Emerges as an alternative to chromite sand that realises a saving of 40% of sand consumption.

In an interview with Willie Nicklin, Commercial Manager for Imerys in South Africa, Nicklin said: “The final quality of the metal casting is the result of a tremendous amount of controlled parameters inside the foundry. On a daily basis, parameters such as pouring temperature, sand quality, moulding conditions, etcetera are leveraged by metal casters to balance quality versus the yield of production, which usually have an opposite trend.”

“The moulding sand and the sand used for core making have a direct impact on the casting quality, and thus on the efficiency of production. The use of special sands has been widely spread to reduce sand fusion, metal penetration, and veining. Despite the high price, such product choices can generate significant savings in the foundry process, particularly referring to the lower scrap percentage as well as the shorter finishing time. On top of that, nowadays, health and environmental conditions are critical and have to be taken into consideration when the sand type is chosen,” continued Nicklin.

“Two of Imerys’ sands, Kersand (AFS 60), which is mined and produced in France and Durandal 60 (AFS 50), which is mined and produced in South Africa, are now used regularly by sand casting foundries and tests show that they fulfil the requirements in terms of refractoriness and thermal expansion. The two products are similar, made with natural minerals. In addition, they are respirable crystalline silica free, and this over the several sand processes. The two sands are performing well in all steel alloys, cast iron and copper alloy foundries and are compatible with all types of binding systems (organic and inorganic), and furthermore, generate no low melting temperature point when mixed with silica sand.”

Market conditions
“Chromite is commonly used for its refractoriness properties as well as for its anti-veining characteristic. Nevertheless, in a two-year time period, chromite prices FOB in South Africa have more than doubled from the initial prices. This clearly shows the high volatility of the chromite sand market price and how it can have a considerable effect on pricing, especially in Europe. This is not surprising, considering that all South African producers are primarily in the ferrochrome business producing metallurgical grade, with non-metallurgical grades being produced as a by-product. The production cost of foundry grade chromite is considerably greater than the production cost of sintered metallurgical grade chromite. The majority of the chrome ore deposits are usually providing undesirable foundry properties due to their formation type, crystal size and impurities, therefore, extra processing is needed to reach the necessary final properties.”

“Special sand, even if used in a lower volume compared to silica sand (for instance 10%), can represent roughly half of the expenses when compared to silica sand, resin and coating cost.”

“New types of special sands were developed over the past 10 years, in order to improve the performance and compensate the high price volatility associated with the traditional chromite sand. Durandal D60 and Kersand are two natural mineral products that have been designed specifically to reduce casting defects and are respectively produced in South Africa and France. European sourcing is an important advantage considering logistic delivery delays as well as the geopolitics stability situation.”

Technical considerations
“Chromite sand is heavy and will need 40% more in weight to fill the same volume of cores compared to Kersand and Durandal 60. This is a key point regarding sand consumption. Indeed, loose bulk density is around 1.6 for Kersand and Durandal 60 whereas chromite sand lies at 2.7. This difference leads to immediate savings of 40% of sand consumption for a constant volume of core produced.”

“In a direct comparison of Kersand and Durandal 60 versus chromite sand, in terms of thermal expansion, both Kersand and Durandal 60 show linear expansion with temperature compared to silica, which exhibits the well-known transition quartz α to β at about 573°C. Furthermore, this expansion is low compared to silica and chromite. Thermal expansion, on top of refractoriness, has a direct impact on veining defects. Anti-veining properties have been proven in numbers of foundries, in tough casting conditions for Kersand and Durandal 60 products.”

“Iron casting has been performed with chromite, silica sand, Durandal 60, and a mix of Durandal 60 and silica sand cores. These cores were made with alkaline phenolic resin. Results show sand fusion defects when silica is used, and clean casting for chromite and Durandal 60. Furthermore, under those casting conditions it is demonstrated that a mix of 50/50 Durandal 60 and silica still leads to clean casting. Also, the cooling time of casting was simulated by using three parameters depending on the temperature (thermal conductivity, heat capacity, and density). These were calculated and measured per the hot wire method until 1 400°C on the bulk sand sample. Those simulations have shown a very similar solidification time for Kersand and chromite sand for a given condition (respectively 32min and 29min).”

Conclusion
“Some foundries switched from chromite to 100% Kersand or Durandal 60 for technical reasons (quality variation of chromite sand) as well as for health and environmental requirements (further regulation on Cr VI hazardness), but mainly for economic constraints. Use of low loose bulk density sand is a strong lever to reduce consumption of sand. Shifting from 100% chromite to 100% Kersand or Durandal 60 will intrinsically lead to an immediate saving of 40% of sand consumption for a constant core volume amount. It should also be pointed out that cores will be 40% lighter by using Kersand or Durandal 60 compared to chromite, which in terms of operator working conditions is a significant improvement.”

“Finally, raw material sourcing is critical in every industry. Its stability in terms of quality, cost and supply conditions, directly impact the quality and efficiency of the final application. We believe Imerys’ Kersand (AFS 60) and Durandal 60 (AFS 50) are definitely a realistic, relevant and sustainable alternative to replace chromite in sand casting applications,” concluded Nicklin.

Imerys supplies the foundry industry with high-performance minerals and innovative solutions for moulds and cores in sand casting and investment casting as well as refractory solutions for both ferrous and non-ferrous foundries. Besides Kersand or Durandal 60 Imerys supplies bentonite to various types of refractory sands and flours, coatings, green moulding sand additives for sand casting, as well as sintered and fused minerals for ceramic moulding, honeycomb casting filters, slag binders, insulation materials, including insulating feeders, mineral mats and insulating furnace and ladle covers, refractory compounds, resin coated sands, filtering systems, graphites and blackings to serve virtually any foundry application. Imerys is also one of the world’s leading producers of calcined products for the refractory industry.

For further details contact Imerys Refractory Minerals SA on TEL: 011 643 5880 or visit www.imerys.com