CPT International 02/2019

IMERYS
Kersand and Durandal –
the right alternative
to chromite sands
Two sands by Imerys, Paris, France, Kersand
(AFS 60) & Durandal 60 (AFS 50) now used
by sand casting foundries, appear to fulfill
requirements in terms of refractoriness
and thermal expansion, as well as in terms
of supplying, and price condition stability.
Those two products are similar, made with natural minerals
with intrinsic high refractoriness and low thermal expansion.
In addition, they are respirable crystalline silica free,
and this over the several sand loops. The two sands are
performing in all steel alloys, cast iron & copper alloy
foundries and are compatible with all type of binding systems
(organic & Inorganic), and furthermore, generate no
low melting temperature point when mixed with silica
sand.
In a two years time period, chromite price FOB South
Africa more than doubled from initial price. This clearly
shows the high volatility of the chromite market price. 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.
Special sand, even if used in lower volume compared to
silica sand (for instance 10 %), can represent roughly 50 %
of the expenses when it is 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 which have been designed
specifically to reduce casting defects and are respectively
produced in South Africa & France. European sourcing is an
important advantage considering logistic delivery delays as
well as geopolitics stability situation.
Chromite 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.
Both, Kersand and Durandal 60 show linear and low
expansion with temperature compared to silica which exhibits
the well know transition quartz a to b at about 573 °C.
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 with alkaline phenolic
resin. Results show sand fusion defect when silica is used,
and clean casting for chromite and Durandal 60. Furthermore,
under those casting conditions it is demonstrated
that a mix 50 %/50 % Durandal 60 and silica still leads to
clean casting. Hall 12, Stand C 34
www.imerys.com
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