UBC Theses and Dissertations
An investigation of the efficacy of a water-cooled chill in improving the as-cast structure of the main bearing bulkhead in A319 engine blocks Farhang Mehr, Farzaneh
In recent years, the automotive industry has been increasing the production of small, high-power gas engines as part of several strategies to achieve the new “Corporate Average Fuel Economy” (CAFE) standards, while at the same time meeting consumer demand for increased performance. This trend requires an improvement in the thermal and mechanical fatigue durability of the aluminium alloys used in the production of the cylinder heads and engine blocks in these engines. In the absence of modifying alloy chemistry, which potentially has significant implications for downstream operations such as heat treating and machining, one viable way to improve fatigue performance is to reduce the length-scales of the microstructural features arising from solidification that limit fatigue life. This, in turn, may be achieved by increasing the cooling rate during solidification (reducing the solidification time). Conventionally, solid chills are employed in industry to achieve this. A potential means of improving the efficacy of these chills is to incorporate water cooling. To assess the effectiveness of this method, a water-cooled chill was designed at UBC and installed in a bonded-sand engine block mould package (1/4 section). Twelve experiments were conducted with both a conventional solid chill and with a water-cooled chill (with and without a delay in water cooling). The moulds were instrumented with thermocouples to measure the evolution of temperature at key locations in the casting, and “Linear Variable Displacement Transducers” (LVDTs) to measure the gap size at the interface between the chill and the casting. A coupled thermal-stress mathematical model was developed in “ABAQUS 2016” to reproduce the experimental conditions and provide insight into interfacial heat transport and gap dynamics. Overall, the experimental and modelling results show the gap dynamics are complex and play a critical role in governing heat transport. If implemented carefully, the adoption of water-cooled chill technology has the potential to improve the cast microstructure, hence, increase the fatigue durability of the engine blocks.
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