圓曲擴散流道設計應用於鋁合金重力鑄造

Curved Diverging Runner Design Applied to Aluminum Gravity Casting

羅章元(Zhang-Yuan Luo) ； 許富淵(Fu-Yuan Hsu) ； 洪啟銘(Chi-Ming Hung) ； 馮玉麟(Yu-Lin Feng)

《鑄造工程學刊》 47卷3期 (2021/09) Pp. 13-26

摘要

鋁合金重力鑄造在流道設計時，需要讓金屬流體進入模穴時之速度降低至所謂的底澆臨界速度（0.5 m/s）以下，讓鋁合金金屬液體穩定的從模穴底部慢慢充填。如果鋁合金金屬液體超過澆鑄臨界速度時，澆鑄時液體表面的氧化膜會捲入至金屬流體的本體內，而造成鋁合金鑄件的品質下降。本研究應用所謂圓曲擴散的流道設計，希望能在最小空間內，設計圓曲擴散流道，連接在豎澆道出口處。在此處的液體動能達到最大，當進入此轉彎且橫向截面漸大的擴散流道形體（圓曲擴散流道），當轉為水平方向的同時將液體橫向分散開，使金屬液體橫向分散增加其截面積。能在質量守恆的情況下，希望流量變大，而擴散的金屬液體流速因而下降。應用計算流體動力模擬軟體，模擬鋁合金液體在不同尺寸的圓曲半徑下，液體經歷轉彎的同時，其橫向截面積擴大的過程，分別針對三階段的轉彎形體的液體速度變化進行分析，以找出最佳的圓曲擴散流道，使用水模實驗驗證電腦模擬的差異性。本研究的最佳圓曲擴散流道之三個階段圓曲半徑分別為50、23及22 mm，以及其入口與出口截面積比分別為1.49、1.5及1.8。由鋁液模擬結果可以預測最佳圓曲擴散流道，能使高動能流體轉換成靜壓力，其壓力回覆係數為1.38，意指能降低鋁液速度至0.42 ±0.01 m/s，此為低於臨界速度以下，如此能有助於避免鑄造過程捲入雙膜缺陷、氣泡等問題。再者，流出係數（Cd）為1.27，鋁液澆鑄流量能增加至為1.24 ×10^(-3) ±0.035 ×10^(-3) m^3/s，此可以縮短整體鑄造時間，以及避免冷接問題。本研究所提出的最佳圓曲擴散流道，可達到降低流體速度並且提高流量，所謂最佳流道方案設計的目的。

關鍵字

鋁合金鑄造 ； 重力鑄造 ； 底澆臨界速度 ； 流道方案設計 ； 圓曲擴散流道 ； 雙膜缺陷

並列摘要

In the runner design of aluminum alloy gravity casting, the velocity of the liquid metal entering the mold cavity needs to be reduced below the so-called critical bottom-ingate velocity (0.5 m/s), so that the aluminum alloy metal liquid is quiescently filled from the bottom of the cavity. If the liquid aluminum alloy exceeds the critical velocity, the oxide film on the surface of the liquid will be entrained into the bulk of the metal fluid during casting, deteriorating its quality. In this study, the so-called curved diverging runners were designed, and were connected to the outlet of the sprue within the compact region of sprue-runner juncture. At that region, the kinetic energy of the liquid metal reaches the maximum. This high speed of liquid metal enters this turning geometry of the runner along an increasing cross-sectional area as it turns in this runner (i.e., the curved diverging runner). During turning from the vertical to horizontal directions, the liquid dispersed crosswise in this curved diverging runner. Based on the mass conservation, it is expected that through this diverging runner the flow rate of the metal liquid is increased as increases the velocity is decreased. A Computational-Fluid-Dynamic package was used to model the liquid aluminum within the various radii of curvatures of the curved runners and to analyze an increase of its cross-sectional area as it diverging transversely along this curved geometry. Finally, the water model experiment was used to verify the difference of the computer simulation. In this study, the optimized curved diverging runner design including in three steps of curved diverging runners. For this three-step runners, their curvature radii are 50, 23, and 22 mm and their inlet and outlet area ratio are 1.49, 1.5, 1.8 respectively. In the aluminum modeling result, the pressure recovery coefficient, which is the efficiency of transforming the kinetic energy to static pressure, is 1.38 for this optimized runner. It is achieved that the velocity of liquid aluminum decreases to 0.42 ±0.01 m/s, which is under the critical bottom-gate velocity. Thus, the entrapment of bifilm defect and bubble during casting can be avoided. Moreover, the coefficient of discharge (Cd) is 1.27 and the flow rate of liquid aluminum increases to 1.24 ±0.035 ×10^(-3) m^3/s. That the filling time can be reduced and the cold-shut problem can be prevented. The optimized runner system with low velocity and high flow rate was achieved by the curved diverging runner proposed by this study.

並列關鍵字

aluminum alloy casting ； gravity casting ； critical bottom-ingate velocity ； runner system design ； curved diverging runner ； bifilm defect

參考文獻

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