Investigation of the Stability of Melt Flow in Gating Systems
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ating technology that is used today is based on comprehensive experiments from the 1950s.[1–4] Systems were developed for the manufacturing technology, casting process technology, and casting requirements of that time. Many experiments were based on studies of water flowing through plastic model gating systems or with low melting point alloys in sand molds. These results were related to metal flow through the Reynolds number.[2,4,5] Researchers also investigated flow control through multiple gates and found guidelines for relations between areas in the gating system that would distribute the melt and secure nonturbulent flow.[1–5] It was from this work that Johnson et al.[6] defined and classified gating systems as pressurized or nonpressurized depending on the strategy used to control melt flow. The results led to the development of a set of design rules that quickly found recognition as the preferred methodology for making gating systems. The system has several advantages, such as it is simple to use, it is easy to manufacture, and it can be used to produce good quality castings for many applications. A more theoretical fluid mechanical approach was taken by Nielsen,[7] who showed how all parts of the gating system could be designed to confine and direct NIELS SKAT TIEDJE, Associate Professor, is with the Department of Mechanical Engineering, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark. Contact e-mail: [email protected]. PER LARSEN, Innovation Manager, is with DISA Industries A/S, Herlev Hovedgade 17, DK-2730 Herlev, Denmark. Manuscript submitted December 7, 2009. Article published online November 2, 2010. METALLURGICAL AND MATERIALS TRANSACTIONS B
flow so that aspiration and vena contracta could be avoided. This approach was intelligent and comprehensive, but it was complicated to use in practice particularly with the manufacturing technology available at the time. The emergence of the vertical molding technology where the pressure head in the gating systems for smalland medium-sized castings were significantly increased, led to the development of a methodology that in essence was a combination of the traditional systems and the principles given by Nielsen.[8–11] Andersen and Ingerslev[12] showed experimentally that metal flow is highly dependent on viscosity and surface tension. They used an experimental approach using both liquid cast iron and water in their work. It was demonstrated that it is not possible to use water as a model material to analyze the initial transients in mold filling if experiments are scaled only by the use of the Reynolds number. Other model numbers such as Weber, Nusselt, and Prandel numbers should be considered. Campbell and coworkers[13–18] showed through years of comprehensive research how turbulence in the gating systems always dominates when the first melt flows through the gating systems. This work showed that the initial filling of gating systems was the cause of many defects found in castings.[15,19,20] It led to recommendations on maximum velocities in the ingates to the castin
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