Papers by Keyword: Twin Roll Caster

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Authors: Toshio Haga, Hiroshi Tsuge, Shinji Kumai, Hisaki Watari
Abstract: A tandem-type roll caster that can cast a three-layered clad strip was developed by mounting one twin roll caster on another twin roll caster. In this caster, the base strip is cast by the upper twin roll caster, and the overlay strips are cast by the lower caster. The three strips are metallurgically bonded by the lower caster. This study investigated three aspects of this caster. First, the clad ratio could be controlled by the solidification lengths of strips from the upper and lower twin roll casters, and a clad ratio of 1:8:1 was attained. Second, although it is known that fabrication of clad strips from Al-Mg alloy and other Al alloys is very difficult, the clad strip with the Al-Mg alloy as the base strip or the overlay strip could be cast. Finally, by adding scrapers, the caster could cast the clad strip with a base strip having a lower melting point than the overlay strip. Element strips of the clad strip are made by many processes, such as direct chill (DC) casting, scraping of the ingot surface, heat treatment, hot rolling, and cold rolling. Typically, surface treatment and hot rolling are used to clad the strips. Since many processes are required, clad strips require consume much energy. Therefore, producing clad strips is expensive. A vertical-type tandem twin roll caster was developed to cast clad strips. This caster has the advantages of process saving and energy saving, and so can fabricate economical clad strips. In the fabrication of clad strips, control of the clad ratio is very important. In the brazing sheet for automobile radiators, the base strip is made from AA3003 and the overlay strips are made from AA4045, and the clad ratio is usually 1:8:1. In the present study, a clad strip with a clad ratio of 1:8:1 was attained. The cladding by hot rolling of Al-Mg and other aluminum alloys, which is considered to be a very difficult process, was also investigated. Clad strips with either a base strip or an overlay strip of an Al-Mg alloy were cast by the roll caster. Although the cladding was not easy, the Al-Mg alloy could be cast into the clad strip. In addition, a clad strip with a base strip having a lower melting point than that of the overlay strip was investigated. Such cladding cannot be cast by the vertical-type tandem twin roll caster as mentioned above because the base strip is re-melted from the heat of the overlay strips. In the present study, a scraper was developed and adopted to cast a clad strip with a base having a lower melting point than that of the overlay strips. This type of clad strip could be cast because the scrapers prevented the re-melting of the base strip. In this paper, these three aspects of fabrication are reported.
Authors: Toshio Haga, Hiroshi Tsuge, Takuya Ishihara, Shinji Kumai, Hisaki Watari
Abstract: A vertical type tandem twin roll caster equipped with a scraper for the clad strip was invented. This roll caster could cast three layers clad strip which base strip had lower melting point than that of the overlay strips. The base strip was cast by an upper twin roll caster and the overlay strips were cast by a lower twin roll caster. The scrapers were attached to the lower twin roll caster, and were innovated to cast this type of three layers of clad strip. Solidification layers those became the overlay strips were pulled from between the scraper and the roll. The melt of the alloy which was as same as the base strip was poured between the scraper and the base strip. This melt connect the overlay strip and the base strip. The base strip was not re-melted. The scraper enabled that the solidification layer of the overlay strip contact to the melt of the base strip without mixing of the melt of the base and overlay strip. In this way, the sound three layers clad strip which base strip had lower melting point than that of the overlay strip could be cast by the vertical type tandem twin roll caster equipped with a scraper.
Authors: Margarita Slámová, Petr Homola, P. Sláma, Miroslav Karlík, Miroslav Cieslar, Yoshitatsu Ohara, Nobuhiro Tsuji
Abstract: Accumulative Roll Bonding (ARB) is a technique of grain refinement by severe plastic deformation, which involves multiple repetitions of surface treatment, stacking, rolling, and cutting. The rolling with 50% reduction in thickness bonds the sheets. After several cycles, ultrafine-grained (UFG) materials are produced. Since ARB enables the production of large amounts of UFG materials, its adoption into industrial practice is favoured. ARB has been successfully used for preparation of UFG sheets from different ingot cast aluminium alloys. Twin-roll casting (TRC) is a cost and energy effective method for manufacturing aluminium sheets. Fine particles and small grain size are intrinsic for TRC sheets making them good starting materials for ARB. The paper presents the results of a research aimed at investigating the feasibility of ARB processing of three TRC alloys, AA8006, AA8011 and AA5754, at ambient temperature. The microstructure and properties of the ARB were investigated by means of light and transmission electron microscopy and hardness measurements. AA8006 specimens were ARB processed without any problems. Sound sheets of AA8011 alloy were also obtained even after 8 cycles of ARB. The AA5754 alloy suffered from severe edge and notch cracking since the first cycle. The work hardening of AA8006 alloy saturated after the 3rd cycle, whereas the hardness of AA5754 alloy increased steadily up to the 5th cycle. Monotonous increase in strength up to 280 MPa was observed in the ARB processed AA8011 alloy.
Authors: Ryoji Nakamura, Kenta Takahashi, Masahiko Ikawa
Abstract: An unequal diameter twin roll caster was devised in order to increase productivity of the strip. This caster could cast the strip thicker than 6mm at the speed of 5m/min. The feature of this caster is that the lower roll was four times larger than the upper roll. The solidification length of the strip could be set longer easily than the conventional twin roll caster for aluminum alloy. Lowsolidification rate semisolid casting and low superheat casting were adopted. These were effective to increase the casting speed without decreasing the thickness of the strip. In the present study, the unequal diameter twin roll caster was designed and assembled. The test castings were operated and the characteristics of this caster were shown.
Authors: Daniel R. East, Michael Kellam, Mark A. Gibson, Aaron Seeber, Daniel Liang, Jian Feng Nie
Abstract: Sheets of a Mg60Cu29Gd11 alloy were produced by twin roll casting with all operational variables, except roll speed, being kept constant. As a function of the roll speed, the structure of the as-cast sheet changed from being crystalline to fully amorphous and then back to crystalline. Through careful selection of the casting speed that is suitable for the selected alloy system and with which the exit temperature of the sheet remains within the supercooled liquid region, a malleable sheet with no surface defects is produced. This work shows that twin roll sheet casting is a viable process for the production of magnesium-based bulk amorphous sheet in a continuous manner and on an industrial scale.
Authors: Guo Dong Shi, Jun Qiao
Abstract: Annealing treatments at 200°C, 250 °C, 300°C, and 350°C were conducted on a twin-roll casted AZ31 sheet with an initial average grain size of 10.11 mm. Microstructure and mechanical behaviors were studied by optical microscope observation and tensile mechanical test. Expermeintal results show that grain size experienced three stage evolution during 180 min annealing at each temperature: recrystallization refinement, stabilization under dynamic balance of recrystallization and grain growth, and grain growth. The minimum average grain size of 5.96 μm was achieved after 120 min annealing at 200°C. The refined grain structure causes a decrease of ultimate tensile strength and an increase of elongation, and facilitates superplastic deformation of the material.
Authors: Toshio Haga, Kenta Takahashi, Shinji Kumai, Hisaki Warari
Abstract: Casting of a wire inserted strip was investigated using a downward melt drag twin roll caster. A nozzle was mounted to each roll. The wire was inserted between the lower and upper strip. Effect of use of two nozzles on the insertion of the wire was investigated. The insertion of the wire by the two nozzles was easier than one nozzle. The surfaces of the wire inserted strip cast using two nozzles was more sound than that cast using one nozzle. The position of the wire at thickness direction was almost center. When different aluminum alloys were poured from an upper nozzle and from a lower nozzle, a wire inserted clad strip could be cast.
Authors: Toshio Haga, Hideto Harada, Shinji Kumai, Hisaki Watari
Abstract: Strip casting of Al-25%Si was tried using the vertical type high speed twin roll caster. Some devices were adopted to enable the strip casting of Al-25%Si. Control of the roll gap, semisolid casting and non-use of the lubricant were useful devices to cast Al-25%Si strip. Roll-casting-ability of the Al-25%Si was discussed. The strip could be cast at 20m/min and 40m/min. As-cast strip was hot rolled down to 1mm by one pass. Bulging was tried at 550°C and it was able.
Authors: Toshio Haga, Kentaro Okamura, Shinichi Nishida, Hisaki Watari, Kunio Matsuzaki
Abstract: Casting of an Mg alloy clad strip was attempted with a twin roll caster equipped with a scraper in an oxidizing atmosphere. The base strip was AM60 and the overlay strip was AZ121. The AM60 strip was cast with a roll, and the upper side of the strip was scribed by the scraper. The molten AZ121 was poured on the scribed AM60 strip. The scribed surface of AM60 contacted the molten metal of AZ121 without exposure to the atmosphere. Therefore, the scribed surface was not oxidized. Most of the AZ121 strip was solidified by the other roll. The casting speed was 30 m/min. The roll load was 0.05 kN/mm. The roll speed was very high and the roll load was very small. However, the strips were bonded, and they did not peel with bending until breaking. The interface between the two strips was clear. When AM60 was on the outer side, the results of the V-bending test and the Erichsen test were better. These results mean that the ductility of AZ121 was improved by cladding with AM60.
Authors: R. Nakamura, Toshio Haga, H. Tsuge, S. Kumai, H. Watari
Abstract: The three layers clad strip was fabricated by a tandem positioned vertical type twin roll casters. The effect of the casting conditions of the overlay strip on the interface between the base strip and the overlay strip was investigated. The temperature of the molten metal, roll-load and solidification length were chosen as the casting conditions. Base strip was AA8079 and overlay strip was AA6022. The proper melt temperature of the overlay strip was above the liquidus line of the base strip. The proper roll-load, which was lower than rolling, was existed. There was not clearance at the interface when the solidification length was appropriate.
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