CHINA Vol.6 No.4

Characteristics and infl uence factors of mold fi lling process in permanent mold with a slot gating system

*Chang Qingming 1, Chen Xia 1, Chen Changjun1, Bao Siqian 1 and David Schwam2 (1. Key Laboratory for Ferrous and Resources Utilization of Ministry of Education, College of Materials & Metallurgy, Wuhan University of Science and Technology, Wuhan 430081, Hubei, China; 2. Department of Materials, Case Western Reserve University, Cleveland, OH 44106, U.S.A )

Abstract: The main problems caused by improper gating are entrained aluminum oxide fi lms and entrapped gas. In this study, the slot gating system is employed to improve mold fi lling behavior and therefore, to improve the quality of aluminum produced in permanent molds. An equipment as well as operation procedures for real-time X-ray radiography of molten aluminum fl owing into permanent molds have been developed. Graphite molds transparent to X-rays are utilized which make it possible to observe the fl ow through a number of vertically oriented gating systems. The investigation discovers that there are many infl uencing factors on the mold fi lling process. This paper focuses its research on some of the factors, such as the dimensions of the vertical riser and slot thickness, as well as roughness of the coating layer. The results indicate that molten metal can smoothly fi ll into cavity with a proper slot gating system. A bigger vertical riser, proper slot thickness and rougher coating can provide not only a better mold fi lling pattern, but also hot melt into the top of the cavity. A proper temperature gradient is obtainable, higher at the bottom and lower at the top of the casting cavity, which is in favor of feeding during casting solidifi cation.

Key words: slot gating system; mold fi lling process; permanent mold CLC number: TG249.3 Document code: A Article ID: 1672-6421(2009)04-328-05

n general, a slot gating system consists of a downsprue, a specially designed slot gating system, e.g., a slot gating Irunner, vertical riser (or feeder) and a slot style of ingate. system with a vertical riser that has a thinner cross section at In this gating system, the hottest metal can be stored in the the bottom and thicker one at the top, can offer this favorable vertical riser and supplied to the casting, via the slot gate, as fi lling pattern. needed. In most cases, the height of the riser must be slightly Lots of research works [2-5] have been conducted using higher than that of the actual casting. This allows for a small water flow that was photographed. Other studies also have amount of excess pressure to counteract capillary forces. shown the behavior of liquid aluminum in sand molds using Because of the counteraction capillary forces in the thinner real time X-ray photography [6-8]. These previous works have slot, the hottest metal is always transported from the bottom shown several features in aluminum gating system that allows to the top of the vertical riser, and thereafter jetting into the the application of the maximum flow velocity while still cavity through the slot under the head pressure. One function maintains a minimum amount of oxide fi lms. However, none of this slot can be expressed as a “transporter.” As a result, a of these X-ray studies can be directly applicable to permanent slot gating system integrates the advantages of both bottom- mold casting process. It is not feasible to use metal molds gating and top gating systems, and therefore, can fi ll the hot in real time X-ray studies because the higher density of the molten metal into the cavity in such a favorable subsequence normal ferrous mold does not allow appropriate definition that can also form a temperature gradient suitable for feeding of the fl owing aluminum alloy melt. In this paper, a graphite during solidification. However, some researches pointed out mold was utilized which is oriented in a vertical direction and that not all slot gating systems have this characteristic [1]. Only parted along the centerline of the casting and gating system. *Chang Qingming The lower density of the graphite allows the fl ow of aluminum through the gating system and into the casting cavity to be Male, born in 1964, Associate professor. Directions of research: Squeezing casting and process, semi-solid metal monitored. , new technologies of materials forming process, numerical simulation for materials forming process, computer fl uid dynamics. 1 Experimental setup E-mail: [email protected] X-rays were discovered in 1895, and records of “industrial” Received: 2009-01-14; Accepted: 2009-08-01 radiographs were taken as early as 1896 [9]. S. L. Fry was

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