Abstract
This article looks at the ways to improve the quality of carbamide-based salt cores by introducing some cryptocrystalline graphite from the Kureysk deposit. It is shown that the introduction of 5-15% graphite activated in the RETSCH РМ 400 МА planetary mill changes the crystallization pattern of the core and turns the cavity into fine gas pores evenly distributed across the core section due to the occurrence of crystallization centers, i.e. active graphite particles which absorb gases produced by the salt mixture during its preparation. The size of the pores and the affected core surface were analysed by studying the photos which were produced on the Zeiss OBSERVER.D1m microscope with the help of the SiamsPhotolab program and processed with the help of a program designed to calculate the surface porosity. It is demonstrated that the introduction of up to 10 wt. % of graphite led to the pore size reduction from 0.19 to 0.14 mm at the core surface and from 1.54 to 0.85 mm in the core; the surface area which had pores was reduced from 1.27 to 0.03%. An increased graphite concentration (up to 15 wt.% or more) would result in zero porosity either on the surface and in the core. The high performance of the salt core surface is due to a smooth, or equilibrium, crystallization of the salt melt, which is confirmed by the results of the differential thermal analysis. The introduction of graphite does not entail a substantial change to the crystallization parameters. The research carried out to determine how the graphite concentration can effect the salt core roughness, which was analysed with the help of the TR200 profilometer, showed that 5% was the optimal graphite concentration for a salt core (with Ra decreased from 0.538 to 0.08) leading to less roughness in the resultant casting.
Keywords
Graphite, hydrochloric rod, roughness, pores, crystallization.
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