Chrome Sand Applications in Mutiple Industries

Because of its higher cost relative to other refractory materials, chrome sand is only used in those applications which produce the highest quality alloys, or in the manufacture of reactor cores. Chromite is not easily wetted, meaning a better surface finish is ensured. Unlike silica, chrome sand is basic in nature(3). For castings where a high level of chemical abrasion is likely, such as the production of high manganese ‘Hadfield’ steel, chrome sand is preferred over silica sand owing to the former’s superior chemical resistance at high temperatures.

Unlike conventional sand moulds, chromite moulds can be hard to recover and reuse should there be moderate-to-high amounts of silica present. This is due to a greater likelihood of the chrome becoming contaminated by the silica, and thus its refractoriness is reduced(4). Chrome sand refractories are typically used as a ‘facing sand’ in silica moulds(5). Contemporary research has, however, displayed some process to allow for release and reuse of chrome sand castings when using an alkali phenolic binder. In terms of economics and environmental sustainability, this is an important step forward. Researchers found that the order of operations in dismantling a chrome sand casting system was important, as was paying attention to the temperatures throughout the process(6).. Chemical analyses performed on the chromite matrix and at the surface/interface - naturally - suggested some chemical change post heat treatment. Whilst more research is needed, the concept that a chrome sand casting is a one time only event may soon be disappearing.

Another study that looked at reusability of chrome sand noted that the higher proportion of silica present in the sand mixture, the less reusable the material is(7). They also observed that chrome sand castings produce fewer finings than an equivalent silica mold would - meaning less new sand needs to be added for subsequent castings. Overall, they regard the material as “green” from an environmental standpoint. This method refers to the repeated use of a single casting mold, as opposed to the earlier reuse method of dismantling and then regenerating another mold.

Casting molds are often made in a traditional way, a box is placed over a shape for which a negative is required, sand is poured in and then the assembly may be heat treated. Green sand - and other types of - molds, on the small scale, have been produced via 3D printing methods(8) with high degrees of precision and success. 3D printing has become a popular choice for laying down chrome sand based molds, with intricate detail available in short times(9). Lower quality chromite - such as that reclaimed from other industrial processes - does not have the same levels of thermomechanical robustness as freshly mined and milled chrome sand. It is likely that sintering will occur during the casting process if low quality chrome sand is used, thereby producing an inferior final product(10).

With regards to sintering - the process of forming a solid mass through heating without melting - chrome sand in its purest form is generally regarded as a material that sinters at a high temperature(11). If sintering occurs at a lower temperature, this is due to the presence of impurities, such as excess silica or other fine particles. Such effects can lead to a higher prevalence for casting defects. Therefore, it is imperative to use the purest chrome sand possible.