Mold sand mixture produced without water which contains oil instead of water (approx. 2%), and modified bentonite swellable in oil as the binding agent (approx. 5 %) in order to achieve the required plasticity.
The binder is sodium bentonite treated with organic salts thus made swellable with oil. The mixture is available ready-for-use. It can only be stored for a limited time and must be well worked. Red iron oxide is frequently added and a relatively fine-grain quartz sand is used to obtain very smooth casting surfaces. The additives required for the refreshment during reprocessing depend on the depth of the heat-loaded sand layer in the cast mold and thus on the casting temperature, the casting wall thickness and the dwell time between casting and demolding.
A leading supplier of water-free mold sand with the brand name “O.B.B. Sand” is Kleine-Brockhoff und Oelschläger GmbH in Bottropp Kirchhellen.