Dummy Bar Research Articles

Hydraulic Jump Behavior during Filling Process of Cast Start II

This paper presents a 0.25-scale quasi-three-dimensional hydraulic model experiment of transient fluid flow phenomena during continuous casting of steel under solidification. Water cooling is performed at the bottom of the mold, and saturated sodium acetate solution is covered on the spring and particle arrangement at the bottom of the mold/on the dummy bar to simulate the solidification phenomenon in the actual continuous casting process. The results show that the solidification on the dummy bar surface is very important to the early stage of the filling process and cannot be ignored. Its influence gradually decreases with the rise of the liquid level, and basically disappears when the liquid level rises to a certain height (steady liquid level, SLL). In SLL, the interface morphology of the solidified layer is more affected by the flow, while the interface morphology of the solidified layer has no significant effect on the liquid surface velocity.

Hydraulic Jump Behavior during Filling Process of Cast Start I

This paper presents a 0.25 scale quasi-three-dimensional hydraulic model experiment of transient fluid flow phenomena during continuous casting of steel. The relationship between the continuous casting process and the hydraulic jump phenomenon is established. The casting process in the mold is divided into four stages (I–IV) from the beginning to the end of continuous casting. The filling process involves stages I–II and is investigated by high-speed camera. The filling process is part of the cast start. In this paper, the hydraulic jump behavior varies and is controlled by different spring and iron chips arrangement on the dummy bar during the filling process. A filling coefficient is proposed to judge the best filling conditions and apply them to the whole filling process. There is an optimal spring and iron chip arrangement, which can adjust the hydraulic jump to optimize the initial flow field during the filling process, even the whole continuous casting process.

Engineering design highlights of high-efficiency slab casters relocated at Baosteel Zhanjiang

Baosteel Group decided in 2013 to relocate the main segment equipment of the 2 single-strand 2,300 mm slab casters which were shut down at its Luojing Plant to the Zhanjiang Plant and transform them into an upgraded two-strand slab caster. CISDI was contracted to supply the overall design and the main equipment packages. CISDI employed a couple of advanced technologies including online mould width adjustment, top-inserted dummy bar, dual strand tracking and casting at constant speeds to enhance the production capacity of the caster; for sake of Opex saving CISDI also optimized the arrangements of the independent mechanical maintenance shop, utilities of compact design, cooling water valve stations and hydraulic valve stations of compact designs, and open-air cooling water pump station, etc.

ЗАСТОСУВАННЯ РОЗРЯДНИКІВ НАПРУЖЕНЬ В ОСНОВНИХ ВУЗЛАХ ТЕХНОЛОГІЧНОГО УСТАТКУВАННЯ МБЛЗ

Presence of cracks and other surface defects is completely prohibited at exploitation of industrial facilities. This condition is of vital importance for component parts of a complex of big equipment. For example, for continuous casting machines (CCMs), whose total weight exceeds several thousand metric tons a failure of a single component part can lead to serious consequences, due to imminent hue material losses. Such hard conditions of such equipment not only influence its operation, reducing its service life, but also may have a negative impact on the quality of production. Such negative influence can be expressed in the following way: regulation of the main units may be altered following overheating of the equipment, due to thermal expansion of mostly heated elements. In case of presence of cracks in the most loaded unit of dummy bar –its head part its bearing capacity may be altered and appearance of excessive deformations may not be excluded, i.e. its transverse dimensions may be changed. Besides, cracks in the locking part of the dummy bar are out of the question, in order to avoid solidification of liquid metal in cracks.The problem of reducing intensity of cracks formation can be solved in different ways. Its practical solution depends upon the part’s design and peculiarities of its loading. For operation of dummy bars of slab casting CCMs it should be noted that this problem is closely connected with asymmetric design of dummy bars heads and one-way heat delivery and removal for its locking part. The finite elements method was used for the analysis of stress-strain state in the article. Three-dimensional simulation models were divided into finite elements and after that they underwent various theoretically possible loads. Simulation made it possible to establish the most vulnerable sections of the design, undergoing most severe loads, in case they are applied. Particularly, it was found out that the edge parts of transverse section of a dummy bar head experience the biggest deformations, consequently, cracks can spring up at a certain pitch and develop on the surface of the projection of the lock. The analysis of the initial data showed that for reduction of thermal strain in the lock projection it was necessary to make deformation inside its upper layers more free. It will be is possible if a transverse slot is made, dividing the projection length into two elements. Heating and cooling of the surface lock’s layer could become safer, at that, from the point of view of elongating stresses, thus reducing the probability of cracks formation.

Distribution of electric drives of pulling rollers on the continuous casting machine: simulation and experiment

The paper presents the results of the study aimed at solving the problem of rational distribution of electric drives of pulling rollers along the technological line of a continuous casting machine and selecting a minimum number of pulling rollers in different areas of the secondary cooling zone. The research includes construction and ranking the criteria for distribution of drive rollers along the production line of the continuous casting machine; development of methods and algorithms for calculating the required distribution of load moments on pulling rollers and distribution of electric drives of pulling rollers along the secondary cooling zone in three modes of the electric drive operation of the pulling-straightening device: containment of the dummy bar in the preparatory casting mode of the continuous casting machine; pulling the dummy bar with the head of the ingot at the initial stage of pouring the metal; withdrawal of the ingot in the working mode of casting. Theoretical studies were carried out with the use of analytical and numerical methods for solving algebraic equations, methods of structural modeling. Experimental studies were carried out in the conditions of a large metallurgical enterprize with subsequent processing of the obtained data by statistical methods. The technical and economic analysis of the options of the electric drive execution of the pulling-straightening device showed that due to a significant reduction in the number of electric drives of pulling rollers, the payback period of replacement of a group scheme of power supply of electric motors to an individual one in new continuous casting machines decreases from 5.8 to 7.8 years with the traditional distribution of pulling rollers along the secondary cooling zone to 2.8–3 years with their rational distribution, calculated by the developed methods. The results of the work were used in the design of a slab machine for continuous casting of curvilinear strands intended for casting wide slabs up to 2.5 m. According to the proposed method, the number of electric drives pulling the rollers was reduced to 56.

Improving the dummy bar in continuous slab-casting machines

Crack formation at the lock of the dummy bar in continuous slab-casting machines is analyzed. The cracks are due to the thermocycling stress. Cooling periods in thermocycling are particularly hazardous. This problem may be addressed by redesigning the head.

Hazard reduction in continuous casting of steel

The influence of dummy-bar defects in continuous-casting machines on accidents at the beginning of casting is analyzed. The stress–strain state of the metal at the head of the dummy bar is investigated. It is shown that residual strain in the head may increase the frictional forces between the ingot and the mold wall and may change the rate of heat transfer, which is a possible source of accidents.

Microstructure Control of Columnar‐Grained Silicon Substrate Solidified from Silicon Melts Using Gas Pressure

A silicon substrate with the dimensions of 100 × 140 × 0.3 mm was grown directly from liquid silicon with gas pressure. The silicon melt in the sealed melting part was injected into the growth part at applied pressure of 780–850 Torr. The solidified silicon substrate was then transferred by the pull of the cooled dummy bar. A desirable structure with a liquid‐solid interface perpendicular to the pulling direction was formed when the mold temperature in the solidification zone of the growth part was much higher than that of the dummy bar, as this technique should be able to overcome thermal loss through the molds and the limited heat flux derived from the very narrow contact area between the silicon melt and the dummy bar. In addition, because the metallic impurities and expansion of volume during solidification are preferably moved to a liquid phase, a high‐quality silicon substrate, without defects such as cracks and impurities in the substrate, could be manufactured in the interface structure. The present study reports the experimental findings on a new and direct growth system for obtaining silicon substrates characterized by high quality and productivity, as a candidate for alternate routes for the fabrication of silicon substrates.

다결정 실리콘 웨이퍼 직접제조에 대한 공정변수 영향

A ribbon-type polycrystalline silicon wafer was directly fabricated from liquid silicon via a novel technique for both a fast growth rate and large grain size by exploiting gas pressure. Effects of processing parameters such as moving speed of a dummy bar and the length of the solidification zone on continuous casting of the silicon wafer were investigated. Silicon melt extruded from the growth region in the case of a solidification zone with a length of 1cm due to incomplete solidification. In case of a solidification zone wieh a length of 2 cm, on the other hand, continuous casting of the wafer was impossible due to the volume expansion of silicon derived from the liquid-solid transformation in solidification zone. Consequently, the optimal length of the solidification zone was 1.5 cm for maintaining the position of the solid-liquid interface in the solidification zone. The silicon wafer could be continuously casted when the moving speed of the dummy bar was 6 cm/min, but liquid silicon extruded from the growth region without solidification when the moving speed of the dummy bar was 9 cm/min. This was due to a shift of the position of the solid-liquid interface from the solidification zone to the moving area. The present study reports experimental findings on a new direct growth system for obtaining silicon wafers with both high quality and productivity, as a candidate for an alternate route for the fabrication of ribbon-type silicon wafers.

Analysis and Prevention of Pulling Inhibition and Stagnation of Slab Casters

For case of pulling inhibition and stagnation of slab casters appeared in one continuous casting department of WISCO, Factors include stress of dummy bar systems, integrated frictional force , compression force and pulling speed control mode are analyzed to get the causes. The case was ultimately changed with countermeasures such as equipment optimizing and technology improving. The stability and productivity of continuous casting was improved obviously as long as more benefit being provided.

Transient Fluid Flow Phenomena during Continuous Casting: Part I—Cast Start

This work presents a three-dimensional numerical simulation of transient fluid flow phenomena during continuous casting of steel. In the Part I, the process of cast start was investigated. Cast start involved the filling process and the caster start process. In the filling process, molten steel was continuously filled into the mold cavity with surrounding mold walls and a dummy bar head at the bottom. To simulate the interface between the molten steel and the air, an algorithm of volume of fluid has been employed. In the cast start process, the dummy bar was gradually dragged out with a low casting speed. The movement of dummy bar was represented using dynamic mesh, and the moving speed of the boundary was controlled by a subroutine. The shape of the air/steel surface was tracked over the time, and the speed variation at a series of points close to the surface was monitored to reflect the fluctuation at top surface during cast start.

Production of Magnesium Alloy Billets by Semisolid Continuous Casting

In order to produce AZ91 and AZ31 magnesium alloy billets semisolid continuous casting by using an inclined cooling plate was carried out. The molten magnesium alloy in an electric furnace was flowed on the inclined cooling plate and then poured in a tundish. The slurry prepared using this process was solidified by drawing a dummy bar from a water-cooled copper mold, consequently producing a billet. As a result, we could produce the magnesium alloy billets by semisolid continuous casting. Magnesium alloy billets with refined and globular primary α crystals were successfully and continuously cast by optimizing the solidification conditions. In this case, the grain size of AZ91 billets was about 55μm and that of AZ31 billets was 50μm. The AZ91 billets produced by semisolid continuous casting were employed in thixocasting experiments. The experiments revealed that thixocasting could produce the mobile phone casings with spherical primary α crystals at 858K. Moreover, we proved that the difference of shot cycle did not influence the microstructures for up to 251 shots.

Microstructure of binary Mg-Al eutectic alloy wires produced by the Ohno continuous casting process

Directionally solidified binary Mg-Al eutectic alloy wires of approximately 5 mm in diameter were produced by the Ohno continuous casting (OCC) process and the mi-crostructure was examined. It was found that the wires possess obvious unidirectional growth characteristic along its axial direction. The micro structure consists of parallel columnar grains that resulted from the competitive growth of equiaxed grains solidified on the head of dummy bar. Each columnar grain comprises regular eutectic αa-Mg and β-Mg17Al12 phases, which grew along the axial direction of the wires. The morphology of the eutectic is mainly lamellar, meanwhile rod eutectic exists. The formation of rod eutectic was attributed to the “bridging effect” caused by incidental elements in the alloy.

Competitive growth of grains in ZA alloys during continuous casting with heated mould

Nucleation and competitive growth of grains in Zn–Al alloys were studied during pulling of ingots under conditions of continuous casting by the Ohno Continuous Casting (OCC) process. Microstructural observation shows that nuclei appearing on the end of the dummy bar have a disordered orientation. However, during competitive growth under conditions of directional heat flow, the ingot grows continuously, and the crystals with less favourable orientations are gradually eliminated. The properties of the alloy greatly influence the selection process. Alloys with a narrow solidification range (ZA5 and ZA8) can directly initiate their columnar structure from nuclei on the end of the dummy bar through competitive growth. Alloys with higher aluminium content (ZA12, ZA22 and ZA27) have a wider solidification range, and their parallel columnar structure evolves only later from the equiaxed crystals on the end of the dummy bar.

Development of Automatic Observation System by Applying Video-Rate Image Processing to Steelmaking Process

For the purpose of automatic diagnosis on operation and critical labor saving in iron & steelmaking industry, the development of operational automatic monitoring system with color time-series image processing technology in continuous casting process was attempted. As a result, the successful recognition rate was achieved. In this system ITV cameras are located on three monitoring areas; mold hot steel surface, dummy bar disconnection and gas cutting. With one image processor, operational and equipment failure in these areas will be automatically detected in real time. This detection system may be quite similar to artificial visual sense from the viewpoint that the algorithm for an object to be recognized is automatically selected from the image processing result.

無鋳型引き上げ連鋳装置の試作および純アルミニウム棒の製造

It has been considered that products with particular crystal structures, such as unidirectionally solidified columnar grains, a single crystal and in-situ composite eutectic structure, can be manufactured with an upward continuous casting process. In this work, after surveying many upward continuous casting processes reported in the literature, a moldless one was selected. An apparatus for this process was constructed while trial experiments with Al were performed, and the manufacturing conditions of aluminum rod by the apparatus were investigated. The temperature distribution along a cast strand was measured by a thermocouple attached to the tip of dummy bar. The crystal structure and the surface conditions of the cast strand were examined.The position of the solidification front of the cast strand was confirmed to be located at 10∼25 mm above the surface of molten metal by the temperature measurement. The configuration of the solidification front of the cast strand was determined to be flat or slightly convex from the observation of the growth direction of its columnar grains. It was confirmed that the diameter of the cast strand was determined by the temperature of the molten metal, the intensity of secondary cooling and the velocity of upward withdrawing. The cast strand with plus taper (growing bigger) was obtained at a lower temperature, a higher intensity and a lower velocity. The crystal structure of dummy bar affected that of the cast strand.The cast strand was composed of columnar crystals solidified unidirectionally. The surface conditions of the cast strand were better at a lower rotation speed of cast strand, a higher temperature of molten metal and a higher velocity of upward withdrawing.