Zircon sand and silica sand used in sand casting

Zircon sand is the common name for zirconium silicate (ZrSiO4). Zircon sand is only one step within the temperature range encountered in metal casting. The linear expansion of zircon depends on the temperature up to 1000uC; from room temperature to 1000uC, extends zircon 0? Beyond 1000uC 0.1 3%, the expansion levels. Figure 1 shows the expansion curve for zircon sand based on data from Henschel et al. 2 Given the hope that the expansion characteristics zircon sand to be very predictable, can zircon cores critical information on restrictive the sand on the steel to provide contracting. Unlike zircon sand, silica sand can undergo a phase transformation related dimensional changes in the temperature range seen in steel casting applications. Therefore, there is a brief discussion of the silica phases and transformations available to understand the experimental results. 22 step is called silica.
However, the discussion will be limited to the low and high quartz, tridymite, and low and high cristobalite. The transition from one phase to another depending on the temperature, time at temperature, and is the point of equilibrium for quartz inversion low to high quartz other substances.3 573uC spot. The inversion is accompanied by extension, reported to be in the range of 1? 1 to 1? 6%. Sources agree that the inversion will occur quickly if the temperature inversion is reached. On cooling, the inversion can return to low quartz also be rapid.1,3-5 the theoretical inversion temperature quartz to tridymite is 870uC. Sosman3 reported that the conversion of quartz to cristobalite favored over converted to tridymite.

Cristobalite is the stable phase of silica over 1470uC. Can convert directly quartz to cristobalite at temperatures as low as 870uC. Sosman reports that the slow pace of formation of cristobalite below 1200uC, but quickly becomes over 1300uC. The reaction heavily influenced by the presence and amount of other substances.3 there is evidence that the transformations occur fast enough sand to affect the model and solutions. For example, common sand casting problems such as spalling, buckling and scabs due to the expansion of sand because Carniglia5 transformations.1 noted that it is impossible to convert cristobalite or tridymite back above 870uC quartz, because not The final phase stable at such high temperatures. At temperatures below 870uC, kinetic barriers are too high to allow the conversion to occur.5 Andrews et al. 6 measuring the linear thermal expansion of the materials molding sand with different binders for different additions of iron oxide, and climate simulation model. The results show for large linear expansion of silica sand up to 12% at temperatures above 1200uC. The expansion is attributed to the formation cristobalite.3,7 The results are shown. searching the literature reveals no methods to predict the contraction of complex metal castings features a priori.

However, to provide for different bodies of research on the topic view. Wallace8 Bates and measuring the displacement wall mold a probe implanted in silicate and sodium bonded green sand molds used for steel castings. For sodium silicate bonded molds, limited the mold wall expansion at the high strength of the bond and the lack of a weak layer of high humidity found in green sand molds. Mould displacements occurred before adequate skin formed solidified steel. Engler et al. 9 had green sand molds, was heated by radiation, mold wall displacements displayed like models in which steel is poured, reflecting not the hydrostatic pressure of the liquid steel important variables.

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