maintain the best comprehensive mechanical properties after corrosion, while the alloys casted using the graphite mold are with the best corrosion resistance.

Correlation between current and cross-sectional area of parallel fixed-movable dual electrodes in ESC

Electroslag casting with parallel fixed-movable dual electrodes is a new method for achieving better quality of castings in complex mold cavities. In this work, a mathematical model, y=kx2+(k+1)x, was established to describe the ideal correlation between the current ratio (y) and the cross-sectional area ratio (x) of the dual electrodes, where k is the filling ratio. Investigation was conducted on the electroslag casting process with dual electrodes of various cross-sectional areas, but at a constant k value. The experimental results indicated that the ideal correlation was obtained at the stable casting stage, and the fitting results were consistent with the experimental results at certain k values. The experimental findings show that better castings can be obtained when the current ratio is greater than 1.536 and the cross-sectional area ratio is greater than 0.5.

The influence of Y3+ and Mg2+ dopants on the transparency behavior of alumina ceramics

The effect of salt solution of magnesium and yttrium addition on the transparent alumina polycrystalline was investigated in the present study. This solution is ionized in the slurry. The ions were adsorbed onto the charged alumina surface by the electrostatic mechanism. Due to the addition of salts solution at the casting stage, the distribution of dopant was uniform. Therefore no secondary phase has been formed in the sample after sintering. The added salts eliminated the intragranular porosity and prevented the growth of the grains. After optimizing the amount of the dispersant (1.3 wt%) and preparing the slurry by using a 3D-mixer, the samples were sintered at a temperature of 1250 °C and at the rate of 20 °C/min by the SPS method, the transparency was increased from 18 to 33% by adding salt solution of the Mg2+ and Y3+ as dopant. Also, the grain size was decreased from 27.37 to 4.29 μm in the sample with dopant, therefore the hardness was increased from 1814 to 2279 HV10.

Application of 2XXX and 7XXX series alloys as input material for the new casting-forging hybrid process

The aim of the work has been to analyze the aluminum alloys for plastic working from the point of view of their usefulnessin the new hybrid manufacturing process which includes gravity casting and forging. The tests have been carried out onpopular aluminum alloys from the 2xxx and 7xxx series: 2017A, 2024, 7022, and 7075, respectively. The authors have focusedon the problem of using these materials at the casting stage. The analyses have included verification of the technologicalproperties of alloys, including fluidity and the tendency to create porosities. Next, the influence of the solidification rate(associated with the use of various molds) on the casting microstructure has been determined. Based on the conducted analyzes, thealloys with the best casting behavior have been indicated. At the same time, possible problems that may occur at the forging stagehave been discussed.

A study of Locke#039;s thought of pluralism and unity

Britain is a typical island country surrounded by water. Britain's three islands are small in area and small in population, but they once led the world trend and opened up the modernization of human society. Politically, it established the first constitutional monarchy in the history of the world; economically, it was the first to adopt machine production for industrial revolution; in its strongest period, its land area once spread all over the world known as the "empire of the sun". One of the important factors for Britain to rise from a small bullet country in a corner to a world-class power is the emergence of a large number of thinkers, politicians and scientists. John Locke is one of the best, at the same time, he is also a big influence. Locke's theory of thought not only has a profound impact on Britain, but also on the whole world. Until now, people can still find the shadow of Locke's thought in many countries. John Locke (1632-1704) is a great British philosopher and politician. Locke was born in the early period of British modernization. At that time, the British political field had undergone profound and dramatic changes, which belonged to the casting stage of the British modern country. At the same time, this period also cast Locke's unique ideological system. People understand his main thoughts through his three major works on" human understanding", "letters on religious tolerance" and" the two chapters on government", in particular, "the two chapters on government" can best reflect his main ideas. Locke himself is also regarded as an important founder of modern political theory and liberalism philosophy. There are also many research papers on Locke's thought, most of which focus on the discussion of one of his ideological fields, such as Locke's property rights, the separation of powers in Locke's political field, and the comparison of British thinkers' thoughts in the same period. These research results play an important role in helping researchers to study Locke's thoughts deeply. But if researchers put all of Locke's philosophical thoughts together, Locke and his thoughts are not as simple as people think, and his various thoughts are not as clear as scholars' division. As far as Locke is concerned, he is full of many contradictions, opposites and unity, and his own contribution to thought is not limited to a single liberalism, but more to the balance and development of pluralism and unity.