68th Annual Technical Conference & Exposition TUESDAY, continued 10:55 a.m. - 11:35 a.m.
Paper No. 13: The Effect of Firing Temperature & Time on Silica Based Investment Shells Strength Samuel Holt, Georgia Southern University Silica based shells are commonly used in the investment casting industry for its superior dimensional stability, thermal shock resistance and ease of removal. Investment shells are generally fired and/or preheated prior to the casting process to remove pattern residue and increase shell strength by sintering. However, it has been found in previous research that, if the firing time is not closely monitored, extended firing/preheating can weaken the room temperature shell strength, due to the coarsening of the ceramic grains. In addition, the reduction of surface area of fused silica impairs the amorphous to cristobalite phase transformation during the casting process, which causes difficulty on shell removal. In this study, the effect of firing time at different firing temperatures on the shell hot strength at elevated temperatures were systematically studied. Recommendations on
maximum firing time were discussed. LE-147is
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11:35 a.m. - 12:15 p.m. Paper No. 14: Process Cycle Time Analysis & Optimisation for Efficient Vaccum Precision Investment Casting Furnaces Iñaki Vicario, Consarc Engineering, Ltd., Booth 313 The production of advanced superalloy components for applications in aerospace, power generation, automotive etc industries is accomplished in Vacuum Precision Investment Casting (VPIC) furnaces. Consarc recognises the technical and commercial importance involved in optimising modern VPIC operation efficiency, and apply these to their state of art VPIC furnace technologies.
The Vacuum Precision Investment Casting process includes many activities to perform a complete casting cycle. There are many sensitive and complex operations, including: mould loading into the furnace, mould pump down stage, mould raise to heating/pouring position, mould heating (DSSX process), liner and ingot loading, alloy melting, mould pouring, casted mould unloading and used liner removal. Among each of these operations, there are many subtasks that should be identified, analysed and optimised.
Proper cycle process time analysis enables a view of the time consumption of each process stage, and the best synchronisation strategies to avoid wasted time and ensure the fastest cycle time is achieved.
This work will show how furnace design principles can permit the operator to achieve the fastest, most productive, most efficient, and reliable casting process.
12:15 p.m. - 1:00 p.m. LUNCH 1:00 p.m. - 1:40 p.m.
Paper No. 15: Pattern Cleaning Mark Oles, Pine Tree Castings Alfred Kaulius, Paramelt, Booth 309 Why clean a wax assembly prior to the application of the prime coat? A pattern cleaning operation involves labor, materials and disposal costs that can be significant. This operation would not be performed unless there was some benefit in casting quality. The most common reason is to improve prime coat wax adhesion to prevent shell buckle.
The adhesion of a prime coat to a wax pattern is dependent on the ability of the prime coat to wet the wax. For successful bonding to occur, the surface tension of the prime coat must be lower than the surface energy of the wax pattern.
This collaborative paper will demonstrate several methods of measuring the surface energy of wax patterns and show the relationship between surface energy and prime coat bond strength.
24 ❘ October 2021 ®
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