Adapting to Inorganic Core Sand Binders
Several machine changes may be necessary for metalcasting facilities converting to inorganic binders. RUDOLF WINTGENS, LAEMPE & MÖSSNER GMBH, SCHOPFHEIM, GERMANY
T
he past 10 years have produced a renais- sance in core sand binder use. Inorganic binders have been
developed and are entering the mar- ketplace due to environmental issues and some advantages in the metalcast- ing process, including improvement of workplace conditions. When manufacturing cores and
castings using inorganic materials, little to no organic substances are released. In addition to an improved working area and environment, economic benefits are realized via the elimination of the emission control system. Especially with permanent molds, where the dies’ efficiency can be reduced by combustible products and binder condensates, inorganic bind- ers increase uptime due to reduced cleaning time. Some inorganic binders can be adjusted to the water solubility required by the metalcasting facility, making it possible to wash the sand out of castings that are traditionally difficult to decore. However, modern inorganic binder
systems use a different reaction in the curing process than conventional carbon dioxide-hardening systems. Te reaction takes place mainly through moisture removal. Terefore, metal-
casting facilities’ core shooters and coreboxes must provide enough heat for the dried purge air to remove the moisture from the corebox. Several different heating methods, each with advantages and disadvantages, can be used. To ensure high quality and eco- nomical production, premature sand hardening must be stopped and the sand must remain flowable.
Sand Mix and Distribution The unique characteristics and
requirements of inorganic sand mixtures must be taken into account during sand preparation. The binder systems contain primarily two liquid
components and one powder com- ponent. Conventional units can be used for the liquid dosing. Because less powder additive is needed in inorganic binders, the dosing accu- racy must be higher.
The inorganic sand mixture
reacts to the loss of moisture with premature curing. To avoid the effect, the sand should be held at a temperature close to that of the mixer. A heat-cool sifter can be used to maintain the proper temperature. Te sand mixer should be a closed unit so no moisture is lost to the sur- rounding area. When using one mixer for several machines, the distribution
Organic binders (left) burn, but inorganic binders are inert. October 2012 MODERN CASTING | 27
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