Effect of Dispersant on Fiber-Reinforced Shell for Investment Casting
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Copyright Ó 2020 American Foundry Society https://doi.org/10.1007/s40962-020-00409-2
Abstract In this study, a novel preparation route of shells for investment casting was proposed. To this end, hydroxypropyl methylcellulose (HPMC) was used as fiber dispersant, and its influences on rheological behaviors of slurry and strength of shell were studied. The addition of carbon fibers with different lengths and concentrations was also explored. The results suggested that suspension and viscosity of the slurries with HPMC were higher than those prepared without HPMC due to dispersion and tackily effects of HPMC on fibers and slurries. The fibers were
found uniformly dispersed in the slurry, and fracture shell was uniformly distributed in the shell thanks to the presence of the dispersant, leading to enhanced shell strength. In addition, higher firing temperatures led to denser shell and superior strength.
Introduction
permeability of shells, as well as enhance stress of shells at high temperatures. Fibers, such as ZrO2, nylon and aluminum silicate, were used during the preparation of fiberreinforced shells.10–13 Shells prepared for investment casting are often subjected to high internal pressure and thermal stress. In particular, the corners and edge regions would be subject to large mechanical stress during processing.14 Wang et al.15 added needle coke to increase the shell thickness by a factor of 30% on flat section and 60% at sharp edges. Needle coke was also used to enhance the permeability of ceramic shells.16 Glass fiber combined with aluminum silicate fiber was added to the slurry to yield fiber-reinforced shell, in which the firing process should affect the properties of shells.17
Investment casting or precision casting is widely used in the production of high-precision castings of various alloys.1 The technological characteristics facilitate the casting process and prevent structure complexity. The deformation and strength are the most important properties among performance requirements of shells. Finite element analysis is often used to evaluate the deformation, as well as for interpretation of the phenomena like generation, propagation, and accumulation of dimensional variation during investment casting process.2–5 The strength of shell service is affected by its thickness, composition, and manufacturing process. However, it is quite difficult to prepare thick shells for large castings. In other words, thicker shells would extend the preparation periods. Refractories and adhesives could also affect the strength of shells. Insufficient strength and long preparation periods of shells would limit the use of casting methods.6–8 Some current research studies have focused on improving shell strength by increasing the thickness of mold shell. However, this would reduce the heat dissipation of the shell and mechanical properties of the casting. The mixture of shell reinforcement is a relatively new route. For instance, Tamta and Karunakar9 used camphor to improve the
International Journal of Metalcasting
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