Fu-Yuan Hsu

Vortex-gate design for gravity casting

Abstract A novel runner system design, named a Vortex-Gate, has been explored for aluminium gravity casting. Using this design, the velocity of flow of the liquid metal was controlled below the critical velocity and, at the same time, a high flowrate was maintained. The flow behaviour achieved did not appear to generate either bifilm or bubble defects. The virtual experiment using a computational modelling package, and the physical experiment, a real-time X-radiography study, were found to be in reasonable agreement.

Bifilm defects in ductile-iron support bracket castings

Abstract Many filling defects such as bi-film defect, gas bubble, loosed sand and etc., are developed by turbulent filling. These defects entrapped and flowed along mold cavity during the filling process. As a result, they makes casting property unreliable and unpredictable. The best way to prevent the filling defect is to control the gating velocity under a critical value using a bottom gating runner system. Two different gating system, top- and bottom- systems, are applied for casting ductile-iron support bracket. For these two runner systems, their filling defects are predicted by a numerical modeling. Two- and three- parameter Weibull probability are plotted to analyze the reliabilities of the mechanical properties of the castings from these two gating systems. A good and reliable runner system for casting a high elongation and fracture toughness of the support bracket was proposed in this study.

Ceramic Foam Filters in Runner System Design for Castings

In the design of runner systems, ceramic foam filters are used for reducing the velocity of liquid metal in order to avoid so called bifilm defect resulting from a high gating velocity (over its critical gating velocity) in aluminum gravity casting. In this study, two types of runner systems incorporated with the ceramic foam filters were designed. In order to observe the flow phenomena in these two runner systems with and without the filters, a water analogy experiment in a transparent plastic mold was utilized. Furthermore, in order to understand the effect of the filters used in these systems, an aluminum sand casting experiment was conducted. The quality of the cast metal in the outlet area of the filter for these systems was investigated. The defect content of this casting sample was measured by the re-melt reduced pressure test (re-melt RPT) and followed by measuring its bulk density. An optimized runner system with the filter was suggested in this study. Keywords: ceramic foam filter, runner system design, gravity casting, critical gating velocity, bifilm defect.

'Designing-in' controlled filling using numerical simulation for gravity sand casting of aluminium alloys

Abstract The requirements of a good running system are briefly outlined. These include classical components such as the pouring basin, downsprue, runner and gating system. Even so, it is noted that putting everything together and achieving a good working solution at the junctions between these features remains a challenge. Some recent results are presented of exploratory designs for the sprue/runner junction. Both good and bad findings are described.

The Reliability of Ductile Casting Iron Dependent on Runner System Design: An Example of Support Bracket of Brake Caliper

Two causes of casting defects are the defects developed by solidification and by filling in mold cavity. For the solidification it is easily predicted from observing casting’s 3D geometry. For the filling, it is very difficult. Since the mold is opaque the filling condition cannot be observed directly. Many casting defects such as bi-film defect, gas bubbles, loosed sand and etc., are produced by turbulent filling. The defects entrapped and floated within casting result in unreliable casting properties.

Bifilm Defect Formation in Hydraulic Jump of Liquid Aluminum

In aluminum gravity casting, as liquid aluminum fell through a vertical sprue and impacted on the horizontal flat surface, a phenomenon known as hydraulic jump (i.e., flow transition from super-critical to sub-critical flows) was observed. As the jump was transformed, a reverse eddy motion on the surface of the jump was created. This motion entrained aluminum oxide film from the surface into aluminum melt. This folded film (so-called “bifilm” defect) was engulfed by the melt and caused its quality to deteriorate. To understand this phenomenon, aluminum casting experiments and computational modeling were conducted. In the casting experiment, a radius (Rj) to the point where the circular hydraulic jump occurred was measured. This is the circular region of ‘irregular surface feature’, a rough oxidized surface texture near the center area of the castings. To quantify contents of the bifilm defects in the outer region of the jump, the samples in this region were sectioned and re-melted for doing re-melted reduced pressure test (re-melt RPT). An “area-normalized” bifilm index map was plotted to analyze bifilms’ population in the samples. The flow transition in the hydraulic jump of liquid aluminum depended on three pressure heads: inertial, gravitational, and surface-tension pressures. A new theoretical equation containing surface tension for describing the flow transition of liquid metal was proposed.

Boiling Phenomena of Cooling Water in the Permanent Mold

The boiling phenomena of water in a cooling channel within a permanent mold were studied. The test consisted of heating the mold to high temperatures 1300°C (2372°F) for 0.5 ms (milliseconds) followed by low temperatures 200°C (392°F) for 49.5 ms. This heating procedure was to simulate the heating condition on the copper wheel mold applied in planar flow casting process.When the velocity of water into the channel was under a critical velocity (1.9 m/s), the boiling condition of the coolant could be attained. In the boiling state, the values of the heat transfer coefficient (i.e., heating capability to coolant) and heat flux (i.e., heat absorption capability by coolant) were much greater than those in the non-boiling state. The initial water temperature affected the time to initiate bubbles.A diagram of the heat flux against the heat transfer coefficient was created to analyze the heat removal efficiency of water coolant. A slope value of the linear relationship in the diagram can be applied to classify the states of the boiling flow patterns, boiling nucleation, bubble flow, and plug flow.

Runner Systems Containing Ceramic Foam Filters Quantified by “Area Normalized” Bifilm Index Map

In the runner system design for aluminum gravity castings, ceramic foam filters were used for reducing the velocity of liquid metal to avoid “bifilm” defects resulting from a high gating velocity (over its critical gating velocity). In this study, three types of runner systems incorporating ceramic foam filters were designed. To observe the flow phenomena in these systems, a water analogy experiment in a transparent plastic mold was utilized. To understand the effect of the filters used in these systems, aluminum sand casting experiments were conducted. The defect contents inside the casting samples in the outlet area of filters were measured by remelt Reduced Pressure Test (remelt RPT) and followed by measuring their bulk densities. A new “bifilm” index map, which uses the index values normalized by the metal area without porosity, was proposed. Finally, an optimized runner system with filter was suggested.

Simulation of Glass Molding Process for Planar Type SOFC Sealing Devices

The glass sealant with pre-forming frame structure, used for joining dissimilar materials of planar type SOFC devices, was fabricated by molding process. The flow phenomena during glass molding were investigated by computational modeling. The physical properties of glass sealant fluid were constructed in numerical models. The process parameters, such as mold pressing velocity, initial glass fluid temperature (or viscosity of glass sealant), and initial mold temperature, were examined. As results, the sealants formability could be characterized by molten glass temperature, near the gap between upper and lower molds. If the temperature is greater than its glass transformation temperature Tg, the formability become better, and vice versa. Keywords: solid oxide fuel cells (SOFCs), computational modeling, glass sealant.