Papers by Author: Ryoji Nakamura

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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.
145
Authors: Shinji Kumai, Yusuke Takayama, Ryoji Nakamura, Daisuke Shimosaka, Yohei Harada, Min Seok Kim
Abstract: A horizontal-type twin roll casting method has been popular for producing aluminum alloy strips, however, it is characterized by a relatively low productivity (1~6 m/min). In contrast, a vertical-type high-speed twin-roll casting method possesses an extremely high productivity (60~120 m/min (1~2 m/s)) and an excellent heat extraction ability. The rapid cooling effect provided significant microstructure refinement and mechanical properties improvement in various kinds of cast aluminum alloy products. Not only “product to product recycling” but also “up-grade recycling” can be achieved by making good use of these merits. Two examples of application showing the potential of vertical-type high-speed twin roll casting method are presented. (1) Several kinds of Al-Si base alloy were cast into the strips. Not only strength and toughness but also formability was increased in the twin roll cast products. In particular, great improvement in deformability shows the potential of the twin-roll cast aluminum alloy products as substitutes for some wrought aluminum alloy products. (2) The vertical-type tandem twin-roll caster was able to fabricate a clad strip by single step. The A4045/A3003/A4045 aluminum alloy clad sheets produced by the twin-roll casting showed better mechanical properties than the conventional hot-roll bonded clad sheets.
56
Authors: Ryoji Nakamura, T. Asai, Hisaki Watari, Shinji Kumai
Abstract: Rheo-casting of 4045 aluminum alloy bar was operated using an unequal diameter twin roll caster and a cooling slope. The semisolid slurry was made by the cooling slope. The thickness of the bar was 12 mm and width was 100mm. The casting speed was 1m/min. Quantity of the melt poured on the cooling slope was important to make sound bar. The primary crystal became spherical, and its size was about 40μm.
295
Authors: Ryoji Nakamura, Ryoji Nakamura, Shinji Kumai, Hisaki Watari
Abstract: A vertical type tandem twin roll caster which can cast clad strip was devised and assembled. The casting of the clad strip was tried. The three layers clad strip could be cast by a vertical type tandem twin roll caster at only one process. The clad strip was connected directly from AA8079 and AA6022 at roll speed of 30m/min. The diffusion area between the strips was very narrow. The interface between the strips was clear and flat. The strips were bonded firmly.
1053
Authors: Ryoji Nakamura, Masakazu Sawai, Ryoji Nakamura, H. Watari, S. Kumai
Abstract: An unequal diameter twin roll caster which can cast clad strips was devised and assembled. The casting of the clad strip was tried, and fabrication of the clad strip was attained. This twin roll caster was planned for the process saving. The clad strip was assembled directly from AA3003 molten metal and AA4045 molten metal at speed of 20m/min. The Si-diffusion-area between the strips was very narrow, and the interface between the strips was clear. The strips were bonded firmly. The strips were not pealed by the cold rolling and the continuous bending.
413
Authors: Ryoji Nakamura, Toshio Haga, Kenta Takahashi, Shinji Kumai, Hisaki Watari
Abstract: The net-inserted metal matrix composite strip could be cast by a twin roll caster at only one process. The net could be inserted in the strip or lower surface of the aluminium alloy strip. The matrix was Al-12mass%Si, and inserted net was made from SUS304 stainless steel. The diameter of the wire of the net was 0.29mm, and distance between the wires was 0.98mm (#20). The roll speed was 30m/min. The net was not reacted with the matrix, and there was not gap between the matrix and the net. The mechanical property of the net-inserted composite strip was affected by the direction of the wire of the net. When the angle of the wire against the tensile direction was 45 degrees, elongation of the composite became better than that of the matrix from 14% up to 23%. This reason was improvement of the local contraction of the composite strip. The net-inserted composite strip could be cold rolled. The reduction of the net was smaller than that of the strip. The reduction of the wire at rolling direction was larger than that of the wire at lateral direction.
1899
Authors: Ryoji Nakamura, Toshio Haga, H. Tsuge, S. Kumai, H. Watari
Abstract: The three layers clad strip was fabricated by a vertical type tandem twin roll caster for clad strip (VTTCC). The effect of the casting conditions of the base strip and the overlay strip on the interface between the base strip and the overlay strip was investigated. The temperature of the molten metal and roll-load were investigated casting conditions. Base strip was AA8079 and overlay strip was AA6022. The proper melt temperature of the overlay strip was around the liquidus line of the base strip. The proper roll-load, which was smaller than rolling, was existed.
4037
Authors: Hisaki Watari, Yoshimasa Nishio, Ryoji Nakamura, Keith Davey, Nobuhio Koga
Abstract: This paper describes the twin-roll casting technology of magnesium alloys that contain relatively high weight ratios of aluminum, such as AM60, AZ91 and AZ121. The magnesium alloy sheets were cast by a vertical roll caster to manufacture relatively high-strength Mg alloys with high aluminum content. The influences of such process parameters as roll materials, casting temperature, and roll speed were ascertained. A simple method of predicting the convection heat transfer coefficient between casting rolls and molten metal is introduced. The microstructures of cast magnesium alloy sheets are microscopically observed to investigate the effects of roll-casting conditions on crystal growth in the cast products. It was found that Mg alloys with high aluminum content can be fabricated at a roll speed of 90m/min with a vertical-roll caster. The grain size of the manufactured wrought magnesium alloy sheet was about 30 micrometers due to rapid solidification in the proposed process.
1077
Authors: Hisaki Watari, Keith Davey, M.T. Alonso Rasgado, L.D. Clark, Ryoji Nakamura, Nobuhio Koga
Abstract: Effects of rolling conditions on warm deep drawability of cast magnesium alloy that were hot rolled after roll strip casting were investigated to ascertain the feasibility of twin-roll strip casting process of AZ31B magnesium alloy. Hot rolling and heat treatment conditions were changed to examine which conditions were appropriate for producing AZ31B wrought magnesium alloys after strip casting process. Microscopic observation of the crystals of the manufactured wrought magnesium alloys was performed. It has been found that a limiting drawing ratio of 2.7 was possible in a warm deep drawing test of the cast magnesium alloy sheets after being hot rolled.
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