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Vol. 26 No. 45 (2017)

Papers

Development of a refractory mold based on chamotte/plaster for jewelry micro-casting with pre-set emeralds

https://doi.org/10.19053/01211129.v26.n45.2017.6421

Published 2017-04-30

  • Carlina Sofía Londoño-Montes
    • ,
  • Mayerly Jhojana Fernández-Torres
    • ,
  • Elcy María Córdoba-Tuta

Carlina Sofía Londoño-Montes
Universidad Industrial de Santander (Bucaramanga-Santander, Colombia).

Mayerly Jhojana Fernández-Torres
Universidad Industrial de Santander (Bucaramanga-Santander, Colombia).

Elcy María Córdoba-Tuta
Universidad Industrial de Santander (Bucaramanga-Santander, Colombia).

Abstract

During the jewelry stone-in-place micro-casting process, the ceramic mold, which is composed of silica and plaster is stabilized at temperatures close to 650 °C, whereas the casting temperature of the precious metal alloy hovers around 1000 °C. Therefore, this type of micro-casting technique is not suitable for gems such as emeralds, since they are highly susceptible to damage at temperatures over 350 °C. In the face of this fact, the main purpose of the present work is to develop a refractory mold based on chamotte and plaster, which can be stabilized at low temperatures, in order to use it for the micro-casting of pre-set emeralds. To achieve this, the experimental methodology was divided into three phases: i) raw chemical materials, mineralogical, granulometric and thermal characterization; ii) preparation and characterization of chamotte-plaster-water mixtures, including the measurement of casting times, mechanical and microstructural properties, permeability, and resistance to thermal shock; and iii) evaluation of the resulting refractory mold in the micro-casting of pre-set emeralds. The results showed that the refractory mold with composition chamotte/plaster 75/25, an addition of 50 % of water to the dried mixture, and fine granulometry (-200 mesh) had a stabilization temperature of 350 °C. Furthermore, it is possible to subject the emeralds to the stone-in-place micro-casting process that employs the refractory mold developed here, with a thermal treatment that does not surpass the 350 °C, along with a low melting point (398 °C) for the precious metal alloy.

Keywords

Chamotte, Emeralds Micro-Casting, Plaster, Refractory Mold, Stone-In-Place

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